Magnetic recording medium and cartridge

Abstract

Provided is a magnetic recording medium capable of achieving both an improvement of electromagnetic conversion characteristics and a reduction of running friction.　The magnetic recording medium is tape-shaped and comprises a base, and a magnetic layer containing magnetic particles. The average thickness of the magnetic recording medium is 5.30 μm or less. In a bearing curve created on the basis of measurement data of a magnetic layer-side surface obtained using an atomic force microscope, a difference Pk (10) between a maximum protrusion height and a height at an area ratio of 10% is 22.0-30.0 nm inclusive. The squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.35 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] The amount of data to be archived is increasing due to the Internet of Things (IoT) and big data analysis, and there is a demand for increased capacity in the recording media used for archiving. Tape-type magnetic recording media for archiving has the advantages of low cost and high capacity.

[0003] In recent years, in tape-type magnetic recording media, it has been desired to reduce the distance between the head and the magnetic recording medium (hereinafter referred to as "spacing") and improve the electromagnetic conversion characteristics. Therefore, studies have been conducted to improve the electromagnetic conversion characteristics by specifying a numerical range for the arithmetic mean roughness Ra of the magnetic surface of the magnetic recording medium. For example, Patent Document 1 discloses that a better SNR can be obtained by setting the arithmetic mean roughness Ra of the magnetic surface of the magnetic recording medium to 2.5 nm or less.

[0004] International Publication No. 2018 / 131507

[0005] However, when the spacing is reduced and the electromagnetic conversion characteristics are improved, the magnetic surface of the magnetic recording medium becomes smooth, which increases the running friction between the head and the magnetic recording medium. Even if the numerical range of the arithmetic mean roughness Ra, which has traditionally been used as an index of the surface properties of the magnetic recording medium, is specified, it may not be possible to achieve both improved electromagnetic conversion characteristics and reduced running friction.

[0006] An object of the present disclosure is to provide a magnetic recording medium that can achieve both improved electromagnetic conversion characteristics and reduced running friction, and a cartridge including the same.

[0007] 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 layer containing magnetic particles, wherein the average thickness of the magnetic recording medium is 5.30 μm or less, in a bearing curve created based on measurement data of the magnetic layer side surface obtained using an atomic force microscope, the difference Pk(10) between the height of the maximum protrusion and the height at an area ratio of 10% is 22.0 nm or more and 30.0 nm or less, and the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.35 or less.

[0008] A cartridge according to the present disclosure includes a magnetic recording medium according to the present disclosure.

[0009] 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 tape-shaped magnetic recording medium. FIG. 4 is a schematic view 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 of a shingled magnetic recording method. 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 a bearing curve. FIG. 11 is an exploded perspective view showing an example of the configuration of a cartridge according to a modified embodiment of the present disclosure. FIGS. 12A and 12B are schematic views of an apparatus for explaining a method for measuring a dynamic friction coefficient. FIG. 13 is an enlarged view of the head block shown in FIG. 12A.

[0010] 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. Effects 7. Modifications

[0011] 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.

[0012] [1 Background to the Creation of the Embodiments of the Present Disclosure] Conventionally, the arithmetic mean roughness Ra has been used as an index representing the surface properties of tape-type magnetic recording media (hereinafter referred to as "magnetic tape"). However, the arithmetic mean roughness Ra is considered to be insufficient as an index representing both the improvement of electromagnetic conversion characteristics and the suppression of running friction. In particular, ３ nm ３ In magnetic tapes containing the following magnetic powder in the magnetic layer, more specifically in magnetic tapes having a high linear recording density of, for example, 545 kfci or more, the arithmetic mean roughness Ra is considered to be insufficient as an indicator of achieving both improved electromagnetic conversion characteristics and suppression of running friction.

[0013] Therefore, the inventors of the present invention have conducted extensive research into an index that indicates both the improvement of electromagnetic conversion characteristics and the suppression of running friction. As a result, data on the surface of the magnetic layer of the magnetic tape is obtained using an atomic force microscope, a bearing curve is created based on the data, and the maximum protrusion height H from the bearing curve is calculated. ｍａｘ and the height H of 10% area ratio １０ The difference Pk(10) (=H ｍａｘ -H １０ ) and found that this could be used as an indicator.

[0014] [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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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, data exchange, etc. are performed.

[0024] 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.

[0025] [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 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 is preferably a perpendicular recording 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 (hereinafter referred to as the "magnetic surface").

[0026] 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).

[0027] 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.

[0028] The magnetic tape MT is preferably reproduced by a reproducing head using a TMR element. The signal reproduced by the reproducing head using the TMR 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).

[0029] (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. From the viewpoint of improving the recording capacity that can be recorded on one data cartridge, the upper limit of the average thickness of the substrate 41 is preferably 4.40 μm or less, more preferably 4.20 μm or less, even more preferably 4.00 μm or less, 3.80 μm or less, or 3.40 μm or less. From the viewpoint of suppressing a decrease in the strength of the substrate 41, the lower limit of the average thickness of the substrate 41 is preferably 3.00 μm or more, more preferably 3.20 μm or more, even more preferably 3.80 μm or more, or 3.9 μm or more. The numerical range of the average thickness of the substrate 41 may be defined by any of the above upper limits and any of the above lower limits, and is preferably 3.80 μm or more and 4.40 μm or less, more preferably 3.90 μm or more and 4.40 μm or less.

[0030] The average thickness of the substrate 41 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 into a length of 250 mm at a position 30 to 40 m longitudinally from one end of the magnetic tape MT on the outer periphery. In this specification, the term "longitudinal direction from one end of the magnetic tape MT on the outer periphery" refers to the direction from one end of the magnetic tape MT on the outer periphery toward the other end on the inner periphery.

[0031] Next, the layers of the sample other than the substrate 41 (i.e., the underlayer 42, magnetic layer 43, and backing layer 44) are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample (substrate 41) is measured at five positions, and the measured values ​​are simply averaged (arithmetic mean) to calculate the average thickness of the substrate 41. Note that the five measurement positions are selected randomly from the sample so that they are each different from the others in the longitudinal direction of the magnetic tape MT.

[0032] 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.

[0033] 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.

[0034] The inclusion of a polyester-based resin in the substrate 41 can be confirmed, for example, as follows. First, similar to the method for measuring the average thickness of the substrate 41, a magnetic tape MT is prepared and cut into a length of 250 mm to prepare a sample, and then 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] 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).

