Magnetic recording medium and cartridge

Abstract

Provided is a magnetic recording medium capable of maintaining good electromagnetic conversion characteristics even under a high-temperature and high-humidity environment.　The magnetic recording medium is shaped like tape and comprises: a base body; and a magnetic layer that contains an acidic compound and magnetic particles having an average particle volume of 1.50×103 nm3 or less. The average thickness of the magnetic recording medium is 5.30 μm or less. If a power spectral density is determined for each of the positions of spatial wavelengths λn=100 / n [μm] (n is an integer of 1-255) by using a two-dimensional surface profile image specific to a measurement range 100 [μm]×100 [μm] and obtained by measuring the surface on the magnetic layer side with an atomic force microscope, Iλn≤5 / I10≤λn≤20, which is the ratio of the average value Iλn≤5 among the integrated values of the power spectral densities within the range of spatial wavelengths λn≤5 μm to the average value I10≤λn≤20 among the integrated values of the power spectral densities within the range of 10 μm≤spatial wavelength λn≤20 μm, is 3.00 or less. The reduction rate of saturation magnetization Ms in an eight-week high-temperature and high-humidity environment test at a temperature of 60°C and a humidity of 90 RH% is 1.00% or less.

Description

Magnetic recording media and cartridges

[0001] The present disclosure relates to a magnetic recording medium and a cartridge including the same.

[0002] In recent years, tape-type magnetic recording media have been widely used to store electronic data. In order to increase the areal recording density of tape-type magnetic recording media, it is desirable to reduce the size of magnetic particles. In Patent Document 1, the average particle volume of magnetic particles is set to 1.50 × 10 ３ nm ３ It states that:

[0003] International Publication No. 2021 / 199453

[0004] In recent years, tape-type magnetic recording media have been increasingly used for archiving purposes, particularly in data centers, and it is therefore desirable to make tape-type magnetic recording media usable in high-temperature, high-humidity environments. However, when the average particle volume of magnetic particles is increased to 1.50 × 10 ３ nm ３ If the temperature is lower than this, there is a risk that good electromagnetic conversion characteristics cannot be maintained in a high-temperature, high-humidity environment.

[0005] An object of the present disclosure is to provide a magnetic recording medium that can maintain good electromagnetic conversion characteristics even in a high-temperature, high-humidity environment, and a cartridge including the same.

[0006] In order to solve the above-mentioned problems, the magnetic recording medium according to the present disclosure is a tape-shaped magnetic recording medium, comprising a substrate and a magnetic recording medium having an average particle volume of 1.50×10 ３ nm ３ and a magnetic layer containing the following magnetic particles and acidic compound, wherein the average thickness of the magnetic recording medium is 5.30 μm or less, and when the power spectral density at each position of spatial wavelength λn=100 / n [μm] (where n is an integer of 1 or more and 255 or less) is determined using a two-dimensional surface profile image of a measurement range of 100 [μm] × 100 [μm] obtained by measuring the surface on the magnetic layer side with an atomic force microscope, the average value I of the integrated value of the power spectral density in the range of spatial wavelength λn≦5 μm λｎ≦５and the average value I of the integrated value of the power spectral density in the range of 10 μm≦spatial wavelength λn≦20 μm １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ is 3.00 or less, and the rate of decrease in saturation magnetization Ms after an 8-week high-temperature, high-humidity environmental test at a temperature of 60° C. and a humidity of 90 RH% is 1.00% or less.

[0007] A cartridge according to the present disclosure includes a magnetic recording medium according to the present disclosure.

[0008] FIG. 1 is an exploded perspective view showing an example of the configuration of a cartridge according to an embodiment of the present disclosure. FIG. 2 is a block diagram showing an example of the configuration of a cartridge memory. FIG. 3 is a cross-sectional view showing an example of the configuration of a magnetic tape. FIG. 4 is a schematic diagram showing an example of the layout of a data band and a servo band. FIG. 5A is an enlarged view showing an example of the configuration of a data band. FIG. 5B is an enlarged view showing an example of a data track in a shingled magnetic recording system. FIG. 6 is an enlarged view showing an example of the configuration of a servo band. FIG. 7 is a perspective view showing an example of the shape of a magnetic particle. FIG. 8 is a diagram showing a first example of a cross-sectional TEM image of a magnetic layer. FIG. 9 is a diagram showing a second example of a cross-sectional TEM image of a magnetic layer. FIG. 10 is a graph showing an example of power spectral density obtained by analyzing a two-dimensional surface profile. FIG. 11 is a graph showing the relationship between the asperities on the surface on the magnetic layer side and the ratio I λｎ≦５ / I １０≦λｎ≦２０ FIG. 12 is a side view of an apparatus for measuring tension acting on a magnetic tape. FIG. 13 is a plan view of an apparatus for measuring tension acting on a magnetic tape. FIG. 14 is an enlarged view of the head block shown in FIG. 12. FIG. 15 is a view for explaining an example in which a protrusion on the surface on the magnetic layer side undergoes plastic deformation or brittle fracture. FIG. 16 is an exploded perspective view showing an example of the configuration of a cartridge according to a modified example of an embodiment of the present disclosure.

[0009] The embodiments of the present disclosure will be described in the following order: 1. Background leading to the creation of the embodiments of the present disclosure 2. Cartridge configuration 3. Cartridge memory configuration 4. Magnetic tape configuration 5. Magnetic tape manufacturing method 6. Functions and effects 7. Modifications

[0010] In this specification, unless a measurement environment is specifically stated in connection with the explanation of the measurement method and evaluation method, the measurement and evaluation are performed in an environment of 25°C ± 2°C and 50% RH ± 5% RH.

[0011] [1 Background to the Creation of the Embodiments of the Present Disclosure] The present inventors have conducted extensive research into the surface properties of a magnetic layer that can provide good electromagnetic conversion characteristics. As a result, the average value I of the integrated value of the power spectral density in the range of spatial wavelength λn≦5 μm was λｎ≦５ and the average value I of the integrated value of the power spectral density in the range of 10 μm≦spatial wavelength λn≦20 μm １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ It was found that the value of the σ should be 3.00 or less.

[0012] However, according to the findings of the present inventors, in order to increase the areal recording density, the average grain volume of the magnetic grains is increased to 1.50×10 ３ nm ３ If the temperature is lower than this, there is a risk that good electromagnetic conversion characteristics cannot be maintained in a high-temperature, high-humidity environment. The present inventors have conducted extensive research into the cause of this, and as a result, have discovered that the deterioration of the characteristics occurs in the following manner.

[0013] When moisture diffuses into the magnetic layer in a high-temperature, high-humidity environment, acidic compounds contained in the magnetic layer may dissolve in the moisture, generating an acidic aqueous solution. When acidic compounds that are not adsorbed to magnetic particles are present in the magnetic layer, acidic aqueous solutions are particularly likely to be generated due to the above phenomenon. The generated acidic aqueous solution may corrode (dissolve) the magnetic particles. Corrosion of the magnetic particles reduces the particle size of the magnetic particles, which may result in a decrease in magnetic properties (e.g., saturation magnetization Ms), and as a result, a decrease in electromagnetic conversion properties. When the average particle volume of the magnetic particles is large, the specific surface area of ​​the magnetic particles is small, so a decrease in magnetic properties (e.g., saturation magnetization Ms), i.e., a decrease in electromagnetic conversion properties, due to corrosion of the magnetic particles is less noticeable. However, when the average particle volume of the magnetic particles is small, 1.50 × 10 ３ nm ３Below this, the specific surface area of ​​the magnetic particles becomes significantly large, and the deterioration of the magnetic properties (for example, saturation magnetization Ms) due to corrosion of the magnetic particles, that is, the deterioration of the electromagnetic conversion properties, becomes noticeable.

[0014] Taking into consideration the causes of the deterioration of the electromagnetic conversion characteristics, the present inventors have determined that the average particle volume of the magnetic particles is 1.50×10 ３ nm ３ As a result, it was found that by making the rate of decrease in saturation magnetization Ms in an 8-week high-temperature, high-humidity environment test at a temperature of 60°C and a humidity of 90 RH% 1.00% or less, the average particle volume of the magnetic particles can be reduced to 1.50 x 10 ３ nm ３ It has been found that even in the case of the above, good electromagnetic conversion characteristics can be maintained in a high-temperature, high-humidity environment.

[0015] [2 Cartridge Configuration] Figure 1 is an exploded perspective view showing an example of the configuration of a cartridge 10. The cartridge 10 is a single-reel cartridge, and includes a cartridge case 12 composed of a lower shell 12A and an upper shell 12B, a reel 13 on which magnetic tape MT is wound, a reel lock 14 and a reel spring 15 for locking the rotation of the reel 13, a spider 16 for unlocking the locked state of the reel 13, a slide door 17 for opening and closing a tape outlet 12C provided in the cartridge case 12 across the lower shell 12A and the upper shell 12B, a door spring 18 for biasing the slide door 17 to a closed position of the tape outlet 12C, a write protect 19 for preventing accidental erasure, and a cartridge memory 11. The reel 13 for winding the magnetic tape MT is generally disc-shaped with an opening in the center, and is composed of a reel hub 13A and a flange 13B made of a hard material such as plastic. A leader tape LT is connected to the outer peripheral end of the magnetic tape MT, and a leader pin 20 is provided at the tip of the leader tape LT.

[0016] The cartridge 10 may be a magnetic tape cartridge conforming to the LTO (Linear Tape-Open) standard, or may be a magnetic tape cartridge conforming to a standard other than the LTO standard.

[0017] The cartridge memory 11 is provided near one corner of the cartridge 10. When the cartridge 10 is loaded into a recording / playback device, the cartridge memory 11 faces a reader / writer of the recording / playback device. The cartridge memory 11 communicates with the recording / playback device, specifically the reader / writer, using a wireless communication standard that complies with the LTO standard.

[0018] 2 is a block diagram showing an example of the configuration of the cartridge memory 11. The cartridge memory 11 includes an antenna coil (communication unit) 31 that communicates with a reader / writer using a specified communication standard, a rectification / power circuit 32 that generates power by rectifying and generating electricity from radio waves received by the antenna coil 31 using induced electromotive force, a clock circuit 33 that generates a clock from the radio waves received by the antenna coil 31 using induced electromotive force, a detection / modulation circuit 34 that detects the radio waves received by the antenna coil 31 and modulates the signal to be transmitted by the antenna coil 31, a controller (control unit) 35 that is composed of logic circuits and the like for determining commands and data from the digital signal extracted from the detection / modulation circuit 34 and processing them, and a memory (storage unit) 36 that stores information. The cartridge memory 11 also includes a capacitor 37 connected in parallel to the antenna coil 31, and the antenna coil 31 and the capacitor 37 form a resonant circuit.

[0019] The memory 36 stores information relating to the cartridge 10. The memory 36 is a non-volatile memory (NVM). The memory 36 preferably has a storage capacity of approximately 32 KB or more.

[0020] The memory 36 may have a first memory area 36A and a second memory area 36B. The first memory area 36A corresponds to the memory area of ​​a cartridge memory for a magnetic tape standard prior to a specified generation (e.g., an LTO standard prior to LTO8), and is an area for storing information conforming to the magnetic tape standard prior to the specified generation. The information conforming to the magnetic tape standard prior to the specified generation may include, for example, manufacturing information (e.g., a unique number for the cartridge 10), usage history (e.g., the number of times the tape has been pulled out (Thread Count)), etc.

[0021] The second memory area 36B corresponds to an extended memory area for the cartridge memory storage area for magnetic tape standards prior to the specified generation (e.g., LTO standards prior to LTO8). The second memory area 36B is an area for storing additional information. Here, additional information refers to, for example, information related to the cartridge 10 that is not specified in magnetic tape standards prior to the specified generation (e.g., LTO standards prior to LTO8). The additional information includes, but is not limited to, at least one type of information selected from the group consisting of tension adjustment information, management ledger data, index information, and thumbnail information. The tension adjustment information is information for adjusting the tension applied to the magnetic tape MT in the longitudinal direction. The tension adjustment information includes, for example, at least one type of information selected from the group consisting of information obtained by intermittently measuring the width between servo bands in the longitudinal direction of the magnetic tape MT, drive tension information, and drive temperature and humidity information. This information may be managed in conjunction with information regarding the usage status of the cartridge 10. The tension adjustment information is preferably obtained when or before data is recorded on the magnetic tape MT. The tension information of the drive means information about the tension applied to the magnetic tape MT in the longitudinal direction.

[0022] The management ledger data includes at least one type of data selected from the group consisting of the capacity, creation date, edit date, and storage location of the data files recorded on the magnetic tape MT. The index information is metadata for searching the contents of the data files. The thumbnail information is a thumbnail of the moving or still image stored on the magnetic tape MT.

[0023] The memory 36 may have a plurality of banks. In this case, some of the plurality of banks may constitute a first storage area 36A, and the remaining banks may constitute a second storage area 36B.

[0024] The antenna coil 31 induces an induced voltage by electromagnetic induction. The controller 35 communicates with the recording / playback device in accordance with a specified communication standard via the antenna coil 31. Specifically, for example, mutual authentication, sending and receiving of commands, and data exchange are performed.

[0025] The controller 35 stores information received from the recording / playback device via the antenna coil 31 in the memory 36. For example, the controller 35 stores tension adjustment information received from the recording / playback device via the antenna coil 31 in the second storage area 36B of the memory 36. In response to a request from the recording / playback device, the controller 35 reads information from the memory 36 and transmits it to the recording / playback device via the antenna coil 31. For example, in response to a request from the recording / playback device, the controller 35 reads tension adjustment information from the second storage area 36B of the memory 36 and transmits it to the recording / playback device via the antenna coil 31.

[0026] [4. Magnetic Tape Configuration] FIG. 3 is a cross-sectional view showing an example of the configuration of a magnetic tape MT. The magnetic tape MT is an example of a tape-shaped magnetic recording medium, and includes a long substrate 41, an underlayer 42 provided on one main surface (first main surface) of the substrate 41, a magnetic layer 43 provided on the underlayer 42, and a back layer 44 provided on the other main surface (second main surface) of the substrate 41. The underlayer 42 and the back layer 44 are provided as needed and may be omitted. The magnetic tape MT may be a perpendicular recording type magnetic recording medium or a longitudinal recording type magnetic recording medium. From the viewpoint of improving running performance, the magnetic tape MT preferably includes a lubricant. The lubricant may be contained in at least one of the underlayer 42 and the magnetic layer 43. The magnetic tape MT may further include a lubricant layer provided on the surface of the magnetic layer 43. In this specification, the surface of the magnetic tape MT facing the magnetic layer 43 is sometimes referred to as the magnetic surface, and the surface of the magnetic tape MT facing the back layer 44 is sometimes referred to as the back surface.

[0027] The magnetic tape MT may conform to the LTO standard, or may conform to a standard other than the LTO standard. The width of the magnetic tape MT may be 1 / 2 inch, or may be wider than 1 / 2 inch. If the magnetic tape MT conforms to the LTO standard, the width of the magnetic tape MT is 1 / 2 inch. The magnetic tape MT may have a configuration that allows the width of the magnetic tape MT to be kept constant or approximately constant by adjusting the tension applied to the magnetic tape MT in the longitudinal direction during running using a recording / playback device (drive).

[0028] The magnetic tape MT has a long shape and runs longitudinally during recording and playback. The magnetic tape MT is preferably used in a recording and playback device equipped with a ring-type head as a recording head. The magnetic tape MT is configured to be capable of recording signals at a linear recording density D. From the viewpoint of achieving high recording capacity, the lower limit of the linear recording density D of signals recordable on the magnetic tape MT is preferably 545 kfci or more, more preferably 549 kfci or more, even more preferably 550 kfci or more, 552 kfci or more, 577 kfci or more, 600 kfci or more, or 635 kfci or more. The upper limit of the linear recording density D of data recordable on the magnetic tape MT is preferably 1270 kfci or less, taking into account the magnetic particle size.

[0029] The magnetic tape MT is preferably reproduced by a reproducing head using a tunnel magnetoresistance (TMR) element. The signal reproduced by the reproducing head using the TMR element may be data recorded in the data band DB (see FIG. 4) or a servo pattern (servo signal) recorded in the servo band SB (see FIG. 4).

[0030] (Substrate) The substrate 41 is a non-magnetic support that supports the underlayer 42 and the magnetic layer 43. The substrate 41 has a long film shape. The average thickness t １ From the viewpoint of improving the recording capacity that can be recorded on one data cartridge, the upper limit of the average thickness t of the substrate 41 is preferably 4.40 μm or less, more preferably 4.20 μm or less, and even more preferably 4.00 μm or less, 3.80 μm or less, or 3.40 μm or less. １ The lower limit of the average thickness t of the substrate 41 is preferably 3.00 μm or more, more preferably 3.20 μm or more, and even more preferably 3.80 μm or more. １ When the lower limit value is 3.00 μm or more, the decrease in strength of the base 41 can be suppressed.

[0031] Average thickness t of the substrate 41 １is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting out a 250 mm length of the magnetic tape MT at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. In this specification, the "longitudinal direction" when referring to "the longitudinal direction from one end of the outer periphery of the magnetic tape MT" means the direction from one end of the magnetic tape MT on the outer periphery toward the other end on the inner periphery.

[0032] Next, the layers of the sample other than the substrate 41 (i.e., the underlayer 42, the magnetic layer 43, and the back layer 44) are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample (substrate 41) is measured at five positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t of the substrate 41. １ The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT.

[0033] From the viewpoint of cost reduction, the base 41 preferably contains a polyester-based resin as a main component. Examples of polyester-based resins include at least one selected from the group consisting of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene p-oxybenzoate), and polyethylene bisphenoxycarboxylate. When the base 41 contains two or more polyester-based resins, these two or more polyester-based resins may be mixed, copolymerized, or laminated. At least one of the terminals and side chains of the polyester-based resin may be modified. In addition to the polyester-based resin, the base 41 may also contain a resin other than the polyester-based resin described below.

[0034] In this specification, the term "main component" refers to the component that has the highest content ratio among the components that constitute the base 41. For example, when the main component of the base 41 is a polyester-based resin, the content ratio of the polyester-based resin in the base 41 may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more relative to the mass of the base 41, or the base 41 may be composed only of a polyester-based resin.

[0035] The presence of polyester resin in the substrate 41 can be confirmed, for example, as follows. First, the average thickness t １ Similar to the measurement method of (1), a magnetic tape MT is prepared and cut into a length of 250 mm to prepare a sample, and then the layers other than the substrate 41 of the sample are removed. Next, an IR spectrum of the sample (substrate 41) is obtained by infrared absorption spectrometry (IR). Based on this IR spectrum, it can be confirmed that the substrate 41 contains a polyester-based resin.

[0036] The substrate 41 preferably contains a polyester-based resin. By including a polyester-based resin in the substrate 41, the Young's modulus in the longitudinal direction of the substrate 41 can be reduced preferably to 2.5 GPa or more and 7.8 GPa or less, more preferably to 3.0 GPa or more and 7.0 GPa or less. Therefore, by adjusting the tension in the longitudinal direction of the magnetic tape MT during running using a recording / reproducing device, the width of the magnetic tape MT can be kept constant or approximately constant. A method for measuring the Young's modulus in the longitudinal direction of the substrate 41 will be described later.

[0037] The base 41 may contain a resin other than a polyester-based resin. In this case, the resin other than a polyester-based resin may be the main component of the base 41's constituent material. When a resin other than a polyester-based resin is the main component of the base 41's constituent material, the content of the resin other than a polyester-based resin in the base 41 may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more relative to the mass of the base 41. Alternatively, the base 41 may be composed solely of a resin other than a polyester-based resin. The resin other than a polyester-based resin may include, for example, at least one selected from the group consisting of polyolefin-based resins, cellulose derivatives, vinyl-based resins, and other polymer resins. When the base 41 contains two or more of these resins, the two or more materials may be mixed, copolymerized, or laminated.

[0038] The polyolefin resin includes, for example, at least one selected from the group consisting of PE (polyethylene) and PP (polypropylene). The cellulose derivative includes, for example, at least one selected from the group consisting of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). The vinyl resin includes, for example, at least one selected from the group consisting of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0039] Examples of other polymer resins include at least one selected from the group consisting of PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, for example, Zylon (registered trademark)), polyether, PEK (polyether ketone), polyether ester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane). Specifically, for example, the base 41 may contain, as a main component, PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, for example, Zylon (registered trademark)), polyether, PEK (polyether ketone), polyether ester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), or PU (polyurethane).

[0040] The substrate 41 may be biaxially stretched in the longitudinal direction and the width direction. The polymer resin contained in the substrate 41 is preferably oriented in a direction oblique to the width direction of the substrate 41.

[0041] (Magnetic Layer) The magnetic layer 43 is configured to record signals using a magnetization pattern. The magnetic layer 43 may be a perpendicular recording type recording layer or a longitudinal recording type recording layer. The magnetic layer 43 contains, for example, magnetic particles, a binder, and an acidic compound. If necessary, the magnetic layer 43 may further contain at least one additive selected from the group consisting of carbon particles, lubricants, abrasive particles, antistatic agents, hardeners, rust inhibitors, and non-magnetic reinforcing particles. The magnetic layer 43 may have a plurality of protrusions 430 on the magnetic surface. The plurality of protrusions 430 are formed, for example, by carbon particles, abrasive particles, etc. protruding from the magnetic surface.

[0042] The magnetic layer 43 may have a plurality of holes on its surface. A lubricant may be stored in the holes. In this case, the supply of the lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes extend in a direction perpendicular to the magnetic surface.

[0043] As shown in FIG. 4, the magnetic layer 43 may have a plurality of servo bands SB and a plurality of data bands DB in advance. The plurality of servo bands SB are arranged at equal intervals in the width direction of the magnetic tape MT. A data band DB is arranged between adjacent servo bands SB. The servo bands SB are used to guide the head unit (magnetic head) 56 (specifically, servo read heads 56A and 56B) when recording or reproducing data. Servo patterns (servo signals) for tracking control of the head unit 56 are written in advance in the servo bands SB. User data is recorded in the data bands DB.

[0044] In order to read asymmetric servo stripes 113 (see FIG. 6 ), which will be described later, the head unit 56 may be configured to be able to maintain an angle with respect to an axis Ax parallel to the width direction of the magnetic tape MT during data recording and reproduction, as shown in FIG. 4 . Hereinafter, a head unit maintained at an angle with respect to the axis Ax parallel to the width direction of the magnetic tape MT in this manner may be referred to as a “angled head unit.” The angle of inclination of the head unit 56 with respect to the axis Ax parallel to the width direction of the magnetic tape MT is preferably 3° to 18°, more preferably 5° to 15°.

