Magnetic tape, magnetic tape cartridge, and magnetic tape device

Abstract

To provide a magnetic tape that reduces a frequency of missing pulses in a low temperature and low humidity environment and can contribute to improving an operational stability of a drive during recording and / or reproducing after long-term storage.SOLUTION: A magnetic tape has a non-magnetic support body and a magnetic layer containing ferromagnetic powder, in which an absolute value ΔN of a difference between a refractive index Nxy measured in an in-plane direction of the magnetic layer and a refractive index Nz measured in a thickness direction of the magnetic layer is 0.25 or more and 0.40 or less, and a standard deviation σ of the ΔN in a width direction of the magnetic layer is 0.05 or less. A magnetic tape cartridge and a magnetic tape device include this magnetic tape.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Magnetic recording media include tape-type and disk-type recording media, and tape-type magnetic recording media, that is, magnetic tapes, are primarily used for data storage applications such as data backup and archiving (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2016-524774 [Patent Document 2] US2019 / 0164573A1 [Patent Document 3] Patent No. 6590102 specification Summary of the Invention [Problem to be solved by the invention]

[0004] When reproducing information recorded on a magnetic tape, the more frequently a partial drop in the amplitude of the reproduced signal (called a "missing pulse") occurs, the higher the error rate and the lower the reliability of the magnetic tape. Therefore, in order to provide a magnetic tape that can be used with high reliability, it is desirable to reduce the frequency of occurrence of missing pulses.

[0005] In recent years, magnetic tapes used for data storage purposes are sometimes used in low-temperature and low-humidity environments such as data centers where the temperature and humidity are controlled (for example, an environment with a temperature of 10 to 15°C and a relative humidity of about 10 to 20%). Therefore, it is desirable to be able to reduce the frequency of occurrence of the above-mentioned missing pulses in a low-temperature and low-humidity environment.

[0006] Furthermore, data is typically recorded on a magnetic tape by running the magnetic tape in a magnetic tape device (generally called a "drive") and recording data on the data band by moving a magnetic head (hereinafter also simply referred to as a "head") along the data band of the magnetic tape. This forms a data track on the data band. When reproducing the recorded data, the magnetic tape is run in the magnetic tape device and the magnetic head is moved along the data band of the magnetic tape to read the data recorded on the data band. After such recording or reproduction, the magnetic tape is typically stored wound on a reel inside a magnetic tape cartridge or the like until the next recording and / or reproduction is performed.

[0007] In order to improve the accuracy with which the magnetic head follows the data band of the magnetic tape during the above-mentioned recording and / or reproduction, a system (hereinafter, referred to as a "servo system") that performs head tracking using a servo signal has been put into practical use. However, when recording and / or reproduction is performed after the above-mentioned storage, a phenomenon (generally called "off-track") may occur in which the magnetic head for recording and / or reproducing data is displaced from the target track position due to deformation of the tape width of the magnetic tape caused by storage. If the off-track causes overwriting of recorded data, playback failure, etc., the operational stability of the drive is reduced. In recent years, the high density of the track density associated with the high capacity of magnetic tape has made it easier for off-track to occur, and therefore there is an increasing need to improve the operational stability of the drive. On the other hand, in recent years, in the data storage field, long-term storage of data, known as an archive, has been carried out. However, generally, the longer the storage period, the easier it is for the magnetic tape to deform in tape width, and the frequency of off-track occurrence tends to increase.

[0008] In view of the above, one aspect of the present invention aims to provide a magnetic tape in which the frequency of occurrence of missing pulses in a low-temperature, low-humidity environment is reduced, and which can contribute to improving the operational stability of a drive during recording and / or playback after long-term storage. [Means for solving the problem]

[0009] One aspect of the present invention is as follows. [1] A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, The absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 or more and 0.40 or less, and A magnetic tape in which the standard deviation σ of ΔN in the width direction of the magnetic layer is 0.05 or less. [2] The magnetic tape according to [1], wherein the standard deviation σ of the ΔN is 0.02 or less. [3] The magnetic tape according to [1] or [2], wherein the standard deviation σ of the ΔN is 0.01 or more and 0.02 or less. [4] The magnetic tape according to any one of [1] to [3], further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. [5] The non-magnetic powder has an average particle volume of 2.0 × 10 -6 μm 3 The magnetic tape according to [4], comprising the following Fe-based inorganic oxide powder: [6] The magnetic tape according to [4] or [5], wherein the non-magnetic powder contains carbon black having a pH of 9.0 or less. [7] The magnetic tape according to any one of [4] to [6], wherein the nonmagnetic layer has a thickness of 0.1 μm or more and 0.7 μm or less. [8] The magnetic tape according to any one of [1] to [7], further comprising a backcoat layer containing a nonmagnetic powder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer. [9] The magnetic tape according to any one of [1] to [8], wherein the tape thickness is 5.2 μm or less.

[10] The magnetic tape according to any one of [1] to [9], wherein the tape thickness is 5.0 μm or less.

[11] The magnetic tape according to any one of [1] to

[10] , wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.60 or more.

[12] The magnetic tape according to any one of [1] to

[11] , wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.65 or more.

[13] The standard deviation σ of the above ΔN is 0.01 or more and 0.02 or less, a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer, The non-magnetic powder has an average particle volume of 2.0×10 -6 μm 3 The present invention includes the following Fe-based inorganic oxide powder and carbon black having a pH of 9.0 or less: the thickness of the nonmagnetic layer is 0.1 μm or more and 0.7 μm or less, the non-magnetic support further comprises a backcoat layer containing a non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, The tape thickness is 5.0 μm or less, and The magnetic tape according to [1], wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.65 or more.

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

[13] .

[15] A magnetic tape device including the magnetic tape described in any one of [1] to

[13] .

[16] Further comprising a magnetic head, The magnetic head has a module including an element array having a plurality of magnetic head elements between a pair of servo signal read elements; and The magnetic tape device according to

[15] , wherein the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape is changed while the magnetic tape is running within the magnetic tape device. Effect of the Invention

[0010] According to one aspect of the present invention, it is possible to provide a magnetic tape in which the frequency of occurrence of missing pulses in a low-temperature, low-humidity environment is reduced, and which contributes to improving the operational stability of a drive during recording and / or playback after long-term storage. Also, according to one aspect of the present invention, it is possible to provide a magnetic tape cartridge and a magnetic tape device including such a magnetic tape. [Brief description of the drawings]

[0011] [Figure 1] 1 shows an example of a track profile in which the horizontal axis represents the track position and the vertical axis represents the output of the reproduced signal. [Diagram 2] 1 shows an example of a graph relating to an initial nonlinear component. [Diagram 3] 13 shows an example of a graph regarding the nonlinear component after storage. [Figure 4] 13 is an example of a graph showing the absolute value of the difference between the initial nonlinear component and the nonlinear component after storage for each reproducing element (the difference between the nonlinear components before and after storage). [Diagram 5] FIG. 2 is a schematic diagram showing an example of a magnetic head module. [Figure 6] 2 is an explanatory diagram of the relative positional relationship between a module and a magnetic tape while the magnetic tape is running in a magnetic tape device; FIG. [Figure 7] FIG. 11 is an explanatory diagram regarding a change in angle θ while a magnetic tape is running. [Figure 8] 1 shows an example of a manufacturing process for a magnetic tape (schematic diagram of the process). [Figure 9] 2 shows an example of the arrangement of data bands and servo bands. [Figure 10] An example of servo pattern arrangement on an LTO (Linear Tape-Open) Ultrium format tape is shown. [Figure 11] FIG. 4 is an explanatory diagram of a method for measuring an angle θ during a magnetic tape run. [Figure 12] FIG. 1 is a schematic diagram illustrating an example of a magnetic tape device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Magnetic tape] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing a ferromagnetic powder, wherein the absolute value ΔN (hereinafter also simply referred to as "ΔN") of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 to 0.40, and the standard deviation σ of ΔN in the width direction of the magnetic layer (hereinafter also referred to as "width direction σ of ΔN") is 0.05 or less.

[0013] As a result of intensive research, the present inventors have newly discovered that a magnetic tape in which ΔN is within the above range and the width direction σ of ΔN is within the above range can reduce the frequency of missing pulses in a low-temperature, low-humidity environment and can contribute to improving the operational stability of a drive. The present inventors' speculations on this point are described below. However, the present invention is not limited to the speculations described in this specification. In the following, the frequency of missing pulses in a low-temperature, low-humidity environment is also simply referred to as the "frequency of missing pulses." As described above, the deformation of the tape width caused by long-term storage may cause a decrease in the operational stability of the magnetic tape in the drive. In this regard, in recent years, it has been proposed to obtain dimensional information of the magnetic tape in the width direction while the magnetic tape is running by using a servo signal, and to change the angle at which the axial direction of the magnetic head module is tilted with respect to the width direction of the magnetic tape (hereinafter, also referred to as the "head tilt angle") according to the obtained dimensional information (Patent Documents 1 and 2, for example, see paragraphs 0059 to 0067 and 0084 of Patent Document 1). In addition, it has also been practiced to obtain dimensional information of the magnetic tape in the width direction while the magnetic tape is running by using a servo signal, and to control the dimension of the magnetic tape in the width direction by adjusting the tension applied in the longitudinal direction of the magnetic tape according to the obtained dimensional information (for one example, see paragraph 0171 of Patent Document 3). For example, the above-mentioned dynamic track position control means while the magnetic tape is running can be a means for suppressing off-track. However, the present inventors, while conducting intensive research to further improve the operational stability of the drive in recording and / or playback after long-term storage, have noticed that there may be off-track factors that are difficult to compensate for by dynamic track position control means. This point will be further explained below. When the dynamic track position is controlled by changing the head tilt angle, the pitch of the magnetic head element (specifically, the recording element and / or the reproducing element) changes uniformly according to the head tilt angle, regardless of the position in the tape width direction. When the dynamic track position is controlled by adjusting the tension applied in the longitudinal direction of the magnetic tape, the tension is usually adjusted over the entire tape width, so that the tape width changes uniformly by tension adjustment, regardless of the position in the tape width direction. If the degree of tape width deformation is uniform over the entire magnetic tape, that is, if the tape width deformation component is only a linear component, it is possible to completely compensate for off-track by the control means. Therefore, it is possible to completely align the data track and the magnetic head element. On the other hand, if the degree of tape width deformation is different and non-uniform depending on the position, that is, if the tape width deformation component contains a non-linear component, it is difficult for the control means to compensate for off-track caused by the non-linear component. The inventors considered that reducing this non-linear component could contribute to suppressing the deterioration of the operation stability of the drive caused by the off-track factor, which is difficult to compensate for by the dynamic track position control means. In this regard, the present inventor believes that in a magnetic tape, the width direction σ of ΔN being within the above range can contribute to suppressing the occurrence of the nonlinear component of the tape width deformation, and thus the present inventor speculates that the magnetic tape can contribute to improving the operational stability of a drive during recording and / or playback after long-term storage. In addition, the cause of the occurrence of missing pulses is the unstable contact state when the magnetic layer surface and the head slide, and one of the causes of the unstable contact state is the occurrence of head adhesion. In this regard, ΔN is considered to be a value that can be an index of the state of existence of ferromagnetic powder in the surface region of the magnetic layer. This ΔN is considered to be a value that is influenced by various factors such as the state of existence of the binder and the density distribution of the ferromagnetic powder in addition to the orientation state of the ferromagnetic powder in the magnetic layer. And, it is considered that a magnetic layer with ΔN of 0.25 to 0.40 by controlling various factors has a high strength of the magnetic layer surface and is difficult to be scraped by sliding with the head. It is considered that this contributes to suppressing the scraping of the magnetic layer surface and the occurrence of head adhesion, and as a result, leads to a reduction in the frequency of occurrence of missing pulses in a low temperature and low humidity environment.

[0014] <ΔN and ΔN width direction σ> With regard to the widthwise σ of ΔN, the standard deviation σ (i.e., the positive square root of the variance) of the five measured values ​​of ΔN obtained for the five measurement areas of the measurement sample is taken as the standard deviation σ of ΔN in the widthwise direction of the magnetic layer of the magnetic tape being measured (the widthwise σ of ΔN). A measurement sample is cut out from a randomly selected position of the magnetic tape to be measured. The width of the measurement sample cut out here is the same as the width of the magnetic tape to be measured. There is no particular limit to the length of the measurement sample, as long as the size of the measurement sample is a size that allows measurement using the ellipsometer described below. Each of the five regions obtained by dividing the width direction into five with respect to the width of the measurement sample is set as a measurement region. Therefore, if the width of the measurement sample is W, the width of each measurement region is "W / 5". ΔN is measured for a randomly selected analysis region in each measurement region.