[0039] 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.

[0040] (Magnetic Layer) The magnetic layer 43 is configured to be capable of recording signals using a magnetization pattern. The magnetic layer 43 is preferably a perpendicular recording type recording layer. The magnetic layer 43 contains, for example, magnetic particles, a binder, carbon particles, and a lubricant. If necessary, the magnetic layer 43 may further contain at least one additive selected from the group consisting of abrasive particles, an antistatic agent, a hardener, an anticorrosive agent, and non-magnetic reinforcing particles. The magnetic layer 43 may have multiple protrusions on the surface (magnetic surface) facing the magnetic layer 43. The multiple protrusions are formed, for example, by carbon particles and abrasive particles protruding from the magnetic surface.

[0041] 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.

[0042] 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 provided 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.

[0043] 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 inclined position 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 . Alternatively, the head unit 56 may be configured to follow the meandering or deformation of the magnetic tape MT and become inclined with respect to the axis Ax during data recording and reproduction. The inclination angle 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°.

[0044] The total area S of the plurality of servo bands SB relative to the area S of the magnetic surface (surface on the magnetic layer 43 side) 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.

[0045] 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

[0046] 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.

[0047] The number of servo bands SB is determined by the above ratio R Ｓ It can be calculated in the same way as

[0048] 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.

[0049] Servo Bandwidth W ＳＢ The width of the ratio R Ｓ It can be calculated in the same way as

[0050] 5A, the magnetic layer 43 is configured to allow multiple data tracks Tk to 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 1200 nm or less, more preferably 1000 nm or less, and even more preferably 850 nm or less, 800 nm or less, or 600 nm or less. The lower limit of the data track width W is preferably 20 nm or more, taking into account the magnetic grain size.

[0051] 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.

[0052] 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).

[0053] 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).

[0054] 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.

[0055] 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.

[0056] 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 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. 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.

[0057] 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

[0058] The bit area of ​​the signal that can be recorded on the data band DB is preferably 53000 nm from the viewpoint of improving the linear recording density D of the magnetic tape MT. ２or less, more preferably 45,000 nm ２ or less, more preferably 37,000 nm ２ Below 30,000 nm, particularly preferably ２ The following is the result.

[0059] 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.

[0060] 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).

[0061] In the LTO standard, a servo pattern is formed on the servo band SB, as shown in FIG. 6, consisting of a plurality of servo stripes (linear magnetized regions) 113 inclined with respect to an axis Ax parallel to the width direction of the magnetic tape MT.

[0062] 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).

[0063] 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 an asterisk.

[0064] 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 .

[0065] 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.

[0066] 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

[0067] 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 .

[0068] 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 .

[0069] 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.

[0070] 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

[0071] 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.

[0072] Reading the servo bands SB with the head unit 56 provides information for determining the tape speed and the longitudinal position of the head unit 56. The tape speed is calculated from the times between four timing signals (A1-C1, A2-C2, A3-C3, A4-C4). The head position is calculated from the times between the aforementioned four timing signals and another four timing signals (A1-B1, A2-B2, A3-B3, A4-B4). The servo pattern may have a shape including two parallel lines.

[0073] 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.

[0074] The average thickness t of the magnetic layer 43 ２ The upper limit of the average thickness t of the magnetic layer 43 is preferably 0.080 μm or less, more preferably 0.070 μm or less, even more preferably 0.060 μm or less, and particularly preferably 0.050 μm or less. ２If the upper limit value is 0.080 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.

[0075] 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 0.035 μm or more. ２ If the lower limit is 0.035 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.

[0076] The average thickness t of the magnetic layer 43 ２ is 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 image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape MT facing the magnetic layer 43 and the surface facing the back layer 44, and the tungsten layer is then further formed by vapor deposition or sputtering on the surface facing the magnetic layer 43. The thinning is performed along the longitudinal direction of the magnetic tape MT. That is, the thinning process forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape MT.

[0077] 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

[0078] 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].

[0079] (Magnetic Particles) The magnetic particles include, for example, particles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles") or particles containing epsilon iron oxide (ε-iron oxide) (hereinafter referred to as "ε-iron oxide particles"). The magnetic particles may also include 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.

[0080] (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.

[0081] 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, and it is more preferable to contain both Ba and Sr. In addition to the alkaline earth metal, the metal M1 may also contain Pb.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The average atomic ratio of Sr to Ba (Sr / Ba) is preferably 0.1 or more and 1 or less. When the average atomic ratio (Sr / Ba) is 0.1 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 1 or less, it is possible to suppress variations in magnetic properties.

[0087] 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.)

[0088] 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).

[0089] 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).

[0090] 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).

[0091] 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.

[0092] 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 the linear recording density D.

[0093] 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)).

[0094] 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.

[0095] 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.

[0096] 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 meters 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 by vapor deposition on the surface of the magnetic tape MT facing the magnetic layer 43 and the surface facing the back layer 44, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 43. 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.

[0097] 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.

[0098] 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 particle shape 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.

[0099] 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.

[0100] 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.

[0101] 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, 1.30×10 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.

[0102] 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.

[0103] 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 nm ３ The above is 1.20 x 10 ３ nm３ 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.

[0104] 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:

[0105] (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.

[0106] 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.").

[0107] 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 ３The crystal is preferably the main phase, and the single-phase ε-Fe ２ O ３ More preferably, it consists of:

[0108] 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.

[0109] 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.

[0110] The soft magnetic portion may be made of, for example, Fe. ３ O ４ , γ-Fe ２ O ３ , or spinel ferrite, etc.

[0111] 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.

[0112] The ε-iron oxide particles may contain an additive instead of the above-mentioned composite particle structure, or may have the above-mentioned composite particle structure and also contain an additive. In this case, a portion of the Fe in the ε-iron oxide particles is substituted with the additive. By including an 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.

[0113] 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).

[0114] 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 the linear recording density D.

[0115] 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).

[0116] 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.

[0117] 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.

[0118] 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 by vapor deposition on the surface of the magnetic tape MT facing the magnetic layer 43 and the surface facing the back layer 44, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 43. 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.

[0119] 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.

[0120] 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.

[0121] 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 (e.g., SNR). ３ nm ３ or more, more preferably 0.600 × 10 ３ nm ３ That's all.

[0122] 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 ３1.10 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.

