Magnetic tape, magnetic tape cartridge, and magnetic recording and playback device

Abstract

Provided is magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the standard deviation of the frictional force as obtained by measuring the frictional force between the surface of the magnetic layer and a guide roll of an LTO drive is 0.35-0.70 N.

Description

Magnetic tape, magnetic tape cartridge, and magnetic recording / reproducing device

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

[0002] 2. Description of the Related Art Magnetic tapes are widely used as recording media for recording various types of data (see, for example, Patent Documents 1 and 2).

[0003] JP 2006-96850 A JP 2021-106070 A

[0004] The development of magnetic tape has historically been driven by a trade-off between ensuring the smoothness of the magnetic layer surface to improve electromagnetic characteristics and reducing the coefficient of friction with the magnetic head. Until now, the smoothness and friction characteristics of the magnetic layer surface have been designed to match the electromagnetic characteristics required for each generation of drive. However, with each generation, recording capacity has doubled, and not only linear recording density but also the recording density across the width of the magnetic tape, i.e., track density, has increased, resulting in increasingly narrower read element widths for magnetic heads. Therefore, in recent years, there has been a demand for more accurate positioning of the magnetic head across the width of the magnetic tape.

[0005] A servo pattern is recorded on the magnetic tape to determine the position of the magnetic head in the width direction of the magnetic tape. By reading the servo pattern, the position of the magnetic head can be accurately determined. By moving the magnetic head up and down in accordance with the servo pattern, data can be recorded and reproduced at a targeted location. However, there are cases where the up and down movement of the magnetic head cannot keep up with changes in the servo pattern. A value known as a position error signal (PES) is known as an index of this tracking. To improve the running stability of the magnetic tape, it is desirable to keep the fluctuations of this PES below a certain level.

[0006] Until now, efforts to suppress PES fluctuations have been made by reducing the coefficient of friction between the magnetic layer surface and each sliding member as much as possible, as described in Patent Document 1 (JP 2006-96850 A), and by reducing the coefficient of friction with the magnetic head as much as possible, as described in Patent Document 2 (JP 2021-106070 A). Until now, PES fluctuations could be suppressed by simply pursuing low friction, as described in Patent Documents 1 and 2. However, since PES fluctuations become more likely as track density increases, it is desirable to further suppress PES fluctuations in order to accommodate further increases in track density.

[0007] An object of one aspect of the present invention is to provide a magnetic tape with little fluctuation in PES.

[0008] Through further investigation, the inventors have come to the conclusion that as track density increases, the relationship between the followability of the magnetic tape with respect to guide rolls arranged before and after the magnetic head in a magnetic recording / reproducing device (commonly called a "drive") and PES becomes particularly important. As a result of further intensive investigation, the inventors have newly discovered that it is possible to suppress fluctuations in PES by setting the standard deviation of frictional force, which will be described in detail below, within the following range.

[0009] One aspect of the present invention is as follows: [1] A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the standard deviation of frictional force, determined by measuring the frictional force between the surface of the magnetic layer and a guide roll of an LTO (Linear Tape-Open) drive, is 0.35 N (Newton) or more and 0.70 N or less. [2] The magnetic tape according to [1], wherein the area ratio of multiple bright regions having a circle equivalent diameter of 140 nm or more (hereinafter also referred to as "SEM 140 nm or more bright region surface area ratio") in a binarized secondary electron image obtained by imaging the surface of the magnetic layer with a scanning electron microscope (SEM) at an accelerating voltage of 5 kV is 0.010% or more and 0.100% or less. [3] The magnetic tape according to [1] or [2], wherein the standard deviation of the frictional force is 0.45 N or more and 0.70 N or less. [4] The magnetic tape according to any one of [1] to [3], wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.65 or more. [5] The magnetic tape according to any one of [1] to [4], further comprising a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer. [6] The magnetic tape according to any one of [1] to [5], further comprising a backcoat layer containing a non-magnetic powder on the surface of the non-magnetic support opposite to the surface having the magnetic layer. [7] The magnetic tape according to any one of [1] to [6], wherein the total thickness of the magnetic tape is 5.0 μm or less. [8] The magnetic tape according to any one of [1] to [7], wherein the non-magnetic support is a polyester support. [9] The magnetic tape according to any one of [1] to [8], wherein the ferromagnetic powder is hexagonal ferrite powder.

[10] The magnetic tape according to [9], wherein the hexagonal ferrite powder is hexagonal barium ferrite powder.

[11] The magnetic tape according to [9], wherein the hexagonal ferrite powder is hexagonal strontium ferrite powder.

[12] The magnetic tape according to [1], wherein in a binarized secondary electron image obtained by imaging the surface of the magnetic layer with a scanning electron microscope at an acceleration voltage of 5 kV, the area ratio of a plurality of bright regions having a circle equivalent diameter of 140 nm or more is 0.010% to 0.100%, the standard deviation of the frictional force is 0.45 N to 0.70 N, the perpendicular squareness of the magnetic tape is 0.65 or more, the magnetic tape further comprises a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer, and the non-magnetic support further comprises a backcoat layer containing a non-magnetic powder on the surface opposite to the surface having the magnetic layer, the magnetic tape has a total thickness of 5.0 μm or less, the non-magnetic support is a polyester support, and the ferromagnetic powder is selected from the group consisting of hexagonal barium ferrite, hexagonal strontium ferrite powder, and ε-iron oxide powder.

[13] A magnetic tape cartridge comprising the magnetic tape according to any of [1] to

[12] .

[14] A magnetic recording and reproducing device including the magnetic tape according to any one of [1] to

[12] .

[0010] According to one aspect of the present invention, it is possible to provide a magnetic tape with little fluctuation in PES, and also to provide a magnetic tape cartridge and a magnetic recording / reproducing device that include such a magnetic tape.

[0011] 1 shows a schematic diagram (plan view as viewed from the side) of a reel-to-reel measuring device used to measure guide roll friction force.

[0012] [Magnetic Tape] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The standard deviation of the friction force determined by measuring the friction force between the surface of the magnetic layer and a guide roll of an LTO drive is 0.35 N or more and 0.70 N or less. Hereinafter, this standard deviation of the friction force is also referred to as the "guide roll friction force standard deviation."

[0013] <Guide Roll Friction Force Standard Deviation> In the present invention and this specification, the "guide roll friction force standard deviation" is determined by the following method in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60%. FIG. 1 shows a schematic diagram (plan view observed from the side) of a reel-to-reel measuring device used to measure guide roll friction force. FIG. 2 is a schematic diagram showing a part of the measuring device shown in FIG. 1. Hereinafter, of the four pass rolls, the two pass rolls located closer to the guide rolls will be referred to as "pass rolls (upper)," and the other two pass rolls will be referred to as "pass rolls (lower)." In FIG. 1, the magnetic tape MT is fed from a feed roll 1, passes through a pass roll (lower) 7 and a pass roll (upper) 5, is set so that the magnetic layer surface of the magnetic tape MT contacts the guide roll 3, passes through a pass roll (upper) 6 and a pass roll (lower) 8, and is wound around a take-up roll 2. This constitutes one pass. The length per pass is 20 m. In this invention and this specification, the term "surface of the magnetic layer" is synonymous with the surface of the magnetic tape facing the magnetic layer. The guide roll used is a guide roll from an LTO drive. An LTO drive is a drive that complies with the LTO standard. Specifically, a guide roll removed from an IBM TS-1160 tape drive is used. The guide roll is thoroughly washed with ethanol and dried before use. A new (i.e., unused) guide roll is used for each measurement of the magnetic tape (one sample) to be measured, and the same guide roll 3 is used without replacement for the total of 400 passes described below. The length "L" shown in Figure 2 is the distance from the center line of the guide roll 3 to the center lines of the pass rolls 5 and 6. The two Ls are the same length. The guide roll 3 is installed midway between the pass rolls 5 and 6 so that the wrap angle (angle "a" in FIG. 2) is 0.75° with respect to a direction parallel to the direction of the length L, and the length (L x 2) between the pass rolls 5 and 6 is 150 mm or more and 300 mm or less.Regarding the wrap angle, the position of the magnetic tape surface when there are no guide rolls is set to 0 mm, and the wrap angle can be adjusted to 0.75° by pressing the guide roll 3 by the distance L [mm] x tan 0.75° [mm] between the center line of the guide roll 3 and the center line of each pass roll 5, 6. A tension of 0.8 N is applied to the magnetic tape MT, and the acceleration is 2 m / s. ２ The magnetic tape MT is run at a transport speed of 4 m / s, and the frictional force is measured every 2 msec. The frictional force applied to the guide roll 3 is converted into a voltage by the strain gauge 4. The relationship between the voltage of the strain gauge 4 and the load is adjusted in advance. The standard deviation of the frictional force measured during a run of 5 to 15 m is calculated for each pass. Therefore, the number of frictional force data points per pass is approximately 1,250. A total of 400 passes are run, and the arithmetic mean of the standard deviations of the frictional force measured over a total of 200 passes, ranging from 200 to 400 of the 400 passes, is taken as the guide roll frictional force standard deviation of the magnetic tape being measured. In the above measurements, guide rolls for LTO drives are used, considering that the LTO standard is a standard that can accommodate recent trends in high-density recording. However, the magnetic tape is not limited to that used in LTO drives. Data may be recorded and / or reproduced on the magnetic tape in an LTO drive, or data may be recorded and / or reproduced on a drive other than an LTO drive.

[0014] The inventors believe that the guide roll friction force standard deviation can be an indicator of the trackability of the magnetic tape relative to the guide roll. If the guide roll friction force standard deviation of the magnetic tape is 0.35 N or more, the magnetic tape has excellent trackability relative to the guide roll, thereby suppressing fluctuations in PES. Specifically, it is presumed that a guide roll friction force standard deviation of 0.35 N or more can suppress slippage and / or rubbing between the magnetic tape and the guide roll. The guide roll friction force standard deviation is preferably 0.40 N or more, more preferably 0.45 N or more, and even more preferably 0.50 N or more. On the other hand, a guide roll friction force standard deviation of 0.70 N or less can also improve trackability relative to the guide roll and contribute to suppressing fluctuations in PES. It is presumed that a guide roll friction force standard deviation of 0.70 N or less can suppress sticking of the magnetic tape to the guide roll. The guide roll friction force standard deviation can also be, for example, 0.69 N or less, 0.68 N or less, or 0.67 N or less.

[0015] <Surface Area Ratio of Bright Portions of 140 nm or More in SEM> The present inventors believe that improving the followability of the magnetic tape relative to the guide roll can contribute to suppressing fluctuations in PES. On the other hand, in practice, it is preferable for the magnetic tape to have a low coefficient of friction relative to the magnetic head. Known methods for lowering the coefficient of friction relative to the magnetic head include increasing the surface roughness of the magnetic layer surface and increasing the number of surface protrusions. On the other hand, it is presumed that followability of the magnetic tape relative to the guide roll is in a trade-off relationship with the pursuit of low friction characteristics. After extensive research into this point, the present inventors have newly discovered that controlling the surface area ratio of bright portions of 140 nm or more in SEM, as determined by the method described below, leads to the resolution of the above trade-off.

[0016] In the present invention and this specification, the "SEM 140 nm or larger bright portion surface area ratio" is determined by the following method. In the present invention and this specification, the scanning electron microscope used to determine the SEM 140 nm or larger bright portion surface area ratio is a field emission scanning electron microscope (FE-SEM). As the FE-SEM, for example, a Hitachi FE-SEM S4800 can be used. No coating treatment is performed on the magnetic layer surface of the magnetic tape before capturing the SEM image. The captured SEM image is a secondary electron image. The circle equivalent diameter is determined in 1 nm increments by rounding off to one decimal place and discarding values ​​from two decimal places onwards. When counting the number of bright areas, bright areas that are only partially included in the binarized image and the remaining portion outside the binarized image are excluded from the measurement. A secondary electron image of the magnetic layer surface of the magnetic tape to be measured is captured using an FE-SEM. The imaging conditions are an acceleration voltage of 5 kV, a working distance of 5 mm, and a magnification of 9,000x. During imaging, an unimaged area of ​​the magnetic layer surface is selected, the focus is adjusted under the above imaging conditions, and a secondary electron image is captured. Areas indicating size, etc. (micron bars, cross marks, etc.) are erased from the captured image, and a secondary electron image with a pixel count of 960 pixels x 1,280 pixels is obtained. The above operation is performed 10 times at different locations on the magnetic layer surface of the magnetic tape to be measured. The secondary electron image thus obtained is imported into image processing software and binarized using the following procedure. The image analysis software can be, for example, the free software ImageJ. The binarization process divides the image into bright regions (white areas) and dark regions (black areas). The thresholds for binarizing the secondary electron image acquired above are set at a lower limit of 210 gradations and an upper limit of 255 gradations, and the binarization process is performed using these two thresholds. After the binarization process, noise components are removed using image analysis software. The noise component removal process can be performed, for example, by the following method.In the image analysis software ImageJ, the noise cut process "Despeckle" is selected to remove noise components. The image analysis software is used to determine the number of bright areas (i.e., white areas) and the area of ​​each bright area for the binarized image obtained in this way. The circle-equivalent diameter of each bright area is calculated from the area of ​​the bright area thus determined. Specifically, the circle-equivalent diameter L is calculated from the determined area A using the formula 2 × (A / π)^(1 / 2) = L. Here, the operator "^" represents exponentiation. The above process is performed for the binarized images (10 images) obtained above. For all of the multiple bright areas with a circle-equivalent diameter of 140 nm or more in each binarized image, the area ratio (percentage) of the area A of each bright area to the entire image (i.e., the total area of ​​the image at a magnification of 9,000 times) is calculated. The sum of the calculated area ratios is the area ratio of the multiple bright areas with a circle-equivalent diameter of 140 nm or more in that binarized image. This process of determining the area ratio of multiple bright areas with a circular equivalent diameter of 140 nm or more is performed on the binarized images (10 images) obtained above, and the arithmetic average of these images is used as the area ratio of multiple bright areas with a circular equivalent diameter of 140 nm or more for the magnetic tape being measured (SEM bright area surface ratio of 140 nm or more).