[0045] The total area S of the plurality of servo bands SB relative to the area S of the magnetic surface ＳＢ Ratio R Ｓ (=(S ＳＢ From the viewpoint of ensuring a high recording capacity, the upper limit of the ratio (S / S) × 100) is preferably 4.0% or less, more preferably 3.5% or less, and even more preferably 3.0% or less. ＳＢ Ratio R Ｓ The lower limit of is preferably 1.0% or more from the viewpoint of ensuring 5 or more servo bands SB.

[0046] The total area S of the plurality of servo bands SB relative to the area S of the entire magnetic surface ＳＢ Ratio R Ｓ The magnetic tape MT is developed using a ferricolloid developer (Sigma Marker Q, manufactured by Sigma High Chemical Co., Ltd.), and the developed magnetic tape MT is then observed under an optical microscope to determine the servo bandwidth W ＳＢ and the number of servo bands SB. Next, the ratio R is calculated from the following formula: Ｓ Calculate the ratio R Ｓ [%] = (((Servo bandwidth W ＳＢ ) × (number of servo bands SB)) / (width of magnetic tape MT)) × 100

[0047] The number of servo bands SB is, for example, 5+4n (where n is an integer greater than or equal to 0) or more. The number of servo bands SB is preferably 5 or more, and more preferably 9 or more. If the number of servo bands SB is 5 or more, the effect on the servo signal due to dimensional changes in the width direction of the magnetic tape MT can be suppressed, and stable recording and reproduction characteristics with less off-track can be ensured. The upper limit of the number of servo bands SB is not particularly limited, but is, for example, 33 or less.

[0048] The number of servo bands SB is determined by the above ratio R Ｓ It can be calculated in the same way as

[0049] Servo Bandwidth W ＳＢ From the viewpoint of ensuring a high recording capacity, the upper limit of the servo bandwidth W is preferably 95 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less. ＳＢ The lower limit of the servo bandwidth W is preferably 10 μm or more. ＳＢ It is difficult to manufacture a magnetic head that can read such servo signals.

[0050] Servo Bandwidth W ＳＢ The width of the ratio R Ｓ It can be calculated in the same way as

[0051] 5A, the magnetic layer 43 is configured so that multiple data tracks Tk can be formed in the data band DB. From the viewpoint of improving track recording density and ensuring high recording capacity, the upper limit of the data track width W is preferably 700 nm or less, more preferably 650 nm or less, even more preferably 500 nm or less, and particularly preferably 400 nm or less. The lower limit of the data track width W is preferably 20 nm or more, taking into account the magnetic particle size.

[0052] The data track width W is calculated as follows. First, a cartridge 10 is prepared with data recorded on the entire surface of the magnetic tape MT. The magnetic tape MT is unwound from the cartridge 10, and a 250 mm sample is cut from the magnetic tape MT at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the data recording pattern in the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. The MFM used is a Digital Instruments Dimension3100 and its analysis software. The measurement area of ​​the MFM image is 10 μm × 10 μm, and this 10 μm × 10 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Three 10 μm × 10 μm measurement areas in different locations are measured using the MFM, resulting in three MFM images. The track width was measured at 10 locations on each of the three MFM images obtained, for a total of 30 measurement values, and the average value (simple average) of the 30 measurement values ​​was calculated. This average value is the data track width W. The analysis software included with the Dimension3100 was used to measure the track width. The MFM measurement conditions were: sweep speed: 1 Hz, tip used: MFMR-20, lift height: 20 nm, and correction: Flatten order 3.

[0053] 5A shows an example in which adjacent data tracks Tk are recorded so as not to overlap, but the recording method for the data tracks Tk is not limited to this example. For example, as shown in FIG. 5B, adjacent data tracks Tk may be recorded so as to partially overlap each other in the width direction of the magnetic tape MT by using shingled magnetic recording (SMR).

[0054] 5B, head 61 and head 62 represent a recording head and a reproducing head, respectively. In the case of the shingled magnetic recording method, the data track width W is the recording track width W ＲTherefore, in the case of shingled magnetic recording, the width of the read head 62 is narrower than the width of the write head 61. As described above, in the shingled magnetic recording, the data track width W is narrower than the recording track width W Ｒ Since the recording track width W is narrower than the recording track width W, it is advantageous in terms of improving the recording density. Ｒ represents the track width when writing data. When shingled magnetic recording is used as the recording method, the recording track width W Ｒ represents the track width before overwriting (the track width when data is written).

[0055] The magnetic layer 43 has a minimum magnetization reversal distance L min The minimum distance between magnetization reversals L min From the viewpoint of achieving high recording capacity, the upper limit of the distance L is preferably 46.6 nm or less, more preferably 46.3 nm or less, and even more preferably 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less. min Considering the size of the magnetic particles, the lower limit is preferably 20.0 nm or more.

[0056] Minimum distance between magnetization reversals L minis calculated as follows. First, a sample is prepared using the same method as for measuring the data track width W. Next, the data recording pattern in the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. The MFM used is a Dimension3100 manufactured by Digital Instruments and its analysis software. The measurement area of ​​the MFM image is 2 μm × 2 μm, and this 2 μm × 2 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Three 2 μm × 2 μm measurement areas in different locations are measured using the MFM, resulting in three MFM images. Fifty inter-bit distances are measured from a two-dimensional concavo-convex chart of the recording pattern of the obtained MFM image. The inter-bit distances are measured using the analysis software provided with the Dimension3100. The value that is approximately the greatest common divisor of the 50 measured inter-bit distances is set as the minimum value L of the inter-magnetic reversal distance. min The measurement conditions are: sweep rate: 1 Hz, tip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3.

[0057] The magnetic layer 43 is configured to be able to record signals in the data band DB with a bit length (1 bit length) T. From the viewpoint of improving the linear recording density D of the magnetic tape MT, the upper limit of the bit length T of the signal recordable in the data band DB is preferably 47.0 nm or less, more preferably 46.6 nm or less, and even more preferably 46.3 nm or less, 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less. Taking the magnetic particle size into consideration, the lower limit of the bit length T of the signal recordable in the data band DB is preferably 20.0 nm or more.

[0058] The bit length T of the signal that can be recorded in the data band DB is the minimum value L min It can be determined in the same manner as in the measurement method of

[0059] The bit area of ​​the signal that can be recorded on the data band DB is preferably 40,000 nm from the viewpoint of improving the linear recording density D of the magnetic tape MT. ２or less, more preferably 35,000 nm ２ or less, more preferably 30,000 nm ２ Below, 25000nm ２ or below 20,000 nm ２ The following is the result.

[0060] The bit area of ​​a signal recordable on the data band DB can be calculated as follows: First, three MFM images are obtained in the same manner as in the method for measuring the data track width W. Next, the data track width W and bit length T are calculated in the same manner as in the method for measuring the data track width W and bit length T. Next, the bit area (W x T) of a signal recordable on the data band DB is calculated using the data track width W and bit length T.

[0061] The servo patterns are magnetized regions, and are formed by magnetizing specific regions of the magnetic layer 43 in specific directions using a servo write head during magnetic tape manufacturing. The regions of the servo bands SB where no servo patterns are formed (hereinafter referred to as "non-pattern regions") may be magnetized regions where the magnetic layer 43 is magnetized, or may be non-magnetized regions where the magnetic layer 43 is not magnetized. When the non-pattern regions are magnetized regions, the servo pattern forming regions and the non-pattern regions are magnetized in different directions (e.g., opposite directions).

[0062] In the LTO standard, a servo pattern is formed on the servo band SB, as shown in FIG. 6, consisting of multiple servo stripes (linear magnetized regions) 113 inclined with respect to an axis Ax parallel to the width direction of the magnetic tape MT.

[0063] The servo band SB includes a plurality of servo frames 110. Each servo frame 110 is made up of 18 servo stripes 113. Specifically, each servo frame 110 is made up of a servo subframe 1 (111) and a servo subframe 2 (112).

[0064] Servo subframe 1 (111) is composed of an A burst 111A and a B burst 111B. The B burst 111B is arranged adjacent to the A burst 111A. The A burst 111A is inclined at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. １ 6, these five servo stripes 113 are inclined at a regular interval from the EOT (End Of Tape) to the BOT (Beginning Of Tape) of the magnetic tape MT, and are labeled with the symbol A. １ , A ２ , A ３ , A ４ , A ５ are indicated with .

[0065] The B burst 111B is at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. ２ 6, these five servo stripes 113 are inclined at regular intervals from the EOT to the BOT of the magnetic tape MT. １ , B ２ , B ３ , B ４ , B ５ are indicated with .

[0066] The servo stripes 113 of the B burst 111B are inclined in the opposite direction to the servo stripes 113 of the A burst 111A. The servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are asymmetric with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are arranged in a substantially V-shape. Because the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are asymmetric with respect to the axis Ax, when the head unit 56 is tilted obliquely with respect to the axis Ax, there exists a state in which the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are substantially symmetric with respect to the central axis of the sliding surface of the head unit 56. By changing the tilt of the head unit 56 based on this state, it is possible to adjust the distance between the servo read heads 56A and 56B in the width direction of the magnetic tape MT. Therefore, in both cases where the width of the magnetic tape MT is increased and where the width of the magnetic tape MT is decreased, the servo read heads 56A and 56B can be made to face the specified positions of the servo bands SB. Note that the central axis of the sliding surface of the head unit 56 refers to the axis that passes through the centers of the multiple servo read heads 56A and 56B on the sliding surface of the head unit 56.

[0067] A predetermined angle θ, which is the inclination angle of the servo stripe 113 of the A burst 111A １ and a predetermined angle θ which is the inclination angle of the servo stripe 113 of the B burst 111B. ２ More specifically, the predetermined angle θ of the servo stripe 113 of the A burst 111A is different from １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ , or the predetermined angle θ of the servo stripe 113 of the B burst 111B. ２ However, the predetermined angle θ of the servo stripe 113 of the A burst 111A １That is, the inclination of the servo stripes 113 of the A burst 111A may be larger than the inclination of the servo stripes 113 of the B burst 111B, or the inclination of the servo stripes 113 of the B burst 111B may be larger than the inclination of the servo stripes 113 of the A burst 111A. Note that in FIG. 6, the predetermined angle θ of the servo stripes 113 of the A burst 111A １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ In the following, the predetermined angle θ of the servo stripe 113 of the A burst 111A is shown. １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ The case where it is larger than

[0068] Servo subframe 2 (112) is composed of a C burst 112C and a D burst 112D. The D burst 112D is arranged adjacent to the C burst 112C. The C burst 112C is inclined at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. １ 6, the four servo stripes 113 are inclined at a predetermined interval from the EOT to the BOT of the magnetic tape MT and are marked with the symbol C １ , C ２ , C ３ , C ４ are indicated with .

[0069] The D burst 112D is at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. ２ 6, the four servo stripes 113 are inclined at a predetermined interval from the EOT to the BOT of the magnetic tape MT and are indicated by the symbol D. １ , D ２ , D ３ , D ４ are indicated with .

[0070] The servo stripes 113 of the D burst 112D are inclined in the opposite direction to the servo stripes 113 of the C burst 112C. The servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are asymmetric with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are arranged in a generally V-shape. Because the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are asymmetric with respect to the axis Ax, when the head unit 56 is tilted obliquely with respect to the axis Ax, there exists a state in which the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are generally symmetric with respect to the central axis of the head unit 56. By changing the tilt of the head unit 56 based on this state, it is possible to adjust the servo distance.

[0071] The predetermined angle θ is the inclination angle of the servo stripe 113 of the C burst 112C. １ and a predetermined angle θ which is the inclination angle of the servo stripe 113 of the D burst 112D. ２ More specifically, the predetermined angle θ of the servo stripe 113 of the C burst 112C is different from １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２ , or the predetermined angle θ of the servo stripe 113 of the D burst 112D. ２ However, the predetermined angle θ of the servo stripe 113 of the C burst 112C １ That is, the inclination of the servo stripes 113 of the C burst 112C may be larger than the inclination of the servo stripes 113 of the D burst 112D, or the inclination of the servo stripes 113 of the D burst 112D may be larger than the inclination of the servo stripes 113 of the C burst 112C. Note that in FIG. 6, the predetermined angle θ of the servo stripes 113 of the C burst 112C １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２In the following, the predetermined angle θ of the servo stripe 113 of the C burst 112C is １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２ The case where it is larger than

[0072] The predetermined angle θ of the servo stripe 113 in the A burst 111A and the C burst 112C １ is preferably 18° or more and 28° or less, and more preferably 18° or more and 26° or less. ２ is preferably -4° or more and 6° or less, and more preferably -2° or more and 6° or less. The servo stripes 113 in the A burst 111A and the C burst 112C are an example of a first magnetization region. The servo stripes 113 in the B burst 111B and the D burst 112D are an example of a second magnetization region.

[0073] Reading the servo bands SB with the head unit 56 provides information for obtaining the tape speed and the longitudinal position of the head unit 56. The tape speed is calculated from the time between four timing signals (A1-C1, A2-C2, A3-C3, A4-C4). The head position is calculated from the time between the aforementioned four timing signals and another four timing signals (A １ -B １ , A ２ -B ２ , A ３ -B ３ , A ４ -B ４ ) The servo pattern may be a shape that includes two parallel lines.

[0074] 6, the servo patterns (i.e., the plurality of servo stripes 113) are preferably arranged linearly in the longitudinal direction of the magnetic tape MT. That is, the servo bands SB preferably have a linear shape in the longitudinal direction of the magnetic tape MT.

[0075] The average thickness t of the magnetic layer 43 ２The upper limit of the average thickness t of the magnetic layer 43 is preferably 0.08 μm or less, more preferably 0.07 μm or less, even more preferably 0.06 μm or less, and particularly preferably 0.05 μm or less. ２ If the upper limit value is 0.08 μm or less, when a ring-type head is used as the recording head, the influence of the demagnetizing field can be reduced, and therefore, even better electromagnetic conversion characteristics can be obtained.

[0076] The average thickness t of the magnetic layer 43 ２ The lower limit of the average thickness t of the magnetic layer 43 is preferably 0.03 μm or more, and more preferably 0.04 μm or more. ２ If the lower limit is 0.03 μm or more, when an MR type head is used as the reproducing head, output can be ensured, and therefore even better electromagnetic conversion characteristics can be obtained.

[0077] The average thickness t of the magnetic layer 43 ２ The numerical range of may be defined by any one of the above upper limit values ​​and any one of the above lower limit values, and is preferably 0.03 μm or more and 0.08 μm or less, more preferably 0.04 μm or more and 0.07 μm or less, even more preferably 0.04 μm or more and 0.06 μm or less, and particularly preferably 0.04 μm or more and 0.05 μm or less.

[0078] The average thickness t of the magnetic layer 43 ２is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and three 250 mm samples are cut from the magnetic tape MT at positions 10 m to 20 m, 30 m to 40 m, and 50 m to 60 m from one end of the outer periphery of the magnetic tape MT in the longitudinal direction, respectively. Each sample is then thinned using a method such as FIB (Focused Ion Beam). When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM images described below. The carbon layer is formed on the magnetic surface and back surface of the magnetic tape MT by vapor deposition, and the tungsten layer is further formed on the magnetic surface by vapor deposition or sputtering. The thinning is performed along the longitudinal direction of the magnetic tape MT. That is, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape MT.

[0079] The cross section of each obtained thinned sample was observed under the following conditions using a transmission electron microscope (TEM) to obtain a TEM image of each thinned sample. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Device: TEM (H9000NAR manufactured by Hitachi, Ltd.) Acceleration voltage: 300 kV Magnification: 100,000 times

[0080] Next, using the TEM image of each obtained thinned sample, the thickness of the magnetic layer 43 is measured at 10 positions on each thinned sample. The 10 measurement positions on each thinned sample are randomly selected from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT. The measured values ​​of each obtained thinned sample (thickness of the magnetic layer 43 at 30 points in total) are simply averaged (arithmetic average) to obtain an average value, which is the average thickness t of the magnetic layer 43. ２ Let [nm].

[0081] (Magnetic Particles) The magnetic particles are ferrite particles. The ferrite particles may include, for example, particles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles"), particles containing epsilon iron oxide (ε-iron oxide) (hereinafter referred to as "ε-iron oxide particles"), or particles containing Co-containing spinel ferrite (hereinafter referred to as "cobalt ferrite particles"). It is preferable that the magnetic particles have a preferential crystal orientation in the perpendicular direction of the magnetic tape MT. In this specification, the perpendicular direction (thickness direction) of the magnetic tape MT means the thickness direction of the magnetic tape MT in a flat state.

[0082] (Hexagonal Ferrite Particles) The hexagonal ferrite particles have, for example, a plate shape such as a hexagonal plate or a columnar shape such as a hexagonal pillar (however, the thickness or height is smaller than the major axis of the plate surface or base). In the present disclosure, the hexagonal plate shape includes a substantially hexagonal plate shape. Furthermore, the hexagonal pillar shape includes a substantially hexagonal pillar shape.

[0083] The hexagonal ferrite particles contain Fe and a metal M1 other than Fe. The metal M1 contains, for example, at least one alkaline earth metal. The at least one alkaline earth metal contains, for example, at least one selected from the group consisting of Ba, Sr, and Ca. Among these alkaline earth metals, it is preferable to contain at least one of Ba and Sr. The metal M1 may contain Pb in addition to the alkaline earth metal.

[0084] The hexagonal ferrite particles may further contain a metal M2 in addition to Fe and metal M1. The metal M2 is preferably capable of substituting a portion of the Fe sites in the crystal structure of the hexagonal ferrite. The metal M2 includes, for example, at least one selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table, and among these, at least one selected from the group consisting of Ti, Al, and Nd is preferred.

[0085] In the present disclosure, rare earth elements are defined as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Transition metal elements other than Fe are defined as Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Hf, Ta, and W. Metal elements of Group 13 of the periodic table are defined as Al, Ga, In, and Tl.

[0086] Specifically, the hexagonal ferrite particles may be, for example, barium ferrite particles or strontium ferrite particles. In the present disclosure, strontium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic % or more. Therefore, hexagonal ferrite particles containing Sr and a metal M1 other than Sr are included in strontium ferrite particles if the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic % or more. For example, if metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Sr to the total amount of Sr and Ba (Sr / (Sr+Ba)) is 50 atomic % or more are called strontium ferrite particles.

[0087] In the present disclosure, barium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic % or more. Therefore, hexagonal ferrite particles containing Ba and a metal M1 other than Ba ​​are included in barium ferrite particles if the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic % or more. For example, when metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Ba to the total amount of Sr and Ba (Ba / (Sr+Ba)) is 50 atomic % or more are called barium ferrite particles.

[0088] The average atomic ratio of Sr to Ba (Sr / Ba) is preferably 0.02 or more and 2.00 or less, more preferably 0.02 or more and 1.00 or less. When the average atomic ratio (Sr / Ba) is 0.02 or more, it is possible to suppress a decrease in the effect of adding Sr to improve magnetic properties (for example, the effect of improving thermal stability (Ku) derived from strontium ferrite). When the average atomic ratio (Sr / Ba) is 2.00 or less, it is possible to suppress variation in magnetic properties.

[0089] More specifically, the hexagonal ferrite may have an average composition represented by the following general formula (A): （１－ｘ） α ｘ Fe （１２－ｙ） β ｙ O １９ ...(A) (In formula (A), α represents at least one element selected from the group consisting of Sr, Ca, and Pb. β represents at least one element selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table. x is within the range of 0≦x≦0.9, preferably 0≦x≦0.7, and more preferably 0.3≦x≦0.7. y is within the range of 0≦y≦0.80, preferably 0.22≦y≦0.80, and more preferably 0.26≦y≦0.80.)

[0090] The average atomic ratio of Sr to Ba is calculated from analytical values ​​obtained using STEM-EDX (Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy) (HD-2700, manufactured by Hitachi High-Technologies Corporation) as follows. First, the magnetic tape MT is unwound from the cartridge 10, and three magnetic tape MT pieces are cut out at positions 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT to prepare three samples. Next, each sample is processed and sliced ​​using an FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM images described below. The carbon layer is formed by vapor deposition on the surface of the magnetic layer side and the surface of the back layer side of the magnetic tape MT, and the tungsten layer is further formed on the surface of the magnetic layer side by vapor deposition or sputtering. The slices are formed along the longitudinal direction of the magnetic tape MT. That is, this thinning process forms a cross section parallel to both the longitudinal and thickness directions of the magnetic tape MT. The cross section of each obtained thinned sample was observed using a TEM at an acceleration voltage of 200 kV and a total magnification of 500,000 times to obtain a TEM image of each thinned sample. Next, EDX measurement of the magnetic layer portion of each obtained thinned sample was performed to determine the atomic ratio of Sr to Ba (Sr / Ba). The atomic ratios (Sr / Ba) obtained for each of the three thinned samples were simply averaged (arithmetic mean) to obtain the average atomic ratio (Sr / Ba).

[0091] The average atomic ratio of Sr to metal M1 (Sr / M1) is determined as follows. First, TEM images of three sliced ​​samples are obtained in the same manner as for the average atomic ratio of Sr to Ba (Sr / Ba). Next, EDX measurement of the magnetic layer portion is performed from the TEM image of each obtained sliced ​​sample to determine the average atomic ratio of Sr to metal M1 (Sr / M1). The atomic ratios (Sr / M1) determined for each of the three sliced ​​samples are simply averaged (arithmetic mean) to obtain the average atomic ratio (Sr / M1).

[0092] The average atomic ratio of Ba to metal M1 (Ba / M1) is determined as follows. First, TEM images of three sliced ​​samples are obtained in the same manner as for the average atomic ratio of Sr to Ba (Sr / Ba). Next, EDX measurement of the magnetic layer portion is performed from the TEM image of each obtained sliced ​​sample to determine the average atomic ratio of Ba to metal M1 (Ba / M1). The atomic ratios (Ba / M1) determined for each of the three sliced ​​samples are simply averaged (arithmetic mean) to obtain the average atomic ratio (Ba / M1).

[0093] The average composition represented by the general formula (A) can be determined as follows: First, TEM images of three sliced ​​samples are obtained in the same manner as for the average atomic ratio of Sr to Ba (Sr / Ba). Next, EDX measurement is performed on the magnetic layer portion of each obtained TEM image of each sliced ​​sample, and Ba is calculated. 、 α 、 Fe 、 The average composition ratio (average atomic ratio) of each of β is determined.