[0015] In each analysis region, the absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is determined by the following method. The refractive index in each direction of the magnetic layer is determined by using a two-layer model by spectroscopic ellipsometry. In order to determine the refractive index of the magnetic layer by using a two-layer model by spectroscopic ellipsometry, the value of the refractive index of the portion adjacent to the magnetic layer is used. In the following, an example will be described in which the refractive indexes Nxy and Nz of the magnetic layer are determined for a magnetic tape having a layer structure in which a nonmagnetic layer and a magnetic layer are laminated in this order on a nonmagnetic support. However, the magnetic tape according to one embodiment of the present invention can also be a magnetic tape having a layer structure in which a magnetic layer is directly laminated on a nonmagnetic support without a nonmagnetic layer. For a magnetic tape having such a structure, the refractive index in each direction of the magnetic layer is determined in the same manner as in the following method using a two-layer model of a magnetic layer and a nonmagnetic support. In addition, the incidence angle described below is the incidence angle when the incidence angle in the case of perpendicular incidence is set to 0°. (1) Preparation of the measurement sample For magnetic tapes having a backcoat layer on the surface opposite to the surface having the magnetic layer of the non-magnetic support, the backcoat layer of the measurement sample cut out from the magnetic tape is removed before measurement. The backcoat layer can be removed by a known method such as dissolving the backcoat layer with a solvent. As the solvent, for example, methyl ethyl ketone can be used. However, any solvent can be used as long as it can remove the backcoat layer. The surface of the non-magnetic support after the backcoat layer is removed is roughened by a known method so that reflected light from this surface is not detected in the measurement with an ellipsometer. The roughening can be performed, for example, by polishing the surface of the non-magnetic support after the backcoat layer is removed with sandpaper. For measurement samples cut out from magnetic tapes without a backcoat layer, the surface of the non-magnetic support opposite to the surface having the magnetic layer is roughened. In addition, to measure the refractive index of the non-magnetic layer described below, the magnetic layer is further removed to expose the surface of the non-magnetic layer. In order to measure the refractive index of the non-magnetic support described below, the non-magnetic layer is also removed to expose the surface of the non-magnetic support on the magnetic layer side. The removal of each layer can be performed by a known method, as described for removing the backcoat layer. The longitudinal direction described below refers to the direction that was the longitudinal direction of the magnetic tape when the measurement sample was included in the magnetic tape before being cut out. This also applies to the other directions described below. The magnetic layer can also be removed by the method described in paragraph 0054, item (V) of JP-A-10-172131. Specifically, the abrasive tape is brought into contact with the magnetic layer surface of the measurement sample to which an appropriate tension (usually 50 to 500 gf) is applied so that an appropriate tension (usually 50 to 500 gf) is applied, the measurement sample is transported at a low speed (usually 0.005 to 0.1 m / sec), the abrasive tape is transported in the opposite direction to the transport direction of the measurement sample at a high speed (usually 0.1 to 10 m / sec), and the abrasive tape is rubbed against the magnetic layer surface of the measurement sample. By performing this once or multiple times, the magnetic layer can be removed to expose the nonmagnetic layer surface. In addition, regarding the unit "gf (gram weight)", 1 N (Newton) is about 102 gf. The exposure of the non-magnetic layer surface can be confirmed based on the value of the longitudinal magnetization amount Φm per unit area of ​​the measurement sample after the treatment for removing the magnetic layer has been performed. The above Φm is the magnetization amount per unit area measured in the longitudinal direction of the measurement sample. In the present invention and this specification, the above Φm is a value obtained by the following method using a vibrating sample magnetometer. A sample piece is cut out from the measurement sample after the treatment for removing the magnetic layer has been performed. The size of the sample piece may be a size that can be introduced into the vibrating sample magnetometer used for the measurement. A magnetic field is applied to the sample piece in the longitudinal direction using the vibrating sample magnetometer at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep rate of 8.3 kA / m / sec, and the magnetization intensity of the sample piece at the maximum applied magnetic field is measured. The measured value is obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. The magnetization intensity at the maximum applied magnetic field thus measured is then multiplied by the area (unit: cm) of the sample piece. 2 ) is taken as Φm (unit: G (Gauss) μm). If the Φm thus obtained is less than 5 G μm, it can be determined that the surface of the nonmagnetic layer has been exposed by the treatment to remove the magnetic layer. (2) Refractive index measurement of the magnetic layer Using an ellipsometer, the magnetic layer surface is irradiated with incident light of 300 μm diameter from the longitudinal direction at angles of incidence of 65°, 70°, and 75°, to measure Δ (phase difference between s-polarized light and p-polarized light) and Ψ (amplitude ratio between s-polarized light and p-polarized light). Measurements are performed by changing the wavelength of the incident light in 1.5 nm increments in the range of 400 to 700 nm, and measurements are obtained for each wavelength. Using the measured values ​​of Δ and Ψ of the magnetic layer at each wavelength, the refractive index of the non-magnetic layer in each direction obtained by the method described below, and the thickness of the magnetic layer, the refractive index of the magnetic layer at each wavelength is calculated using a two-layer model as follows. The 0th layer, which is the substrate of the two-layer model, is the non-magnetic layer, and the 1st layer is the magnetic layer. A two-layer model is created by considering only the reflection at the interfaces between air / magnetic layer and magnetic layer / non-magnetic layer, and assuming that there is no effect of back surface reflection of the non-magnetic layer. The refractive index of the 1st layer that best matches the obtained measured values ​​is found by fitting using the least squares method. The refractive index Nx of the magnetic layer in the longitudinal direction, and the refractive index Nz1 of the magnetic layer in the thickness direction measured by irradiating incident light from the longitudinal direction are found as values ​​at a wavelength of 600 nm obtained from the fitting results. The procedure is the same as above, except that the direction of incidence of the incident light is the width direction.The refractive index Ny of the magnetic layer in the width direction and the refractive index Nz2 of the magnetic layer in the thickness direction measured by irradiating light from the width direction are calculated as values ​​at a wavelength of 600 nm obtained from the fitting results. The fitting is performed by the following method. Generally, the complex refractive index is n = η + iκ. Here, η is the real part of the refractive index, κ is the extinction coefficient, and i is an imaginary number. The complex dielectric constant ε = ε1 + iε2 (ε1 and ε2 satisfy the Kramers-Kronig relationship) and ε1 = η 2 -κ 2 The relationship is ε2=2ηκ, and when calculating Nx and Nz1, the complex dielectric constant of Nx is set to ε x =ε x 1+iε x 2. The complex dielectric constant of Nz1 is ε z1 =ε z1 1+iε z1 Let's say it's 2. ε x 2 is taken as a Gaussian, and an arbitrary point with a peak position of 5.8 to 5.1 eV and σ of 4 to 3.5 eV is taken as the starting point. A parameter that offsets the dielectric constant is placed outside the measurement wavelength range (400 to 700 nm), and Nx is calculated by least-squares fitting of the measured value. Similarly, ε z12, an arbitrary point where the peak position is 3.2 to 2.9 eV and σ is 1.5 to 1.2 eV is used as the starting point, and Nz1 is calculated by setting an offset parameter and performing least squares fitting on the measured values. Ny and Nz2 are calculated in the same manner. The refractive index Nxy measured in the in-plane direction of the magnetic layer is calculated as "Nxy = (Nx + Ny) / 2". The refractive index Nz measured in the thickness direction of the magnetic layer is calculated as "Nz = (Nz1 + Nz2) / 2". From the calculated Nxy and Nz, the absolute value ΔN of the difference between them is calculated. (3) Refractive index measurement of non-magnetic layer The refractive index of the non-magnetic layer at a wavelength of 600 nm (refractive index in the longitudinal direction, refractive index in the width direction, refractive index in the thickness direction measured with light incident from the longitudinal direction, and refractive index in the thickness direction measured with light incident from the width direction) is determined in the same manner as above, except for the following points. The wavelength of the incident light is changed in increments of 1.5 nm within the range of 250 to 700 nm. Using a two-layer model of a non-magnetic layer and a non-magnetic support, the 0th layer, which is the substrate of the two-layer model, is the non-magnetic support, and the 1st layer is the non-magnetic layer. The two-layer model is created by considering only the reflections at the interfaces between air / non-magnetic layer and non-magnetic layer / non-magnetic support, and assuming that there is no effect from the back surface reflection of the non-magnetic support. In the fitting, seven peaks (0.6 eV, 2.3 eV, 2.9 eV, 3.6 eV, 4.6 eV, 5.0 eV, 6.0 eV) are assumed in the imaginary part of the complex dielectric constant (ε2), and a parameter that offsets the dielectric constant outside the measurement wavelength range (250 to 700 nm) is placed. (4) Refractive index measurement of non-magnetic support The refractive index at a wavelength of 600 nm of the non-magnetic support used to determine the refractive index of the non-magnetic layer using the two-layer model (refractive index in the longitudinal direction, refractive index in the width direction, refractive index in the thickness direction measured with light incident from the longitudinal direction, and refractive index in the thickness direction measured with light incident from the width direction) is determined in the same manner as the method described above for measuring the refractive index of the magnetic layer, except for the following points. Instead of using a two-layer model, a one-layer model with only surface reflection is used. The fitting is done using the Cauchy model (n=A+B / λ 2 , n is the refractive index, A and B are constants determined by fitting, and λ is the wavelength). The above "(2) Measurement of the refractive index of the magnetic layer" and "(4) Measurement of the refractive index of the non-magnetic support" are performed in each of the analysis target areas of the five measurement areas divided as described above. For each of the five measurement areas, the values ​​obtained by measurement in the analysis target area of ​​each measurement area are used as the refractive index of the magnetic layer and the refractive index of the non-magnetic support. The above "(3) Measurement of the refractive index of the non-magnetic layer" is performed in the analysis target area of ​​the central area (i.e., measurement area 3 when the five measurement areas are called measurement areas 1, 2, 3, 4, and 5 from one end to the other end in the width direction) of the five measurement areas divided as described above. Then, for each of the five measurement areas, the value obtained by measurement in the analysis target area of ​​the central area is used as the refractive index of the non-magnetic layer.

[0016] (ΔN) The ΔN of the magnetic tape is 0.25 or more and 0.40 or less. As described above, it is presumed that a magnetic layer having a ΔN of 0.25 or more and 0.40 or less has a high strength of the magnetic layer surface and is not easily worn away by sliding with a head. Therefore, it is considered that a magnetic layer having a ΔN in the above range is not easily worn away by sliding between the magnetic layer surface and the head when reproducing information recorded on the magnetic layer under a low temperature and low humidity environment. It is presumed that this contributes to reducing the frequency of occurrence of missing pulses. ΔN is 0.40 or less, and can also be 0.38 or less or 0.36 or less. In addition, ΔN is 0.25 or more, and from the viewpoint of further reducing the frequency of occurrence of missing pulses, it is preferably 0.27 or more, more preferably 0.29 or more, and even more preferably 0.31 or more.

[0017] ΔN is the absolute value of the difference between Nxy and Nz. Nxy is the refractive index measured in the in-plane direction of the magnetic layer, and Nz is the refractive index measured in the thickness direction of the magnetic layer. In one form, "Nxy > Nz" can be satisfied, and in another form, "Nxy < Nz" can be satisfied. From the viewpoint of the electromagnetic conversion characteristics of the magnetic tape, it is preferable that Nxy > Nz, and thus it is preferable that the difference (Nxy - Nz) between Nxy and Nz is 0.25 or more and 0.40 or less.

[0018] (Standard deviation σ of ΔN in the width direction) The standard deviation σ of ΔN (standard deviation σ of ΔN in the width direction) in the width direction of the magnetic layer of the magnetic tape is 0.05 or less from the viewpoint of improving the operation stability of the drive in recording and / or reproduction after long-term storage. From the above viewpoint, the standard deviation σ of ΔN in the width direction is preferably 0.04 or less, and more preferably 0.03 or less and 0.02 or less in this order. The standard deviation σ of ΔN in the width direction can be, for example, 0.00 or more, more than 0.00 or 0.01 or more. From the viewpoint of improving the operation stability of the drive in recording and / or reproduction after long-term storage, it is presumed that the smaller the value of the standard deviation σ of ΔN in the width direction, the more preferable.

[0019] Specific examples of the control method of ΔN and the standard deviation σ of ΔN in the width direction will be described later.

[0020] <Nonlinear component of tape width deformation> The present inventor believes that for the nonlinear component of the tape width deformation described above, the "nonlinear component in the tape width direction caused by storage for 10 days in an environment of a temperature of 60 °C and a relative humidity of 20%", which is obtained by the following method, can be an index thereof. The storage condition of "storage for 10 days in an environment of a temperature of 60 °C and a relative humidity of 20%" is an example of the storage condition in an accelerated environment corresponding to long-term data storage called archival, and the magnetic tape is not limited to those stored under such storage conditions. The following operations and measurements are performed in an environment where the temperature is 20 to 25 °C and the relative humidity is 40 to 60% unless otherwise specified. The magnetic tape to be measured must be 200m or longer. The magnetic tape to be measured is wound onto a magnetic tape reel with a hub diameter (outer diameter, the same applies below) of 44 mm, with a tension of 0.6 N (Newton) applied to the magnetic tape in the longitudinal direction by a device having a winding mechanism that winds the magnetic tape by applying tension to the magnetic tape in the longitudinal direction. The magnetic tape thus wound onto the reel is stored for 24 hours or more in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60% before the following measurement. Regarding one end and the other end of the magnetic tape, the end at the start point of winding onto the reel is called the inner edge of the tape, and the other end is called the outer edge of the tape. The following measurements are performed in the area within 100 m from the outer edge of the tape (hereinafter referred to as the "outer edge of the tape") and in the area within 100 m from the inner edge of the tape (hereinafter referred to as the "inner edge of the tape"), at the center wrap of each data band. The following measurements are performed using a magnetic head equipped with a reproducing module including an element array having 10 or more channels of reproducing elements with an element width (specifically, reproducing element width) of 0.2 μm to 1.0 μm between a pair of servo signal reading elements, and a recording module including an element array having 10 or more channels of recording elements with an element width (specifically, recording element width) of 1.2 μm to 2.9 μm between a pair of servo signal reading elements. The "element width" is the physical dimension of the element width, and can be measured by an optical microscope, a scanning electron microscope, or the like. In the recording module, the distance between two adjacent recording elements in the head width direction is 83.25 μm. In the reproducing module, the distance between two adjacent reproducing elements in the head width direction is 83.25 μm. The above distance is the distance between the centers of two adjacent recording elements in the recording module, and is the distance between the centers of two adjacent reproducing elements in the reproducing module, and can be measured by an optical microscope, or the like. In measurements for the examples and comparative examples described below, a magnetic head was used that included a recording module including an element array having 32 channels (channel 0 to channel 31) of recording elements between a pair of servo signal reading elements, and a reproduction module including an element array having 32 channels (channel 0 to channel 31) of reproduction elements between a pair of servo signal reading elements. The reel on which the magnetic tape to be measured is wound and the magnetic head are attached to the tape transport system of the magnetic tape device to record and reproduce data. The tape transport system is attached to a recording and reproducing amplifier capable of driving the magnetic head elements (more specifically, the recording element and the reproducing element) of the magnetic head. The recording and reproducing amplifier can be controlled from a computer (PC: Personal Computer) via a controller. The magnetic head is attached to an actuator (piezo motor or VCM (voice coil motor)) that operates in the tape width direction, and can perform servo following so that the magnetic head is at a constant track position while the tape is running based on the servo signal of the magnetic tape. In addition, in order to compensate for the linear component of the tape width deformation, the head tilt angle of the magnetic head can be changed to perform dynamic track position control so that the difference (difference between PES1 and PES2) between the read position signal PES in the width direction based on the servo signal obtained by the two servo signal reading elements above and below is constant. The above servo following and dynamic track position control are performed during the following recording and reproduction. Next, while running the magnetic tape at a constant speed of 3.0 m / sec, for three consecutive wraps in the same running direction, a DC (Direct Current) pattern is recorded on the first wrap, a single frequency signal of 255 kfci is recorded on the second wrap, and a DC pattern is recorded on the third wrap. The unit "kfci" is a unit of linear recording density (cannot be converted to SI units). Shingle recording is performed on three or more tracks so that the difference between (PES1+PES2) / 2 is 1200 nm. Shingle recording is also called shingled recording. Next, data is reproduced over a length of 90 m from the central wrap of three consecutive wraps in an area within 100 m from the outer edge of the tape (outer tape area) and an area within 100 m from the inner edge of the tape (inner tape area). The reproduced signal waveform and servo signal waveform are acquired and stored using an oscilloscope. For each measurement, the track position of the reproducing element is moved in the tape width direction at intervals of 1 / 30 or less of the track pitch. The "reproduced signal output" is calculated for each reproducing element from the reproduced signal waveform acquired and stored using the oscilloscope, and the track position is calculated from the servo signal waveform. From these results, a track profile is created with the track position plotted on the horizontal axis and the reproduced signal output plotted on the vertical axis. Figure 1 shows an example of a track profile created in this way. The median between two track positions that are 1 dB or more lower than the maximum output of the reproduction signal is found, and the median is plotted on the vertical axis for each reproduction element, and a linear approximation line is obtained by linear fitting using the least squares method. For each reproduction element in the outer and inner tape regions, the difference between the linear approximation line and the actual measurement value is found, and this is defined as the "initial nonlinear component." Figure 2 shows an example of a graph related to the initial nonlinear component. In the example shown in Figure 2 and the example shown in Figure 3 described below, the number of reproduction elements (number of channels) is 32 channels (reproduction element numbers (No.): channel 0 to channel 31). After measuring the initial nonlinear component, the magnetic tape to be measured is wound onto a magnetic tape reel with a hub diameter of 44 mm, with a tension of 0.6 N applied to the magnetic tape in the longitudinal direction by a device having a winding mechanism that applies tension to the magnetic tape in the longitudinal direction. During this winding, the magnetic tape is wound so that the end that was the inner end of the tape when wound onto the reel before the measurement of the initial nonlinear component becomes the inner end of the tape. The magnetic tape thus wound onto the reel is stored in an environment with a temperature of 60°C and a relative humidity of 20% for 10 days. After the above storage, the magnetic tape to be measured is stored in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60% for 24 hours or more (but up to 120 hours at the maximum) while still wound on the reel, and then the magnetic tape device used for measuring the initial nonlinear components is used to run the magnetic tape to be measured back and forth once (in the forward and reverse directions). Using the same recording element, reproducing element, magnetic tape device, and reproducing conditions as those used for measuring the initial nonlinear components, data is reproduced over a length of 90 m in an area within 100 m from the outer edge of the tape (outer tape area) and an area within 100 m from the inner edge of the tape (inner tape area). The output of the reproduced signal and the servo signal waveform are obtained and stored using the same oscilloscope as used for measuring the initial nonlinear components. The track position of the reproducing element is moved in the tape width direction for each measurement at the same intervals as those used for measuring the initial nonlinear components. The "output of the reproduced signal" is calculated for each reproducing element from the reproduced signal waveforms obtained and stored using the oscilloscope, and the track position is calculated from the servo signal waveforms. From these results, a track profile is created by plotting the track position on the horizontal axis and the playback signal output on the vertical axis. Figure 1 is an example of a track profile created in this way. The median value between two track positions where the playback signal output is 1 dB or more lower than the maximum value is found, and the median value is plotted on the vertical axis for each playback element, and a linear approximation line is obtained by linear fitting using the least squares method. The difference between the linear approximation line and the actual measured value is found for each playback element for both the outer and inner tape regions, and this is defined as the "nonlinear component after storage." Figure 3 shows an example of a graph related to the nonlinear component after storage. The absolute value of the difference between the "initial nonlinear component" and the "nonlinear component after storage" for each reproducing element (the difference in the nonlinear component before and after storage) is calculated. Figure 4 shows an example of a graph showing the absolute value of the difference thus calculated for each reproducing element. The maximum value of the absolute value in the outer tape area and the inner tape area is taken as the "nonlinear component of tape width deformation" of the magnetic tape being measured. It is believed that the initial nonlinear component can be said to be a nonlinear component caused by factors other than the magnetic tape. Therefore, the inventor believes that by calculating the difference in the nonlinear component before and after storage as described above, it is possible to accurately evaluate the nonlinear component caused by the magnetic tape.