[0123] 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

[0124] When the ε-iron oxide particles have a cubic shape, the average particle 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 other methods 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 by vapor deposition on the surface of the magnetic tape MT facing the magnetic layer 43 and the surface facing the back layer 44, and the tungsten thin film is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 43. 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.

[0125] 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 following formula, the average volume V of the magnetic particles is calculated. ave (average particle volume) is calculated. ave = DC ave 3

[0126] (Binder) The binder includes, for example, a thermoplastic resin, and may further include a thermosetting resin or a reactive resin.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] The polyester includes, for example, at least one selected from the group consisting of phthalic acid polyesters and aliphatic polyesters.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] (Carbon Particles) Some of the carbon particles contained in the magnetic layer 43 may protrude from the magnetic surface, forming multiple protrusions. The carbon particles forming the multiple protrusions reduce the electrical resistance of the magnetic surface, suppressing charging of the magnetic surface. This also reduces dynamic friction between the head unit 56 and the magnetic surface while the magnetic tape MT is running.

[0137] 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.

[0138] The carbon particles may be, for example, one or more 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.

[0139] 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.

[0140] (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.

[0141] 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).

[0142] 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).

[0143] 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.

[0144] 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.)

[0145] 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.)

[0146] 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.)

[0147] 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.)

[0148] 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.)

[0149] (Abrasive particles) Some of the abrasive particles contained in the magnetic layer 43 may protrude from the magnetic surface to form multiple protrusions. When the head unit 56 slides over the magnetic tape MT, the protrusions formed by the abrasive particles can come into contact with the head unit 56.

[0150] 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.

[0151] 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.

[0152] (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.

[0153] (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.

[0154] 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.

[0155] (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.

[0156] (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).

[0157] (Underlayer) The underlayer 42 is intended to reduce the unevenness of the surface of the substrate 41 and adjust the unevenness of the magnetic surface. The underlayer 42 is a non-magnetic layer containing non-magnetic particles, a binder, and a lubricant. The underlayer 42 supplies the 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, etc.

[0158] 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.

[0159] Average thickness t of the underlayer 42 ３ The upper limit of the average thickness t of the underlayer 42 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.３ When the average thickness t of the underlayer 42 is 0.90 μm or less, the amount of binder that comes out onto the magnetic surface can be suppressed, and therefore, an increase in running friction between the head and the magnetic tape MT can be suppressed. 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 .

[0160] 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.

[0161] Average thickness t of the substrate 41 １ Whereas, the average thickness t 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 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.

[0162] 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 with 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, even better running stability can be obtained.

[0163] (Non-magnetic particles) Non-magnetic particles include, for example, at least one of inorganic particles and organic particles. 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. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, or metal sulfides. The shapes of non-magnetic particles include, for example, various shapes such as needles, spheres, cubes, and plates, but are not limited to these shapes.

[0164] (Binder, Lubricant) The binder and lubricant are the same as those in the magnetic layer 43 described above.

[0165] (Additives) The antistatic agent, hardener, and anticorrosive agent are the same as those in the magnetic layer 43 described above.

[0166] (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.

[0167] 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.

[0168] Average thickness t of the back layer 44 ４ The upper limit of the average thickness t of the back layer 44 is preferably 0.60 μm or less. ４ When the upper limit of t is 0.60 μm or less, the average thickness t Ｔ Even if the average thickness t of the back layer 44 is 5.30 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 in a recording / reproducing device can be maintained. ４The lower limit of the thickness is not particularly limited, but is, for example, 0.20 μm or more.

[0169] 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]

[0170] (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.

[0171] (Average thickness of magnetic tape) Average thickness (average total thickness) t of magnetic tape MT Ｔ The upper limit of the average thickness t of the magnetic tape MT is preferably 5.30 μm or less, more preferably 5.10 μm or less, even more preferably 4.90 μm or less, and particularly preferably 4.70 μm or less. Ｔ When the average thickness t of the magnetic tape MT is 5.30 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to that of a general magnetic tape. ＴThe lower limit of the thickness is not particularly limited, but is, for example, 3.50 μm or more.

[0172] 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.

[0173] (Pk(10)) Pk(10) is the maximum protrusion height H in a bearing curve created based on measurement data of the magnetic layer side surface obtained using an atomic force microscope (AFM). ｍａｘ and the height H of 10% area ratio １０ The difference (= H ｍａｘ -H １０ This index clearly indicates the contact state between the magnetic tape MT and the head, and by using this index, it is possible to evaluate both the improvement of the electromagnetic conversion characteristics and the suppression of running friction.

[0174] Pk(10) is 22.0 nm or more and 30.0 nm or less, preferably 23.4 nm or more and 26.1 nm or less. If Pk(10) exceeds 30.0 nm, the spacing between the head and the magnetic tape becomes too large, which may result in deterioration of the electromagnetic conversion characteristics. On the other hand, if Pk(10) is less than 22.0 nm, the negative pressure generated at the edge of the head may become too large, which may result in excessive contact pressure between the head and the magnetic tape MT. Therefore, noise may increase, which may result in deterioration of the electromagnetic conversion characteristics. Furthermore, if the contact pressure between the head and the magnetic tape MT becomes too large, there is a risk of an increase in running friction between the head and the magnetic tape MT.

[0175] (Creating a Bearing Curve) The bearing curve is created as follows. First, the uneven shape of the magnetic layer side surface of the magnetic tape MT (magnetic recording medium) is measured using an AFM. The measurement is performed at 256 x 256 (65,536) measurement points within an area of ​​40 μm x 40 μm. An AFM suitable for the measurement is shown below. AFM: Dimension 3100 manufactured by Digital Instruments Cantilever: NCH-10T manufactured by NanoWorld The measurement conditions for the AFM are shown below. Measurement area: 40 μm x 40 μm Resolution: 256 x 256 Scan direction of the AFM probe: MD direction (longitudinal direction) of the magnetic tape Measurement mode: Tapping mode Scan ratio: 1 Hz

[0176] Next, the data obtained by the measurement was displayed in a binary editor (Binary Editor Bz), and the values ​​of Sens.Zscan [nm / V] and Z_Scale [V], as well as the measured values ​​pAFM for each measurement point, were obtained from the data. a,b The obtained Sens.Zscan and Z_Scale values ​​are loaded into the National Instruments program LabVIEW, the matrix is ​​inverted, and 2 bits of redundant data are deleted. The values ​​obtained from LabVIEW are loaded into a calculation program. This calculation program provides the coordinate values ​​for drawing the bearing curve. The calculation flow in this calculation program is as follows:

[0177] First, calculate the height of each measurement point using the AFM by the following formula: a,b Ask for.

