Magnetic tape, magnetic tape cartridge and magnetic tape device

Abstract

To provide a magnetic tape that hardly deteriorates in electromagnetic conversion characteristics even if it is repeatedly run in a high-temperature environment.SOLUTION: A magnetic tape has a non-magnetic support and a magnetic layer containing ferromagnetic powder. The amount of fluid lubricant extracted from a surface of the magnetic layer after sliding on a magnetic head in an environment with a temperature of 60°C ± 1°C and relative humidity of 10% is 50% or more of the amount of fluid lubricant extracted from the surface of the magnetic layer before sliding based on the mass. A magnetic tape cartridge and a magnetic tape device include 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 tape device. [Background technology]

[0002] 2. Description of the Related Art In recent years, magnetic recording media have come into widespread use as recording media for recording various types of data (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-239575 A [Patent Document 2] JP 2012-014809 A Summary of the Invention [Problem to be solved by the invention]

[0004] Magnetic recording media include tape-type and disk-type magnetic recording media, and tape-type magnetic recording media, that is, magnetic tapes, are primarily used for data storage applications such as data backup and archiving.

[0005] In Patent Document 1, studies are carried out to make a magnetic recording medium suitable for use in a low-temperature environment (see paragraphs 0004 and 0005 of Patent Document 1).

[0006] In response to this, the present inventors have investigated the use of magnetic tapes in high-temperature environments. This is for the following reasons. Magnetic tapes used for data storage purposes are sometimes used in temperature-controlled data centers. Meanwhile, data centers are required to save power in order to reduce costs. In order to save power, it is desirable to be able to relax the temperature control conditions in data centers from the current level, or to make such control unnecessary. However, if the temperature control conditions are relaxed or no control is performed, it is expected that the magnetic tapes will be exposed to high temperatures.

[0007] Regarding the above point, the inventor's research has revealed that in a high-temperature environment (for example, an extremely high-temperature environment with an ambient temperature of 40° C. or higher, or even 60° C. or higher), when a magnetic tape is repeatedly run to record data on the magnetic tape and / or to reproduce data recorded on the magnetic tape, the electromagnetic conversion characteristics tend to be easily degraded. Neither Patent Document 1 nor Patent Document 2 makes any mention of such a tendency regarding the use of magnetic tape in a high-temperature environment.

[0008] An object of one aspect of the present invention is to provide a magnetic tape whose electromagnetic conversion characteristics are less deteriorated even when repeatedly run in a high-temperature environment. [Means for solving the problem]

[0009] One aspect of the present invention is A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, a magnetic tape in which the amount of fluid lubricant extracted from the surface of the magnetic layer after sliding with a magnetic head in an environment of a temperature of 60° C.±1° C. and a relative humidity of 10% is 50% or more, by mass, of the amount of fluid lubricant extracted from the surface of the magnetic layer before the sliding; Regarding.

[0010] In one embodiment, the magnetic tape can further include a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0011] In one embodiment, the non-magnetic powder of the non-magnetic layer can be a non-magnetic powder selected from the group consisting of carbon black and non-magnetic iron oxide powder.

[0012] In one embodiment, the fluid lubricant may include a fluid lubricant that satisfies at least one of the following (1) and (2). (1) Boiling point is 400°C or higher (2) Molecular weight of 400 or more

[0013] In one embodiment, the fluid lubricant that satisfies at least one of the above (1) and (2) can be a fatty acid ester.

[0014] In one embodiment, the fluid lubricant that satisfies at least one of the above (1) and (2) can be a carbonate ester.

[0015] In one embodiment, the fluid lubricant that satisfies at least one of the above (1) and (2) can be an organic amine.

[0016] In one embodiment, the magnetic tape can further have a backcoat layer containing a nonmagnetic powder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer.

[0017] One aspect of the present invention relates to a magnetic tape cartridge including the above-mentioned magnetic tape.

[0018] One aspect of the present invention relates to a magnetic tape device including the above-mentioned magnetic tape. Effect of the Invention

[0019] According to one aspect of the present invention, it is possible to provide a magnetic tape whose electromagnetic conversion characteristics deteriorate little even when repeatedly run in a high-temperature environment, as well as a magnetic tape cartridge and a magnetic tape device including this magnetic tape. [Brief description of the drawings]

[0020] [Figure 1]An example of a device used for sliding a magnetic tape and a magnetic head is shown. [Diagram 2] 2 shows an example of the arrangement of data bands and servo bands. [Diagram 3] An example of servo pattern arrangement on an LTO (Linear Tape-Open) Ultrium format tape is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] [Magnetic tape] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, in which the amount of fluid lubricant extracted from the surface of the magnetic layer after sliding with a magnetic head in an environment of a temperature of 60° C.±1° C. and a relative humidity of 10% is 50% or more by mass of the amount of fluid lubricant extracted from the surface of the magnetic layer before the sliding. The magnetic tape will be described in more detail below. Note that the above environment is used as an example of a high temperature environment, and the magnetic tape is not limited to being used in the above environment.

[0022] <Extracted amount of fluid lubricant> In the present invention and this specification, the term "fluid lubricant" refers to a compound selected from the group consisting of fatty acid esters, carbonate esters, organic amines and fluorine-containing compounds.

[0023] In the present invention and this specification, the amount of fluid lubricant extracted from the surface of the magnetic layer before and after the sliding is determined by the following method. The amount of fluid lubricant extracted is a value based on mass. Hereinafter, the amount of fluid lubricant extracted from the surface of the magnetic layer before the sliding is also referred to as the "amount of fluid lubricant extracted before sliding", and the amount of fluid lubricant extracted from the surface of the magnetic layer after the sliding is also referred to as the "amount of fluid lubricant extracted after sliding". In addition, in the present invention and this specification, the "surface of the magnetic layer" is synonymous with the surface of the magnetic layer side of the magnetic tape.

[0024] (Tape sample preparation) A 5 cm long tape sample and a 100 m long tape sample are cut out from any position in the longitudinal direction of the magnetic tape to be measured.

[0025] (Amount of fluid lubricant extracted before sliding) The above 5 cm long tape sample is heated and immersed in 30 mL of methanol at 60°C (liquid temperature) for 3 hours. If the magnetic tape has a backcoat layer as described below, the backcoat layer is removed by a known method at any stage before the above heat immersion, and the tape sample from which the backcoat layer has been removed is subjected to the above heat immersion. This point is also applied when determining the amount of fluid lubricant after extraction. The components extracted into methanol by the above-mentioned heat immersion are qualitatively and quantitatively analyzed by gas chromatography after evaporating the methanol. The content of the components classified as fluid lubricants in the present invention and this specification contained in the above-mentioned extracted components is obtained by such analysis. The content thus obtained is the amount of fluid lubricant extracted before sliding. When two or more components classified as fluid lubricants in the present invention and this specification are detected by the above-mentioned qualitative analysis, the total content of the two or more components is the amount of fluid lubricant extracted before sliding. This point is also the same for the amount of fluid lubricant extracted after sliding described below.

[0026] (Sliding between magnetic tape and magnetic head) A reel tester having two tape reels is used to slide the magnetic head over the surface of the magnetic layer of the 100 m long tape sample. The reel tester may be a commercially available product or one assembled by a known method. As an example, FIG. 1 shows an example of a device used to slide the magnetic tape over the magnetic head. The magnetic tape and magnetic head are slid against each other in an environment with an ambient temperature of 60°C ± 1°C and a relative humidity of 10%. The tape sample is attached to a reel tester with one end of the tape sample secured to one tape reel of the reel tester and the other end of the tape sample secured to the other tape reel of the reel tester. An LTO (Linear Tape-Open) 8 head is used as the magnetic head attached to the reel tester. In the present invention and this specification, the term "LTO8 head" refers to a magnetic head conforming to the LTO8 standard. As the LTO8 head, a magnetic head mounted on an LTO8 drive may be removed and used, or a magnetic head commercially available as a magnetic head for an LTO8 drive may be used. Here, the term "LTO8 drive" refers to a drive (magnetic tape device) conforming to the LTO8 standard. This also applies to drives of other generations. For example, an "LTO9 drive" refers to a drive conforming to the LTO9 standard. In addition, the LTO8 head is adopted as the magnetic head for the sliding, taking into consideration that the LTO8 standard is a standard that can accommodate the recent trend toward high density recording, and the magnetic tape is not limited to that used in an LTO8 drive. Data may be recorded and / or reproduced on the magnetic tape in an LTO8 drive, an LTO9 drive or a drive of a later generation, or a drive of an earlier generation than LTO8, such as an LTO7. The above tape sample is run in a reel tester, and the surface of the magnetic layer is brought into contact with the magnetic head and slid. The running conditions for the magnetic tape (above tape sample) are as follows. The tension values ​​applied in the longitudinal direction of the magnetic tape and the running speed of the magnetic tape are the settings for the reel tester. Regarding units, "gf" is gram force, and 1 N (Newton) is approximately 102 gf. Magnetic tape running speed: 4m / sec Tension applied to magnetic tape in the longitudinal direction: 100gf Magnetic tape travel passes: 20,000 single passes Wrap angle θ: 1°

[0027] (amount of fluid lubricant extracted after sliding) After the sliding, one end of the tape sample is set at 0 (zero) m in length and the other end at 100 m in length, and a 5 cm tape sample is cut out from any position between 25 m and 75 m in the longitudinal direction. The cut tape sample is immersed in 30 mL of methanol at 60°C (liquid temperature) for 3 hours. The components extracted into methanol by the above-mentioned heat soaking are qualitatively and quantitatively analyzed by gas chromatography after evaporating the methanol. By such analysis, the content of the components classified as fluid lubricants in the present invention and this specification contained in the above-mentioned extracted components is determined. The content thus determined is the amount of fluid lubricant extracted after sliding.

[0028] <Fluid lubricant remaining rate> In the magnetic tape, the amount of fluid lubricant extracted from the surface of the magnetic layer after sliding with a magnetic head in an environment of a temperature of 60°C ± 1°C and a relative humidity of 10% is 50% or more by mass of the amount of fluid lubricant extracted from the surface of the magnetic layer before the sliding. That is, for the magnetic tape, the value calculated from the amount of fluid lubricant extracted before sliding and the amount of fluid lubricant extracted after sliding obtained by the above method as "(amount of fluid lubricant extracted after sliding / amount of fluid lubricant extracted before sliding) x 100" is 50% or more. This value is referred to as the "fluid lubricant residual rate." In the magnetic tape, the residual rate of the fluid lubricant is 50% by mass or more. As a result of intensive research by the present inventor, it has been newly discovered that, with such a magnetic tape, the deterioration of the electromagnetic conversion characteristics can be suppressed even if the magnetic tape is repeatedly run in a high-temperature environment. This point will be further explained below. Recording data on a magnetic tape and reproducing the recorded data are usually performed by running the magnetic tape and contacting and sliding the magnetic head with the magnetic layer surface. When a large amount of deposits are generated on the magnetic head due to contact and sliding with the magnetic layer surface by repeatedly running the magnetic tape, the deposits cause spacing loss and the electromagnetic conversion characteristics are deteriorated. In this regard, it is considered that the fluid lubricant can play a role in suppressing the generation of deposits (called debris) on the magnetic head by dissipating the heat of running. However, it is presumed that when the magnetic tape is repeatedly run in a higher temperature environment (for example, an ambient temperature of 40°C or higher, or even a harsh high-temperature environment of 60°C or higher) than the environment in which the magnetic tape was mainly used in the past, the fluid lubricant is more likely to be depleted from the magnetic layer surface compared to running in the mainly used environment in the past, and as a result, debris is more likely to be generated. In response to this, the present inventor has newly found, as a result of intensive research, that a magnetic tape with a fluid lubricant remaining rate of 50% by mass or more determined by the method described above has little deterioration in electromagnetic conversion characteristics even when repeatedly run in a high-temperature environment. This is believed to be because depletion of the fluid lubricant during repeated running in a high-temperature environment is suppressed. However, the above includes the speculations of the inventors, and the present invention is not limited to the speculations described in this specification.