[0094] When the magnetic particles are hexagonal ferrite particles, the upper limit of the average particle size of the magnetic particles is preferably 19.0 nm or less, more preferably 18.0 nm or less, and even more preferably 17.0 nm or less, 16.0 nm or less, or 15.0 nm or less, from the viewpoint of improving linear recording density.

[0095] When the magnetic particles are hexagonal ferrite particles, the lower limit of the average particle size of the magnetic particles is preferably 13.0 nm or more, and more preferably 14.0 nm or more, from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (e.g., SNR (Signal-to-Noise Ratio)).

[0096] When the magnetic particles are hexagonal ferrite particles, the numerical range of the average particle size of the magnetic particles may be defined by any one of the upper limit values ​​and any one of the lower limit values, and is preferably 13.0 nm or more and 19.0 nm or less, more preferably 13.0 nm or more and 18.0 nm or less, even more preferably 13.0 nm or more and 17.0 nm or less, 14.0 nm or more and 17.0 nm or less, or 14.0 nm or more and 16.0 nm or less.

[0097] When the magnetic particles are hexagonal ferrite particles, the average aspect ratio of the magnetic particles is preferably 1.0 or more and 3.0 or less, more preferably 1.5 or more and 2.8 or less, and even more preferably 1.8 or more and 2.7 or less. When the average aspect ratio of the magnetic particles is within the range of 1.0 or more and 3.0 or less, aggregation of the magnetic particles can be suppressed. Furthermore, when the magnetic particles are vertically oriented in the process of forming the magnetic layer 43, the resistance applied to the magnetic particles can be suppressed. Therefore, the vertical orientation of the magnetic particles can be improved.

[0098] When the magnetic particles are hexagonal ferrite particles, the average particle size and average aspect ratio of the magnetic particles can be determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut out at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the magnetic tape MT to be measured is processed and thinned using an FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed on the magnetic surface and back surface of the magnetic tape MT by vapor deposition, and the tungsten layer is further formed on the magnetic surface by vapor deposition or sputtering. The thinning is performed along the length (longitudinal direction) of the magnetic tape MT. In other words, the thinning results in a cross section parallel to both the longitudinal and thickness directions of the magnetic tape MT.

[0099] The cross section of the obtained thin sample is observed using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so as to include the entire magnetic layer 43 in the thickness direction of the magnetic layer 43, and a TEM image is taken. The number of TEM images prepared is such that 50 particles can be extracted that can measure the plate diameter DB and plate thickness DA (see Figure 7) shown below.

[0100] In this specification, the size of a hexagonal ferrite particle (hereinafter referred to as "particle size") is defined as the plate diameter DB, which is the major axis of the plate surface or bottom surface, when the shape of the particle observed in the TEM image is plate-like or columnar (however, the thickness or height is smaller than the major axis of the plate surface or bottom surface) as shown in FIG. 7 . The thickness or height of the particle observed in the TEM image is defined as the plate thickness DA. When the thickness or height of a particle observed in the TEM image is not constant, the thickness or height of the largest particle is defined as the plate thickness DA.

[0101] Next, 50 particles are selected from the captured TEM image based on the following criteria: Particles with parts outside the field of view of the TEM image are not measured, and only particles with clear outlines and that exist independently are measured. When particles overlap, particles with clear boundaries and whose overall shape can be determined are measured as individual particles, but particles with unclear boundaries and whose overall shape cannot be determined are not measured as their shape cannot be determined.

[0102] 8 and 9 show a first example and a second example of TEM images, respectively. In FIGS. 8 and 9, for example, the particles indicated by arrows a and d are selected because their plate thickness (thickness or height) DA can be clearly confirmed. The plate thickness DA of each of the selected 50 particles is measured. The plate thicknesses DA thus obtained are simply averaged (arithmetic mean) to obtain the average plate thickness DA. ａｖｅ Calculate the average plate thickness DA ａｖｅ is the average particle plate thickness. Next, the plate diameter DB of each magnetic particle is measured. To measure the plate diameter DB of the particles, 50 particles whose plate diameter DB can be clearly confirmed are selected from the TEM image. For example, in Figures 8 and 9, the particles indicated by arrows b and c are selected because their plate diameter DB can be clearly confirmed. The plate diameter DB of each of the selected 50 particles is measured. The plate diameter DBs thus determined are simply averaged (arithmetic averaged) to obtain the average plate diameter DB. ａｖｅ Average plate diameter DB ａｖｅ is the average grain size. And the average plate thickness DA ａｖｅ and average plate diameter DB ａｖｅThe average aspect ratio of the particles (DB ａｖｅ / DA ａｖｅ ) is required.

[0103] When the magnetic particles are hexagonal ferrite particles, the upper limit of the average particle volume of the magnetic particles is preferably 1.50×10 ３ nm ３ or less, more preferably 1.40 × 10 ３ nm ３ More preferably, 1.37 × 10 ３ nm ３ Below, 1.30 x 10 ３ nm ３ Below, 1.20 x 10 ３ nm ３ Below, 1.10 x 10 ３ nm ３ or less or 1.00 x 10 ３ nm ３ The following is the result.

[0104] When the magnetic particles are hexagonal ferrite particles, the lower limit of the average particle volume of the magnetic particles is preferably 0.500×10 from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (for example, SNR). ３ nm ３ or more, more preferably 0.600 × 10 ３ nm ３ That's all.

[0105] When the magnetic particles are hexagonal ferrite particles, the numerical range of the average particle volume of the magnetic particles may be defined by any one of the upper limit values ​​and any one of the lower limit values, and is preferably 0.500×10 ３ nm ３ Above 1.50 x 10 ３ nm ３ or less, more preferably 0.500 × 10 ３ nm ３ The above is 1.40 x 10 ３ nm ３ or less, more preferably 0.500 × 10 ３ nm ３ The above is 1.30 x 10 ３ nm ３ Below, 0.500 x 10 ３ nm３ The above is 1.20 x 10 ３ nm ３ Below, 0.600 x 10 ３ nm ３ The above is 1.20 x 10 ３ nm ３ Below, 0.600 x 10 ３ nm ３ 1.10 x 10 ３ nm ３ or less or 0.600 x 10 ３ nm ３ Above 1.00 x 10 ３ nm ３ The following is the result.

[0106] The average particle volume of the magnetic particles can be calculated as follows: First, as described above in relation to the method for calculating the average particle size of the magnetic particles, the average plate thickness DA ａｖｅ and average plate diameter DB ａｖｅ Next, the average particle volume V of the magnetic particles is calculated using the following formula:

[0107] (ε-Iron Oxide Particles) ε-Iron oxide particles are hard magnetic particles that can achieve high coercivity even in the form of fine particles. ε-Iron oxide particles have a spherical or cubic shape. In this specification, spherical includes an almost spherical shape. Furthermore, cubic includes an almost cubic shape. Because ε-Iron oxide particles have the above-described shape, when ε-Iron oxide particles are used as magnetic particles, the contact area between particles in the thickness direction of the magnetic tape MT can be reduced and particle aggregation can be suppressed compared to when hexagonal plate-shaped barium ferrite particles are used as magnetic particles. Therefore, the dispersibility of the magnetic particles can be improved, and even better electromagnetic conversion characteristics (e.g., SNR) can be obtained.

[0108] The ε-iron oxide particles may have a composite particle structure, specifically, an ε-iron oxide particle and a soft magnetic portion or a magnetic portion having a higher saturation magnetization σs and a lower coercive force Hc than ε-iron oxide (hereinafter referred to as "soft magnetic portion, etc.").

[0109] The ε-iron oxide portion contains ε-iron oxide. The ε-iron oxide contained in the ε-iron oxide portion is ε-Fe ２ O ３ The crystal is preferably the main phase, and the single-phase ε-Fe ２ O ３ More preferably, it consists of:

[0110] The saturation magnetization σs of the soft magnetic portion is preferably 40 emu / g or more. This suppresses a decrease in the saturation magnetization σs of the composite particles, thereby improving the output characteristics of the magnetic tape MT. The soft magnetic portion is in contact with at least a portion of the ε-iron oxide portion. Specifically, the soft magnetic portion may partially cover the ε-iron oxide portion, or may completely cover the ε-iron oxide portion.

[0111] The soft magnetic portion (the magnetic portion having a higher saturation magnetization σs and a smaller coercive force Hc than ε-iron oxide) contains a soft magnetic material such as α-Fe, a Ni-Fe alloy, or an Fe-Si-Al alloy. α-Fe may be obtained by reducing ε-iron oxide contained in the ε-iron oxide portion.

[0112] The soft magnetic portion may be made of, for example, Fe. ３ O ４ , γ-Fe ２ O ３ , or spinel ferrite, etc.

[0113] By providing the ε-iron oxide particle with a portion having soft magnetic properties as described above, the coercive force Hc of the ε-iron oxide portion alone can be maintained at a high value to ensure thermal stability, while the coercive force Hc of the ε-iron oxide particle (composite particle) as a whole can be adjusted to a coercive force Hc suitable for recording.

[0114] The ε-iron oxide particles may contain an additive instead of the composite particle structure, or may have the composite particle structure and contain an additive. In this case, a portion of the Fe in the ε-iron oxide particles is substituted with the additive. By containing the additive in the ε-iron oxide particles, the coercivity Hc of the ε-iron oxide particles as a whole can be adjusted to a coercivity Hc suitable for recording, thereby improving ease of recording. The additive is a metal element other than iron, preferably a trivalent metal element, more preferably at least one selected from the group consisting of Al, Ga, and In, and even more preferably at least one selected from the group consisting of Al and Ga.

[0115] Specifically, the ε-iron oxide containing additives is ε-Fe ２－ｘ M ｘ O ３ crystal (wherein M is a metal element other than iron, preferably a trivalent metal element, more preferably at least one selected from the group consisting of Al, Ga, and In, and even more preferably at least one selected from the group consisting of Al and Ga; and x is, for example, 0<x<1).

[0116] When the magnetic particles are ε-iron oxide particles, the upper limit of the average particle size of the magnetic particles is preferably 14.5 nm or less, more preferably 13.5 nm or less, and even more preferably 13.0 nm or less, 12.5 nm or less, or 12.0 nm or less, from the viewpoint of improving linear recording density.

[0117] When the magnetic particles are ε-iron oxide particles, the lower limit of the average particle size of the magnetic particles is preferably 10.0 nm or more, from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (for example, SNR).

[0118] When the magnetic particles are ε iron oxide particles, the numerical range of the average particle size of the magnetic particles may be defined by any one of the upper limit values ​​and any one of the lower limit values, and is preferably 10.0 nm or more and 14.5 nm or less, more preferably 10.0 nm or more and 13.5 nm or less, even more preferably 10.0 nm or more and 13.0 nm or less, 10.0 nm or more and 12.5 nm or less, or 10.0 nm or more and 12.0 nm or less.

[0119] When the magnetic particles are ε-iron oxide particles, the average aspect ratio of the magnetic particles is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.5 or less, and even more preferably 1.0 or more and 2.1 or less, or 1.0 or more and 1.8 or less. When the average aspect ratio of the magnetic particles is within the range of 1.0 or more and 3.0 or less, aggregation of the magnetic particles can be suppressed. Furthermore, when the magnetic particles are vertically oriented in the process of forming the magnetic layer 43, the resistance applied to the magnetic particles can be suppressed. Therefore, the vertical orientation of the magnetic particles can be improved.

[0120] When the magnetic particles are ε-iron oxide particles, the average particle size and average aspect ratio of the magnetic particles can be determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut out at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the magnetic tape MT to be measured is processed and thinned using an FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective layers as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed on the magnetic surface and back surface of the magnetic tape MT by vapor deposition, and the tungsten layer is further formed on the magnetic surface by vapor deposition or sputtering. The thinning is performed along the length (longitudinal direction) of the magnetic tape MT. In other words, the thinning results in a cross section parallel to both the longitudinal and thickness directions of the magnetic tape MT.

[0121] The cross section of the obtained thin film sample was observed using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so as to include the entire magnetic layer 43 in the thickness direction of the magnetic layer 43, and a TEM image was taken. Next, 50 particles whose particle shape can be clearly confirmed were selected from the taken TEM image, and the major axis length DL and minor axis length DS of each particle were measured. Here, the major axis length DL refers to the longest distance between two parallel lines drawn from any angle so as to be tangent to the contour of each particle (the so-called maximum Feret diameter). Meanwhile, the minor axis length DS refers to the longest length of the particle in the direction perpendicular to the major axis (DL) of the particle. Next, the major axis lengths DL of the measured 50 particles were simply averaged (arithmetic mean) to obtain the average major axis length DL ave The average major axis length DL obtained in this way is ave is the average particle size of the magnetic particles. The minor axis lengths DS of the measured 50 particles are simply averaged (arithmetic mean) to obtain the average minor axis length DS ave Then, calculate the average major axis length DL ave and mean minor axis length DS ave From the average aspect ratio of the particles (DL ave / DS ave ) is required.

[0122] When the magnetic particles are ε-iron oxide particles, the upper limit of the average particle volume of the magnetic particles is preferably 1.50×10 ３ nm ３ or less, more preferably 1.40 × 10 ３ nm ３ More preferably, 1.30×10 ３ nm ３ Below, 1.20 x 10 ３ nm ３ Below, 1.10 x 10 ３ nm ３ or less or 1.00 x 10 ３ nm ３ The following is the result.

[0123] When the magnetic particles are ε-iron oxide particles, the lower limit of the average particle volume of the magnetic particles is preferably 0.500×10 from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (for example, SNR). ３ nm ３ or more, more preferably 0.600 × 10 ３ nm ３ That's all.

[0124] When the magnetic particles are ε-iron oxide particles, the numerical range of the average particle volume of the magnetic particles may be defined by any one of the upper limit values ​​and any one of the lower limit values, and is preferably 0.500×10 ３ nm ３ Above 1.50 x 10 ３ nm ３ or less, more preferably 0.500 × 10 ３ nm ３ The above is 1.40 x 10 ３ nm ３ or less, more preferably 0.500 × 10 ３ nm ３ The above is 1.30 x 10 ３ nm ３ Below, 0.600 x 10 ３ nm ３ The above is 1.20 x 10 ３ nm ３ Below, 0.600 x 10 ３ nm ３ 1.10 x 10 ３ nm ３ or less or 0.600 x 10 ３ nm ３ Above 1.00 x 10 ３ nm ３ The following is the result.

[0125] When the ε-iron oxide particles are spherical, the average particle volume of the magnetic particles can be calculated as follows: First, the average major axis length DL is calculated in the same manner as in the above-mentioned method for calculating the average particle size of the magnetic particles. ave Next, the average particle volume V of the magnetic particles is calculated using the following formula: V = (π / 6) × DL ave 3

[0126] When the ε-iron oxide particles have a cubic shape, the average volume of the magnetic particles can be determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut out at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the cut magnetic tape MT is processed by FIB or the like to be thinned. When the FIB method is used, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon film is formed on the magnetic surface and back surface of the magnetic tape MT by vapor deposition, and the tungsten thin film is further formed on the magnetic surface by vapor deposition or sputtering. The thinning is performed along the length (longitudinal direction) of the magnetic tape MT. In other words, the thinning results in a cross section parallel to both the longitudinal and thickness directions of the magnetic tape MT.

[0127] The obtained thin section sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times to observe the cross section of the magnetic layer 43 in the thickness direction so as to include the entire magnetic layer 43, and a TEM image is obtained. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Next, 50 particles whose particle shape is clear are selected from the TEM image taken, and the side length DC of each particle is measured. Next, the side lengths DC of the measured 50 particles are simply averaged (arithmetic mean) to obtain the average side length DC ave Next, calculate the average side length DC ave Using the formula below, the average particle volume V of the magnetic particles is calculated. ave V ave = DC ave 3

[0128] (Cobalt ferrite particles) The cobalt ferrite particles preferably have uniaxial crystal anisotropy. The uniaxial crystal anisotropy of the cobalt ferrite particles allows the magnetic particles to be preferentially crystalline oriented in the perpendicular direction of the magnetic tape MT. The cobalt ferrite particles have, for example, a cubic shape. In this specification, cubic shape includes a nearly cubic shape. The Co-containing spinel ferrite may further contain at least one element selected from the group consisting of Ni, Mn, Al, Cu, and Zn in addition to Co.

[0129] The Co-containing spinel ferrite has an average composition represented by the following formula, for example: Co ｘ M ｙ Fe ２ O Ｚ (In the formula, M is at least one metal selected from the group consisting of, for example, Ni, Mn, Al, Cu, and Zn. x is a value within the range of 0.4≦x≦1.0. y is a value within the range of 0≦y≦0.3. However, x and y satisfy the relationship (x+y)≦1.0. z is a value within the range of 3≦z≦4. A portion of Fe may be substituted with another metal element.)

[0130] When the magnetic particles are cobalt ferrite particles, the upper limit of the average particle size of the magnetic particles is preferably 16.0 nm or less, more preferably 13.0 nm or less, and even more preferably 10.0 nm or less, from the viewpoint of improving linear recording density.

[0131] When the magnetic particles are cobalt ferrite particles, the lower limit of the average particle size of the magnetic particles is preferably 8.0 nm or more, from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (for example, SNR).

[0132] When the magnetic particles are cobalt ferrite particles, the numerical range of the average particle size of the magnetic particles may be defined by any one of the above upper limits and the above lower limit, and is preferably 8.0 nm or more and 16.0 nm or less, more preferably 8.0 nm or more and 13.0 nm or less, and even more preferably 8.0 nm or more and 10.0 nm or less. The method for calculating the average particle size of the magnetic particles is the same as the method for calculating the average particle size of the magnetic particles when the magnetic particles are ε-iron oxide particles.

[0133] When the magnetic particles are cobalt ferrite particles, the average aspect ratio of the magnetic particles is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.5 or less, and even more preferably 1.0 or more and 2.0 or less. When the average aspect ratio of the magnetic particles is within the range of 1.0 or more and 3.0 or less, aggregation of the magnetic particles can be suppressed. Furthermore, when the magnetic particles are vertically oriented in the process of forming the magnetic layer 43, the resistance applied to the magnetic particles can be suppressed. Therefore, the vertical orientation of the magnetic particles can be improved. The method for calculating the average aspect ratio of the magnetic particles is the same as the method for calculating the average aspect ratio of the magnetic particles when the magnetic particles are ε-iron oxide particle powder.

[0134] When the magnetic particles are cobalt ferrite particles, the upper limit of the average particle volume of the magnetic particles is preferably 4.00×10 ３ nm ３ or less, more preferably 2.00 x 10 ３ nm ３ or less, and even more preferably 1.50 x 10 ３ nm ３ or less or 1.00 x 10 ３ nm ３ The following is the result.

[0135] When the magnetic particles are cobalt ferrite particles, the lower limit of the average particle volume of the magnetic particles is preferably 0.5×10 from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics (for example, SNR). ３ nm ３ or more, more preferably 0.6 × 10 ３ nm ３ That's all.

[0136] When the magnetic particles are cobalt ferrite particles, the numerical range of the average particle volume of the magnetic particles may be defined by any one of the upper limit values ​​and any one of the lower limit values, and is preferably 0.5×10 ３ nm ３ Above 4.00 x 10 ３ nm ３ Less than or equal to 0.6 × 10, more preferably 0.6 × 10 ３ nm ３ Above 2.00 x 10 ３ nm ３ or less, and even more preferably 0.6 × 10 ３ nm ３ Above 1.50 x 10 ３ nm ３ or less than 0.6 x 10 ３ nm ３ Above 1.00 x 10 ３ nm ３ The method for calculating the average particle volume of the magnetic particles is the same as the method for calculating the average particle volume when the ε iron oxide particles have a cubic shape.

[0137] (Binder) The binder includes, for example, a thermoplastic resin, and may further include a thermosetting resin or a reactive resin.

[0138] The thermoplastic resin includes, for example, a first thermoplastic resin (first binder) containing chlorine atoms and a second thermoplastic resin (second binder) containing nitrogen atoms. More specifically, the thermoplastic resin includes a vinyl chloride resin and a urethane resin. In this specification, the vinyl chloride resin refers to a polymer containing a structural unit derived from vinyl chloride. More specifically, for example, the vinyl chloride resin refers to a homopolymer of vinyl chloride, a polymer of vinyl chloride and a comonomer copolymerizable therewith, and a mixture of these polymers.

[0139] The vinyl chloride resin includes, for example, at least one selected from the group consisting of vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, and methacrylic acid ester-vinyl chloride copolymer.

[0140] The term "urethane-based resin" refers to a resin containing a urethane bond in at least a portion of the molecular chain constituting the resin, and may be a urethane resin or a copolymer containing a urethane bond in a portion of the molecular chain. The urethane-based resin may be, for example, one obtained by reacting a polyisocyanate with a polyol. Alternatively, the urethane-based resin may be, for example, one obtained by reacting a polyester with a polyol. In this specification, the term "urethane-based resin" also includes one obtained by reaction with a curing agent.

[0141] The polyisocyanate includes, for example, at least one selected from the group consisting of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In this specification, polyisocyanate refers to a compound having two or more isocyanate groups in the molecule. The polyisocyanate may be the polyisocyanate contained in the curing agent.

[0142] Any suitable polyol having two or more OH groups can be used as the polyol. The polyol may include, for example, at least one selected from the group consisting of a polyol (diol) having two OH groups, a polyol (triol) having three OH groups, a polyol (tetraol) having four OH groups, a polyol (pentaol) having five OH groups, and a polyol (hexaol) having six OH groups. Specific examples of the polyol include at least one selected from the group consisting of polyester polyols, polyether polyols, polycarbonate polyols, polyesteramide polyols, and acrylate polyols.

[0143] The polyester includes, for example, at least one selected from the group consisting of phthalic acid polyesters and aliphatic polyesters.

[0144] The thermoplastic resin may further include a thermoplastic resin other than a vinyl chloride resin or a urethane resin. Examples of such a thermoplastic resin include at least one selected from the group consisting of vinyl acetate, an acrylic acid ester-acrylonitrile copolymer, an acrylic acid ester-acrylonitrile copolymer, an acrylic acid ester-vinylidene chloride copolymer, a methacrylic acid ester-vinylidene chloride copolymer, a methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, a vinylidene chloride-acrylonitrile copolymer, an acrylonitrile-butadiene copolymer, a polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), a styrene-butadiene copolymer, a polyester resin, an amino resin, and synthetic rubber.