[0178] (In the above formula, AFM a,b is the height of each measurement point, and pAFM a,b is the measured value at each measurement point, and a and b are each independently an integer selected from the range of 1 to 256.) The values ​​of a and b in the above formula identify the position of each measurement point within the 40 μm × 40 μm area.

[0179] In the magnetic recording medium of the present disclosure, the "height data of the magnetic layer side surface obtained using an atomic force microscope" (hereinafter also simply referred to as "height data of the magnetic layer side surface") is calculated by the height AFM of each measurement point obtained by the above formula. a,b means.

[0180] Next, a bearing curve is created based on the height data of the magnetic layer side surface. Specifically, first, the height AFM of each measurement point calculated by the above formula is a,b Average height H a ) is calculated. Next, the height of each measurement point (AFM) a,b From the value of a The height difference H of each measurement point is calculated by subtracting the value of d That is, the height difference H d is calculated by the following formula: d [nm] = (height of each measurement point AFM a,b ) - (average height H a )

[0181] Height difference H between each measurement point d are arranged as a one-dimensional array. The one-dimensional array is rearranged in descending order of values. H of the one-dimensional array after the rearrangement d is the Y coordinate value of each point that describes the bearing curve. In other words, the Y coordinate value of the bearing curve is the height difference H d In this specification, the height difference H d is called the height on the bearing curve.

[0182] Next, the X coordinate value of each point on the bearing curve is calculated using the following formula: X coordinate value [%] = Data Number / Total number of data × 100 (In the above formula, Data Number is the element number of the one-dimensional array after sorting in descending order, and Total number of data is the number of all measurement points.)

[0183] In this way, the X and Y coordinate values ​​are obtained by the calculation program. Table 1 shows an example of the Data Number, X and Y coordinate values ​​obtained by the calculation program.

[0184]

[0185] Finally, the obtained X and Y coordinate values ​​are plotted on the XY coordinate system to create a bearing curve. An example of a bearing curve is shown in FIG. 10. In the XY coordinate system, the X axis represents the area ratio, and the Y axis represents the height (specifically, the height difference H d The area ratio is calculated by multiplying the height (height difference H d ) That is, the area ratio is the cumulative ratio of the height (height difference H d ) are accumulated in descending order of frequency, and the total number of measurement points (65,536) measured by AFM is set to 100, and the percentage is expressed as a percentage. For example, if the X coordinate of point P on the bearing curve is 10 (%) and the Y coordinate is 2.0 (nm), the height (height difference H d The number of measurement points where the average particle size is 2.0 nm or more is 10% of the total number of measurement points.

[0186] (Calculation Method of Pk(10)) A calculation method of Pk(10) will be described with reference to FIG. 10. First, the height of the magnetic layer side surface is measured by AFM. a,b In the data (65,536 pieces), the center plane (average height H a The slice level is parallel to the plane having the a,b When moving downward (in the -Y-axis direction) from a position higher than the maximum value of the data, the position where the area of ​​the cut surface of the largest protrusion is 3 pixels is extracted, and that position is the height of the largest protrusion AFM ｍａｘ The area of ​​the cut surface of the largest protrusion where the area is less than 3 pixels may be a peak caused by noise, and it is difficult to determine whether a protrusion is actually formed. Therefore, as described above, the position where the area of ​​the cut surface of the largest protrusion is 3 pixels is determined as the height of the largest protrusion AFM. ｍａｘ Let's say.

[0187] Next, the maximum protrusion height AFM ｍａｘ From the value of a The maximum protrusion height H ｍａｘ That is, the maximum protrusion height H ｍａｘ The maximum protrusion height H is calculated by the following formula: ｍａｘ [nm] = (maximum protrusion height AFM ｍａｘ) - (average height H a )

[0188] Next, in the bearing curve, the height H １０ The maximum projection height H is calculated. ｍａｘ Height H of 10% of the area ratio １０ Pk(10) is calculated by subtracting the maximum protrusion height H ｍａｘ ) - (10% area ratio height H １０ )

[0189] (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.

[0190] 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.

[0191] 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 m to 40 m 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 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, etc., 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.

[0192] 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.

[0193] 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.

[0194] (Squareness Ratio) The lower limit of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 0.62 or more, more preferably 0.65 or more, and even more preferably 0.68 or more, 0.72 or more, or 0.75 or more. When the squareness ratio S1 is 0.62 or more, the perpendicular orientation of the magnetic particles is sufficiently high, thereby improving the electromagnetic conversion characteristics.

[0195] When the magnetic powder contains hexagonal ferrite particles, the upper limit of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 0.85 or less, more preferably 0.80 or less. When the upper limit of the squareness ratio S1 is 0.85 or less, it is possible to prevent the plate faces of the hexagonal ferrite particles from being excessively aligned on the surface of the magnetic layer 43. Therefore, it is possible to suppress running friction between the magnetic tape MT and the head.

[0196] When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio S1 of the magnetic layer 43 may be defined by any of the above lower limit values ​​and any of the above upper limit values, and is preferably 0.62 or more and 0.85 or less, more preferably 0.65 or more and 0.85 or less, even more preferably 0.68 or more and 0.85 or less, 0.72 or more and 0.80 or less, or 0.75 or more and 0.80 or less.

[0197] 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.

[0198] 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."

[0199] 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)

[0200] The upper limit of the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT is preferably 0.35 or less, more preferably 0.30 or less, and even more preferably 0.29 or less, 0.25 or less, 0.20 or less, or 0.15 or less. When the squareness ratio S2 is 0.35 or less, the perpendicular orientation of the magnetic particles is sufficiently high, thereby improving the electromagnetic conversion characteristics.

[0201] When the magnetic powder contains hexagonal ferrite particles, the lower limit of the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT is preferably 0.26 or more. When the lower limit of the squareness ratio S2 is 0.26 or more, it is possible to prevent the plate faces of the hexagonal ferrite particles from being excessively aligned on the surface of the magnetic layer 43. Therefore, it is possible to suppress running friction between the magnetic tape MT and the head.

[0202] When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio S2 of the magnetic layer 43 may be defined by any of the above upper limits and the above lower limit, and is preferably 0.26 or more and 0.35 or less, more preferably 0.26 or more and 0.30 or less, and even more preferably 0.26 or more and 0.29 or less.