[0021] The nonlinear component of the tape width deformation obtained by the method described above for the magnetic tape is preferably 100 nm or less, more preferably 95 nm or less, and further preferably 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, and 50 nm or less in this order, from the viewpoint of improving the operation stability of the drive in recording and / or reproduction after long-term storage. The width direction σ of ΔN being in the above range can contribute to controlling the value of the nonlinear component within the above range. In addition, the nonlinear component of the tape width deformation can be, for example, 0 nm or more, more than 0 nm, 1 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, or 40 nm or more. From the viewpoint of improving the operation stability of the drive, the smaller the nonlinear component of the tape width deformation, the more preferable it is.

[0022] <Explanation of head tilt angle> As described above, one example of a means for controlling the dynamic track position while the magnetic tape is running is to change the head tilt angle. In this regard, the configuration of the magnetic head, the head tilt angle, etc. will be described below. Furthermore, the reason why it is possible to control the dynamic track position while the magnetic tape is running by tilting the axial direction of the magnetic head module relative to the width direction of the magnetic tape while the magnetic tape is running will be described below.

[0023] The magnetic head may have one or more modules, two or more modules, or three or more modules, each module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements. The total number of such modules may be, for example, five or less, four or less, or three or less, or the magnetic head may include a number of modules exceeding the total number exemplified here. Examples of the arrangement of a plurality of modules include "recording module-playback module" (total number of modules: 2), "recording module-playback module-recording module" (total number of modules: 3), etc. However, the arrangement is not limited to the examples shown here.

[0024] Each module may include an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, i.e., an array of elements. A module having a recording element as a magnetic head element is a recording module for recording data onto a magnetic tape. A module having a reproducing element as a magnetic head element is a reproducing module for reproducing data recorded onto a magnetic tape. In a magnetic head, a plurality of modules are arranged, for example, in a recording / reproducing head unit, with the axes of the element arrays of the respective modules oriented in parallel. Such "parallel" does not necessarily mean only parallel in the strict sense, but includes the range of error normally permitted in the technical field to which the present invention belongs. The range of error may mean, for example, a range of strict parallelism ±10° or less.

[0025] In each element array, a pair of servo signal read elements and a plurality of magnetic head elements (i.e., recording elements or reproducing elements) are usually arranged in a line, spaced apart from each other. Here, "arranged in a line" means that each magnetic head element is arranged on a line connecting the center of one servo signal read element and the center of the other servo signal read element. In this invention and this specification, the "axis of the element array" means the line connecting the center of one servo signal read element and the center of the other servo signal read element.

[0026] Next, the configuration of the module will be further described with reference to the drawings. However, the embodiments shown in the drawings are merely examples and do not limit the present invention.

[0027] FIG. 5 is a schematic diagram showing an example of a magnetic head module. The module shown in FIG. 5 has multiple magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). The magnetic head elements are also called "channels." "Ch" in the figure is an abbreviation for Channel. The module shown in FIG. 5 has a total of 32 magnetic head elements, Ch0 to Ch31.

[0028] In Fig. 5, "L" is the distance between a pair of servo signal read elements, i.e., the distance between one servo signal read element and the other servo signal read element. In the module shown in Fig. 5, "L" is the distance between servo signal read element 1 and servo signal read element 2. More specifically, it is the distance between the center of servo signal read element 1 and the center of servo signal read element 2. Such a distance can be measured, for example, by an optical microscope.

[0029] FIG. 6 is an explanatory diagram of the relative positional relationship between a module and a magnetic tape in a magnetic tape device while the magnetic tape is running. In FIG. 6, dotted line A indicates the width direction of the magnetic tape. Dotted line B indicates the axis of the element array. Angle θ can be said to be the head tilt angle while the magnetic tape is running, and is the angle formed by dotted lines A and B. When angle θ is 0° while the magnetic tape is running, the distance in the magnetic tape width direction between one servo signal reading element and the other servo signal reading element of the element array (hereinafter also referred to as "effective distance between servo signal reading elements") is "L". In contrast, when angle θ is greater than 0°, the effective distance between servo signal reading elements is "Lcosθ", and Lcosθ is smaller than L. In other words, "Lcosθ" <L」である。

[0030] As described above, when recording or reproducing, if the magnetic head for recording or reproducing data deviates from the target track position due to the deformation of the magnetic tape, phenomena such as overwriting of recorded data and reproduction failure may occur. For example, when the width of the magnetic tape shrinks or expands, a phenomenon may occur in which the magnetic head element that should record or reproduce at the target track position records or reproduces at a different track position. In addition, when the width of the magnetic tape expands, the effective distance between the servo signal reading elements becomes shorter than the distance between two adjacent servo bands sandwiching the data band (also referred to as the "servo band distance" or "servo band distance". More specifically, the distance between the two servo bands in the width direction of the magnetic tape.), and a phenomenon may occur in which data is not recorded or reproduced near the edge of the magnetic tape. In contrast, when the element array is tilted at an angle θ exceeding 0°, the effective distance between the servo signal reading elements is “Lcosθ” as described above. The larger the value of θ, the smaller the value of Lcosθ, and the smaller the value of θ, the larger the value of Lcosθ. Therefore, by changing the value of θ according to the degree of dimensional change in the width direction of the magnetic tape (i.e., contraction or expansion), it is possible to make the effective distance between the servo signal reading elements approach or match the interval of the servo band. This makes it possible to prevent or reduce the frequency of occurrence of phenomena such as overwriting of recorded data and playback failure caused by the magnetic head for recording or playing back data being shifted from the target track position due to the width deformation of the magnetic tape during recording or playback.

[0031] FIG. 7 is an explanatory diagram regarding the change in angle θ during the running of the magnetic tape. θ is the angle θ at the start of travel. initial can be set, for example, to be equal to or greater than 0°. The central diagram in Figure 7 shows the state of the module at the start of driving. In Figure 7, the right diagram shows the angle θ as θ initial The larger angle, angle θ cThe effective distance between the servo signal reading elements Lcosθ is shown. c is Lcosθ when the magnetic tape starts running initial It is preferable to perform such an angle adjustment when the width of the magnetic tape contracts during its running. On the other hand, in the left diagram of FIG. 7, the angle θ is initial The smaller angle, θ e The effective distance between the servo signal reading elements Lcosθ is shown. e is Lcosθ when the magnetic tape starts running initial It is preferable to perform such an angle adjustment when the width of the magnetic tape expands during its running.

[0032] As described above, changing the head tilt angle while the magnetic tape is running can help prevent phenomena such as overwriting of recorded data and playback failures that occur when the magnetic head for recording or reproducing data deviates from the target track position due to deformation of the magnetic tape during recording or reproduction, or can help reduce the frequency of such occurrences. However, for example, in the dynamic track position control means as described above, while it is usually possible to compensate for off-track caused by the linear component of the tape width deformation, it is difficult to suppress off-track caused by the nonlinear component. In contrast, in the magnetic tape, it is presumed that the above range of ΔN width direction σ contributes to reducing the nonlinear component of the tape width deformation. It is considered that this makes it possible to improve the operating stability of the drive. Such a magnetic tape is preferable for increasing the track density.

[0033] The above magnetic tape will now be described in more detail.

[0034] <Magnetic layer> (Ferromagnetic powder) As the ferromagnetic powder contained in the magnetic layer, one or more of the ferromagnetic powders known as ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. It is preferable to use ferromagnetic powders with a small average particle size 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.

[0035] 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, JP2011-225417A, paragraphs 0012-0030, JP2011-216149A, paragraphs 0134-0136, JP2012-204726A, paragraphs 0013-0030, and JP2015-127985A, paragraphs 0029-0084.

[0036] In the present invention and this specification, the term "hexagonal ferrite powder" refers to a ferromagnetic powder in which the crystal structure of hexagonal ferrite is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the diffraction peak with the highest intensity is assigned in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when the diffraction peak with the highest intensity in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the crystal structure of hexagonal ferrite, it is determined that the crystal structure of hexagonal ferrite is detected as the main phase. When only a single structure is detected by X-ray diffraction analysis, the detected structure is regarded as the main phase. The crystal structure of hexagonal ferrite contains at least an iron atom, a divalent metal atom, and an oxygen atom as constituent atoms. The divalent metal atom is a metal atom that can become a divalent cation as an ion, and examples of the divalent metal atom include an alkaline earth metal atom such as a strontium atom, a barium atom, and a calcium atom, and a lead atom. In the present invention and this specification, the hexagonal strontium ferrite powder refers to a powder in which the main divalent metal atom contained therein is a strontium atom, and the 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 of the divalent metal atoms contained in the powder on an atomic % basis. However, the above divalent metal atoms do not include rare earth atoms. In the present invention and this specification, the "rare earth atom" is selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanoid atoms. The lanthanide atom is selected from the group consisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), a europium atom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), a ytterbium atom (Yb), and a lutetium atom (Lu).

[0037] Hereinafter, hexagonal strontium ferrite powder, which is one form of hexagonal ferrite powder, will be described in more detail.

[0038] The activation volume of hexagonal strontium ferrite powder is 2500 nm 3 Preferably, it is 2300 nm or less. 3 More preferably, it is 2000 nm or less. 3 On the other hand, from the viewpoint of magnetization stability, the activation volume of the hexagonal strontium ferrite powder is, for example, 800 nm 3 It is preferable that the thickness is 1000 nm or more. 3 More preferably, it is 1200 nm or more. 3 The activation volume of the hexagonal barium ferrite powder is more preferably equal to or larger than this value.

[0039] "Activation volume" is a unit of magnetization reversal and is an index showing the magnetic size of a particle. The activation volume and the anisotropy constant Ku described in the present invention and this specification are values ​​obtained by measuring the coercive force Hc measurement section at magnetic field sweep speeds of 3 minutes and 30 minutes (measurement temperature: 23°C ± 1°C) using a vibrating sample magnetometer, and calculating from the following relationship 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 It is. 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)]

[0040] The anisotropy constant Ku can be used as an index of reduction in thermal fluctuation, in other words, improvement in thermal stability. The hexagonal strontium ferrite powder is preferably 1.8×10 5 J / m 3 More preferably, the Ku is 2.0×10 or more.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 preferable, the Ku value is not limited to the above-mentioned values.

[0041] 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 are 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 uneven distribution of rare earth atoms in the surface layer portion. In the present invention and this specification, the term "surface distribution of rare earth atoms" refers to 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 content of rare earth atoms" or simply "surface content" for rare earth atoms), which is greater than 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), Rare earth atom surface content / rare earth atom bulk content>1.0 The rare earth atom content of the hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. 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 of "rare earth atom surface layer content / rare earth atom bulk content>1.0" means that the rare earth atoms are unevenly distributed (i.e., more present in the surface layer) in the particles constituting the hexagonal strontium ferrite powder. In the present invention and this specification, the surface layer refers to a portion of the region extending from the surface of the particles constituting the hexagonal strontium ferrite powder toward the inside.

[0042] 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 % relative to 100 atomic % of iron atoms. It is considered that the rare earth atoms contained in the bulk content in the above range and the rare earth atoms unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder contribute to suppressing the decrease in the reproduction output during repeated reproduction. This is presumed to be because the hexagonal strontium ferrite powder contains rare earth atoms in the bulk content in the above range and the rare earth atoms unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in the reproduction output during repeated reproduction can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the surface layer of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of the iron (Fe) sites in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. In addition, it is presumed that using the hexagonal strontium ferrite powder having rare earth atom uneven distribution on the surface as the ferromagnetic powder of the magnetic layer also contributes to suppressing the wear of the magnetic layer surface due to sliding with the magnetic head. That is, it is presumed that the hexagonal strontium ferrite powder having rare earth atom uneven distribution on the surface can also contribute to improving the running durability of the magnetic tape. This is presumed to be because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surface and the organic substance (e.g., binder and / or additive) contained in the magnetic layer, and as a result, the strength of the magnetic layer is improved. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic %, 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 %.

[0043] The bulk content is the content obtained 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 obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one rare earth atom as a rare earth atom, or may contain two or more rare earth atoms. When two or more rare earth atoms are contained, the bulk content is obtained for the total of two or more rare earth atoms. This point is the same for other components in the present invention and this specification. That is, unless otherwise specified, a certain component may be used in only one type, or in two or more types. When two or more types are used, the content or content refers to the total of two or more types.

