Magnetic Tape, Magnetic Tape Cartridge, and Magnetic Recording / Reproducing Apparatus

Abstract

To provide a magnetic tape which can record and / or regenerate stored data desirably.SOLUTION: The present invention relates to a magnetic tape having a nonmagnetic supporting body and a magnetic layer containing ferromagnetic powders. The nonmagnetic supporting body is a polyamide supporting body. The ratio of deformation of the magnetic tape in the width direction to the deformation of the magnetic tape in the longer direction measured after a load is applied for 96 hours in the longer direction of the magnetic tape is 0.45 or smaller. The present invention also relates to a magnetic tape cartridge and a magnetic record regenerator including the magnetic tape.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] A magnetic recording medium generally includes a magnetic layer and a nonmagnetic support (see, for example, Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Japanese Patent Application Laid-Open No. 2001-011215 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-132523 (Patent Document 2), the Poisson's ratio is defined for the film used as the nonmagnetic support of the magnetic recording medium. The Poisson's ratio is measured as the ratio of the longitudinal strain to the lateral strain that occurs when the film is pulled in the longitudinal direction (see paragraphs 0083 to 0088 of Patent Document 1 and paragraphs 0058 to 0059 of Patent Document 2).

[0005] On the one hand, magnetic recording media include tape-shaped and disk-shaped ones. For data storage applications, tape-shaped magnetic recording media, i.e., magnetic tapes, are mainly used. Regarding magnetic tapes, as a result of the inventor's study, after storing a magnetic tape on which data has been recorded, when recording and / or reproducing on the magnetic tape, phenomena such as recording defects (e.g., overwriting of recorded data, etc.), reproduction defects (e.g., poor data reading), etc. are observed, and it has been found that it is difficult to suppress such phenomena by controlling the Poisson's ratio described in Patent Document 1 and Patent Document 2.

[0006] In view of the above, an aspect of the present invention aims to provide a magnetic tape capable of performing good recording and / or reproduction in recording and / or reproduction of data after storage.

Means for Solving the Problem

[0007] An aspect of the present invention is a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the non-magnetic support is a polyamide support, and the deformation rate ratio of the width direction deformation rate to the longitudinal direction deformation rate of the magnetic tape measured after applying a 96-hour load in the longitudinal direction of the magnetic tape, width direction deformation rate / longitudinal direction deformation rate, is 0.45 or less. It relates to.

[0008] In one form, the deformation rate ratio can be 0.15 or more and 0.45 or less.

[0009] In one form, the magnetic tape can further have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0010] In one form, the magnetic tape can further have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support.

[0011] In one form, the ferromagnetic powder can be hexagonal barium ferrite powder.

[0012] In one form, the ferromagnetic powder can be hexagonal strontium ferrite powder.

[0013] In one form, the ferromagnetic powder can be ε-iron oxide powder.

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

[0015] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including the magnetic tape.

Advantages of the Invention

[0016] According to one aspect of the present invention, it is possible to provide a magnetic tape capable of performing good recording and / or reproduction in recording and / or reproduction of data after storage. Further, according to one aspect of the present invention, it is possible to provide a magnetic tape cartridge and a magnetic recording and reproducing apparatus including such a magnetic tape.

Embodiments for Carrying Out the Invention

[0017] [Magnetic Tape] One aspect of the present invention relates to a magnetic tape having a nonmagnetic support and a magnetic layer containing a ferromagnetic powder. In the magnetic tape, the nonmagnetic support is a polyamide support, and the deformation rate ratio (width direction deformation rate / longitudinal direction deformation rate) of the width direction deformation rate and the longitudinal direction deformation rate of the magnetic tape measured after applying a load in the longitudinal direction of the magnetic tape for 96 hours is 0.45 or less.

[0018] Hereinafter, the magnetic tape will be described in more detail.

[0019] <Nonmagnetic Support> The non-magnetic support of the magnetic tape is a polyamide support. In the present invention and this specification, "polyamide" means a resin containing a plurality of amide bonds. "Polyamide support" means a support containing at least one layer of polyamide film. "Polyamide film" means a film in which the component that occupies the most in terms of mass among the components constituting the film is polyamide. The "polyamide support" in the present invention and this specification includes those in which all the resin films contained in the support are polyamide films and those containing a polyamide film and other resin films. Specific forms of the polyamide support include a single-layer polyamide film, a laminated film of two or more polyamide films having the same constituent components, a laminated film of two or more polyamide films having different constituent components, a laminated film containing one or more polyamide films and one or more resin films other than polyamide, and the like. An adhesive layer or the like may be optionally included between two adjacent layers in the laminated film.

[0020] (Deformation rate ratio) In order to obtain a magnetic tape capable of performing good recording and / or reproduction in the recording and / or reproduction of data after storage, the present inventors newly found that making the above deformation rate ratio 0.45 or less in a magnetic tape containing a polyamide support can contribute to making it possible to perform good recording and / or reproduction in the recording and / or reproduction of data with respect to the magnetic tape after storage. Such a deformation rate ratio is obtained by the following method. The magnetic tape to be measured is subjected to the following measurement after being stored in a storage environment of an ambient temperature of 23°C and a relative humidity of 50% for 24 hours or more. The magnetic tape accommodated in the magnetic tape cartridge is stored in the above storage environment together with the magnetic tape cartridge. As the measuring device, a device capable of measuring the length and width of the magnetic tape while applying a load in the longitudinal direction of the magnetic tape is used. As such a device, for example, a measuring device (TDSMS 102H) manufactured by Measurement Analysis Corporation (U.S.A) can be used. The measurement is carried out in a measurement environment with an ambient temperature of 32°C and a relative humidity of 65%. A tape piece with a length of 600 mm in the longitudinal direction is cut out from an arbitrary position of the magnetic tape after the above storage. The cut-out tape piece is set in the measuring device. When the ambient temperature and relative humidity of the environment where the measuring device with the tape piece set is installed are already the ambient temperature and relative humidity of the above measurement environment, after 30 minutes or more have elapsed since the tape piece was set in the measuring device, it is held in a state where a load of 0.20 N (Newton) is applied in the longitudinal direction of the tape piece. When the ambient temperature and relative humidity of the environment where the measuring device with the tape piece set is installed are different from the ambient temperature and relative humidity of the above measurement environment, temperature and humidity adjustment is performed so that the ambient temperature and relative humidity of this environment become the ambient temperature and relative humidity of the above measurement environment. After 30 minutes or more have elapsed since the ambient temperature and relative humidity of the environment where the measuring device with the tape piece set is installed reached the ambient temperature and relative humidity of the above measurement environment by temperature and humidity adjustment, it is held in a state where a load of 0.20 N is applied in the longitudinal direction of the tape piece. Taking the start time point of applying a load of 0.20 N as 0 minutes, the dimensions in the width direction (i.e., width) and the longitudinal direction (i.e., length) of the tape piece when 30 minutes have elapsed are measured. The measurement of the dimensions in the width direction and the longitudinal direction can be carried out by a measuring device unit (for example, a laser scan micrometer) attached to the measuring device. The same applies to the measurement of the dimensions described below. The dimension in the width direction measured here is taken as the initial value "W 0 " in the width direction, and the dimension in the longitudinal direction is taken as the initial value "L 0 " in the longitudinal direction. After 30 minutes have elapsed since the start of applying a load of 0.20 N, the load applied in the longitudinal direction is set to 0.55 N, and a load of 0.55 N is applied for 96 hours. After applying a load of 0.55 N in the longitudinal direction for 96 hours, the load applied in the longitudinal direction is changed to 0.20 N and held in the state where a load of 0.20 N is applied. Measure the dimensions in the width direction and the longitudinal direction of the tape piece when 5 minutes have elapsed since the load was changed to 0.20 N. The dimension in the width direction measured here is defined as "W 96 ", and the dimension in the longitudinal direction is defined as "L 96 ". The reason for setting the load at the start of load application to 0.20 N is to hold the tape piece so that no slack occurs. On the other hand, the reason for applying a load of 0.20 N and performing the above measurement after applying a load of 0.55 N in the longitudinal direction for 96 hours is to measure the residual strain after applying a load of 0.55 N for 96 hours. The present inventor believes that this residual strain includes irreversible creep and / or reversible strain with a long time constant. The width direction deformation rate of the magnetic tape measured after applying a load in the longitudinal direction of the magnetic tape for 96 hours is calculated by multiplying the value obtained by dividing the absolute value of the difference between W 96 and W 0 by W 96 and W 0 by 10 0 (width direction deformation rate = |W 6 - W 96 | / W 0 × 10 0 × 10 6 ). The units of the width direction deformation rate and the following longitudinal direction deformation rate are ppm (parts per million). When calculating the width direction deformation rate, the values of W 96 and W 0 shall be values in the same unit. When calculating the following longitudinal direction deformation rate, the values of L 96 and L 0 shall be values in the same unit. The unit is, for example, "mm". The longitudinal direction deformation rate of the magnetic tape measured after applying a load in the longitudinal direction of the magnetic tape for 96 hours is calculated by multiplying the value obtained by dividing the absolute value of the difference between L 96 and L 0 by L 96 and L 0 by 10 0 by 10 6 (longitudinal direction deformation rate = |L96 -L 0 | / L 0 ×10 6 ) is calculated as And the above deformation rate ratio is calculated as the ratio of the above width direction deformation rate to the longitudinal direction deformation rate (width direction deformation rate / longitudinal direction deformation rate).