[0203] 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.

[0204] 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.

[0205] (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.

[0206] 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 90 nm or less. ２ If the thickness exceeds 90 nm, 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 even better electromagnetic conversion characteristics may not be obtained.

[0207] 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.

[0208] 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.

[0209] (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.

[0210] 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 ))

[0211] 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.

[0212] (irreversible magnetic susceptibility Χ ｉｒｒ ) Irreversible magnetic susceptibility Χ ｉｒｒis 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:

[0213] (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.

[0214] (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)

[0215] (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.

[0216] 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 (the surface on the magnetic layer 43 side) 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: correction 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 Sａ (nm) is the surface roughness R ｂ (nm).

[0217] (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 more accurately reproduced. 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 running stability can be suppressed.

[0218] 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.

[0219] 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.

[0220] 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.

[0221] (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, deterioration of running stability can be suppressed.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] [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.

[0226] (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, etc. in a solvent. 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.

[0227] 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.

[0228] 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.

[0229] (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.

[0230] 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.

[0231] (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 .

[0232] (Calendering Process) Next, the obtained magnetic tape MT is subjected to a calendering process to smooth the magnetic surface.

[0233] (Aging Step) Next, if necessary, the obtained magnetic tape MT is subjected to an aging treatment.

[0234] (Cutting Step) Next, the magnetic tape MT is cut to a predetermined width (for example, 1 / 2 inch width). In this way, the magnetic tape MT is obtained.

[0235] (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.

[0236] (Adjusting Pk(10)) Pk(10) can be set to a desired value by adjusting, for example, at least one of the coating thickness of the magnetic layer-forming paint and the conditions of the aging process (e.g., environmental temperature and time). In order to adjust Pk(10) within the above numerical range, the coating thickness of the magnetic layer-forming paint is preferably set so that the thickness of the magnetic layer 43 upon completion of the magnetic tape is 40 nm or more and 80 nm or less. In order to adjust Pk(10) within the above numerical range, the environmental temperature for the aging treatment is preferably 45°C or more and 75°C or less. In order to adjust Pk(10) within the above numerical range, the time for the aging treatment is preferably 0 hours or more and 80 hours or less.

[0237] [6. Effect] As described above, in the magnetic tape MT according to one embodiment, in the bearing curve created based on the measurement data of the magnetic layer side surface obtained using an atomic force microscope, the maximum protrusion height H ｍａｘ and the height H of 10% area ratio １０ The difference Pk(10) (=H ｍａｘ -H １０) is 22 nm or more and 30 nm or less, and the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is 0.35 or less. This makes it possible to achieve both improved electromagnetic conversion characteristics and reduced running friction.

[0238] Particle volume 1.50 x 10 ３ nm ３ In conventional magnetic tapes containing the following magnetic powder in the magnetic layer, more specifically in conventional magnetic tapes having a high linear recording density of, for example, 545 kfci or more, it is particularly difficult to achieve both improved electromagnetic conversion characteristics and reduced running friction. In contrast, in the magnetic tape MT according to one embodiment, the magnetic layer 43 contains a particle volume of 1.50×10 ３ nm ３ Even when the magnetic powder described below is contained, more specifically, even when the magnetic layer 43 has a high linear recording density of 545 kfci or more, it is possible to achieve both improved electromagnetic conversion characteristics and reduced running friction.

[0239] [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.

[0240] 11 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.

[0241] 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.

[0242] 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.

[0243] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0244] In the following examples and comparative examples, the average thickness t of the magnetic tape and the average thickness t of the PEN film (substrate) １ , the average thickness of the magnetic layer t ２ , the average thickness of the underlayer t ３ , the average thickness of the back layer t ４ The average particle volume V of the magnetic particles and the average atomic ratio of strontium (Sr) to barium (Ba) (Sr / Ba) are values ​​determined by the measurement method described in the above embodiment.

[0245] 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 (a rocking shaker manufactured by Seiwa Giken), and mixed for 10 hours. Similarly, a third composition having the following formulation was placed in a polyethylene bottle, attached to a paint shaker (a rocking shaker manufactured by Seiwa Giken), and mixed for 10 hours. Next, the kneaded first composition was placed in a stirring tank equipped with a disperser, and the mixed second and third compositions were added. 350.0 parts by mass of methyl ethyl ketone, 90.0 parts by mass of toluene, and 150.0 parts by mass of cyclohexanone were then added, followed by premixing. Subsequently, further dispersion was performed using a Dynomill, followed by filtering, to prepare a magnetic layer-forming coating.

[0246] (First composition) Barium ferrite (Ba ０．５３ Sr ０．４７ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.00 × 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 composition: polyurethane resin 30.0 mass%, cyclohexanone 70.0 mass%): 25.0 mass parts (polyurethane resin: number average molecular weight Mn = 25,000, glass transition temperature Tg = 110°C)

[0247] (Second composition) Aluminum oxide powder: 3.0 parts by mass (α-Al ２ O ３ , average particle size 0.1 μm) Vinyl chloride resin solution (resin solution composition: vinyl chloride resin 30.0 mass %, cyclohexanone solution 70.0 mass %): 3.0 mass parts (vinyl chloride resin: degree of polymerization 300, number average molecular weight Mn = 10,000, polar group OSO３ K = 0.07 mmol / g, secondary OH = 0.3 mmol / g.) Cyclohexanone: 10.0 parts by mass

[0248] (Third composition) Carbon black: 2.0 parts by mass (manufactured by Tokai Carbon Co., Ltd., product name: Seast S, arithmetic average particle diameter 70 nm) Polyurethane resin solution (resin solution: polyurethane resin 30.0 mass%, cyclohexanone 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

[0249] Finally, 1.8 parts by mass of polyisocyanate (product name: Coronate L, manufactured by Tosoh Corporation) and 2.0 parts by mass of stearic acid were added as curing agents to the magnetic layer-forming coating material prepared as described above.

[0250] (Preparation process of paint for forming base layer) The paint for forming 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 base layer.