[0017] The magnetic layer is typically formed using a magnetic layer-forming composition containing one or more non-magnetic powders in addition to a ferromagnetic powder. The inventors believe that the non-magnetic powder (hereinafter also referred to as "abrasive") contained in the magnetic layer to impart abrasive properties to the magnetic layer surface is observed as the bright regions. Specifically, the SEM 140 nm or larger bright region surface area ratio can be considered to be the magnetic layer surface area occupied by abrasives present on the magnetic layer surface with relatively large equivalent circle diameters of 140 nm or larger. From the perspective of resolving the trade-off described above, the SEM 140 nm or larger bright region surface area ratio is preferably 0.010% or larger. Specifically, from the perspective of suppressing adhesion to the magnetic head, the SEM 140 nm or larger bright region surface area ratio is preferably 0.010% or larger. From this perspective, the SEM 140 nm or larger bright region surface area ratio is more preferably 0.012% or larger, and even more preferably 0.015% or larger. Furthermore, from the viewpoint of eliminating the trade-off described above, the surface area ratio of bright portions having a SEM of 140 nm or more is preferably 0.100% or less. Specifically, from the viewpoint of improving the followability to the guide roll, the surface area ratio of bright portions having a SEM of 140 nm or more is preferably 0.100% or less. From this viewpoint, the surface area ratio of bright portions having a SEM of 140 nm or more is more preferably 0.060% or less, and even more preferably 0.050% or less.

[0018] The present inventors consider the following as a means for controlling the SEM 140 nm or larger bright surface area ratio. One method for controlling the SEM 140 nm or larger bright surface area ratio within the above range is to adjust the classification conditions of the abrasive dispersion (hereinafter also referred to as "abrasive liquid"). In the classification, it is preferable to perform a flow-type centrifugation process to remove only coarse particles without significantly changing the average particle size distribution of the abrasive dispersion. If the lower limit of the particle size range to be removed is D, the gravitational acceleration is adjusted by changing the rotation speed of the cylinder according to Stokes' equation so as to enable the removal of abrasives with particle sizes D or larger in the flow-type centrifugation process. In this way, it is possible to remove abrasives within the desired particle size range (i.e., particle sizes D or larger). By using an abrasive dispersion that has been centrifuged in this way, it is possible to relatively easily control the SEM 140 nm or larger bright surface area ratio without changing the amount of abrasive added. For details on abrasives, see paragraphs 0030 to 0032 of JP 2004-273070 A, for example. The abrasive has a specific surface area measured by the BET (Brunauer-Emmett-Teller) method (hereinafter referred to as "BET specific surface area") of 17 m ２ / g or more 40m ２ / g or less of an abrasive is preferably used. The abrasive content in the magnetic layer can be, for example, 1.0 part by mass or more and 10.0 parts by mass or less per 100.0 parts by mass of ferromagnetic powder. For example, by adjusting the abrasive size, the abrasive classification conditions (more specifically, the centrifugation conditions), and the abrasive content in the magnetic layer-forming composition, the SEM 140 nm or more bright area surface area ratio can be controlled within the range described above.

[0019] The magnetic tape will now be described in more detail.

[0020] <Magnetic Layer> (Ferromagnetic Powder) The ferromagnetic powder contained in the magnetic layer can be one or a combination of two or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media. Using a ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0021] Hexagonal Ferrite Powder A preferred specific example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, see, for example, JP 2011-225417 A, paragraphs 0012 to 0030, JP 2011-216149 A, paragraphs 0134 to 0136, JP 2012-204726 A, paragraphs 0013 to 0030, and JP 2015-127985 A, paragraphs 0029 to 0084.

[0022] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the most intense diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, if the most intense diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the hexagonal ferrite crystal structure, it is determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure is considered to be the main phase. The hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples of such atoms include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and this specification, "hexagonal strontium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is a strontium atom, and "hexagonal barium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is a barium atom. The main divalent metal atom refers to the divalent metal atom that is the most abundant, on an atomic percentage basis, among the divalent metal atoms contained in the powder. However, the above divalent metal atoms do not include rare earth atoms. In the present invention and this specification, the "rare earth atom" is selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanoid atoms. The lanthanoid atom is selected from the group consisting of lanthanum atom (La), cerium atom (Ce), praseodymium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), europium atom (Eu), gadolinium atom (Gd), terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu).

[0023] Hereinafter, hexagonal strontium ferrite powder, which is one form of hexagonal ferrite powder, will be described in more detail.

[0024] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm ３ The microparticulated hexagonal strontium ferrite powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm ３ or more, for example, 850 nm ３ From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder can be 1500 nm or more. ３ More preferably, it is 1400 nm or less. ３ More preferably, it is 1300 nm or less. ３ More preferably, it is 1200 nm or less. ３ It is even more preferable that the value is 1100 nm or less. ３ It is even more preferable that the activation volume of the hexagonal barium ferrite powder is equal to or less than 10 ...

[0025] "Activation volume" is a unit of magnetization reversal and is an index showing the magnetic size of a particle. The activation volume described in this invention and this specification and the anisotropy constant Ku described below are values ​​obtained by measuring the coercive force Hc using a vibrating sample magnetometer at magnetic field sweep rates of 3 minutes and 30 minutes (measurement temperature: 23°C ± 1°C) in the coercive force Hc measurement section, and by using the following relational expression between Hc and activation volume V. The unit of the anisotropy constant Ku is 1 erg / cc = 1.0 x 10 －１ J / m ３ Hc = 2Ku / Ms {1 - [(kT / KuV)ln(At / 0.693)] １／２} [In the above formula, Ku: anisotropy constant (unit: J / m ３ ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activation volume (unit: cm ３ ), A: spin precession frequency (unit: s －１ ), t: magnetic field reversal time (unit: s)]

[0026] The anisotropy constant Ku can be used as an index of the reduction in thermal fluctuation, in other words, the improvement in thermal stability. The hexagonal strontium ferrite powder preferably has an anisotropy constant of 1.8×10 ５ J / m ３ and more preferably 2.0 × 10 ５ J / m ３ The Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 ５ J / m ３ However, since a higher Ku value means higher thermal stability and is therefore preferred, the Ku value is not limited to the above-mentioned values.

[0027] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms be contained at a content (bulk content) of 0.5 to 5.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have rare earth atoms unevenly distributed in the surface layer portion. In the present invention and this specification, "surface layer distribution of rare earth atoms" means that the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by partially dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "surface layer content of rare earth atoms" or simply "surface layer content" for rare earth atoms) satisfies the ratio of the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by completely dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "bulk content of rare earth atoms" or simply "bulk content" for rare earth atoms) > 1.0. The rare earth atom content of the hexagonal strontium ferrite powder described below is synonymous with the bulk content of rare earth atoms. In contrast, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. The rare earth atom surface layer content satisfying the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0" means that rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder (i.e., more present in the surface layer than in the interior). In the present invention and this specification, the surface layer refers to a partial region extending from the surface toward the interior of the particles constituting the hexagonal strontium ferrite powder.

[0028] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic percent relative to 100 atomic percent of iron atoms. The presence of rare earth atoms at a bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder is believed to contribute to suppressing a decrease in playback output during repeated playback. This is presumably because the hexagonal strontium ferrite powder contains rare earth atoms at a bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the anisotropy constant Ku, the more the occurrence of a phenomenon known as thermal fluctuation can be suppressed (in other words, thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in playback output during repeated playback can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the particle surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of the iron (Fe) site in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. From the viewpoint of further suppressing the decrease in playback output during repeated playback, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic %, even more preferably in the range of 1.0 to 4.5 atomic %, and even more preferably in the range of 1.5 to 4.5 atomic %.

[0029] The bulk content is the content determined by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the content of an atom refers to the bulk content determined by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one type of rare earth atom as the rare earth atom, or may contain two or more types of rare earth atoms. When two or more types of rare earth atoms are contained, the bulk content is determined for the total of the two or more types of rare earth atoms. This also applies to other components in the present invention and this specification. That is, unless otherwise specified, a certain component may be used alone or in combination with two or more types. When two or more types are used, the content or content refers to the total of the two or more types.

[0030] When the hexagonal strontium ferrite powder contains a rare earth atom, the rare earth atom may be any one or more of rare earth atoms. From the viewpoint of further suppressing a decrease in the reproduction output during repeated reproduction, preferred rare earth atoms include neodymium, samarium, yttrium, and dysprosium atoms, with neodymium, samarium, and yttrium atoms being more preferred, and neodymium atoms being even more preferred.

[0031] In a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the rare earth atoms need only be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that rare earth atoms are unevenly distributed in the surface layer (i.e., present in greater amounts than in the interior) in the particles constituting the hexagonal strontium ferrite powder. Furthermore, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "surface content / bulk content," can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the exemplified upper or lower limits.

[0032] The partial dissolution and total dissolution of hexagonal strontium ferrite powder are described below. For hexagonal strontium ferrite powder present as a powder, sample powders to be partially and completely dissolved are collected from the same powder lot. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a portion of the hexagonal strontium ferrite powder removed from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. Removal of the hexagonal strontium ferrite powder from the magnetic layer can be performed, for example, by the method described in paragraph 0032 of JP 2015-91747 A. The partial dissolution refers to dissolving the hexagonal strontium ferrite powder to such an extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, partial dissolution can dissolve 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, the term "complete dissolution" refers to dissolution to the point where no residual hexagonal strontium ferrite powder is visually detectable in the solution at the end of dissolution. The partial dissolution and surface layer content measurement are performed, for example, by the following method. However, the dissolution conditions, such as the amount of sample powder, described below are merely examples, and any dissolution conditions that allow partial or complete dissolution can be adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is placed on a hot plate set at 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate obtained in this manner is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms relative to 100 atomic % of iron atoms can be determined. If multiple rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. The same applies to the measurement of the bulk content. Meanwhile, the total dissolution and bulk content measurements are carried out, for example, by the following method: A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is placed on a hot plate set at 80° C. for 3 hours.Thereafter, the same procedures as in the partial dissolution and measurement of the surface layer content are carried out, and the bulk content relative to 100 atomic % of iron atoms can be determined.

[0033] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but not having uneven distribution of rare earth atoms in the surface layer has been shown to have a tendency to have a significantly lower σs than hexagonal strontium ferrite powder not containing rare earth atoms. In contrast, hexagonal strontium ferrite powder having uneven distribution of rare earth atoms in the surface layer is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of the hexagonal strontium ferrite powder is 45 A m ２ / kg or more, and ２ On the other hand, from the viewpoint of noise reduction, σs is 80 A m ２ / kg or less, and ２ / kg or less is more preferable. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. The conversion factor from the unit Oe (oersted) to the SI unit A / m is 10 ３ / 4π.

[0034] Regarding the content (bulk content) of the constituent atoms of the hexagonal strontium ferrite powder, the strontium atom content can be, for example, in the range of 2.0 to 15.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder can contain only strontium atoms as divalent metal atoms. In another embodiment, the hexagonal strontium ferrite powder can contain one or more other divalent metal atoms in addition to strontium atoms. For example, barium atoms and / or calcium atoms can be contained. When divalent metal atoms other than strontium atoms are contained, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can each be, for example, in the range of 0.05 to 5.0 atomic % relative to 100 atomic % of iron atoms.

[0035] Known crystal structures of hexagonal ferrite include magnetoplumbite type (also called "M type"), W type, Y type, and Z type. The hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may be one in which a single crystal structure or two or more types of crystal structures are detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder may be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, the M-type hexagonal ferrite is AFe １２ O １９The composition is represented by the formula: where A represents a divalent metal atom. When the hexagonal strontium ferrite powder is of M type, A is only strontium atom (Sr). Alternatively, when A contains multiple divalent metal atoms, strontium atom (Sr) accounts for the majority on an atomic % basis as described above. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystalline structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may further contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % relative to 100 atomic % of iron atoms. From the viewpoint of further suppressing a decrease in playback output during repeated playback, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic % or less, more preferably in the range of 0 to 5.0 atomic %, relative to 100 atomic % of iron atoms, and may even be 0 atomic %. That is, in one embodiment, the hexagonal strontium ferrite powder does not need to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic % above is determined by converting the content (unit: mass %) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic % using the atomic weight of each atom. Furthermore, in the present invention and this specification, "not containing" a certain atom means that the content measured by completely dissolving the powder and using an ICP analyzer is 0 mass %. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less by mass. The above term "free from" is used to mean that the amount is below the detection limit of the ICP analyzer.In one form, the hexagonal strontium ferrite powder can be one that does not contain bismuth atoms (Bi).

