Magnetic recording medium, magnetic recording cartridge, and recording / reproducing device

Abstract

Provided is a magnetic recording medium which undergoes only a small amount of dimensional change caused by changes in temperature / humidity conditions. The magnetic recording medium is a tape-type magnetic recording medium having an average thickness of 5.3μｍ or less, and the magnetic recording medium includes a substrate and a magnetic layer disposed on the substrate. In an environmental relative humidity in the range of 10-80%RH, the coefficient of temperature expansion of the magnetic recording medium is 6.0-8.0 ppm / ℃.

Description

[Technical Field]

[0001] The present disclosure relates to a magnetic recording medium, and a magnetic recording cartridge and a recording / reproducing device including the same. [Background technology]

[0002] Tape-type magnetic recording media are widely used for storing electronic data. For example, Patent Document 1 proposes a magnetic recording medium that has excellent electromagnetic conversion characteristics in a high-temperature environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 203468 Summary of the Invention

[0004] In such tape-type magnetic recording media, there is a demand for improved recording density.

[0005] Therefore, a magnetic recording medium is desired that undergoes minimal dimensional changes due to changes in the temperature and humidity environment, even when such changes occur.

[0006] A magnetic recording medium according to one embodiment of the present disclosure is a tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, and includes a substrate and a magnetic layer disposed on the substrate. Between 10% RH and 80% RH, there exists an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less.

[0007] The magnetic recording medium according to one embodiment of the present disclosure has the above-described configuration, so that even if the relative humidity fluctuates within a range of, for example, 10% RH to 80% RH, fluctuations in the amount of deformation are suppressed in a specified temperature environment. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating a configuration example of a magnetic recording cartridge according to a first embodiment of the present disclosure. [Figure 2] 1 is a cross-sectional view of a magnetic recording medium according to a first embodiment of the present disclosure. [Figure 3A] 3 is a schematic explanatory diagram showing the layout of data bands and servo bands in the magnetic recording medium shown in FIG. 2. FIG. [Figure 3B] FIG. 3B is a schematic explanatory diagram showing an enlarged view of the data band shown in FIG. 3A. [Figure 4] FIG. 3 is a cross-sectional view that schematically shows the cross-sectional structure of an ε-iron oxide particle contained in the magnetic layer shown in FIG. [Figure 5] 3 is a graph showing an example of an SFD curve of the magnetic recording medium shown in FIG. 2. [Figure 6] FIG. 1 is a schematic diagram illustrating the appearance of a measuring device used to measure the width of a magnetic recording medium. [Figure 7] FIG. 2 is a schematic diagram illustrating a method for measuring a dynamic friction coefficient. [Figure 8] 2 is a schematic diagram illustrating an example of the configuration of a recording / reproducing device equipped with the magnetic recording cartridge of FIG. 1. [Figure 9] FIG. 2 is a cross-sectional view of an ε-iron oxide particle according to a modified example of the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view of a magnetic recording medium according to another modified example of the first embodiment. [Figure 11] FIG. 4 is a cross-sectional view of a magnetic recording medium according to a second embodiment of the present disclosure. [Figure 12] 12 is a schematic diagram illustrating an example of the configuration of a sputtering apparatus used in manufacturing the magnetic recording medium shown in FIG. [Figure 13] FIG. 10 is a characteristic diagram showing the temperature expansion coefficient in an example of the present disclosure. [Figure 14] FIG. 10 is a characteristic diagram showing the humidity expansion coefficient in an example of the present disclosure. [Figure 15] FIG. 10 is a schematic diagram illustrating a configuration example of a magnetic recording cartridge according to a modified example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are representative embodiments of the present technology, and the present technology is not limited to the following embodiments.

[0010] The explanation will be given in the following order. 1. Overview of this technology 2. First embodiment (example of magnetic recording cartridge including coated magnetic recording medium) 2-1. Structure of magnetic recording cartridge 2-2. Structure of magnetic recording media 2-3. Manufacturing method of magnetic recording media 2-4. Recording and playback equipment 2-5.Effects 2-6. Variations 3. Second embodiment (example of magnetic recording cartridge including sputter-type magnetic recording medium) 3-1. Structure of magnetic recording cartridge 3-2. Structure of magnetic recording media 3-3.Configuration of sputtering equipment 3-4. Manufacturing method of magnetic recording medium Effects 3-6. Variations 4. Working Example

[0011] <1. Overview of this technology> First, the background to the creation of the technology of the present disclosure will be explained. In recent years, there has been a demand for a further increase in the recording capacity per magnetic recording cartridge. For example, in order to increase the recording capacity, the magnetic recording medium (e.g., magnetic recording tape) contained in the magnetic recording cartridge has been increased. One possible solution is to make the magnetic recording medium thinner (reducing the overall thickness) to increase the tape length per magnetic recording cartridge. However, thinner magnetic recording media can be more susceptible to dimensional changes in the track width direction. Dimensional changes in the width direction can cause undesirable phenomena in magnetic recording, such as off-track phenomena. The off-track phenomenon refers to a situation in which the track to be read by the magnetic head is not present at the track position where it should be read, or to a situation in which the magnetic head reads information from the wrong track position.

[0012] Previously, methods for suppressing dimensional changes in magnetic recording media have been tried, such as adding a layer to suppress dimensional changes in the magnetic recording media, but adding such a new layer ultimately increases the thickness of the magnetic recording media, preventing further increases in recording capacity per magnetic recording cartridge.

[0013] Furthermore, in order to achieve high density recording, it is important to overcome the fact that the temperature and humidity environment around the magnetic recording medium has a large effect on the deformation of the magnetic recording medium. The magnetic recording medium may be operated in an environment where the temperature is kept constant but the humidity is not controlled, or in an environment where the temperature is kept constant but the humidity is not controlled, thereby reducing environmental management costs. Therefore, even in such environments, there is a demand for magnetic recording media that exhibit minimal deformation due to temperature and humidity. Under these circumstances, the present applicant has discovered that the humidity expansion coefficient of a magnetic recording medium when the environmental temperature is kept constant and the temperature expansion coefficient of a magnetic recording medium when the environmental humidity is kept constant vary depending on the environmental temperature and humidity. Based on this finding, the present disclosure proposes a magnetic recording medium that optimizes the temperature expansion coefficient and humidity expansion coefficient of the magnetic recording medium, thereby reducing fluctuations in deformation, whether in an environment where the temperature or humidity changes or whether one of them is kept constant.