[0251] (Fourth composition) Acicular iron oxide powder: 100.0 parts by mass (α-Fe ２ O ３ , average major axis length 0.15 μm) Vinyl chloride resin solution (resin solution composition: vinyl chloride resin 30.0 mass %, cyclohexanone solution 70.0 mass %): 55.0 mass parts (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 , average particle size 0.1 μm)

[0252] (Fifth composition) Carbon black: 30.0 parts by mass (manufactured by Asahi Carbon Co., Ltd., product name: #80) Polyurethane resin solution (resin solution blending amount: polyurethane resin 30.0 mass%, cyclohexanone 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

[0253] Finally, 1.5 parts by mass of polyisocyanate (product name: Coronate L, manufactured by Tosoh Corporation) and 1.5 parts by mass of stearic acid were added as a curing agent to the paint for forming the base layer prepared as described above.

[0254] (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 filtered to prepare the paint for forming back layer. Carbon black (manufactured by Asahi Carbon Co., Ltd., trade name: #80): 100.0 parts by mass Polyester polyurethane: 100.0 parts by mass (manufactured by Nippon Polyurethane Co., Ltd., trade name: N-2304) Methyl ethyl ketone: 250.0 parts by mass Toluene: 150.0 parts by mass Cyclohexanone: 250.0 parts by mass Polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation): 10.0 parts by mass

[0255] (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 (average thickness of the primer layer after calendaring) upon completion of the magnetic tape would be 0.80 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 (average thickness of the magnetic layer after calendaring) upon completion of the magnetic tape would be 0.070 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.

[0256] 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 having an average thickness of 0.35 μm (average thickness after calendering) when the magnetic tape was completed.

[0257] (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.

[0258] (Calendering Step) The magnetic tape after curing was subjected to a calendering process to smooth the surface of the magnetic layer, at a calendering temperature of 100° C. and a calendering pressure of 200 kg / cm.

[0259] (Cutting Step) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining a magnetic tape with an average thickness of 5.22 μm.

[0260] (Servo writing process) After the cutting, the magnetic tape was demagnetized, and then a servo pattern was written on the magnetic tape using a servo writer to form five servo bands. The servo pattern was in accordance with the LTO-9 standard. In this way, the desired magnetic tape was obtained.

[0261] [Example 2] In the coating process, the magnetic layer-forming paint was applied so that the average thickness of the magnetic layer on the completed magnetic tape would be 0.060 μm. A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0262] [Example 3] In the coating process, the coating material for forming the back layer was applied so that the average thickness of the back layer on the completed magnetic tape would be 0.40 μm. Between the calendaring process and the cutting process, the magnetic tape was subjected to an aging treatment in an environment of 60° C. for 20 hours. A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0263] [Example 4] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was changed to barium ferrite (Ba ０．５３ Sr ０．４７ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.05 × 10 ３ nm ３ ) In the coating process, the primer layer-forming paint was applied so that the average thickness of the primer layer on the completed magnetic tape would be 0.80 μm, the magnetic layer-forming paint was applied so that the average thickness of the magnetic layer on the completed magnetic tape would be 0.065 μm, and the back layer-forming paint was applied so that the average thickness of the back layer on the completed magnetic tape would be 0.38 μm. Between the calendaring process and the cutting process, the magnetic tape was subjected to an aging treatment in an environment of 60° C. for 20 hours. A magnetic tape was obtained in the same manner as in Example 1, except for the points mentioned above.

[0264] [Comparative Example 1] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was changed to barium ferrite (Ba ０．５５ Sr ０．４５ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.20 × 10 ３ nm ３In the coating process, the magnetic layer-forming paint was applied so that the average thickness of the magnetic layer on the completed magnetic tape would be 0.075 μm. A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0265] [Comparative Example 2] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was changed to barium ferrite (Ba ０．５５ Sr ０．４５ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.00 × 10 ３ nm ３ ), and the dispersion time using the Dynomill was doubled. In the coating process, the magnetic layer-forming paint was applied so that the average thickness of the magnetic layer on the completed magnetic tape would be 0.080 μm. A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0266] [Comparative Example 3] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was replaced with barium ferrite (BaFe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.60 × 10 ３ nm ３ A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0267] [Comparative Example 4] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was replaced with barium ferrite (BaFe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.05 × 10 ３ nm ３ ). In the coating process, the PEN film (substrate) was changed to one with an average thickness of 3.60 μm, the primer layer-forming paint was applied so that the average thickness of the primer layer on the completed magnetic tape would be 1.10 μm, and the back layer-forming paint was applied so that the average thickness of the back layer on the completed magnetic tape would be 0.45 μm. When the magnetic layer-forming paint was dried, the magnetic field orientation process using a permanent magnet was omitted, and a non-oriented magnetic layer was formed. A magnetic tape was obtained in the same manner as in Example 1, except for the points mentioned above.

[0268] [Comparative Example 5] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was changed to barium ferrite (Ba０．５５ Sr ０．４５ Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.05 × 10 ３ nm ３ ), and the dispersion time using the Dynomill was extended by two times. Between the calendaring process and the cutting process, the magnetic tape was subjected to an aging treatment in an environment of 60°C for 20 hours. A magnetic tape was obtained in the same manner as in Example 1, except for the above points.

[0269] [Comparative Example 6] In the preparation process of the coating material for forming the magnetic layer, the magnetic powder was replaced with barium ferrite (BaFe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1.60 × 10 ３ nm ３ ). In the coating process, the PEN film (substrate) was changed to one with an average thickness of 4.20 μm, the primer layer-forming paint was applied so that the average thickness of the primer layer on the completed magnetic tape would be 0.65 μm, and the magnetic layer-forming paint was applied so that the average thickness of the magnetic layer on the completed magnetic tape would be 0.060 μm. Between the calendaring process and the cutting process, the magnetic tape was subjected to an aging treatment in an environment of 60° C. for 20 hours. A magnetic tape was obtained in the same manner as in Example 1, except for the points mentioned above.

[0270] [Evaluation] (Squareness Ratio S2) The squareness ratio S2 of the magnetic layer in the longitudinal direction of the magnetic tape was measured as described in the above embodiment.