[0036] Metal Powder A preferred specific example of the ferromagnetic powder is ferromagnetic metal powder. For details of the ferromagnetic metal powder, see, for example, paragraphs

[0137] to

[0141] of JP 2011-216149 A and paragraphs

[0009] to

[0023] of JP 2005-251351 A.

[0037] ε-Iron Oxide Powder A preferred example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, the term "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide crystal structure is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the ε-iron oxide crystal structure, it is determined that the ε-iron oxide crystal structure has been detected as the main phase. Known methods for producing ε-iron oxide powder include a method of producing it from goethite and a reverse micelle method. All of these production methods are publicly known. Furthermore, a method for producing ε-iron oxide powder in which part of the Fe is substituted with a substitution atom such as Ga, Co, Ti, Al, or Rh is described, for example, in J. Jpn. Soc. Powder Metallurgy, Vol. 61, Supplement, No. S1, pp. 111-115. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the methods mentioned here.

[0038] The activation volume of the ε-iron oxide powder is preferably 300 to 1500 nm ３ The finely divided ε-iron oxide powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm ３ or more, for example, 500 nm ３From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder can be 1400 nm or more. ３ More preferably, it is 1300 nm or less. ３ More preferably, it is 1200 nm or less. ３ More preferably, it is 1100 nm or less. ３ It is even more preferred that:

[0039] The anisotropy constant Ku can be used as an index of the reduction in thermal fluctuation, in other words, the improvement in thermal stability. The ε-iron oxide powder preferably has an anisotropy constant Ku of 3.0×10 ４ J / m ３ and more preferably 8.0 × 10 ４ J / m ３ The Ku of the ε-iron oxide powder can be, for example, 3.0×10 ５ J / m ３ However, since a higher Ku value means higher thermal stability and is therefore preferred, the Ku value is not limited to the above-mentioned values.

[0040] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, in one embodiment, the σs of the ε-iron oxide powder is 8 A m ２ / kg or more, and ２ On the other hand, the σs of the ε-iron oxide powder can be 40 A m ２ / kg or less, and 35 A m ２ / kg or less is more preferable.

[0041] Unless otherwise specified, in this invention and this specification, the average particle size of various powders, such as ferromagnetic powders, is a value measured using a transmission electron microscope by the following method. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and a photograph of the particles constituting the powder is obtained by printing it on photographic paper or displaying it on a display so that the total magnification is 500,000x. From the obtained particle photograph, a target particle is selected, and the particle outline is traced with a digitizer to measure the particle (primary particle) size. Primary particles refer to independent particles without agglomeration. The above measurement is performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. Furthermore, particle size measurement can be performed using known image analysis software, such as Carl Zeiss KS-400 image analysis software. Unless otherwise specified, the average particle size described in the Examples section below is a value measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In this invention and this specification, powder refers to an aggregate of multiple particles. For example, ferromagnetic powder refers to an aggregate of multiple ferromagnetic particles. Furthermore, an aggregate of multiple particles is not limited to a form in which the particles constituting the aggregate are in direct contact with each other, but also includes forms in which a binder, additive, etc., described below, is interposed between the particles. The term "particle" is sometimes used to refer to powder.

[0042] As a method for collecting sample powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP-A-2011-048878 can be used.

[0043] In the present invention and this specification, unless otherwise specified, the size of particles constituting a powder (particle size) is expressed as the length of the major axis constituting the particle, i.e., the major axis length, when the shape of the particle observed in the particle photograph is: (1) needle-like, spindle-like, columnar (however, the height is greater than the maximum major axis of the base), etc. (2) plate-like or columnar (however, the thickness or height is smaller than the maximum major axis of the plate surface or base), it is expressed as the maximum major axis of the plate surface or base, (3) spherical, polyhedral, amorphous, etc., and when the major axis constituting the particle cannot be identified from the shape, it is expressed as the circle-equivalent diameter. The circle-equivalent diameter is determined by the circle projection method.

[0044] The average acicular ratio of a powder refers to the arithmetic average of the minor axis length of the particles measured in the above measurement, i.e., the minor axis length, the value of (major axis length / minor axis length) for each particle, and the values ​​obtained for the 500 particles. Here, unless otherwise specified, the minor axis length refers to the length of the minor axis constituting the particle in the above particle size definition (1), and the thickness or height in the above particle size definition (2). In the above particle size definition (3), since there is no distinction between the major axis and the minor axis, the (major axis length / minor axis length) is considered to be 1 for convenience. Unless otherwise specified, when the particle shape is specific, for example, in the above particle size definition (1), the average particle size is the average major axis length, and in the above definition (2), the average particle size is the average plate diameter. In the above definition (3), the average particle size is the average diameter (also called the average particle diameter or average particle size).

[0045] The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90 mass %, and more preferably in the range of 60 to 90 mass %, relative to the total mass of the magnetic layer. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving recording density.

[0046] (Binder) The magnetic tape may be a coated magnetic tape, and the magnetic layer may contain a binder. The binder is one or more resins. Various resins commonly used as binders for coated magnetic recording media can be used as binders. For example, binders may be selected from polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, polyvinyl acetal, polyvinyl butyral, etc., and may be used alone or in combination. Among these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the nonmagnetic layer and / or backcoat layer, as described below. For details on the binders mentioned above, see paragraphs 0028 to 0031 of JP 2010-24113 A. The binder may also be a radiation-curable resin such as an electron beam-curable resin. For details of radiation-curable resins, see paragraphs 0044 to 0045 of Japanese Patent Application Laid-Open No. 2011-048878. The average molecular weight of the resin used as the binder may be, for example, 10,000 to 200,000 in weight average molecular weight. The weight-average molecular weight in this specification and the present invention is a value determined by converting a value measured by gel permeation chromatography (GPC) under the following measurement conditions into a polystyrene equivalent. The weight-average molecular weight described in the Examples section below is a value determined by converting a value measured under the following measurement conditions into a polystyrene equivalent. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder. GPC apparatus: HLC-8120 (manufactured by Tosoh Corporation) Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mm ID (Inner Diameter) × 30.0 cm) Eluent: tetrahydrofuran (THF)

[0047] (Curing Agent) A curing agent can also be used together with a resin that can be used as a binder. In one form, the curing agent can be a thermosetting compound, which is a compound that undergoes a curing reaction (crosslinking reaction) upon heating. In another form, the curing agent can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) upon irradiation with light. As the curing reaction progresses during the magnetic layer formation process, at least a portion of the curing agent can 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 compositions used to form other layers that contain a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For details on polyisocyanates, see paragraphs 0124 to 0125 of JP 2011-216149 A. The curing agent can be used in the magnetic layer-forming composition in an amount of, for example, 0 to 80.0 parts by weight per 100.0 parts by weight of binder, preferably 50.0 to 80.0 parts by weight from the perspective of improving the strength of the magnetic layer.

[0048] (Additives) The magnetic layer may contain one or more additives as needed. Commercially available additives can be selected and used depending on the desired properties. Alternatively, compounds synthesized by known methods can be used as additives. Additives can be used in any amount. Examples of additives include the curing agents described above. Examples of additives contained in the magnetic layer include non-magnetic powders (e.g., inorganic powders, carbon black, etc.), lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, and antioxidants. For details about dispersants, see paragraphs

[0061] and

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

[0061] of JP 2012-133837 A. Non-magnetic powders that can be contained in the magnetic layer include non-magnetic powders that can function as abrasives, and non-magnetic powders (e.g., carbon black, non-magnetic colloidal particles, etc.) that can function as protrusion-forming agents that form moderately protruding protrusions on the surface of the magnetic layer. The average particle size of 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. The abrasives are as described above.

[0049] Fatty acids, fatty acid esters, fatty acid amides. The magnetic tape may contain one or more components selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the portion of the non-magnetic support facing the magnetic layer. The portion facing the magnetic layer may contain only one, two, or three components selected from fatty acids, fatty acid esters, and fatty acid amides. The fatty acid may contain only one or more fatty acids. This also applies to fatty acid esters and fatty acid amides. In this specification and the present invention, "the portion facing the magnetic layer on the non-magnetic support" refers to the magnetic layer for a magnetic tape having a magnetic layer directly on the non-magnetic support, and to the magnetic layer and / or non-magnetic layer for a magnetic tape having a non-magnetic layer (described below) between the non-magnetic support and the magnetic layer. The "portion facing the magnetic layer on the non-magnetic support" is also simply referred to as "the portion facing the magnetic layer." The presence on the surface facing the magnetic layer of the magnetic tape is also included in the portion facing the magnetic layer.

[0050] Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. Stearic acid, myristic acid, and palmitic acid are preferred, with stearic acid being more preferred. Fatty acids may be contained in the magnetic layer in the form of salts such as metal salts. Examples of fatty acid esters include esters of the various fatty acids listed above. Specific examples include butyl myristate, butyl palmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, and butoxyethyl stearate. Examples of fatty acid amides include amides of the various fatty acids listed above. Specific examples include lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, etc. With regard to fatty acids and fatty acid derivatives (amides, esters, etc.), it is preferable that the fatty acid-derived portion of the fatty acid derivative has the same or similar structure as the fatty acid used in combination. For example, when stearic acid is used as the fatty acid, it is preferable to use stearic acid amide and / or stearic acid ester in combination.

[0051] In one embodiment, a magnetic tape containing one or more components selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the magnetic layer can be produced by forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above components. In another embodiment, a magnetic tape containing one or more of the above components in the magnetic layer can be produced by forming a nonmagnetic layer using a nonmagnetic layer-forming composition containing one or more of the above components. In another embodiment, a magnetic tape containing one or more of the above components in the magnetic layer can be produced by forming a nonmagnetic layer using a nonmagnetic layer-forming composition containing one or more of the above components and then forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above components. The nonmagnetic layer can retain and supply components that function as lubricants, such as fatty acids, fatty acid esters, and fatty acid amides, to the magnetic layer. Lubricants such as fatty acids, fatty acid esters, and fatty acid amides contained in the nonmagnetic layer can migrate to the magnetic layer and remain there.

[0052] Regarding the fatty acid content, the fatty acid content of the magnetic layer-forming composition is preferably 0.5 to 3.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder.

[0053] Regarding the fatty acid ester content, the fatty acid ester content of the magnetic layer-forming composition is, for example, 0 to 10.0 parts by mass, and preferably 1.0 to 7.0 parts by mass per 100.0 parts by mass of ferromagnetic powder.

[0054] The fatty acid amide content in the magnetic layer-forming composition is, for example, 0 to 1.0 part by mass, and preferably 0.1 to 1.0 part by mass, per 100.0 parts by mass of the ferromagnetic powder.

[0055] The fatty acid content of the non-magnetic layer-forming composition is preferably 0.5 to 3.0 parts by mass per 100.0 parts by mass of non-magnetic powder. The fatty acid ester content of the non-magnetic layer-forming composition is, for example, 0 to 10.0 parts by mass, preferably 0 to 7.0 parts by mass per 100.0 parts by mass of non-magnetic powder. The fatty acid amide content of the non-magnetic layer-forming composition is, for example, 0 to 1.0 part by mass, preferably 0.1 to 1.0 part by mass per 100.0 parts by mass of non-magnetic powder.

[0056] Fluorine-Based Compound In one embodiment, the magnetic tape may contain one or more fluorine-based compounds in the magnetic layer side. As the fluorine-based compound, one of commercially available compounds or compounds that can be synthesized by known methods may be used, or two or more compounds may be mixed in any ratio. The fluorine atom may be, for example, —CF ３ , -CHF ２ , -CH ２ The fluorine-based compound may be contained in various forms, such as a fluorine-containing substituent such as F. Furthermore, the fluorine-based compound is preferably a compound having a reactive group capable of forming a crosslinked structure (hereinafter referred to as a "crosslinking group"). Examples of the crosslinking group include an epoxy group and an isocyanate group. Other examples include the crosslinking groups described below. For example, it is believed that the anchoring effect of the fluorine-based compound is achieved by directly forming a crosslinked structure between the crosslinking group of such a fluorine-based compound and another component (e.g., a binder) contained in the magnetic layer.

[0057] A specific example of the fluorine-based compound is a crosslinkable fluorine-containing polystyrene derivative containing 1% by mass to 99% by mass of repeating units represented by the following formula [1] and 1% by mass to 95% by mass of repeating units containing a crosslinkable group. Such a crosslinkable fluorine-containing polystyrene derivative can be contained in the magnetic tape in the form of a crosslinked product formed by crosslinking at least a part of the crosslinkable groups.