[0014] 2. First embodiment (example of magnetic recording cartridge including coated magnetic recording medium) [2-1. Configuration of Magnetic Recording Cartridge 1] First, with reference to FIG. 1, the configuration of a magnetic recording cartridge 1 according to a first embodiment of the present disclosure will be described. FIG. 1 is a schematic diagram showing an example of the magnetic recording cartridge 1. The magnetic recording cartridge 1 includes a cartridge case 2 and a reel 3 provided therein. A tape-like magnetic recording medium 10 is wound around the reel 3. When recording to the magnetic recording medium 10 or when reproducing from the magnetic recording medium 10, the magnetic recording medium 10 runs along its own longitudinal direction. The magnetic recording medium 10 is preferably used in a recording / reproducing device equipped with, for example, a ring-type head as a recording head.

[0015] [2-2. Configuration of the magnetic recording medium 10] FIG. 2 is a schematic diagram illustrating an example of the cross-sectional configuration of a magnetic recording medium 10. As shown in FIG. 2, the magnetic recording medium 10 has a laminated structure in which multiple layers are stacked. Specifically, the magnetic recording medium 10 includes a long, tape-shaped substrate 11, an underlayer 12 provided on one major surface 11A of the substrate 11, a magnetic layer 13 provided on the underlayer 12, and a back layer 14 provided on the other major surface 11B of the substrate 11. A surface 13S of the magnetic layer 13 is the surface against which a magnetic head will run while making contact. The underlayer 12 and the back layer 14 are provided as needed and are not required.

[0016] It is desirable for the environmental relative humidity to be between 10% and 80% RH so that the temperature expansion coefficient α of the magnetic recording medium 10 is between 6.0 ppm / °C and 8.0 ppm / °C. If these conditions are met, for example, when the magnetic recording medium 10 is running in a recording / reproducing device 30 (described later), the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made closer by adjusting the ambient relative humidity to an appropriate relative humidity between 10% and 80% RH. Therefore, even if the environmental temperature changes, the deformation amounts of the magnetic recording medium and the magnetic head are approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained. Therefore, for example, when recording and reproducing data on the magnetic recording medium 10 while the magnetic recording medium 10 is running in the recording / reproducing device 30, the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin.

[0017] In particular, it is preferable that the temperature expansion coefficient α of the magnetic recording medium 10 under a relative humidity environment of 10% RH, a relative humidity environment of 40% RH, and a relative humidity environment of 80% RH all be between 4.5 ppm / °C and 9.5 ppm / °C. If this condition is satisfied, for example, when the magnetic recording medium 10 is running in a recording / reproducing device 30, the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made close to each other even when the relative humidity of the surrounding environment is adjusted to between 10% RH and 80% RH. Therefore, even when the environmental temperature changes, the deformation amounts of the magnetic recording medium and the magnetic head are approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained. Therefore, for example, when recording and reproducing data on the magnetic recording medium 10 while the magnetic recording medium 10 is running in a recording / reproducing device 30, the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin.

[0018] Furthermore, it is desirable to have an environmental temperature between 10°C and 60°C where the humidity expansion coefficient β of the magnetic recording medium 10 is between -3.0 ppm / °C and 3.0 ppm / °C. If these conditions are met, for example, when the magnetic recording medium 10 is running in a recording / reproducing device 30, the humidity expansion coefficient of the magnetic recording medium 10 and the humidity expansion coefficient of the magnetic head can be made closer by adjusting the ambient temperature to an appropriate temperature between 10°C and 60°C. Therefore, even if changes in environmental humidity occur, the deformation amounts of the magnetic recording medium and the magnetic head are approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained. Therefore, for example, when recording and reproducing data on the magnetic recording medium 10 while the magnetic recording medium 10 is running in a recording / reproducing device 30, the difference between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin.

[0019] Furthermore, when the weight of the magnetic recording medium 10 is taken as 1, the moisture content of the magnetic recording medium 10 is preferably, for example, 0.2% by weight or more and 0.64% by weight or less. The moisture content of the magnetic recording medium 10 is particularly preferably 0.3% by weight or less. The moisture content of the magnetic recording medium 10 referred to here refers to the moisture content of the magnetic recording medium 10 when stabilized in an environment at a temperature of 23°C and a relative humidity of 45% RH. In other words, it does not refer to the moisture content of the magnetic recording medium when temporarily dried in a special environment, such as a high-temperature vacuum environment. It refers to the moisture content of the magnetic recording medium 10 when placed in an environment at a temperature of 23°C and a relative humidity of 45% RH for at least 24 hours. The average thickness of the magnetic recording medium 10 is, for example, 4.0 μm or more and 5.3 μm or less, and particularly preferably 4.0 μm or more and 5.1 μm or less. If the upper limit of the average thickness of the magnetic recording medium 10 is 5.3 μm or less, the recording capacity that can be recorded on one magnetic recording cartridge 1 can be further increased. For example, the recording capacity that can be recorded on one LTO-shaped magnetic recording cartridge 1 can be increased to 15 TB or more. In addition, the total surface area of ​​the magnetic recording medium 10 wound around the reel 3 of the magnetic recording cartridge 1 on the magnetic layer 13 side (hereinafter simply referred to as the total surface area of ​​the magnetic recording medium 10) is, for example, 6.3 m 2 More than 25m 2 less than 12m, more preferably 2 More than 25m 2 less than 15m, and even more preferably 2 More than 25m 2 It is preferable that the total surface area of ​​the magnetic recording medium 10 is equal to or less than 1000 m. The length of the magnetic recording medium 10 wound on the reel 3 of the magnetic recording cartridge 1 is, for example, 1000 m. The total surface area of ​​the magnetic recording medium 10 does not include the area of ​​the surface on the side of the substrate 11 on which the back layer 14 is provided, but refers to the sum of the areas of the surfaces on the side of the substrate 11 on which the magnetic layer 13 is provided. Specifically, it is calculated by multiplying the total length of the magnetic recording medium 10 included in the magnetic recording cartridge 1 by the width of the magnetic recording medium 10. Note that the total surface area of ​​the magnetic recording medium 10 referred to here does not include the area of ​​the surface of the magnetic recording medium 10 corresponding to the region on which the magnetic layer 13 is not formed.