[0029] The fluid lubricant residual rate of the magnetic tape is 50% or more, and from the viewpoint of further suppressing the deterioration of the electromagnetic conversion characteristics during repeated running in a high temperature environment, it is preferably 52% or more, more preferably 55% or more, and further preferably 57% or more, 60% or more, 62% or more, 65% or more, 67% or more, 70% or more, 72% or more, 75% or more, 77% or more, 80% or more, 82% or more, and 85% or more in that order. In addition, the fluid lubricant residual rate of the magnetic tape can be 100% or less or less than 100%, for example, 99% or less, 98% or less, or 95% or less. For the reasons described above, the higher the fluid lubricant residual rate of the magnetic tape, the more preferable it is.

[0030] The present inventors have conducted extensive research and have come to the following findings regarding control of the residual rate of fluid lubricant on magnetic tapes.

[0031] The use of a fluid lubricant that satisfies at least one of the following (1) and (2) can contribute to increasing the fluid lubricant residual rate. Such a fluid lubricant is unlikely to volatilize in a high-temperature environment, and it is believed that it is possible to suppress volatilization or to suppress the amount of volatilization to a small amount during driving in a high-temperature environment. (1) Boiling point is 400°C or higher (2) Molecular weight of 400 or more

[0032] In the present invention and this specification, the "boiling point" refers to the equilibrium reflux boiling point as defined in JIS K 2233:2017, and is determined according to JIS K 2233:2017. The boiling point of the fluid lubricant that satisfies the above (1) is preferably 420°C or higher, more preferably 450°C or higher, and even more preferably 470°C or higher. The boiling point of the fluid lubricant that satisfies the above (1) can be, for example, 700°C or lower, 650°C or lower, or 600°C or lower, or can exceed the values ​​exemplified here.

[0033] In the present invention and this specification, the "molecular weight" of a fluid lubricant is the molecular weight calculated from the structural formula for a monomeric fluid lubricant. For a polymeric fluid lubricant (including homopolymer and copolymer), it refers to the number average molecular weight. The number average molecular weight is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene equivalent. The GPC measurement conditions include the following conditions, and the number average molecular weight of the fluid lubricant shown in the examples below is a value obtained under the following conditions. Measuring instrument: HLC-8320GPC (Tosoh Corporation) Column: 3 TSKgel Super AWM-H (Tosoh Corporation) Eluent: N-methyl-2-pyrrolidone (with 10 mM lithium bromide as an additive) Flow rate: 0.35mL / min Column temperature: 40℃ Detector: Refractive Index (RI) detector

[0034] The molecular weight of the fluid lubricant satisfying the above (2) is 420 or more, more preferably 450 or more, even more preferably 470 or more, and even more preferably 500 or more. The molecular weight of the fluid lubricant satisfying the above (2) can be, for example, 700 or less, 650 or less, or 600 or less, or can exceed the values ​​exemplified herein.

[0035] As previously described, the "fluid lubricant" of the present invention and herein is a compound selected from the group consisting of fatty acid esters, carbonate esters, organic amines and fluorine-containing compounds. Examples of the fatty acid ester include mono-, di- or tri-fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, etc. The fatty acid esters also include those containing a branched structure and / or an unsaturated bond. Carbonate ester is R 1 OC(=O)-OR 2 R 1 and R 2 each independently represents a substituent, and such a substituent can be a linear saturated hydrocarbon group or a saturated hydrocarbon group containing a branched structure. The organic amine includes organic primary amine, organic secondary amine, and organic tertiary amine, preferably organic secondary amine and organic tertiary amine, more preferably organic tertiary amine. The organic tertiary amine is preferably a trialkylamine. The alkyl group of the trialkylamine is preferably an alkyl group having 1 to 18 carbon atoms. The three alkyl groups of the trialkylamine may be the same or different. In addition, polyalkyleneimine is also preferable as the organic amine. Polyalkyleneimine is a polymer that can be obtained by ring-opening polymerization of alkyleneimine. An example of the alkyleneimine is ethyleneimine. For example, a polyalkyleneimine obtained by ring-opening polymerization of ethyleneimine is polyethyleneimine. The fluorine-containing compound is a compound containing one or more fluorine atoms (F) per molecule, and specific examples include fluoroalkyl carboxylates, etc. Examples of the fluoroalkyl carboxylates include perfluoroalkyl carboxylates in which all hydrogen atoms constituting the alkyl group are substituted with fluorine atoms. The fluid lubricant extracted from the magnetic tape by the method described above preferably contains one or more selected from the group consisting of fatty acid esters satisfying at least one of the above (1) and (2); carbonate esters satisfying at least one of the above (1) and (2); organic amines satisfying at least one of the above (1) and (2); and fluorine-containing compounds satisfying at least one of the above (1) and (2). Specific examples of the fluid lubricant include the fluid lubricants used in the examples described below, but the fluid lubricant contained in the magnetic tape is not limited to these specific examples.

[0036] For example, for a magnetic tape having a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, it is preferable to include one or more fluid lubricants satisfying at least one of the above (1) and (2) in the non-magnetic layer forming composition and / or the magnetic layer forming composition, and it is more preferable to include one or more fluid lubricants satisfying at least one of the above (1) and (2) in the non-magnetic layer forming composition. When preparing the non-magnetic layer forming composition, the fluid lubricant is added in an amount of preferably 0.2 to 7.0 parts by mass, more preferably 1.0 to 4.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder. In one embodiment, only one nonmagnetic layer can be formed on the nonmagnetic support, and in another embodiment, two or more nonmagnetic layers can be formed on the nonmagnetic support. When two or more nonmagnetic layers are formed on the nonmagnetic support, these nonmagnetic layers can be formed using a nonmagnetic layer forming composition having the same composition in one embodiment, and can be formed using a nonmagnetic layer forming composition having different compositions in another embodiment. In either embodiment, the total amount of the fluid lubricant added to the nonmagnetic layer forming composition can be a fluid lubricant that satisfies at least one of the above (1) and (2). In another embodiment, a part of the fluid lubricant added to the nonmagnetic layer forming composition can be a fluid lubricant that satisfies at least one of the above (1) and (2). In this case, the fluid lubricant that satisfies at least one of the above (1) and (2) preferably accounts for 30% or more by mass, and more preferably accounts for 50% or more (for example, 50% to 90%) of the total amount of the fluid lubricant contained in the nonmagnetic layer forming composition. In addition, when two or more nonmagnetic layers are formed on a nonmagnetic support, in one embodiment, all of the nonmagnetic layer-forming compositions for forming these nonmagnetic layers can contain a fluid lubricant that satisfies at least one of the above (1) and (2). In another embodiment, the nonmagnetic layer-forming compositions for forming some of the nonmagnetic layers can contain no fluid lubricant that satisfies at least one of the above (1) and (2), and the nonmagnetic layer-forming compositions for forming the other nonmagnetic layers can contain a fluid lubricant that satisfies at least one of the above (1) and (2).

[0037] Regarding the control of the residual rate of the fluid lubricant in the magnetic tape, for the magnetic tape having a non-magnetic layer, the higher the filling rate of the non-magnetic powder in the non-magnetic layer, the less space the fluid lubricant can be present in the non-magnetic layer. In such a magnetic tape, when the composition for forming the non-magnetic layer applied on the non-magnetic support dries and / or at the beginning of the running of the magnetic tape, the fluid lubricant is likely to migrate out of the non-magnetic layer, and as a result, it is presumed that the amount of fluid lubricant removed from the surface of the magnetic layer by sliding with the magnetic head at the beginning of the running becomes large. In contrast, forming a non-magnetic layer using a non-magnetic powder that can appropriately control the filling rate of the non-magnetic powder in the non-magnetic layer can contribute to increasing the residual rate of the fluid lubricant in the magnetic tape. From this point of view, the preferred non-magnetic powder will be described later.

[0038] By the way, when manufacturing magnetic tape, magnetic layer can be formed by directly applying magnetic layer forming composition on the surface of non-magnetic support, or by applying it in layers successively or simultaneously with non-magnetic layer forming composition.Here, adopting successive coating as coating method can contribute to increasing the residual rate of fluid lubricant in magnetic tape.It is presumed that this is because, compared with simultaneous multi-layer coating, successive coating can suppress the migration of fluid lubricant from non-magnetic layer to magnetic layer formed on non-magnetic layer.

[0039] The residual rate of the fluid lubricant on the magnetic tape can be controlled to 50% or more by, for example, combining the above control means.

[0040] The magnetic tape will now be described in more detail.

[0041] <Magnetic layer> (Ferromagnetic powder) As the ferromagnetic powder contained in the magnetic layer, one or more of the ferromagnetic powders known as ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. It is preferable to use a ferromagnetic powder with a small average particle size from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0042] Regarding the particle size of the ferromagnetic powder, the average particle volume can be used as an index of the particle size. From the viewpoint of improving the recording density, the average particle volume is set to 2500 nm 3 Preferably, it is 2300 nm or less. 3 More preferably, it is 2000 nm or less. 3 More preferably, it is 1500 nm or less. 3 From the viewpoint of magnetization stability, the average particle volume of the ferromagnetic powder is preferably 500 nm or less. 3 It is preferable that the thickness is 600 nm or more. 3 More preferably, it is 650 nm or more. 3 More preferably, it is 700 nm or more. 3 The above average particle volume is a value determined as a sphere-equivalent volume from an average particle size determined by a method described below.

[0043] Hexagonal Ferrite Powder A preferred specific example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, see, for example, JP2011-225417A, paragraphs 0012-0030, JP2011-216149A, paragraphs 0134-0136, JP2012-204726A, paragraphs 0013-0030, and JP2015-127985A, paragraphs 0029-0084.

[0044] In the present invention and this specification, the term "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to a structure to which the most intense diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when the most intense diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to a hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure has been detected as the main phase. When only a single structure is detected by X-ray diffraction analysis, the detected structure is regarded as the main phase. The hexagonal ferrite type crystal structure contains at least an iron atom, a divalent metal atom, and an oxygen atom as constituent atoms. The divalent metal atom is a metal atom that can become a divalent cation as an ion, and examples of such include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and this specification, the hexagonal strontium ferrite powder refers to a powder in which the main divalent metal atom contained therein is a strontium atom, and the hexagonal barium ferrite powder refers to a powder in which the main divalent metal atom contained therein is a barium atom. The main divalent metal atom refers to the divalent metal atom that is the most abundant of the divalent metal atoms contained in the powder on an atomic % basis. However, the above divalent metal atoms do not include rare earth atoms. In the present invention and this specification, the "rare earth atom" is selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanoid atoms. The lanthanide atom is selected from the group consisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), a europium atom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), a ytterbium atom (Yb), and a lutetium atom (Lu).

[0045] Hereinafter, hexagonal strontium ferrite powder, which is one form of hexagonal ferrite powder, will be described in more detail.

[0046] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm 3 The finely divided hexagonal strontium ferrite powder having an 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 For example, 850 nm or more. 3 From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder can be 1500 nm or more. 3 More preferably, it is 1400 nm or less. 3 More preferably, it is 1300 nm or less. 3 More preferably, it is 1200 nm or less. 3 More preferably, it is equal to or less than 1100 nm. 3 It is even more preferable that the activation volume of the hexagonal barium ferrite powder is equal to or less than 1000 nm. The same is true for the activation volume of the hexagonal barium ferrite powder.