[0044] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained therein may be any one or more of rare earth atoms. From the viewpoint of further suppressing the decrease in the reproduction output during repeated reproduction, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms and dysprosium atoms, more preferred are neodymium atoms, samarium atoms and yttrium atoms, and even more preferred are neodymium atoms.

[0045] In the hexagonal strontium ferrite powder having rare earth atom uneven distribution in the surface layer, the rare earth atoms may 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 the hexagonal strontium ferrite powder having rare earth atom uneven distribution in the surface layer, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms obtained by complete dissolution under the dissolution conditions described below, "surface content / bulk content", is more than 1.0 and can be 1.5 or more. The "surface content / bulk content" being greater than 1.0 means that the rare earth atoms are unevenly distributed in the surface layer (i.e., more than in the interior) in the particles constituting the hexagonal strontium ferrite powder. In addition, the ratio of the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface layer 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 atom surface layer uneven distribution, 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 layer content / bulk content" is not limited to the upper or lower limit exemplified.

[0046] The partial and total dissolution of hexagonal strontium ferrite powder will be described below. For hexagonal strontium ferrite powder present as powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution, and the other part is subjected to total dissolution. The hexagonal strontium ferrite powder can be taken out from the magnetic layer by, for example, the method described in paragraph 0032 of JP 2015-91747 A. The above-mentioned partial dissolution means that the hexagonal strontium ferrite powder is dissolved to such an extent that the remaining powder can be visually confirmed in the liquid at the end of dissolution. For example, the partial dissolution can dissolve a region of 10 to 20 mass% of the particles constituting the hexagonal strontium ferrite powder, with the whole particles being 100 mass%. On the other hand, the above-mentioned complete dissolution means that the hexagonal strontium ferrite powder is dissolved to such an extent that the remaining powder cannot be visually confirmed in the liquid at the end of dissolution. The partial dissolution and the surface layer content are measured, for example, by the following method. Note that the dissolution conditions such as the amount of sample powder are merely examples, and any dissolution conditions that allow partial or complete dissolution can be used. 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 thus obtained 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. When multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. This is also true for the measurement of bulk content. On the other hand, the total dissolved and bulk contents are measured, 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. After that, the bulk content relative to 100 atomic % of iron atoms can be calculated by carrying out the same procedure as the partial dissolution and surface layer content measurement described above.

[0047] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, hexagonal strontium ferrite powder that contains rare earth atoms but does not have uneven distribution of rare earth atoms in the surface layer has a tendency to have a significantly lower σs than hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder that has uneven distribution of rare earth atoms in the surface layer is considered to be preferable in terms of suppressing 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 47A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, σs is 80A·m 2 / kg or less, and 60A·m 2 / kg or less. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. 1 [kOe]=10 6 / 4π[A / m].

[0048] 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 divalent metal atoms contained in the hexagonal strontium ferrite powder can be only strontium atoms. In another embodiment, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to strontium atoms. For example, it can contain barium atoms and / or calcium atoms. 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.

[0049] 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 the 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, M-type hexagonal ferrite is AFe 12 O 19Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is of the M type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms, the strontium atom (Sr) accounts for the largest proportion 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 crystal 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 an iron atom, a strontium atom, and an oxygen atom, and may further contain a rare earth atom. 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 an aluminum atom (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 the decrease in the reproduction output during repeated reproduction, 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 be 0 atomic %. That is, in one embodiment, the hexagonal strontium ferrite powder may not contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic % above is obtained 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. In addition, in the present invention and this specification, "not containing" a certain atom means that the content measured by an ICP analyzer after completely dissolving is 0 mass %. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above term "free" is used to mean that the content 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).

[0050] metal powder A specific preferred example of the ferromagnetic powder is a ferromagnetic metal powder. For details of the ferromagnetic metal powder, reference can be made to, for example, paragraphs 0137 to 0141 of JP 2011-216149 A and paragraphs 0009 to 0023 of JP 2005-251351 A.

[0051] ε-iron oxide powder A preferred specific 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 the ε-iron oxide crystal structure is detected as the main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the 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 is 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 the above production methods are publicly known. In addition, for a method for producing ε-iron oxide powder in which a part of Fe is replaced by a substitution atom such as Ga, Co, Ti, Al, or Rh, reference can be made to, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp.5200-5206, etc. However, the method for producing 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 method given here.

[0052] 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 exhibiting excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm 3 For example, 500 nm or more.3 From 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 equal to or less than 1100 nm. 3 It is even more preferred that:

[0053] 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 is preferably 3.0×10 4 J / m 3 More preferably, the Ku is 8.0×10 or more. 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 preferable, the Ku value is not limited to the above-mentioned values.

[0054] 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 12 A m 2 On the other hand, the σs of ε-iron oxide powder is 40 A m 2 / kg or less, and 35A·m 2 It is more preferable that the amount is not more than 1 / kg.

[0055] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope. The powder is photographed at a magnification of 100,000 times using a transmission electron microscope, and a photograph of the particles that make up the powder is obtained by printing it on photographic paper or displaying it on a display so that the total magnification is 500,000 times. From the obtained particle photograph, the target particle is selected, and the particle outline is traced with a digitizer to measure the particle (primary particle) size. Primary particles are independent particles that are not aggregated. The above measurements are carried out for 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, Carl Zeiss image analysis software KS-400. The average particle size described in the Examples section below is a value measured using a Hitachi transmission electron microscope H-9000 type as the transmission electron microscope and Carl Zeiss image analysis software KS-400 as the image analysis software, unless otherwise specified. In the present invention and this specification, powder means a collection of multiple particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. In addition, the collection of multiple particles is not limited to a form in which the particles constituting the collection are in direct contact with each other, and also includes a form in which a binder, additive, etc., described later, are interposed between the particles. The term particle is sometimes used to refer to powder.

[0056] 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 2011-048878 A can be used.

[0057] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is determined by the shape of the particles observed in the particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (where the height is greater than the maximum major axis of the base), etc., it is expressed by the length of the major axis that constitutes the particle, i.e., the major axis length. (2) In the case of a plate or columnar shape (where the thickness or height is smaller than the maximum long diameter of the plate or base), it shall be expressed by the maximum long diameter of the plate or base. (3) In the case of a particle having a spherical, polyhedral, or amorphous shape, and in which the major axis of the particle cannot be identified from its shape, the particle is expressed as the equivalent circle diameter, which is determined by the circle projection method.

[0058] The average acicular ratio of a powder refers to the arithmetic average of the short axis length of the particles, i.e., the short axis length, the (long axis length / short axis length) value of each particle, and the values ​​obtained for the 500 particles. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the above definition of particle size (1), and to the thickness or height in the above definition of particle size (2), and in the above definition of particle size (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for the sake of convenience. Unless otherwise specified, when the particle shape is specific, for example, in the case of the above definition of particle size (1), the average particle size is the average major axis length, in the case of definition (2), the average particle size is the average plate diameter, and in the case of definition (3), the average particle size is the average diameter (also called the average particle diameter or average particle size).

[0059] 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.

[0060] (Binding Agent) The magnetic tape may be a coated magnetic tape, and may contain a binder in the magnetic layer. The binder is one or more kinds of resin. As the binder, various resins that are usually used as binders for coated magnetic recording media may be used. For example, as the binder, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral, etc. may be used alone or in combination of a plurality of resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins may also be used as binders in the nonmagnetic layer and / or backcoat layer described below. For the above binders, refer to paragraphs 0028 to 0031 of JP-A-2010-24113. The binder may also be a radiation curable resin such as an electron beam curable resin. For information on radiation curable resins, see paragraphs 0044 to 0045 of JP2011-048878A. The average molecular weight of the resin used as the binder may be, for example, 10,000 or more and 200,000 or less in weight average molecular weight. The weight average molecular weight in the present invention and this specification is a value obtained by converting a value measured under the following measurement conditions by gel permeation chromatography (GPC) into polystyrene equivalent. The weight average molecular weight described in the Examples section below is a value obtained by converting a value measured under the following measurement conditions into polystyrene equivalent. GPC equipment: HLC-8120 (Tosoh Corporation) Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (inner diameter) × 30.0 cm) Eluent: tetrahydrofuran (THF)

[0061] In one embodiment, a binder containing an acidic group can be used as the binder. In the present invention and this specification, an acidic group is a group that reacts with H in water or a solvent containing water (aqueous solvent). + The term "acidic group" is used to include groups capable of releasing anions and dissociating into anions, and their salt forms. Specific examples of acidic groups include sulfonic acid groups, sulfate groups, carboxy groups, phosphoric acid groups, and their salt forms. For example, the salt form of a sulfonic acid group (-SO3H) refers to a group represented by -SO3M, where M represents an atom (e.g., an alkali metal atom) that can become a cation in water or an aqueous solvent. This also applies to the salt forms of the above-mentioned various groups. An example of a binder containing an acidic group is a resin (e.g., polyurethane resin, vinyl chloride resin, etc.) containing at least one acidic group selected from the group consisting of sulfonic acid groups and their salts. However, the resin contained in the magnetic layer is not limited to these resins. In addition, in a binder containing an acidic group, the acidic group content can be in the range of, for example, 20 to 500 eq / ton. The unit "eq" is "equivalent" and cannot be converted to SI units. The content of various functional groups, such as acidic groups, contained in a resin can be determined by a known method depending on the type of functional group. The more acidic group a binder is used, the larger the ΔN value tends to be. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass, preferably 1.0 to 20.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The more the amount of binder used relative to the ferromagnetic powder, the larger the ΔN value tends to be.

[0062] (hardening agent) A curing agent can be used together with the resin usable as a binder. In one embodiment, the curing agent can be a thermosetting compound, which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating, and in another embodiment, the curing agent can be a photocuring compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation. As the curing reaction proceeds in the magnetic layer forming process, at least a part of the curing agent can be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as the binder. This point is also true for layers formed using a composition used to form other layers that contains a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For details on polyisocyanate, refer to paragraphs 0124 to 0125 of JP 2011-216149 A. The curing agent can be used in an amount of, for example, 0 to 80.0 parts by mass relative to 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of the magnetic layer.

[0063] (Additives) The magnetic layer may contain one or more additives as necessary. The additives may be selected from commercially available products according to the desired properties. Alternatively, compounds synthesized by known methods may be used as additives. The additives may be used in any amount. An example of the additive is the above-mentioned curing agent. 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, antioxidants, etc. For example, reference may be made to paragraphs 0030 to 0033, 0035, and 0036 of JP-A-2016-126817 for lubricants. The non-magnetic layer described below may contain a lubricant. Reference may be made to paragraphs 0030 to 0031, 0034, 0035, and 0036 of JP-A-2016-126817 for lubricants that may be contained in the non-magnetic layer. For the dispersant, refer to paragraphs 0061 and 0071 of JP 2012-133837 A. The dispersant may be added to the non-magnetic layer forming composition. For the dispersant that can be added to the non-magnetic layer forming composition, refer to paragraph 0061 of JP 2012-133837 A. In addition, examples of non-magnetic powders that can be included in the magnetic layer include non-magnetic powders that can function as abrasives, and non-magnetic powders (e.g., non-magnetic colloidal particles) that can function as protrusion forming agents that form protrusions that protrude appropriately on the magnetic layer surface. For example, for the abrasives, refer to paragraphs 0030 to 0032 of JP 2004-273070 A. As the abrasives, refer to a non-magnetic powder having a specific surface area measured by the BET (Brunauer-Emmett-Teller) method (hereinafter referred to as "BET specific surface area") of 14 m. 2 / g or more 40m 2 It is preferable to use an abrasive having a surface roughness of 100 nm or less. As the protrusion-forming agent, colloidal particles are preferable, inorganic colloidal particles are preferable from the viewpoint of availability, inorganic oxide colloidal particles are more preferable, and silica colloidal particles (colloidal silica) are even more preferable. The average particle size of the protrusion-forming agent is preferably in the range of 30 to 200 nm, more preferably in the range of 50 to 100 nm.

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

[0065] <Nonmagnetic layer> Next, the non-magnetic layer will be described. The magnetic tape may have a magnetic layer directly on the non-magnetic support, or may have a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used in the non-magnetic layer may be a powder of an inorganic substance (inorganic powder) or a powder of an organic substance (organic powder). Carbon black and the like can also be used. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available, and can also be produced by known methods. For details, refer to paragraphs 0146 to 0150 of JP-A-2011-216149. For carbon black usable in the non-magnetic layer, refer to paragraphs 0040 to 0041 of JP-A-2010-24113. The content (filling rate) of the nonmagnetic powder in the nonmagnetic 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 nonmagnetic layer.

[0066] In one embodiment, the non-magnetic layer may contain Fe-based inorganic oxide powder as the non-magnetic powder. In the present invention and this specification, the term "Fe-based inorganic oxide powder" refers to an inorganic oxide powder containing iron as a constituent element. Specific examples of the Fe-based inorganic oxide powder include α-iron oxide powder and goethite powder. In the present invention and this specification, the term "α-iron oxide powder" refers to a non-magnetic powder in which the crystal structure of α-iron oxide is detected as the main phase by X-ray diffraction analysis. α-iron oxide powder is also generally called hematite.

[0067] From the viewpoint of controlling the width direction σ of ΔN within the range described above, the nonmagnetic powder for the nonmagnetic layer is preferably a powder having an average particle volume of 2.0×10 -6 μm 3As a result of the investigations conducted by the present inventors, it has become clear that it is preferable to use the following Fe-based inorganic oxide powder. Therefore, the average particle volume of the Fe-based inorganic oxide powder contained in the nonmagnetic layer is 2.0×10 -6 μm 3 It is preferable that the value is less than 1.5×10 -6 μm 3 More preferably, it is 1.0×10 -6 μm 3 The average particle volume is preferably, for example, 1.0×10 -9 μm 3 or more than 1.0×10 -8 μm 3 It can be greater than or less than the values ​​exemplified herein.