[0058]

[0059] In formula [1], Y represents a hydrogen atom or an alkyl group having 6 or less carbon atoms, Q represents a divalent group containing at least one ether bond and having 5 or less carbon atoms in total, and Rf ０ represents a monovalent perfluoroether group containing at least one ether group and having a total of 25 or less carbon atoms, which may contain one hydrogen atom. z is an integer ranging from 1 to 3. The bonding position of Q to the aromatic nucleus may be any of the ortho, meta, or para positions relative to the bonding position of the aromatic nucleus to the polymer main chain. Some or all of the hydrogen atoms bonded to the aromatic nucleus in formula [1] may be substituted with fluorine atoms.

[0060] The formula [1] will be explained in more detail below.

[0061] Y in formula [1] is a hydrogen atom or an alkyl group having 6 or less carbon atoms. The alkyl group having 6 or less carbon atoms may be either a linear alkyl group or a branched alkyl group, and specific examples thereof include a methyl group, an ethyl group, an n (normal)-propyl group, an isopropyl group, an n-butyl group, a tert (tertiary)-butyl group, an isobutyl group, a sec (secondary)-butyl group, an n-amyl group, and an n-hexyl group. Y is preferably a hydrogen atom or an alkyl group having 4 or less carbon atoms, and particularly preferably a hydrogen atom or a methyl group.

[0062] Q in formula [1] is a divalent group containing at least one ether bond and having a total of 5 or less carbon atoms, and examples thereof include divalent groups represented by the following formula [2]:

[0063]

[0064] In formula [2], a is 0 or 1, and b is 0 or an integer ranging from 1 to 3. The bond on the right side of formula [2] is Rf ０ It is a hand that combines with.

[0065] Examples of Q include -O- and -OCH ２ -, -OCH ２ CH ２ -, -OCH ２ CH ２ CH ２ -, -OCH ２ CH ２ CH ２ CH ２ -, -OCH(CH ３ ) CH ２ -, -OCH ２ CH (CH ３ ) -, -OCH ２ CH(OH)CH ２ -, -OCH ２ CH(OH)CH ２ OCH ２ -, -CH ２ O-, -CH ２ OCH ２ -, -CH２ OCH ２ CH ２ -, -CH ２ OCH ２ CH ２ CH ２ -, -CH ２ OCH ２ CH ２ CH ２ CH ２ -, -CH ２ OCH ２ CH (CH ３ ) OCH ２ -, -OCH ２ CH ２ OCH ２ -, -OCH ２ CH ２ OCH ２ CH ２ -, -CH ２ OCH ２ CH ２ OCH ２ -, -CH ２ OCH ２ CH ２ OCH ２ CH ２ -, etc. (the bond on the right side of each group is Rf ０ (This is the hand that joins with the

[0066] Among the above, —O—, —OCH ２ -, -OCH ２ CH ２ -, -CH ２ OCH ２ - and -CH ２ OCH ２ CH ２ - is preferred because the polymer can be easily synthesized, and -O- and -OCH ２ - and -CH ２ OCH ２ - is more preferred, and -O- is particularly preferred in that it has particularly excellent chemical stability.

[0067] Rf in formula [1] ０ is a monovalent perfluoroether group containing at least one ether bond and optionally containing one hydrogen atom, and Rf ０ The total number of carbon atoms in Rf is 25 or less.０ The ratio of [total number of carbon atoms / number of ether bonds] is usually 2.0 or more and 9.0 or less, preferably 2.2 or more and 8.0 or less, more preferably 3.3 or more and 6.0 or less, and particularly preferably 3.5 or more and 5.0 or less.

[0068] Rf ０ Examples of the group include a group represented by the following formula [3]:

[0069]

[0070] In formula [3], Rf １ is a perfluoroalkyl group having 7 or less carbon atoms, and Rf ２ is one or more perfluoroalkylene groups selected from linear or branched perfluoroalkylene groups having 4 or less carbon atoms, and Rf ３ is a perfluoroalkylene group having 3 or less carbon atoms, or a polyfluoroalkylene group having a structure in which one fluorine atom of a perfluoroalkylene group having 3 or less carbon atoms is substituted with a hydrogen atom, and L is 0 or an integer in the range of 1 to 10.

[0071] Rf １ Examples of the alkyl group include linear or branched perfluoroalkyl groups having 7 or less carbon atoms, preferably 6 or less carbon atoms, and more preferably 3 or less carbon atoms.

[0072] Rf １ A specific example of this is CF ３ -, CF ３ CF ２ -, CF ３ CF ２ CF ２ -, (CF ３ ) ２ CF-, CF ３ CF ２ CF ２ CF ２ -, CF ３ CF ２ CF ２ CF ２ CF ２ -, CF ３ CF ２ CF ２ CF２ CF ２ CF ２ - and CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ CF ２ Among these, CF ３ CF ２ CF ２ -, CF ３ CF ２ CF ２ CF ２ - and CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ - is preferred, and CF is particularly preferred because of ease of synthesis. ３ CF ２ CF ２ - is preferred.

[0073] Rf ２ Rf represents one or more perfluoroalkylene groups selected from linear or branched perfluoroalkylene groups having 4 or less carbon atoms. ２ The number of carbon atoms therein is usually in the range of 1 to 4, preferably in the range of 1 to 3, and particularly preferably 3.

[0074] Rf ２ Specific examples of -CF(CF ３ )CF ２ -, -CF(CF ３ ) -, -CF ２ -, -CF ２ CF ２ -, -CF ２ CF ２ CF ２ -, -CF ２ CF ２ CF ２ CF ２ - and -CF ２ CF (CF ３ )CF ２ Among these, -CF (CF ３ )CF ２ -, -CF ２-, -CF ２ CF ２ - and -CF ２ CF ２ CF ２ - is preferred, and -CF(CF) is particularly preferred because of ease of synthesis. ３ )CF ２ - and -CF ２ CF ２ CF ２ - is preferred. ２ The bond on the right side of each group in the specific examples is (Rf ２ O) unit.

[0075] L in formula [3] is 0 or an integer in the range of 1 to 10, preferably 0 or an integer in the range of 1 to 6, more preferably 0 or an integer in the range of 1 to 3, even more preferably 0 or an integer in the range of 1 to 2, and particularly preferably 0 or 1.

[0076] (Rf ２ O) Ｌ In the segment, Rf ２ When the group is composed of multiple types of perfluoroalkylene groups, -CF(CF ３ )CF ２ O-CF ２ CF ２ CF ２ O-CF (CF ３ )CF ２ O-..., and different types of Rf ２ may be arranged randomly, or the same type of Rf ２ A plurality of such may be arranged side by side.

[0077] Rf ２ (Rf ２ O) Ｌ Specific examples of the group include a group represented by the following formula [4]:

[0078] -[CF(CF ３ )CF ２ O] ｎ１ -[CF ２ CF ２ CF ２ O]ｎ２ -[CF ２ CF ２ O] ｎ３ -[CF ２ O] ｎ４ [4]

[0079] In formula [4], n1, n2, n3, and n4 each independently represent 0 or an integer ranging from 1 to 6. The sum of n1, n2, n3, and n4 (n1 + n2 + n3 + n4) is the same as L in formula [3].

[0080] Rf ３ is a perfluoroalkylene group having 3 or less carbon atoms, or a polyfluoroalkylene group having a structure in which one fluorine atom of a perfluoroalkylene group having 3 or less carbon atoms is substituted with a hydrogen atom.

[0081] Rf ３ Specific examples of the group include -CF ２ -, -CF ２ CF ２ -, -CF(CF ３ ) -, -CF ２ CF ２ CF ２ -, -CF(CF ３ )CF ２ -, -CF ２ CF (CF ３ )-, -CHFCF ２ -, -CF ２ CHFCF ２ Among these, -CF ２ CF ２ -, -CF(CF ３ )- and -CHFCF ２ - is preferred, and -CHFCF is particularly preferred because of ease of synthesis. ２ - is preferred. ３ In the specific examples, the bond on the right side of each group is the bond to Q.

[0082] Rf ０ Specific examples of the formula include a group represented by the following formula [R-1], a group represented by the following formula [R-2], a group represented by the following formula [R-3], and a group represented by the following formula [R-4].

[0083]

[0084]

[0085]

[0086]

[0087] Specific examples of the group represented by formula [R-1] include CF ３ CF ２ CF ２ OCHFCF ２ -, CF ３ CF ２ CF ２ OCF (CF ３ )CF ２ OCHFCF ２ -, CF ３ CF ２ CF ２ OCF (CF ３ )CF ２ OCF (CF ３ )CF ２ OCHFCF ２ - and CF ３ CF ２ CF ２ OCF (CF ３ )CF ２ OCF (CF ３ )CF ２ OCF (CF ３ )CF ２ OCHFCF ２ - are listed.

[0088] Specific examples of the group represented by formula [R-2], formula [R-3], or formula [R-4] include the terminal CHFCF of each structure given as specific examples of the group represented by formula [R-1] above. ２ The groups are CF(CF ３ ) group, CF ２ CF ２ group or CF ２ CHFCF ２ Examples of groups include those in which the structure is replaced by

[0089] Also, Rf ０ represents the terminal group CF in each group of formula [R-1], formula [R-2], formula [R-3] or formula [R-4]. ３ CF２ CF ２ The group may be replaced with a linear or branched perfluoroalkyl group having 1 to 7 carbon atoms, preferably 1 to 6 carbon atoms. Examples of such perfluoroalkyl groups include CF ３ -, CF ３ CF ２ -, (CF ３ ) ２ CF-, CF ３ CF ２ CF ２ CF ２ -, CF ３ CF ２ CF ２ CF ２ CF ２ - and CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ - are listed.

[0090] In the formula [1], z is an integer ranging from 1 to 3, and it is more preferable that z is 1 in terms of ease of synthesis.

[0091] The bonding position of Q to the aromatic nucleus in formula [1] may be any of the ortho, meta, or para positions relative to the bonding position between the aromatic nucleus and the polymer main chain, and the para position is preferred from the viewpoints of ease of synthesis and easy availability of raw materials.

[0092] Some or all of the hydrogen atoms bonded to the aromatic nucleus in formula [1] may be substituted with fluorine atoms, but from the viewpoint of ease of synthesis, it is more preferable that they are not substituted with fluorine atoms.

[0093] As the repeating unit represented by formula [1], a repeating unit represented by the following formula [1-1] is preferred, and a repeating unit represented by the following formula [1-2] is more preferred.

[0094]

[0095] In formula [1-1], Y １ represents a hydrogen atom or a methyl group, and Q １ represents a divalent group containing an ether bond and having 3 or less carbon atoms. ０１is Rfa １ -O-[CF(CF ３ )CF ２ O] ｍ１ -[CF ２ CF ２ CF ２ O] ｍ２ -[CF ２ CF ２ O] ｍ３ -[CF ２ O] ｍ４ -Rfc １ - and Rfa １ represents a perfluoroalkyl group having 1 to 6 carbon atoms; m1, m2, m3, and m4 each independently represent 0 or an integer ranging from 1 to 6; the sum of m1, m2, m3, and m4 (m1 + m2 + m3 + m4) represents 0 or an integer ranging from 1 to 6; Rfc １ represents a perfluoroalkylene group having 3 or less carbon atoms which may contain one hydrogen atom.

[0096] Formula [1-1] will be explained in more detail below.

[0097] Q １ is a divalent group containing an ether bond and having 3 or less carbon atoms, and specific examples thereof include -O- and -OCH ２ -, -CH ２ O-, -OCH ２ CH ２ -, -CH ２ OCH ２ -, -CH ２ OCH ２ CH ２ - etc. １ Examples thereof include —O—, —CH ２ OCH ２ - or -OCH ２ - is more preferred, and -O- is particularly preferred. １ The bond on the right side of each group in the specific examples is Rf in formula [1-1]. ０１ It is a hand that combines with.

[0098] The sum of m1, m2, m3 and m4 (m1+m2+m3+m4) is 0 or an integer ranging from 1 to 6, preferably 0 to 3, more preferably 0 to 2, and particularly preferably 0 or 1. １is a perfluoroalkylene group having 3 or less carbon atoms which may contain one hydrogen atom, and specific examples thereof include -CF ２ CF ２ -, -CF(CF ３ ) -, -CF ２ -, -CF ２ CHFCF ２ - and - CHFCF ２ - is included. １ As -CF(CF ３ )- and -CHFCF ２ - is more preferred, and -CHFCF ２ - is particularly preferred. １ The bond on the right side of each group in the specific examples is Q in formula [1-1]. １ It is a hand that combines with.

[0099] Q in formula [1-1] １ The bonding position of to the aromatic nucleus may be any of the ortho, meta or para positions relative to the bonding position between the aromatic nucleus and the polymer main chain, and the para position is preferred from the viewpoints of ease of synthesis and availability of raw materials.

[0100]

[0101] In formula [1-2], Y ２ represents a hydrogen atom or a methyl group, L １ is 0 or an integer ranging from 1 to 6, and Rfa ２ represents a perfluoroalkyl group having 1 to 6 carbon atoms.