[0047] "Activation volume" is a unit of magnetization reversal and is an index showing the magnetic size of a particle. The activation volume described in this invention and this specification and the anisotropy constant Ku described below are values ​​obtained by measuring the coercive force Hc measurement section at magnetic field sweep speeds of 3 minutes and 30 minutes (measurement temperature: 23°C ± 1°C) using a vibrating sample magnetometer and calculating from the following relationship between Hc and activation volume V. The unit of the anisotropy constant Ku is 1 erg / cc = 1.0 x 10 -1 J / m 3 It is. Hc=2Ku / Ms{1-[(kT / KuV)ln(At / 0.693)] 1 / 2} [In the above formula, Ku: anisotropy constant (unit: J / m 3 ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activation volume (unit: cm 3), A: spin precession frequency (unit: s -1 ), t: magnetic field reversal time (unit: s)]

[0048] The anisotropy constant Ku can be used as an index of reduction in thermal fluctuation, in other words, improvement in thermal stability. The hexagonal strontium ferrite powder is preferably 1.8×10 5 J / m 3 More preferably, the Ku is 2.0×10 or more. 5 J / m 3 The Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 5 J / m 3 However, since a higher Ku value means higher thermal stability and is preferable, the Ku value is not limited to the above-mentioned values.

[0049] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are contained at a content (bulk content) of 0.5 to 5.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have uneven distribution of rare earth atoms in the surface layer portion. In the present invention and this specification, the term "surface distribution of rare earth atoms" refers to the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by partially dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "surface content of rare earth atoms" or simply "surface content" for rare earth atoms), which is greater than the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by completely dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "bulk content of rare earth atoms" or simply "bulk content" for rare earth atoms), Rare earth atom surface content / rare earth atom bulk content>1.0 The rare earth atom content of the hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. The rare earth atom surface layer content satisfying the ratio of "rare earth atom surface layer content / rare earth atom bulk content>1.0" means that the rare earth atoms are unevenly distributed (i.e., more present in the surface layer) in the particles constituting the hexagonal strontium ferrite powder. In the present invention and this specification, the surface layer refers to a portion of the region extending from the surface of the particles constituting the hexagonal strontium ferrite powder toward the inside.

[0050] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic % relative to 100 atomic % of iron atoms. It is considered that the rare earth atoms contained in the bulk content in the above range and the rare earth atoms unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder contribute to suppressing the decrease in the reproduction output during repeated reproduction. This is presumed to be because the hexagonal strontium ferrite powder contains rare earth atoms in the bulk content in the above range and the rare earth atoms unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in the reproduction output during repeated reproduction can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the surface layer of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of the iron (Fe) sites in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. In addition, it is presumed that using the hexagonal strontium ferrite powder having rare earth atom uneven distribution on the surface as the ferromagnetic powder of the magnetic layer also contributes to suppressing the wear of the magnetic layer surface due to sliding with the magnetic head. That is, it is presumed that the hexagonal strontium ferrite powder having rare earth atom uneven distribution on the surface can also contribute to improving the running durability of the magnetic tape. This is presumed to be because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surface and the organic substance (e.g., binder and / or additive) contained in the magnetic layer, and as a result, the strength of the magnetic layer is improved. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic %, even more preferably in the range of 1.0 to 4.5 atomic %, and even more preferably in the range of 1.5 to 4.5 atomic %.

[0051] The bulk content is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the content of an atom refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one rare earth atom as a rare earth atom, or may contain two or more rare earth atoms. When two or more rare earth atoms are contained, the bulk content is obtained for the total of two or more rare earth atoms. This point is the same for other components in the present invention and this specification. That is, unless otherwise specified, a certain component may be used in only one type or in two or more types. When two or more types are used, the content or content refers to the total of two or more types.

[0052] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained therein may be any one or more of rare earth atoms. From the viewpoint of further suppressing the decrease in the reproduction output during repeated reproduction, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms and dysprosium atoms, more preferred are neodymium atoms, samarium atoms and yttrium atoms, and even more preferred are neodymium atoms.

[0053] In the hexagonal strontium ferrite powder having rare earth atom uneven distribution in the surface layer, the rare earth atoms may be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for the hexagonal strontium ferrite powder having rare earth atom uneven distribution in the surface layer, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms obtained by complete dissolution under the dissolution conditions described below, "surface content / bulk content", is more than 1.0 and can be 1.5 or more. The "surface content / bulk content" being greater than 1.0 means that the rare earth atoms are unevenly distributed in the surface layer (i.e., more than in the interior) in the particles constituting the hexagonal strontium ferrite powder. In addition, the ratio of the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface layer content / bulk content", can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in a hexagonal strontium ferrite powder having rare earth atom surface layer uneven distribution, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface layer content / bulk content" is not limited to the upper or lower limit exemplified.

[0054] The partial and total dissolution of hexagonal strontium ferrite powder will be described below. For hexagonal strontium ferrite powder present as powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution, and the other part is subjected to total dissolution. The hexagonal strontium ferrite powder can be taken out from the magnetic layer by, for example, the method described in paragraph 0032 of JP 2015-91747 A. The above-mentioned partial dissolution means that the hexagonal strontium ferrite powder is dissolved to such an extent that the remaining powder can be visually confirmed in the liquid at the end of dissolution. For example, the partial dissolution can dissolve a region of 10 to 20 mass% of the particles constituting the hexagonal strontium ferrite powder, with the whole particles being 100 mass%. On the other hand, the above-mentioned complete dissolution means that the hexagonal strontium ferrite powder is dissolved to such an extent that the remaining powder cannot be visually confirmed in the liquid at the end of dissolution. The partial dissolution and the surface layer content are measured, for example, by the following method. Note that the dissolution conditions such as the amount of sample powder are merely examples, and any dissolution conditions that allow partial or complete dissolution can be used. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is placed on a hot plate set at 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms relative to 100 atomic % of iron atoms can be determined. When multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. This is also true for the measurement of bulk content. On the other hand, the total dissolved and bulk contents are measured, for example, by the following method. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is placed on a hot plate set at 80° C. for 3 hours. After that, the bulk content relative to 100 atomic % of iron atoms can be calculated by carrying out the same procedure as the partial dissolution and surface layer content measurement described above.

[0055] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, hexagonal strontium ferrite powder that contains rare earth atoms but does not have uneven distribution of rare earth atoms in the surface layer has a tendency to have a significantly lower σs than hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder that has uneven distribution of rare earth atoms in the surface layer is considered to be preferable in terms of suppressing such a large decrease in σs. In one embodiment, the σs of the hexagonal strontium ferrite powder is 45 A·m 2 / kg or more, and 47A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, σs is 80A·m 2 / kg or less, and 60A·m 2 / kg or less. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. 1 [kOe]=10 6 / 4π[A / m].

[0056] Regarding the content (bulk content) of the constituent atoms of the hexagonal strontium ferrite powder, the strontium atom content can be, for example, in the range of 2.0 to 15.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the divalent metal atoms contained in the hexagonal strontium ferrite powder can be only strontium atoms. In another embodiment, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to strontium atoms. For example, it can contain barium atoms and / or calcium atoms. When divalent metal atoms other than strontium atoms are contained, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can each be, for example, in the range of 0.05 to 5.0 atomic % relative to 100 atomic % of iron atoms.

[0057] Known crystal structures of hexagonal ferrite include magnetoplumbite type (also called "M type"), W type, Y type, and Z type. The hexagonal strontium ferrite powder may have any of the crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may be one in which a single crystal structure or two or more types of crystal structures are detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder may be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe 12 O 19Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is of the M type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms, the strontium atom (Sr) accounts for the largest proportion on an atomic % basis as described above. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least an iron atom, a strontium atom, and an oxygen atom, and may further contain a rare earth atom. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain an aluminum atom (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % relative to 100 atomic % of iron atoms. From the viewpoint of further suppressing the decrease in the reproduction output during repeated reproduction, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic % or less, more preferably in the range of 0 to 5.0 atomic %, relative to 100 atomic % of iron atoms, and may be 0 atomic %. That is, in one embodiment, the hexagonal strontium ferrite powder may not contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic % above is obtained by converting the content (unit: mass %) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic % using the atomic weight of each atom. In addition, in the present invention and this specification, "not containing" a certain atom means that the content measured by an ICP analyzer after completely dissolving is 0 mass %. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above term "free" is used to mean that the content is below the detection limit of the ICP analyzer.In one form, the hexagonal strontium ferrite powder can be one that does not contain bismuth atoms (Bi).

[0058] metal powder A specific preferred example of the ferromagnetic powder is a ferromagnetic metal powder. For details of the ferromagnetic metal powder, reference can be made to, for example, paragraphs 0137 to 0141 of JP 2011-216149 A and paragraphs 0009 to 0023 of JP 2005-251351 A.

[0059] ε-iron oxide powder A preferred specific example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, the term "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as the main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to an ε-iron oxide type crystal structure, it is determined that the ε-iron oxide type crystal structure is detected as the main phase. Known methods for producing ε-iron oxide powder include a method of producing it from goethite and a reverse micelle method. All of the above production methods are publicly known. In addition, for a method for producing ε-iron oxide powder in which a part of Fe is replaced by a substitution atom such as Ga, Co, Ti, Al, or Rh, reference can be made to, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp.5200-5206, etc. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method given here.

[0060] The activation volume of the ε-iron oxide powder is preferably 300 to 1500 nm 3 The finely divided ε-iron oxide powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm 3For example, 500 nm or more. 3 From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder can be 1400 nm or more. 3 More preferably, it is 1300 nm or less. 3 More preferably, it is 1200 nm or less. 3 More preferably, it is equal to or less than 1100 nm. 3 It is even more preferred that:

[0061] The anisotropy constant Ku can be used as an index of the reduction in thermal fluctuation, in other words, the improvement in thermal stability. The ε-iron oxide powder is preferably 3.0×10 4 J / m 3 More preferably, the Ku is 8.0×10 or more. 4 J / m 3 The Ku of the ε-iron oxide powder can be, for example, 3.0×10 5 J / m 3 However, since a higher Ku value means higher thermal stability and is preferable, the Ku value is not limited to the above-mentioned values.

[0062] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, in one embodiment, the σs of the ε-iron oxide powder is 8 A m 2 / kg or more, and 12 A m 2 On the other hand, the σs of ε-iron oxide powder is 40 A m 2 / kg or less, and 35A·m 2 It is more preferable that the amount is not more than 1 / kg.

[0063] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope. The powder is photographed at a magnification of 100,000 times using a transmission electron microscope, and a photograph of the particles that make up the powder is obtained by printing it on photographic paper or displaying it on a display so that the total magnification is 500,000 times. From the obtained particle photograph, the target particle is selected, and the particle outline is traced with a digitizer to measure the particle (primary particle) size. Primary particles are independent particles that are not aggregated. The above measurements are carried out for 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, Carl Zeiss image analysis software KS-400. The average particle size shown in the examples described below is a value measured using a Hitachi transmission electron microscope H-9000 type as the transmission electron microscope and Carl Zeiss image analysis software KS-400 as the image analysis software, unless otherwise specified. In the present invention and this specification, powder means a collection of multiple particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. In addition, the collection of multiple particles is not limited to a form in which the particles constituting the collection are in direct contact with each other, and also includes a form in which a binder, additive, etc., described later, are interposed between the particles. The term particle is sometimes used to refer to powder.

[0064] As a method for collecting sample powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP 2011-048878 A can be used.

[0065] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is determined by the shape of the particles observed in the particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (where the height is greater than the maximum major axis of the base), etc., it is expressed by the length of the major axis that constitutes the particle, i.e., the major axis length. (2) In the case of a plate or columnar shape (where the thickness or height is smaller than the maximum long diameter of the plate or base), it shall be expressed by the maximum long diameter of the plate or base. (3) In the case of a particle having a spherical, polyhedral, or amorphous shape, and in which the major axis of the particle cannot be identified from its shape, the particle is expressed as the equivalent circle diameter, which is determined by the circle projection method.