[0020] (Base 11) The substrate 11 is a non-magnetic support that supports the underlayer 12 and the magnetic layer 13. The substrate 11 is in the form of a long film. The upper limit of the average thickness of the substrate 11 is preferably 4.4 μm or less, more preferably 4.2 μm or less. When the upper limit of the average thickness of the substrate 11 is 4.2 μm or less, the recording capacity that can be recorded on one magnetic recording cartridge 1 can be increased compared to that of a general magnetic recording medium. For example, the recording capacity that can be recorded on one LTO-shaped magnetic recording cartridge 1 can be increased to 15 TB or more. The lower limit of the average thickness of the substrate 11 is preferably 3 μm or more, more preferably 3.2 μm or more. When the lower limit of the average thickness of the substrate 11 is 3 μm or more, a decrease in the strength of the substrate 11 can be suppressed.

[0021] The average thickness of the substrate 11 is determined as follows. First, a ½-inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to prepare a sample. Next, all layers of the sample other than the substrate 11, i.e., the underlayer 12, magnetic layer 13, and back layer 14, are removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample substrate 11 is measured at five or more positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device. The measured values ​​are then simply averaged (arithmetic mean) to calculate the average thickness of the substrate 11. Note that the measurement positions are selected randomly from the sample.

[0022] The substrate 11 contains, for example, polyesters as a main component. Alternatively, the substrate 11 may contain PEEK (polyether ether ketone) as a main component. In addition to polyesters or PEEK, the substrate 11 may also contain at least one of polyolefins, cellulose derivatives, vinyl resins, and other polymer resins. When the substrate 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

[0023] The polyesters contained in the base 11 include, for example, at least one of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate), and polyethylene bisphenoxycarboxylate.

[0024] The polyolefins contained in the base 11 include, for example, at least one of PE (polyethylene) and PP (polypropylene). The cellulose derivatives include, for example, at least one of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). The vinyl resins include, for example, at least one of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0025] Other polymer resins contained in the base 11 include, for example, at least one of PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, such as Zylon (registered trademark)), polyether, PEK (polyetherketone), polyetherester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

[0026] (Magnetic layer 13) The magnetic layer 13 is a recording layer for recording signals. The magnetic layer 13 contains, for example, magnetic powder, a binder, and a lubricant. The magnetic layer 13 may further contain additives such as conductive particles, an abrasive, and an anti-rust agent, as necessary.

[0027] The arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is 2.5 nm or less, preferably 2.2 nm or less, and more preferably 1.9 nm or less. When the arithmetic mean roughness Ra is 2.5 nm or less, excellent electromagnetic conversion characteristics can be obtained. The lower limit of the arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is preferably 1.0 nm or more, more preferably 1.2 nm or more, and even more preferably 1.4 nm or more. When the lower limit of the arithmetic mean roughness Ra of the surface 13S of the magnetic layer 13 is 1.0 nm or more, deterioration of running performance due to increased friction can be suppressed.

[0028] The arithmetic mean roughness Ra of the surface 13S is determined as follows. First, the surface of the magnetic layer 13 is observed with an AFM (Atomic Force Microscope) to obtain a 40 μm × 40 μm AFM image. The AFM used is a Nano Scope IIIa D3100 manufactured by Digital Instruments, and the cantilever is made of single crystal silicon, with measurements performed at a tapping frequency tuning of 200 Hz to 400 Hz. For example, the cantilever that can be used is the "SPM Probe NCH Normal Type PointProbe L (cantilever length = 125 μm)" manufactured by Nano World. Next, the AFM image is divided into 512 x 512 (= 262,144) measurement points, and the height Z(i) (i: measurement point number, i = 1 to 262,144) is measured at each measurement point. The heights Z(i) at each measurement point are simply averaged (arithmetic mean) to determine the average height (average surface) Zave (= (Z(1) + Z(2) + ··· + Z(262,144)) / 262,144). Next, the deviation Z"(i) from the average center line at each measurement point (= |Z(i) - Zave|) is calculated, and the arithmetic mean roughness Ra [nm] (= (Z"(1) + Z"(2) + ··· + Z"(262,144)) / 262,144) is calculated. In this case, the image is filtered using Flatten order 2 and planefit order 3 XY before use.

[0029] The magnetic layer 13 preferably has a plurality of servo bands SB and a plurality of data bands DB in advance, as shown in FIG. 3A, for example. FIG. 3A is a schematic diagram showing the layout of the data bands DB and servo bands SB in the magnetic recording medium 10, illustrating the layout in a plane perpendicular to the stacking direction of the magnetic recording medium 10 having a stacked structure. As shown in FIG. 3A, the plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic recording medium 10. The width direction of the magnetic recording medium 10 is a direction perpendicular to both the longitudinal direction of the magnetic recording medium 10 and the stacking direction of the magnetic recording medium 10. A data band DB is provided between adjacent servo bands SB in the width direction. Servo signals for tracking control of the magnetic head are written in advance in the servo bands SB. User data is recorded in the data bands DB.

[0030] The total area S of the servo bands SB relative to the area S of the surface 13S of the magnetic layer 13 SB The 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 3.0% or less, and even more preferably 2.0% or less. SB The ratio R S The lower limit is preferably 0.8% or more from the viewpoint of ensuring five or more servo tracks.

[0031] The total area S of the servo bands SB relative to the surface area S of the magnetic layer 13 SB The ratio R S is the ratio of the total area S of the servo bands SB to the surface area S of the magnetic layer 13. SB The ratio R S For example, the servo bandwidth W can be measured by developing the magnetic recording medium 10 using a ferricolloid developer (Sigma Hi-Chemical Co., Ltd., Sigma Car Q) and then observing the developed magnetic recording medium 10 with an optical microscope. SBand the number of servo bands SB. Next, calculate the ratio R from the following formula: S Ask for. Ratio R S [%]=(((Servo bandwidth W SB )×(number of servo bands)) / (width of magnetic recording medium 10))×100

[0032] The number of servo bands SB is preferably 5 or more, and more preferably 5+4n (where n is a positive integer) or more. If the number of servo bands SB is 5 or more, the influence of dimensional changes in the width direction of the magnetic recording medium 10 on the servo signal can be suppressed, and stable recording and reproduction characteristics with little off-track can be ensured.