[0102] L １ is 0 or an integer ranging from 1 to 6, preferably 0 to 4, more preferably 0 to 2, and particularly preferably 0 or 1. ２ is a perfluoroalkyl group having 1 to 6 carbon atoms, preferably a perfluoroalkyl group having 2 to 4 carbon atoms, and particularly preferably CF ３ CF ２ CF ２ - is.

[0103] The fluorine-containing polystyrene derivative containing the repeating unit represented by formula [1], formula [1-1] or formula [1-2] can be produced by reacting a reactive group-containing polystyrene derivative, such as a polymer containing a p-hydroxystyrene type repeating unit or a polymer containing a repeating unit derived from p-chloromethylstyrene, with a perfluoro(poly)ether compound or polyfluoro(poly)ether compound containing an active terminal group. For example, a polymer containing a p-hydroxystyrene type repeating unit and CF ２ =CF-[OCF ２ CF (CF ３ )] Ｌ１ -ORfa ２ Type monomer (L １ and Rfa ２ is the same as in formula [1-2]), a polystyrene derivative containing a repeating unit of formula [1-2] can be produced. ２ =CY-Ph-[Q-Rf ０ ] Ｚ Monomer having the structure (Y, Q, Rf ０ and z is the same as in formula [1], and Ph is an abbreviation for phenylene group), a fluorine-containing polystyrene derivative containing a repeating unit represented by formula [1] can also be produced by copolymerization of

[0104] The content of the repeating unit represented by formula [1] (preferably formula [1-1], more preferably formula [1-2]) in the crosslinking group-containing fluorine-containing polystyrene derivative is 1% by mass or more and 99% by mass or less. The lower limit of the content of the repeating unit represented by formula [1] in the crosslinking group-containing fluorine-containing polystyrene derivative is 1% by mass or more, and may be 5% by mass or more, 10% by mass or more, 30% by mass or more, or 50% by mass or more. The upper limit of the content of the repeating unit is 99% by mass or less, and may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0105] The crosslinking group-containing fluorine-containing polystyrene derivative contains, in addition to the repeating unit represented by formula [1], repeating units containing a crosslinking group in an amount of 1% by mass or more and 95% by mass or less. The crosslinking group-containing repeating units in the crosslinking group-containing fluorine-containing polystyrene derivative are preferably, for example, repeating units containing at least one type of crosslinking group selected from an active hydrogen-containing group, a carbon-carbon multiple bond-containing group, an epoxy group, an isocyanate group, and an alkoxysilane group. Examples of the active hydrogen-containing group include a hydroxy group (phenolic hydroxy group, alcoholic hydroxy group), an amino group, a thiol group, and a carboxyl group. Examples of the carbon-carbon multiple bond-containing group include an acrylate group, a methacrylate group, a styrenyl group, an allyl group, a vinyloxy group, and a trifluorovinyloxy group (CF ２ Examples of the epoxy group include a glycidyl group linked to various groups. Examples of the isocyanate group include an aliphatic isocyanate group or an aromatic isocyanate group. Examples of the alkoxysilane group include a trialkoxysilane group, a dialkoxymonoalkylsilane group, and a monoalkoxydialkylsilane group.

[0106] The crosslinking groups in the repeating units containing the crosslinking groups can undergo crosslinking reactions in various ways, including, for example, the following crosslinking reactions:

[0107] (i) Type that crosslinks by reaction between an active hydrogen type crosslinking group and a polyfunctional substance (e.g., crosslinking by reaction between an active hydrogen (alcohol, phenol, amine, thiol, carboxylic acid, etc.) type crosslinking group and a polyfunctional compound (polyisocyanate, polyepoxy, etc.))

[0108] (ii) A type that crosslinks by the reaction of a highly active crosslinking group with a polyfunctional substance (e.g., crosslinking by the reaction of an isocyanate-type crosslinking group or an epoxy-type crosslinking group with a polyvalent active hydrogen compound (polyhydric alcohol, polyhydric phenol, polyvalent amine, polyvalent thiol, polycarboxylic acid-type compound))

[0109] (iii) A type in which a single type of crosslinking group is polymerized to crosslink (e.g., (meth)acrylate-type crosslinking group, styrenyl-type crosslinking group, epoxy-type crosslinking group, oxetane-type crosslinking group, episulfide-type crosslinking group, etc. Examples of polymerization methods: radical polymerization, cationic polymerization, anionic polymerization, thermal polymerization, ultraviolet irradiation).

[0110] The (meth)acrylates include acrylates and methacrylates.

[0111] (iv) A type in which several crosslinking groups of the same type are linked together to form a crosslink (e.g., ethynyl or propargyl crosslinking groups, alkoxysilane crosslinking groups, trifluorovinyloxy crosslinking groups, etc.)

[0112] Specific examples of the repeating unit containing a crosslinking group in the above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative are shown below, however, the repeating unit containing a crosslinking group in the above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative is not limited to these.

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] The crosslinking group-containing repeating unit in the crosslinking group-containing fluorine-containing polystyrene derivative can be introduced by various methods.

[0120] For example, a polymer containing p(para)-hydroxystyrene units as repeating units can be produced by, for example, hydrolysis of a polymer containing repeating units derived from p-acetoxystyrene. The p-hydroxystyrene units can be used as phenolic active hydrogen-type crosslinking groups. Furthermore, the p-hydroxystyrene units can be easily converted into various crosslinking group-containing repeating units by utilizing their high reactivity. Examples include converting the -OH group of the p-hydroxystyrene unit into various types of crosslinking groups such as those shown below. Similarly, the aliphatic alcohol groups of copolymers containing repeating units such as 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate can also be converted into various types of crosslinking groups such as those shown below.

[0121]

[0122] The crosslinking group-containing repeating unit in the above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative can also be introduced by copolymerization of a vinyl polymerizable monomer containing various crosslinking groups with a polystyrene derivative monomer that forms a repeating unit represented by formula [1] (preferably formula [1-1], more preferably formula [1-2]). Examples of vinyl polymerizable (radical polymerizable, cation polymerizable, or anion polymerizable) monomers containing crosslinking groups that can be introduced in this way are shown below. However, the vinyl polymerizable monomers containing various crosslinking groups are not limited to these. Furthermore, a method can also be employed in which active groups such as active hydrogen groups, isocyanate groups, etc. in the vinyl polymerizable monomer are stabilized with protecting groups, copolymerized, and then the protecting groups are removed to activate them.

[0123]

[0124]

[0125]

[0126]

[0127]

[0128] The content of the crosslinking group-containing repeating unit in the crosslinking group-containing fluorine-containing polystyrene derivative is 1% by mass or more and 95% by mass or less. The content of the crosslinking group-containing repeating unit in the crosslinking group-containing fluorine-containing polystyrene derivative is preferably selected from the range of 1% by mass or more and 80% by mass or less, 1% by mass or more and 60% by mass or less, or 1% by mass or more and 50% by mass or less. The crosslinking group-containing repeating unit in the crosslinking group-containing fluorine-containing polystyrene derivative may be of one type or of multiple types.

[0129] The above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative may contain, in addition to the repeating unit represented by formula [1], formula [1-1] or formula [1-2] and the crosslinking group-containing repeating unit, one or more types of repeating units having various structures in order to adjust the properties of the crosslinked body formed by crosslinking at least a part of the crosslinking groups of the above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative.

[0130] For example, the crosslinkable group-containing fluorine-containing polystyrene derivative may contain one or more types of various radically polymerizable, cationically polymerizable, or anionically polymerizable monomer units as repeating units other than the repeating unit represented by formula [1], formula [1-1], or formula [1-2] and the crosslinkable group-containing repeating unit. Specific examples of the polymerizable monomer include various polymerizable monomers such as various substituted styrenes such as α-methylstyrene, p-methylstyrene, p-alkoxystyrene, p-acetoxystyrene, and p-hydroxystyrene (synthesized using a deprotection reaction), unsubstituted styrene, vinylnaphthalene, acenaphthylene, maleic anhydride or a derivative thereof, maleimide derivatives, (meth)acrylonitrile, (meth)acrylamide and its derivatives, various (meth)acrylic acid esters, fluorine-containing (meth)acrylic acid esters, various fluorine-containing olefins, various vinyl carboxylates, and various vinyl ethers.

[0131] In the above-mentioned crosslinking group-containing fluorine-containing polystyrene derivative, the content of the repeating unit represented by formula [1], formula [1-1] or formula [1-2] and the repeating unit other than the crosslinking group-containing repeating unit may be in the range of 0 mass % or more and 90 mass % or less, 0 mass % or more and 60 mass % or less, or 0 mass % or more and 40 mass % or less, based on the total mass of the crosslinking group-containing fluorine-containing polystyrene derivative.

[0132] Examples of methods for producing a crosslinkable polystyrene derivative containing a repeating unit other than the repeating unit represented by the formula [1] and the crosslinkable repeating unit include, but are not limited to, the following methods: (1) CF to a phenolic hydroxy group in a copolymer consisting of a p-hydroxystyrene unit, a crosslinkable repeating unit, and various monomer units ２ =CF-[OCF ２ CF (CF ３ )] Ｌ１ -ORfa ２ active end group-containing perfluoro(poly)ether compounds (L １ , Rfa ２ is the same as in formula [1-2]). (2) CH ２ =CY-Ph-[Q-Rf ｏ ] Ｚ Monomer having the structure (Y, Q, Rf ｏ and z are the same as in formula [1], and Ph is an abbreviation for phenylene group), and a production method utilizing copolymerization of a crosslinking group-containing monomer with various monomers.

[0133] As the crosslinking group-containing fluorine-containing polystyrene derivative, polymers of various structures and sequences produced by various production methods can be used. For example, the crosslinking group-containing fluorine-containing polystyrene derivative can be produced by various copolymerization methods such as radical copolymerization, cationic copolymerization, or anionic copolymerization. Furthermore, the reactive groups contained in the copolymer produced by such copolymerization can be converted to other types of reactive groups to produce a polymer having the desired crosslinking reactivity. Furthermore, as the crosslinking group-containing fluorine-containing polystyrene derivative, polymers of various structures such as random copolymers, block copolymers, graft copolymers, or star polymers can be used.

[0134] One or more fluorine-based compounds can be used to produce the magnetic tape. In one embodiment, a magnetic tape containing a fluorine-based compound in the magnetic layer side can be produced by adding the fluorine-based compound as a component of the magnetic layer-forming composition (so-called internal addition to the magnetic layer). Internal addition is an abbreviation for internal addition. In another embodiment, a coating liquid containing the fluorine-based compound is prepared and applied to the surface of the magnetic layer (so-called overcoat), thereby allowing the fluorine-based compound to be present in the magnetic layer side. The amount of the fluorine-based compound added to the magnetic layer-forming composition can be, for example, 0.3 to 3.0 parts by weight, 0.3 to 2.0 parts by weight, or 0.5 to 1.5 parts by weight per 100.0 parts by weight of ferromagnetic powder. However, the above ranges are merely examples, and the amount added can be adjusted depending on the type of fluorine-based compound, etc.

[0135] The magnetic layer described above can be provided directly on the surface of the non-magnetic support, or indirectly via a non-magnetic layer.

[0136] <Nonmagnetic Layer> The magnetic tape may have a magnetic layer directly on the surface of the nonmagnetic support, or may have a nonmagnetic layer containing nonmagnetic powder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder contained in the nonmagnetic layer may be inorganic or organic. Carbon black or the like may also be used. Examples of inorganic powders include powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are commercially available or can be produced by known methods. For details, see paragraphs 0036 to 0039 of JP 2010-24113 A. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90% by mass, more preferably 60 to 90% by mass, based on the total mass of the nonmagnetic layer.

[0137] The non-magnetic layer contains a non-magnetic powder and may also contain a binder together with the non-magnetic powder. For details of the binder, additives, etc. of the non-magnetic layer, known techniques related to non-magnetic layers can be applied. Furthermore, for example, known techniques related to magnetic layers can also be applied to the type and content of the binder and the type and content of the additives.

[0138] The non-magnetic layer of the magnetic tape also includes a substantially non-magnetic layer that contains a small amount of ferromagnetic powder, either as an impurity or intentionally, along with the non-magnetic powder. Here, a substantially non-magnetic layer refers to a layer having a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a layer having a residual magnetic flux density of 10 mT or less and a coercive force of 7.96 kA / m (100 Oe) or less. It is preferable that the non-magnetic layer have no residual magnetic flux density or coercive force.

[0139] <Backcoat Layer> The magnetic tape may have a backcoat layer containing a nonmagnetic powder on the surface of the nonmagnetic support opposite to the surface having the magnetic layer. Alternatively, the magnetic tape may not have a backcoat layer. The backcoat layer may contain either or both of carbon black and inorganic powder.