[0068] In the present invention and this specification, the above average particle volume is a value determined by the following method. In order to observe the Fe-based inorganic oxide powder contained in the non-magnetic layer of the magnetic tape, the sample is first sliced ​​by a microtome method as a sample pretreatment. The slices are cut along the longitudinal direction of the magnetic tape so as to obtain a thin sample that allows observation of the cross section in the thickness direction of the magnetic tape. In the examples described later, a Leica EM UC6 manufactured by Leica was used as a microtome to determine the average particle volume of the Fe-based inorganic oxide powder. The obtained thin sample is observed in cross section using a transmission electron microscope (TEM) at an acceleration voltage of 300 kV and a total magnification of 200,000 times, so as to include the range from the non-magnetic support to the magnetic layer, and a cross-sectional TEM image is obtained. As the transmission electron microscope, for example, JEOL's JEM-2100Plus can be used. In the examples described later, in order to determine the average particle volume of the Fe-based inorganic oxide powder, JEOL's JEM-2100Plus was used as the transmission electron microscope. In the obtained cross-sectional TEM image, 50 particles of the Fe-based inorganic oxide powder are identified from the particles contained in the nonmagnetic layer by using the ultrafine electron beam diffraction method. Electron beam diffraction by the ultrafine electron beam diffraction method is performed using a transmission electron microscope at an acceleration voltage of 200 kV and a camera length of 50 cm. In the examples described later, a JEM-2100Plus manufactured by JEOL was used as the transmission electron microscope for electron beam diffraction by the ultrafine electron beam diffraction method. Thereafter, the average particle volume is calculated as follows using 50 particles of the Fe-based inorganic oxide powder identified as above. First, the major axis length (hereinafter referred to as "DL") and minor axis length (hereinafter referred to as "DS") of each particle are measured. The major axis length DL means the maximum distance between two parallel lines drawn at any angle so as to be tangent to the contour of the particle (so-called maximum Feret's diameter). If the direction of the major axis length defined as above is referred to as the major axis direction, the minor axis length DS means the maximum length of the particle in the direction perpendicular to the major axis direction of the particle. Next, the average major axis length DLave is calculated as the arithmetic mean of the major axis lengths DL of the measured 50 particles. ave is an abbreviation for average. In addition, the average minor axis length DSave is calculated as the arithmetic mean of the minor axis lengths DS of the above 50 particles. The average particle volume Vave is calculated from the average major axis length DLave and the average minor axis length DSave using the following formula. Vave = π / 6 × DSave 2 ×DLave

[0069] In one embodiment, the non-magnetic layer may also contain carbon black as a non-magnetic powder. The average particle size of the carbon black may be, for example, 10 nm or more and 50 nm or less. From the viewpoint of controlling the width direction σ of ΔN within the range described above, it has become clear from the results of the study by the present inventor that it is preferable to use carbon black having a pH of 9.0 or less as the non-magnetic powder of the non-magnetic layer. Therefore, the pH of the carbon black contained in the non-magnetic layer is preferably 9.0 or less, more preferably 8.5 or less, even more preferably 8.0 or less, and even more preferably 7.5 or less. The above pH may be, for example, 1.0 or more, 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more, or 6.0 or more, or may be lower than the values ​​exemplified here.

[0070] For the purposes of this invention and the present specification, the pH of carbon black is determined according to standard test method ASTM D1512.

[0071] The non-magnetic layer has an average grain volume of 2.0×10 -6 μm 3 It is preferable to include at least one of the following Fe-based inorganic oxide powder and carbon black having a pH of 9.0 or less, and more preferable to include both. -6 μm 3 The content of the Fe-based inorganic oxide powder described below can be 50.0 parts by mass or more, 60.0 parts by mass or more, or 70.0 parts by mass or more, and can be, for example, 90.0 parts by mass or less. The content of the carbon black having a pH of 9.0 or less, relative to 100.0 parts by mass of the total amount of nonmagnetic powder contained in the nonmagnetic layer, can be 10.0 parts by mass or more, or 20.0 parts by mass or more, and can be, for example, 50.0 parts by mass or less, 40.0 parts by mass or less, or 30.0 parts by mass or less.

[0072] The non-magnetic layer may contain a binder and may also contain an additive. For other details of the binder, additive, etc. of the non-magnetic layer, known techniques related to non-magnetic layers can be applied. In addition, for example, for the type and content of the binder, the type and content of the additive, known techniques related to magnetic layers can also be applied.

[0073] The non-magnetic layer of the magnetic tape includes a substantially non-magnetic layer that contains a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with the non-magnetic powder. A substantially non-magnetic layer here 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 has no residual magnetic flux density or coercive force.

[0074] <Nonmagnetic support> Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter, simply referred to as "support") include known biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, aromatic polyamide, and the like. 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, and the like.

[0075] <Backcoat layer> The tape may or may not have a backcoat layer containing a nonmagnetic powder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. The backcoat layer preferably contains one or both of carbon black and inorganic powder. The backcoat layer may contain a binder and may also contain additives. For details of the nonmagnetic powder, binder, additives, etc. of the backcoat layer, known techniques related to the backcoat layer may be applied, and known techniques related to the magnetic layer and / or nonmagnetic layer may also be applied. For example, the descriptions of paragraphs 0018 to 0020 of JP 2006-331625 A and US Pat. No. 7,029,774, column 4, line 65 to column 5, line 38, may be referred to for the backcoat layer.

[0076] <Various thicknesses> Regarding the thickness (total thickness) of the magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for magnetic recording media to have higher recording capacity (higher capacity). As a means for increasing the capacity of tape-shaped magnetic recording media (i.e., magnetic tape), there is the reduction in the thickness of the magnetic tape and the increase in the length of the magnetic tape accommodated in one magnetic tape cartridge. From this point of view, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, 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. From the viewpoint of ease of handling, the 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.

[0077] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized according to the saturation magnetization amount of the magnetic head used, the head gap length, the band of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, and from the viewpoint of high-density recording, 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 having different magnetic properties, and a known configuration related to a multilayer magnetic layer can be applied. When the magnetic layer is separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers. The thickness of the nonmagnetic 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. The thickness of each layer and non-magnetic support is determined by exposing a cross section of the magnetic tape in the thickness direction by a known method such as an ion beam or a microtome, and then observing the exposed cross section with a scanning transmission electron microscope (STEM). For specific examples of thickness measurement methods, see the description of the thickness measurement method in the Examples section below.

[0078] <Manufacturing process> (Preparation of compositions for forming each layer) The composition for forming the magnetic layer, non-magnetic layer, or backcoat layer usually contains a solvent in addition to the various components described above. As the solvent, one or more of various organic solvents generally used for manufacturing particulate magnetic recording media can be used. For details of the solvent, see, for example, paragraph 0153 of JP2011-216149A. The process of preparing the composition for forming each layer can usually include at least a kneading process, a dispersing process, and a mixing process provided before or after these processes as necessary. Each of the individual processes may be divided into two or more stages. The components used in the preparation of the composition for forming each layer may be added at the beginning or during any process. Also, each component may be added in portions in two or more processes. For example, the binder may be added in portions in the kneading process, the dispersing process, and the mixing process for adjusting the viscosity after dispersion. In order to manufacture the magnetic tape, conventional known manufacturing techniques can be used in various processes. In the kneading process, a device having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder can be used. For details of these kneading processes, refer to JP-A-1-106338 and JP-A-1-79274. Known dispersing machines can be used. Regarding ΔN, the value of ΔN tends to be larger as the dispersion time of the dispersion liquid containing the ferromagnetic powder, binder, and solvent (hereinafter referred to as "magnetic liquid") is longer and / or the dispersion beads with a smaller bead diameter are used. This is thought to be because the dispersibility of the ferromagnetic powder in the coating layer of the composition for forming a magnetic layer is increased as the dispersion time of the magnetic liquid is longer and / or the dispersion beads with a smaller bead diameter are used, and the orientation state of the ferromagnetic particles constituting the ferromagnetic powder tends to be more uniform by the orientation treatment. In addition, the value of ΔN tends to be larger as the dispersion time when the various components of the composition for forming a nonmagnetic layer are mixed and dispersed is longer. The dispersion time of the magnetic liquid, the bead diameter of the dispersion beads, and the dispersion time of the composition for forming a nonmagnetic layer are set so that ΔN of 0.25 or more and 0.40 or less can be realized. In addition, filtration may be performed by a known method at any stage of preparing the composition for forming each layer. Filtration can be performed by, for example, filter filtration. The filter used for filtration may be, for example, a filter with a pore size of 0.01 to 3 μm (eg, a glass fiber filter, a polypropylene filter, etc.).

[0079] (Coating process, cooling process, heating and drying process) The magnetic layer can be formed by directly applying the magnetic layer forming composition onto the non-magnetic support, or by applying the magnetic layer forming composition successively or simultaneously in a multi-layer manner. For details of the coating for forming each layer, refer to paragraph 0066 of JP-A-2010-231843. Also, the coating process for forming each layer can be performed in two or more steps. For example, in one embodiment, the magnetic layer forming composition can be applied in two or more steps. In this case, a heat drying treatment may or may not be applied between the two coating steps. Also, an orientation treatment may or may not be applied between the two coating steps. For details of the coating for forming each layer, refer to paragraph 0066 of JP-A-2010-231843. With regard to the magnetic layer forming composition, the lower the atmospheric temperature of the transport path (e.g., the orientation zone) through which the coating layer formed by applying the magnetic layer forming composition is transported, the larger the value of ΔN tends to be. The above-mentioned atmospheric temperature may be set so as to realize a ΔN of 0.25 or more and 0.40 or less.

[0080] As described above, in one embodiment, the magnetic tape can have a non-magnetic layer between the non-magnetic support and the magnetic layer. Such a magnetic tape can be preferably manufactured by successive multi-layer coating. The manufacturing process of successive multi-layer coating can be preferably carried out as follows. The non-magnetic layer is formed through a coating process in which a non-magnetic layer-forming composition is applied to a non-magnetic support to form a coating layer, and a heat-drying process in which the formed coating layer is dried by heat treatment. Then, the magnetic layer is formed through a coating process in which a magnetic layer-forming composition is applied to the formed non-magnetic layer to form a coating layer, and a heat-drying process in which the formed coating layer is dried by heat treatment.

[0081] The inventors believe that in the non-magnetic layer formation step of such a manufacturing method involving successive multi-layer coating, it is preferable to carry out a coating step using a non-magnetic layer forming composition to form a coating layer, and to carry out a cooling step to cool the coating layer between the coating step and the heat drying step, in order to control the width direction σ value of ΔN to 0.05 or less.

[0082] An example of a manufacturing process for the magnetic tape will be described below with reference to Fig. 8. However, the present invention is not limited to the following example.

[0083] Fig. 8 is a process schematic diagram showing an example of a process for producing a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one side of a nonmagnetic support and a backcoat layer on the other side. In the example shown in Fig. 8, the nonmagnetic support (long film) is continuously wound from the unwinding section to the winding section, and various treatments such as coating, drying, and orientation are performed in each section or zone shown in Fig. 8, so that a nonmagnetic layer and a magnetic layer can be formed by successive multilayer coating on one side of the running nonmagnetic support, and a backcoat layer can be formed on the other side. The example shown in Fig. 8 can be the same as a manufacturing process usually performed for the production of coating-type magnetic recording media, except that a cooling zone is included.

[0084] In the first coating section, the nonmagnetic support delivered from the delivery section is coated with a nonmagnetic layer forming composition (a step of applying the nonmagnetic layer forming composition).

[0085] After the coating step, the coating layer of the nonmagnetic layer-forming composition formed in the coating step is cooled in a cooling zone (cooling step). For example, the cooling step can be performed by passing the nonmagnetic support on which the coating layer is formed through a cooling atmosphere. The temperature of the cooling atmosphere can be preferably in the range of -10°C to 0°C, and more preferably in the range of -5°C to 0°C. The time for performing the cooling step (for example, the time from when any part of the coating layer is carried into the cooling zone until it is carried out (hereinafter, also referred to as "residence time")) is not particularly limited. The longer the residence time, the smaller the value of ΔN in the width direction σ tends to be. In the cooling step, cooled gas may be blown onto the surface of the coating layer.

[0086] After the cooling zone, in the first heat treatment zone, the coating layer after the cooling step is heated to dry the coating layer (heat drying step). The heat drying step can be performed by passing the non-magnetic support having the coating layer after the cooling step through a heated atmosphere. The temperature of the heated atmosphere here, as well as the temperature of the heated atmosphere in the heat drying step in the second heat treatment zone and the heat drying step in the third heat treatment zone, which will be described later, are also called "drying temperature". Increasing the drying temperature in each heat treatment zone can contribute to reducing the value of ΔN in the width direction σ. From this point of view, the drying temperature in each heat treatment zone is preferably 95°C or higher, and more preferably 100°C or higher. In addition, the drying temperature in each heat treatment zone can be, for example, 140°C or lower or 130°C or lower, and can also be higher than the temperatures listed here. Optionally, heated gas may be blown onto the surface of the coating layer.

[0087] Next, in the second coating section, a magnetic layer-forming composition is coated onto the non-magnetic layer formed by the heat drying step in the first heat treatment zone (magnetic layer-forming composition coating step).

[0088] In the case of the embodiment in which the orientation treatment is performed after that, while the coating layer of the magnetic layer forming composition is in a wet state, the orientation treatment of the ferromagnetic powder in the coating layer is performed in the orientation zone. From the viewpoint of the ease of realizing ΔN of 0.25 to 0.40, the orientation treatment is preferably performed by arranging a magnet so that a magnetic field is applied perpendicularly to the surface of the coating layer of the magnetic layer forming composition (i.e., vertical orientation treatment). The strength of the magnetic field during the orientation treatment may be set so that ΔN of 0.25 to 0.40 can be realized. In addition, when the coating process of the magnetic layer forming composition is performed by two or more coating steps, it is preferable to perform the orientation treatment at least after the last coating step, and it is more preferable to perform the vertical orientation treatment. For example, when the magnetic layer is formed by two coating steps, the first coating step is followed by a heating and drying treatment without performing the orientation treatment, and then the coating layer formed in the second coating step can be subjected to the orientation treatment.

[0089] The coated layer after the orientation treatment is subjected to a heat drying step in the second heat treatment zone.

[0090] Next, in the third coating section, a backcoat layer forming composition is applied to the surface of the non-magnetic support opposite to the surface on which the non-magnetic layer and the magnetic layer are formed, forming a coating layer (a backcoat layer forming composition application step).Then, in the third heat treatment zone, the coating layer is heat treated and dried.

[0091] Through the above steps, a magnetic tape can be obtained which has a nonmagnetic layer and a magnetic layer in that order on one side of a nonmagnetic support and a backcoat layer on the other side.

[0092] (Other processes) In the manufacturing process of magnetic tapes, calendering is usually performed to improve the surface smoothness of the magnetic tape. Strengthening the calendering conditions can contribute to reducing the value of ΔN in the width direction σ. Specific examples of strengthening the calendering conditions include increasing the calendering pressure, increasing the calendering temperature, and decreasing the calendering speed. Regarding the calendering conditions, the calendering pressure (linear pressure) is preferably 300 to 500 kN / m, more preferably 310 to 350 kN / m, the calendering temperature (calender roll surface temperature) is preferably 95 to 120° C., more preferably 100 to 120° C., and the calendering speed is preferably 50 to 75 m / min. For other various steps in manufacturing the magnetic tape, reference can be made to paragraphs 0067 to 0070 of JP2010-231843A. A long magnetic tape roll can be obtained through various processes. The obtained magnetic tape roll is cut (slit) to the width of the magnetic tape to be housed in a magnetic tape cartridge, for example, by a known cutter. The width can be determined according to standards and is usually 1 / 2 inch. 1 inch = 2.54 cm. A servo pattern is usually formed on the magnetic tape obtained by slitting.

[0093] (Formation of servo pattern) “Formation of a servo pattern” can also be called “recording of a servo signal.” The formation of a servo pattern will be described below.