[0033] 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 60 μm or less, and even more preferably 30 μm or less. SB From the viewpoint of manufacturing a recording head, the lower limit of the servo bandwidth W is preferably 10 μm or more. SB The width of the servo band width W is determined as follows. First, the magnetic recording medium 10 is developed using a ferricolloid developer (Sigma Hi-Chemical Co., Ltd., Sigma Car Q). Next, the developed magnetic recording medium 10 is observed with an optical microscope to determine the servo band width W. SB The width can be measured.

[0034] As shown in Figure 3B, the magnetic layer 13 is configured so that a plurality of data tracks Tk can be formed on the data band DB. Figure 3B is a schematic explanatory diagram showing an enlarged view of the data band DB shown in Figure 3A. In this case, the data track width W Tk From the viewpoint of ensuring a high recording capacity, the upper limit of the data track width W is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. Tk The lower limit is preferably 0.02 μm or more from the viewpoint of the magnetic particle size.

[0035] From the viewpoint of ensuring a high recording capacity, the magnetic layer 13 is configured to be able to record data such that the minimum value of the distance L between magnetization reversals is preferably 48 nm or less, more preferably 44 nm or less, and even more preferably 40 nm or less. From the viewpoint of the magnetic grain size, the lower limit of the minimum value of the distance L between magnetization reversals is preferably 20 nm or more.

[0036] The upper limit of the average thickness of magnetic layer 13 is preferably 90 nm or less, particularly preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. If the upper limit of the average thickness of magnetic layer 13 is 90 nm or less, when a ring-type head is used as the recording head, magnetization can be recorded uniformly in the thickness direction of magnetic layer 13, thereby improving the electromagnetic conversion characteristics.

[0037] The lower limit of the average thickness of magnetic layer 13 is preferably 35 nm or more. If the upper limit of the average thickness of magnetic layer 13 is 35 nm or more, output can be ensured when an MR head is used as the reproducing head, thereby improving the electromagnetic conversion characteristics.

[0038] The average thickness of the magnetic layer 13 is determined as follows.

[0039] First, the magnetic recording medium 10 is thinned by processing using a focused ion beam (FIB) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by vapor deposition, and the tungsten thin film is further formed on the magnetic layer side surface by vapor deposition or sputtering. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. In other words, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10. The cross section of the obtained thinned sample is observed using a transmission electron microscope (TEM) under the following conditions to obtain a TEM image. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Apparatus: TEM (Hitachi H9000NAR) Accelerating voltage: 300 kV Magnification: 100,000x

[0040] Next, using the obtained TEM image, the thickness of the magnetic layer 13 is measured at at least 10 positions in the longitudinal direction of the magnetic recording medium 10. The obtained measurements are simply averaged (arithmetic mean) to obtain the average thickness of the magnetic layer 13. The positions where the measurement is performed are selected randomly from the test piece.

[0041] (magnetic powder) The magnetic powder includes, for example, a powder of nanoparticles containing ε-iron oxide (hereinafter referred to as "ε-iron oxide particles"). Even fine particles of ε-iron oxide particles can achieve high coercivity. It is preferable that the ε-iron oxide contained in the ε-iron oxide particles has a crystal orientation preferentially in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

[0042] FIG. 4 is a cross-sectional view schematically illustrating an example of the cross-sectional structure of the ε-iron oxide particles 20 contained in the magnetic layer 13. As shown in FIG. 4, the ε-iron oxide particles 20 are spherical or nearly spherical, or cubic or nearly cubic. Because the ε-iron oxide particles 20 have the above-described shape, when the ε-iron oxide particles 20 are used as the magnetic particles, the contact area between the particles in the thickness direction of the magnetic recording medium 10 can be reduced and aggregation between the particles can be suppressed compared to when hexagonal plate-shaped barium ferrite particles are used as the magnetic particles. This improves the dispersibility of the magnetic powder and allows for a better SNR (Signal-to-Noise Ratio).

[0043] The ε-iron oxide particles 20 have, for example, a core-shell structure. Specifically, as shown in Fig. 4, the ε-iron oxide particles 20 include a core 21 and a two-layer shell 22 provided around the core 21. The two-layer shell 22 includes a first shell 22a provided on the core 21 and a second shell 22b provided on the first shell 22a.

[0044] The core 21 of the ε-iron oxide particle 20 contains ε-iron oxide. The ε-iron oxide contained in the core 21 preferably has ε-Fe2O3 crystals as its main phase, and more preferably is made of single-phase ε-Fe2O3.

[0045] The first shell portion 22a covers at least a portion of the periphery of the core portion 21. Specifically, the first shell portion 22a may cover a portion of the periphery of the core portion 21, or may cover the entire periphery of the core portion 21. From the viewpoint of ensuring sufficient exchange coupling between the core portion 21 and the first shell portion 22a and improving magnetic properties, it is preferable that the entire surface of the core portion 21 be covered.

[0046] The first shell portion 22a is a so-called soft magnetic layer and includes a soft magnetic material such as α-Fe, a Ni-Fe alloy, or an Fe-Si-Al alloy. The α-Fe may be obtained by reducing ε-iron oxide contained in the core portion 21.

[0047] The second shell portion 22b is an oxide coating serving as an anti-oxidation layer. The second shell portion 22b contains α-iron oxide, aluminum oxide, or silicon oxide. The α-iron oxide contains at least one iron oxide selected from Fe3O4, Fe2O3, and FeO. When the first shell portion 22a contains α-Fe (soft magnetic material), the α-iron oxide may be obtained by oxidizing the α-Fe contained in the first shell portion 22a.

[0048] By having the first shell portion 22a as described above, the ε-iron oxide particles 20 can maintain a high coercivity Hc of the core portion 21 alone to ensure thermal stability, while adjusting the coercivity Hc of the entire ε-iron oxide particles (core-shell particles) 20 to a coercivity Hc suitable for recording. Furthermore, by having the second shell portion 22b as described above, the ε-iron oxide particles 20 can be prevented from deteriorating in the properties of the ε-iron oxide particles 20 due to rust or the like occurring on the particle surface when exposed to air during or before the manufacturing process of the magnetic recording medium 10. Therefore, by covering the first shell portion 22a with the second shell portion 22b, deterioration in the properties of the magnetic recording medium 10 can be prevented.

[0049] The average particle size (average maximum particle size) of the magnetic powder is preferably 25 nm or less, more preferably 8 nm to 22 nm, and even more preferably 12 nm to 22 nm. In the magnetic recording medium 10, the actual magnetization region is a region half the size of the recording wavelength. Therefore, a good S / N ratio can be obtained by setting the average particle size of the magnetic powder to half the shortest recording wavelength or less. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high-recording-density magnetic recording medium 10 (e.g., a magnetic recording medium 10 configured to record signals at the shortest recording wavelength of 50 nm or less). On the other hand, when the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.