[0021] The above deformation rate ratio is significantly different from the deformation rate ratio between the width direction and the longitudinal direction generally called the Poisson's ratio. The speculation of the present inventor regarding this point is described below. However, the present invention is not limited to the speculation described in this specification. As described above, the above deformation rate ratio can be an index of the deformation characteristics of the magnetic tape to which a load is applied for a long time of 96 hours. Note that 96 hours of the load application time is a value adopted as an example of the storage time when storing the magnetic tape after data recording, and does not limit the storage period of the magnetic tape in any way. On the other hand, the Poisson's ratio is a measured value for a phenomenon observed in a short time (at most within about several minutes) when a so-called viscoelastic body such as a magnetic tape behaves elastically. The present inventor believes that such a Poisson's ratio cannot be an index of the deformation characteristics of the magnetic tape that occur during storage of the magnetic tape, which is considered to behave more viscously. In fact, as shown in the examples described later, no correlation was found between the above deformation rate ratio and the deformation rate ratio between the width direction and the longitudinal direction under short-time load application. And the present inventor believes that making such a deformation rate ratio 0.45 or less in a magnetic tape including a polyamide support can contribute to suppressing the situation where, after storing the magnetic tape on which data has been recorded and then performing recording and / or reproduction, the magnetic head for recording and / or reproducing data deviates from the target track position due to the deformation of the magnetic tape and recording and / or reproduction of data is performed. This point will be described in more detail below. Recording and playback of data on a magnetic tape are usually performed as follows. A magnetic tape is run in a magnetic recording and playback device (commonly referred to as a "drive"). During such running, head tracking using a servo signal is performed. Specifically, by causing the servo signal reading element of the magnetic head to follow a predetermined servo track on the magnetic tape, the recording element for data recording is controlled to pass over the target data track and data is recorded. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction. Also, during playback of the recorded data, usually, the magnetic tape is run in the magnetic recording and playback device, and by causing the servo signal reading element of the magnetic head to follow a predetermined servo track on the magnetic tape, the reproducing element for data reproduction is controlled to pass over the target data track and the recorded data is read. And after such recording or playback, the magnetic tape is usually stored until the next recording and / or playback is performed. After the above storage, when recording and / or playback is performed, if the magnetic head for recording and / or playing back data is displaced from the target track position due to deformation of the magnetic tape and recording and / or playback of data is performed, phenomena such as recording failure (e.g., overwriting of recorded data, etc.), playback failure (e.g., poor data reading), etc. will occur. The inventor believes that a magnetic tape including a polyamide support and having a deformation rate ratio of 0.45 or less is a magnetic tape in which deformation that can cause such phenomena is unlikely to occur. As a result, the inventor infers that according to the above magnetic tape, it becomes possible to perform recording and / or playback satisfactorily in recording and / or playback of data on the magnetic tape after storage. In recent years, in the data storage field, the need for long-term storage of data such as data backup and archive has been increasing. However, generally, the longer the storage period, the more likely the magnetic tape is to be deformed. Therefore, the inventor considers that a magnetic tape that can suppress the occurrence of the above phenomena after storage is a preferable magnetic tape that can meet the future needs for long-term storage.

[0022] The deformation rate ratio of the magnetic tape is 0.45 or less, and from the viewpoint of enabling better recording and / or playback in recording and / or playback of data after storage, it is preferably 0.43 or less, more preferably 0.40 or less, 0.38 or less, 0.35 or less, 0.33 or less, 0.30 or less, 0.28 or less, 0.25 or less, 0.20 or less in this order. The deformation rate ratio can be, for example, 0.10 or more or 0.15 or more, or can also be less than the values exemplified herein.

[0023] The deformation rate ratio can be controlled, for example, by the manufacturing conditions of the magnetic tape. Details in this regard will be described later.

[0024] Regarding the magnetic tape, if the deformation rate ratio is 0.45 or less, the values of the width direction deformation rate and the longitudinal direction deformation rate of the magnetic tape measured after applying a load in the longitudinal direction for 96 hours are not particularly limited. The width direction deformation rate can be, for example, 85 ppm or less, 80 ppm or less, or 75 ppm or less, and can also be, for example, 10 ppm or more, 15 ppm or more, or 20 ppm or more. Also, the longitudinal direction deformation rate can be, for example, 185 ppm or less or 180 ppm or less, and can also be, for example, 50 ppm or more, 55 ppm or more, or 60 ppm or more.

[0025] For the non-magnetic support, one or more of treatments such as corona discharge, plasma treatment, and easy adhesion treatment may be performed before forming layers such as a magnetic layer thereon.

[0026] <Magnetic layer> (Ferromagnetic powder) The magnetic layer contains ferromagnetic powder. As the ferromagnetic powder contained in the magnetic layer, known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used. From the viewpoint of improving the recording density, it is preferable to use ferromagnetic powder with a small average particle size. From this point, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, still more preferably 40 nm or less, even more preferably 35 nm or less, yet even more preferably 30 nm or less, and still even more preferably 25 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, still more preferably 10 nm or more, even more preferably 15 nm or more, yet even more preferably 20 nm or more.

[0027] Hexagonal ferrite powder Preferable specific examples of the ferromagnetic powder include hexagonal ferrite powder. For details of the hexagonal ferrite powder, reference can be made to, for example, paragraphs 0012 to 0030 of JP-A-2011-225417, paragraphs 0134 to 0136 of JP-A-2011-216149, paragraphs 0013 to 0030 of JP-A-2012-204726, and paragraphs 0029 to 0084 of JP-A-2015-127985.

[0028] In the present invention and in this specification, the "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 in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed. For example, when the diffraction peak with the highest intensity in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of hexagonal ferrite, it is determined that the crystal structure of hexagonal ferrite has been detected as the main phase. When only a single phase is detected by X-ray diffraction analysis, this detected structure is taken as the main phase. The crystal structure of hexagonal ferrite contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. The divalent metal atom is a metal atom that can become a divalent cation as an ion, and examples thereof include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and in this specification, the hexagonal strontium ferrite powder refers to a powder in which the main divalent metal atom contained in this powder is a strontium atom, and the hexagonal barium ferrite powder refers to a powder in which the main divalent metal atom contained in this powder is a barium atom. The main divalent metal atom refers to the divalent metal atom that occupies the largest proportion on an atomic % basis among the divalent metal atoms contained in this powder. However, rare earth atoms are not included in the above divalent metal atoms. The "rare earth atoms" in the present invention and in this specification are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanoid atoms. The lanthanoid atoms are selected from the group consisting of lanthanum atoms (La), cerium atoms (Ce), praseodymium atoms (Pr), neodymium atoms (Nd), promethium atoms (Pm), samarium atoms (Sm), europium atoms (Eu), gadolinium atoms (Gd), terbium atoms (Tb), dysprosium atoms (Dy), holmium atoms (Ho), erbium atoms (Er), thulium atoms (Tm), ytterbium atoms (Yb), and lutetium atoms (Lu).

[0029] Hereinafter, the hexagonal strontium ferrite powder, which is a form of the hexagonal ferrite powder, will be described in more detail.

[0030] The activation volume of the hexagonal strontium ferrite powder is preferably in the range of 800 to 1500 nm 3 The particulate hexagonal strontium ferrite powder showing the activation volume in the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm 3 or more, for example, 850 nm 3 or more. Further, from the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder is more preferably 1400 nm 3 or less, still more preferably 1300 nm 3 or less, even more preferably 1200 nm 3 or less, and still even more preferably 1100 nm 3 or less.

[0031] The "activation volume" is a unit of magnetization reversal and is an index indicating the magnetic size of particles. The activation volume described in the present invention and this specification and the anisotropy constant Ku described later are measured using a vibrating sample magnetometer at magnetic field sweep rates of 3 minutes and 30 minutes in the coercive force Hc measurement section (measurement temperature: 23°C ± 1°C), and are values obtained from the following relational expression between Hc and the activation volume V. Regarding the unit of the anisotropy constant Ku, 1 erg / cc = 1.0×10 -1 J / m 3 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)]

[0032] As an index for reducing thermal fluctuations, in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder preferably has a Ku of 1.8×10 5 J / m 3 or more, more preferably 2.0×10 5 J / m 3 or more. Also, the Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 5 J / m 3 or less. However, since a higher Ku means higher thermal stability and is preferable, it is not limited to the values exemplified above.

[0033] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it preferably contains rare earth atoms at a content rate (bulk content rate) of 0.5 to 5.0 atomic% with respect to 100 atomic% of iron atoms. The hexagonal strontium ferrite powder containing rare earth atoms can, in one form, have a rare earth atom surface layer partiality. The "rare earth atom surface layer partiality" in the present invention and this specification means the rare earth atom content rate (hereinafter, referred to as "rare earth atom surface layer content rate" or simply "surface layer content rate" with respect to rare earth atoms) with respect to 100 atomic% of iron atoms in the dissolution liquid obtained by partially dissolving the hexagonal strontium ferrite powder with an acid is different from the rare earth atom content rate (hereinafter, referred to as "rare earth atom bulk content rate" or simply "bulk content rate" with respect to rare earth atoms) with respect to 100 atomic% of iron atoms in the dissolution liquid obtained by completely dissolving the hexagonal strontium ferrite powder with an acid, and Rare earth atom surface layer content rate / Rare earth atom bulk content rate > 1.0 It means satisfying the ratio. The rare earth atom content of the hexagonal ferrite powder described later is synonymous with the rare earth atom bulk content. On the other hand, since partial dissolution using an acid dissolves the surface layer part of the particles constituting the hexagonal strontium ferrite powder, the rare earth atom content in the dissolution solution obtained by partial dissolution is the rare earth atom content in the surface layer part of the particles constituting the hexagonal strontium ferrite powder. That the rare earth atom surface layer content satisfies the ratio of "rare earth atom surface layer content / rare earth atom bulk content > 1.0" means that in the particles constituting the hexagonal strontium ferrite powder, the rare earth atoms are unevenly distributed in the surface layer part (that is, there are more than in the interior). The surface layer part in the present invention and in this specification means a partial region from the surface of the particles constituting the hexagonal strontium ferrite powder toward the interior.