[0145] The thermosetting resin includes at least one selected from the group consisting of, for example, phenolic resin, epoxy resin, polyurethane curing resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin.

[0146] All of the above binders contain -SO ３ M, -OSO ３ M, -COOM, P=O(OM) ２ (wherein M represents a hydrogen atom or an alkali metal such as lithium, potassium, or sodium), or -NR1R2, -NR1R2R3 ＋ X － a side chain amine having a terminal group represented by >NR1R2 ＋ X － (wherein R1, R2, and R3 represent a hydrogen atom or a hydrocarbon group, and X － represents a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic ion or an organic ion.) Polar functional groups such as -OH, -SH, -CN, and epoxy groups may also be introduced. The amount of these polar functional groups introduced into the binder is 10 －１ 10 above －８ It is preferably 10 mol / g or less.－２ 10 above －６ It is more preferably mol / g or less.

[0147] (Acidic Compound) The acidic compound may include, for example, at least one selected from the group consisting of dispersants and additives other than dispersants. The binder may be an acidic compound. The dispersant may be a compound that has the effect of assisting the dispersion of magnetic particles by interacting with the magnetic particles in the coating material for forming the magnetic layer. The acidic compound may include one or both of a monobasic acid and a polybasic acid. The acidic compound may include one or both of an organic acid and an inorganic acid. The dispersant may be, for example, a surfactant, a polymer dispersant, or a thickener.

[0148] The acidic compound may be capable of adsorbing to the surfaces of magnetic particles contained in the magnetic layer 43. In this case, some of the acidic compound may adsorb to the surfaces of the magnetic particles contained in the magnetic layer 43, while the remaining acidic compound may exist within the magnetic layer 43 without adsorbing to the surfaces of the magnetic particles contained in the magnetic layer 43. Non-adsorbed acidic compounds that are not adsorbed to the surfaces of the magnetic particles are likely to dissolve in water and produce an acidic aqueous solution when water diffuses into the magnetic layer 43 under conditions such as high temperature and high humidity. Therefore, non-adsorbed acidic compounds are likely to promote corrosion of the magnetic particles. Therefore, non-adsorbed acidic compounds are likely to promote the reduction in particle size of the magnetic particles and may reduce magnetic properties (e.g., saturation magnetization Ms). In other words, non-adsorbed acidic compounds may cause a deterioration in electromagnetic conversion properties under conditions such as high temperature and high humidity. Considering the mechanism of deterioration of electromagnetic conversion properties described above, limiting the numerical range of the reduction rate of saturation magnetization Ms after an 8-week high-temperature and high-humidity storage test at a temperature of 60°C and a humidity of 90% RH is particularly effective when non-adsorbed acidic compounds are present in the magnetic layer 43.

[0149] Furthermore, as the particle size of the magnetic particles decreases, the binder may no longer be able to maintain the binding between the magnetic particles themselves and between the magnetic particles and other particles (e.g., abrasive particles, carbon particles, etc.). When this phenomenon occurs on the surface of the magnetic layer 43 or in its vicinity, the unevenness of the magnetic surface becomes brittle, making the protrusions 430 more susceptible to plastic deformation or brittle fracture. As a result, the dynamic friction coefficient increases in high-temperature, high-humidity environments, potentially reducing the running stability of the magnetic tape MT. Considering the mechanism of this reduction in running stability, limiting the numerical range of the average dynamic friction coefficient μ after a two-week high-temperature, high-humidity storage test at 60°C and 90% RH is particularly effective when non-adsorbed acidic compounds are present in the magnetic layer 43.

[0150] The acidic compound has, for example, at least one acidic functional group. The acidic functional group may be an acidic adsorption group that can adsorb to the surface of the magnetic particles through interaction with the magnetic particles. The at least one acidic functional group includes, for example, at least one selected from the group consisting of a phosphate group, a carboxyl group, a sulfonic acid group, and the like.

[0151] The acidic compound may include, for example, at least one selected from the group consisting of phosphonic acid compounds, carboxylic acid compounds, and sulfonic acid compounds. More specifically, the acidic compound includes, for example, at least one selected from the group consisting of phenylphosphonic acid, benzoic acid, naphthoic acid, hydroxybenzoic acid, isophthalic acid, oleic acid, cyclohexanecarboxylic acid, adipic acid, and citric acid. The naphthoic acid includes, for example, 1-naphthoic acid. The hydroxybenzoic acid includes, for example, 4-hydroxybenzoic acid.

[0152] The phosphonic acid compound includes, for example, at least one selected from the group consisting of aromatic phosphonic acid compounds, chain aliphatic phosphonic acid compounds, and cyclic aliphatic phosphonic acid compounds. The phosphonic acid compound may include, for example, one or both of a monovalent phosphonic acid compound and a polyvalent phosphonic acid compound. The aromatic phosphonic acid may include, for example, phenylphosphonic acid.

[0153] The carboxylic acid compound includes, for example, at least one selected from the group consisting of aromatic carboxylic acid compounds, chain aliphatic carboxylic acid compounds, and cyclic aliphatic carboxylic acid compounds. The carboxylic acid compound may include, for example, one or both of a monocarboxylic acid compound and a polycarboxylic acid compound. The aromatic carboxylic acid compound includes, for example, at least one selected from the group consisting of benzoic acid, naphthoic acid, hydroxybenzoic acid, and isophthalic acid. The chain aliphatic carboxylic acid compound includes, for example, at least one selected from the group consisting of adipic acid, citric acid, and oleic acid. The cyclic aliphatic carboxylic acid compound includes, for example, cyclohexanecarboxylic acid.

[0154] Examples of carboxylic acid compounds that can be used include fatty acids having 12 to 18 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearic acid [RCOOH (R is an alkyl or alkenyl group having 11 to 17 carbon atoms)]; metallic soaps made from alkali metals or alkaline earth metals 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; trialkylpolyolefinoxy quaternary ammonium salts (wherein the alkyl has 1 to 5 carbon atoms and the olefin is ethylene, propylene, or the like); phenylphosphenic acid; and copper phthalocyanine. These may be used alone or in combination.

[0155] The sulfonic acid compound includes, for example, at least one selected from the group consisting of aromatic sulfonic acid compounds, chain aliphatic sulfonic acid compounds, and cyclic aliphatic sulfonic acid compounds, etc. The sulfonic acid compound may include, for example, one or both of a monovalent sulfonic acid compound and a polyvalent sulfonic acid compound.

[0156] The acid dissociation constant (pKa) of the acidic compound is, for example, 5.0 or less, 4.9 or less, 4.8 or less, 4.7 or less, 4.6 or less, 4.5 or less, 4.4 or less, 4.3 or less, 4.2 or less, 4.1 or less, 4.0 or less, 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, or 3.5 or less.

[0157] The acid dissociation constant (pKa) is a parameter that indicates the degree of dissociation of an acid. If the ionization constant of an acid is Ka, then pKa = -log １０ The acid dissociation constant (pKa) is defined as Ka, and the smaller the value of the acid dissociation constant (pKa), the stronger the acidic compound is. In the present disclosure, the acid dissociation constant (pKa) is measured at an ambient temperature of 25°C by potentiometric titration (JIS K 0070:1992).

[0158] As described above, when the acid dissociation constant (pKa) of an acidic compound is 5.0 or less, hydrogen ions are easily released from the acidic compound. This makes it easier for an acidic aqueous solution to be generated in the magnetic layer 43, accelerating the deterioration of the magnetic particles. The average particle volume V of the magnetic particles ave is 1.50 x 10 ３ nm ３ Therefore, limiting the range of the decrease in saturation magnetization Ms after an 8-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90 RH% and limiting the range of the average dynamic friction coefficient μ after a 2-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90 RH% are particularly effective when the acid dissociation constant (pKa) of the acidic compound is 5.0 or less.

[0159] An acidic compound may have one acid dissociation constant (pKa) or multiple acid dissociation constants (pKa). When an acidic compound has multiple acid dissociation constants (pKa), the acid dissociation constant (pKa) of the acidic compound being 5 or less means that the smallest acid dissociation constant (pKa) among the multiple acid dissociation constants (pKa) possessed by the acidic compound is 5 or less.

[0160] (Carbon Particles) Some of the carbon particles contained in the magnetic layer 43 may protrude from the magnetic surface, forming multiple protrusions 430. By forming the multiple protrusions 430 from carbon particles, the electrical resistance of the magnetic surface can be reduced, and charging of the magnetic surface can be suppressed. In addition, the coefficient of dynamic friction between the head unit 56 and the magnetic surface during running of the magnetic tape MT can be reduced.

[0161] The carbon particles may function as an antistatic agent and a solid lubricant. The carbon particles preferably have an average primary particle size of 100.0 nm or less. When the carbon particles have an average primary particle size of 100.0 nm or less, even when the carbon particles are particles with a wide particle size distribution (e.g., carbon black), the inclusion of particles that are excessively large relative to the thickness of the magnetic layer 43 is suppressed.

[0162] The carbon particles may be, for example, at least one selected from the group consisting of carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene, and among these carbon particles, carbon black is preferably used. Examples of carbon black that can be used include Seast TA manufactured by Tokai Carbon Co., Ltd., and Asahi #15 and #15HS manufactured by Asahi Carbon Co., Ltd.

[0163] The magnetic layer 43 may contain hybrid particles instead of carbon particles, or may contain hybrid particles together with carbon particles. The hybrid particles contain carbon and a material other than carbon. The material other than carbon is, for example, an organic material or an inorganic material. The hybrid particles may be hybrid particles in which carbon is attached to the surface of inorganic particles. Specifically, for example, they may be hybrid carbon in which carbon is attached to the surface of silica particles.

[0164] (Lubricant) The lubricant may be a liquid lubricant. The lubricant may be, for example, at least one selected from a fatty acid and a fatty acid ester, preferably both a fatty acid and a fatty acid ester. The inclusion of a lubricant in the magnetic layer 43, particularly the inclusion of both a fatty acid and a fatty acid ester in the magnetic layer 43, contributes to improving the running stability of the magnetic tape MT. More particularly, the magnetic layer 43 containing a lubricant and having pores achieves good running stability. This improvement in running stability is thought to be due to the lubricant adjusting the dynamic friction coefficient of the magnetic layer 43-side surface of the magnetic tape MT to a value suitable for running the magnetic tape MT.

[0165] The fatty acid may preferably be a compound represented by the following general formula (1) or (2). For example, the fatty acid may contain either or both of the compound represented by the following general formula (1) and the compound represented by the general formula (2).

[0166] The fatty acid ester may preferably be a compound represented by the following general formula (3), (4), or (5). For example, the fatty acid ester may contain one, two, or three of the compounds represented by the following general formula (3), (4), and (5).

[0167] By including in the lubricant one or both of the compound represented by general formula (1) and the compound represented by general formula (2), and one, two or three of the compound represented by general formula (3), the compound represented by general formula (4) and the compound represented by general formula (5), it is possible to suppress an increase in the coefficient of dynamic friction due to repeated recording or reproduction of the magnetic tape MT.

[0168] CH3 (CH2) k COOH (1) (In general formula (1), k is an integer selected from the range of 14 to 22, more preferably from the range of 14 to 18.)

[0169] CH3 (CH2) n CH=CH(CH2) mCOOH (2) (In the general formula (2), the sum of n and m is an integer selected from the range of 12 to 20, more preferably from the range of 14 to 18.)

[0170] CH3 (CH2) p COO(CH2) q CH3 (3) (wherein, in general formula (3), p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is an integer selected from the range of 2 or more and 5 or less, more preferably 2 or more and 4 or less.)

[0171] CH3 (CH2) r COO-(CH2) s CH(CH3)2 (4) (In the general formula (4), r is an integer selected from the range of 14 to 22, and s is an integer selected from the range of 1 to 3.)

[0172] CH3 (CH2) ｔ COO-(CH)(CH3)CH2(CH3) ｕ ...(5) (In general formula (5), t is an integer selected from the range of 14 to 22, and u is an integer selected from the range of 1 to 3.)

[0173] (Abrasive particles) Some of the abrasive particles contained in the magnetic layer 43 may protrude from the magnetic surface to form a plurality of protrusions 430. When the head unit 56 slides over the magnetic tape MT, the protrusions 430 formed by the abrasive particles can come into contact with the head unit 56.

[0174] The lower limit of the Mohs hardness of the abrasive particles is preferably 7.0 or more, more preferably 7.5 or more, even more preferably 8.0 or more, and particularly preferably 8.5 or more, from the viewpoint of suppressing deformation due to contact with the head unit 56. The upper limit of the Mohs hardness of the abrasive particles is preferably 9.5 or less, from the viewpoint of suppressing wear of the head unit 56.

[0175] The abrasive particles are preferably inorganic particles. Examples of inorganic particles include α-alumina with an α-conversion rate of 90% or more, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, acicular α-iron oxide obtained by dehydrating and annealing magnetic iron oxide raw materials, optionally surface-treated with aluminum and / or silica, and diamond powder. Examples of inorganic particles that are preferably used include alumina particles such as α-alumina, β-alumina, and γ-alumina, and silicon carbide. The abrasive particles may be acicular, spherical, or cubic, but those with angular shapes are preferred because they have high abrasiveness.

[0176] (Antistatic Agent) The antistatic agent reduces the electrical resistance of the magnetic surface and can suppress charging of the magnetic surface. The antistatic agent includes, for example, at least one selected from the group consisting of natural surfactants, nonionic surfactants, and cationic surfactants.

[0177] (Curing Agent) The curing agent includes, for example, polyisocyanate. The polyisocyanate may include, for example, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI) as an isocyanate source. The polyisocyanate may have a TMP adduct structure, an isocyanurate structure, a biuret structure, an allophanate structure, or the like.

[0178] Specific examples of polyisocyanates include aromatic polyisocyanates such as an adduct of tolylene diisocyanate (TDI) and an active hydrogen compound, and aliphatic polyisocyanates such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. The weight average molecular weight of these polyisocyanates is preferably in the range of 100 to 3,000.

[0179] (Rust inhibitor) Examples of the rust inhibitor include phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, heterocyclic compounds containing an oxygen atom, and heterocyclic compounds containing a sulfur atom.

[0180] (Non-magnetic reinforcing particles) Examples of non-magnetic reinforcing particles include aluminum oxide (α-, β-, or γ-alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, and titanium oxide (rutile or anatase titanium oxide).

[0181] (Underlayer) The underlayer 42 is intended to reduce the surface irregularities of the substrate 41 and adjust the irregularities of the magnetic surface. The underlayer 42 is a non-magnetic layer and contains, for example, non-magnetic particles, a binder, and a lubricant. It is preferable that the underlayer 42 be capable of supplying a lubricant to the magnetic surface. If necessary, the underlayer 42 may further contain at least one additive selected from the group consisting of an antistatic agent, a hardener, an anti-rust agent, and the like.

[0182] The underlayer 42 may have a plurality of holes. A lubricant may be stored in the holes. In this case, the supply of the lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes extend in a direction perpendicular to the magnetic surface. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes in the underlayer 42 and the holes in the magnetic layer 43 are connected to each other.

[0183] Average thickness t of the underlayer 42 ３From the viewpoint of improving the elasticity of the magnetic surface, the upper limit of is preferably 0.90 μm or less, more preferably 0.80 μm or less, even more preferably 0.70 μm or less, and particularly preferably 0.60 μm or less. Since the elasticity of the substrate 41 is higher than that of the underlayer 42, making the underlayer 42 thinner improves the elasticity of the magnetic surface. The average thickness t of the underlayer 42 ３ The lower limit of the thickness is preferably 0.30 μm or more from the viewpoint of reducing the unevenness on the surface of the substrate 41 .

[0184] Average thickness t of the underlayer 42 ３ The numerical range of may be defined by any one of the above upper limits and the above lower limit, and is preferably 0.30 μm or more and 0.90 μm or less, more preferably 0.30 μm or more and 0.80 μm or less, even more preferably 0.30 μm or more and 0.70 μm or less, and particularly preferably 0.30 μm or more and 0.60 μm or less.

[0185] Average thickness t of the underlayer 42 ３ is the average thickness t of the magnetic layer 43 ２ However, the magnification of the TEM image is adjusted appropriately depending on the thickness of the underlayer 42.

[0186] Average thickness t of the substrate 41 １ Whereas the average thickness t of the magnetic layer 43 ２ and the average thickness t of the underlayer 42 ３ If the total thickness of the substrate 41 is too large, the bending rigidity will increase, and the stability of contact between the magnetic tape MT and the head may decrease. １ Whereas the average thickness t of the magnetic layer 43 ２ and the average thickness t of the underlayer 42 ３ If the total thickness of the substrate 41 is too small, the surface properties of the magnetic surface of the magnetic tape MT may be reduced. １ The average thickness t of the magnetic layer 43 ２ and the average thickness t of the underlayer 42 ３ The ratio of the total thickness ((t ２ +t ３ ) / t １ ) is preferably 0.19 or more and 0.28 or less.

[0187] The underlayer 42 preferably has a plurality of holes. By storing lubricant in these holes, it is possible to further suppress a decrease in the amount of lubricant supplied between the magnetic surface and the head unit 56, even after repeated recording or reproduction (i.e., after repeated running of the head unit 56 in contact with the surface of the magnetic tape MT). This further suppresses an increase in the dynamic friction coefficient. In other words, it is possible to obtain even better running stability of the magnetic tape MT.

[0188] (Non-magnetic particles) The non-magnetic particles include, for example, at least one of inorganic particles and organic particles. The non-magnetic particles may also be carbon particles such as carbon black. One type of non-magnetic particle may be used alone, or two or more types of non-magnetic particles may be used in combination. The inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, or metal sulfides. The shapes of the non-magnetic particles include, for example, various shapes such as needles, spheres, cubes, and plates, but are not limited to these shapes.

[0189] (Binder, Lubricant) The binder and lubricant are the same as those in the magnetic layer 43 described above.

[0190] (Additives) The antistatic agent, hardener, and anticorrosive agent are the same as those in the magnetic layer 43 described above.

[0191] (Back Layer) The back layer 44 contains a binder and non-magnetic particles. If necessary, the back layer 44 may further contain at least one additive selected from the group consisting of a lubricant, a hardener, an antistatic agent, etc. The binder and non-magnetic particles are the same as those in the underlayer 42 described above. The hardener and antistatic agent are the same as those in the magnetic layer 43 described above.

[0192] The average particle size of the non-magnetic particles is preferably 10.0 nm or more and 150.0 nm or less, more preferably 15.0 nm or more and 110.0 nm or less. The average particle size of the non-magnetic particles is determined in the same manner as the average particle size of the magnetic particles. The non-magnetic particles may include non-magnetic particles having two or more particle size distributions.

[0193] Average thickness t of the back layer 44 ４ When the upper limit of the average thickness of the back layer 44 is 0.60 μm or less, the average thickness t Ｔ Even if the average thickness t of the back layer 44 is 5.40 μm or less, the thickness of the underlayer 42 and the substrate 41 can be kept large, so that the running stability of the magnetic tape MT can be maintained in the recording / reproducing device. ４ The lower limit of the thickness is not particularly limited, but is, for example, 0.20 μm or more.

[0194] Average thickness t of the back layer 44 ４ is calculated as follows: First, the average thickness t of the magnetic tape MT Ｔ Measure the average thickness t Ｔ The method for measuring the average thickness of the magnetic tape is as described below in "Average Thickness of Magnetic Tape." Next, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT into a length of 250 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the back layer 44 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five positions using a laser hologram gauge (LGH-110C) manufactured by Mitutoyo Corporation, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t Ｂ Then, the average thickness t of the back layer 44 is calculated using the following formula: ４ The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT. ４ [μm] = t Ｔ [μm]-t Ｂ [μm]

[0195] (Lubricant Layer) The lubricant layer contains a lubricant. The lubricant is the same as the lubricant contained in the magnetic layer 43. The lubricant layer may be formed from a lubricant supplied to the magnetic surface from the magnetic layer 43 and the underlayer 42.

[0196] (Average Thickness of Magnetic Tape) By reducing the average thickness of the magnetic tape MT, the length of tape wound into one cartridge 10 can be increased, thereby increasing the recording capacity per cartridge 10. Therefore, from the viewpoint of improving the recording capacity of the cartridge 10, the average thickness (average total thickness) t Ｔ The upper limit of the average thickness t of the magnetic tape MT is 5.30 μm or less, preferably 5.10 μm or less, more preferably 4.90 μm or less, and even more preferably 4.70 μm or less. Ｔ The lower limit of the thickness is not particularly limited, but is, for example, 3.50 μm or more.

[0197] Average thickness t of magnetic tape MT Ｔ is obtained as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is cut out of the magnetic tape MT at a length of 250 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the thickness of the sample is measured at five positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t Ｔ The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT.

[0198] (Comparative I λｎ≦５ / I １０≦λｎ≦２０ A two-dimensional surface profile image with a measurement range of 100 [μm] × 100 [μm] obtained by measuring the magnetic surface with an atomic force microscope (hereinafter referred to as "AFM") was used to measure the spatial wavelength λ ｎ When the power spectral density (hereinafter referred to as "PSD") at each position of λ = 100 / n [μm] (where n is an integer of 1 to 255) is calculated, the spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦5 μm λｎ≦５ and 10 μm≦spatial wavelength λ ｎAverage value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ The upper limit of the ratio I is 3.00 or less, preferably 2.80 or less, more preferably 2.60 or less, and even more preferably 2.40 or less, 2.20 or less, 2.10 or less, or 2.01 or less. λｎ≦５ / I １０≦λｎ≦２０ If the ratio exceeds 3.00, the components of short wavelength λ (λ≦5 μm) become more numerous than the components of long wavelength λ (10 μm≦λ≦20 μm) in the unevenness of the magnetic surface, and the distance between the magnetic tape MT and the head unit 56 (hereinafter referred to as "spacing") becomes wider, thereby deteriorating the electromagnetic conversion characteristics.

[0199] The above ratio I λｎ≦５ / I １０≦λｎ≦２０ The lower limit of the ratio I is preferably 0.50 or more. λｎ≦５ / I １０≦λｎ≦２０ If the lower limit of is 0.50 or more, it is possible to prevent the short wavelength λ (λ≦5 μm) component from becoming too small relative to the long wavelength λ (10 μm≦λ≦20 μm) component in the unevenness of the magnetic surface, and to prevent an excessive decrease in the small undulations that support the head unit 56. This prevents an excessive increase in the contact area between the magnetic tape MT and the head unit 56, and prevents deterioration of running performance.