[0066] The acicular ratio of a powder is determined by measuring the length of the minor axis of the particle in the above measurement, i.e., the minor axis length, and calculating the arithmetic average of the major axis lengths (average major axis length) and the minor axis lengths (average minor axis length) obtained for the above 500 particles, as the "average major axis length / average minor axis length." Unless otherwise specified, the minor axis length in the above definition of particle size refers to the length of the minor axis constituting the particle in the case of (1), and to the thickness or height in the case of (2), and in the case of (3), there is no distinction between the major axis and the minor axis, so for convenience, (average major axis length / average minor axis length) is considered to be 1. Unless otherwise specified, when the particle shape is specific, for example, in the case of the above definition of particle size (1), the average particle size is the average major axis length, in the case of definition (2), the average particle size is the average plate diameter, and in the case of definition (3), the average particle size is the average diameter (also called the average particle diameter or average particle size).

[0067] The content of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass.

[0068] (Binding Agent) The magnetic tape may be a coated magnetic tape, and may contain a binder in the magnetic layer. The binder is one or more kinds of resin. As the binder, various resins that are usually used as binders for coated magnetic recording media may be used. For example, as the binder, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral, etc. may be used alone or in combination. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins may also be used as binders in the non-magnetic layer and / or backcoat layer described below. For the above binders, reference can be made to paragraphs 0028 to 0031 of JP 2010-24113 A. The average molecular weight of the resin used as the binder can be, for example, 10,000 to 200,000 in weight average molecular weight. The weight average molecular weight of the binder in the present invention and this specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene equivalent. The weight average molecular weight of the binder shown in the examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene equivalent. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. GPC equipment: HLC-8120 (Tosoh Corporation) Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (inner diameter) × 30.0 cm) Eluent: tetrahydrofuran (THF)

[0069] (hardening agent) A curing agent can be used together with the resin usable as a binder. In one embodiment, the curing agent can be a thermosetting compound, which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating, and in another embodiment, the curing agent can be a photocuring compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation. As the curing reaction proceeds in the magnetic layer forming process, at least a part of the curing agent can be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as the binder. This point is also true for layers formed using a composition used to form other layers that contains a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For details on polyisocyanate, refer to paragraphs 0124 to 0125 of JP 2011-216149 A. The curing agent can be used in an amount of, for example, 0 to 80.0 parts by mass relative to 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of the magnetic layer.

[0070] (Additives) The magnetic layer may contain one or more additives as necessary. The additives may be selected from commercially available products or produced by known methods according to the desired properties and used in any amount. Examples of additives include the above-mentioned curing agents. Examples of additives contained in the magnetic layer include non-magnetic powders, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, and antioxidants. For dispersants, refer to paragraphs 0061 and 0071 of JP-A-2012-133837. A dispersant may be added to the non-magnetic layer-forming composition. For dispersants that can be added to the non-magnetic layer-forming composition, refer to paragraph 0061 of JP-A-2012-133837.

[0071] Examples of non-magnetic powders that can be included in the magnetic layer include non-magnetic powders that can function as abrasives. Examples of additives that can be used to improve the dispersibility of an abrasive in a magnetic layer that contains an abrasive include the dispersants described in paragraphs 0012 to 0022 of JP 2013-131285 A.

[0072] Examples of non-magnetic powders that can be contained in the magnetic layer include non-magnetic powders (e.g., non-magnetic colloidal particles, carbon black, etc.) that can function as protrusion-forming agents that form protrusions that protrude appropriately on the magnetic layer surface. For example, protrusion-forming agents having an average particle size of 5 to 300 nm can be used. The average particle size of colloidal silica (silica colloidal particles) shown in the examples described below is a value determined by the method described as a method for measuring average particle size in paragraph 0015 of JP-A-2011-048878. The content of the protrusion-forming agent in the magnetic layer is, for example, preferably 0.1 to 3.5 parts by mass, more preferably 0.1 to 3.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder.

[0073] The magnetic layer described above can be provided directly on the surface of the non-magnetic support, or indirectly via a non-magnetic layer.

[0074] The magnetic tape may contain one or more fluid lubricants in the magnetic layer side portion on the non-magnetic support. In the present invention and this specification, the "magnetic layer side portion on the non-magnetic support" is the magnetic layer for a magnetic tape having a magnetic layer directly on the non-magnetic support, and is the magnetic layer and / or non-magnetic layer for a magnetic tape having a non-magnetic layer between the non-magnetic support and the magnetic layer. Hereinafter, the "magnetic layer side portion on the non-magnetic support" is also simply referred to as the "magnetic layer side portion". The presence on the surface of the magnetic layer side of the magnetic tape is also included in the portion on the magnetic layer side. In the magnetic tape, it is considered that the fluid lubricant contained in the magnetic layer side portion of the magnetic tape can be sheared and / or pressured during sliding between the magnetic head and the magnetic layer surface, and can seep out in an appropriate amount from within the layer of the magnetic layer side portion to the surface of the magnetic layer, which the inventors speculate will lead to the suppression of the deterioration of the electromagnetic conversion characteristics during repeated running in a high temperature environment.

[0075] A magnetic tape containing a fluid lubricant in the magnetic layer side portion can be produced, for example, as described above, using a non-magnetic layer composition and / or a magnetic layer composition containing a fluid lubricant. The content of the fluid lubricant in the magnetic layer composition is preferably in the range of 0.2 to 7.0 parts by mass, more preferably in the range of 1.0 to 4.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The content of the fluid lubricant in the non-magnetic layer composition is as described above.

[0076] Regarding the lubricant, the magnetic tape may contain at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer. Fatty acids and fatty acid amides are said to be components that can function as boundary lubricants. Boundary lubricants are considered to be components that can adsorb to the surface of powders to form a lubricating film. Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, elaidic acid, etc., with stearic acid, myristic acid, and palmitic acid being preferred, and stearic acid being more preferred. The fatty acid may be contained in the portion on the magnetic layer side in the form of a salt such as a metal salt. Examples of the fatty acid amide include amides of the above-mentioned various fatty acids, such as lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. The amount of fatty acid, as the content in the magnetic layer-forming composition, is, for example, 0.1 to 5.0 parts by mass, and preferably 0.3 to 2.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder. The fatty acid amide content in the magnetic layer-forming composition is, for example, 0.1 to 1.0 part by mass, and preferably 0.2 to 0.6 part by mass, per 100.0 parts by mass of the ferromagnetic powder. The fatty acid and / or fatty acid amide can also be added to the composition for forming the nonmagnetic layer. The fatty acid content in the nonmagnetic layer forming composition is, for example, 0.5 to 10.0 parts by mass, and preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. The fatty acid amide content in the nonmagnetic layer forming composition is, for example, 0.1 to 3.0 parts by mass, and preferably 0.1 to 1.0 part by mass, per 100.0 parts by mass of the nonmagnetic powder.

[0077] <Nonmagnetic layer> Next, the non-magnetic layer will be described. The above magnetic tape may have a magnetic layer directly on the surface of a non-magnetic support, or may have a magnetic layer on the surface of the non-magnetic support via one or more non-magnetic layers containing non-magnetic powder.

[0078] In order to improve the surface smoothness of the magnetic layer, it is preferable to improve the surface smoothness of the non-magnetic layer on which the magnetic layer is formed. From this point of view, it is preferable to use a non-magnetic powder with a small average particle size as the non-magnetic powder contained in the non-magnetic layer. The average particle size of the non-magnetic powder is preferably in the range of 500 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and even more preferably 50 nm or less. In addition, from the viewpoint of the ease of improving the dispersibility of the non-magnetic powder, the average particle size of the non-magnetic powder is preferably 5 nm or more, more preferably 7 nm or more, and even more preferably 10 nm or more.

[0079] The non-magnetic powder used in the non-magnetic layer may be an inorganic powder or an organic powder, and carbon black or the like may also be used.

[0080] For carbon black usable in the non-magnetic layer, for example, refer to paragraphs 0040-0041 of JP-A-2010-24113. Carbon black generally tends to have a large particle size distribution and poor dispersibility. Therefore, non-magnetic layers containing carbon black tend to have low surface smoothness. From this point of view, in one embodiment, it is preferable to provide a non-magnetic layer containing non-magnetic powder other than carbon black as the non-magnetic layer adjacent to the magnetic layer. It is also preferable to provide multiple non-magnetic layers, and make the non-magnetic layer located closest to the magnetic layer a non-magnetic layer containing non-magnetic powder other than carbon black. For example, it is preferable to provide two non-magnetic layers between the non-magnetic support and the magnetic layer, and make the non-magnetic layer on the non-magnetic support side (also described as the "lower non-magnetic layer") a non-magnetic layer containing carbon black, and the non-magnetic layer on the magnetic layer side (also described as the "upper non-magnetic layer") a non-magnetic layer containing non-magnetic powder other than carbon black. In addition, in a non-magnetic layer forming composition containing multiple types of non-magnetic powder, the dispersibility of the non-magnetic powder tends to be lower than in a non-magnetic layer forming composition containing one type of non-magnetic powder. From this point of view, it is preferable to provide multiple non-magnetic layers and reduce the number of types of non-magnetic powder contained in each non-magnetic layer. In one embodiment, it is preferable to use a dispersant in a non-magnetic layer forming composition containing multiple types of non-magnetic powder to increase the dispersibility of the non-magnetic powder. Such dispersants will be described later.

[0081] Examples of inorganic powders include powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available, and can also be produced by known methods. For details, see paragraphs 0146 to 0150 of JP 2011-216149 A.

[0082] One form of the non-magnetic powder is non-magnetic iron oxide powder. A non-magnetic layer formed using non-magnetic iron oxide powder tends to have a harder time increasing the filling of the non-magnetic powder in the non-magnetic layer than a non-magnetic layer formed using titanium oxide powder, for example. This also applies to a non-magnetic layer formed using carbon black. This is because the particle shape of titanium oxide powder is generally spherical, so the filling of the non-magnetic powder is easier to increase in a non-magnetic layer formed using titanium oxide powder. The present inventors speculate that the fact that the filling of the non-magnetic powder in the non-magnetic layer is hard to increase is preferable in terms of increasing the value of the residual rate of the fluid lubricant. In one form, the non-magnetic iron oxide powder is preferably α-iron oxide powder. α-iron oxide is iron oxide whose main phase is α-phase.

[0083] The nonmagnetic powder content in the nonmagnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass. When multiple nonmagnetic layers are provided, it is preferable that the nonmagnetic powder content in at least one of the nonmagnetic layers is in the above range, and it is more preferable that the nonmagnetic powder content in more of the nonmagnetic layers is in the above range.

[0084] The non-magnetic layer contains a non-magnetic powder, and may contain a binder together with the non-magnetic powder. For other details of the binder, additives, etc. of the non-magnetic layer, known techniques related to non-magnetic layers can be applied. In addition, for example, for the type and content of the binder, the type and content of the additives, known techniques related to magnetic layers can also be applied.

[0085] Additives that can be included in the nonmagnetic layer include dispersants that can contribute to improving the dispersibility of nonmagnetic powders. Examples of such dispersants include fatty acids represented by RCOOH (R is an alkyl group or an alkenyl group) (e.g., caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, etc.); alkali metal salts or alkaline earth metal salts of the above fatty acids; esters of the above fatty acids; fluorine-containing compounds of the above fatty acid esters; amides of the above fatty acids; polyalkylene oxide alkyl phosphate esters; lecithin; trialkyl polyolefinoxy quaternary ammonium salts (the alkyl group contained is an alkyl group having 1 to 5 carbon atoms, and the olefin contained is ethylene, propylene, etc.); phenylphosphonic acid; and copper phthalocyanine. These may be used alone or in combination of two or more. The content of the dispersant is preferably 0.2 to 5.0 parts by mass relative to 100.0 parts by mass of the nonmagnetic powder.

[0086] An example of the additive is an organic tertiary amine. For organic tertiary amine, refer to paragraphs 0011 to 0018 and 0021 of JP 2013-049832 A. The organic tertiary amine can contribute to improving the dispersibility of carbon black. For the formulation of a composition for increasing the dispersibility of carbon black by using an organic tertiary amine, refer to paragraphs 0022 to 0024 and 0027 of the same publication.