[0034] When the hexagonal 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% with respect to 100 atomic% of iron atoms. It is considered that the inclusion of rare earth atoms with the bulk content in the above range and the uneven distribution of rare earth atoms in the surface layer part of the particles constituting the hexagonal strontium ferrite powder contribute to suppressing the decrease in the reproduction output in repeated reproduction. This is presumably because the hexagonal strontium ferrite powder contains rare earth atoms with the bulk content in the above range and the rare earth atoms are unevenly distributed in the surface layer part of the particles constituting the hexagonal strontium ferrite powder, so that the anisotropy constant Ku can be increased. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called so-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 in repeated reproduction can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the particle surface layer part of the hexagonal strontium ferrite powder contributes to stabilizing the spin of the iron (Fe) sites in the crystal lattice of the surface layer part, thereby increasing the anisotropy constant Ku. In addition, it is presumed that using hexagonal strontium ferrite powder having a rare earth atom surface layer bias 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 hexagonal strontium ferrite powder having a rare earth atom surface layer bias can contribute to improving the running durability of the magnetic tape. This is presumably because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surface and the organic substances (for example, 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 the reproduction output during repeated reproduction and / or from the viewpoint of further improving the running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic%, still 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%.

[0035] The above 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 atoms refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one kind of rare earth atom as the rare earth atom, or may contain two or more kinds of rare earth atoms. The above bulk content in the case of containing two or more kinds of rare earth atoms is obtained for the total of two or more kinds of rare earth atoms. This also applies to other components in the present invention and this specification. That is, unless otherwise specified, one kind of a certain component may be used, or two or more kinds may be used. The content or content rate in the case of using two or more kinds refers to the total of two or more kinds.

[0036] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained may be any one or more of the rare earth atoms. From the viewpoint of further suppressing the decrease in the regeneration output in repeated regeneration, preferable rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, more preferably neodymium atoms, samarium atoms, and yttrium atoms, and even more preferably neodymium atoms.

[0037] In the hexagonal strontium ferrite powder having rare earth atom surface layer partiality, the rare earth atoms only need to 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 surface layer partiality, the ratio of the surface layer content rate of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content rate of rare earth atoms obtained by complete dissolution under the dissolution conditions described later, "surface layer content rate / bulk content rate" is more than 1.0, and can be 1.5 or more. That the "surface layer content rate / bulk content rate" is greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, the rare earth atoms are unevenly distributed in the surface layer (that is, there are more than in the interior). Also, the ratio of the surface layer content rate of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content rate of rare earth atoms obtained by complete dissolution under the dissolution conditions described later, "surface layer content rate / bulk content rate" 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 the hexagonal strontium ferrite powder having rare earth atom surface layer partiality, the rare earth atoms only need to be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface layer content rate / bulk content rate" is not limited to the exemplified upper or lower limits.

[0038] The partial dissolution and complete dissolution of hexagonal strontium ferrite powder will be described below. For the hexagonal strontium ferrite powder existing as powder, the sample powders for partial dissolution and complete dissolution are taken from the same lot of powder. On the other hand, for the hexagonal strontium ferrite powder contained in the magnetic layer of the 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 complete dissolution. The extraction of the hexagonal strontium ferrite powder from the magnetic layer can be carried out, for example, by the method described in paragraph 0032 of JP-A-2015-91747. The above partial dissolution means dissolution to such an extent that the residue of the hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, by partial dissolution, for the particles constituting the hexagonal strontium ferrite powder, a region of 10 to 20% by mass can be dissolved with the whole particle being 100% by mass. On the other hand, the above complete dissolution means dissolution until no residue of the hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. The measurement of the above partial dissolution and the surface layer portion content is carried out, for example, by the following method. However, the dissolution conditions such as the amount of the sample powder below are examples, and any dissolution conditions that enable partial dissolution and complete dissolution can be arbitrarily adopted. A container (for example, a beaker) containing 12 mg of sample powder and 10 ml of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The obtained dissolution solution is filtered through a 0.1 μm membrane filter. The elemental analysis of the filtrate thus obtained is carried out by an inductively coupled plasma (ICP) analyzer. Thus, the surface layer portion content of the rare earth atoms with respect to 100 atomic% of iron atoms can be determined. When a plurality of types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer portion content. This is the same also in the measurement of the bulk content. On the other hand, the measurement of the above complete dissolution and the bulk content is carried out, for example, by the following method. Place a container (e.g., a beaker) containing 12 mg of sample powder and 10 ml of 4 mol / L hydrochloric acid on a hot plate set at 80°C and hold for 3 hours. Thereafter, perform the same operations as the above partial dissolution and measurement of the surface layer content rate, and the bulk content rate with respect to 100 atomic% of iron atoms can be determined.

[0039] From the viewpoint of increasing the playback output when playing back the data recorded on the magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, the hexagonal strontium ferrite powder containing rare earth atoms but having no uneven distribution of rare earth atoms in the surface layer portion has a tendency that σs is significantly reduced compared to the hexagonal strontium ferrite powder not containing rare earth atoms. On the other hand, in order to suppress such a significant decrease in σs, the hexagonal strontium ferrite powder having uneven distribution of rare earth atoms in the surface layer portion is considered preferable. In one form, the σs of the hexagonal strontium ferrite powder can be 45 A·m 2 / kg or more, and can also be 47 A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, σs is preferably 80 A·m 2 / kg or less, and more preferably 60 A·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 the value measured at a magnetic field strength of 1194 kA / m (15 kOe).

[0040] Regarding the content ratio (bulk content ratio) of constituent atoms of the hexagonal ferrite powder, the strontium atom content ratio can be in the range of, for example, 2.0 to 15.0 atomic% with respect to 100 atomic% of iron atoms. In one form, the hexagonal strontium ferrite powder can be such that the divalent metal atoms contained in this powder are only strontium atoms. In another form, 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 other divalent metal atoms other than strontium atoms are contained, the barium atom content ratio and calcium atom content ratio in the hexagonal strontium ferrite powder can each be in the range of, for example, 0.05 to 5.0 atomic% with respect to 100 atomic% of iron atoms.

[0041] As the crystal structure of hexagonal ferrite, the magnetoplumbite type (also called "M type"), W type, Y type and Z type are known. The hexagonal strontium ferrite powder can take any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can be such that a single crystal structure or two or more crystal structures are detected by X-ray diffraction analysis. For example, in one form, the hexagonal strontium ferrite powder can be such that only the M-type crystal structure is detected by X-ray diffraction analysis. For example, the M-type hexagonal ferrite is AFe 12 O 19It is represented by the following compositional formula. Here, A represents a divalent metal atom. 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) occupies the most in terms of atomic percentage as described above. The content rate of the divalent metal atom in 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 rate and the oxygen atom content rate. 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 rate of the aluminum atom can be, for example, 0.5 to 10.0 atomic% with respect to 100 atomic% of the iron atom. From the viewpoint of further suppressing the reduction in the reproduction output in repeated reproduction, the hexagonal strontium ferrite powder contains an iron atom, a strontium atom, an oxygen atom, and a rare earth atom, and the content rate of atoms other than these atoms is preferably 10.0 atomic% or less, more preferably in the range of 0 to 5.0 atomic%, and may be 0 atomic% with respect to 100 atomic% of the iron atom. That is, in one form, the hexagonal strontium ferrite powder may not contain atoms other than an iron atom, a strontium atom, an oxygen atom, and a rare earth atom. The content rate expressed in the above atomic percentage is obtained by converting the content rate (unit: mass%) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic percentage using the atomic weight of each atom. Also, in the present invention and this specification, "not containing" a certain atom means that the content rate measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of the ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above "not containing" is used in the sense of including being contained in an amount less than the detection limit of the ICP analyzer.The hexagonal strontium ferrite powder can, in one form, be free of bismuth atoms (Bi).

[0042] Metal powder Preferable specific examples of the ferromagnetic powder can also include ferromagnetic metal powders. For details of the ferromagnetic metal powders, reference can be made to, for example, paragraphs 0137 to 0141 of JP-A-2011-216149 and paragraphs 0009 to 0023 of JP-A-2005-251351.

[0043] ε-iron oxide powder Preferable specific examples of the ferromagnetic powder can also include ε-iron oxide powder. In the present invention and this specification, the "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystal structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, in the X-ray diffraction spectrum obtained by X-ray diffraction analysis, when the diffraction peak with the highest intensity is attributed to the crystal structure of ε-iron oxide, it is determined that the crystal structure of ε-iron oxide has been detected as the main phase. As methods for producing ε-iron oxide powder, a method of producing from goethite, an inverse micelle method, etc. are known. All of the above production methods are well-known. Also, for methods of producing ε-iron oxide powder in which a part of Fe is substituted by substitution atoms such as Ga, Co, Ti, Al, Rh, etc., 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 ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the above magnetic tape is not limited to the methods listed here.

[0044] The activation volume of the ε-iron oxide powder is preferably in the range of 300 to 1500 nm 3 is. The micronized ε-iron oxide powder showing the activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm 3 or more, for example 500 nm3 It can also be as described above. Further, from the viewpoint of further improving the electromagnetic conversion characteristics, the activated volume of the ε-iron oxide powder is 1400 nm 3 It is more preferably below, and 1300 nm 3 It is still more preferably below, and 1200 nm 3 It is even more preferably below, and 1100 nm 3 It is still even more preferably below.