[0094] The servo pattern is usually formed along the longitudinal direction of the magnetic tape. Control methods that use servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0095] As shown in ECMA (European Computer Manufacturers Association)-319 (June 2001), a magnetic tape (generally called "LTO tape") conforming to the LTO (Linear Tape-Open) standard employs 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 called "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. In the present invention and this specification, the "timing-based servo pattern" refers to a servo pattern that enables head tracking in a servo system of the timing-based servo system. As described above, the servo pattern is formed by a pair of non-parallel magnetic stripes in order to inform the servo signal reading element passing over the servo pattern of its passing position. Specifically, the pair of magnetic stripes is formed so that the interval between them changes continuously along the width direction of the magnetic tape, and the servo signal reading element can know the relative position between the servo pattern and the servo signal reading element by reading the interval. This relative position information enables tracking of the data track. For this reason, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

[0096] A servo band is made up of a continuous servo pattern in the longitudinal direction of the magnetic tape. Usually, multiple servo bands are provided on a magnetic tape. For example, there are five servo bands on an LTO tape. The area between two adjacent servo bands is the data band. The data band is made up of multiple data tracks, and each data track corresponds to one servo track.

[0097] Also, in one embodiment, as shown in JP 2004-318983 A, information indicating the number of the servo band (also called "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 relatively in 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, so that the servo band can be uniquely identified simply by reading one servo band with a servo signal reading element.

[0098] As a method for uniquely identifying servo bands, there is also a method using a staggered method as shown in ECMA-319 (June 2001). In this staggered method, a group of pairs of non-parallel magnetic stripes (servo stripes) arranged continuously in the longitudinal direction of the magnetic tape are recorded so that they are shifted in the longitudinal direction of the magnetic tape for each servo band. Since the combination of the shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify the servo bands when reading the servo pattern using two servo signal reading elements.

[0099] Also, 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 with this LPOS information.

[0100] It is also possible to embed information other than the above 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. Also, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of pairs of servo stripes.

[0101] The head for forming a servo pattern is called a servo write head. The servo write head usually has a pair of gaps corresponding to the pair of magnetic stripes, the number of which is equal to the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and a magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps by supplying a current pulse to the coil. When forming a servo pattern, a magnetic pattern corresponding to the pair of gaps can be transferred to the magnetic tape by inputting a current pulse while running the magnetic tape on the servo write head, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, or 10 μm or more.

[0102] Before forming a servo pattern on the 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. There are two types of erase processes: DC (Direct Current) erase and AC (Alternating Current) erase. AC erase is performed by gradually lowering the strength of the magnetic field applied to the magnetic tape while reversing the direction of the magnetic field. On the other hand, DC erase is performed by applying a unidirectional magnetic field to the magnetic tape. There are two more methods of DC erase. The first method is horizontal DC erase, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erase, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape, or may be performed for each servo band of the magnetic tape.

[0103] The direction of the magnetic field of the formed servo pattern is determined according to the direction of erasure. For example, when the magnetic tape is subjected to horizontal DC erasure, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of erasure. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in JP2012-53940A, when the magnetic pattern is transferred to the magnetic tape that has been vertically DC erased using the above gap, the servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when the magnetic pattern is transferred to the magnetic tape that has been horizontally DC erased using the above gap, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0104] <Vertical squareness ratio> In one embodiment, the squareness ratio of the magnetic tape in the perpendicular direction can be, for example, 0.55 or more, and from the viewpoint of improving the electromagnetic conversion characteristics, it is preferably 0.60 or more, and more preferably 0.65 or more. The upper limit of the squareness ratio is, in principle, 1.00 or less. The squareness ratio of the magnetic tape in the perpendicular direction can be 1.00 or less, and can be 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. It is preferable that the squareness ratio of the magnetic tape in the perpendicular direction is large from the viewpoint of improving the electromagnetic conversion characteristics. The squareness ratio of the magnetic tape in the perpendicular direction can be controlled by a known method such as carrying out a perpendicular orientation process.

[0105] In the present invention and this specification, the "perpendicular squareness" refers to the squareness measured in the perpendicular direction of the magnetic tape. The "perpendicular direction" described in relation to the squareness is the direction perpendicular to the magnetic layer surface, and can also be called the thickness direction. In the present invention and this specification, the perpendicular squareness is determined by the following method. A sample piece of a size that can be introduced into a vibration sample magnetometer is cut out from the magnetic tape to be measured. A magnetic field is applied to this sample piece in a vertical direction (perpendicular to the magnetic layer surface) using a vibration sample magnetometer at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA / m / sec, and the magnetization strength of the sample piece against the applied magnetic field is measured. The measured value of the magnetization strength is obtained as a value after demagnetization field correction and a value obtained by subtracting the magnetization of the sample probe of the vibration sample magnetometer as background noise. When the magnetization strength at the maximum applied magnetic field is Ms and the magnetization strength at zero applied magnetic field is Mr, the squareness ratio SQ is a value calculated as SQ=Mr / Ms. The measurement temperature refers to the temperature of the sample piece, and by setting the ambient temperature around the sample piece to the measurement temperature, the temperature equilibrium is established and the temperature of the sample piece can be set to the measurement temperature.

[0106] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-mentioned magnetic tape.

[0107] The details of the magnetic tape contained in the magnetic tape cartridge are as described above. The magnetic tape cartridge can be mounted in a magnetic tape device equipped with a magnetic head and used to record and / or reproduce data.

[0108] In a magnetic tape cartridge, the magnetic tape is generally accommodated inside the cartridge body in a state where it is wound around a reel. The reel is provided rotatably inside the cartridge body. As the magnetic tape cartridge, a single-reel type magnetic tape cartridge having one reel inside the cartridge body and a twin-reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When a single-reel type magnetic tape cartridge is loaded into a magnetic tape device for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound around the reel on the magnetic tape device side. A magnetic head is disposed on 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 side and the reel (take-up reel) on the magnetic tape device side. For example, during this time, the magnetic head comes into contact with and slides on the surface of the magnetic layer of the magnetic tape, thereby recording and / or reproducing data. In contrast, a dual-reel magnetic tape cartridge is provided with both a supply reel and a take-up reel inside the magnetic tape cartridge.

[0109] In one embodiment, the magnetic tape cartridge may include a cartridge memory. The cartridge memory may be, for example, a non-volatile memory, and in one embodiment, head tilt angle adjustment information is already recorded or head tilt angle adjustment information is recorded. The head tilt angle adjustment information is information for adjusting the head tilt angle while the magnetic tape is running in the magnetic tape device. For example, the head tilt angle adjustment information may record the value of the servo band interval at each position in the longitudinal direction of the magnetic tape when data is recorded. For example, when reproducing data recorded on the magnetic tape, the value of the servo band interval is measured during reproduction, and the head tilt angle can be adjusted by the control device of the magnetic tape device so that the absolute value of the difference between the servo band interval at the same longitudinal position recorded in the cartridge memory during recording approaches 0. The head tilt angle may be, for example, the angle θ described above.

[0110] The magnetic tape and magnetic tape cartridge can be suitably used in a magnetic tape device (in other words, a magnetic recording and reproducing system) that records and / or reproduces data at different head tilt angles. In one embodiment of such a magnetic tape device, the head tilt angle can be changed while the magnetic tape is running to record and / or reproduce data. For example, the head tilt angle can be changed according to dimensional information in the width direction of the magnetic tape acquired while the magnetic tape is running. In another embodiment, the head tilt angle is changed from the head tilt angle in a certain recording and / or reproduction to the head tilt angle in the next and subsequent recording and / or reproduction, and the head tilt angle is fixed without being changed during the magnetic tape running for each recording and / or reproduction.

[0111] [Magnetic tape device] One aspect of the present invention relates to a magnetic tape device including the magnetic tape. In the magnetic tape device, data can be recorded on the magnetic tape and / or data recorded on the magnetic tape can be reproduced, for example, by contacting and sliding a magnetic head against the surface of the magnetic layer of the magnetic tape.

[0112] In one embodiment, the magnetic tape is treated as a removable medium (so-called exchangeable medium), and a magnetic tape cartridge containing the magnetic tape is inserted into and removed from a magnetic tape device, whereas in another embodiment, the magnetic tape is not treated as an exchangeable medium, and the magnetic tape is wound on a reel of a magnetic tape device equipped with a magnetic head, and the magnetic tape is stored in the magnetic tape device.

[0113] In the present invention and this specification, the term "magnetic tape device" refers to a device that can perform at least one of recording data on a magnetic tape and reproducing data recorded on a magnetic tape. Such a device is generally called a drive.

[0114] <Magnetic head> The magnetic tape device may include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as described above with reference to Figs. 5 to 7. When the magnetic head includes a reproducing element, the reproducing element is preferably a magnetoresistive (MR: Magnetoresistive) element capable of reading information recorded on a magnetic tape with good sensitivity. As the MR element, various known MR elements (for example, a GMR (Giant Magnetoresistive) element, a TMR (Tunnel Magnetoresistive) element, etc.) can be used. Hereinafter, a magnetic head that records data and / or reproduces recorded data is also referred to as a "recording and reproducing head". An element for recording data (recording element) and an element for reproducing data (reproducing element) are collectively referred to as a "magnetic head element".

[0115] When recording data and / or reproducing recorded data, tracking can be performed using servo signals first. That is, by making the servo signal reading element follow a specific servo track, the magnetic head element can be controlled to pass over the target data track. The data track is moved by changing the servo track read by the servo signal reading element in the tape width direction. The recording / reproducing head can also record and / or reproduce data on other data bands by using the UDIM information described above to move the servo signal reading element to a specific servo band and start tracking on that servo band.

[0116] FIG. 9 shows an example of the arrangement of data bands and servo bands. In FIG. 9, a plurality of servo bands 1 are arranged on the magnetic layer of the magnetic tape MT, sandwiched between guide bands 3. A plurality of regions 2 sandwiched between two servo bands are data bands. A servo pattern is a magnetized region, and is formed by magnetizing a specific region of the magnetic layer with a servo write head. The region magnetized by the servo write head (the position where the servo pattern is formed) is determined by a standard. For example, in an LTO Ultrium format tape, which is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction are formed on the servo band during the manufacturing of the magnetic tape, as shown in FIG. 10. More specifically, in FIG. 10, a servo frame SF on the servo band 1 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (symbol A in FIG. 10) and a B burst (symbol B in FIG. 10). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (symbol C in FIG. 10) and a D burst (symbol D in FIG. 10). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in a subframe arranged in a 5, 5, 4, 4 arrangement in a set of 5 and 4, and are used to identify a servo frame. For the sake of explanation, one servo frame is shown in FIG. 10. However, in reality, a plurality of servo frames are arranged in the running direction in each servo band on the magnetic layer of a magnetic tape where head tracking of the timing-based servo method is performed. In FIG. 10, the arrow indicates the magnetic tape running direction. For example, an LTO Ultrium format tape usually has 5000 or more servo frames per meter of tape length in each servo band on the magnetic layer.

[0117] In one embodiment, in the magnetic tape device, the head tilt angle can be changed while the magnetic tape is running inside the magnetic tape device. The head tilt angle is, for example, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape. The angle θ is as described above. For example, by providing an angle adjustment unit that adjusts the angle of the magnetic head module in the recording / reproducing head unit of the magnetic head, the angle θ can be variably adjusted while the magnetic tape is running. Such an angle adjustment unit can include, for example, a rotation mechanism that rotates the module. Publicly known technology can be applied to the angle adjustment unit.

[0118] Regarding the head tilt angle during magnetic tape running, if the magnetic head includes multiple modules, the angle θ described with reference to Figures 5 to 7 can be specified for randomly selected modules. initial can be set to 0° or more or greater than 0°. initial The larger the angle θ, the larger the change in the effective distance between the servo signal reading elements becomes, and therefore this is preferable in terms of the ability to adjust the effective distance between the servo signal reading elements in response to the change in the width direction of the magnetic tape. initial is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. On the other hand, with regard to the angle (generally called the "wrap angle") formed between the magnetic layer surface and the contact surface of the magnetic head when the magnetic tape runs and comes into contact with the magnetic head, keeping the deviation in the tape width direction small is effective in increasing the uniformity in the tape width direction of the friction generated by contact between the magnetic head and the magnetic tape while the magnetic tape is running. Also, increasing the uniformity of the above-mentioned friction in the tape width direction is desirable from the viewpoint of the position tracking ability and running stability of the magnetic head. From the viewpoint of reducing the deviation in the tape width direction of the above-mentioned wrap angle, θ initial is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

[0119] Regarding the change in the angle θ during the magnetic tape running, while the magnetic tape is running in the magnetic tape device for recording data on the magnetic tape and / or for reproducing data recorded on the magnetic tape, the angle θ of the magnetic head is changed from θ at the start of the running initial When the angle θ changes from max and Δθ min The maximum value of the angle θ during the magnetic tape running is θ max and the minimum value is θ min Note that "max" is an abbreviation for maximum, and "min" is an abbreviation for minimum. Δθ max =θ max -θ initial Δθ min =θ initial -θ min

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

[0121] 6 and 7, the axis of the element array is inclined toward the magnetic tape running direction. However, the present invention is not limited to such an example. The present invention also includes an embodiment in which the axis of the element array in the above magnetic tape device is inclined toward the opposite direction to the magnetic tape running direction.

[0122] The head inclination angle θ when the magnetic tape starts to run initialcan be set by the control device of the magnetic tape device, etc. With regard to the head tilt angle during magnetic tape running, FIG. 11 is an explanatory diagram of a method for measuring the angle θ during magnetic tape running. The angle θ during magnetic tape running can be obtained, for example, by the following method. When the angle θ during magnetic tape running is obtained by the following method, the angle θ is changed in the range of 0 to 90° during magnetic tape running. That is, if the axis of the element array is tilted toward the magnetic tape running direction at the start of magnetic tape running, the element array is not tilted so that the axis of the element array is tilted toward the opposite direction to the magnetic tape running direction at the start of magnetic tape running during magnetic tape running, and if the axis of the element array is tilted toward the opposite direction to the magnetic tape running direction at the start of magnetic tape running, the element array is not tilted so that the axis of the element array is tilted toward the magnetic tape running direction at the start of magnetic tape running during magnetic tape running. The phase difference (i.e., time difference) ΔT between the playback signals of a pair of servo signal read elements 1 and 2 is measured. The measurement of ΔT can be performed by a measurement unit provided in the magnetic tape device. The configuration of such a measurement unit is publicly known. The distance L between the center of the servo signal read element 1 and the center of the servo signal read element 2 can be measured by an optical microscope or the like. When the running speed of the magnetic tape is v, the distance between the centers of the two servo signal read elements in the magnetic tape running direction is Lsinθ, and the relationship Lsinθ=v×ΔT holds. Therefore, the angle θ during magnetic tape running can be calculated by the formula "θ=arcsin(vΔT / L)". Note that the right diagram of FIG. 11 shows an example in which the axis of the element array is inclined toward the magnetic tape running direction. In this example, the phase difference (i.e., time difference) ΔT between the phase of the playback signal of the servo signal read element 1 and the phase of the playback signal of the servo signal read element 2 is measured. When the axis of the element array is tilted toward the opposite direction to the running direction of the magnetic tape, θ can be found by the above method, except that ΔT is measured as the phase difference (i.e., time difference) between the phase of the playback signal of servo signal read element 1 relative to the phase of the playback signal of servo signal read element 2. The measurement pitch of the angle θ, i.e., the measurement interval of the angle θ relative to the tape longitudinal direction, can be selected according to the frequency of the tape width deformation relative to the tape longitudinal direction. As an example, the measurement pitch can be set to 250 μm.