[0200] The above ratio I λｎ≦５ / I １０≦λｎ≦２０ The numerical range of may be defined by any one of the above upper limits and the above lower limit, and is preferably 0.50 or more and 3.00 or less, more preferably 0.50 or more and 2.80 or less, even more preferably 0.50 or more and 2.60 or less, 0.50 or more and 2.40 or less, 0.50 or more and 2.20 or less, 0.50 or more and 2.10 or less, or 0.50 or more and 2.01 or less.

[0201] The above ratio I λｎ≦５ / I １０≦λｎ≦２０is obtained as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut into a length of about 10 cm from a position approximately 20 m from one end of the magnetic tape MT on the outermost periphery to obtain sample 1. Furthermore, the magnetic tape MT is cut into a length of about 10 cm from a position approximately 50 m from the other end of the magnetic tape MT on the innermost periphery to obtain sample 2. Next, sample 1 is cut into a size that fits the sample holder and attached to the sample holder. After that, the magnetic surface of sample 1 is observed with an AFM at three randomly selected points on sample 1 to obtain three two-dimensional surface profile images.

[0202] The AFM measurement conditions were as follows: Measuring device: Medium-sized probe microscope system AFM5500M (manufactured by Hitachi High-Technologies Corporation) Measurement range: 100 μm×100 μm Resolution: X direction 512×Y direction 512 Measurement mode: DFM (shape) Cantilever: SI-DF40P2 Automatic tilt correction: 1st order Automatic tilt correction: 3rd order

[0203] The settings for AFM flattening are as follows: Calculation target: Off Mask: Off Tilt correction: Off Line arrangement: Off Calculation direction: XY

[0204] Next, three two-dimensional surface profile images are obtained from Sample 2 in the same manner as the three two-dimensional surface profile images were obtained from Sample 1. In this way, a total of six two-dimensional surface profile images are obtained.

[0205] Next, the average X-PSD profile of the two-dimensional surface profile image is obtained using image analysis software (Image Metrology, SPIP (registered trademark) version 6.7.3) as follows: (1) Using the image analysis software, open the two-dimensional surface profile image to be analyzed. (2) Select 2D FFT / PSD analysis from the analysis tab of the image analysis software to display the 2D FFT / PSD analysis menu, select average X-PSD profile from the displayed menu, and perform average X-PSD analysis of the two-dimensional surface profile image. This obtains the average X-PSD value of the two-dimensional surface profile image.

[0206] Next, the average X-PSD value was substituted into the following formula to obtain the PSD [nm ２ ] is calculated. ２ ] = (average X-PSD value) × 2 × minimum wave number (1.00 × 10 －５ ) In the above formula, the minimum value of the wave number (1.00 × 10 －５ ) represents the minimum wave number corresponding to the unevenness of the magnetic surface. The minimum wave number is determined from the measurement range of 100 μm×100 μm. That is, 1.00 / 100 μm=1.00 / 100000 nm=1.00×10 －５ nm －１ Figure 10 shows an example of the PSD calculated by the above steps.

[0207] Next, for each of the six two-dimensional surface profile images, the spatial wavelength λ ｎ PSD in the range of ≦5 μm [nm ２ ] integrated value I １ , spatial wavelength λ ｎ PSD in the range of ≦10 μm [nm ２ ] integrated value I ２ , and the spatial wavelength λ ｎ PSD in the range of ≦20 μm [nm ２ ] integrated value I ３ Calculate the integrated value I １ , integrated value I ２ and the integrated value I ３ To calculate the spatial wavelength λ ｎ= 100 / n [μm] (where n is an integer between 1 and 255). ｎ PSD in the range of ≦5 μm [nm ２ ] integrated value I １ is the spatial wavelength λ ｎ１ = 100 / n １ [μm] (where n １ is an integer between 20 and 255.) ｎ Integrated value I in the range of ≦10 μm ２ is the spatial wavelength λ ｎ２ = 100 / n ２ [μm] (where n ２ is an integer between 10 and 255.) ｎ Integrated value I in the range of ≦20 μm ３ is the spatial wavelength λ ｎ３ = 100 / n ３ [μm] (where n ３ is an integer between 5 and 255.

[0208] Next, six integrated values ​​I calculated from the six two-dimensional surface profile images are １ Simply average (arithmetic mean) the integrated value I １ The average value of I λｎ≦５ Next, the six integrated values ​​I calculated from the six two-dimensional surface profile images are calculated. ２ Simply average (arithmetic mean) the integrated value I ２ The average value of I λｎ≦１０ Next, the six integrated values ​​I calculated from the six two-dimensional surface profile images are calculated. ３ Simply average (arithmetic mean) the integrated value I ３ The average value of I λｎ≦２０ Calculate.

[0209] Next, the average value I λｎ≦２０ From the average value I λｎ≦１０ Subtract the average value I １０≦λｎ≦２０ (I λｎ≦２０ -I λｎ≦１０ ) is calculated. Next, the average value I λｎ≦５and the average value I １０≦λｎ≦２０ The ratio of (I λｎ≦５ / I １０≦λｎ≦２０ ) is calculated.

[0210] (Average value of integrated value I λｎ≦５ ) The spatial wavelength λ obtained by measuring the magnetic surface with an AFM ｎ Average value I of the integrated value of PSD in the range of ≦5 μm λｎ≦５ is preferably 2.20 nm ２ Less than or equal to 2.00 nm, more preferably ２ or less, and even more preferably 1.80 nm ２ Below, 1.60nm ２ Below, 1.40nm ２ or less than 1.35 nm ２ The average value of the integrated value I λｎ≦５ is 2.20 nm ２ If the thickness is less than this, the increase in the component of short wavelength λ (λ≦5 μm) in the unevenness of the magnetic surface is suppressed, and the spacing becomes narrower, thereby improving the electromagnetic conversion characteristics.

[0211] (Average value of integrated value I １０≦λｎ≦２０ ) 10 μm≦spatial wavelength λ obtained by measuring the magnetic surface with an AFM ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ The lower limit of is preferably 0.60 nm ２ More preferably, 0.62 nm ２ That's all. The average value of the integrated value I １０≦λｎ≦２０ is 0.60 nm ２ In this way, the contact state between the magnetic tape MT and the head unit 56 is stabilized, powder falling off is reduced, and deterioration of the running performance of the magnetic tape MT is suppressed.

[0212] 10 μm≦spatial wavelength λ obtained by measuring the magnetic surface with an AFM ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ The upper limit is preferably 0.72 nm. ２ or less, more preferably 0.69 nm ２ or less, and even more preferably 0.67 nm ２ or less than 0.66 nm ２ The average value of the integrated value I １０≦λｎ≦２０ is 0.72 nm２ If it is equal to or less than this, the spacing between the head unit 56 and the magnetic tape MT can be reduced, and the electromagnetic conversion characteristics are stabilized.

[0213] 10μm≦spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ The numerical range may be defined by any of the above upper limit values ​​and any of the above lower limit values, and is preferably 0.60 nm. ２ 0.72nm or more ２ Less than or equal to 0.60 nm, more preferably ２ More than 0.69 nm ２ or less, and even more preferably 0.60 nm ２ More than 0.67 nm ２ Below, 0.60nm ２ 0.66nm or more ２ or less than 0.62 nm ２ 0.66nm or more ２ The following is the result.

[0214] (Irregularities and ratios of magnetic surface λｎ≦５ / I １０≦λｎ≦２０ Figure 11 shows the relationship between the roughness of the magnetic surface and the ratio I λｎ≦５ / I １０≦λｎ≦２０ 11 is a diagram for explaining the relationship between the unevenness of the magnetic surface and the unevenness of the magnetic tape MT. The uneven shapes (1) to (5) shown in FIG. 11 are merely an image of the unevenness and do not accurately represent the unevenness of an actual magnetic tape MT. Small waviness 430A corresponds to the component of the short wavelength λ (λ≦5 μm) in the unevenness of the magnetic surface, and large waviness 430B corresponds to the component of the long wavelength λ (10 μm≦λ≦20 μm) in the unevenness of the magnetic surface.

[0215] Ratio I λｎ≦５ / I １０≦λｎ≦２０ The ratio I decreases in the order of uneven shapes (1), (2), (3) (or (4)), and (5). λｎ≦５ / I １０≦λｎ≦２０ have different I λｎ≦５ and different I １０≦λｎ≦２０ It has a ratio I λｎ≦５ / I １０≦λｎ≦２０If the coefficient of friction exceeds 3.00, the number of small undulations 430A will be greater than the number of large undulations 430B, and the small undulations 430A will be more likely to come into contact with the head unit 56. This will increase the spacing, which will tend to deteriorate the electromagnetic conversion characteristics. Furthermore, if the small undulations 430A are more likely to come into contact with the head unit 56, the small undulations 430A will be more likely to undergo plastic deformation or brittle fracture in a high-temperature, high-humidity environment. Therefore, there is a risk that the dynamic friction coefficient will increase in a high-temperature, high-humidity environment.

[0216] (Reduction rate of saturation magnetization Ms after 8-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90 RH%) The reduction rate of saturation magnetization Ms after 8-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90 RH% (hereinafter referred to as "reduction rate of saturation magnetization Ms after high-temperature, high-humidity storage test") is preferably 1.00% or less, more preferably 0.55% or less, even more preferably 0.50% or less, 0.40% or less, 0.30% or less, 0.20% or less, 0.10% or less, or 0.05% or less.

[0217] The reason why it is preferable that the rate of decrease in saturation magnetization Ms after the high-temperature, high-humidity storage test is 1.00% or less is as follows: A decrease in saturation magnetization Ms means a decrease in thermal stability. The average particle volume V of the magnetic particles contained in the magnetic layer 43 ave is 1.50 x 10 ３ nm ３ If the magnetic powder has a density below 1.00%, even a slight deterioration in the magnetic properties can easily cause degradation of the reproduced signal. Since the reproduced signal is easily affected by components with low magnetic properties, if the magnetic properties of the magnetic powder as a whole deteriorate, the components that tend to attenuate the reproduced output increase. If the rate of decrease in saturation magnetization Ms due to the high-temperature, high-humidity storage test exceeds 1.00%, such components are particularly likely to increase, easily leading to a deterioration in the electromagnetic conversion properties.

[0218] The numerical range of the decrease rate of the saturation magnetization Ms in the high-temperature, high-humidity storage test is limited by the average particle volume V of the magnetic particles. ave is 1.50 x 10 ３ nm ３This is particularly effective in the magnetic layer 43 below. The reason is as follows: When moisture diffuses into the magnetic layer 43 due to a high temperature and humidity environment, acidic compounds in the magnetic layer 43 may dissolve in the moisture, producing an acidic aqueous solution. This aqueous solution has the property of corroding (dissolving) the magnetic particles. The average particle volume V of the magnetic particles ave is 1.50 x 10 ３ nm ３ If the specific surface area of ​​the magnetic particles is below this value, the magnetic particles are susceptible to the effects of the acidic aqueous solution due to their large specific surface area, which may accelerate the deterioration of the magnetic particles and accelerate the deterioration of their magnetic properties (e.g., saturation magnetization Ms), which may result in a deterioration of the electromagnetic conversion properties.

[0219] Considering the reasons for the deterioration of the electromagnetic conversion characteristics, the average particle volume V of the magnetic particles ave is 1.50 x 10 ３ nm ３ In the magnetic layer 43 described below, it is particularly effective to set the rate of decrease in saturation magnetization Ms due to a high-temperature, high-humidity storage test to 1.00% or less.

[0220] (Method for Measuring the Rate of Decrease in Saturation Magnetization Ms Due to High-Temperature, High-Humidity Storage Test) The rate of decrease in saturation magnetization Ms due to the high-temperature, high-humidity storage test is determined as follows.

[0221] (Preparation of Extraction Samples) The magnetic tape MT housed in the cartridge 10 is unwound, and four 20 cm long pieces of the magnetic tape MT are cut out from a position 30 m to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT, thereby obtaining four extraction samples. The width of the extraction samples is the same as the width of the magnetic tape MT when wound in the cartridge 10.

[0222] (Preparation of Measurement Samples) Two measurement samples are prepared from two extracted samples as follows. One extracted sample is cut into five pieces, and then the five extracted samples are stacked so that the longitudinal direction of the magnetic tape MT is the same. Then, the five pieces are punched out with a φ6.39 mm punch to prepare one measurement sample. At this time, marking is performed with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic tape MT can be identified. In the same manner, one measurement sample is prepared from the other extracted sample.

[0223] (Preparation of Background Correction Samples) Two correction samples are prepared from the remaining two extracted samples as follows. The coating (underlayer 42, magnetic layer 43, back layer 44, etc.) of one extracted sample is wiped off using acetone, ethanol, or the like, leaving only the substrate 41. The obtained substrate 41 is then cut into five pieces, and the five substrates 41 are stacked with double-sided tape and punched out with a φ6.39 mm punch to prepare a background correction sample (hereinafter simply referred to as a "correction sample"). At this time, marking is performed with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic tape MT can be identified. In the same manner, one correction sample is prepared from the other extracted sample.

[0224] (Measurement of saturation magnetization Ms1 before environmental storage) Using one measurement sample and one correction sample, the saturation magnetization Ms1 before environmental storage is measured as follows. Using a vibrating sample magnetometer (VSM), the M-H loop of the measurement sample (entire magnetic tape MT) corresponding to the longitudinal direction (running direction) of the magnetic tape MT is measured. Using the VSM, the M-H loop of the correction sample (substrate 41) corresponding to the longitudinal direction of the substrate 41 (longitudinal direction of the magnetic tape MT) is measured.

[0225] The M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41) are measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.

[0226] Background correction is performed by subtracting the M-H loop of the correction sample from the M-H loop of the measurement sample, resulting in a background-corrected M-H loop. The measurement and analysis program included with the VSM-P7-15 is used to calculate this background correction. The saturation magnetization Ms1 before environmental storage is calculated from the resulting background-corrected M-H loop. The measurement and analysis program included with the VSM-P7-15 is used to calculate this saturation magnetization Ms1. All of the above M-H loop measurements are performed at 25°C ± 2°C and 50% RH ± 5% RH. Furthermore, "demagnetization correction" is not performed when measuring the M-H loop in the longitudinal direction of the magnetic tape MT.

[0227] (Measurement of saturation magnetization Ms2 after environmental storage) Using the remaining one measurement sample and one correction sample, the saturation magnetization Ms2 after environmental storage is measured as follows. The measurement sample and the correction sample are placed on a petri dish and stored in an environment at a temperature of 60°C and a humidity of 90% RH for 8 weeks. After 8 weeks of storage, the saturation magnetization Ms2 after environmental storage is determined in the same manner as in the above "Measurement of saturation magnetization Ms1 before environmental storage."

[0228] (Calculation of the reduction rate of saturation magnetization Ms due to high-temperature, high-humidity storage test) The reduction rate [%] of saturation magnetization Ms due to high-temperature, high-humidity storage test is calculated by the following formula: Reduction rate [%] of saturation magnetization Ms due to high-temperature, high-humidity storage test=100−[(Ms2 / Ms1)×100]

[0229] (Average dynamic friction coefficient μ of the magnetic surface measured by moving the magnetic tape MT in the longitudinal direction at a speed of 6 mm / s after a two-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90% RH.) If the magnetic layer 43 contains an acidic compound, the running stability of the magnetic tape MT may be reduced in a high-temperature, high-humidity environment. The reason for this is explained below. As described above, when moisture diffuses into the magnetic layer 43 in a high-temperature, high-humidity environment, the acidic compound contained in the magnetic layer 43 may dissolve in the moisture, producing an acidic aqueous solution. The acidic aqueous solution produced in the magnetic layer 43 may corrode (dissolve) the magnetic particles. When the magnetic particles corrode, their particle size decreases, which may make it impossible to maintain the binding between the magnetic particles and between the magnetic particles and particles other than the magnetic particles (e.g., abrasive particles, carbon particles, etc.) by the binder. When such a phenomenon occurs on the surface of the magnetic layer 43 and in its vicinity, the irregularities on the magnetic surface become brittle, making the protrusions 430 more susceptible to plastic deformation or brittle fracture. Specifically, for example, as shown in FIG. 15, when the magnetic tape MT runs along the edge of the head unit 56, the protrusions 430 are more susceptible to plastic deformation or brittle fracture. When the protrusions 430 are plastically deformed or brittle fractured, the running stability of the magnetic tape MT tends to decrease. When the average particle volume of the magnetic particles is large, the specific surface area of ​​the magnetic particles is small, so the tendency for the running stability to decrease due to corrosion of the magnetic particles is less noticeable. However, when the average particle volume of the magnetic particles is 1.50 x 10 ３ nm ３ If the specific surface area of ​​the magnetic particles is below this value, the tendency for deterioration in running stability due to corrosion of the magnetic particles becomes conspicuous.

[0230] As described above, if the magnetic layer 43 contains an acidic compound, the running stability of the magnetic tape MT may be reduced in a high-temperature, high-humidity environment. For this reason, in one embodiment, the numerical range of the average dynamic friction coefficient μ of the magnetic surface measured by moving the magnetic tape MT in the longitudinal direction at a speed of 6 mm / s after a two-week high-temperature, high-humidity storage test at a temperature of 60° C. and a humidity of 90% RH (hereinafter referred to as the “average dynamic friction coefficient μ after a high-temperature, high-humidity storage test”) is limited. Specifically, the average dynamic friction coefficient μ after a high-temperature, high-humidity storage test is preferably 0.35 or less, more preferably 0.34 or less, and even more preferably 0.33 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, 0.28 or less, 0.27 or less, or 0.26 or less. If the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is 0.35 or less, it is possible to suppress wobbling of the magnetic tape MT due to the stick-slip phenomenon when the magnetic tape MT is recorded or reproduced by a drive with the oblique head unit 56. In other words, when the magnetic tape MT is recorded or reproduced by a drive with the oblique head unit 56, it is possible to suppress the deviation (error) of the reading position of the servo pattern in the width direction of the magnetic tape MT, and it is possible for the oblique head unit 56 to accurately trace the data track Tk. Therefore, even when the magnetic tape MT is recorded or reproduced by a drive with the oblique head unit 56 in a high-temperature, high-humidity environment, it is possible to maintain running stability of the magnetic tape MT.

[0231] (Configuration of Measuring Apparatus 70) Before describing the method for measuring the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test, the configuration of the measuring apparatus 70 used in the method for measuring the average dynamic friction coefficient μ will be described with reference to Figures 12, 13, and 14.

[0232] The measuring device 70 includes a base 71 , a driving device 72 , a load cell 73 , two plate-like members 74 A and 74 B, two guides 75 A and 75 B, and a head block 76 .

[0233] (Driver 72) The driver 72 is fixed on the base 71. The driver 72 is configured to be movable in a direction to move the load cell 73 toward and away from the guide 75A.

[0234] (Load cell 73) The load cell 73 is supported on the drive device 72. One end of the magnetic tape MT is connected to the load cell 73 via a jig 77. The load cell 73 can measure the tension applied to the magnetic tape MT in the longitudinal direction. A ZTS-5N manufactured by Imada Co., Ltd. is used as the load cell 73. The positions of the load cell 73 and the guide 75A are set so that the magnetic tape MT is approximately horizontal between the jig 77 and the guide 75A.

[0235] (Plate-like members 74A, 74B) The plate-like members 74A, 74B are supported on the base 71 at a predetermined distance apart so that their main surfaces face each other and are parallel to each other. The plate-like members 74A, 74B are made of highly rigid metal plates. Note that the plate-like member 74B is not shown in Figure 12.

[0236] (Guides 75A, 75B) The two guides 75A, 75B are arranged parallel to each other and spaced apart from each other. Bearings (not shown) are provided at both ends of the two guides 75A, 75B, respectively, and the ends of the two guides 75A, 75B are fixed to the plate-like members 74A, 74B via these bearings. This allows the two guides 75A, 75B to rotate smoothly in accordance with the reciprocating movement of the magnetic tape MT, and also fixes the relative positions of the two guides 75A, 75B. As described above, the smooth rotation of the two guides 75A, 75B prevents the dynamic friction between the guides 75A, 75B and the magnetic tape MT from affecting the tension measurement of the magnetic tape MT. The guide 75A is made of a round bar 75A. １ and roll member 75A ２ The guide 75B has a round bar 75B １ and roll member 75B ２ It has the following.

[0237] Round bar 75A １ A bearing (not shown) is provided at each end of the round bar 75B. １ Bearings (not shown) are also provided at both ends of the round bar 75A. １ is the roll member 75A２ The roll member 75A is inserted into the hole of the roll member 75A. ２ is round bar 75A １ Similarly, the round bar 75B is fixed to the peripheral surface of the １ is the roll member 75B ２ The roll member 75B is inserted into the hole of the roll member 75B. ２ Round bar 75B １ The roller member 75A is fixed to the peripheral surface of the roller member 75A. ２ , 75B ２ The peripheral surface of the round bar 75A is the surface that comes into contact with the magnetic tape MT when measuring the tension. １ , 75B １ A 3 mm diameter stainless steel round bar (RGOS3-150 Kenma Rod RGOS, manufactured by Misumi Corporation) is used as the roll member 75A. ２ , 75B ２ A cylindrical member made of SUS and having a diameter of 15 mm is used as the casing.

[0238] (Head Block 76) The head block 76 is movably attached to the plate-like members 74A and 74B so that the wrap angle θ can be changed. Once the wrap angle θ (°) reaches the desired angle (25° in this measurement) by moving the head block 76, the head block 76 can be fixed in that position, thereby fixing the positional relationship between the guides 75A and 75B and the head block 76. When measuring tension, the head block 76 is fixed between the guides 75A and 75B and at a position approximately equidistant from each of the guides 75A and 75B. A recording / playback head for an LTO4 drive manufactured by Hewlett-Packard Enterprises (HPE) is used as the head block 76.

[0239] (Sample Preparation) The sample used to measure the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is prepared as follows. First, the cartridge 10 with the magnetic tape MT wound thereon is stored for two weeks in an environment of a temperature of 60°C and a humidity of 90% RH. The cartridge case 12 used is one conforming to the LTO9 standard. Next, the magnetic tape MT is cut to a length of 50 cm at a position 30 m longitudinally from one end of the outer periphery of the magnetic tape MT to prepare a sample (hereinafter referred to as "Sample 1") having a width of 1 / 2 inch and a length of 50 cm.