[0045] As an index for reducing thermal fluctuations, in other words, improving thermal stability, the anisotropy constant Ku can be cited. The ε-iron oxide powder preferably has a Ku of 3.0×10 4 J / m 3 or more, and more preferably has a Ku of 8.0×10 4 J / m 3 or more. Further, the Ku of the ε-iron oxide powder can be, for example, 3.0×10 5 J / m 3 or less. However, the higher the Ku, the higher the thermal stability, which is preferable, so it is not limited to the values exemplified above.

[0046] From the viewpoint of increasing the reproduction output when reproducing the data recorded on the 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 form, the σs of the ε-iron oxide powder can be 8 A·m 2 / kg or more, and can also be 12 A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, the σs of the ε-iron oxide powder is preferably 40 A·m 2 / kg or less, and more preferably 35 A·m 2 / kg or less.

[0047] 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. Photograph the powder at a magnification of 100,000 times using a transmission electron microscope, and print it on a photographic paper or display it on a display at a total magnification of 500,000 times, etc., to obtain a photograph of the particles constituting the powder. Select the target particles from the obtained particle photograph and trace the outline of the particles with a digitizer to measure the size of the particles (primary particles). The primary particles refer to independent particles without aggregation. Perform the above measurements on 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is defined as the average particle size of the powder. As the above transmission electron microscope, for example, a Hitachi transmission electron microscope model H-9000 can be used. Also, the measurement of the particle size can be performed using known image analysis software, for example, Carl Zeiss image analysis software KS-400. Unless otherwise specified, the average particle size shown in the examples described later is a value measured using a Hitachi transmission electron microscope model H-9000 as the transmission electron microscope and Carl Zeiss image analysis software KS-400 as the image analysis software. In the present invention and this specification, the powder means a collection of a plurality of particles. For example, the ferromagnetic powder means a collection of a plurality of ferromagnetic particles. Also, the collection of a plurality of particles is not limited to the mode in which the particles constituting the collection are in direct contact, and modes in which binders, additives, etc. described later are interposed between the particles are also included. The term "particle" may also be used to represent the powder.

[0048] As a method for collecting the sample powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of Japanese Patent Application Laid-Open No. 2011-048878 can be adopted.

[0049] In the present invention and this specification, unless otherwise specified, the size of the particles (particle size) constituting the powder is such that the shape of the particles observed in the above particle photograph is (1) In the case of acicular, spindle-shaped, columnar (however, the height is larger than the maximum major axis of the bottom surface), etc., it is represented by the length of the major axis constituting the particle, that is, the major axis length. (2) In the case of being plate-shaped or columnar (however, the thickness or height is smaller than the maximum major axis diameter of the plate surface or bottom surface), it is represented by the maximum major axis diameter of the plate surface or bottom surface, (3) In the case of being spherical, polyhedral, irregular, etc., and the major axis constituting the particles cannot be specified from the shape, it is represented by the equivalent circle diameter. The equivalent circle diameter refers to that obtained by the circular projection method.

[0050] Also, the average aspect ratio of the powder refers to measuring the length of the minor axis of the particles, that is, the minor axis length, in the above measurement, obtaining the value of (major axis length / minor axis length) for each particle, and taking the arithmetic mean of the values obtained for the above 500 particles. Here, unless otherwise specified, the minor axis length refers to the length of the minor axis constituting the particles in case (1) of the above particle size definition, the thickness or height in case (2), respectively. In case (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience. And, unless otherwise specified, when the shape of the particles is specified, for example, in case (1) of the above particle size definition, the average particle size is the average major axis length, and in case (2), the average particle size is the average plate diameter. In case (3) of the same definition, the average particle size is the average diameter (also referred to as the average particle diameter, average grain diameter).

[0051] The content rate (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on 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 the recording density.

[0052] (Binder) The above magnetic tape can be a coating type magnetic tape and can contain a binder in the magnetic layer. That is, in one form, the above magnetic tape excludes the metal thin film type magnetic tape. As is well known, the metal thin film type magnetic tape is a magnetic tape having a ferromagnetic metal thin film layer formed by vacuum evaporation, sputtering, ion plating, etc. as the magnetic layer.

[0053] The binder is one or more resins. As the binder, various resins commonly used as binders for coated magnetic recording media can be used. For example, as the binder, a polyurethane resin, a polyester resin, a polyamide resin, a vinyl chloride resin, an acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., a cellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin, a polyvinyl acetal, a polyvinyl butyral, etc. A resin selected from polyvinyl alkylal resins can be used alone or a plurality of resins can be mixed and used. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin. These resins may be homopolymers or copolymers. These resins can also be used as binders in the nonmagnetic layer and / or backcoat layer described later. Regarding the above binders, reference can be made to paragraphs 0028 to 0031 of JP-A-2010-24113, paragraphs 0006 to 0021 of JP-A-2004-5795, etc. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The average molecular weight in the present invention and this specification is a value obtained by converting the value measured under the following measurement conditions by gel permeation chromatography (GPC) into polystyrene. The average molecular weight of the binder shown in the examples described later is a value obtained by converting the value measured under the following measurement conditions into polystyrene. The binder can be used in an amount of, for example, 1.0 to 80.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. Regarding the amount of the binder in the nonmagnetic layer and the backcoat layer, the description regarding the amount of the binder in the magnetic layer can be applied by substituting the ferromagnetic powder with the nonmagnetic powder. GPC apparatus: HLC-8120 (manufactured by Tosoh Corporation) Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mm ID (Inner Diameter) × 30.0 cm) Eluent: Tetrahydrofuran (THF)

[0054] A curing agent can also be used together with a resin that can be used as a binder. The curing agent can be a thermosetting compound which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating in one form, and can be a photocurable compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation in another form. The curing agent can be contained in the magnetic layer at least partially in a state of reacting (crosslinking) with other components such as a binder by the progress of the curing reaction in the magnetic layer forming step. This also applies to the layer formed using this composition when the composition used for forming other layers contains a curing agent. A preferable curing agent is a thermosetting compound, and polyisocyanate is suitable. For details of polyisocyanate, paragraphs 0124 to 0125 of JP-A No. 2011-216149 can be referred to. The content of the curing agent in the composition for forming the magnetic layer can be, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder, and can be 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of the magnetic layer. This also applies to the composition for forming the non-magnetic layer and the composition for forming the backcoat layer.

[0055] (Additive) The magnetic layer may contain one or more additives as necessary. Examples of the additives include the above-mentioned curing agent. Examples of the additives contained in the magnetic layer include non-magnetic powders (such as inorganic powders, carbon black, etc.), lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants, etc. For example, regarding the lubricant, reference can be made to paragraphs 0030 to 0033, 0035, and 0036 of JP-A-2016-126817. The lubricant may be contained in the non-magnetic layer described later. Regarding the lubricant that can be contained in the non-magnetic layer, reference can be made to paragraphs 0030 to 0031, 0034, 0035, and 0036 of JP-A-2016-126817. Regarding the dispersant, reference can be made to paragraphs 0061 and 0071 of JP-A-2012-133837. Also, regarding the additives of the magnetic layer, reference can be made to paragraphs 0035 to 0077 of JP-A-2016-51493. The dispersant may be added to the composition for forming the non-magnetic layer. Regarding the dispersant that can be added to the composition for forming the non-magnetic layer, reference can be made to paragraph 0061 of JP-A-2012-133837. Examples of the non-magnetic powder that can be contained in the magnetic layer include non-magnetic powders that can function as abrasives, non-magnetic powders that can function as protrusion-forming agents for forming protrusions that moderately protrude from the surface of the magnetic layer (such as non-magnetic colloidal particles, etc.). The average particle size of the colloidal silica (silica colloidal particles) shown in the examples described later was determined by the method described in paragraph 0015 of JP-A-2011-048878 as the method for measuring the average particle diameter. The additives can be appropriately selected from commercially available products according to the desired properties, or manufactured by known methods and used in any amount. An example of the additive that can be used to improve the dispersibility of the abrasive in the magnetic layer containing the abrasive can include the dispersants described in paragraphs 0012 to 0022 of JP-A-2013-131285.

[0056] The magnetic layer described above can be provided directly on the surface of the non-magnetic support or indirectly via the non-magnetic layer.

[0057] <Non-magnetic layer> Next, the non-magnetic layer will be described. The magnetic tape may have a magnetic layer directly on the surface of the non-magnetic support, or may have a magnetic layer via a non-magnetic layer containing non-magnetic powder on the surface of the non-magnetic support. The non-magnetic powder used for the non-magnetic layer may be either inorganic powder or organic powder. Also, carbon black or the like can be used. Examples of the inorganic powder include powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. These non-magnetic powders are available as commercial products and can also be manufactured by known methods. For details thereof, reference can be made to paragraphs 0146 to 0150 of JP-A-2011-216149. Regarding the carbon black that can be used for the non-magnetic layer, reference can also be made to paragraphs 0040 to 0041 of JP-A-2010-24113. The content rate (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on the total mass of the non-magnetic layer.

[0058] The non-magnetic layer can contain a binder and can also contain additives as necessary. For other details such as the binder and additives of the non-magnetic layer, known techniques regarding the non-magnetic layer can be applied. Also, for example, regarding the type and content of the binder, the type and content of the additives, etc., known techniques regarding the magnetic layer can also be applied.