[0271] (Arithmetic mean roughness Ra and maximum height Rmax of the surface of the magnetic layer) The arithmetic mean roughness Ra was determined as follows. First, a 1 / 2-inch wide magnetic tape was cut into a length of 250 mm to prepare a sample. Next, the magnetic surface of the sample was observed with an AFM (Atomic Force Microscope), and a 40 μm x 40 μm AFM image was obtained. The AFM used was a NanoScope IV Dimension ICON (Bruker) manufactured by Digital Instruments, and the cantilever was made of single crystal silicon (Note 1). Measurements were performed with a lift height of 20 nm and a tapping frequency tuning of 200 to 400 Hz. Next, the AFM image was divided into 256 x 256 (= 65,536) measurement points, and the height Z(i) (i: measurement point number, i = 1 to 65,536) was measured at each measurement point. The heights Z(i) measured at each measurement point were simply averaged (arithmetic mean) to determine the average height (average surface) Zave (= (Z(1) + Z(2) + ... + Z(65,536)) / 65,536). Next, the deviation Z"(i) (= Z(i) - Zave) from the average center line at each measurement point was determined, and the arithmetic mean roughness Ra [nm] (= (Z"(1) + Z"(2) + ... + Z"(65,536)) / 65,536) was calculated. In addition, the distance between the highest value (maximum peak height) and the lowest value (maximum valley depth) among the measurement points was determined to calculate the maximum height Rmax. In this case, the image was filtered using Flatten order 2 and planefit order 3 XY. (Note 1) Nano World SPM probe NCH-10T normal type PointProbe L (cantilever length) = 125 μm

[0272] Pk(10) Pk(10) was measured as described in one embodiment above.

[0273] (Running Friction) The running friction was evaluated by the dynamic friction coefficient μ. The dynamic friction coefficient μ is determined by the average tension T of the magnetic tape MT during sliding. ave. [N] and the tension T of the magnetic tape MT in a stationary state ０ [N] was calculated.

[0274] Average tension T of the magnetic tape MT during sliding ０ [N] was determined as follows. First, a 1 / 2-inch wide magnetic tape MT was cut into a length of 250 mm. Next, as shown in FIG. 12A, the 1 / 2-inch wide magnetic tape MT was placed on two cylindrical guide rolls 73A and 73B arranged parallel to each other at a distance from each other, with the magnetic surfaces in contact with each other. The two guide rolls 73A and 73B were fixed to a hard plate-like member 76, which fixed their relative positions. The two guide rolls 73A and 73B were stainless steel (SUS) round bars with a diameter of 3 mm.

[0275] Next, one end of the magnetic tape MT was connected to a load cell (ZTS-5N, manufactured by Imada Co., Ltd.) 71 via a jig 72. One end of the magnetic tape MT was fixed to the jig 72 as shown in FIG. 12B. A weight 75 with a mass of 100 g was connected to the other end of the magnetic tape MT. The weight 75 applied a tension of 100 gf (0.98 N) in the longitudinal direction of the magnetic tape MT. The load cell 71 was fixed on a base 77. The positional relationship between the base 77 and the plate-like member 76 was also fixed, and thus the positional relationship between the guide rolls 73A and 73B, the head block 74, and the load cell 71 was also fixed.

[0276] Next, as shown in FIG. 13 , the magnetic surface of the magnetic tape MT was brought into contact with a head block (for recording and playback) 74 so that the wrap angle θ (°) was 25°. Here, the wrap angle θ was calculated from the curvature R of the head block 74 and the amount of pressure the head block 74 exerted on the magnetic tape MT. A recording and playback head from an LTO4 drive manufactured by Hewlett-Packard Enterprise (HPE) was used as the head block 74. The head block 74 was positioned approximately at the center of the guide rolls 73A and 73B. The head block 74 was movably attached to a plate-like member 76 so that the wrap angle θ could be changed. However, when the wrap angle θ (°) reached 25°, its position was fixed relative to the plate-like member 76, thereby fixing the positional relationship between the guide rolls 73A and 73B and the head block 74.

[0277] Next, the head block 74 was slid over the magnetic surface of the magnetic tape MT while repeatedly moving back and forth 10 times relative to the magnetic tape MT. The tension T [N] of the magnetic tape MT during this reciprocating motion was measured by the load cell 71. Hereinafter, the period when the magnetic tape MT was pulled in the direction in which one end of the magnetic tape MT (the end attached to the jig 72) approached the load cell 71 (the pulling direction) will be referred to as the "forward path," and the period when the one end of the magnetic tape MT was fed in the direction away from the load cell 71 (the opposite direction to the pulling direction) will be referred to as the "return path." The reciprocating motion was controlled so that the sliding distance for each of the forward and return paths was 55 mm, and the sliding speed of the magnetic tape MT relative to the head block 74 was 6 mm / s.

[0278] During the eighth, ninth, and tenth outward sliding operations (pulling operations), the tension T [N] at 16 measurement points was obtained by the load cell 71, and a total of 48 measurement points were obtained. Next, the tension T [N] at the 48 measurement points was simply averaged to obtain T ave. [N] was calculated.

[0279] Specifically, the tension T [N] at 16 measurement points during each forward sliding operation was obtained as follows. Sampling of the tension T [N] was performed at a sampling rate of 0.5 points / sec during 9.2 seconds of one forward sliding operation (pulling operation time), and tension T [N] at 18 measurement points was obtained during one sliding operation (pulling operation). Of the obtained tension T [N], the tension T [N] at two measurement points, the first and last, of one forward sliding operation were excluded. As a result, tension T [N] at a total of 16 measurement points was obtained. The measurement environment for tension T [N] was maintained at 25°C ± 2°C and 50% RH ± 5% RH.

[0280] The tension of the magnetic tape MT in a stationary state (T ０The tension T [N] was calculated as follows. After measuring the tension T [N], the device shown in Fig. 12A was rotated 90° so that the jig 72 was positioned directly below the load cell 71. The device was then held so that the longitudinal direction of the magnetic tape MT coincided with the direction of gravity and the magnetic tape MT was hanging directly down without being passed through the guide rolls 73A and 73B or the head block 74. In this state, the tension applied to the magnetic tape MT was measured by the load cell 71, and this tension was calculated as the tension T of the magnetic tape MT in a stationary state. ０ [N]. The tension T ０ The measurement environment for [N] was maintained at 25°C ± 2°C and 50% RH ± 5% RH.

[0281] Average tension T ave. [N] and tension T ０ [N] was substituted into the following equation to determine the dynamic friction coefficient μ. (where θ [°] represents the wrap angle of the magnetic tape MT with respect to the head block 74, and T ０ [N] represents the tension of the magnetic tape MT in a stationary state, and T ave. represents the average tension of the magnetic tape MT during sliding.)

[0282] If the dynamic friction coefficient μ exceeds 0.65, there is a concern that the PES (Position Error Signal) characteristic may deteriorate due to increased running friction. The PES indicates the deviation (error) of the servo pattern reading position in the width direction of the magnetic tape when the servo pattern is reproduced (read) by a tape storage drive.