[0050] The average aspect ratio of the magnetic powder is preferably 1 or more and 3.0 or less, more preferably 1 or more and 2.8 or less, and even more preferably 1 or more and 1.8 or less. When the average aspect ratio of the magnetic powder is within the range of 1 or more and 3.0 or less, aggregation of the magnetic powder can be suppressed, and the resistance applied to the magnetic powder when the magnetic powder is vertically oriented in the process of forming the magnetic layer 13 can be suppressed. Therefore, the vertical orientation of the magnetic powder can be improved.

[0051] The average particle size and average aspect ratio of the magnetic powder are determined as follows. First, the magnetic recording medium 10 to be measured is processed and thinned using a method such as FIB (Focused Ion Beam). The thinning is performed along the length (longitudinal direction) of the magnetic tape. That is, this thinning results in a cross section parallel to both the longitudinal and thickness directions of the magnetic recording medium 10. The obtained thin section 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 13 in the thickness direction of the magnetic layer 13, and a TEM photograph is taken. Next, 50 particles are randomly selected from the TEM photograph, and the major axis length DL and minor axis length DS of each particle are measured. Here, the major axis length DL refers to the longest distance between two parallel lines drawn from any angle so as to tangent to the outline of each particle (the so-called maximum Feret diameter). On the other hand, the minor axis length DS means the maximum length of the particle in the direction perpendicular to the major axis length DL of the particle.

[0052] Next, the long axis lengths DL of the measured 50 particles are simply averaged (arithmetic mean) to determine the average long axis length DLave. The average long axis length DLave thus determined is the average particle size of the magnetic powder. The short axis lengths DS of the measured 50 particles are also simply averaged (arithmetic mean) to determine the average short axis length DSave. The average aspect ratio of the particles (DLave / DSave) is then calculated from the average long axis length DLave and the average short axis length DSave.

[0053] The average particle volume of the magnetic powder is preferably 5500 nm3 Less than 270 nm, preferably 3 More than 5500nm 3 or less, and even more preferably 900 nm 3 More than 5500nm 3 The average particle volume of the magnetic powder is 5500 nm or less. 3 When the average particle size of the magnetic powder is 270 nm or less, the same effect as when the average particle size of the magnetic powder is 22 nm or less can be obtained. 3 If the average particle size of the magnetic powder is 8 nm or more, the same effect as when the average particle size of the magnetic powder is 8 nm or more can be obtained.

[0054] When the ε iron oxide particles 20 are spherical or nearly spherical, the average particle volume of the magnetic powder can be calculated as follows. First, the average major axis length DLave is calculated using the same method as for calculating the average particle size of the magnetic powder described above. Next, the average particle volume V of the magnetic powder is calculated using the following formula: V = (π / 6) × (DLave) 3

[0055] (binder) As the binder, a resin having a structure in which a crosslinking reaction is imparted to a polyurethane resin, a vinyl chloride resin, or the like is preferred. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required of the magnetic recording medium 10. There is no particular limitation on the resin to be blended, so long as it is a resin that is generally used in coating-type magnetic recording media 10.

[0056] Examples of the polymer include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, amino resin, and synthetic rubber.

[0057] Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, and urea-formaldehyde resins.

[0058] Furthermore, to improve the dispersibility of the magnetic powder, polar functional groups such as -SO3M, -OSO3M, -COOM, and P=O(OM)2 may be introduced into each of the binders described above, where M in the above chemical formula is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

[0059] Furthermore, polar functional groups include -NR1R2 and -NR1R2R3 + X - Side chain type with terminal group of >NR1R2 + X - In the above formula, R1, R2, and R3 are hydrogen atoms or hydrocarbon groups, and X -is a halogen ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. Examples of polar functional groups include -OH, -SH, -CN, and epoxy groups.

[0060] (lubricant) The lubricant contained in the magnetic layer 13 contains, for example, a fatty acid and a fatty acid ester. The fatty acid contained in the lubricant is, for example, a compound represented by the following general formula: <1> and compounds represented by the general formula <2> In addition, the fatty acid ester contained in the lubricant preferably contains at least one of compounds represented by the following general formula: <3> and compounds represented by the general formula <4> It is preferred that the lubricant contains at least one of compounds represented by the general formula: <1> and compounds represented by the general formula <3> By including two kinds of compounds represented by the general formula <2> and compounds represented by the general formula <3> By including two kinds of compounds represented by the general formula <1> and compounds represented by the general formula <4> By including two kinds of compounds represented by the general formula <2> and compounds represented by the general formula <4> By including two kinds of compounds represented by the general formula <1> a compound represented by the general formula <2> and compounds represented by the general formula <3> By including three kinds of compounds represented by the general formula <1> a compound represented by the general formula <2> and compounds represented by the general formula <4> By including three kinds of compounds represented by the general formula <1> a compound represented by the general formula <3> and compounds represented by the general formula <4> By including three kinds of compounds represented by the general formula <2> a compound represented by the general formula <3> and compounds represented by the general formula <4> or by including three kinds of compounds represented by the general formula <1> a compound represented by the general formula <2> a compound represented by the general formula <3> and compounds represented by the general formula <4> By including these four compounds, it is possible to suppress an increase in the dynamic friction coefficient due to repeated recording or reproduction on the magnetic recording medium 10. As a result, the running properties of the magnetic recording medium 10 can be further improved. CH3(CH2) k COOH... <1> (However, the general formula <1> In the formula, k is an integer selected from the range of 14 to 22, more preferably from the range of 14 to 18. CH3(CH2) n CH=CH(CH2) m COOH... <2> (However, the general formula <2> In the formula, 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. CH3(CH2) p COO(CH2) q CH3... <3> (However, the general formula <3> In the formula, 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. CH3(CH2) p COO-(CH2) q CH(CH3)2… <4> (However, the general formula <4> In the formula, p is an integer selected from the range of 14 to 22, and q is an integer selected from the range of 1 to 3.

[0061] (additives) The magnetic layer 13 may further contain non-magnetic reinforcing particles such as aluminum oxide (α, β or γ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile or anatase titanium oxide), etc.