[0240] Next, the magnetic tape MT is further unwound, and the magnetic tape MT is cut into a length of 50 cm at a position 50 m longitudinally from one end of the inner circumference of the magnetic tape MT to prepare a sample (hereinafter referred to as "Sample 2") having a width of 1 / 2 inch and a length of 50 cm.

[0241] (Measurement of Average Dynamic Friction Coefficient μ After High-Temperature, High-Humidity Storage Test) The average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is measured as follows.

[0242] Using the sample 1 prepared as described above, the tension T [N] of the sample 1 during sliding is measured as follows. First, the magnetic tape MT of the sample 1 is placed on the two guides 75A and 75B so as to straddle the two guides 75A and 75B, and the head block 76 is brought into contact with the magnetic surface of the magnetic tape MT. At this time, as shown in FIG. 14 , the magnetic surface of the magnetic tape MT is brought into contact with the head block (for recording and playback) 76 so that the wrap angle θ (°) is 25°. Here, the wrap angle θ is calculated from the curvature R of the head block 76 and the amount of pressurization of the head block 76 against the magnetic tape MT. Next, one end of the magnetic tape MT is connected to the load cell 73 via a jig 77. One end of the magnetic tape MT is fixed to the jig 77. Next, a weight 78 with a mass of 100 g is connected to the other end of the magnetic tape MT. The weight 78 applies a tension of 100.0 gf (approximately 0.9807 N) to the magnetic tape MT in the longitudinal direction.

[0243] Next, the head block 76 is slid over the magnetic surface of the magnetic tape MT while repeatedly moving back and forth five times relative to the magnetic tape MT. The tension T [N] of the magnetic tape MT during this moving back and forth is measured by the load cell 73. The moving back and forth motion is controlled so that the sliding distance (moving distance) for each of the forward and backward motions is 55 mm, and the sliding speed (moving distance) of the magnetic tape MT relative to the head block 76 is 6 mm / s. The sliding speed (moving speed) of 6 mm / s is set in consideration of the shift speed in the width direction of the magnetic tape MT during actual running.

[0244] The pulling time (time for one forward movement) and the letting-off time (time for one return movement) are both set to 9.2 seconds. The sampling rate of the load cell 73 is set to 0.5 points / second. Therefore, the number of measurement points during one pulling (one forward movement) is 18 points. The environment during measurement of the tension T [N] is maintained at 23°C ± 2°C and 45% RH ± 5% RH.

[0245] Next, the tension T [N] of sample 2 is measured in the same manner as the measurement of the tension T [N] of the magnetic tape of sample 1 above, except that sample 2 prepared as described above is used.

[0246] Next, the average tension values ​​during tension on the fourth and fifth outbound passes of Samples 1 and 2 are calculated. Specifically, data for one point before and after is removed from the measurement data (tension) for each of the fourth outbound pass (18 point) of Sample 1, the fifth outbound pass (18 point) of Sample 1, the fourth outbound pass (18 point) of Sample 2, and the fifth outbound pass (18 point) of Sample 2. Then, the measurement data for the fourth outbound pass (16 point) of Sample 1, the measurement data for the fifth outbound pass (16 point) of Sample 1, the measurement data for the fourth outbound pass (16 point) of Sample 2, and the measurement data for the fifth outbound pass (16 point) of Sample 2 (a total of 16 x 4 measurement data) are simply averaged to obtain the average tension T during sliding. ave. Find [N].

[0247] The tension of the magnetic tape MT in a stationary state (T ０The tension T [N] of the sample 1 is calculated as follows: After measuring the tension T [N] of the sample 1, the device shown in FIG. 12 is rotated 90° so that the jig 77 is positioned directly below the load cell 73. The device is then held so that the longitudinal direction of the magnetic tape MT coincides with the direction of gravity and the magnetic tape MT hangs directly down without passing through the guides 75A and 75B and the head block 76. In this state, the tension applied to the magnetic tape MT is measured by the load cell 73, and this tension is calculated as the tension T of the magnetic tape MT in the stationary state. ０１ [N]. The tension T ０１ The measurement environment for the tension T [N] is maintained at 23°C ± 2°C and 45% RH ± 5% RH. Next, except for using Sample 2 after measuring the tension T [N], the tension T of the magnetic tape of Sample 1 is measured. ０１ In the same manner as in the measurement of [N], the tension T of the magnetic tape of Sample 2 ０２ [N] is measured. Then, the tension T ０１ [N] and tension T ０２ [N] to obtain the average tension T ０ Find [N].

[0248] Average tension T ave. [N] and the average tension T ０ [N] is substituted into the following formula to determine the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test. (where θ [°] represents the wrap angle of the magnetic tape MT with respect to the head block 76, and T ０ [N] represents the tension of the magnetic tape MT in a stationary state, and T ave. [N] represents the average tension of the magnetic tape MT during sliding.

[0249] (Coercive force Hc2) The upper limit of the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is preferably 2000 Oe or less, more preferably 1900 Oe or less, and even more preferably 1800 Oe or less. If the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is 2000 Oe or less, sufficient electromagnetic conversion characteristics can be obtained even at high recording densities.

[0250] The lower limit of the coercive force Hc2 of the magnetic layer 43 measured in the longitudinal direction of the magnetic tape MT is preferably 1000 Oe or more. When the coercive force Hc2 of the magnetic layer 43 measured in the longitudinal direction of the magnetic tape MT is 1000 Oe or more, demagnetization due to leakage flux from the recording head can be suppressed.

[0251] The coercive force Hc2 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and six magnetic tape MTs are cut out at positions 30 to 40 meters longitudinally from one end of the outer periphery of the magnetic tape MT. At this time, markings are made with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic tape MT can be identified. Next, the three cut-out magnetic tape MTs are stacked with double-sided tape so that the longitudinal direction of the three cut-out magnetic tape MTs is the same, and then punched out with a φ6.39 mm punch to prepare a measurement sample. Next, the M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the longitudinal direction (running direction) of the magnetic tape MT is measured using a vibrating sample magnetometer (VSM). Next, the coatings (underlayer 42, magnetic layer 43, back layer 44, etc.) of the remaining three cut-out magnetic tape MTs are wiped off using acetone, ethanol, or the like, leaving only the substrate 41. Three of the obtained substrates 41 are then stacked together with double-sided tape, and punched out with a φ6.39 mm punch to prepare a sample for background correction (hereinafter simply referred to as a "correction sample"). Thereafter, the M-H loop of the correction sample (substrate 41) corresponding to the longitudinal direction of the substrate 41 (the longitudinal direction of the magnetic tape MT) is measured using a VSM.

[0252] The MH loop of the measurement sample (the entire magnetic tape MT) and the MH loop of the correction sample (substrate 41) are measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.

[0253] After obtaining the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), background correction is performed by subtracting the M-H loop of the correction sample (substrate 41) from the M-H loop of the measurement sample (the entire magnetic tape MT), thereby obtaining the background-corrected M-H loop. This background correction calculation is performed using the measurement and analysis program included with the VSM-P7-15. The coercive force Hc2 is calculated from the obtained background-corrected M-H loop. Note that this calculation is performed using the measurement and analysis program included with the VSM-P7-15. Note that all of the above M-H loop measurements are performed at 25°C ± 2°C and 50% RH ± 5% RH. Furthermore, "demagnetization field correction" is not performed when measuring the M-H loop in the longitudinal direction of the magnetic tape MT.

[0254] (Squareness Ratio) The squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 62% or more, more preferably 65% ​​or more, and even more preferably 68% or more, 72% or more, or 75% or more. When the squareness ratio S1 is 62% or more, the perpendicular orientation of the magnetic particles is sufficiently high, thereby achieving even better electromagnetic conversion characteristics.

[0255] The squareness ratio S1 in the perpendicular direction of the magnetic tape MT is determined as follows. First, a measurement sample is prepared in the same manner as in the above-described method for measuring the coercive force Hc2. Next, an M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the perpendicular direction of the magnetic tape MT (the perpendicular direction of the magnetic tape MT) is measured using a VSM. Next, a correction sample is prepared in the same manner as in the above-described method for measuring the coercive force Hc2. Thereafter, an M-H loop of the correction sample (substrate 41) corresponding to the perpendicular direction of the substrate 41 (the perpendicular direction of the magnetic tape MT) is measured using a VSM.

[0256] After obtaining the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), background correction is performed by subtracting the M-H loop of the correction sample (substrate 41) from the M-H loop of the measurement sample (the entire magnetic tape MT), thereby obtaining the M-H loop after background correction. This background correction calculation is performed using the measurement and analysis program included with the "VSM-P7-15 Model."

[0257] The saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the M-H loop after background correction are substituted into the following formula to calculate the squareness ratio S1 (%). Note that all of the above M-H loop measurements are performed at 25°C ± 2°C and 50% RH ± 5% RH. Also, no "demagnetizing field correction" is performed when measuring the M-H loop in the perpendicular direction to the magnetic tape MT. Note that this calculation uses the measurement and analysis program included with the "VSM-P7-15 model." Squareness ratio S1 (%) = (Mr / Ms) × 100

[0258] The squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT is preferably 35% or less, more preferably 30% or less, and even more preferably 25% or less, 20% or less, or 15% or less. When the squareness ratio S2 is 35% or less, the perpendicular orientation of the magnetic particles is sufficiently high, thereby achieving even better electromagnetic conversion characteristics. Note that one of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT and the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT may be within the above-mentioned preferred range, while the other may be outside the above-mentioned preferred range. Alternatively, both the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT and the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT may be within the above-mentioned preferred range.

[0259] The squareness ratio S2 in the longitudinal direction of the magnetic tape MT is determined in the same manner as the squareness ratio S1, except that the MH loop is measured in the longitudinal direction (running direction) of the magnetic tape MT and the substrate 41.

[0260] (Ratio Hc2 / Hc1) The ratio Hc2 / Hc1 of the coercive force Hc1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT to the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT preferably satisfies the relationship Hc2 / Hc1≦0.8, more preferably Hc2 / Hc1≦0.75, and even more preferably Hc2 / Hc1≦0.7, H2 / Hc1≦0.65, or H2 / Hc1≦0.6. When the coercive forces Hc1 and Hc2 satisfy the relationship Hc2 / Hc1≦0.8, the degree of perpendicular orientation of the magnetic particles can be increased. Therefore, the magnetization transition width can be reduced and a high-output signal can be obtained during signal reproduction, resulting in even better electromagnetic conversion characteristics. As described above, a small Hc2 allows the magnetization to respond more sensitively to the perpendicular magnetic field from the recording head, thereby forming a good recording pattern.

[0261] When the ratio Hc2 / Hc1 is Hc2 / Hc1≦0.8, the average thickness t ２ It is particularly effective that the average thickness t of the magnetic layer 43 is 0.090 μm or less. ２ If the thickness exceeds 0.090 μm, when a ring-type head is used as the recording head, the lower region of the magnetic layer 43 (the region on the underlayer 42 side) may be magnetized in the longitudinal direction of the magnetic tape MT, which may prevent uniform magnetization of the magnetic layer 43 in the thickness direction. Therefore, even if the ratio Hc2 / Hc1 is set to Hc2 / Hc1≦0.8 (i.e., even if the degree of perpendicular orientation of the magnetic particles is increased), there is a risk that further excellent electromagnetic conversion characteristics may not be obtained.

[0262] The lower limit of Hc2 / Hc1 is not particularly limited, but for example, it is 0.5≦Hc2 / Hc1. Note that Hc2 / Hc1 represents the degree of perpendicular orientation of the magnetic grains, and the smaller Hc2 / Hc1, the higher the degree of perpendicular orientation of the magnetic grains.

[0263] The method for calculating the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is as described above. The coercive force Hc1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is determined in the same manner as the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT, except that the M-H loop is measured in the perpendicular direction (thickness direction) of the magnetic tape MT and the substrate 41.

[0264] (Activation volume V ａｃｔ ) Activation volume V ａｃｔ However, preferably 8000 nm ３ Less than 6000 nm, more preferably ３ or less, more preferably 5000 nm ３ Below, 4000nm ３ or below 3000 nm ３ The activation volume V is ａｃｔ is 8000 nm ３ If the magnetic grains are dispersed at or below this value, the bit inversion region can be made steeper, and the magnetic signal recorded on the adjacent track can be prevented from being degraded by the leakage magnetic field from the recording head, thereby achieving even better electromagnetic conversion characteristics.

[0265] The activation volume V ａｃｔ is calculated by the following formula derived by Street & Woolley: ａｃｔ (nm ３ ) = k Ｂ ×T×X ｉｒｒ / (μ ０ × Ms × S) (where k Ｂ : Boltzmann constant (1.38 × 10 －２３ J / K), T: temperature (K), Χ ｉｒｒ : Irreversible magnetic susceptibility, μ ０ : magnetic permeability of vacuum, S: magnetic viscosity coefficient, Ms: saturation magnetization (emu / cm ３ ))

[0266] Irreversible magnetic susceptibility X substituted into the above formula ｉｒｒ The saturation magnetization Ms and magnetic viscosity coefficient S are determined using a VSM as follows. The measurement direction using the VSM is the perpendicular direction (thickness direction) of the magnetic tape MT. Measurement using the VSM is performed on a measurement sample cut out from a long magnetic tape MT at 25°C ± 2°C and 50% RH ± 5% RH. When measuring the M-H loop in the perpendicular direction (thickness direction) of the magnetic tape MT, no "demagnetizing field correction" is performed.

[0267] (irreversible magnetic susceptibility Χ ｉｒｒ ) Irreversible magnetic susceptibility Χｉｒｒ is defined as the slope of the remanent magnetization curve (DCD curve) near the remanent coercivity Hr. First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic tape MT, and the magnetic field is returned to zero, resulting in a remanent magnetization state. Then, a magnetic field of approximately 15.9 kA / m (200 Oe) is applied in the opposite direction, and the magnetic field is returned to zero again, and the amount of remanent magnetization is measured. After that, similar measurements are repeated, applying a magnetic field 15.9 kA / m greater than the previously applied magnetic field and returning it to zero, and the amount of remanent magnetization is plotted against the applied magnetic field to measure the DCD curve. From the obtained DCD curve, the point where the amount of magnetization is zero is taken as the remanent coercivity Hr, and the DCD curve is further differentiated to determine the slope of the DCD curve at each magnetic field. In the slope of this DCD curve, the slope near the remanent coercivity Hr is X. ｉｒｒ This becomes:

[0268] (Saturation magnetization Ms) First, an MH loop after background correction is obtained in the same manner as in the measurement method for the squareness ratio S1 described above. Next, the value of the saturation magnetization Ms (emu) of the obtained MH loop and the volume (cm ３ ) to Ms (emu / cm ３ The volume of the magnetic layer 43 is calculated by multiplying the area of ​​the measurement sample by the average thickness t ２ The average thickness t of the magnetic layer 43 required to calculate the volume of the magnetic layer 43 is ２ The calculation method is as described above.

[0269] (Magnetic viscosity coefficient S) First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic tape MT (measurement sample), and the magnetic field is returned to zero to create a state of remanent magnetization. Then, a magnetic field equivalent to the value of the remanent coercivity Hr obtained from the DCD curve is applied in the opposite direction. With the magnetic field applied, the amount of magnetization is continuously measured at regular time intervals for 1000 seconds. The relationship between time t and amount of magnetization M(t) obtained in this way is compared with the following formula to calculate the magnetic viscosity coefficient S: M(t) = M0 + S × ln(t) (where M(t): amount of magnetization at time t, M0: initial amount of magnetization, S: magnetic viscosity coefficient, ln(t): natural logarithm of time)

[0270] (Surface roughness R of the back surface ｂ) Surface roughness of the back surface (surface roughness of the back layer 44) R ｂ The upper limit of the surface roughness R of the back surface is preferably 7.5 nm or less, more preferably 7.2 nm or less, and even more preferably 7.0 nm or less, 6.5 nm or less, 6.3 nm or less, or 6.0 nm or less. ｂ When the surface roughness R of the back surface is 7.5 nm or less, the influence of the unevenness of the back surface on the surface of the magnetic layer 43 during winding of the magnetic tape MT can be reduced, and adverse effects on the electromagnetic conversion characteristics can be suppressed. ｂ The lower limit of is preferably 3.0 nm or more, more preferably 3.2 nm or more, and even more preferably 3.4 nm or more.

[0271] Surface roughness R of the back surface ｂ is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT to a length of 100 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the sample is placed on a slide glass with the surface to be measured (magnetic surface) facing up, and the end of the sample is fixed with mending tape. The surface shape is measured using a VertScan (20x objective lens) as a measuring device, and the surface roughness R of the back surface is calculated from the following formula based on the ISO 25178 standard. ｂ The measurement conditions are as follows: Equipment: Non-contact roughness meter using optical interference (Non-contact surface / layer cross-sectional shape measurement system VertScan R5500GL-M100-AC manufactured by Ryoka Systems Co., Ltd.) Objective lens: 20x Measurement area: 640 x 480 pixels (field of view: approximately 237 μm x 178 μm field of view) Measurement mode: phase Wavelength filter: 520 nm CCD: 1 / 3 inch Noise reduction filter: Smoothing 3 x 3 Surface correction: Corrected using quadratic polynomial approximation surface Measurement software: VS-Measure Version 5.5.2 Analysis software: VS-viewer Version 5.5.5 As described above, after measuring the surface roughness at five positions in the longitudinal direction of the magnetic tape MT, the arithmetic mean roughness S ａ(nm) is the surface roughness R ｂ (nm).

[0272] (Young's modulus in the longitudinal direction of the magnetic tape) The upper limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is preferably 9.0 GPa or less, more preferably 8.0 GPa or less, even more preferably 7.5 GPa or less, and particularly preferably 7.1 GPa or less. When the Young's modulus in the longitudinal direction of the magnetic tape MT is 9.0 GPa or less, the elasticity of the magnetic tape MT due to external forces is further increased, making it easier to adjust the width of the magnetic tape MT by adjusting the tension. Therefore, off-track can be more appropriately suppressed, and data recorded on the magnetic tape MT can be reproduced more accurately. The lower limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is preferably 3.0 GPa or more, more preferably 4.0 GPa or more. When the lower limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is 3.0 GPa or more, deterioration of the running stability of the magnetic tape MT can be suppressed.

[0273] The Young's modulus in the longitudinal direction of the magnetic tape MT is a value that indicates the resistance of the magnetic tape MT to expansion and contraction in the longitudinal direction due to external forces; the larger this value, the less the magnetic tape MT is able to expand and contract in the longitudinal direction due to external forces, and the smaller this value, the more easily the magnetic tape MT is able to expand and contract in the longitudinal direction due to external forces.

[0274] The Young's modulus in the longitudinal direction of the magnetic tape MT is a value related to the longitudinal direction of the magnetic tape MT, but it also correlates with the resistance to expansion and contraction in the width direction of the magnetic tape MT. In other words, the larger this value, the less the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces. Therefore, from the viewpoint of tension adjustment, it is advantageous for the Young's modulus in the longitudinal direction of the magnetic tape MT to be small as described above, 9.0 GPa or less.

[0275] A tensile tester (AG-100D, manufactured by Shimadzu Corporation) is used to measure Young's modulus in the longitudinal direction of the tape. When measuring Young's modulus in the longitudinal direction of the tape, the magnetic tape MT housed in the cartridge 10 is unwound and cut into a length of 180 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT to prepare a measurement sample. A jig capable of fixing the tape width (1 / 2 inch) is attached to the tensile tester, and the top and bottom of the tape width are fixed. The distance (length of tape between chucks) is set to 100 mm. After chucking the tape sample, stress is gradually applied in the direction of pulling the sample. The pulling speed is set to 0.1 mm / min. Young's modulus is calculated from the change in stress and the amount of elongation at this time using the following formula: E (N / m ２ )=((ΔN / S) / (Δx / L))×10 ６ ΔN: Change in stress (N) S: Cross-sectional area of ​​test piece (mm ２ ) Δx: elongation (mm) L: distance between gripping jigs (mm) The cross-sectional area S of the measurement sample is the cross-sectional area before the pulling operation and is calculated by multiplying the width (½ inch) of the measurement sample by the thickness of the measurement sample. The range of tensile stress during measurement is set to a linear region of tensile stress depending on the thickness of the magnetic tape MT, etc. Here, the stress range is set to 0.2 N to 0.7 N, and the stress change (ΔN) and elongation (Δx) at this time are used for calculation. The above Young's modulus measurement is performed at 25°C ± 2°C and 50% RH ± 5% RH.

[0276] (Young's modulus in the longitudinal direction of the substrate) The Young's modulus of the substrate 41 in the longitudinal direction is preferably 7.8 GPa or less, more preferably 7.0 GPa or less, even more preferably 6.6 GPa or less, and particularly preferably 6.4 GPa or less. When the Young's modulus of the substrate 41 in the longitudinal direction is 7.8 GPa or less, the elasticity of the magnetic tape MT due to external forces is further increased, making it easier to adjust the width of the magnetic tape MT by adjusting the tension. Therefore, off-track can be more appropriately suppressed, and data recorded on the magnetic tape MT can be more accurately reproduced. The lower limit of the Young's modulus of the substrate 41 in the longitudinal direction is preferably 2.5 GPa or more, more preferably 3.0 GPa or more. When the lower limit of the Young's modulus of the substrate 41 in the longitudinal direction is 2.5 GPa or more, the deterioration of the running stability of the magnetic tape MT can be suppressed.

[0277] The Young's modulus in the longitudinal direction of the substrate 41 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut into a length of 180 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the underlayer 42, magnetic layer 43, and back layer 44 are removed from the cut magnetic tape MT to obtain the substrate 41. Using this substrate 41, the Young's modulus in the longitudinal direction of the substrate 41 is determined using the same procedure as for the Young's modulus in the longitudinal direction of the magnetic tape MT.

[0278] The thickness of the substrate 41 accounts for more than half of the total thickness of the magnetic tape MT. Therefore, the Young's modulus in the longitudinal direction of the substrate 41 correlates with the resistance of the magnetic tape MT to expansion and contraction due to external forces, and the larger this value, the less the magnetic tape MT is able to expand and contract in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is able to expand and contract in the width direction due to external forces.