[0140] The backcoat layer contains a non-magnetic powder, may contain a binder, and may also contain one or more additives. Known techniques for backcoat layers can be applied to the binder and additives of the backcoat layer, and known techniques for formulating magnetic and / or non-magnetic layers can also be applied. For example, see paragraphs

[0018] to

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

[0141] <Non-magnetic Support> Next, the non-magnetic support will be described. Examples of non-magnetic supports (hereinafter also simply referred to as "support") include known materials such as biaxially stretched polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides such as aromatic polyamides, and polyamideimides. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be previously subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, etc.

[0142] In one embodiment, the support included in the magnetic tape can be a polyester support. In the present invention and this specification, "polyester" refers to a resin containing multiple ester bonds. A "polyester support" refers to a support containing at least one layer of polyester film. A "polyester film" refers to a film in which the component that constitutes the film in the largest proportion by mass is polyester. In the present invention and this specification, the term "polyester support" encompasses support in which all resin films contained in the support are polyester films and support in which polyester films are mixed with other resin films. Specific forms of polyester support include a single-layer polyester film, a laminate film of two or more polyester film layers with the same constituent components, a laminate film of two or more polyester film layers with different constituent components, and a laminate film containing one or more polyester film layers and one or more resin film layers other than polyester. An adhesive layer or the like may optionally be included between two adjacent layers in the laminate film. Furthermore, the polyester support may optionally include a metal film and / or metal oxide film formed by vapor deposition or the like on one or both surfaces. The same applies to "aromatic polyester support," "polyethylene terephthalate support," and "polyethylene naphthalate support" in the present invention and this specification.

[0143] The polyester support may be an aromatic polyester support. In the present invention and the present specification, "aromatic polyester" means a resin containing an aromatic backbone and a plurality of ester bonds, and "aromatic polyester support" means a support comprising at least one layer of an aromatic polyester film.

[0144] The aromatic ring contained in the aromatic skeleton of the aromatic polyester is not particularly limited. Specific examples of aromatic rings include a benzene ring and a naphthalene ring. For example, polyethylene terephthalate (PET) is a polyester containing a benzene ring and is a resin obtained by polycondensation of ethylene glycol with terephthalic acid and / or dimethyl terephthalate. The term "polyethylene terephthalate" in this invention and this specification also includes structures having one or more other components (e.g., copolymerized components, components introduced into the terminal or side chain) in addition to the above components. Polyethylene naphthalate (PEN) is a polyester containing a naphthalene ring and is a resin obtained by esterification of dimethyl 2,6-naphthalenedicarboxylate with ethylene glycol, followed by transesterification and polycondensation reactions. The term "polyethylene naphthalate" in this invention and this specification also includes structures having one or more other components (e.g., copolymerized components, components introduced into the terminal or side chain) in addition to the above components.

[0145] <Various Thicknesses> The 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, even more preferably 5.2 μm or less, even more preferably 5.0 μm or less, and even more preferably 4.8 μm or less. With the enormous increase in the amount of information in recent years, there is a demand for magnetic tapes to have higher recording capacities (higher capacity). For example, with regard to tape-shaped magnetic tapes (i.e., magnetic tapes), one way to increase the capacity is to reduce the thickness of the magnetic tape and increase the length of magnetic tape accommodated in one magnetic tape cartridge. Furthermore, from the viewpoint of ease of handling, the total thickness of the magnetic tape is preferably 3.0 μm or more, more preferably 3.5 μm or more, and even more preferably 4.0 μm or more.

[0146] For example, the total thickness of a magnetic tape can be measured by the following method. Ten samples (e.g., 5 to 10 cm long) are cut from any part of the magnetic tape, and these samples are stacked and the thickness is measured. The measured thickness is divided by 10, and the resulting value (thickness per sample) is taken as the total thickness. The thickness measurement can be performed using a known measuring device capable of measuring thickness on the order of 0.1 μm.

[0147] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized depending on the saturation magnetization of the magnetic head used, the head gap length, the bandwidth of the recording signal, etc., and is generally 0.01 μm to 0.15 μm. From the viewpoint of high-density recording, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers with different magnetic properties, and known multilayer magnetic layer configurations can be applied. When the magnetic layer is separated into two or more layers, the thickness refers to the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.7 μm. The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. Various thicknesses, such as the thickness of the magnetic layer, can be determined by the following method. After exposing a cross section of the magnetic tape in the thickness direction with an ion beam, the exposed cross section is observed using a scanning electron microscope or a transmission electron microscope. The thicknesses can be calculated as the arithmetic mean of the thicknesses measured at any two points during the cross section observation. Alternatively, the thicknesses can be calculated as the design thickness calculated from the manufacturing conditions, etc.

[0148] <Manufacturing Process> The compositions for forming the magnetic layer, non-magnetic layer, and backcoat layer typically contain a solvent in addition to the various components described above. The solvent can be one or more of the various organic solvents commonly used in the production of particulate magnetic recording media. Specifically, any ratio of ketone-based solvents, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, or tetrahydrofuran, alcohol-based solvents, such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, or methylcyclohexanol, ester-based solvents, such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, or glycol acetate, glycol ether-based solvents, such as glycol dimethyl ether, glycol monoethyl ether, or dioxane, aromatic hydrocarbon-based solvents, such as benzene, toluene, xylene, cresol, or chlorobenzene, chlorinated hydrocarbon-based solvents, such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, or dichlorobenzene, N,N-dimethylformamide, hexane, or the like, can be used. In particular, from the viewpoint of the solubility of binders typically used in particulate magnetic recording media, it is preferred that the magnetic layer-forming composition contain one or more ketone-based solvents. The amount of solvent in each layer-forming composition is not particularly limited, and can be the same as that in each layer-forming composition of typical particulate magnetic recording media.

[0149] The process for preparing each layer-forming composition usually includes at least a kneading process, a dispersing process, and a mixing process performed before or after these processes as needed. Each process may be divided into two or more stages. The various components used in preparing each layer-forming composition may be added at the beginning or during any process. Alternatively, each component may be added in portions in two or more processes.

[0150] Known techniques can be used to prepare each layer-forming composition. For the kneading process, it is preferable to use a kneader with strong kneading power, such as an open kneader, continuous kneader, pressure kneader, or extruder. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-79274. Furthermore, to disperse each layer-forming composition, one or more dispersing beads selected from the group consisting of glass beads and other dispersing beads can be used as a dispersing medium. High-specific-gravity dispersing beads such as zirconia beads, titania beads, and steel beads are suitable. The particle size (bead diameter) and packing rate of these dispersing beads can be optimized. Known dispersing machines can be used. Each layer-forming composition may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration. Filters with pore sizes of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.) can be used for filtration.

[0151] Regarding the preparation of the magnetic layer-forming composition, the centrifugation for preparing the abrasive dispersion is as described above.

[0152] The magnetic layer can be formed, for example, by directly applying the magnetic layer-forming composition onto the non-magnetic support, or by sequentially or simultaneously applying a multilayer coating together with the non-magnetic layer-forming composition. The backcoat layer can be formed by applying the backcoat layer-forming composition to the side of the non-magnetic support opposite to the side on which the magnetic layer is present (or on which the magnetic layer will be subsequently formed). For details on the coating for forming each layer, see paragraph 0051 of JP 2010-24113 A.

[0153] After the coating step, various treatments can be performed, such as a drying treatment, a magnetic layer orientation treatment, a surface smoothing treatment (calendering treatment), etc. For the various treatments, reference can be made to known techniques such as those described in paragraphs 0052 to 0057 of JP 2010-24113 A.

[0154] For example, a coating layer of a magnetic layer-forming composition can be subjected to an orientation treatment while the coating layer is still wet. Various known techniques, including those described in paragraph 0067 of JP 2010-231843 A, can be applied to the orientation treatment. For example, vertical orientation treatment can be performed by known methods, such as a method using magnets with opposite poles facing each other. In the orientation zone, the drying rate of the coating layer can be controlled by the temperature and volume of the drying air and / or the transport speed of the non-magnetic support on which the coating layer is formed. The coating layer may also be pre-dried before being transported to the orientation zone. Strengthening the orientation conditions tends to increase the squareness ratio of the magnetic tape. The squareness ratio of the magnetic tape can be controlled by whether or not an orientation treatment is performed, the orientation conditions of the orientation treatment, etc. Orientation conditions include the strength of the magnet used in the orientation treatment and the duration of magnetic field application.

[0155] Regarding calendering, increasing the calendering conditions tends to result in a smoother surface of the magnetic layer of the magnetic tape. Calendering conditions include calendering pressure, calendering temperature (calender roll surface temperature), calendering speed, and calender roll hardness. The higher the calendering pressure, calendering temperature, and calender roll hardness, the stronger the calendering, and the slower the calendering speed. For example, the calendering pressure (linear pressure) can be 200 to 500 kN / m, preferably 250 to 350 kN / m. The calendering temperature (calender roll surface temperature) can be, for example, 85 to 120°C, preferably 90 to 110°C, and more preferably 95 to 110°C. The calendering speed can be, for example, 50 to 300 m / s, preferably 50 to 200 m / s.

[0156] <Perpendicular Squareness> In one embodiment, the perpendicular squareness of the magnetic tape can be 0.60 or more, preferably 0.63 or more, and more preferably 0.65 or more. The maximum value of the perpendicular squareness is 1.00 in principle. Therefore, the perpendicular squareness of the magnetic tape is 1.00 or less, and can be 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, or 0.70 or less. A large perpendicular squareness is preferable from the viewpoint of improving electromagnetic conversion characteristics.

[0157] In the present invention and this specification, the perpendicular squareness of a magnetic tape is the squareness measured in the perpendicular direction of the magnetic tape. The perpendicular direction is the direction perpendicular to the surface of the magnetic tape, and can also be called the thickness direction. The perpendicular squareness is determined from the perpendicular M-H curve. The perpendicular squareness is determined by measurements performed using a vibrating sample magnetometer, sweeping an external magnetic field on the magnetic tape over a magnetic field strength range of -1197 kA / m to 1197 kA / m. With regard to magnetic field strength, the conversion factor from the unit Oe (oersted) to the SI unit A / m is 10 ３ / 4π. The range of -1197 kA / m to 1197 kA / m is synonymous with the range of -15 kOe to 15 kOe. In this invention and this specification, measurements using a vibrating sample magnetometer are performed at a measurement temperature of 24°C ± 1°C. The external magnetic field is swept using a measurement sample cut from the magnetic tape to be measured, according to the sweep conditions shown in Table 2 below, with the average number at each step being 1. By sweeping the external magnetic field in this manner, a hysteresis curve (called an "M-H curve") is obtained over a magnetic field strength range of -1197 kA / m to 1197 kA / m. An M-H curve obtained by measurement in which the measurement sample is placed in a vibrating sample magnetometer so that the direction of application of the external magnetic field is perpendicular to the surface of the measurement sample is called a "perpendicular M-H curve." The above term "perpendicular" is intended to include the range of error acceptable in the technical field to which this invention pertains. The error range means, for example, a range of less than ±10° from the exact orthogonal angle, preferably within ±5° from the exact orthogonal angle, and more preferably within ±3°. The measured value is obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. The squareness ratio is the squareness ratio without demagnetizing field correction. As the vibrating sample magnetometer (VSM), a known device such as the device used in the examples described later can be used. The measurement sample has a saturation magnetization of 5×10 calculated from the M-H curve obtained in this way. －６ ~10 x 10 －６ A.m. ２ (5 x 10 －３ ~10 x 10 －３ The size and shape are not limited as long as the saturation magnetization in this range is obtained.

[0158] The magnetic tape is housed in, for example, a magnetic tape cartridge, and the magnetic tape cartridge is loaded into a magnetic recording and reproducing device. Servo patterns can be formed on the magnetic tape by a known method to enable head tracking in the magnetic recording and reproducing device. "Formation of servo patterns" can also be referred to as "recording of servo signals." The formation of servo patterns will be explained below using magnetic tape as an example.

[0159] The servo patterns are usually formed along the longitudinal direction of the magnetic tape. Control methods using servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0160] As specified in ECMA (European Computer Manufacturers Association)-319 (June 2001), magnetic tapes (commonly referred to as "LTO tapes") conforming to the LTO (Linear Tape-Open) specification employ a timing-based servo system. In this timing-based servo system, a servo pattern is formed by a pair of non-parallel magnetic stripes (also referred to as "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. As described above, the reason why the servo pattern is formed by a pair of non-parallel magnetic stripes is to inform a servo signal reading element passing over the servo pattern of its passing position. Specifically, the pair of magnetic stripes is formed so that the spacing between them changes continuously 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 the spacing. This relative position information enables tracking of data tracks. For this reason, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

[0161] A servo band is made up of a series of servo signals that run longitudinally on the magnetic tape. A magnetic tape typically has multiple servo bands. For example, an LTO tape has five servo bands. The area between two adjacent servo bands is called a data band. A data band is made up of multiple data tracks, each corresponding to a servo track.

[0162] Also, in one embodiment, as disclosed in Japanese Patent Laid-Open Publication No. 2004-318983, information indicating the servo band number (also referred to as "servo band ID (identification)" or "UDIM (Unique Data Band Identification Method) information") is embedded in each servo band. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the way in which a specific one of a plurality of pairs of servo stripes is shifted is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, and therefore, simply by reading one servo band with a servo signal reading element, that servo band can be uniquely identified.