[0087] The amine is more preferably a trialkylamine. The alkyl group of the trialkylamine is preferably an alkyl group having 1 to 18 carbon atoms. The three alkyl groups of the trialkylamine may be the same or different. For details of the alkyl group, refer to paragraphs 0015 to 0016 of JP2013-049832A. As the trialkylamine, trioctylamine is particularly preferable.

[0088] The additives exemplified above include compounds that correspond to the fluid lubricants of the present invention and this specification. Such compounds can function as fluid lubricants, dispersants, etc. in magnetic tapes.

[0089] In the present invention and this specification, the nonmagnetic layer also includes a substantially nonmagnetic layer that contains a small amount of ferromagnetic powder, for example as an impurity or intentionally, together with the nonmagnetic powder. Here, the substantially nonmagnetic layer refers to a layer having a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a layer having a residual magnetic flux density of 10 mT or less and a coercive force of 7.96 kA / m (100 Oe) or less. It is preferable that the nonmagnetic layer has no residual magnetic flux density or coercive force.

[0090] <Nonmagnetic support> Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter, simply referred to as "support") include known biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, aromatic polyamide, and the like. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be previously subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, and the like.

[0091] <Backcoat layer> The magnetic tape may or may not have a backcoat layer containing a nonmagnetic powder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. The backcoat layer preferably contains either one or both of carbon black and inorganic powder. The backcoat layer may contain a binder and may also contain additives. For the binder and additives of the backcoat layer, known techniques related to the backcoat layer may be applied, and known techniques related to the formulation of the magnetic layer and / or nonmagnetic layer may also be applied. For example, the descriptions of paragraphs 0018 to 0020 of JP 2006-331625 A and US Pat. No. 7,029,774, column 4, line 65 to column 5, line 38, may be referred to for the backcoat layer.

[0092] <Various thicknesses> Regarding the thickness (total thickness) of the magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for the magnetic tape to have an increased recording capacity (high capacity). Means for increasing the capacity include reducing the thickness of the magnetic tape (hereinafter also referred to as "thinning") and increasing the length of the magnetic tape contained in one magnetic tape cartridge. From this point of view, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, more preferably 5.4 μm or less, even more preferably 5.3 μm or less, and even more preferably 5.2 μm or less. From the viewpoint of ease of handling, the thickness of the magnetic tape is preferably 3.0 μm or more, and more preferably 3.5 μm or more.

[0093] For example, the thickness (total thickness) of the magnetic tape can be measured by the following method. Ten tape samples (e.g., 5 to 10 cm long) are cut out from any part of the magnetic tape, and the tape samples are stacked and the thickness is measured. The measured thickness is divided by 10 to obtain the value (thickness per tape sample), which is the tape thickness. The thickness measurement can be performed using a known measuring device capable of measuring thickness to the order of 0.1 μm.

[0094] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

[0095] The thickness of the magnetic layer can be optimized depending on the saturation magnetization amount of the magnetic head used, the head gap length, the band of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, and from the viewpoint of high-density recording, is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration related to a multi-layer magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers. This point is also true for the thickness of the nonmagnetic layer in a magnetic tape having a plurality of nonmagnetic layers.

[0096] Regarding the thickness of the nonmagnetic layer, the thicker the nonmagnetic layer, the more likely it is that the state of the nonmagnetic powder particles will be non-uniform during the coating and drying process of the nonmagnetic layer-forming composition, and the greater the difference in thickness at each position, which tends to make the surface of the nonmagnetic layer rough. From the viewpoint of improving the smoothness of the magnetic layer surface, it is preferable that the nonmagnetic layer has high surface smoothness, and from this viewpoint, the thickness of the nonmagnetic layer is preferably 1.5 μm or less, and more preferably 1.0 μm or less. Moreover, from the viewpoint of improving the uniformity of the coating of the nonmagnetic layer-forming composition, the thickness of the nonmagnetic layer is preferably 0.05 μm or more, and more preferably 0.1 μm or more.

[0097] The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.

[0098] Various thicknesses such as the thickness of the magnetic layer can be determined by the following method. A cross section of the magnetic tape in the thickness direction is exposed by an ion beam, and then the exposed cross section is observed by a scanning electron microscope or a transmission electron microscope. Various thicknesses can be obtained as the arithmetic average of thicknesses obtained at any two points in the cross section observation. Alternatively, various thicknesses can be obtained as design thicknesses calculated from manufacturing conditions, etc. The thicknesses of the nonmagnetic layer shown in Table 2 below are design thicknesses calculated from manufacturing conditions.

[0099] <Manufacturing process> (Preparation of compositions for forming each layer) The process of preparing the composition for forming the magnetic layer, non-magnetic layer or backcoat layer can usually include at least a kneading process, a dispersion process, and a mixing process provided before or after these processes as necessary. Each process may be divided into two or more stages. The components used in the preparation of the composition for forming each layer may be added at the beginning or during any process. As the solvent, one or more of various solvents usually used in the manufacture of coating-type magnetic recording media can be used. For the solvent, refer to paragraph 0153 of JP-A-2011-216149. Also, each component may be added in two or more steps in a divided manner. For example, the binder may be added in a divided manner in the kneading process, the dispersion process, and the mixing process for adjusting the viscosity after dispersion. In order to manufacture the magnetic tape, known manufacturing techniques can be used in various steps. In the kneading process, it is preferable to use a kneader with a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. For details of the kneading treatment, reference can be made to JP-A-1-106338 and JP-A-1-79274. A known dispersing machine can be used. At any stage of preparing each layer-forming composition, filtration may be performed by a known method. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter with a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

[0100] (Coating process) The magnetic layer can be formed by directly applying the magnetic layer forming composition onto the surface of the non-magnetic support, or by successively or simultaneously applying the magnetic layer forming composition and the non-magnetic layer forming composition in a multi-layer manner. As described above, the adoption of successive coating as the coating method is preferable in terms of increasing the residual rate of the fluid lubricant in the magnetic tape. The backcoat layer can be formed by applying a composition for forming a backcoat layer to the surface of the nonmagnetic support opposite to the surface having a nonmagnetic layer and / or a magnetic layer (or on which a nonmagnetic layer and / or a magnetic layer will be provided later). For details of the coating for forming each layer, reference can be made to paragraph 0066 of JP2010-231843A.

[0101] (Other processes) After the coating process, various treatments such as drying, orientation of the magnetic layer, and surface smoothing (calendering) can be performed. For various processes, reference can be made to known techniques such as paragraphs 0052 to 0057 of JP-A-2010-24113. For example, the coating layer of the magnetic layer-forming composition can be subjected to orientation while the coating layer is in a wet state. For the orientation process, various known techniques including those described in paragraph 0067 of JP-A-2010-231843 can be applied. For example, the vertical orientation process can be performed by known methods such as a method using magnets with opposite poles facing each other. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature and volume of the drying air and / or the conveying speed of the non-magnetic support on which the coating layer is formed in the orientation zone. In addition, the coating layer may be pre-dried before being conveyed to the orientation zone. In addition, in the calendering process, the smoothness of the magnetic layer surface tends to increase when the calendering conditions are strengthened. The calendering conditions include the number of times calendering is performed (hereinafter also referred to as "calendering times"), calendering pressure, calendering temperature (surface temperature of the calender roll), calendering speed, hardness of the calender roll, and the like. The more the calendering times are increased, the stronger the calendering is. The calendering pressure, calendering temperature, and hardness of the calender roll are increased, and the calendering speed is decreased, the stronger the calendering is. For example, the calendering pressure (linear pressure) can be 200 to 500 kg / cm, and preferably 250 to 350 kg / cm. The calendering temperature (surface temperature of the calender roll) can be, for example, 85 to 120°C, and preferably 90 to 110°C, and the calendering speed can be, for example, 50 to 300 m / min, and preferably 50 to 200 m / min. A long magnetic tape roll can be obtained through various processes. The obtained magnetic tape roll is cut (slit) by a known cutter to the width of the magnetic tape to be wound into a magnetic tape cartridge, for example. The width is determined according to standards and is usually 1 / 2 inch. 1 / 2 inch = 12.65 mm. A servo pattern is usually formed on the magnetic tape obtained by slitting, as will be described in detail later.

[0102] (Heat treatment) In one embodiment, the magnetic tape can be a magnetic tape manufactured through a heat treatment such as the following. In another embodiment, the magnetic tape can be a magnetic tape manufactured without undergoing a heat treatment such as the following.

[0103] The heat treatment can be carried out by winding the magnetic tape, which has been slit and cut to a width determined in accordance with a standard, around a core member and carrying out the heat treatment in the wound state.

[0104] In one embodiment, the above-mentioned heat treatment is performed with the magnetic tape wound around a core-shaped member for heat treatment (hereinafter referred to as the "heat treatment core"), and the magnetic tape after heat treatment is wound onto a reel of a magnetic tape cartridge, thereby producing a magnetic tape cartridge in which the magnetic tape is wound around a reel. The heat treatment core may be made of metal, resin, paper, or the like. The material of the heat treatment core is preferably a material with high rigidity from the viewpoint of suppressing the occurrence of winding failures such as sporking. From this viewpoint, the heat treatment core is preferably made of metal or resin. As an index of rigidity, the flexural modulus of the material of the heat treatment core is preferably 0.2 GPa (gigapascal) or more, more preferably 0.3 GPa or more. On the other hand, since high rigidity materials are generally expensive, using a heat treatment core of a material having a rigidity exceeding the rigidity that can suppress the occurrence of winding failures leads to an increase in cost. In consideration of the above, the flexural modulus of the material of the heat treatment core is preferably 250 GPa or less. The flexural modulus is a value measured according to ISO (International Organization for Standardization) 178, and the flexural modulus of various materials is publicly known. The heat treatment core may be a solid or hollow core-shaped member. In the case of a hollow core, the wall thickness is preferably 2 mm or more from the viewpoint of maintaining rigidity. The core for heat treatment may or may not have a flange.It is preferable to prepare a magnetic tape having a length equal to or greater than the length to be finally accommodated in a magnetic tape cartridge (hereinafter referred to as "final product length") as the magnetic tape to be wound around the core for heat treatment, and to perform heat treatment by placing the magnetic tape wound around the core for heat treatment in a heat treatment environment. The length of the magnetic tape to be wound around the core for heat treatment is equal to or greater than the final product length, and from the viewpoint of ease of winding around the core for heat treatment, it is preferable that the length is "final product length + α". From the viewpoint of ease of winding, this α is preferably 5 m or more. The tension during winding around the core for heat treatment is preferably 0.1 N (Newton) or more. In addition, from the viewpoint of suppressing the occurrence of excessive deformation, the tension during winding around the core for heat treatment is preferably 1.5 N or less, more preferably 1.0 N or less. The outer diameter of the core for heat treatment is preferably 20 mm or more, more preferably 40 mm or more, from the viewpoint of ease of winding and suppression of coiling (curl in the longitudinal direction). The outer diameter of the heat treatment core is preferably 100 mm or less, more preferably 90 mm or less. The width of the heat treatment core may be equal to or greater than the width of the magnetic tape wound around the core. After the heat treatment, when removing the magnetic tape from the heat treatment core, it is preferable to remove the magnetic tape from the heat treatment core after the magnetic tape and the heat treatment core have been sufficiently cooled in order to prevent unintended deformation of the tape during the removal operation. The removed magnetic tape is preferably once wound around another core (called a "temporary winding core"), and then the magnetic tape is preferably wound from the temporary winding core onto a reel of a magnetic tape cartridge (generally with an outer diameter of about 40 to 50 mm). This allows the magnetic tape to be wound around the reel of a magnetic tape cartridge while maintaining the relationship between the inside and outside of the magnetic tape with respect to the heat treatment core during the heat treatment. For details of the temporary winding core and the tension when winding the magnetic tape around this core, the above description of the heat treatment core can be referred to. In a form in which the above-mentioned heat treatment is performed on a magnetic tape having a length of "final product length + α", the length of "+ α" can be cut off at any stage. For example, in one form, the magnetic tape of the final product length can be wound from a temporary winding core onto a reel of a magnetic tape cartridge, and the remaining length of "+ α" can be cut off.From the viewpoint of reducing the portion that is cut off and discarded, the above α is preferably 20 m or less.