[0059] In the present invention and this specification, the non-magnetic layer is also intended to include a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example, as an impurity or intentionally, together with the non-magnetic powder. Here, the substantially non-magnetic layer means 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. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

[0060] <Backcoat layer> The magnetic tape may or may not have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. It is preferable that the back coat layer contains either one or both of carbon black and inorganic powder. As the carbon black, for example, carbon black having an average particle size of 17 nm or more and 50 nm or less (hereinafter referred to as "fine particle carbon black") can be used, and carbon black having an average particle size of more than 50 nm and 300 nm or less (hereinafter referred to as "coarse particle carbon black") can also be used. Further, fine particle carbon black and coarse particle carbon black can be used in combination. Examples of the inorganic powder include non-magnetic powders generally used for non-magnetic layers, non-magnetic powders generally used as abrasives for magnetic layers, etc. Among them, α-iron oxide, α-alumina, etc. are preferable. The average particle size of the inorganic powder in the back coat layer can be, for example, in the range of 5 to 250 nm. When carbon black and inorganic powder are used in combination as the non-magnetic powder in the back coat layer, in one embodiment, it is preferable that the inorganic powder is contained in an amount exceeding 50.0 parts by mass and more preferably 70.0 to 90.0 parts by mass with respect to 100.0 parts by mass of the total amount of the non-magnetic powder. The above description regarding the non-magnetic powder in the back coat layer can be applied to the non-magnetic powder in the non-magnetic layer in one embodiment.

[0061] The back coat layer can contain a binder and, if necessary, can also contain additives. Regarding the binder and additives in the back coat layer, known techniques regarding the back coat layer can be applied, and known techniques regarding the formulations of the magnetic layer and / or non-magnetic layer can also be applied. For example, the descriptions in paragraphs 0018 to 0020 of JP-A-2006-331625 and lines 65 to 38 of column 5 of U.S. Patent No. 7,029,774 can be referred to for the back coat layer.

[0062] <Various Thicknesses> The thin thickness of the magnetic tape is preferable from the viewpoint of increasing the capacity per reel of the magnetic tape cartridge. Making the thickness of the non-magnetic support thin is preferable because it can lead to making the thickness of the magnetic tape thin. From this point, the thickness of the non-magnetic support included in the magnetic tape is preferably less than 10.0 μm, more preferably 9.0 μm or less, still more preferably 8.0 μm or less, even more preferably 7.0 μm or less, and yet even more preferably 6.0 μm or less. Also, the thickness of the non-magnetic support can be, for example, 0.5 μm or more or 1.0 μm or more.

[0063] 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. Generally, it is 0.01 μm to 0.15 μm. From the viewpoint of high-density recording, it is preferably 0.015 μm to 0.12 μm, and more preferably 0.02 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 configuration regarding a known multi-layer magnetic layer can be applied. The thickness of the magnetic layer in the case of separating into two or more layers is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, and preferably 0.1 to 1.0 μm. The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.

[0064] The thickness of the non-magnetic support and the thickness of each layer in the present invention and this specification can be determined by known methods. For example, the thickness of the magnetic layer can be determined by the following method. After exposing the cross-section in the thickness direction of the magnetic tape by known techniques such as an ion beam or a microtome, a cross-sectional image of the exposed cross-section is obtained by a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Cross-sectional images are obtained at 10 randomly selected locations. For the 10 images thus obtained, the thickness of the magnetic layer is measured at one randomly selected location in each image. The thickness of the magnetic layer can be determined as the arithmetic mean of the 10 measured values obtained for the 10 images. When determining the thickness of the magnetic layer, the interface between the magnetic layer and the adjacent portion (for example, the non-magnetic layer) can be specified by the method described in paragraph 0029 of JP-A-2017-33617. Other thicknesses can also be determined in the same manner. Alternatively, the various thicknesses can also be determined as the designed thicknesses calculated from the manufacturing conditions and the like.

[0065] <Manufacturing process> (Preparation of the composition for forming each layer) The process of preparing a composition for forming a magnetic layer, a non-magnetic layer, or a backcoat layer can usually include at least a kneading process, a dispersion process, and, if necessary, a mixing process provided before and after these processes. Each individual process may be divided into two or more steps. The components used in the preparation of each layer-forming composition may be added at the beginning or during any of the processes. As the solvent, one or more of various solvents commonly used in the manufacture of coated magnetic recording media can be used. For the solvent, reference can be made to, for example, paragraph 0153 of JP-A-2011-216149. Also, the individual components may be added in portions over two or more processes. For example, the binder may be added in portions in the kneading process, the dispersion process, and the mixing process for adjusting the viscosity after dispersion. To manufacture the above magnetic tape, known manufacturing techniques can be used in various processes. In the kneading process, it is preferable to use one having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, an extruder, etc. For details of the kneading process, reference can be made to JP-A-1-106338 and JP-A-1-79274. Known dispersers can be used. At any stage of preparing each layer-forming composition, filtration may be carried out by a known method. Filtration can be carried out, for example, by filter filtration. As the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

[0066] (Coating process) The magnetic layer can be formed by directly coating a composition for forming the magnetic layer on the surface of a non-magnetic support, or by applying a multi-layer coating sequentially or simultaneously with a composition for forming a non-magnetic layer. The backcoat layer can be formed by applying a composition for forming the backcoat layer to the surface of the non-magnetic support opposite to the surface having the non-magnetic layer and / or the magnetic layer (or to which the non-magnetic layer and / or the magnetic layer will be subsequently provided). For details of the coating for forming each layer, reference can be made to paragraph 0066 of JP-A-2010-231843. In the production of a magnetic tape, the non-magnetic support is usually used with the MD direction (Machine direction) of the film as the longitudinal direction and the TD direction (Transverse direction) as the width direction.

[0067] (Other processes) For various other processes for the production of the magnetic tape, known techniques can be applied. For details of the various processes, reference can be made to paragraphs 0067 to 0070 of JP-A-2010-231843, for example. For example, an orientation treatment can be applied to the coating layer of the composition for forming the magnetic layer while this coating layer is in a wet (undried) state. For the orientation treatment, various known techniques can be applied, including the description in paragraph 0052 of JP-A-2010-24113. For example, the perpendicular orientation treatment can be carried out by a known method such as a method using a magnet with opposite poles facing each other. In the orientation zone, the drying rate of the coating layer can be controlled by the temperature, air volume of the drying air and / or the conveyance speed in the orientation zone. Also, the coating layer may be pre-dried before being conveyed to the orientation zone. By going through various processes, a long magnetic tape web can be obtained. The obtained magnetic tape web is slit by a known cutting machine to the width of the magnetic tape to be wound on a magnetic tape cartridge. The above width is determined according to the standard and is, for example, 1 / 2 inch. 1 inch = 0.0254 meters.

[0068] For example, by placing the magnetic tape web before slitting under high temperature and high humidity conditions with a high load applied in the longitudinal direction (hereinafter also referred to as "pre-slitting high temperature and high humidity load application treatment"), a magnetic tape with the above-described deformation rate ratio within the previously described range can be obtained. Here, the high temperature can be, for example, an ambient temperature of 30 to 60°C, the high humidity can be, for example, a relative humidity of 40 to 100%, and the high load can be, for example, a load of 1.0 to 5.0 N. Such a load can be, for example, a load applied in the longitudinal direction of the magnetic tape web when rewinding the magnetic tape web wound in a roll shape. The above rewinding can be performed in a chamber capable of controlling the internal temperature and humidity. For example, the magnetic tape web wound in a roll shape is placed in a chamber in a state where the temperature and humidity are not controlled, a load is applied in the longitudinal direction for rewinding, and the chamber in which the magnetic tape web wound in a roll shape is placed is heated and humidified to a high temperature and high humidity state and held for a predetermined time, and then cooled and dehumidified. The above predetermined time can be, for example, 10 to 60 hours. After the above holding, the chamber can be cooled and dehumidified without performing rewinding, or the chamber can be cooled and dehumidified after performing rewinding with different loads applied. The heating rate, humidifying rate, cooling rate, and dehumidifying rate are not particularly limited. As an example, for example, the heating rate can be 20 to 60°C / hour, the humidifying rate can be 40 to 90% / hour, the cooling rate can be 5 to 60°C / hour, and the dehumidifying rate can be 80 to 120% / hour.

[0069] In order to enable tracking control of the magnetic head and control of the running speed of the magnetic tape in a magnetic recording and reproducing apparatus, a servo pattern can be formed on the magnetic tape manufactured as described above by a known method. "Formation of the servo pattern" can also be referred to as "recording of the servo signal". The formation of the servo pattern will be described below.

[0070] Servo patterns are usually formed along the longitudinal direction of a magnetic tape. Examples of control methods (servo control) using servo signals include timing-based servo (TBS), amplitude servo, frequency servo, and the like.

[0071] As shown in ECMA (European Computer Manufacturers Association) - 319 (June 2001), in a magnetic tape compliant with the LTO (Linear Tape-Open) standard (commonly referred to as an "LTO tape"), a timing-based servo method is adopted. In this timing-based servo method, a servo pattern is constituted by continuously arranging a plurality of pairs of magnetic stripes (also called "servo stripes") that are non-parallel to each other along the longitudinal direction of the magnetic tape. A servo system is a system that performs head tracking using a servo signal. In the present invention and this specification, a "timing-based servo pattern" refers to a servo pattern that enables head tracking in a servo system of the timing-based servo method. As described above, the reason why the servo pattern is constituted by a pair of non-parallel magnetic stripes is to inform the servo signal reading element passing over the servo pattern of its passing position. Specifically, the interval between the above-mentioned pair of magnetic stripes is formed so as to continuously change along the width direction of the magnetic tape, and by the servo signal reading element reading the interval, the relative position between the servo pattern and the servo signal reading element can be known. This relative position information enables tracking of the data track. For this purpose, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

[0072] The servo band is composed of servo patterns continuous in the longitudinal direction of the magnetic tape. Usually, a plurality of servo bands are provided on the magnetic tape. For example, in the case of an LTO tape, the number is five. The area sandwiched between two adjacent servo bands is the data band. The data band is composed of a plurality of data tracks, and each data track corresponds to each servo track.