[0283] (Evaluation of electromagnetic conversion characteristics) The electromagnetic conversion characteristics were evaluated by SNR. The SNR was measured as follows. First, a loop tester (manufactured by Microphysics) was used to obtain a playback signal from the magnetic tape. The conditions for obtaining the playback signal are shown below. 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

[0284] 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 used 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 Comparative Example 2 as the reference media. Since it is believed that a SNR value equal to or greater than that of Comparative Example 2 would provide sufficiently good electromagnetic conversion characteristics (SNR) for a tape storage drive, the SNR of Comparative Example 2 was used as the reference.

[0285]

[0286] The above evaluation results reveal the following. In the magnetic tapes of Examples 1 to 3, in which Pk(10) is 22.0 nm or more and 30.0 nm or less and the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic tape is 0.26 or more and 0.35 or less, it is possible to achieve both improved electromagnetic conversion characteristics and suppression of running friction. In the magnetic tapes of Comparative Examples 1 and 3, in which Pk(10) is less than 22.0 nm, the electromagnetic conversion characteristics deteriorate and running friction cannot be suppressed. In Comparative Examples 2 and 5, in which the squareness ratio S2 of the magnetic layer in the longitudinal direction of the magnetic tape is less than 0.26, running friction cannot be suppressed. Note that the reason why the squareness ratio S2 is a low value of less than 0.26 in the magnetic tapes of Comparative Examples 2 and 5 is thought to be because the magnetic particles may have been destroyed as the dispersion of the magnetic layer-forming paint progressed. In Comparative Example 4, in which the average thickness of the underlayer exceeds 0.90 μm and the squareness ratio S2 of the magnetic layer in the longitudinal direction of the magnetic tape exceeds 0.35, the electromagnetic conversion characteristics deteriorate and running friction cannot be suppressed. In the magnetic tape of Comparative Example 5, in which Pk(10) exceeds 30.0 nm, the electromagnetic conversion characteristics deteriorate.

[0287] Conventionally, it has been considered preferable for the arithmetic mean roughness Ra to be 2.5 nm or less from the viewpoint of improving electromagnetic conversion characteristics. Although the arithmetic mean roughness Ra of the magnetic tapes of Comparative Examples 1 to 4 is 2.5 nm or less, the electromagnetic conversion characteristics are deteriorated and running friction cannot be suppressed. This shows that it is difficult to achieve both improved electromagnetic conversion characteristics and suppressed running friction by simply specifying the arithmetic mean roughness Ra.

[0288] 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.

[0289] 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.

[0290] The present disclosure may also employ the following configurations: (1) A tape-shaped magnetic recording medium comprising: a substrate; and a magnetic layer containing magnetic particles, wherein the average thickness of the magnetic recording medium is 5.30 μm or less, a difference Pk(10) between the height of the maximum protrusion and the height at an area ratio of 10% in a bearing curve created based on measurement data of the magnetic layer side surface obtained using an atomic force microscope is 22.0 nm or more and 30.0 nm or less, and a squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.35 or less. (2) The average particle volume of the magnetic particles is 1.50×10 ３ nm ３ (3) The magnetic recording medium according to (1), wherein the difference Pk(10) between the height of the largest protrusion and the height at 10% area ratio is 23.4 nm or more and 26.1 nm or less. (4) The magnetic recording medium according to any one of (1) to (3), wherein the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.29 or less. (5) The magnetic recording medium according to any one of (1) to (4), wherein the magnetic particles include hexagonal ferrite particles, and the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.26 or more. (6) The magnetic recording medium according to any one of (1) to (4), wherein the magnetic particles include hexagonal ferrite particles containing barium (Ba) and strontium (Sr). (7) The magnetic recording medium according to (6), wherein the average atomic ratio (Sr / Ba) of the strontium (Sr) to the barium (Ba) is 0.1 or more and 1 or less. (8) The magnetic recording medium according to any one of (1) to (4), wherein the magnetic particles include epsilon iron oxide particles. (9) The magnetic recording medium according to any one of (1) to (8), further comprising an underlayer provided between the substrate and the magnetic layer, wherein the underlayer has an average thickness of 0.90 μm or less. (10) The magnetic recording medium according to any one of (1) to (9), wherein the substrate has an average thickness of 3.80 μm or more and 4.40 μm or less. (11) A cartridge comprising the magnetic recording medium according to any one of (1) to (10).

[0291] 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 44 Back layer 56 Head unit 56A, 56B Servo read head 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 a magnetic layer containing magnetic particles; wherein the average thickness of the magnetic recording medium is 5.30 μm or less; in a bearing curve created based on measurement data of the magnetic layer side surface obtained using an atomic force microscope, the difference Pk(10) between the height of the maximum protrusion and the height at an area ratio of 10% is 22.0 nm or more and 30.0 nm or less; and the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.35 or less.

2. The average particle volume of the magnetic particles is 1.50 x 10 ３ nm ３ The magnetic recording medium according to claim 1 , wherein:

3. The magnetic recording medium according to claim 1, wherein the difference Pk(10) between the height of the maximum protrusion and the height at an area ratio of 10% is 23.4 nm or more and 26.1 nm or less.

4. The magnetic recording medium according to claim 1, wherein the squareness ratio of said magnetic layer in the longitudinal direction of said magnetic recording medium is 0.29 or less.

5. The magnetic recording medium according to claim 1, wherein the magnetic particles include hexagonal ferrite particles, and the squareness ratio of the magnetic layer in the longitudinal direction of the magnetic recording medium is 0.26 or more.

6. The magnetic recording medium according to claim 1, wherein the magnetic particles include hexagonal ferrite particles containing barium (Ba) and strontium (Sr).

7. The magnetic recording medium according to claim 6, wherein the average atomic ratio (Sr / Ba) of said strontium (Sr) to said barium (Ba) is 0.1 or more and 1 or less.

8. The magnetic recording medium according to claim 1, wherein the magnetic particles include epsilon iron oxide particles.

9. The magnetic recording medium according to claim 1, further comprising an underlayer provided between said substrate and said magnetic layer, said underlayer having an average thickness of 0.90 μm or less.

10. The magnetic recording medium according to claim 1, wherein the average thickness of the substrate is 3.80 μm or more and 4.40 μm or less.

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

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