[0279] The Young's modulus of the substrate 41 in the longitudinal direction is a value related to the longitudinal direction of the magnetic tape MT, but it also correlates with the resistance to expansion and contraction of the magnetic tape MT in the width direction. In other words, the larger this value, the less the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces. Therefore, from the perspective of tension adjustment, it is advantageous for the Young's modulus of the substrate 41 in the longitudinal direction to be small, as described above, at 7.8 GPa or less.

[0280] [5. Method for Manufacturing Magnetic Tape] Next, an example of a method for manufacturing the magnetic tape MT having the above-described configuration will be described.

[0281] (Paint preparation process) First, a paint for forming a base layer is prepared by kneading and dispersing non-magnetic particles, a binder, etc. in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and dispersing magnetic particles, a binder, and an acidic compound as an additive in a solvent. For example, the following solvents, dispersing devices, and kneading devices can be used to prepare the paint for forming a magnetic layer and the paint for forming a base layer.

[0282] Examples of solvents used in preparing the coating material include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, and propanol, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These may be used alone or in appropriate combinations.

[0283] Examples of the kneading apparatus used in preparing the above coating material include, but are not limited to, a continuous twin-screw kneader, a continuous twin-screw kneader capable of multi-stage dilution, a kneader, a pressure kneader, a roll kneader, etc. Examples of the dispersing apparatus used in preparing the above coating material include, but are not limited to, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (e.g., the "DCP Mill" manufactured by Eirich), a homogenizer, an ultrasonic disperser, etc.

[0284] (Amount of Acidic Compound) If the amount of acidic compound is too small relative to the amount of magnetic particles, the amount of acidic compound adsorbed to the surface of the magnetic particles will decrease. This will reduce the dispersibility of the magnetic particles in the magnetic layer coating material, and there is a risk that the desired uneven magnetic surface shape will not be obtained. That is, the ratio I λｎ≦５ / I １０≦λｎ≦２０ There is a risk that the value will not be 3.00 or less.

[0285] On the other hand, if the amount of acidic compound relative to the amount of magnetic particles is too high, the amount of acidic compound present in the magnetic layer 43 without adsorbing to the magnetic particle surface increases. Acidic compounds that do not adsorb to the magnetic particle surface tend to promote corrosion of the magnetic particles in high-temperature, high-humidity environments, which can lead to a decrease in the particle size of the magnetic particles and a decrease in magnetic properties (e.g., saturation magnetization Ms). Therefore, there is a risk of a decrease in electromagnetic conversion characteristics in high-temperature, high-humidity environments. Furthermore, as the particle size of the magnetic particles decreases, there is a risk that the binding between the magnetic particles by the binder and between the magnetic particles and particles other than the magnetic particles (e.g., abrasive particles, carbon particles, etc.) by the binder cannot be maintained. When this phenomenon occurs on the surface of the magnetic layer or in its vicinity, the unevenness of the magnetic surface becomes brittle. For example, as shown in Figure 15, when the magnetic tape MT runs along the edge of the head unit 56, the protrusions 430 are prone to plastic deformation or brittle fracture. As a result, there is a risk that the average dynamic friction coefficient μ will exceed 0.35 after a high-temperature, high-humidity storage test. Therefore, there is a risk that the running stability of the magnetic tape MT may be reduced in a high-temperature, high-humidity environment.Furthermore, when the protrusions 530 undergo plastic deformation or brittle fracture, powder may fall off from the magnetic surface.

[0286] Considering the above points, the amount of the acidic compound to be blended per 100.0 parts by mass of magnetic particles is preferably 1.0 part by mass or more and 4.0 parts by mass or less.

[0287] (Coating Process) Next, a base layer forming paint is applied to one main surface of the substrate 41 and dried to form the base layer 42. Subsequently, a magnetic layer forming paint is applied to the base layer 42 and dried to form the magnetic layer 43 on the base layer 42. During drying, the magnetic particles may be magnetically oriented in the thickness direction of the substrate 41, for example, using a permanent magnet. After the magnetic layer 43 is formed, a back layer 44 is formed on the other main surface of the substrate 41. This results in a magnetic tape MT. The order in which the base layer 42, magnetic layer 43, and back layer 44 are formed is not limited to the above example. For example, the back layer 44 may be formed on the other main surface of the substrate 41, and then the base layer 42 and magnetic layer 43 may be formed in that order on one main surface of the substrate 41.

[0288] The squareness ratios S1 and S2 can be set to desired values ​​by, for example, adjusting the strength of the magnetic field applied to the coating film of the magnetic layer-forming paint, the concentration of solids in the magnetic layer-forming paint, and the drying conditions (drying temperature and drying time) of the coating film of the magnetic layer-forming paint. The strength of the magnetic field applied to the coating film is preferably between two and three times the coercive force of the magnetic particles. To further increase the squareness ratio S1 (i.e., to further reduce the squareness ratio S2), it is preferable to improve the dispersion state of the magnetic particles in the magnetic layer-forming paint. To further increase the squareness ratio S1, it is also effective to magnetize the magnetic particles before the magnetic layer-forming paint enters an orientation device for magnetically orienting the magnetic particles. The above methods for adjusting the squareness ratios S1 and S2 may be used alone or in combination.

[0289] (Hardening Step) Next, after the magnetic tape MT is wound into a roll, the magnetic tape MT is subjected to a heat treatment in this state, thereby hardening the underlayer 42 and the magnetic layer 43 .

[0290] (Calendering Process) Next, the obtained magnetic tape MT is subjected to a calendering process to smooth the magnetic surface.

[0291] (Cutting Process and Strain Relief Process) Next, the magnetic tape MT is cut to a predetermined width (for example, 1 / 2 inch width) and wound onto a take-up hub. Next, the wound magnetic tape MT is subjected to a strain relief process by being held in an environment at a predetermined temperature for a predetermined time. In this manner, the magnetic tape MT is obtained.

[0292] (Servo Write Process) Next, if necessary, the magnetic tape MT may be demagnetized and then a servo pattern may be written onto the magnetic tape MT.

[0293] (I λｎ≦５ , I １０≦λｎ≦２０ and ratio I λｎ≦５ / I １０≦λｎ≦２０ Adjustment method) I λｎ≦５ , I １０≦λｎ≦２０ and ratio I λｎ≦５ / I １０≦λｎ≦２０can be adjusted, for example, by adjusting at least one of the particle size and amount of inorganic additives added to the magnetic layer-forming paint, the type and amount of acidic compound added to the magnetic layer-forming paint, the heat treatment conditions in the curing step (e.g., heat treatment temperature and heat treatment time), the treatment conditions in the calendaring step (e.g., calendaring temperature and pressure), and the thicknesses of the underlayer 42 and the magnetic layer 43. Examples of the inorganic additives include inorganic particles such as carbon particles, and abrasive particles such as alumina particles.

[0294] (Method for adjusting the rate of decrease in saturation magnetization Ms due to high temperature, high humidity storage test and the average dynamic friction coefficient μ after high temperature, high humidity storage test) The rate of decrease in saturation magnetization Ms due to high temperature, high humidity storage test and the average dynamic friction coefficient μ after high temperature, high humidity storage test can be adjusted to desired values, for example, by adjusting the type and amount of acidic compound added to the magnetic layer forming coating material, and the heat treatment conditions in the curing process (e.g., heat treatment temperature and heat treatment time, etc.).

[0295] As described above, the amount of the acidic compound to be blended relative to 100.0 parts by mass of the magnetic particles is preferably 1.0 part by mass or more and 4.0 parts by mass or less.

[0296] The heat treatment temperature in the curing step is preferably 55° C. or higher and 75° C. or lower. A heat treatment temperature of 55° C. or higher can reduce the amount of acidic compounds that are present in magnetic layer 43 without adsorbing to the surface of the magnetic particles. A heat treatment temperature of 75° C. or lower can prevent the binder from flowing, thereby preventing deterioration of surface roughness.

[0297] The heat treatment time in the curing step is preferably 15 hours or more and 100 hours or less. If the heat treatment time is 15 hours or more, the amount of acidic compounds remaining in the magnetic layer 43 without adsorbing to the surfaces of the magnetic particles can be reduced. If the heat treatment time is 100 hours or less, a decrease in productivity of the magnetic tape MT can be suppressed.

[0298] [6. Effects] As described above, in the magnetic tape MT according to one embodiment, a two-dimensional surface profile image of a measurement range of 100 [μm]×100 [μm] obtained by measuring the magnetic surface with an AFM is used to measure the spatial wavelength λ ｎ When the power spectral density at each position of λ = 100 / n [μm] (where n is an integer of 1 to 255) is calculated, the spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦5 μm λｎ≦５ and 10 μm≦spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ is 3.00 or less. This allows the spacing amount that affects the electromagnetic conversion characteristics to be set within a preferred range, thereby achieving good electromagnetic conversion characteristics.

[0299] In addition, in the magnetic tape MT according to one embodiment, the rate of decrease in saturation magnetization Ms in a high-temperature, high-humidity environment test is 1.00% or less. ３ nm ３ Even when the temperature is below 100°C, it is possible to suppress the deterioration of magnetic properties (for example, saturation magnetization Ms) in a high-temperature, high-humidity environment, and therefore it is possible to maintain good electromagnetic conversion properties in a high-temperature, high-humidity environment.

[0300] Furthermore, in the magnetic tape MT according to one embodiment, the average dynamic friction coefficient μ after a high-temperature, high-humidity storage test is 0.35 or less, which allows the magnetic tape MT to maintain running stability even when recording or reproducing the magnetic tape MT in a drive with an oblique head unit 56 under high-temperature, high-humidity conditions.

[0301] [7 Modifications] In the above embodiment, the magnetic tape cartridge 10 is a one-reel type cartridge, but it may also be a two-reel type cartridge.

[0302] 16 is an exploded perspective view showing an example of the configuration of a two-reel type cartridge 321. The cartridge 321 comprises an upper half 302 made of synthetic resin, a transparent window member 323 fitted into and fixed to a window 302a opened in the top surface of the upper half 302, a reel holder 322 fixed to the inside of the upper half 302 to prevent the reels 306 and 307 from floating up, a lower half 305 corresponding to the upper half 302, the reels 306 and 307 stored in the space formed when the upper half 302 and lower half 305 are combined, the magnetic tape MT wound on the reels 306 and 307, a front lid 309 closing the front opening formed when the upper half 302 and lower half 305 are combined, and a back lid 309A protecting the magnetic tape MT exposed in this front opening.

[0303] The reels 306 and 307 are used to wind the magnetic tape MT. The reel 306 includes a lower flange 306b having a cylindrical hub portion 306a in the center around which the magnetic tape MT is wound, an upper flange 306c having approximately the same size as the lower flange 306b, and a reel plate 311 sandwiched between the hub portion 306a and the upper flange 306c. The reel 307 has the same configuration as the reel 306.

[0304] The window member 323 has mounting holes 323a for assembling reel holders 322, which are reel holding means for preventing the reels from floating up, at positions corresponding to the reels 306 and 307. The magnetic tape MT is the same as the magnetic tape MT in the embodiment.

[0305] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0306] In the following examples and comparative examples, the average thickness of the magnetic tape, the average thickness of the substrate (PEN film and aramid film), the average thickness of the magnetic layer, the average thickness of the underlayer, the average thickness of the back layer, the composition of the magnetic particles (magnetic powder), and the average particle volume of the magnetic particles (magnetic powder) are values ​​determined by the measurement method described in the above embodiment.

[0307] Example 1 (Preparation Process of Magnetic Layer-Forming Coating) A magnetic layer-forming coating was prepared as follows. First, a first composition having the following formulation was kneaded using an extruder. Next, a second composition having the following formulation was placed in a polyethylene bottle (a resin container made of polyethylene), attached to a paint shaker (manufactured by Seiwa Giken Co., Ltd., rocking shaker), and mixed for 10 hours. Similarly, a third composition having the following formulation was placed in a polyethylene bottle, attached to a paint shaker (manufactured by Seiwa Giken Co., Ltd., rocking shaker), and mixed for 10 hours. Next, the kneaded first composition and the mixed second and third compositions were added to a stirring tank equipped with a disperser, and then 400.0 parts by mass of methyl ethyl ketone, 140.0 parts by mass of toluene, and 180.0 parts by mass of cyclohexanone were added, followed by premixing. Subsequently, further mixing was performed using a Dyno Mill and filtering was performed to prepare a magnetic layer-forming coating.

[0308] (First composition) Barium ferrite (Ba ０．６ Sr ０．４ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.37 × 10 ３ nm ３ Vinyl chloride resin solution (resin solution composition: vinyl chloride resin 30.0% by mass, cyclohexanone solution 70.0% by mass): 25.0 parts by mass (vinyl chloride resin: degree of polymerization 300, number average molecular weight Mn = 10,000, polar group OSO ３ K = 0.07 mmol / g, secondary OH = 0.3 mmol / g.) Polyurethane resin solution (resin solution formulation: polyurethane resin formulation amount 30.0 mass%, cyclohexanone formulation amount 70.0 mass%): 25.0 parts by mass (polyurethane resin: number average molecular weight Mn = 25,000, glass transition temperature Tg = 110°C) Phenylphosphonic acid (acidic compound): 3.0 parts by mass

[0309] (Second composition) Aluminum oxide powder (α-Al ２ O ３, arithmetic mean particle diameter 0.10 μm): 4.0 parts by mass Vinyl chloride resin solution (resin solution composition: vinyl chloride resin 30.0 mass%, cyclohexanone solution 70.0 mass%): 4.0 parts by mass (vinyl chloride resin: degree of polymerization 300, number average molecular weight Mn = 10,000, polar group OSO ３ K = 0.07 mmol / g, secondary OH = 0.3 mmol / g.) Cyclohexanone: 10.0 parts by mass

[0310] (Third composition) Carbon black (manufactured by Tokai Carbon Co., Ltd., product name: SEAT S, arithmetic average particle size 70 nm): 2.0 parts by mass Polyurethane resin solution (resin solution composition: polyurethane resin content 30.0 mass%, cyclohexanone content 70.0 mass%): 4.0 parts by mass (polyurethane resin: number average molecular weight Mn = 25,000, glass transition temperature Tg = 110°C) Cyclohexanone: 18.5 parts by mass

[0311] Finally, 1.7 parts by mass of polyisocyanate (equivalent to Coronate L manufactured by Tosoh Corporation) and 2.0 parts by mass of stearic acid were added as a curing agent to the magnetic layer-forming coating material prepared as described above.

[0312] (Preparation process of paint for forming base layer) The paint for forming the base layer was prepared as follows. First, the fourth composition having the following formulation was kneaded using an extruder. Next, the kneaded fourth composition and the fifth composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, further mixing was performed using a Dynomill and filtering was performed to prepare the paint for forming the base layer.

[0313] (Fourth composition) Acicular iron oxide powder (α-Fe ２ O ３ , average major axis length 0.15 μm): 100.0 parts by mass Vinyl chloride resin solution (resin solution composition: vinyl chloride resin 30.0 mass%, cyclohexanone solution 70.0 mass%): 55.0 parts by mass (vinyl chloride resin: degree of polymerization 300, number average molecular weight Mn = 10,000, polar group OSO ３ K = 0.07 mmol / g, secondary OH = 0.3 mmol / g.) Aluminum oxide powder: 3.0 parts by mass (α-Al ２ O ３, arithmetic mean particle size 0.1 μm) Citric acid: 1.5 parts by mass

[0314] (Fifth composition) Carbon black: 30.0 parts by mass (manufactured by Asahi Carbon Co., Ltd., product name: #80) Polyurethane resin solution (resin solution formulation: polyurethane resin blending amount 30.0 mass%, cyclohexanone blending amount 70.0 mass%): 45.0 parts by mass (polyurethane resin: number average molecular weight Mn = 25,000, glass transition temperature Tg = 70°C) n-butyl stearate: 2.0 parts by mass Methyl ethyl ketone: 220.0 parts by mass Toluene: 50.0 parts by mass Cyclohexanone: 50.0 parts by mass

[0315] Finally, 1.5 parts by mass of polyisocyanate (equivalent to Coronate L manufactured by Tosoh Corporation) as a curing agent and 1.5 parts by mass of stearic acid were added to the paint for forming the undercoat layer prepared as described above.

[0316] (Step of preparing paint for forming back layer) The paint for forming back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the paint for forming back layer.

[0317] Carbon black (manufactured by Asahi Carbon Co., Ltd., trade name: #80): 100.0 parts by mass Polyester polyurethane (manufactured by Nippon Polyurethane Co., Ltd., trade name: N-2304): 50.0 parts by mass Methyl ethyl ketone: 500.0 parts by mass Toluene: 400.0 parts by mass Cyclohexanone: 100.0 parts by mass Polyisocyanate (equivalent to Coronate L manufactured by Tosoh Corporation): 10.0 parts by mass

[0318] (Coating Process) Using the magnetic layer-forming paint and primer layer-forming paint prepared as described above, a primer layer and a magnetic layer were formed on one main surface of a long PEN film (substrate) having an average thickness of 4.00 μm as follows. First, the primer layer-forming paint was applied to one main surface of the PEN film and dried to form a primer layer such that the average thickness of the primer layer upon completion of the magnetic tape (average thickness of the primer layer after the cutting process) would be 0.85 μm. Next, the magnetic layer-forming paint was applied to the primer layer and dried to form a magnetic layer such that the average thickness of the magnetic layer upon completion of the magnetic tape (average thickness of the magnetic layer after the cutting process) would be 0.07 μm. During drying of the magnetic layer-forming paint, the barium ferrite magnetic powder was magnetically oriented in the thickness direction of the PEN film by a permanent magnet. This adjusted the squareness ratio S2 in the longitudinal direction of the magnetic tape.

[0319] After the underlayer and magnetic layer were formed, a coating material for forming a back layer was applied to the other main surface of the PEN film and dried to form a back layer so that the average thickness of the completed magnetic tape (average thickness after cutting) would be 0.30 μm. This gave a magnetic tape.

[0320] (Curing Step) After the magnetic tape was wound into a roll, the magnetic tape was subjected to a heat treatment at 60° C. for 50 hours in this state to cure the underlayer, magnetic layer and back layer.

[0321] (Calendering process) The cured magnetic tape was subjected to a calendering process to smooth the surface of the magnetic layer. The calendering process was carried out at a temperature close to (slightly higher than) the glass transition temperature Tg (=110°C) of the polyurethane resin (binder) contained in the magnetic layer.

[0322] (Aging Step) After the calendering, the magnetic tape was subjected to an aging treatment in an environment of 60° C. for 20 hours.

[0323] (Cutting Step) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm) to obtain a magnetic tape with an average thickness of 5.22 μm.

[0324] (Servo writing process and assembly process) After demagnetizing the obtained magnetic tape, a servo writer was used to write a servo pattern on the magnetic tape, thereby forming five servo bands. The magnetic tape after the servo bands were formed was assembled into a cartridge case to obtain a cartridge (LTO cartridge). The cartridge case used was one conforming to the LTO9 standard.

[0325] [Example 2] In the preparation process of the magnetic layer-forming paint, the amount of carbon black was changed from 2.0 parts by mass to 1.0 part by mass, and 2.5 parts by mass of citric acid was added instead of 3.0 parts by mass of phenylphosphonic acid as the acidic compound. In the curing process, the curing temperature was changed from 60°C to 70°C, and the curing time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0326] [Example 3] In the preparation process of the coating material for forming the magnetic layer, barium ferrite (Ba ０．６ Sr ０．４ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.37 × 10 ３ nm ３ ) 100.0 parts by mass of barium ferrite (Ba ０．６ Sr ０．４ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.16 × 10 ３ nm ３ ) was blended in 100.0 parts by mass. In addition, in the preparation process of the magnetic layer-forming paint, the blending amount of carbon black was changed from 2.0 parts by mass to 0.6 parts by mass, and 2.5 parts by mass of 4-hydroxybenzoic acid was blended in instead of 3.0 parts by mass of phenylphosphonic acid as the acidic compound. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0327] Example 4 In the preparation process of the magnetic layer-forming paint, the amount of carbon black added was changed from 2.0 parts by mass to 0.6 parts by mass, and 4.0 parts by mass of 4-hydroxybenzoic acid was added as the acidic compound instead of 3.0 parts by mass of phenylphosphonic acid. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0328] [Example 5] In the preparation process of the magnetic layer-forming paint, the amount of carbon black was changed from 2.0 parts by mass to 0.6 parts by mass, and 4.0 parts by mass of 4-hydroxybenzoic acid was used as the acidic compound instead of 3.0 parts by mass of phenylphosphonic acid. In the coating process, a long aramid film having an average thickness of 3.20 μm was used as the substrate instead of a long PEN film having an average thickness of 4.00 μm. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0329] [Example 6] In the preparation process of the magnetic layer-forming paint, the amount of carbon black was changed from 2.0 parts by mass to 0.6 parts by mass, and 4.0 parts by mass of 4-hydroxybenzoic acid was added as the acidic compound instead of 3.0 parts by mass of phenylphosphonic acid. In the coating process, the coating conditions for the primer layer-forming paint were adjusted to change the average thickness of the primer layer upon completion of the magnetic tape from 0.85 μm to 0.60 μm. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0330] Comparative Example 1 In the preparation process of the coating material for forming the magnetic layer, the amount of carbon black added was changed from 2.0 parts by mass to 2.5 parts by mass, and aluminum oxide powder (α-Al ２ O ３ The amount of the phenylphosphonic acid (as an acidic compound) was changed from 3.0 parts by mass to 5.0 parts by mass. In the curing step, the curing treatment time was changed from 50 hours to 25 hours. Except for the above points, a cartridge was obtained in the same manner as in Example 1.