[0073] Also, in one form, as shown in Japanese Patent Application Laid-Open No. 2004-318983, each servo band is embedded with information indicating the number of the servo band (also referred to as "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information"). This servo band ID is recorded by shifting a specific one of a pair of servo stripes among a plurality in the servo band so that its position is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the shifting method of a specific one of a plurality of pairs of servo stripes is changed for each servo band. As a result, the recorded servo band ID becomes unique for each servo band, so that by simply reading one servo band with a servo signal reading element, the servo band can be uniquely identified.

[0074] Note that there is also a method of uniquely identifying a servo band using a staggered method as shown in ECMA-319 (June 2001). In this staggered method, a group of a pair of magnetic stripes (servo stripes) arranged continuously in the longitudinal direction of the magnetic tape and non-parallel to each other is recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. Since the combination of the shifting methods between adjacent servo bands is unique throughout the magnetic tape, it is also possible to uniquely identify the servo band when reading the servo pattern with two servo signal reading elements.

[0075] Also, in each servo band, as shown in ECMA-319 (June 2001), information indicating the longitudinal position of the magnetic tape (also called "LPOS (Longitudinal Position) information") is usually embedded. This LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape, similar to the UDIM information. However, different from the UDIM information, the same signal is recorded in each servo band for this LPOS information.

[0076] It is also possible to embed other information different from the above UDIM information and LPOS information in the servo band. In this case, the information to be embedded may be different for each servo band like the UDIM information, or may be common to all servo bands like the LPOS information. Also, as a method of embedding information in the servo band, it is possible to adopt a method other than the above. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of a pair of servo stripes.

[0077] The head for forming the servo pattern is called a servo write head. The servo write head usually has a pair of gaps corresponding to the above pair of magnetic stripes, the number of which is the same as the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, the magnetic field generated in the core can cause a leakage magnetic field in the pair of gaps. When forming the 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, 10 μm or more, etc.

[0078] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a DC magnet or an AC magnet. There are two types of erase processes: DC (Direct Current) erase and AC (Alternating Current) erase. The AC erase is performed by gradually decreasing the intensity of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, the DC erase is performed by applying a magnetic field in one direction to the magnetic tape. There are further two methods for DC erase. The first method is a horizontal DC erase in which a magnetic field in one direction is applied along the longitudinal direction of the magnetic tape. The second method is a vertical DC erase in which a magnetic field in one direction is applied along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape or for each servo band of the magnetic tape.

[0079] The direction of the magnetic field of the servo pattern to be formed is determined according to the direction of the erase. For example, when a horizontal DC erase is performed on the magnetic tape, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. Thereby, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred using the above-described gap to a vertically DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a monopolar pulse shape. On the other hand, when a magnetic pattern is transferred using the above-described gap to a horizontally DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0080] The magnetic tape is usually housed in a magnetic tape cartridge.

[0081] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-described magnetic tape.

[0082] The details of the magnetic tape included in the magnetic tape cartridge are as described above.

[0083] In a magnetic tape cartridge, generally, the magnetic tape is accommodated in a state of being wound around a reel inside the cartridge body. The reel is rotatably provided 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 double-reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When the single-reel type magnetic tape cartridge is mounted on a magnetic recording and reproducing apparatus 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 recording and reproducing apparatus side. A magnetic head is disposed in the magnetic tape conveyance path from the magnetic tape cartridge to the take-up reel. Feeding and take-up of the magnetic tape are performed between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic recording and reproducing apparatus side (take-up reel). During this period, for example, data recording and / or reproduction are performed by the magnetic head coming into contact with and sliding on the surface of the magnetic layer of the magnetic tape. On the other hand, in the double-reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single-reel type or a double-reel type magnetic tape cartridge. The magnetic tape cartridge may be any one that includes the magnetic tape according to one aspect of the present invention, and known techniques can be applied to other aspects.

[0084] [Magnetic Recording and Reproducing Apparatus] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including the above magnetic tape.

[0085] In the present invention and in this specification, the "magnetic recording and reproducing apparatus" shall mean an apparatus capable of performing at least one of recording data on a magnetic tape and reproducing data recorded on a magnetic recording medium. Such an apparatus is generally called a drive. The magnetic recording and reproducing apparatus can be, for example, a sliding type magnetic recording and reproducing apparatus. The sliding type magnetic recording and reproducing apparatus refers to an apparatus in which the magnetic head contacts and slides on the surface of the magnetic layer of the magnetic tape when recording data on the magnetic tape and / or reproducing the recorded data. For example, the magnetic recording and reproducing apparatus can detachably include the magnetic tape cartridge.

[0086] The above magnetic recording and reproducing apparatus can include a magnetic head. The magnetic head can be a recording head capable of recording data on a magnetic tape, or can also be a reproducing head capable of reproducing data recorded on the magnetic tape. Further, in one form, the above magnetic recording and reproducing apparatus can include both a recording head and a reproducing head as separate magnetic heads. In another form, the magnetic head included in the above magnetic recording and reproducing apparatus can have a configuration in which both an element for data recording (recording element) and an element for data reproduction (reproducing element) are provided in one magnetic head. Hereinafter, the element for data recording and the element for reproduction are collectively referred to as a "data element". As the reproducing head, a magnetic head (MR head) including a magnetoresistive (MR) element capable of sensitively reading data recorded on a magnetic tape as a reproducing element is preferable. As the MR head, various known MR heads such as an AMR (Anisotropic Magnetoresistive) head, a GMR (Giant Magnetoresistive) head, and a TMR (Tunnel Magnetoresistive) head can be used. Further, the magnetic head for data recording and / or data reproduction may include a servo signal reading element. Alternatively, a magnetic head (servo head) provided with a servo signal reading element may be included in the above magnetic recording and reproducing apparatus as a head separate from the magnetic head for data recording and / or data reproduction. For example, a magnetic head for data recording and / or reproduction of the recorded data (hereinafter also referred to as a "recording and reproducing head") can include two servo signal reading elements, and each of the two servo signal reading elements can simultaneously read two adjacent servo bands. One or more data elements can be arranged between the two servo signal reading elements.

[0087] In the above magnetic recording and reproducing apparatus, recording of data on a magnetic tape and / or reproduction of data recorded on a magnetic recording medium can be performed, for example, by bringing the surface of the magnetic layer of the magnetic tape into contact with and sliding it against a magnetic head. The above magnetic recording and reproducing apparatus only needs to include a magnetic tape according to one aspect of the present invention, and known techniques can be applied to other aspects.

[0088] For example, when recording data and / or reproducing recorded data, first, head tracking using a servo signal can be performed. That is, by causing the servo signal reading element to follow a predetermined servo track, the data element can be controlled to pass over the target data track. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction. In addition, the recording and reproducing head can also perform recording and / or reproduction on other data bands. In that case, the servo signal reading element can be moved to a predetermined servo band using the UDIM information described above, and tracking for that servo band can be started.

Example

[0089] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the embodiments shown. The "parts" and "%" described below indicate "parts by mass" and "mass%" unless otherwise specified. "eq" is equivalent, which is a unit that cannot be converted into SI units. The following steps and evaluations were performed in the atmosphere at 23°C ± 1°C unless otherwise specified.

[0090] [Example 1] (1) Preparation of alumina dispersion To 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) with an alpha conversion rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 20 m 2 / g, 10.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.) and SO as a polar group3 A 32% solution of a polyester polyurethane resin having a Na group (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq / kg)) (the solvent is a mixed solvent of methyl ethyl ketone and toluene), 31.3 parts, and a mixed solution of methyl ethyl ketone and cyclohexanone 1:1 (mass ratio) of 570.0 parts as a solvent were mixed. The resulting mixture was placed in a horizontal bead mill disperser together with zirconia beads having a bead diameter of 0.3 mm, and adjusted so that "(bead volume / (volume of the above mixture + bead volume)) × 100" was 80%, and bead mill dispersion treatment was performed for 120 minutes. The liquid after the bead mill dispersion treatment was taken out, and the taken-out liquid was subjected to ultrasonic dispersion filtration treatment using a flow-type ultrasonic dispersion filtration device. Thus, an alumina dispersion was prepared.