[0105] A specific embodiment of the heat treatment performed in the state where the material is wound around the core member as described above will be described below. The atmospheric temperature at which the heat treatment is performed (hereinafter referred to as "heat treatment temperature") is preferably 40° C. or higher, and more preferably 50° C. or higher. On the other hand, from the viewpoint of suppressing excessive deformation, the heat treatment temperature is preferably 75° C. or lower, more preferably 70° C. or lower, and even more preferably 65° C. or lower. The weight absolute humidity of the atmosphere in which the heat treatment is carried out is preferably 0.1 g / kg dry air or more, more preferably 1 g / kg dry air or more. An atmosphere with a weight absolute humidity in the above range is preferable because it can be prepared without using a special device for reducing moisture. On the other hand, the weight absolute humidity is preferably 70 g / kg dry air or less, more preferably 66 g / kg dry air or less, from the viewpoint of suppressing the occurrence of condensation and the deterioration of workability. The heat treatment time is preferably 0.3 hours or more, more preferably 0.5 hours or more. Moreover, the heat treatment time is preferably 48 hours or less from the viewpoint of production efficiency.

[0106] (Formation of servo pattern) The magnetic tape may have a servo pattern in the magnetic layer. "Formation of a servo pattern" may also be referred to as "recording of a servo signal." The formation of a servo pattern will be described below.

[0107] The servo pattern is usually formed along the longitudinal direction of the magnetic tape. Control methods that use servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0108] As shown in ECMA (European Computer Manufacturers Association)-319 (June 2001), magnetic tapes (generally called "LTO tapes") conforming to the LTO (Linear Tape-Open) standard employ a timing-based servo system. In this timing-based servo system, a servo pattern is formed by a pair of non-parallel magnetic stripes (also called "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. In this invention and this specification, the "timing-based servo pattern" refers to a servo pattern that enables head tracking in a servo system of the timing-based servo system. As described above, the servo pattern is formed by a pair of non-parallel magnetic stripes in order to inform the servo signal reading element passing over the servo pattern of its passing position. Specifically, the pair of magnetic stripes is formed so that the interval between them changes continuously along the width direction of the magnetic tape, and the servo signal reading element can know the relative position between the servo pattern and the servo signal reading element by reading the interval. This relative position information enables tracking of the data track. For this reason, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

[0109] A servo band is made up of a continuous servo pattern in the longitudinal direction of the magnetic tape. Usually, multiple servo bands are provided on a magnetic tape. For example, there are five servo bands on an LTO tape. The area between two adjacent servo bands is the data band. The data band is made up of multiple data tracks, and each data track corresponds to one servo track.

[0110] Also, in one embodiment, as shown in JP 2004-318983 A, information indicating the number of the servo band (also called "servo band ID (identification)" or "UDIM (Unique Data Band Identification Method) information") is embedded in each servo band. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that its position is displaced relatively in the longitudinal direction of the magnetic tape. Specifically, the way in which a specific one of a plurality of pairs of servo stripes is shifted is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, so that the servo band can be uniquely identified simply by reading one servo band with a servo signal reading element.

[0111] As a method for uniquely identifying servo bands, there is also a method using the staggered method as shown in ECMA-319 (June 2001). In this staggered method, a group of pairs of non-parallel magnetic stripes (servo stripes) arranged continuously in the longitudinal direction of the magnetic tape are recorded so that they are shifted in the longitudinal direction of the magnetic tape for each servo band. The combination of the shift between adjacent servo bands is unique across the entire magnetic tape, so when the servo pattern is read by two servo signal reading elements, it is possible to uniquely identify the servo bands.

[0112] Also, as specified in ECMA-319 (June 2001), information indicating the longitudinal position of the magnetic tape (also called "LPOS (Longitudinal Position) information") is usually embedded in each servo band. Like UDIM information, this LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike UDIM information, the same signal is recorded in each servo band with this LPOS information.

[0113] It is also possible to embed information other than the above UDIM information and LPOS information in the servo bands. In this case, the embedded information may be different for each servo band, such as UDIM information, or may be common to all servo bands, such as LPOS information. Also, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of pairs of servo stripes.

[0114] The head for forming a servo pattern is called a servo write head. The servo write head usually has a pair of gaps corresponding to the pair of magnetic stripes, the number of which is equal to the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and a magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps by supplying a current pulse to the coil. When forming a servo pattern, a magnetic pattern corresponding to the pair of gaps can be transferred to the magnetic tape by inputting a current pulse while running the magnetic tape on the servo write head, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, or 10 μm or more.

[0115] Before forming a servo pattern on the magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a direct current magnet or an alternating current magnet. There are two types of erase processes: DC (Direct Current) erase and AC (Alternating Current) erase. AC erase is performed by gradually lowering the strength of the magnetic field applied to the magnetic tape while reversing the direction of the magnetic field. On the other hand, DC erase is performed by applying a unidirectional magnetic field to the magnetic tape. There are two more methods of DC erase. The first method is horizontal DC erase, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erase, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape, or may be performed for each servo band of the magnetic tape.

[0116] The direction of the magnetic field of the formed servo pattern is determined according to the direction of erasure. For example, when the magnetic tape is subjected to horizontal DC erasure, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of erasure. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in JP2012-53940A, when the magnetic pattern is transferred to the magnetic tape that has been vertically DC erased using the above gap, the servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when the magnetic pattern is transferred to the magnetic tape that has been horizontally DC erased using the above gap, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0117] In one embodiment, the servo signal is used to obtain dimensional information of the magnetic tape in the width direction while the magnetic tape is running, and the tension applied to the magnetic tape in the longitudinal direction is adjusted and changed in accordance with the obtained dimensional information, thereby controlling the width direction of the magnetic tape. Adjusting the tension in this manner can contribute to preventing the magnetic head for recording or reproducing data from being shifted from the target track position due to the width deformation of the magnetic tape during recording or reproduction.

[0118] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-mentioned magnetic tape.

[0119] The details of the magnetic tape contained in the tape cartridge are as described above.

[0120] In a magnetic tape cartridge, the magnetic tape is generally accommodated inside the cartridge body in a state where it is wound around a reel. The reel is provided rotatably inside the cartridge body. As the magnetic tape cartridge, a single-reel type magnetic tape cartridge having one reel inside the cartridge body and a twin-reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When a single-reel type magnetic tape cartridge is loaded into a magnetic tape device for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound around the reel on the magnetic tape device side. A magnetic head is disposed on the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound between the reel (supply reel) on the magnetic tape cartridge side and the reel (take-up reel) on the magnetic tape device side. During this time, the magnetic head comes into contact with and slides on the surface of the magnetic layer of the magnetic tape, thereby recording and / or reproducing data. In contrast, a dual-reel magnetic tape cartridge is provided with both a supply reel and a take-up reel inside the magnetic tape cartridge.

[0121] [Magnetic tape device] One aspect of the present invention relates to a magnetic tape device including the magnetic tape. In the magnetic tape device, data can be recorded on the magnetic tape and / or data recorded on the magnetic tape can be reproduced, for example, by contacting and sliding a magnetic head against the surface of the magnetic layer of the magnetic tape.

[0122] In the present invention and this specification, the term "magnetic tape device" refers to a device capable of at least one of recording data on a magnetic tape and reproducing data recorded on the magnetic tape. Such a device is generally called a drive. The magnetic tape device can include a magnetic head. The magnetic head can be a recording head capable of recording data on a magnetic tape, or a reproducing head capable of reproducing data recorded on the magnetic tape. In one embodiment, the magnetic tape device can include both a recording head and a reproducing head as separate magnetic heads. In another embodiment, the magnetic head included in the magnetic tape device can have a configuration in which both a recording element and a reproducing element are provided in one magnetic head. As the reproducing head, a magnetic head (MR head) including a magnetoresistive (MR) element capable of reading information recorded on a magnetic tape with good sensitivity as a reproducing element is preferable. As the MR head, various known MR heads (for example, a giant magnetoresistive (GMR) head, a tunnel magnetoresistive (TMR) head, etc.) can be used. Also, the magnetic head that records and / or reproduces data may include a servo signal reading element. Alternatively, the magnetic tape device may include a magnetic head (servo head) equipped with a servo signal reading element as a head separate from the magnetic head that records and / or reproduces data. For example, a magnetic head that records and / or reproduces recorded data (hereinafter also referred to as a "recording and reproducing head") may include two servo signal reading elements, and each of the two servo signal reading elements can simultaneously read two adjacent servo bands sandwiching a data band. One or more data elements may be disposed between the two servo signal reading elements. The element for recording data (recording element) and the element for reproducing data (reproducing element) are collectively referred to as the "data element."

[0123] When recording data and / or reproducing recorded data, tracking can be performed using servo signals first. That is, by making the servo signal reading element follow a specific servo track, the data element can be controlled to pass over the target data track. The data track is moved by changing the servo track read by the servo signal reading element in the tape width direction. The recording / reproducing head can also record and / or reproduce data on other data bands by using the UDIM information described above to move the servo signal reading element to a specific servo band and start tracking on that servo band.

[0124] FIG. 2 shows an example of the arrangement of data bands and servo bands. In FIG. 2, a plurality of servo bands 1 are arranged on the magnetic layer of the magnetic tape MT, sandwiched between guide bands 3. A plurality of regions 2 sandwiched between two servo bands are data bands. A servo pattern is a magnetized region, and is formed by magnetizing a specific region of the magnetic layer with a servo write head. The region magnetized by the servo write head (the position where the servo pattern is formed) is determined by a standard. For example, in an LTO Ultrium format tape, which is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction are formed on the servo band during the manufacturing of the magnetic tape, as shown in FIG. 3. More specifically, in FIG. 3, a servo frame SF on the servo band 1 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (symbol A in FIG. 3) and a B burst (symbol B in FIG. 3). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (symbol C in FIG. 3) and a D burst (symbol D in FIG. 3). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in a subframe arranged in a 5, 5, 4, 4 arrangement in a set of 5 and 4, and are used to identify a servo frame. For the sake of explanation, one servo frame is shown in FIG. 3. However, in reality, a plurality of servo frames are arranged in the running direction in each servo band on the magnetic layer of a magnetic tape where head tracking of the timing-based servo method is performed. In FIG. 3, the arrow indicates the running direction. For example, an LTO Ultrium format tape usually has 5,000 or more servo frames per meter of tape length in each servo band on the magnetic layer.

[0125] In one embodiment of the above magnetic tape device, the magnetic tape is treated as a removable medium (so-called replaceable medium), and a magnetic tape cartridge containing the magnetic tape is inserted into and removed from the magnetic tape device. In another embodiment, the magnetic tape is not treated as a replaceable medium, and the magnetic tape is wound around a reel of a magnetic tape device equipped with a magnetic head, and the magnetic tape is contained within the magnetic tape device. In one embodiment, in such a magnetic tape device, the magnetic tape and the magnetic head can be contained within an enclosed space in the magnetic tape device. In the present invention and this specification, the term "enclosed space" refers to a space having an airtightness of 10×10, as evaluated by an immersion method (bombing method) using helium (He) as specified in JIS Z 2331:2006 Helium Leak Test Method. -8 Pa·m 3 / sec or less. The degree of airtightness of an enclosed space is, for example, 5 x 10 ―9 Pa·m 3 / sec or more 10x10 -8 Pa·m 3 / sec or less, or may be below the above range. In one embodiment, the entire space in the housing can be the sealed space, and in another embodiment, a part of the space in the housing can be the sealed space. The sealed space can be an internal space of a housing that covers the whole or part of the magnetic tape device. The material and shape of the housing are not particularly limited, and can be the same as the material and shape of the housing of a normal magnetic tape device, for example. As an example, the material of the housing can be metal, resin, etc. EXAMPLES

[0126] An embodiment of the present invention will be described below based on an example. However, the present invention is not limited to the embodiment shown in the example. The indications of "parts" and "%" below mean "parts by mass" and "% by mass" unless otherwise specified. "eq" is an equivalent, and is a unit that cannot be converted to SI units. In addition, the following various steps and operations were carried out in a room temperature environment at a temperature of 20 to 25° C. and a relative humidity of 40 to 60%, unless otherwise specified.