[0062] (base layer 12) The underlayer 12 is a nonmagnetic layer containing a nonmagnetic powder and a binder. The underlayer 12 may further contain at least one additive, such as a lubricant, conductive particles, a hardener, or an anti-rust agent, if necessary. The underlayer 12 may also have a multilayer structure formed by stacking multiple layers. The average thickness of the underlayer 12 is preferably 0.5 μm to 0.9 μm, more preferably 0.5 μm to 0.7 μm. By reducing the average thickness of the underlayer 12 to 0.9 μm or less, the Young's modulus of the entire magnetic recording medium 10 is more effectively reduced than when the thickness of the substrate 11 is reduced. This facilitates tension control for the magnetic recording medium 10. Furthermore, by reducing the average thickness of the underlayer 12 to 0.5 μm or more, the adhesive strength between the substrate 11 and the underlayer 12 is ensured. Furthermore, the variation in the thickness of the underlayer 12 can be reduced, preventing the surface 13S of the magnetic layer 13 from becoming rough.

[0063] The average thickness of the underlayer 12 can be determined, for example, as follows: First, a ½-inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to prepare a sample. Next, the underlayer 12 and magnetic layer 13 of the sample magnetic recording medium 10 are peeled off from the substrate 11. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the laminate of the underlayer 12 and magnetic layer 13 peeled off from the substrate 11 is measured at five or more positions. After that, the measured values ​​are simply averaged (arithmetic averaged) to calculate the average thickness of the laminate of the underlayer 12 and magnetic layer 13. Note that the measurement positions are selected randomly from the sample. Finally, the average thickness of the underlayer 12 is determined by subtracting the average thickness of the magnetic layer 13 measured using the TEM as described above from the average thickness of the laminate.

[0064] The underlayer 12 preferably has a large number of holes. By storing lubricant in these holes, it is possible to further suppress a decrease in the amount of lubricant supplied between the surface 13S of the magnetic layer 13 and the magnetic head, even after repeated recording or reproduction (i.e., after repeated running of the magnetic head with the magnetic head in contact with the surface of the magnetic recording medium 10). Therefore, it is possible to further suppress an increase in the coefficient of dynamic friction.

[0065] (Non-magnetic powder in the underlayer 12) The non-magnetic powder includes, for example, at least one of inorganic particle powder and organic particle powder. The non-magnetic powder may also include carbon powder such as carbon black. One type of non-magnetic powder may be used alone, or two or more types of non-magnetic powder may be used in combination. The inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, or metal sulfides. The shape of the non-magnetic powder may be, for example, acicular, spherical, cubic, plate-like, or other shapes, but is not limited thereto.

[0066] (Binder for base layer 12) The binder in the underlayer 12 is the same as that in the magnetic layer 13 described above.

[0067] (Back layer 14) The back layer 14 contains, for example, a binder and a non-magnetic powder. The back layer 14 may further contain at least one additive selected from the group consisting of a lubricant, a curing agent, and an antistatic agent, as necessary. The binder and non-magnetic powder in the back layer 14 are the same as those in the underlayer 12 described above.

[0068] The average particle size of the non-magnetic powder in back layer 14 is preferably 10 nm or more and 150 nm or less, and more preferably 15 nm or more and 110 nm or less. The average particle size of the non-magnetic powder in back layer 14 is determined in the same manner as the average particle size of the magnetic powder in magnetic layer 13. The non-magnetic powder may contain powder having two or more particle size distributions.

[0069] The upper limit of the average thickness of the back layer 14 is preferably 0.6 μm or less, and particularly preferably 0.5 μm or less. If the upper limit of the average thickness of the back layer 14 is 0.6 μm or less, the thickness of the underlayer 12 and the substrate 11 can be kept thick even when the average thickness of the magnetic recording medium 10 is 5.3 μm or less, thereby maintaining running stability of the magnetic recording medium 10 within a recording and reproducing device. The lower limit of the average thickness of the back layer 14 is not particularly limited, but is, for example, 0.2 μm or more, and particularly preferably 0.3 μm or more.

[0070] The average thickness of the back layer 14 is determined as follows. First, a magnetic recording medium 10 having a width of 1 / 2 inch is prepared and cut into a length of 250 mm to prepare a sample. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample magnetic recording medium 10 is measured at five or more points, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t T [μm] is calculated. Note that the measurement position is selected randomly from the sample. Next, the back layer 14 is removed from the sample magnetic recording medium 10 using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. After that, the above-mentioned laser hologram is used again to measure the thickness of the sample from which the back layer 14 has been removed at five or more points, and these measurements are simply averaged (arithmetic mean) to obtain the average thickness t of the magnetic recording medium 10 from which the back layer 14 has been removed. B [μm] is calculated. The measurement position is selected randomly from the sample. Finally, the average thickness t of the back layer 14 is calculated using the following formula: b Calculate [μm]. t b [μm]=t T [μm]-t B [μm]

[0071] (Average thickness of magnetic recording medium 10) As mentioned above, the upper limit of the average thickness (average total thickness) of the magnetic recording medium 10 is preferably 5.8 μm or less, and more preferably 5.3 μm or less. When the average thickness of the magnetic recording medium 10 is 5.8 μm or less, the recording capacity that can be recorded on one magnetic recording cartridge 1 can be increased compared to that of a typical magnetic recording medium. Furthermore, the lower limit of the average thickness of the magnetic recording medium 10 is preferably, for example, 4.0 μm or more. When the average thickness of the magnetic recording medium 10 is 4.0 μm or more, deformation of the magnetic recording medium 10 can be effectively suppressed.

[0072] The average thickness tT of the magnetic recording medium 10 is determined as follows. First, a 1 / 2-inch wide magnetic recording medium 10 is prepared and cut into 250 mm lengths to prepare samples. Next, a Mitutoyo Laser Hologram (LGH-110C) is used as a measuring device to measure the thickness of the sample at five or more positions, and the measured values ​​are simply averaged (arithmetic mean) to calculate the average value tT [μm]. Note that the measurement positions are selected randomly from the sample.

[0073] (Coercive force Hc) The upper limit of the coercive force Hc in the longitudinal direction of the magnetic recording medium 10 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 in the longitudinal direction is 2000 Oe or less, the magnetization reacts sensitively to the perpendicular magnetic field from the recording head, allowing for the formation of a good recording pattern.

[0074] The lower limit of the coercive force Hc measured in the longitudinal direction of the magnetic recording medium 10 is preferably 1000 Oe or more. If the lower limit of the coercive force Hc in the longitudinal direction is 1000 Oe or more, demagnetization due to leakage flux from the recording head can be suppressed.