[0091] (2) Composition formulation for forming a magnetic layer (Magnetic liquid) Ferromagnetic powder 100.0 parts Hexagonal barium ferrite powder with an average particle size (average plate diameter) of 21 nm ("BaFe" in Table 1) SO 3 Na group-containing polyurethane resin 14.0 parts Weight average molecular weight: 70,000, SO 3 Na group: 0.2 meq / g Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid) 6.0 parts of the alumina dispersion prepared in (1) above (Silica sol (protrusion-forming agent liquid)) Colloidal silica (average particle size 120 nm) 2.0 parts Methyl ethyl ketone 1.4 parts (Other components) Stearic acid 2.0 parts Stearamide 0.2 parts Butyl stearate 2.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation) 2.5 parts (Solvent-1) Cyclohexanone 200.0 parts 200.0 parts of methyl ethyl ketone (Solvent - 2) 350.0 parts of cyclohexanone 350.0 parts of methyl ethyl ketone

[0092] (3) Formulation of the composition for forming the non - magnetic layer Non - magnetic inorganic powder: 100.0 parts of α - iron oxide Average particle size (average major axis length): 150 nm Average aspect ratio: 7 BET specific surface area: 52 m 2 / g 20.0 parts of carbon black Average particle size: 20 nm SO 3 18.0 parts of Na - group - containing polyurethane resin Weight - average molecular weight: 70,000, SO 3 Na - group: 0.2 meq / g 2.0 parts of stearic acid 0.2 part of stearic acid amide 2.0 parts of butyl stearate 300.0 parts of cyclohexanone 300.0 parts of methyl ethyl ketone

[0093] (4) Preparation of the composition for forming each layer The composition for forming the magnetic layer was prepared by the following method. The magnetic liquid was prepared by dispersing (bead dispersion) the above - mentioned components using a batch - type vertical sand mill for 24 hours. As the dispersion beads, zirconia beads with a bead diameter of 0.5 mm were used. Using the above - mentioned sand mill, the prepared magnetic liquid, the above - mentioned abrasive liquid, silica sol, other components and Solvent - 1 were mixed, introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m / s for 30 minutes, and then treated with a flow - type ultrasonic disperser at a flow rate of 7.5 kg / min for 3 passes. Then, after filtration using a filter with a pore diameter of 0.5 μm, Solvent - 2 was added to prepare the composition for forming the magnetic layer. The composition for forming a non-magnetic layer was prepared by the following method. The above components excluding the lubricants (stearic acid, stearic acid amide, and butyl stearate) were kneaded and diluted by an open kneader, and then dispersed by a horizontal bead mill disperser. Thereafter, the lubricants (stearic acid, stearic acid amide, and butyl stearate) were added, and stirring and mixing were performed with a dissolver stirrer to prepare the composition for forming a non-magnetic layer. The composition for forming a back coat layer was prepared by adding and diluting the following solvents to the composition prepared by the method described for the above non-magnetic layer forming composition. Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

[0094] (5) Method for manufacturing a magnetic tape On the surface of a commercially available polyamide support with a thickness of 3.6 μm, the composition for forming a non-magnetic layer was applied and dried so that the thickness after drying would be 0.7 μm to form a non-magnetic layer. Next, on the surface of the non-magnetic layer, the composition for forming a magnetic layer was applied and dried so that the thickness after drying would be 0.1 μm to form a magnetic layer. Thereafter, on the surface of the support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed, the composition for forming a back coat layer was applied and dried so that the thickness after drying would be 0.5 μm to form a back coat layer. Thereafter, using a calendar roll composed of two metal rolls, surface smoothing treatment (calendering) was performed at a speed of 100 m / min, a linear pressure of 294 kN / m (300 kg / cm), and a calendar temperature (surface temperature of the calendar roll) of 95°C. Then, heat treatment was performed by storing in a heat treatment furnace with an ambient temperature in the furnace of 70°C for 40 hours, and it was wound into a roll shape with a load of 0.3 N applied in the longitudinal direction. After being wound into a roll shape in this way, the magnetic tape master reel (length 5500 m) was subjected to a load application treatment under high temperature and high humidity before slitting by the method described below. After the magnetic tape master roll wound in the above-mentioned roll form was placed in a chamber capable of controlling the internal temperature and humidity, rewinding was performed while applying a load of 3.0 N in the longitudinal direction (in Table 1, "longitudinal applied load") without controlling the temperature and humidity in the chamber. In the state where the temperature and humidity were not controlled, the temperature in the chamber was 25 °C and the relative humidity was 30%. The inside of the chamber in which the magnetic tape master roll wound in a roll form by the above rewinding was placed was heated and humidified to the chamber internal temperature and chamber internal relative humidity shown in Table 1 at the heating rate and humidifying rate shown in Table 1, and then held for 48 hours. Since the above heating and humidifying were performed after rewinding with the above longitudinal applied load, "Yes" was described in the column of "load during chamber heating and humidifying" in Table 1. Next, after rewinding the magnetic tape master roll while applying a load of 0.3 N in the longitudinal direction (in Table 1, "load during chamber cooling and dehumidifying") in the chamber with the chamber internal temperature and chamber internal relative humidity shown in Table 1, the inside of the chamber in which the magnetic tape master roll wound in a roll form by this rewinding was placed was cooled and dehumidified to 25 °C and 30% relative humidity at the cooling rate and dehumidifying rate shown in Table 1. The magnetic tape master roll taken out from the chamber was slit into a width of 1 / 2 inch (1 inch = 0.0254 meters), and a tape cleaning device equipped with a feeding and winding device for the slit product was used to clean the surface of the magnetic layer by attaching a non-woven fabric and a razor blade so as to press against the surface of the magnetic layer. Thereafter, a servo pattern (timing-based servo pattern) having an arrangement and shape conforming to the LTO Ultrium format was formed on the magnetic layer by a commercially available servo writer. In the state where the magnetic tape master roll was wound in a roll shape after the load application treatment under high temperature and high humidity before slitting, the end on the winding reel side of the magnetic tape master roll was called the position of 0 m, and the other end was called the position of 5500 m. When the side from the end at the position of 5500 m toward the end at the position of 0 m was called the inner side and the other was called the outer side, a region having a length of 1100 m extending inward in the longitudinal direction from the position of 5400 m of the magnetic tape after the formation of the above-described servo pattern was cut out to obtain a magnetic tape having a length of 1100 m. This magnetic tape was wound around the reel of a single-reel type magnetic tape cartridge and housed in the magnetic tape cartridge. Thus, the magnetic tape cartridge of Example 1 was manufactured.

[0095] [Examples 2 to 7, Comparative Example 1] A magnetic tape cartridge was manufactured by the method described for Example 1, except that the various items were changed as shown in Table 1. In Examples 3 and 4, the load application treatment under high temperature and high humidity before slitting on the magnetic tape master roll after winding in a roll shape with a load of 0.3 N applied in the longitudinal direction as described for Example 1 was performed as follows. The magnetic tape master roll wound in the above-described roll shape was placed in a chamber capable of controlling the internal temperature and humidity in the chamber, and rewinding was performed while applying a load of 3.0 N (in Table 1, "longitudinal applied load") in the longitudinal direction in a state where the temperature and humidity in the chamber were not controlled. In a state where the temperature and humidity were not controlled, the temperature in the chamber was 25°C and the relative humidity was 30%. After the magnetic tape master reel wound in a roll by the above rewinding was placed in the chamber, the temperature and humidity were raised to the chamber temperature and the relative humidity in the chamber shown in Table 1 at the temperature rising rate and the humidity rising rate shown in Table 1, and then held for 48 hours. Since the above temperature and humidity increase was performed after applying the above longitudinal load and rewinding, "Yes" was described in the column of "Load during temperature and humidity increase in the chamber" in Table 1. After the above holding, the temperature and humidity in the chamber were decreased to 25°C and 30% relative humidity at the temperature decreasing rate and the humidity decreasing rate shown in Table 1, and then the magnetic tape master reel was rewound with a 0.3 N load applied in the longitudinal direction. Since rewinding was not performed before the temperature and humidity decrease, the same value as the "longitudinal applied load" was described in the column of "Load during temperature and humidity decrease in the chamber" in Table 1. For Example 5, the 1100 m long magnetic tape housed in the magnetic tape cartridge was obtained by cutting out a 1100 m long region extending outward in the longitudinal direction from the 100 m position. For Comparative Example 1, the load application treatment under high temperature and high humidity before slitting was not performed.

[0096] For Examples 1 to 7 and Comparative Example 1, two magnetic tape cartridges were produced respectively. One was used for measuring the deformation rate ratio described later, and the other one was used for evaluating the error rate in the drive after storage described later.

[0097] [Method for producing ferromagnetic powder] <Method for producing hexagonal strontium ferrite powder> "SrFe" shown in Table 1 is hexagonal strontium ferrite powder produced by the following method. SrCO 3 of 1707 g, H 3 BO 3 of 687 g, Fe 2 O 3 of 1120 g, Al(OH) 3 of 45 g, BaCO 3 of 24 g, CaCO 3 of 13 g, and Nd 2 O 3 of 235 g were weighed and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390 °C, and while stirring the melt, the outlet provided at the bottom of the platinum crucible was heated, and the melt was discharged in a rod shape at about 6 g / second. The discharged liquid was subjected to rolling and rapid cooling with a water-cooled double roller to produce an amorphous body. 280 g of the produced amorphous body was charged into an electric furnace, heated to 635 °C (crystallization temperature) at a heating rate of 3.5 °C / min, and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was roughly pulverized in a mortar, 1000 g of zirconia beads with a particle size of 1 mm and 800 mL of an acetic acid aqueous solution with a concentration of 1% were added to a glass bottle, and dispersion treatment was performed with a paint shaker for 3 hours. Then, the obtained dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 100 °C for 3 hours to dissolve the glass component, then precipitated with a centrifuge and decantation was repeated for washing, and dried in a heating furnace at a furnace temperature of 110 °C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the hexagonal strontium ferrite powder obtained above was 18 nm, and the activation volume was 902 nm 3 , and the anisotropy constant Ku was 2.2×10 5 J / m 3 , and the mass magnetization σs was 49 A·m 2 / kg. 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by partially dissolving this sample powder under the dissolution conditions exemplified above was performed using an ICP analyzer to determine the surface layer content rate of neodymium atoms. Separately, 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by completely dissolving this sample powder under the dissolution conditions exemplified above was performed using an ICP analyzer to determine the bulk content rate of neodymium atoms. The content rate (bulk content rate) of neodymium atoms with respect to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. Also, the surface layer content rate of neodymium atoms was 8.0 atomic %. The ratio of the surface layer content rate to the bulk content rate, "surface layer content rate / bulk content rate", was 2.8, and it was confirmed that neodymium atoms were unevenly distributed on the surface of the particles.