[0331] [Comparative Example 2] In the magnetic layer-forming paint preparation process, the arithmetic mean particle diameter of the carbon black was changed from 70 nm to 50 nm, and the amount of carbon black was changed from 2.0 parts by mass to 1.5 parts by mass. Furthermore, in the magnetic layer-forming paint preparation process, 4.5 parts by mass of citric acid was added instead of 3.0 parts by mass of phenylphosphonic acid as the acidic compound. In the coating process, a long PEN film having an average thickness of 4.50 μm was used as the substrate instead of a long PEN film having an average thickness of 4.00 μm, and the coating conditions for the primer layer-forming paint were adjusted to change the average thickness of the primer layer upon completion of the magnetic tape from 0.85 μm to 0.75 μm. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0332] Comparative Example 3 In the preparation process of the coating material for forming the magnetic layer, the arithmetic mean particle size of the carbon black was changed from 70 nm to 50 nm, and aluminum oxide powder (α-Al ２ O ３ The arithmetic mean particle diameter of the base material was changed from 0.10 μm to 0.13 μm, and 5.0 parts by mass of 4-hydroxybenzoic acid was used instead of 3.0 parts by mass of phenylphosphonic acid as the acidic compound. In the coating process, a long PEN film having an average thickness of 4.20 μm was used as the substrate instead of a long PEN film having an average thickness of 4.00 μm, and the average thickness of the base layer upon completion of the magnetic tape was changed from 0.85 μm to 0.65 μm by adjusting the coating conditions of the base layer-forming paint. In the curing process, the curing treatment time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0333] [Comparative Example 4] In the preparation process of the magnetic layer-forming coating material, 1.0 part by mass of 4-hydroxybenzoic acid was added as the acidic compound instead of 3.0 parts by mass of phenylphosphonic acid. In the calendaring process, the calendaring temperature was lowered by 5°C compared to the calendaring temperature in Example 1. In the curing process, the curing time was changed from 50 hours to 25 hours. A cartridge was obtained in the same manner as in Example 1, except for the above points.

[0334] [Comparative Example 5] In the preparation process of the coating material for forming the magnetic layer, barium ferrite (Ba ０．６ Sr ０．４ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.37 × 10 ３ nm ３ ) 100.0 parts by mass of barium ferrite (Ba ０．６ Sr ０．４ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.60 × 10 ３ nm ３ 100.0 parts by mass of phenylphosphonic acid was blended in, and 3.0 parts by mass of 4-hydroxybenzoic acid was blended in instead of 3.0 parts by mass of phenylphosphonic acid as the acidic compound. A cartridge was obtained in the same manner as in Example 1 except for the above points.

[0335] [Evaluation] The magnetic tape in the cartridge obtained as described above was evaluated as follows.

[0336] (spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦5 μm λｎ≦５ , 10μm≦spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ , Relative I λｎ≦５ / I １０≦λｎ≦２０ ) The spatial wavelength λ described in the above embodiment ｎ Average value I of the integrated value of PSD in the range of ≦5 μm λｎ≦５ , 10μm≦spatial wavelength λ ｎ Average value I of the integrated value of PSD in the range of ≦20 μm １０≦λｎ≦２０ , and the ratio I λｎ≦５ / I １０≦λｎ≦２０ The results are shown in Table 1.

[0337] (Reduction rate of saturation magnetization Ms due to high temperature and high humidity storage test) The reduction rate of saturation magnetization Ms due to the high temperature and high humidity storage test was measured using the method for measuring the reduction rate of saturation magnetization Ms due to the high temperature and high humidity storage test described in the embodiment above. The results are shown in Table 1.

[0338] (Evaluation of SNR before high-temperature, high-humidity storage test) First, the magnetic tape was unwound from the cartridge (LTO cartridge), and a section approximately 20 m long was cut and removed from the outermost tip. Next, the cartridge was attached to a 1 / 2-inch tape transport device (MTS Transport 2'x3' Deck manufactured by Mountain Engineering II) equipped with a recording / playback head and a recording / playback amplifier. The magnetic tape was then set in the tape transport device's running path, and one end of the magnetic tape was fixed to the reel. The magnetic tape was then run by the tape transport device, and a playback signal was obtained. The conditions for obtaining the playback signal are as follows: Head: LTO9 recording / playback head Head speed: 1.85 m / s Signal: Single recording frequency 10 MHz (2T half Nyquist frequency) Equivalent to 549 kfci Recording current: Optimum recording current

[0339] Next, the playback signal was captured using a spectrum analyzer with a span of 0 to 20 MHz (resolution bandwidth = 100 kHz, VBW = 30 kHz). The peak of the captured spectrum was then taken as the signal amount S, and the floor noise excluding the peak was integrated from 3 MHz to 20 MHz to obtain the noise amount N. The ratio S / N of the signal amount S to the noise amount N was calculated as the SNR (Signal-to-Noise Ratio). The calculated SNR was then converted into a relative value (dB) based on the SNR of Example 1 used as the reference media. The results are shown in Table 1. Hereinafter, the SNR after conversion into a relative value will be referred to as the SNR before the high-temperature, high-humidity storage test.

[0340] (SNR after high-temperature, high-humidity storage test, and SNR degradation due to high-temperature, high-humidity storage test) First, the magnetic tape that had been wound onto the reel during the SNR evaluation was rewound into the cartridge, and then the cartridge was removed from the running device. Next, the cartridge was stored for two weeks in an environment with a temperature of 60°C and a humidity of 90% RH. Next, the magnetic tape was unwound from the cartridge after storage, and a section of approximately 20 m long was cut and removed from the tip on the outer periphery. This was done because the portion of the magnetic tape located on the outer periphery of the cartridge during storage was too strongly affected by the high-temperature, high-humidity storage test, and this portion was removed.

[0341] Next, the SNR was determined in the same manner as the evaluation of the SNR before the high-temperature, high-humidity storage test, except that the cartridge after the high-temperature, high-humidity storage test was used. The determined SNR was then converted into a relative value (dB) based on the SNR of Example 1 (reference media) before the high-temperature, high-humidity storage test. The results are shown in Table 1. Hereinafter, the SNR converted into a relative value in this manner will be referred to as the SNR after the high-temperature, high-humidity storage test. Next, the SNR degradation due to the high-temperature, high-humidity storage test (= [SNR before the high-temperature, high-humidity storage test] - [SNR after the high-temperature, high-humidity storage test]) was determined by subtracting the SNR after the high-temperature, high-humidity storage test from the SNR before the high-temperature, high-humidity storage test. The results are shown in Table 1.

[0342] If the SNR after the high temperature and high humidity storage test is −1.00 dB or higher, the tape storage drive can maintain sufficiently good electromagnetic conversion characteristics (SNR) even in a high temperature and high humidity environment.

[0343] (Average Dynamic Friction Coefficient μ After High-Temperature, High-Humidity Storage Test) The average dynamic friction coefficient μ after the high-temperature, high-humidity storage test was measured by the method for measuring the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test described in the embodiment above. The results are shown in Table 1. The high-temperature, high-humidity storage test was carried out by storing the sample at a temperature of 60°C and a humidity of 90 RH% for two weeks, as described in the embodiment.

[0344]

[0345] The above evaluation results revealed the following: In the magnetic tapes of Examples 1 to 6, the ratio I λｎ≦５ / I １０≦λｎ≦２０ is 3.00 or less. This makes it possible to maintain the SNR at 0 dB or more before the high-temperature, high-humidity storage test. Furthermore, in the magnetic tapes of Examples 1 to 6, the rate of decrease in saturation magnetization Ms is 1.00% or less. This makes it possible to suppress the amount of SNR degradation due to the high-temperature, high-humidity storage test to 1.00 dB or less. Therefore, it is possible to maintain the SNR (electromagnetic conversion characteristics) at -1.00 dB or more after the high-temperature, high-humidity storage test. Furthermore, in the magnetic tapes of Examples 1 to 6, the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is 0.35 or less. This makes it possible to maintain the running stability of the magnetic tape MT even after the high-temperature, high-humidity storage test.

[0346] In the magnetic tape of Comparative Example 1, the ratio I λｎ≦５ / I １０≦λｎ≦２０ is 3.19, so the SNR before the high-temperature, high-humidity storage test is -0.30 dB. Furthermore, in the magnetic tape of Comparative Example 1, the reduction rate of saturation magnetization Ms is 1.85%, so the amount of SNR degradation after the high-temperature, high-humidity storage test is 1.08 dB. Therefore, the SNR (electromagnetic conversion characteristics) cannot be maintained at -1.00 dB or more after the high-temperature, high-humidity storage test. Furthermore, in the magnetic tape of Comparative Example 1, the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is 0.38, so the running stability of the magnetic tape MT cannot be maintained after the high-temperature, high-humidity storage test.

[0347] In the magnetic tape of Comparative Example 2, the ratio I λｎ≦５ / I １０≦λｎ≦２０ is 3.32, so the SNR before the high-temperature, high-humidity storage test is -1.00 dB. Furthermore, in the magnetic tape of Comparative Example 2, the reduction rate of saturation magnetization Ms is 2.72%, so the amount of SNR degradation due to the high-temperature, high-humidity storage test is 1.87 dB. Therefore, it is not possible to maintain the SNR (electromagnetic conversion characteristics) at -1.00 dB or higher after the high-temperature, high-humidity storage test. Furthermore, in the magnetic tape of Comparative Example 2, the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is 0.40, so it is not possible to maintain the running stability of the magnetic tape MT after the high-temperature, high-humidity storage test.

[0348] In the magnetic tape of Comparative Example 3, the ratio I λｎ≦５ / I １０≦λｎ≦２０ is 2.70 or less, so the SNR before the high-temperature, high-humidity storage test is 0.10 dB. However, in the magnetic tape of Comparative Example 3, the reduction rate of saturation magnetization Ms is 2.97%, so the amount of SNR degradation due to the storage test is 2.01 dB. Therefore, it is not possible to maintain the SNR (electromagnetic conversion characteristics) at -1.00 dB or more after the high-temperature, high-humidity storage test. Furthermore, in the magnetic tape of Comparative Example 3, the average dynamic friction coefficient μ after the high-temperature, high-humidity storage test is 0.41, so it is not possible to maintain the running stability of the magnetic tape MT after the high-temperature, high-humidity storage test.

[0349] In addition, in the magnetic tapes of Comparative Examples 1 to 3, the rate of decrease in saturation magnetization Ms exceeded 1.00%, which is thought to be due in part to the fact that the amount of acidic compound (dispersant) mixed into the paint for forming the magnetic layer was excessive, resulting in a large amount of acidic compound not adsorbed to the surface of the ferrite particles being contained in the magnetic layer.

[0350] In the magnetic tape of Comparative Example 4, the reduction rate of the saturation magnetization Ms is 0.45%, so the SNR deterioration amount due to the high temperature and high humidity storage test can be suppressed to 0.50 dB. λｎ≦５ / I １０≦λｎ≦２０ Since the SNR before the high-temperature, high-humidity storage test is 3.19, the SNR has decreased to −0.52 dB. Therefore, even if the SNR degradation due to the high-temperature, high-humidity storage test is suppressed to 0.50 dB, the SNR (electromagnetic conversion characteristics) cannot be maintained at −1.00 dB or higher after the high-temperature, high-humidity storage test.

[0351] In addition, in the magnetic tape of Comparative Example 4, the rate of decrease in saturation magnetization Ms after the high-temperature, high-humidity storage test was reduced to 0.45%, while the SNR before the high-temperature, high-humidity storage test was a low value of -0.52 dB. This is thought to be due in part to the phenomenon described below. Specifically, in the magnetic tape of Comparative Example 4, the amount of acidic compound (dispersant) blended into the magnetic layer-forming paint was as low as 1.0 part by mass, so the content of acidic compound not adsorbed to the surface of the ferrite particles in the magnetic layer was reduced. As a result, the generation of an acidic aqueous solution was suppressed during the high-temperature, high-humidity storage test, and corrosion of the ferrite particles was suppressed. By suppressing corrosion of the ferrite particles, the rate of decrease in saturation magnetization Ms after the high-temperature, high-humidity storage test was reduced. However, because the amount of acidic compound (dispersant) blended into the magnetic layer-forming paint was as low as 1.0 part by mass, the dispersibility of the magnetic powder was insufficient during the preparation process of the magnetic layer-forming paint. As a result, the ratio I λｎ≦５ / I １０≦λｎ≦２０ becomes large to 3.19, and the SNR before the high-temperature, high-humidity storage test decreases.

[0352] In the magnetic tape of Comparative Example 5, the average particle volume of the ferrite particles was 1.60 × 10 ３ nm ３ Therefore, the rate of decrease in saturation magnetization Ms due to the high temperature and high humidity storage test is small, at 0.02%. However, the average particle volume of the ferrite particles is 1.60×10 ３ nm ３ Since the temperature is large, the SNR is significantly reduced to −2.00 dB before the high-temperature, high-humidity storage test.

[0353] In the magnetic tape of Comparative Example 5, the decrease rate of the saturation magnetization Ms after the high-temperature, high-humidity storage test is reduced to 0.02%. One of the reasons is thought to be the phenomenon described below. That is, in the magnetic tape of Comparative Example 5, the average particle volume of the ferrite particles is 1.60 × 10 ３ nm ３ , the specific surface area of ​​the ferrite particles is smaller than that of the magnetic tape of Example 1. Therefore, compared to the magnetic tape of Example 1, the effects of corrosion of the ferrite particles by the acidic aqueous solution are less apparent.

[0354] Although the embodiments and modifications of the present disclosure have been specifically described above, the present disclosure is not limited to the above embodiments and modifications, and various modifications based on the technical concepts of the present disclosure are possible. For example, the configurations, methods, steps, shapes, materials, and numerical values ​​described in the above embodiments and modifications are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values ​​may be used as necessary. The configurations, methods, steps, shapes, materials, and numerical values ​​of the above embodiments and modifications can be combined with each other as long as they do not deviate from the spirit of the present disclosure.

[0355] The chemical formulas of the compounds exemplified in the above embodiments and modifications are representative, and are not limited to the valences described, etc., as long as they are the general names of the same compounds. In the numerical ranges described in stages in the above embodiments and modifications, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in the above embodiments and modifications can be used alone or in combination of two or more.

[0356] The present disclosure may also employ the following configuration: (1) A tape-shaped magnetic recording medium, comprising: a substrate; ３ nm ３ and a magnetic layer containing the following magnetic particles and acidic compound, wherein the magnetic recording medium has an average thickness of 5.30 μm or less, and when a power spectral density at each position of a spatial wavelength λn=100 / n [μm] (where n is an integer of 1 or more and 255 or less) is determined using a two-dimensional surface profile image of a measurement range of 100 [μm]×100 [μm] obtained by measuring the surface on the magnetic layer side with an atomic force microscope, the average value I of integrated values ​​of the power spectral density in the range of spatial wavelength λn≦5 μm λｎ≦５ and the ratio I10≦λn≦20 of the integrated value of the power spectral density in the range of 10 μm≦spatial wavelength λn≦20 μm. λｎ≦５ / I １０≦λｎ≦２０(2) A magnetic recording medium having an average dynamic friction coefficient μ of 0.35 or less on the surface of the magnetic layer side, measured by moving the magnetic recording medium in the longitudinal direction at a speed of 6 mm / s after a two-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90% RH. (3) The magnetic recording medium of (1) or (2), wherein the acidic compound has at least one acidic functional group. (4) The magnetic recording medium of (3), wherein the at least one acidic functional group includes at least one selected from the group consisting of a phosphate group, a carboxyl group, and a sulfonic acid group. (5) The magnetic recording medium of any one of (1) to (4), wherein the acid dissociation constant (pKa) of the acidic compound is 5.0 or less. (6) The magnetic recording medium according to any one of (1) to (5), wherein the acidic compound is capable of adsorbing to the magnetic particles. (7) The magnetic recording medium according to any one of (1) to (6), wherein the acidic compound contains a dispersant. (8) The magnetic recording medium according to any one of (1) to (7), wherein the rate of decrease in the saturation magnetization Ms is 0.55% or less. (9) The ratio I λｎ≦５ / I １０≦λｎ≦２０ (10) The magnetic recording medium according to any one of (1) to (8), wherein the average value I of the integrated values ​​is 2.80 or less. λｎ≦５ But 2.20 nm ２ The average value I of the integrated values ​​is less than or equal to １０≦λｎ≦２０ But 0.72 nm ２The magnetic recording medium according to any one of (1) to (9), wherein: (11) the magnetic layer has a servo pattern, the servo pattern includes a plurality of first magnetization regions and a plurality of second magnetization regions, and the plurality of first magnetization regions and the plurality of second magnetization regions are asymmetric with respect to an axis parallel to the width direction of the magnetic recording medium. (12) the magnetic recording medium according to (11), wherein an inclination angle of the first magnetization region with respect to the axis is different from an inclination angle of the second magnetization region with respect to the axis, and the larger of the inclination angles of the first magnetization region and the second magnetization region is 18° or more and 28° or less. (13) the magnetic recording medium according to any one of (1) to (12), wherein the magnetic layer is configured to be capable of recording signals with a data track width of 650 nm or less and a bit length of 47.0 nm or less. (14) The magnetic recording medium according to any one of (1) to (13), further comprising an underlayer, wherein the underlayer has an average thickness of 0.90 μm or less. (15) The magnetic recording medium according to any one of (1) to (14), wherein the magnetic layer has an average thickness of 0.08 μm or less. (16) The magnetic recording medium according to any one of (1) to (15), wherein the substrate has an average thickness of 4.40 μm or less. (17) The magnetic recording medium according to any one of (1) to (16), wherein the magnetic particles contain hexagonal ferrite or epsilon iron oxide. (18) The magnetic particles have an average particle volume of 1.37×10 ３ nm ３ (19) A cartridge comprising the magnetic recording medium according to any one of (1) to (18). (20) A tape-shaped magnetic recording medium comprising: a substrate; and an average particle volume of 1.50×10 ３ nm ３and a magnetic layer containing the following magnetic particles and acidic compound, wherein the magnetic recording medium has an average thickness of 5.30 μm or less, and when the power spectral density at each position of a spatial wavelength λn=100 / n [μm] (where n is an integer of 1 or more and 255 or less) is determined using a two-dimensional surface profile image of a measurement range of 100 [μm] × 100 [μm] obtained by measuring the surface on the magnetic layer side with an atomic force microscope, the average value Iλn≦5 of the integrated value of the power spectral density in the range of spatial wavelength λn≦5 μm and the average value Iλn≦5 of the integrated value of the power spectral density in the range of 10 μm≦spatial wavelength λn≦20 μm are obtained. １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ is 3.00 or less, and the average dynamic friction coefficient μ of the surface on the magnetic layer side, measured by moving the magnetic recording medium in the longitudinal direction at a speed of 6 mm / s after a two-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90 RH%, is 0.35 or less.

[0357] 10, 321 Cartridge 11 Cartridge memory 31 Antenna coil 32 Rectification and power supply circuit 33 Clock circuit 34 Detection and modulation circuit 35 Controller 36 Memory 36A First memory area 36B Second memory area 41 Substrate 42 Underlayer 43 Magnetic layer 430 Protrusion 430A Small waviness 430B Large waviness 44 Back layer 56 Head unit 56A, 56B Servo read head 57 Powder 61, 62 Head 110 Servo frame 111 Servo subframe 1 112 Servo subframe 2 113 Servo stripe 111A A burst 111B B burst 112C C burst 112D D burst MT Magnetic tape SB Servo band DB Data band Tk Data track

Claims

1. A tape-shaped magnetic recording medium comprising a substrate and an average particle volume of 1.50 x 10 ３ nm ３ and a magnetic layer containing the following magnetic particles and acidic compound, wherein the magnetic recording medium has an average thickness of 5.30 μm or less, and when a power spectral density at each position of a spatial wavelength λn=100 / n [μm] (where n is an integer of 1 or more and 255 or less) is determined using a two-dimensional surface profile image of a measurement range of 100 [μm]×100 [μm] obtained by measuring the surface on the magnetic layer side with an atomic force microscope, the average value I of integrated values ​​of the power spectral density in the range of spatial wavelength λn≦5 μm λｎ≦５ and the average value I of the integrated value of the power spectral density in the range of 10 μm≦spatial wavelength λn≦20 μm １０≦λｎ≦２０ Relative to I λｎ≦５ / I １０≦λｎ≦２０ is 3.00 or less, and the rate of decrease in saturation magnetization Ms after an 8-week high-temperature, high-humidity environmental test at a temperature of 60° C. and a humidity of 90% RH is 1.00% or less.

2. The magnetic recording medium according to claim 1, wherein the average dynamic friction coefficient μ of the surface on the magnetic layer side measured by moving the magnetic recording medium in the longitudinal direction at a speed of 6 mm / s after a two-week high-temperature, high-humidity storage test at a temperature of 60°C and a humidity of 90% RH is 0.35 or less.

3. The magnetic recording medium according to claim 1, wherein the acidic compound has at least one acidic functional group.

4. The magnetic recording medium according to claim 3, wherein said at least one acidic functional group comprises at least one selected from the group consisting of a phosphoric acid group, a carboxyl group and a sulfonic acid group.

5. The magnetic recording medium according to claim 1, wherein the acid dissociation constant (pKa) of the acidic compound is 5.0 or less.

6. The magnetic recording medium according to claim 1, wherein the acidic compound is capable of being adsorbed onto the magnetic particles.

7. The magnetic recording medium according to claim 1, wherein the acidic compound comprises a dispersant.

8. The magnetic recording medium according to claim 1, wherein the rate of decrease in the saturation magnetization Ms is 0.55% or less.

9. The above ratio I λｎ≦５ / I １０≦λｎ≦２０ The magnetic recording medium according to claim 1 , wherein the ratio of the surface roughness to the surface roughness is 2.80 or less.

10. Average value of the integrated value I λｎ≦５ But 2.20 nm ２ The average value I of the integrated values ​​is less than or equal to １０≦λｎ≦２０ But 0.72 nm ２ The magnetic recording medium according to claim 1 , wherein:

11. The magnetic recording medium according to claim 1, wherein the magnetic layer has a servo pattern, the servo pattern includes a plurality of first magnetized regions and a plurality of second magnetized regions, and the plurality of first magnetized regions and the plurality of second magnetized regions are asymmetric with respect to an axis parallel to the width direction of the magnetic recording medium.

12. The magnetic recording medium according to claim 11, wherein the tilt angle of the first magnetization region relative to the axis is different from the tilt angle of the second magnetization region relative to the axis, and the larger of the tilt angles of the first magnetization region and the second magnetization region is 18° or more and 28° or less.

13. The magnetic recording medium according to claim 1, wherein the magnetic layer is configured to be capable of recording signals with a data track width of 650 nm or less and a bit length of 47.0 nm or less.

14. The magnetic recording medium according to claim 1, further comprising an underlayer, the average thickness of which is 0.90 μm or less.

15. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic layer is 0.08 μm or less.

16. The magnetic recording medium according to claim 1, wherein the average thickness of the substrate is 4.40 μm or less.

17. The magnetic recording medium according to claim 1, wherein the magnetic particles comprise hexagonal ferrite or epsilon iron oxide.

18. The average particle volume of the magnetic particles is 1.37 x 10 ３ nm ３ The magnetic recording medium according to claim 1 , wherein:

19. A cartridge comprising the magnetic recording medium according to claim 1.

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