[0163] One method for uniquely identifying servo bands is to use the staggered method as specified in ECMA-319 (June 2001). In this staggered method, a group of pairs of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded so that each servo band is shifted along the longitudinal direction of the magnetic tape. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern using two servo signal reading elements.

[0164] Furthermore, as specified in ECMA-319 (June 2001), information indicating the longitudinal position of the magnetic tape (also called "LPOS (Longitudinal Position) information") is usually embedded in each servo band. Like UDIM information, this LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike UDIM information, the same signal is recorded in each servo band for this LPOS information.

[0165] It is also possible to embed information other than the above-mentioned UDIM information and LPOS information in the servo bands. In this case, the embedded information may be different for each servo band, such as UDIM information, or may be common to all servo bands, such as LPOS information. Furthermore, methods other than those described above can also be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of pairs of servo stripes.

[0166] The servo pattern forming head is called a servo write head. The servo write head has pairs of gaps corresponding to the pairs of magnetic stripes, the number of which is equal to the number of servo bands. Typically, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, the magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps. When forming a servo pattern, a current pulse is input while running a magnetic tape over the servo write head, thereby transferring the magnetic pattern corresponding to the pair of gaps to the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set depending on the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, or 10 μm or more.

[0167] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a direct current magnet or an alternating current magnet. Erase processes include DC (direct current) erase and AC (alternating current) erase. AC erase is performed by gradually reducing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erase is performed by applying a unidirectional magnetic field to the magnetic tape. There are two other DC erase methods. The first method is horizontal DC erase, in which a unidirectional magnetic field is applied along the longitudinal direction of the magnetic tape. The second method is vertical DC erase, in which a unidirectional magnetic field is applied along the thickness direction of the magnetic tape. The erase process can be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0168] The direction of the magnetic field of the formed servo pattern is determined depending on the erase direction. For example, when horizontal DC erasure is performed on a magnetic tape, the servo pattern is formed so that the direction of the magnetic field is opposite to the erase direction. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred using the above-mentioned gap to a magnetic tape that has been vertically DC erased, the servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when a magnetic pattern is transferred using the above-mentioned gap to a magnetic tape that has been horizontally DC erased, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0169] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape described above.

[0170] The details of the magnetic tape contained in the magnetic tape cartridge are as described above.

[0171] A magnetic tape cartridge generally contains a magnetic tape wound on a reel within the cartridge body. The reel is rotatably mounted within the cartridge body. Widely used magnetic tape cartridges include single-reel magnetic tape cartridges with one reel within the cartridge body and dual-reel magnetic tape cartridges with two reels within the cartridge body. When a single-reel magnetic tape cartridge is loaded into a magnetic recording and playback device for recording and / or playback of data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound onto a reel on the magnetic recording and playback device. A magnetic head is disposed along the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound between the reel (supply reel) on the magnetic tape cartridge and the reel (take-up reel) on the magnetic recording and playback device. During this process, the magnetic head comes into contact with and slides against the surface of the magnetic layer of the magnetic tape, thereby recording and / or playback of data. In contrast, a dual-reel magnetic tape cartridge has both a supply reel and a take-up reel inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single-reel or dual-reel magnetic tape cartridge. The magnetic tape cartridge may include the magnetic tape according to one aspect of the present invention, and other known technologies may be applied.

[0172] [Magnetic Recording and Reproducing Apparatus] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including the above-described magnetic tape.

[0173] In this invention and this specification, the term "magnetic recording and reproducing device" refers to a device capable of at least one of recording data to a magnetic tape and reproducing data recorded on the magnetic tape. Such devices are generally called drives. The magnetic recording and reproducing device may be, for example, a sliding-type magnetic recording and reproducing device. A sliding-type magnetic recording and reproducing device is a device in which a magnetic head contacts and slides against the surface of the magnetic layer of the magnetic tape when recording data on the magnetic tape and / or reproducing recorded data. For example, the magnetic recording and reproducing device may include a detachable magnetic tape cartridge.

[0174] The magnetic recording and reproducing device may include a magnetic head. The magnetic head may be a recording head capable of recording data on a magnetic tape, or a reproducing head capable of reproducing data recorded on the magnetic tape. In one embodiment, the magnetic recording and reproducing device may include both a recording head and a reproducing head as separate magnetic heads. In another embodiment, the magnetic head included in the magnetic recording and reproducing device may have a configuration in which a single magnetic head includes both an element for recording data (a recording element) and an element for reproducing data (a reproducing element). Hereinafter, the element for recording data and the element for reproducing data are collectively referred to as a "data element." The reproducing head is preferably a magnetic head (MR head) including a magnetoresistive (MR) element as a reproducing element, capable of sensitively reading data recorded on a magnetic tape. The MR head may be any of various known MR heads, such as an AMR (Anisotropic Magnetoresistive) head, a GMR (Giant Magnetoresistive) head, or a TMR (Tunnel Magnetoresistive) head. The magnetic head that records and / or reproduces data may include a servo signal read element. Alternatively, the magnetic recording and reproducing device may include a magnetic head (servo head) equipped with a servo signal read element, separate from the magnetic head that records and / or reproduces data. For example, the magnetic head that records and / or reproduces recorded data (hereinafter also referred to as a "recording and reproducing head") may include two servo signal read elements, each capable of simultaneously reading two adjacent servo bands. One or more data elements may be disposed between the two servo signal read elements.

[0175] In the magnetic recording and reproducing device, recording of data on the magnetic tape and / or reproducing of data recorded on the magnetic tape can be performed, for example, by contacting and sliding a magnetic head against the surface of the magnetic tape on the magnetic layer side. The magnetic recording and reproducing device may be any device that includes the magnetic tape according to one aspect of the present invention, and publicly known techniques may be applied for other aspects.

[0176] For example, when recording data and / or reproducing recorded data, tracking using a servo signal is first performed. That is, by making the servo signal read element follow a predetermined servo track, the data element is controlled so that it passes over the target data track. The data track is moved by changing the servo track read by the servo signal read element in the tape width direction. The recording / reproducing head can also record and / or reproduce data on other data bands. In this case, the servo signal read element is moved to a predetermined servo band using the UDIM information described above, and tracking on that servo band is then started.

[0177] The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the embodiments shown in the examples. "Parts" and "%" described below refer to "parts by mass" and "% by mass" unless otherwise specified. The following steps and evaluations were carried out in air at room temperature (20 to 25°C) unless otherwise specified. "eq" described below is equivalent, and is a unit that cannot be converted to SI units.

[0178] [Ferromagnetic Powder] In Table 1, "BaFe" in the "Ferromagnetic Powder" column represents hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm.

[0179] In Table 1, "SrFe" in the "Ferromagnetic Powder" column indicates a hexagonal strontium ferrite powder prepared as follows: SrCO ３ 1707g, H ３ BO ３ 687g, Fe ２ O ３1120 g of Al(OH) ３ 45g, BaCO ３ 24 g, CaCO ３ 13 g, and Nd ２ O ３ 235 g of the above was weighed and mixed in a mixer to obtain a raw material mixture. The resulting raw material mixture was melted in a platinum crucible at a melting temperature of 1390 ° C., and the melt was stirred while heating the tapping port at the bottom of the platinum crucible, and the melt was poured into a rod-like shape at approximately 6 g / sec. The tapped liquid was rolled and quenched with a water-cooled twin roller to produce an amorphous body. 280 g of the produced amorphous body was charged into an electric furnace, heated to 635 ° C (crystallization temperature) at a heating rate of 3.5 ° C / min, and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was coarsely crushed in a mortar, and 1000 g of zirconia beads with a particle size of 1 mm and 800 mL of a 1% acetic acid aqueous solution were added to a glass bottle containing the crushed product, and the mixture was dispersed for 3 hours using a paint shaker. The resulting dispersion was then separated from the beads and placed in a stainless steel beaker. The dispersion was left to stand for 3 hours at a liquid temperature of 100°C to dissolve the glass component, and then precipitated in a centrifuge, washed by repeated decantation, and dried for 6 hours in a heating furnace at a furnace temperature of 110°C to obtain a hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder obtained above had an average particle size of 18 nm and an activation volume of 902 nm. ３ , the anisotropy constant Ku is 2.2 × 10 ５ J / m ３ , mass magnetization σs is 49A・m ２ / kg. 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and this sample powder was partially dissolved under the dissolution conditions exemplified above. The obtained filtrate was subjected to elemental analysis using an ICP analyzer to determine the surface content of neodymium atoms. Separately, 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above. This sample powder was completely dissolved under the dissolution conditions exemplified above. The obtained filtrate was subjected to elemental analysis using an ICP analyzer to determine the bulk content of neodymium atoms. The content of neodymium atoms (bulk content) relative to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. The surface content of neodymium atoms was 8.0 atomic %. The ratio of the surface content to the bulk content, "surface content / bulk content," was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layers of the particles.

[0180] The powder obtained above was confirmed to have a hexagonal ferrite crystal structure by scanning with CuKα radiation at a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. The crystalline phase detected by X-ray diffraction analysis was a single magnetoplumbite-type phase. PANalytical X'Pert Pro diffractometer, PIXcel detector. Soller slits for incident beam and diffracted beam: 0.017 radians. Fixed angle of dispersion slit: 1 / 4 degree. Mask: 10 mm. Anti-scatter slit: 1 / 4 degree. Measurement mode: continuous. Measurement time per step: 3 seconds. Measurement speed: 0.017 degrees per second. Measurement step: 0.05 degrees.

[0181] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powder were determined by the method described above using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) and the mass magnetization σs was measured at a magnetic field strength of 1194 kA / m (15 kOe) using the vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.).

[0182] Example 1 Preparation of Alumina Dispersion A (Abrasive Liquid) Alumina dispersion A had an alpha conversion rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of ​​21 m ２ 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) with a molecular weight of 1 / g, 3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), SO as a polar group, ３ 31.3 parts of a 32% solution (solvent: a mixed solvent of methyl ethyl ketone and toluene) of a polyester polyurethane resin having Na groups (UR-4800 (polar group amount: 80 meq / kg) manufactured by Toyobo Co., Ltd.) was mixed with 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone at a 1:1 (mass ratio) as the solvent, and the mixture was dispersed for 5 hours using a paint shaker in the presence of zirconia beads. After dispersion, the dispersion and the beads were separated using a mesh to obtain an alumina dispersion. Next, this alumina dispersion was subjected to a flow centrifuge (Hitachi ultracentrifuge CP100WX) and classified by the following method. The viscosity of the alumina dispersion prepared above was measured, and the gravitational acceleration was adjusted by changing the rotation speed of the cylinder according to the Stokes equation and centrifugal theory to match the lower limit of the particle size range (hereinafter also referred to as "D") to be removed. In the case of alumina dispersion A used as the polishing compound liquid in Example 1, D was set to 130 nm, and centrifugal separation was carried out at 6000 G to remove particles with a diameter of 130 nm or more. ２ The supernatant liquid obtained after centrifugal separation for 1 hour was designated as Alumina Dispersion A. The solid content of Alumina Dispersion A was adjusted to 12% with a mixed solution of methyl ethyl ketone and cyclohexanone in a 1:1 (mass ratio).