[0127] Table 1 shows details of the fluid lubricants shown in Table 2 below as components in the composition for forming the nonmagnetic layer.

[0128] [Table 1]

[0129] In Table 2 described later, "BaFe" represents hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm.

[0130] In Table 2 described later, "SrFe" represents hexagonal strontium ferrite powder prepared by the method described below, and "ε-iron oxide" represents ε-iron oxide powder prepared by the method described below. The average particle volumes of the various ferromagnetic powders described below are values ​​determined by the method described above. The various values ​​relating to the particle sizes of the various powders described below are also values ​​determined by the method described above. The anisotropy constant Ku is a value determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). Moreover, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[0131] [How to prepare ferromagnetic powder] <How to prepare hexagonal strontium ferrite powder> 1707 g of SrCO3, 687 g of H3BO3, 1120 g of Fe2O3, 45 g of Al(OH)3, 24 g of BaCO3, 13 g of CaCO3, and 235 g of Nd2O3 were weighed out and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390°C, and the melt was poured into a rod shape at about 6 g / sec by heating the tapping hole at the bottom of the platinum crucible while stirring the melt. The tapped liquid was rolled and quenched with a water-cooled twin roller to produce an amorphous body. 280 g of the produced amorphous body was placed in an electric furnace, heated to 635°C (crystallization temperature) at a heating rate of 3.5°C / min, and held at that temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized material obtained above containing hexagonal strontium ferrite particles was coarsely crushed in a mortar, and 1000 g of zirconia beads with a particle size of 1 mm and 800 mL of 1% aqueous acetic acid solution were added to a glass bottle and dispersed for 3 hours using a paint shaker. The resulting dispersion was then separated from the beads and placed in a stainless steel beaker. The dispersion was left to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass components, and then precipitated in a centrifuge and washed by repeated decantation, and dried for 6 hours in a heating furnace at a furnace temperature of 110°C to obtain hexagonal strontium ferrite powder. The average particle volume of the hexagonal strontium ferrite powder obtained above ("SrFe" in Table 2 below) was 900 nm 3 , the anisotropy constant Ku is 2.2×10 5 J / m 3 , mass magnetization σs is 49A m 2 / kg. A 12 mg sample powder was taken from the hexagonal strontium ferrite powder obtained above, and this sample powder was partially dissolved under the dissolution conditions exemplified above. The elemental analysis of the filtrate obtained was performed using an ICP analyzer to determine the surface layer content of neodymium atoms. Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and this sample powder was completely dissolved under the dissolution conditions exemplified above. The elemental analysis of the filtrate obtained was performed using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) relative to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. The surface layer content of neodymium atoms was 8.0 atomic %. The ratio of the surface layer content to the bulk content, "surface layer content / bulk content," was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layers of the particles.

[0132] It was confirmed that the powder obtained above exhibited a hexagonal ferrite crystal structure by scanning with CuKα radiation at a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. The crystal phase detected by the X-ray diffraction analysis was a single phase of magnetoplumbite type. PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slits for incident and diffracted beams: 0.017 radians Dispersion slit fixed angle: 1 / 4 degree Mask: 10mm Anti-scatter slit: 1 / 4 degree Measurement mode: Continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0133] <How to prepare ε-iron oxide powder> 8.3g of iron (III) nitrate nonahydrate, 1.3g of gallium (III) nitrate octahydrate, 190mg of cobalt (II) nitrate hexahydrate, 150mg of titanium (IV) sulfate, and 1.5g of polyvinylpyrrolidone (PVP) were dissolved in 90g of pure water, and 4.0g of ammonia solution with a concentration of 25% was added under the condition of an atmospheric temperature of 25°C while stirring with a magnetic stirrer in the air atmosphere, and the mixture was stirred for 2 hours at an atmospheric temperature of 25°C. A citric acid solution obtained by dissolving 1g of citric acid in 9g of pure water was added to the obtained solution, and the mixture was stirred for 1 hour. The powder precipitated after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace at an internal temperature of 80°C. 800g of pure water was added to the dried powder, and the powder was dispersed in water again to obtain a dispersion. The obtained dispersion was heated to 50°C, and 40g of 25% ammonia aqueous solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50°C, 14mL of tetraethoxysilane (TEOS) was added dropwise and stirred for 24 hours. 50g of ammonium sulfate was added to the obtained reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried for 24 hours in a heating furnace with an internal temperature of 80°C to obtain a precursor of ferromagnetic powder. The obtained precursor of the ferromagnetic powder was placed in a heating furnace at an internal temperature of 1000° C. in an air atmosphere and subjected to a heat treatment for 4 hours. The heat-treated ferromagnetic powder precursor was placed in a 4 mol / L aqueous solution of sodium hydroxide (NaOH), and the liquid temperature was maintained at 70°C while stirring for 24 hours, thereby removing impurities such as silicate compounds from the heat-treated ferromagnetic powder precursor. Thereafter, the silicic acid compound was removed by centrifugation, and the ferromagnetic powder was collected and washed with pure water to obtain a ferromagnetic powder. The composition of the obtained ferromagnetic powder was confirmed by inductively coupled plasma-optical emission spectrometry (ICP-OES). The results showed that the powder was composed of Ga, Co, and Ti substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62 In addition, X-ray diffraction analysis was performed under the same conditions as those described above for the preparation method of hexagonal strontium ferrite powder, and it was confirmed from the peaks in the X-ray diffraction pattern that the obtained ferromagnetic powder had a single-phase ε-phase crystal structure (ε-iron oxide type crystal structure) that did not contain α-phase or γ-phase crystal structures. The average particle volume of the obtained ε-iron oxide powder (referred to as "ε-iron oxide" in Table 2 below) was 750 nm 3 , the anisotropy constant Ku is 1.2×10 5 J / m 3 , mass magnetization σs is 16A m 2 / kg.

[0134] In Table 2 described later, for the examples and comparative examples in which only one nonmagnetic layer was formed, the details relating to the nonmagnetic layer are shown in the column "Lower nonmagnetic layer".

[0135] [Example 1] (1) Preparation of alumina dispersion Alpha conversion rate approximately 65%, BET (Brunauer-Emmett-Teller) specific surface area 20m 2 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) with a molecular weight of 100 g / g was mixed with 3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) of polyester polyurethane resin having SO3Na groups as polar groups (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq / kg)), and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1:1 (mass ratio) as a solvent, and dispersed for 5 hours using a paint shaker in the presence of zirconia beads. After dispersion, the dispersion liquid and the beads were separated using a mesh to obtain an alumina dispersion.

[0136] (2) Magnetic layer forming composition formulation (Magnetic liquid) Ferromagnetic powder (type: see Table 2) 100.0 parts SO3Na group-containing polyurethane resin 14.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive liquid) 6.0 parts of the alumina dispersion prepared in (1) above (Protrusion forming agent liquid) Protrusion forming agent 2.0 parts Type: Colloidal silica (average particle size 120 nm) Methyl ethyl ketone 1.4 parts (Other Ingredients) Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark) L) 2.5 parts (Finishing solvent) Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

[0137] (3) Formulation of composition for forming nonmagnetic layer Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15μm Acicular ratio: 7 BET specific surface area: 52m 2 / g Carbon black 20.0 parts Average particle size: 20nm SO3Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid 2.0 parts Stearic acid amide 0.2 parts Fluid lubricant (type: see Table 2) See Table 2 Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

[0138] (4) Formulation of composition for forming backcoat layer Carbon black 100.0 parts DBP (Dibutyl phthalate) oil absorption: 74cm 3 / 100g Nitrocellulose 27.0 parts Polyester polyurethane resin containing sulfonic acid groups and / or their salts 62.0 copies Polyester resin 4.0 parts Alumina powder (BET specific surface area: 17m 2 / g) 0.6 parts Methyl ethyl ketone 600.0 parts Toluene 600.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark) L) 15.0 parts

[0139] (5) Preparation of compositions for forming each layer The magnetic layer forming composition was prepared by the following method. The magnetic liquid was prepared by dispersing the above components for 24 hours (bead dispersion) using a batch-type vertical sand mill. Zirconia beads with a bead diameter of 0.5 mm were used as the dispersion beads. The magnetic liquid prepared using the sand mill was mixed with the above abrasive liquid and other components (protrusion forming agent liquid, other components, and finishing additive solvent) and bead dispersed for 5 minutes, and then treated with a batch-type ultrasonic device (20 kHz, 300 W) for 0.5 minutes (ultrasonic dispersion). Thereafter, filtration was performed using a filter with a pore size of 0.5 μm to prepare the magnetic layer forming composition. The nonmagnetic layer-forming composition was prepared by the following method. The above components, except for the lubricants (stearic acid, stearic acid amide, and the fluid lubricants shown in Table 2), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser. The lubricants (stearic acid, stearic acid amide, and the fluid lubricants shown in Table 2) were then added, and the mixture was stirred and mixed using a dissolver stirrer to prepare the nonmagnetic layer-forming composition. The composition for forming a backcoat layer was prepared by the following method. The above components except for the polyisocyanate were introduced into a dissolver mixer, stirred at a peripheral speed of 10 m / sec for 30 minutes, and then dispersed using a horizontal bead mill disperser. Then, the polyisocyanate was added, and the mixture was stirred and mixed using the dissolver mixer to prepare the composition for forming a backcoat layer.

[0140] (6) Manufacturing of magnetic tapes and magnetic tape cartridges The non-magnetic layer-forming composition prepared in (5) above was applied and dried on the surface of a biaxially stretched polyethylene terephthalate support having a thickness of 4.1 μm to a thickness of 0.7 μm after drying to form a non-magnetic layer. Next, the magnetic layer-forming composition prepared in (5) above was applied on the non-magnetic layer to a thickness of 0.1 μm after drying to form a coating layer. Thereafter, while the coating layer of the magnetic layer-forming composition was in a wet state, a magnetic field with a magnetic field strength of 0.3 T was applied perpendicularly to the surface of the coating layer to perform a vertical orientation treatment, and then the coating layer was dried to form a magnetic layer. That is, sequential coating was adopted as the coating method. Then, the backcoat layer-forming composition prepared in (5) above was applied and dried on the surface of the support opposite to the surface on which the non-magnetic layer and magnetic layer were formed to a thickness of 0.3 μm after drying to form a backcoat layer. Thereafter, using a calender roll consisting only of a metal roll, the surface was smoothed (calendered) at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a calender temperature (surface temperature of the calender roll) of 90°C (calendering number of times: 2). Thereafter, the long magnetic tape was heat-treated by storing it in a heat treatment furnace at an atmospheric temperature of 70°C (heat treatment time: 36 hours). After the heat treatment, the magnetic tape was slit into 1 / 2 inch width to obtain a magnetic tape. A servo signal was recorded on the magnetic layer of the obtained magnetic tape by a commercially available servo writer to obtain a magnetic tape having a data band, a servo band, and a guide band in an arrangement according to the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) on the servo band with an arrangement and shape according to the LTO Ultrium format. The servo pattern thus formed is a servo pattern according to the descriptions of JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4. The magnetic tape (length 970 m) after the servo pattern was formed was wound around a core for heat treatment, and heat treatment was performed while the tape was wound around the core. A solid core-shaped member (outer diameter: 50 mm) made of resin with a flexural modulus of 0.8 GPa was used as the core for heat treatment, and the tension during winding was 0.6 N. The heat treatment was performed for 5 hours at a heat treatment temperature of 50°C. The weight absolute humidity of the atmosphere in which the heat treatment was performed was 10 g / kg dry air. After the above heat treatment, the magnetic tape and the core for heat treatment were sufficiently cooled, and then the magnetic tape was removed from the core for heat treatment and wound onto the core for temporary winding, and then the magnetic tape for the final product length (960 m) was wound from the core for temporary winding onto the reel of the magnetic tape cartridge (reel outer diameter: 44 mm), and the remaining 10 m was cut off, and a leader tape was joined to the end of the cut-off side using a commercially available splicing tape in accordance with item 9 of Standard ECMA (European Computer Manufacturers Association)-319 (June 2001) Section 3. The core for temporary winding was a solid core member made of the same material and having the same outer diameter as the core for heat treatment, and the tension during winding was 0.6 N. As a result of the above, a single-reel magnetic tape cartridge was produced, in which a 960m long magnetic tape was wound on a reel.