[0075] The coercive force Hc is determined as follows. Three magnetic recording media 10 are stacked and adhered with double-sided tape, and then punched out with a 6.39 mm diameter punch to create a measurement sample. At this time, markings are made with any nonmagnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium can be identified. Then, using a vibrating sample magnetometer (VSM), the MH loop of the measurement sample (the entire magnetic recording medium 10) corresponding to the longitudinal direction (running direction of the magnetic recording medium 10) of the magnetic recording medium 10 is measured. Next, the coating film (underlayer 12, magnetic layer 13, back layer 14, etc.) is wiped off with acetone or ethanol, leaving only the substrate 11. Three of the resulting substrates 11 are then stacked and adhered with double-sided tape, and then punched out with a 6.39 mm diameter punch to obtain a sample for background correction (hereinafter simply referred to as the correction sample). Thereafter, the MH loop of the correction sample (substrate 11) corresponding to the longitudinal direction of the substrate 11 (the running direction of the magnetic recording medium 10) is measured using the VSM.

[0076] The MH loops of the measurement sample (the entire magnetic recording medium 10) and the correction sample (substrate 11) are measured using, for example, a high-sensitivity vibrating sample magnetometer, model 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.

[0077] After obtaining the two M-H loops, background correction is performed by subtracting the M-H loop of the correction sample (substrate 11) from the M-H loop of the measurement sample (entire magnetic recording medium 10), thereby obtaining the M-H loop after background correction. This background correction calculation is performed using the measurement and analysis program included with the "VSMP7-15 model."

[0078] The coercive force Hc is calculated from the obtained MH loop after background correction. Note that this calculation uses the measurement and analysis program attached to the "VSM-P7-15 model." Note that all of the above MH loop measurements are performed at 25°C. Furthermore, "demagnetizing field correction" is not performed when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10.

[0079] (Square ratio) The squareness ratio S1 in the perpendicular direction (thickness direction) of the magnetic recording medium 10 is, for example, 65% or more, preferably 67% or more, more preferably 70% or more, even more preferably 75% or more, and particularly preferably 80% or more. When the squareness ratio S1 is 65% or more, the perpendicular orientation of the magnetic powder is sufficiently high, and therefore a better SNR can be obtained.

[0080] The squareness ratio S1 is calculated as follows. Three magnetic recording media 10 are stacked and adhered with double-sided tape, and then punched out with a 6.39 mm diameter punch to create a measurement sample. At this time, markings are made with a non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium can be identified. Then, a vibrating sample magnetometer (VSM) is used to measure the MH loop of the measurement sample (the entire magnetic recording medium 10) corresponding to the perpendicular direction (thickness direction of the magnetic recording medium 10) of the magnetic recording medium 10. Next, the coating (underlayer 12, magnetic layer 13, back layer 14, etc.) is wiped off with acetone or ethanol, leaving only the substrate 11. Three of the obtained substrates 11 are then stacked and adhered with double-sided tape, and then punched out with a 6.39 mm diameter punch to obtain a sample for background correction (hereinafter simply referred to as the correction sample). Thereafter, the MH loop of the correction sample (substrate 11) corresponding to the perpendicular direction of the substrate 11 (thickness direction of the magnetic recording medium 10) is measured using a VSM.

[0081] The MH loops of the measurement sample (the entire magnetic recording medium 10) and the correction sample (substrate 11) are measured using, for example, a high-sensitivity vibrating sample magnetometer, model 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.

[0082] After obtaining the two M-H loops, background correction is performed by subtracting the M-H loop of the correction sample (substrate 11) from the M-H loop of the measurement sample (entire magnetic recording medium 10), thereby obtaining the M-H loop after background correction. This background correction calculation is performed using the measurement and analysis program included with the "VSMP7-15 model."

[0083] The saturation magnetization Ms (emu) and remanent magnetization Mr (emu) of the MH loop after background correction are substituted into the following equation to calculate the squareness ratio S1 (%). Squareness ratio S1(%)=(Mr / Ms)×100 It should be noted that all of the above MH loop measurements are performed at 25° C. Furthermore, when measuring the MH loop in the perpendicular direction to the magnetic recording medium 10, "demagnetization field correction" is not performed.

[0084] The squareness ratio S2 in the longitudinal direction (running direction) of the magnetic recording medium 10 is preferably 35% or less, more preferably 30% or less, even more preferably 25% or less, particularly preferably 20% or less, and most preferably 15% or less. When the squareness ratio S2 is 35% or less, the magnetic powder has a sufficiently high perpendicular orientation, resulting in a better SNR.

[0085] The squareness ratio S2 is determined in the same manner as the squareness ratio S1, except that the MH loop is measured in the longitudinal direction (traveling direction) of the magnetic recording medium 10 and the substrate 11.

[0086] (SFD) In the SFD (Switching Field Distribution) curve of the magnetic recording medium 10, the peak ratio X / Y, where X is the main peak height and Y is the sub-peak height near zero magnetic field, is preferably 3.0 or greater, more preferably 5.0 or greater, even more preferably 7.0 or greater, particularly preferably 10.0 or greater, and most preferably 20.0 or greater (see FIG. 5). FIG. 5 is a graph showing an example of the SFD curve of the magnetic recording medium 10 shown in FIG. 2. A peak ratio X / Y of 3.0 or greater can prevent the magnetic powder from containing large amounts of low-coercivity components specific to ε-iron oxide (e.g., soft magnetic particles, superparamagnetic particles, etc.) in addition to the ε-iron oxide particles 20 that contribute to actual recording. This prevents the magnetic signal recorded on adjacent tracks from being degraded by the leakage magnetic field from the recording head, resulting in a higher SNR. The upper limit of the peak ratio X / Y is not particularly limited, but is, for example, 100 or less.

[0087] The peak ratio X / Y is calculated as follows. First, a background-corrected MH loop is obtained using the same method as in the above-described method for measuring coercivity Hc. Next, an SFD curve is calculated from the obtained MH loop. The SFD curve can be calculated using a program provided with the measuring instrument or other programs. The absolute value of the point where the calculated SFD curve crosses the Y axis (dM / dH) is defined as "Y," and the height of the main peak observed in the MH loop near the coercivity Hc is defined as "X," to calculate the peak ratio X / Y. Note that the MH loop is measured at 25°C, as in the above-described method for measuring coercivity Hc. Furthermore, when measuring the MH loop in the thickness direction (perpendicular direction) of the magnetic recording medium 10, "demagnetization field correction" is not performed. Furthermore, the MH loop may be measured by stacking multiple samples to be measured depending on the sensitivity of the VSM used.