[0123] <Magnetic tape device configuration> A magnetic tape device 10 shown in FIG. 12 controls a recording / reproducing head unit 12 in response to commands from a control device 11, and records and reproduces data on a magnetic tape MT. The magnetic tape device 10 has a configuration capable of detecting and adjusting tension applied to the magnetic tape in the longitudinal direction from spindle motors 17A, 17B that control the rotation of the magnetic tape cartridge reel and take-up reel and their drive devices 18A, 18B. The magnetic tape device 10 has a configuration in which a magnetic tape cartridge 13 can be loaded. The magnetic tape device 10 has a cartridge memory read / write device 14 capable of reading from and writing to a cartridge memory 131 in the magnetic tape cartridge 13 . From the magnetic tape cartridge 13 attached to the magnetic tape device 10, the end or leader pin of the magnetic tape MT is pulled out by an automatic loading mechanism or manually, and the magnetic tape MT passes over the recording / playback head via guide rollers 15A and 15B with the magnetic layer surface in a direction facing the recording / playback head surface of the recording / playback head unit 12, and the magnetic tape MT is wound onto the take-up reel 16. The rotation and torque of spindle motors 17A and 17B are controlled by signals from control device 11, and magnetic tape MT runs at any speed and tension. Servo patterns formed in advance on the magnetic tape can be used to control the tape speed and head tilt angle. A tension detection mechanism may be provided between magnetic tape cartridge 13 and take-up reel 16 to detect tension. In addition to control by spindle motors 17A and 17B, tension control may also be performed using guide rollers 15A and 15B. The cartridge memory read / write device 14 is configured to be able to read and write information from and to the cartridge memory 131 in response to commands from the control device 11. As a communication method between the cartridge memory read / write device 14 and the cartridge memory 131, for example, the ISO (International Organization for Standardization) 14443 method can be adopted.

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

[0125] The recording and reproducing head unit 12 is composed of, for example, a recording and reproducing head, a servo tracking actuator that adjusts the position of the recording and reproducing head in the track width direction, a recording and reproducing amplifier 19, a connector cable for connecting to the control device 11, etc. The recording and reproducing head is composed of, for example, a recording element that records data on the magnetic tape, a reproducing element that reproduces the data on the magnetic tape, and a servo signal reading element that reads the servo signal recorded on the magnetic tape. One magnetic head is equipped with, for example, one or more of each of the recording element, reproducing element, and servo signal reading element. Alternatively, each element may be provided separately in a plurality of magnetic heads according to the running direction of the magnetic tape.

[0126] The recording / reproducing head unit 12 is configured to be capable of recording data onto the magnetic tape MT in response to a command from the control device 11. Also, the recording / reproducing head unit 12 is configured to be capable of reproducing the data recorded onto the magnetic tape MT in response to a command from the control device 11.

[0127] The control device 11 has a mechanism for determining the running position of the magnetic tape from the servo signals read from the servo bands while the magnetic tape MT is running, and for controlling the servo tracking actuator so that the recording element and / or the reproducing element are positioned at the target running position (track position). The control of the track position is performed, for example, by feedback control. The control device 11 has a mechanism for determining the servo band interval from the servo signals read from two adjacent servo bands while the magnetic tape MT is running. The control device 11 can store information on the determined servo band interval in a storage unit inside the control device 11, a cartridge memory 131, an external connected device, or the like. The control device 11 can also change the head tilt angle according to dimensional information in the width direction of the magnetic tape while it is running. This allows the effective distance between the servo signal reading elements to be close to or match the interval between the servo bands. The above dimensional information can be acquired by utilizing a servo pattern formed in advance on the magnetic tape. For example, in this way, while the magnetic tape is running in the magnetic tape device, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape can be changed according to the dimensional information of the magnetic tape in the width direction acquired during the running. The head tilt angle can be adjusted, for example, by feedback control. Also, for example, the head tilt angle can be adjusted by the method described in JP2016-524774A (Patent Document 1) or US2019 / 0164573A1 (Patent Document 2). EXAMPLES

[0128] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. The "parts" and "%" described below indicate "parts by mass" and "% by mass", respectively. In addition, the steps and evaluations described below were carried out in an environment at a temperature of 23°C ± 1°C unless otherwise specified.

[0129] [Example 1] 1. Preparation of alumina dispersion (abrasive liquid) Alpha conversion rate approx. 65%, BET specific surface area 20m 2100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) with a molecular weight of 100 g / g was mixed with 3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) of polyester polyurethane resin having SO3Na groups as polar groups (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq / kg)), and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1:1 (mass ratio) as a solvent, and dispersed for 5 hours by a paint shaker in the presence of zirconia beads. After dispersion, the dispersion liquid and the beads were separated by a mesh to obtain an alumina dispersion.

[0130] 2. Formulation of the composition for forming the magnetic layer (Magnetic liquid) Ferromagnetic powder (hexagonal barium ferrite powder, activation volume: 1500 nm 3 ):100.0 copies SO3Na group-containing polyurethane resin: See Table 1 Weight average molecular weight: 70,000, SO3Na group: See Table 1 Cyclohexanone: 150.0 parts Methyl ethyl ketone: 170.0 parts (abrasive liquid) Alumina dispersion prepared in 1 above: 6.0 parts (Other ingredients) Colloidal Silica: 2.0 parts Average particle size: 100nm Stearic acid: 10.0 parts Butyl stearate: 6.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark)): 2.5 parts (Finishing additive) Cyclohexanone: 300.0 parts Methyl ethyl ketone: 140.0 parts

[0131] 3. Formulation of composition for forming nonmagnetic layer α-Iron oxide powder (average particle volume: see Table 1): 100.0 parts Carbon black (average particle size: 20 nm, pH: see Table 1): 25.0 parts SO3Na group-containing polyurethane resin: 18.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid: 1.0 parts Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

[0132] 4. Formulation of the composition for forming the backcoat layer α-iron oxide powder: 80.0 parts Average particle size (average major axis length): 0.15μm, average acicular ratio: 7, BET specific surface area: 52m 2 / g Carbon black: 20.0 parts Average particle size: 20nm Vinyl chloride copolymer: 13.0 parts Sulfonate group-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 355.0 parts Methyl ethyl ketone: 155.0 parts Stearic acid: 3.0 parts Butyl stearate: 3.0 parts Polyisocyanate: 5.0 parts

[0133] 5. Preparation of compositions for forming each layer A magnetic layer forming composition was prepared by the following method. The various components of the magnetic liquid were mixed using a homogenizer, and then dispersed in a continuous horizontal bead mill using dispersion beads (zirconia beads) with the bead diameters shown in Table 1 for the dispersion time shown in Table 1 to prepare the magnetic liquid. The magnetic liquid was mixed with the abrasive liquid, other components, and finishing additive solvent using the bead mill, and then treated (ultrasonic dispersion) for 0.5 minutes using a batch ultrasonic device (20 kHz, 300 W). Then, filtration was performed using a filter with a pore size of 0.5 μm to prepare a magnetic layer-forming composition. A composition for forming a nonmagnetic layer was prepared by the following method. The above components were dispersed for 24 hours using a batch-type vertical sand mill. Zirconia beads with a bead diameter of 0.1 mm were used as dispersion beads. The resulting dispersion 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. After the various components except stearic acid, butyl stearate, polyisocyanate and cyclohexanone were kneaded and diluted by an open kneader, the dispersion treatment was carried out by a horizontal bead mill using zirconia beads with a bead diameter of 1 mm, with a bead filling rate of 80% by volume, a rotor tip peripheral speed of 10 m / sec, a residence time of 2 minutes per pass, and 12 passes.Then, the remaining components were added to the obtained dispersion liquid, and the dispersion liquid was stirred by a disperser.The dispersion liquid thus obtained was filtered using a filter with a pore size of 1 μm to prepare a composition for forming a backcoat layer.

[0134] 6. Preparation of Magnetic Tape A magnetic tape was produced according to the manufacturing process shown in Figure 8. More specifically, the process was as follows. A polyethylene naphthalate support having a thickness of 3.7 μm was sent out from a sending section, and a coating layer was formed by applying a nonmagnetic layer-forming composition to one surface in a first coating section so that the thickness after drying would be 0.7 μm. The formed coating layer was passed through a cooling zone adjusted to an atmospheric temperature of 0° C. for the residence time shown in Table 1 while still in a wet state to carry out a cooling step, and then passed through a first heat treatment zone having a drying temperature (atmospheric temperature, the same applies below) shown in Table 1 to carry out a heat drying step to form a nonmagnetic layer. Thereafter, in the second coating section, the magnetic layer-forming composition prepared above was coated on the non-magnetic layer so that the thickness after drying would be 0.06 μm to form a coating layer. While this coating layer was still wet, a magnetic field with a magnetic field strength of 0.5 T was applied in the direction perpendicular to the surface of the coating layer of the magnetic layer-forming composition in the transport path (ambient temperature: see Table 1) to perform a vertical orientation treatment, and then the coating layer was dried in the second heat treatment zone at the drying temperature shown in Table 1. Thereafter, in a third coating section, the composition for forming a backcoat layer prepared above was applied to the surface of the polyethylene naphthalate support opposite to the surface on which the nonmagnetic layer and magnetic layer were formed, to form a coating layer having a thickness after drying of 0.3 μm, and the formed coating layer was dried in a third heat treatment zone at the drying temperature shown in Table 1. Thereafter, calendering (surface smoothing) was performed under the calendering conditions shown in Table 1 using a calender roll consisting of only a metal roll. Thereafter, the sample was subjected to a heat treatment for 36 hours in an atmosphere at 70° C. After the heat treatment, the sample was slit into a 1 / 2 inch width to prepare a magnetic tape. In a state where the magnetic layer of the magnetic tape obtained above was demagnetized, a servo signal was recorded on the magnetic layer by a commercially available servo writer, to obtain a magnetic tape having a data band, a servo band, and a guide band in an arrangement according to the LTO (Linear Tape-Open) Ultrium format, and a servo pattern (timing-based servo pattern) on the servo band in an arrangement and shape according to the LTO Ultrium format. The servo pattern thus formed is a servo pattern according to the descriptions in JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4. In this way, a magnetic tape (length 960 m) on which a servo signal was recorded was produced.

[0135] [Examples 2, 3, and 5, and Comparative Examples 1 and 5] A magnetic tape was obtained by the method described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1. In Comparative Example 1, in which "None" is written in the "Cooling zone residence time" column in Table 1, the magnetic tape was produced by a manufacturing process that did not include a cooling zone in the nonmagnetic layer formation step. This also applies to Comparative Examples described below, in which "None" is written in the "Cooling zone residence time" column in Table 1. In Example 5, in which "vertical orientation 0.2 T" is written in the "magnetic layer formation and orientation" column in Table 1, the magnetic field strength in the vertical orientation treatment was 0.2 T. In Comparative Example 1, in which "no orientation treatment" is written in the "magnetic layer formation and orientation" column, the magnetic tape was produced without performing an orientation treatment on the coating layer of the magnetic layer-forming composition.

[0136] [Example 4] After the non-magnetic layer was formed, a magnetic layer-forming composition was applied onto the surface of the non-magnetic layer so that the thickness after drying was 30 nm to form a first coating layer. This first coating layer was transported in a transport path with an atmospheric temperature shown in Table 1 without the application of a magnetic field to form a first magnetic layer (without orientation treatment). Thereafter, a magnetic layer-forming composition was applied onto the surface of the first magnetic layer so as to have a thickness of 30 nm after drying to form a second coating layer. While this second coating layer was still wet, a magnetic field having the strength shown in Table 1 was applied perpendicularly to the surface of the second coating layer within a transport path having an atmospheric temperature shown in Table 1 to perform a vertical orientation treatment, and then the second coating layer was dried in a second heat treatment zone having a drying temperature shown in Table 1. A magnetic tape was obtained by the method described in Example 1, except that a multilayer magnetic layer was formed as described above.

[0137] [Comparative Example 2] After the non-magnetic layer was formed, a magnetic layer-forming composition was applied onto the surface of the non-magnetic layer so that the thickness after drying would be 30 nm to form a first coating layer. While this first coating layer was still wet, a magnetic field of the strength shown in Table 1 was applied perpendicularly to the surface of the first coating layer within a transport path having an atmospheric temperature shown in Table 1, to perform a vertical alignment process and a drying process, thereby forming a first magnetic layer. Thereafter, a magnetic layer-forming composition was applied onto the surface of the first magnetic layer so as to have a dry thickness of 30 nm to form a second coating layer. This second coating layer was transported through a transport path with an atmospheric temperature shown in Table 1 without the application of a magnetic field to form a second magnetic layer (without orientation treatment). A magnetic tape was obtained by the method described in Example 1, except that a multilayer magnetic layer was formed as described above and the items shown in Table 1 were changed as shown in Table 1.

[0138] [Comparative Example 3] A magnetic tape was obtained by the method described in Example 4, except that the items shown in Table 1 were changed as shown in Table 1.

[0139] [Comparative Example 4] A magnetic tape was obtained by the method described for Comparative Example 2, except that the items shown in Table 1 were changed as shown in Table 1.

[0140] For each of the Examples and Comparative Examples, four magnetic tapes each having a length of 960 m were prepared and used for the following evaluations (1) to (4).

[0141] [Evaluation method] (1) ΔN, ΔN width direction σ For each of the magnetic tapes of the Examples and Comparative Examples, ΔN and ΔN in the width direction σ were determined by the method described above. More specifically, ΔN in the analysis target area of ​​each of the five measurement areas was determined by the following method.

[0142] (i) Preparation of specimens for cross-sectional observation Samples were cut out from randomly selected positions of the magnetic tapes of the Examples and Comparative Examples, and a cross-sectional observation sample was prepared including the entire region in the thickness direction from the magnetic layer side surface to the backcoat layer side surface of the magnetic tape according to the method described in paragraphs 0193 to 0194 of JP 2016-177851 A. This cross-sectional observation sample was used for the following thickness measurement.