[0141] [Examples 2 to 6] A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1, except that the fluid lubricant in the composition for forming the nonmagnetic layer was changed to one shown in Table 2.

[0142] [Example 7] A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1, except that a two-layer nonmagnetic layer was formed as described below, a magnetic layer was formed by applying a magnetic layer-forming composition to the upper nonmagnetic layer as in Example 1, and the number of calendering passes was limited to one.

[0143] <Formulation of composition for forming lower nonmagnetic layer> Carbon black (average particle size: 20 nm) 100.0 parts Trioctylamine (molecular weight: 354, boiling point: 365°C) 4.0 parts Vinyl chloride resin 12.0 parts Stearic acid 1.5 parts Stearic acid amide 0.3 parts Fluid lubricant (type: see Table 2) See Table 2 Cyclohexanone 200.0 parts Methyl ethyl ketone 510.0 parts

[0144] <Formulation of composition for forming upper nonmagnetic layer> Non-magnetic inorganic powder α-iron oxide 100.0 parts Average particle size (average major axis length): 30nm Average short axis length: 15nm Acicular ratio: 2.0 SO3Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid 1.0 parts Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

[0145] The above-mentioned components of the composition for forming the lower non-magnetic layer and the composition for forming the upper non-magnetic layer were kneaded for 240 minutes in an open kneader, and then dispersed in a sand mill. The dispersion conditions for each composition for forming the non-magnetic layer were a dispersion time of 24 hours, and zirconia beads with a bead diameter of 0.1 mm were used as the dispersion beads. 4.0 parts of polyisocyanate (Tosoh Corporation's Coronate 3041) were added to the dispersion thus obtained, and the mixture was stirred and mixed for another 20 minutes, and then filtered using a filter with a pore size of 0.5 μm. In this manner, a composition for forming a lower non-magnetic layer and a composition for forming an upper non-magnetic layer were prepared. The composition for forming a lower non-magnetic layer was applied to one surface of a biaxially stretched polyethylene terephthalate support having a thickness of 4.1 μm so that the thickness after drying was 0.25 μm, and dried in an environment with an atmospheric temperature of 100° C. to form a lower non-magnetic layer. The composition for forming an upper non-magnetic layer was applied to the lower non-magnetic layer so that the thickness after drying was 0.25 μm, and dried in an environment with an atmospheric temperature of 100° C. to form an upper non-magnetic layer.

[0146] [Examples 8 and 9] A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 7, except that the ferromagnetic powders shown in the "Ferromagnetic Powder" column in Table 2 were used as the ferromagnetic powders.

[0147] [Comparative Example 1] A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1, except that the fluid lubricant in the composition for forming the nonmagnetic layer was changed to one shown in Table 2.

[0148] [Comparative Example 2] A magnetic tape was produced according to the description of Example 8 of Patent Document 1 (JP 2008-239575 A). As described in paragraph 0107 and Table 1 of this publication, the composition for forming a magnetic layer and the composition for forming a nonmagnetic layer contain carbonate ester B described in Table 1 above. As described in paragraph 0107 of this publication, the nonmagnetic powder of the composition for forming a nonmagnetic layer contains titanium oxide powder. Also, as described in paragraph 0108 of this publication, the coating method for the magnetic layer and the nonmagnetic layer is simultaneous multilayer coating. A servo pattern was formed on the prepared magnetic tape in the same manner as in Example 1, and the magnetic tape was then housed in a magnetic tape cartridge. In this way, a single-reel magnetic tape cartridge was produced, with a magnetic tape length of 960 m wound on a reel.

[0149] [Comparative Example 3] A magnetic tape was produced according to the description of Example 1 of Patent Document 2 (JP 2012-014809 A). As described in paragraphs 0071 and 0073 of this publication, the magnetic layer forming composition and the non-magnetic layer forming composition contain isohexadecyl stearate as shown in Table 1 above. As described in paragraph 0073 of this publication, the non-magnetic powder of the non-magnetic layer forming composition contains titanium oxide powder. Also, as described in paragraph 0075 of this publication, the magnetic layer and non-magnetic layer are applied by sequential coating. A servo pattern was formed on the prepared magnetic tape in the same manner as in Example 1, and the magnetic tape was then housed in a magnetic tape cartridge. In this way, a single-reel magnetic tape cartridge was produced, with a magnetic tape length of 960 m wound on a reel.

[0150] For each of the examples and comparative examples, two magnetic tape cartridges were prepared, one of which was used for measuring the residual rate of fluid lubricant described below, and the other was used for evaluating the electromagnetic conversion characteristics described below.

[0151] [Evaluation method] <Fluid lubricant remaining rate> (Tape sample preparation) A 5 cm long tape sample and a 100 m long tape sample were cut out from any position in the longitudinal direction of the magnetic tape taken out of the magnetic tape cartridge.

[0152] (Amount of fluid lubricant extracted before sliding) The backcoat layer of the 5 cm long tape sample was removed by rubbing it against a filter paper soaked in tetrahydrofuran (THF). After the removal operation was continued until the black material from the backcoat layer was no longer attached to the filter paper, the tape sample was placed in a beaker, 30 mL of methanol was poured into the beaker, and the beaker was then covered. The methanol in which the tape sample had been immersed was then heated to a liquid temperature of 60° C., and the extraction operation was carried out for 3 hours. The liquid after extraction was transferred to a recovery flask, and the methanol was evaporated using a rotary evaporator. To the above-mentioned recovery flask, 1 mL of a 1:1 (volume ratio) mixed solution of methanol and chloroform was added using a volumetric pipette, and then 50 μL of a methylating agent (tetramethylethylenediamine) was added using a microsyringe and mixed. The mixture was allowed to react for 30 minutes at room temperature as described above to obtain a sample for gas chromatographic measurement. Then, the components corresponding to the fluid lubricant of the present invention and this specification were detected by gas chromatography under the following measurement conditions, and each detected component was quantified using a calibration curve prepared in advance. The total amount of the fluid lubricant thus quantified is the amount of the fluid lubricant before sliding. (Measurement conditions) Equipment: Agilent Technologies Agilent 7890A Column: Agilent J&W DB-1HT (Agilent Technologies) Oven temperature: 150℃ / 2 minutes → 10℃ / 1 minute to 300℃ Injection port temperature: 310℃, pulsed splitless injection Injection volume: 1μL Detector: FID (Flame Ionization Detector) (340℃) Carrier gas: He

[0153] (Sliding between magnetic tape and magnetic head) The above 100 m long tape sample was attached to a 1 / 2 inch reel tester equipped with a recording / playback head mounted on an IBM LTO8 tape drive as described above, and was run against a magnetic head (LTO8 head) under the running conditions described above in an environment with an ambient temperature of 60°C ± 1°C and a relative humidity of 10%.

[0154] (amount of fluid lubricant extracted after sliding) After the above sliding, a tape sample with a length of 5 cm was cut out as described above. The backcoat layer of this tape sample was removed by rubbing it against filter paper soaked in tetrahydrofuran (THF). After the removal operation was continued until the black matter originating from the backcoat layer was no longer attached to the filter paper, the amount of fluid lubricant extracted after sliding was determined for the tape sample using the same method as that used to determine the amount of fluid lubricant extracted before sliding.

[0155] (Calculation of fluid lubricant residual rate) From the amounts of fluid lubricant extracted before and after sliding determined by the above method, the fluid lubricant remaining rate was calculated as "(amount of fluid lubricant extracted after sliding / amount of fluid lubricant extracted before sliding)×100".

[0156] [Evaluation of electromagnetic conversion characteristics during repeated driving in high temperature environments] The following evaluations were carried out in an environment with an ambient temperature of 60°C ± 1°C and a relative humidity of 10%. For each of the examples and comparative examples, a 100m long tape sample was cut from an arbitrary position in the longitudinal direction of the magnetic tape taken out of the magnetic tape cartridge, and attached to a 1 / 2 inch reel tester with a recording / reproducing head mounted on an IBM LTO8 tape drive as described above, and data was recorded and reproduced. The running conditions during recording and reproduction were the same as those described above, in order to determine the amount of fluid lubricant extracted after sliding. Recording was performed at a linear recording density of 300 kfci, and the playback output was measured during playback to determine the signal-to-noise ratio (ratio of playback output to noise). The unit kfci is the unit of linear recording density (not convertible to SI units). The difference between the SNR when recording and reproducing in the first single pass and the SNR when recording and reproducing in the 20,000th single pass (SNR in the 20,000th single pass - SNR in the 1st single pass) was calculated. The calculated values ​​are shown in the "SNR Decrease" column in Table 2. In Comparative Example 2, a large amount of debris was generated on the magnetic head during repeated running, making it impossible to detect the signal, and therefore the SNR at the 20,000th single pass could not be determined (indicated as "Cannot be evaluated" in Table 2).

[0157] The above results are shown in Table 2.

[0158] [Table 2]

[0159] As shown in Table 2, the residual rate of the fluid lubricant in the magnetic tapes of Examples 1 to 9 was 50% or more. As shown in Table 2, the magnetic tapes of Examples 1 to 9 suppressed the decrease in SNR during repeated running in a high-temperature environment compared to the magnetic tapes of Comparative Examples 1 to 3. From this result, it can be confirmed that the magnetic tapes of Examples 1 to 9 are magnetic tapes with little decrease in electromagnetic conversion characteristics even when repeatedly run in a harsh high-temperature environment. [Industrial Applicability]

[0160] One aspect of the present invention is useful in the field of magnetic tape for data storage.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing a ferromagnetic powder and a binder, A magnetic tape in which the amount of fluid lubricant extracted from the surface of the magnetic layer after sliding against a magnetic head in an environment with a temperature of 60°C±1°C and a relative humidity of 10% is 50% or more, by mass, of the amount of fluid lubricant extracted from the surface of the magnetic layer before the sliding.

2. 2. The magnetic tape of claim 1, further comprising a non-magnetic layer between the non-magnetic support and the magnetic layer, the non-magnetic layer comprising a non-magnetic powder and a binder.

3. 3. The magnetic tape of claim 2, wherein the non-magnetic powder in the non-magnetic layer is a non-magnetic powder selected from the group consisting of carbon black and non-magnetic iron oxide powder.

4. The fluid lubricant comprises the following (1) and (2): (1) A boiling point of 400°C or higher (2) Molecular weight of 400 or more 4. The magnetic tape according to claim 1, further comprising a fluid lubricant which satisfies at least one of the above.

5. 5. The magnetic tape according to claim 4, wherein the fluid lubricant that satisfies at least one of (1) and (2) is a fatty acid ester.

6. 5. The magnetic tape according to claim 4, wherein the fluid lubricant that satisfies at least one of (1) and (2) is a carbonate ester.

7. 5. The magnetic tape according to claim 4, wherein the fluid lubricant that satisfies at least one of (1) and (2) is an organic amine.

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

9. A magnetic tape cartridge comprising the magnetic tape according to any one of claims 1 to 8.

10. A magnetic tape device comprising the magnetic tape according to any one of claims 1 to 8.

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