[0098] That the powder obtained above exhibits the crystal structure of hexagonal ferrite was confirmed by scanning with CuKα rays under the conditions of a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited the crystal structure of magnetoplumbite-type (M-type) hexagonal ferrite. Also, the crystal phase detected by X-ray diffraction analysis was a single phase of the magnetoplumbite type. PANalytical X‘Pert Pro diffractometer, PIXcel detector Soller slits for incident beam and diffracted beam: 0.017 radians Fixed angle of dispersion slit: 1 / 4 degree Mask: 10 mm Anti-scattering slit: 1 / 4 degree Measurement mode: continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0099] <Method for producing ε-iron oxide powder> The "ε-iron oxide" shown in Table 1 is ε-iron oxide powder produced by the following method. Dissolve 8.3 g of iron(III) nitrate nonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg of cobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5 g of polyvinylpyrrolidone (PVP) in 90 g of pure water. While stirring using a magnetic stirrer, add 4.0 g of an aqueous ammonia solution with a concentration of 25% under an air atmosphere at an ambient temperature of 25 °C, and stir for 2 hours while maintaining the temperature condition of 25 °C. To the resulting solution, add an aqueous citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water, and stir for 1 hour. Collect the precipitated powder after stirring by centrifugation, wash it with pure water, and dry it in a heating furnace with a furnace temperature of 80 °C. Add 800 g of pure water to the dried powder and disperse the powder in water again to obtain a dispersion. Raise the temperature of the obtained dispersion to 50 °C, and while stirring, dropwise add 40 g of an aqueous ammonia solution with a concentration of 25%. After stirring for 1 hour while maintaining the temperature of 50 °C, dropwise add 14 mL of tetraethoxysilane (TEOS), and stir for 24 hours. Add 50 g of ammonium sulfate to the obtained reaction solution, collect the precipitated powder by centrifugation, wash it with pure water, and dry it in a heating furnace with a furnace temperature of 80 °C for 24 hours to obtain a precursor of ferromagnetic powder. Load the obtained precursor of ferromagnetic powder into a heating furnace with a furnace temperature of 1000 °C under an air atmosphere, and perform a heat treatment for 4 hours. Put the heat-treated precursor of ferromagnetic powder into an aqueous sodium hydroxide (NaOH) solution with a concentration of 4 mol / L, maintain the liquid temperature at 70 °C, and stir for 24 hours to remove the silicate compound, which is an impurity, from the heat-treated precursor of ferromagnetic powder. After that, collect the ferromagnetic powder from which the silicate compound has been removed by centrifugation, wash it with pure water, and obtain ferromagnetic powder. When the composition of the obtained ferromagnetic powder was confirmed by high-frequency inductively coupled plasma optical emission spectrometry (ICP-OES; Inductively Coupled Plasma-Optical Emission Spectrometry), Ga, Co, and Ti-substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62 O 3) It was. Also, X-ray diffraction analysis was performed under the same conditions as those described above for the method of producing hexagonal strontium ferrite powder. From the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder had a single-phase crystal structure of the ε-phase (crystal structure of ε-iron oxide) that did not contain the crystal structures of the α-phase and γ-phase. The average particle size of the obtained ε-iron oxide powder was 12 nm, and the activation volume was 746 nm 3 , and the anisotropy constant Ku was 1.2×10 5 J / m 3 , and the mass magnetization σs was 16 A·m 2 / kg.

[0100] The activation volume and anisotropy constant Ku of the above hexagonal strontium ferrite powder and ε-iron oxide powder are the values obtained by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) for each ferromagnetic powder. Also, the mass magnetization σs is the value measured at a magnetic field strength of 1194 kA / m (15 kOe) using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[0101] [Evaluation Method] (1) Deformation rate ratio As a measuring device, a measuring device (TDSMS 102H) manufactured by Measurement Analysis Corporation (U.S.A.) was used, and the longitudinal deformation rate and widthwise deformation rate after applying a load in the longitudinal direction of the magnetic tape for 96 hours were determined by the method described above. The measurements of the dimensions in the widthwise and longitudinal directions were performed using a laser scan micrometer attached to the above measuring device. The deformation rate ratio (widthwise deformation rate / longitudinal deformation rate) was calculated from the widthwise deformation rate and longitudinal deformation rate of the magnetic tape thus obtained.

[0102] (2) Reference value: Deformation rate ratio (short-time evaluation) In order to show that the measured value of the phenomenon observed in a short time, generally called Poisson's ratio, is not correlated with the above deformation rate ratio, the deformation rate ratio of short-time evaluation was determined as a reference value by the following method. The measurement was carried out in a measurement environment with an ambient temperature of 32 °C and a relative humidity of 65%. After storing in the storage environment in the measurement by the method described above (1), a tape piece with a length of 600 mm cut from an arbitrary position of the magnetic tape cartridge was set in the measuring device used in the above (1). After 30 minutes had elapsed since the ambient temperature and relative humidity of the environment where this measuring device was installed reached an ambient temperature of 32 °C and a relative humidity of 65%, it was held in a state where a load of 0.2 N was applied in the longitudinal direction of the tape piece. Taking the start point of applying the 0.2 N load as 0 minutes, the dimensions in the width direction and the longitudinal direction of the tape piece when 30 minutes had elapsed were measured by the laser scan micrometer attached to the above measuring device. The dimension in the width direction measured here is taken as the initial value in the width direction "W ref(0) ", and the dimension in the longitudinal direction is taken as the initial value in the longitudinal direction "L ref(0) ". These units are in mm. ref is an abbreviation for reference. After 30 minutes had elapsed since the start of applying the 0.2 N load, while changing the load applied in the longitudinal direction from 0.2 N to 1.0 N at a deformation rate of 20 μm / second, the dimensions in the width direction and the longitudinal direction were measured over time by the laser scan micrometer attached to the above measuring device. The number of measurement points during the above measurement over time was set to 20 points or more. Let the dimension in the width direction of the magnetic tape at time t during the above change in the applied load be W ref(t) , and the dimension in the longitudinal direction be L ref(t) . These units are in mm. Taking time t as a mediating variable, for the group of (X, Y) = (L ref(t) / L ref(0) , W ref(t) / W ref(0) ), the value of a when performing the least squares calculation with a linear equation of Y = a×X + b was taken as the deformation rate ratio for the short-time evaluation of the reference value.

[0103] (3) Error rate evaluation in the drive after storage Each of the magnetic tape cartridges of Examples 1 to 7 and Comparative Example 1 was set in a drive (magnetic recording and reproducing apparatus), and while performing head tracking using a servo signal so that the winding stress in the longitudinal direction of the tape (tension applied per cross-sectional area of the tape) became 6 MPa (megapascal), a signal was recorded in the longitudinal direction of the magnetic tape, and the error rate at the time of this recording was measured by a measuring device attached to the drive. The magnetic tape cartridge containing the magnetic tape after the above recording was stored for 3 months in a storage environment of an ambient temperature of 32°C and a relative humidity of 65%, and then set again in a drive (magnetic recording and reproducing apparatus), and the magnetic tape was run in the drive so that the winding stress in the longitudinal direction of the tape became 6 MPa, and the signal recorded on the magnetic tape was reproduced while performing head tracking using a servo signal, and the error rate at the time of this reproduction was measured by a measuring device attached to the drive. In Table 1, when an increase in the error rate was observed in the running after storage compared to before storage, it was described as "with increase", and when no increase in the error rate was observed compared to before storage, it was described as "without increase".

[0104] The above results are shown in Table 1.

[0105]

Table 1

[0106] From the results shown in Table 1, in Examples 1 to 7, it was confirmed that in the reproduction of data on the magnetic tape after storage, the data recorded before storage could be reproduced well while suppressing the occurrence of reproduction failure. With such a magnetic tape, even in the recording of data after storage, it is possible to perform good recording while suppressing the occurrence of recording failures such as overwriting of the data recorded before storage. In addition, from the comparison between the deformation rate ratio shown in Table 1 and the reference value (deformation rate ratio of short-time evaluation), it was confirmed that the deformation rate ratio shown in Table 1 has no correlation with the reference value.

Industrial Applicability

[0107] One aspect of the present invention is useful in various data storage applications such as data backup and archiving.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the non-magnetic support is a polyamide support, and the deformation rate ratio, width direction deformation rate / longitudinal direction deformation rate, of the magnetic tape measured after applying a load of 0.55 N in the longitudinal direction of the magnetic tape for 96 hours in a measurement environment of an ambient temperature of 32 ° C and a relative humidity of 65% is 0.45 or less, wherein the width direction deformation rate and the longitudinal direction deformation rate are measured by applying a load of 0.20 N in the longitudinal direction of the magnetic tape. Magnetic tape.

2. The magnetic tape according to claim 1, wherein the deformation rate ratio is 0.15 or more and 0.45 or less.

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

4. The magnetic tape according to any one of claims 1 to 3, further having a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support.

5. The magnetic tape according to any one of claims 1 to 4, wherein the ferromagnetic powder is hexagonal barium ferrite powder.

6. The magnetic tape according to any one of claims 1 to 4, wherein the ferromagnetic powder is hexagonal strontium ferrite powder.

7. The magnetic tape according to any one of claims 1 to 4, wherein the ferromagnetic powder is ε-iron oxide powder.

8. A magnetic tape cartridge including the magnetic tape according to any one of claims 1 to 7.

9. A magnetic recording and reproducing apparatus including the magnetic tape according to any one of claims 1 to 7.

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