[0143] (ii) Thickness measurement The prepared cross-sectional observation sample was observed by STEM, and a STEM image was taken. This STEM image was a STEM-HAADF (High-Angle Annular Dark Field) image taken at an acceleration voltage of 300 kV and an imaging magnification of 450,000 times, and was taken so that one image included the entire area in the thickness direction from the magnetic layer side surface of the magnetic tape to the backcoat layer side surface. In the STEM image thus obtained, a straight line connecting both ends of the line segment representing the magnetic layer surface was defined as a reference line representing the magnetic layer side surface of the magnetic tape. The straight line connecting both ends of the above line segment is, for example, a straight line connecting the intersection point between the left side of the image (rectangle or square shape) of the STEM image and the above line segment and the intersection point between the right side of the STEM image and the above line segment when the STEM image is taken so that the magnetic layer side of the cross-sectional observation sample is located at the top of the image and the backcoat layer side is located at the bottom. Similarly, a reference line representing the interface between the magnetic layer and non-magnetic layer, a reference line representing the interface between the non-magnetic layer and the non-magnetic support, a reference line representing the interface between the non-magnetic support and the backcoat layer, and a reference line representing the surface of the magnetic tape on the backcoat layer side were defined. The thickness of the magnetic layer was determined as the shortest distance from a randomly selected point on the reference line representing the magnetic layer side surface of the magnetic tape to the reference line representing the interface between the magnetic layer and the nonmagnetic layer. Similarly, the thicknesses of the nonmagnetic layer, the nonmagnetic support, and the backcoat layer were determined. In each cross-sectional observation sample, the thickness of the magnetic layer was 0.06 μm, the thickness of the nonmagnetic layer was 0.7 μm, the thickness of the nonmagnetic support was 3.7 μm, and the thickness of the backcoat layer was 0.3 μm. The thicknesses of the magnetic layer, the nonmagnetic layer, and the nonmagnetic support measured here were used to calculate the refractive index below.

[0144] In the following, the ellipsometer used was the M-2000U manufactured by Woollam Co., Ltd. The creation and fitting of the two-layer model and the one-layer model were performed using the analysis software WVASE32 manufactured by Woollam Co., Ltd.

[0145] Measurement samples for refractive index measurements were cut from randomly selected positions of the magnetic tapes of the examples and comparative examples. The backcoat layer of the measurement sample was wiped off with a cloth soaked in methyl ethyl ketone. After removing the backcoat layer to expose the non-magnetic support surface, the surface was roughened with sandpaper so that reflected light from the exposed surface would not be detected in the measurement with an ellipsometer. The measurement sample from which the backcoat layer had been removed and the non-magnetic support surface had been roughened in this way was used for the following measurement of the refractive index of the magnetic layer. After measuring the refractive index of the magnetic layer, the measurement sample was subjected to a magnetic layer removal process by the method described in paragraph 0054, item (V) of JP-A-10-172131. The measurement sample from which the backcoat layer had been removed, the surface of the nonmagnetic support had been roughened, and the magnetic layer had been removed was used to measure the refractive index of the nonmagnetic layer below. In addition, the longitudinal magnetization Φm per unit area of ​​a sample piece cut from the measurement sample after the magnetic layer removal process was measured, and it was confirmed that the surface of the nonmagnetic layer had been exposed when the value of Φm was less than 5 G·μm. The nonmagnetic layer was wiped off from the measurement sample after the refractive index measurement of the nonmagnetic layer using a cloth soaked in methyl ethyl ketone. The measurement sample from which the backcoat layer had been removed, the surface of the nonmagnetic support had been roughened, the magnetic layer had been removed, and the nonmagnetic layer had been removed was used for the following measurement of the refractive index of the nonmagnetic support.

[0146] (iii) Refractive index measurement of non-magnetic support The measurement sample, which had been subjected to the removal of the backcoat layer, the roughening of the nonmagnetic support surface, the removal of the magnetic layer, and the removal of the nonmagnetic layer, was attached with the roughened surface to the silicon wafer surface using static electricity. Thus, the measurement sample was placed on the silicon wafer with the nonmagnetic support surface exposed by removing the magnetic layer and nonmagnetic layer (hereinafter referred to as the "magnetic layer side surface of the nonmagnetic support") facing upward. An ellipsometer was used to measure Δ and Ψ by irradiating incident light onto the magnetic layer side surface of the non-magnetic support of the measurement sample on the silicon wafer as described above. Using the measured values ​​and the thickness of the non-magnetic support determined in (ii) above, the refractive index of the non-magnetic support (the refractive index in the longitudinal direction, the refractive index in the width direction, the refractive index in the thickness direction measured by irradiating incident light from the longitudinal direction, and the refractive index in the thickness direction measured by irradiating incident light from the width direction) was determined by the method described above.

[0147] (iv) Refractive index measurement of non-magnetic layer The measurement sample from which the backcoat layer had been removed, the surface of the non-magnetic support had been roughened and the magnetic layer had been removed was placed on a silicon wafer in the same manner as in (iii) above. The surface of the nonmagnetic layer of the measurement sample on this silicon wafer was measured using an ellipsometer, and the refractive index of the nonmagnetic layer (refractive index in the longitudinal direction, refractive index in the width direction, refractive index in the thickness direction measured with incident light from the longitudinal direction, and refractive index in the thickness direction measured with incident light from the width direction) was determined by spectroscopic ellipsometry using the method described above.

[0148] (v) Refractive index measurement of magnetic layer The measurement sample from which the backcoat layer had been removed and the surface of the non-magnetic support had been roughened was placed on a silicon wafer in the same manner as in (iii) above. The magnetic layer surface of the measurement sample on the silicon wafer was measured using an ellipsometer, and the refractive indexes of the magnetic layer (the refractive index in the longitudinal direction Nx, the refractive index in the width direction Ny, the refractive index in the thickness direction measured by irradiating light from the longitudinal direction Nz1, and the refractive index in the thickness direction measured by irradiating light from the width direction Nz2) were determined by spectroscopic ellipsometry using the method described above. From the values ​​thus determined, Nxy and Nz were calculated, and the absolute value ΔN of the difference between these values ​​was also calculated. For both the magnetic tapes of the examples and the comparative examples, the determined Nxy was a value greater than Nz (i.e., Nxy>Nz).

[0149] (2) Nonlinear component of tape width deformation For each of the magnetic tapes of the examples and comparative examples, the nonlinear component of the tape width deformation caused by storage for 10 days in an environment of a temperature of 60° C. and a relative humidity of 20% was measured by the method described above.

[0150] (3) Recording and playback performance (after storage) For each of the magnetic tapes of the Examples and Comparative Examples, the recording and reproducing performance (after storage) was evaluated by the following method. The magnetic head used was equipped with a reproducing module including an element array having 10 or more channels of reproducing elements with a reproducing element width of 0.2 μm or less between a pair of servo signal reading elements, and a recording module including an element array having 10 or more channels of recording elements with a recording element width of 1.5 times or more between a pair of servo signal reading elements. In the element array, the distance between two adjacent elements (i.e., two adjacent reproducing elements and two adjacent recording elements) in the head width direction is 40 μm or more. The environment for recording and reproducing data was set to a temperature of 20 to 25°C and a relative humidity of 40 to 60%. A magnetic tape device with a magnetic tape and a magnetic head attached to a tape transport system (reel tester) was placed in this environment for more than 24 hours, and then data was recorded and reproduced. The recording and reproducing amplifier attached to the tape transport system of the magnetic tape device was the recording and reproducing amplifier described above for measuring the nonlinear component of tape width deformation. When recording and reproducing data, the servo following and dynamic track position control (change in head tilt angle) described above were performed. In detail, data recording and reproducing were performed as follows. Signals were recorded by the recording element while the magnetic tape was running at a constant speed of 5 m / sec. The bit sequence used for recording was a 255-bit pseudo random bit sequence (PRBS) generated according to the generating polynomial x^8+x^6+x^5+x^4+1. The symbol "^" indicates exponentiation. The linear recording density was 600 kbpi. The unit "kbpi" is the unit of linear recording density (cannot be converted to SI units). Shingle recording was performed on three or more tracks so that the difference in (PES1+PES2) / 2 between adjacent tracks was 1.5 times the playback track width. The magnetic pattern recorded on the magnetic tape is reproduced by the immediately succeeding reproducing element (i.e., the reproducing element with the same channel number), and the signal is amplified by the reproducing amplifier. The reproduced signal is processed by PLL (Phase Lock Loop) and AGC (Auto Gain Control), and then decoded into a bit sequence based on DD-NPML (Data Dependent Noise Predictive Maximum Likelihood) signal processing. The recorded bit sequence and the reproduced and decoded bit sequence are compared bit by bit, and if the two are different, a one-bit error is counted as having occurred. The data is compared over 10 Mbits, and the cumulative error bit count divided by 10 Mbits is defined as the bit error rate. It was confirmed that the bit error rate of the reproduced signal immediately after recording was 1 / 1000 or less in all channels. Next, the magnetic tape was stored for 10 days in an environment having a temperature of 60° C. and a relative humidity of 20% while being wound on the reel of the reel tester. After the above storage, the magnetic tape was removed from the storage environment and placed in the same magnetic tape device as the one used before storage in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60% for 24 hours or more, and then the data tracks recorded before storage were played back (no recording was performed) in the same environment. At this time, playback was performed only for data tracks that had data tracks recorded on both sides. The bit error rate of all channels was calculated, and channels with a bit error rate of 1 / 100 or more were considered to be defective channels, and the recording and playback performance (after storage) was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The ratio of defective channels to the total number of channels is less than 5%. B: The ratio of defective channels to the total number of channels is 5% or more and less than 10%. C: The ratio of defective channels to the total number of channels is 10% or more.

[0151] (4) Missing pulse occurrence frequency in low temperature and low humidity environments The following measurements were carried out in a low-temperature, low-humidity environment at a temperature of 13° C. and a relative humidity of 15%. A magnetic tape having a length of 500 m was cut out from each of the magnetic tapes of the Examples and Comparative Examples. The magnetic tape cartridge containing the cut out magnetic tape was set in an IBM LTO-G6 (Linear Tape-Open Generation 6) drive, and the magnetic tape was run 1500 times back and forth at a tension of 0.6 N and a running speed of 6 m / sec. The magnetic tape cartridge after the above running was set in a reference drive (IBM LTO-G6 drive), and the magnetic tape was run to perform recording and playback. The playback signal during running was input to an external AD (Analog / Digital) conversion device, and a signal where the playback signal amplitude was 70% or more lower than the average (average of the measured values ​​for all tracks) was defined as a missing pulse, and the frequency of occurrence (number of occurrences) was divided by the total length of the magnetic tape to obtain the missing pulse occurrence frequency (unit: times / m) per unit length (per 1m) of the magnetic tape. If the missing pulse occurrence frequency is 5 times / m or less, the magnetic tape can be judged to be highly reliable for practical use.

[0152] The above results are shown in Table 1 (Table 1-1 to Table 1-2).

[0153] [Table 1-1]

[0154] [Table 1-2]

[0155] As shown in Table 1, the magnetic tapes of Examples 1 to 5 exhibited superior recording and reproducing performance after being stored under an accelerated environment equivalent to long-term storage, compared with the magnetic tapes of Comparative Examples 1 to 3. From this result, it can be confirmed that the magnetic tapes of Examples 1 to 5 contributed to improving the operational stability of the drive (magnetic tape device). Furthermore, it can be seen from the results shown in Table 1 that the magnetic tapes of Examples 1 to 5 have a reduced frequency of missing pulse occurrence in a low-temperature, low-humidity environment, compared to the magnetic tapes of Comparative Examples 1, 2, 4 and 5.

[0156] A magnetic tape was produced in the same manner as in Example 1, except that no perpendicular orientation treatment was performed during the production of the magnetic tape. A sample piece was cut out from the magnetic tape, and the squareness in the vertical direction of the sample piece was measured by the above-mentioned method using a vibrating sample magnetometer, TM-TRVSM5050-SMSL model, manufactured by Tamagawa Seisakusho, and was found to be 0.55. The perpendicular squareness ratio of a sample piece cut out from the magnetic tape of Example 1 was similarly determined and was found to be 0.65.

[0157] The two magnetic tapes were each attached to a 1 / 2 inch reel tester, and the electromagnetic conversion characteristics (SNR: Signal-to-Noise Ratio) were evaluated by the following method. As a result, the magnetic tape of Example 1 had an SNR value 4 dB higher than that of the magnetic tape produced without the vertical orientation treatment. In an environment with a temperature of 23°C and a relative humidity of 50%, 10 passes of recording and reproduction were performed with a tension of 0.7 N (Newton) applied in the longitudinal direction of the magnetic tape. The relative speed between the magnetic tape and the magnetic head was 6 m / sec. Recording was performed using a MIG (Metal-in-gap) head (gap length 0.15 μm, track width 1.0 μm) as the recording head, and the recording current was set to the optimal recording current for each magnetic tape. Reproduction was performed using a GMR (Giant-magnetoresistive) head (element thickness 15 nm, shield spacing 0.1 μm, reproducing element width 0.8 μm) as the reproducing head. The head tilt angle was 0°. A signal with a linear recording density of 300 kfci was recorded, and the reproduced signal was measured with a spectrum analyzer manufactured by Shibasoku. The unit kfci is a unit of linear recording density (not convertible to SI units). The signal was used at a portion where the signal was sufficiently stable after the magnetic tape started running. [Industrial Applicability]

[0158] One aspect of the present invention is useful in various data storage technical fields.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, The absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 or more and 0.40 or less, and A magnetic tape in which the standard deviation σ of ΔN in the width direction of the magnetic layer is 0.05 or less.

2. 2. The magnetic tape according to claim 1, wherein the standard deviation σ of ΔN is 0.02 or less.

3. 2. The magnetic tape according to claim 1, wherein the standard deviation σ of ΔN is equal to or greater than 0.01 and equal to or less than 0.

02.

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

5. The non-magnetic powder has an average particle volume of 2.0×10 －６ μm ３ 5. The magnetic tape according to claim 4, comprising the following Fe-based inorganic oxide powder:

6. 5. The magnetic tape according to claim 4, wherein the non-magnetic powder comprises carbon black having a pH of 9.0 or less.

7. 5. The magnetic tape according to claim 4, wherein the nonmagnetic layer has a thickness of 0.1 [mu]m or more and 0.7 [mu]m or less.

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

9. 2. The magnetic tape of claim 1, wherein the tape thickness is 5.2 μm or less.

10. 2. The magnetic tape of claim 1, wherein the tape thickness is 5.0 μm or less.

11. 2. The magnetic tape of claim 1, wherein the perpendicular squareness of the magnetic tape is 0.60 or more.

12. 2. The magnetic tape of claim 1, wherein the perpendicular squareness of the magnetic tape is 0.65 or greater.

13. The standard deviation σ of ΔN is 0.01 or more and 0.02 or less, a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer, The non-magnetic powder has an average particle volume of 2.0×10 －６ μm ３ The composition comprises the following Fe-based inorganic oxide powder and carbon black having a pH of 9.0 or less: the thickness of the nonmagnetic layer is 0.1 μm or more and 0.7 μm or less, a backcoat layer containing a nonmagnetic powder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer, The tape thickness is 5.0 μm or less, and 2. The magnetic tape of claim 1, wherein the perpendicular squareness of the magnetic tape is 0.65 or greater.

14. A magnetic tape cartridge comprising the magnetic tape according to any one of claims 1 to 13.

15. A magnetic tape device comprising the magnetic tape according to any one of claims 1 to 13.

16. Further comprising a magnetic head; the magnetic head has a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements; and 16. The magnetic tape device according to claim 15, wherein the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape is changed while the magnetic tape is running inside the magnetic tape device.

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