[0183] <Formulation of composition for forming magnetic layer> (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts SO ３ Na group-containing vinyl chloride copolymer: 10.0 parts Weight average molecular weight: 70,000, SO ３ Na group: 0.2 meq / g SO ３ Na group-containing polyurethane resin: 4.0 parts Weight average molecular weight: 70,000, SO ３Na group: 0.2 meq / g Cyclohexanone: 150.0 parts Methyl ethyl ketone: 170.0 parts (Abrasive liquid) Alumina dispersion A: 50.0 parts (6.0 parts as abrasive (solid content)) (Other components) Carbon black: 0.5 parts Average particle size: 80 nm Stearic acid: 1.0 part Stearic acid amide: 0.3 parts Butyl stearate: 6.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark)): 2.5 parts (Finishing additive solvent) Cyclohexanone: 300.0 parts Methyl ethyl ketone: 140.0 parts

[0184] <Formulation of composition for forming non-magnetic layer> Non-magnetic inorganic powder (α-iron oxide): 100.0 parts Average particle size (average major axis length): 0.15 μm, average acicular ratio: 7, BET specific surface area: 52 m ２ / g Carbon black: 30.0 parts Average particle size: 20 nm SO ３ Na group-containing vinyl chloride copolymer: 20.0 parts Weight average molecular weight: 70,000, SO ３ Na group: 0.2 meq / g SO ３ Na group-containing polyurethane resin: 100.0 parts Weight average molecular weight: 70,000, SO ３ Na group: 0.2 meq / g Trioctylamine: 1.0 part Phenylphosphonic acid: 4.0 parts Stearic acid: 1.0 part Stearic acid amide: 0.3 parts Butyl stearate: 3.0 parts Cyclohexanone: 450.0 parts Methyl ethyl ketone: 450.0 parts

[0185] <Formulation of composition for forming backcoat layer> Carbon black: 100.0 parts Average particle size: 40 nm, DBP (Dibutyl phthalate) oil absorption: 74 cm ３ / 100g Copper phthalocyanine: 3.0 parts Nitrocellulose: 25.0 parts Sulfonic acid group-containing polyester polyurethane resin (UR-8401 manufactured by Toyobo Co., Ltd.): 60 parts Polyester resin (Vylon 500 manufactured by Toyobo Co., Ltd.): 4.0 parts Alumina powder (specific surface area 17 m ２ / g α-alumina): 1.0 part Polyisocyanate (Takenate D-101E manufactured by Mitsui Chemicals): 15.0 parts Methyl ethyl ketone: 600.0 parts Toluene: 600.0 parts

[0186] <Preparation of Compositions for Forming Each Layer> A magnetic layer-forming composition was prepared using the following method. The various components of the magnetic liquid were mixed using a homogenizer, and then bead-dispersed for 10 minutes using zirconia beads with a bead diameter of 0.05 mm in a continuous horizontal bead mill to prepare a magnetic liquid. Using the bead mill, the magnetic liquid was mixed with the abrasive liquid, other components, and finishing additive, and then treated (ultrasonic dispersion) for 0.5 minutes using a batch ultrasonicator (20 kHz, 300 W). The mixture was then filtered using a filter with a pore size of 0.5 μm to prepare a magnetic layer-forming composition. A non-magnetic layer-forming composition was prepared using the following method. The various components, excluding stearic acid and butyl stearate, were dispersed for 12 hours using a batch vertical sand mill to obtain a dispersion. Zirconia beads with a bead diameter of 0.1 mm were used as dispersing beads. The remaining components were then added to the resulting dispersion and stirred with a disperser. The dispersion thus obtained was filtered using a filter with a pore size of 0.5 μm to prepare a composition for forming a nonmagnetic layer. A composition for forming a backcoat layer was prepared by the following method. The above components, excluding the polyisocyanate, were introduced into a dissolver mixer and stirred at a peripheral speed of 10 m / s for 30 minutes, and then dispersed using a horizontal bead mill disperser. The polyisocyanate was then added, and the mixture was stirred and mixed using the dissolver mixer to prepare a composition for forming a backcoat layer.

[0187] <Magnetic Tape Preparation> A nonmagnetic layer-forming composition was applied to the surface of a 3.6 μm-thick polyethylene naphthalate support, resulting in a dried thickness of 0.7 μm, and then dried to form a nonmagnetic layer. A magnetic layer-forming composition was then applied to the surface of the formed nonmagnetic layer, resulting in a dried thickness of 70 nm, to form a coating layer. While this coating layer was still wet, a magnetic field with a strength of 0.4 T was applied perpendicularly to the surface of the coating layer to perform a vertical orientation treatment, and the coating layer was then dried. A backcoat layer-forming composition was then applied to the surface of the polyethylene naphthalate support opposite the surface on which the nonmagnetic and magnetic layers were formed, resulting in a dried thickness of 0.3 μm, and then dried. The surface was then smoothed (calendered) using a calender roll consisting solely of a metal roll at a speed of 100 m / s, a linear pressure of 300 kg / cm (294 kN / m), and a calender temperature of 100° C. (calender roll surface temperature). The magnetic tape was then subjected to a heat treatment in an ambient temperature of 70° C. for 36 hours and then slit into a width of 1 / 2 inch (0.0127 m) to obtain a magnetic tape. The thickness of each layer was a design thickness calculated from the manufacturing conditions.

[0188] Examples 2 to 13, Comparative Examples 1 to 4 Magnetic tapes were prepared using the same method as in Example 1, except that the items shown in Table 1 were changed as shown in Table 1. For Examples 9 to 12, a fluorine-based compound was added to the magnetic layer-forming composition. The fluorine-based compound added was a crosslinkable fluorine-containing polystyrene derivative containing 1% by mass to 99% by mass of the repeating unit represented by the aforementioned formula [1-2] and 1% by mass to 95% by mass of a crosslinkable repeating unit. The crosslinkable repeating unit has an epoxy group as the crosslinking group. Specifically, when preparing the magnetic liquid, a commercially available additive containing the crosslinkable fluorine-containing polystyrene derivative (fluorine resin additive Neofluoripeal "NFR-325" manufactured by Noda Screen Co., Ltd.) was used in an amount corresponding to the amount of the additive per 100.0 parts of ferromagnetic powder contained in the magnetic layer-forming composition shown in Table 1. For Comparative Example 3, no classification was performed in the preparation of alumina dispersion A (abrasive liquid).

[0189]

[0190] [Evaluation Method] <Standard Deviation of Guide Roll Friction Force> For each of Examples 1 to 13 and Comparative Examples 1 to 4, a magnetic tape approximately 100 m long was cut out from the magnetic tape produced above and wound around the feed roll 1 of a reel-to-reel measuring device configured as shown in Figure 1. The magnetic tape was wound so that the backcoat layer was in contact with pass rolls 5 and 6. Thereafter, the standard deviation of the guide roll friction force was determined by the method described above.

[0191] <SEM 140 nm or larger bright portion surface area ratio> For each of Examples 1 to 13 and Comparative Examples 1 to 4, a measurement sample was cut out from the magnetic tape prepared as described above, and a Hitachi FE-SEM S4800 was used as the FE-SEM to determine the SEM 140 nm or larger bright portion surface area ratio by the method described above. ImageJ was used as the image analysis software. Noise removal processing was performed by the following method. That is, in the image analysis software ImageJ, the noise cut processing Despeckle was selected and noise components were removed.

[0192] <Total Thickness of Magnetic Tape> For each of Examples 1 to 13 and Comparative Examples 1 to 4, ten 5 cm long measurement samples were cut from the magnetic tape prepared above, and these measurement samples were stacked and measured for thickness. The thickness was measured using a digital thickness meter equipped with a Millimar 1240 compact amplifier and a Millimar 1301 inductive probe manufactured by MARH. The measured thickness was divided by 10 to obtain the value (thickness per measurement sample) as the total thickness of the magnetic tape. In all of Examples 1 to 13 and Comparative Examples 1 to 4, the total thickness of the magnetic tape was 4.7 μm.

[0193] <Vertical Squareness Ratio> For each of Examples 1 to 13 and Comparative Examples 1 to 4, three measurement samples measuring 12 mm short x 32 mm long were cut from the magnetic tape prepared above. Each measurement sample was folded once along the short side and twice along the long side to a size of 6 mm x 8 mm. The three folded measurement samples were stacked and placed in a vibrating sample magnetometer. The three measurement samples were stacked so that their orientations (the longitudinal and transverse directions of the measurement sample) were aligned. A Toei Industry Co., Ltd. TEM-WF82.5R-152 vibrating sample magnetometer was used, and an external magnetic field was swept at a measurement temperature of 24°C to obtain hysteresis curves (M-H curves). Measurements to obtain the vertical M-H curves were performed by placing the measurement sample in the vibrating sample magnetometer so that the magnetic field application direction and the surface of the measurement sample were perpendicular to each other. The external magnetic field was swept according to the sweep conditions shown in Table 2, with the average number at each step being 1, starting from a magnetic field strength of 1197 kA / m, swept down to -1197 kA / m, and then swept back down to 1197 kA / m. The sweep conditions shown in Table 2 were performed sequentially from top to bottom. The total sweep time was 312 seconds. Furthermore, the magnetization of only the measurement sample probe was measured in advance, and this was subtracted as background noise during measurement. The saturation magnetization calculated from the perpendicular M-H curves thus obtained for each measurement sample was 5 x 10 －６ ~10 x 10 －６ A.m. ２ (5 x 10 －３ ~10 x 10 －３ The perpendicular squareness ratio of each magnetic tape was determined from the perpendicular MH curve obtained by the above measurement.

[0194]

[0195] <ΔσPES> In an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60%, an LTO-G (Generation) 9 drive was used as the evaluation drive. The drive was run for 10,000 passes at a drive tension of 0.6 N, followed by 200 passes at a drive tension of 1.3 N, and then 200 passes at a drive tension of 0.4 N. The difference (calculated using the following formula) between the maximum σPES value during the 200 passes run at 0.4 N and the maximum σPES value during the 1.3 N run was defined as ΔσPES. σPES was calculated by analyzing the dump file of the drive. ΔσPES = (maximum σPES value during the 200 passes run at 0.4 N) - (maximum σPES value during the 1.3 N run). The smaller the ΔσPES value calculated in this way, the smaller the PES fluctuation. For Comparative Example 1, the run stopped midway, so ΔσPES could not be calculated.

[0196] <Coefficient of friction> Measurement samples were cut out from the magnetic tape prepared above for each of Examples 1 to 13 and Comparative Examples 1 to 4. The magnetic tape (measurement sample) was wrapped around an AlTiC (alumina titanium carbide) round rod having a diameter of 4 mm and an arithmetic mean roughness Ra of 15 nm when measured over a 40 μm × 40 μm area with an atomic force microscope (AFM), with the magnetic tape (measurement sample) being parallel to the axial direction of the round rod and with the magnetic layer surface in contact with the round rod. A 100 g weight was hung from one end of the magnetic tape at a wrap angle of 20°, and the other end was attached to a load cell. The magnetic tape was then slid 45 mm per pass at a speed of 14 mm / s, for a total of 100 repeated passes. The load during sliding at a constant speed on the first and 100th passes was detected with a load cell to obtain measurements, and the friction coefficients on the first and 100th passes were calculated using the following formula: Friction coefficient = ln(measured value (g) / 100(g)) / 0.349 (the denominator of the formula is the 20° wrap angle converted to radians). The measurement environment was a low-temperature, high-humidity environment, which is considered to have the highest friction coefficient among the guaranteed environments of LTO (Linear Tape-Open) drives, specifically an environment with a temperature of 13°C and a relative humidity of 80%. Regarding the evaluation results, if adhesion occurred between the magnetic layer surface of the magnetic tape and the round bar during measurement and the friction coefficient could not be evaluated, the evaluation result was rated "D." Furthermore, since the friction coefficient corresponding to the upper measurement limit of the load cell is 0.80, friction coefficients exceeding 0.80 cannot be measured. If the friction coefficient exceeded the upper measurement limit of the load cell, the evaluation result was rated "C." If the coefficient of friction is less than 0.6, the evaluation result is "A," and if the coefficient of friction is 0.6 or more and 0.80 or less, the evaluation result is "B." A magnetic tape with an evaluation result of A or B is preferable because it can exhibit a low coefficient of friction with the magnetic head.

[0197] The results are shown in Table 3.

[0198]

[0199] The results shown in Table 3 confirm that there was little variation in PES for the magnetic tapes of Examples 1 to 13. Furthermore, the results shown in Table 3 also confirm that the magnetic tapes of Examples 1 to 13 are magnetic tapes that can exhibit a low coefficient of friction with respect to the magnetic head.

[0200] The present invention is useful in the field of magnetic tape technology, such as data storage applications.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the standard deviation of the friction force determined by measuring the friction force between the surface of the magnetic layer and the guide roll of an LTO drive is 0.35 N or more and 0.70 N or less.

2. The magnetic tape of claim 1, wherein the area ratio of multiple bright areas with a circular equivalent diameter of 140 nm or more in a binary-processed secondary electron image obtained by imaging the surface of the magnetic layer with a scanning electron microscope at an acceleration voltage of 5 kV is 0.010% or more and 0.100% or less.

3. The magnetic tape according to claim 1, wherein the standard deviation of the frictional force is 0.45N or more and 0.70N or less.

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

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

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

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

8. The magnetic tape of claim 1, wherein said non-magnetic support is a polyester support.

9. The magnetic tape of claim 1, wherein said ferromagnetic powder is a hexagonal ferrite powder.

10. The magnetic tape of claim 9, wherein said hexagonal ferrite powder is hexagonal barium ferrite powder.

11. The magnetic tape of claim 9, wherein said hexagonal ferrite powder is hexagonal strontium ferrite powder.

12. The magnetic tape of claim 1, wherein in a binarized secondary electron image obtained by imaging the surface of the magnetic layer using a scanning electron microscope at an acceleration voltage of 5 kV, the area ratio of multiple bright regions having a circle equivalent diameter of 140 nm or more is 0.010% or more and 0.100% or less, the standard deviation of the friction force is 0.45 N or more and 0.70 N or less, the perpendicular squareness ratio of the magnetic tape is 0.65 or more, a non-magnetic layer containing non-magnetic powder is further provided between the non-magnetic support and the magnetic layer, and a backcoat layer containing non-magnetic powder is further provided on the surface of the non-magnetic support opposite to the surface having the magnetic layer, the total thickness of the magnetic tape is 5.0 μm or less, the non-magnetic support is a polyester support, and the ferromagnetic powder is selected from the group consisting of hexagonal barium ferrite and hexagonal strontium ferrite powder.

13. A magnetic tape cartridge containing the magnetic tape according to any one of claims 1 to 12.

14. A magnetic recording and reproducing device comprising the magnetic tape according to any one of claims 1 to 12.

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