[0088] (Activation volume Vact) The activation volume Vact is preferably 8000 nm 3 Below 6000 nm, preferably 3 or less, and even more preferably 5000 nm 3Below 4000 nm, particularly preferably 3 Below 3000 nm, most preferably 3 The activation volume Vact is 8000 nm 3 If the magnetic powder is 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, resulting in a better SNR.

[0089] The activation volume Vact is calculated by the following formula derived by Street & Woolley. Vact(nm 3 )=kB×T×Xirr / (μ0×Ms×S) (where kB is Boltzmann's constant (1.38 x 10 -23 J / K), T: temperature (K), Χirr: irreversible magnetic susceptibility, μ0: vacuum permeability, S: magnetorheological coefficient, Ms: saturation magnetization (emu / cm 3 ))

[0090] The irreversible magnetic susceptibility X, saturation magnetization M, and magnetic viscosity coefficient S, which are substituted into the above equation, are calculated using VSM as follows. The measurement sample used for VSM is prepared by punching three magnetic recording media 10 stacked with double-sided tape using a 6.39 mm diameter punch. Marking is performed with a nonmagnetic ink to identify the longitudinal direction (running direction) of the magnetic recording medium 10. The measurement direction using VSM is the thickness direction (vertical direction) of the magnetic recording medium 10. Measurement using VSM is performed at 25°C on a measurement sample cut from a long magnetic recording medium 10. Furthermore, "demagnetization field correction" is not performed when measuring the MH loop in the thickness direction (vertical direction) of the magnetic recording medium 10. Furthermore, a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo Co., Ltd. is used to measure the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11). 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 seconds, waiting time: 1 second, number of MH averages: 20.

[0091] (irreversible magnetic susceptibility Χirr) The irreversible magnetic susceptibility χirr is defined as the slope of the remanence curve (DCD curve) near the remanence Hr. First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic recording medium 10, then returned to zero, creating a remanence state. A magnetic field of approximately 15.9 kA / m (200 Oe) is then applied in the opposite direction, returned to zero, and the remanence is measured. A magnetic field 15.9 kA / m greater than the previous applied field is then applied, and the measurement is repeated. The remanence is plotted against the applied magnetic field, and the DCD curve is measured. The point at which the magnetization becomes zero is taken as the remanence Hr. The DCD curve is then differentiated to determine the slope of the DCD curve at each magnetic field. The slope of this DCD curve near the remanence Hr is the slope of the DCD curve.

[0092] (Saturation magnetization Ms) First, a background-corrected MH loop is obtained in the same manner as in the above-described method for measuring the coercive force Hc. Next, the value of the saturation magnetization Ms (emu) of the obtained MH loop and the volume (cm 3 ) to Ms(emu / cm 3 ) is calculated. The volume of magnetic layer 13 is found by multiplying the area of ​​the measurement sample by the average thickness of magnetic layer 13. The method for calculating the average thickness of magnetic layer 13, which is necessary for calculating the volume of magnetic layer 13, is as described above.

[0093] (Magnetic viscosity coefficient S) First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic recording medium 10 (measurement sample), and then the magnetic field is returned to zero, resulting in a state of remanence. Then, a magnetic field equivalent to the value of the remanence Hr obtained from the DCD curve is applied in the opposite direction. With the magnetic field applied, the magnetization is continuously measured at regular intervals for 1000 seconds. The magnetic viscosity coefficient S is calculated by applying the relationship between time t and magnetization M(t) obtained in this way to the following equation: M(t) = M0 + S × ln(t) (where M(t) is the amount of magnetization at time t, M0 is the initial amount of magnetization, S is the magnetic viscosity coefficient, and ln(t) is the natural logarithm of time.)

[0094] (dimensional change Δw) The dimensional change Δw [ppm / N] in the width direction of the magnetic recording medium 10 in response to a change in tension in the longitudinal direction of the magnetic recording medium 10 is preferably 650 ppm / N≦Δw, more preferably 700 ppm / N≦Δw, even more preferably 750 ppm / N≦Δw, and particularly preferably 800 ppm / N≦Δw. When the dimensional change Δw is 650 ppm / N≦Δw, changes in the width of the magnetic recording medium 10 can be more effectively suppressed by adjusting the tension in the longitudinal direction of the magnetic recording medium 10 using a recording / reproducing device 30, which will be described later. The upper limit of the dimensional change Δw is not particularly limited, but can be, for example, Δw≦1,700,000 ppm / N, preferably Δw≦20,000 ppm / N, more preferably Δw≦8,000 ppm / N, even more preferably Δw≦5,000 ppm / N, Δw≦4,000 ppm / N, Δw≦3,000 ppm / N, or Δw≦2,000 ppm / N.

[0095] The dimensional change Δw can be set to a desired value by selecting the substrate 11. For example, the dimensional change Δw can be set to a desired value by selecting at least one of the thickness of the substrate 11 and the material of the substrate 11. The dimensional change Δw may also be set to a desired value by adjusting the stretching strength of the substrate 11 in the width direction and the longitudinal direction. For example, by stretching the substrate 11 more strongly in the width direction, the dimensional change Δw decreases, and conversely, by strengthening the stretching of the substrate 11 in the longitudinal direction, the dimensional change Δw increases.

[0096] The dimensional change Δw is calculated as follows. First, a magnetic recording medium 10 having a width of 1 / 2 inch is prepared and cut into a length of 250 mm to obtain a sample 10S. Next, loads of 0.2 N, 0.6 N, and 1.0 N are applied in that order along the length of the sample 10S, and the width of the sample 10S is measured at loads of 0.2 N, 0.6 N, and 1.0 N. Next, the dimensional change Δw is calculated using the following formula. Note that the measurement when a load of 0.6 N is applied is performed to check for any abnormalities in the measurement (especially to check that the results of these three measurements are linear), and the measurement result is not used in the following formula.

number

[0097] The width of the sample 10S when each load is applied is measured using, for example, the measuring device shown in Fig. 6. Fig. 6 is a schematic diagram showing the appearance of a measuring device 210 used to measure the width of the magnetic recording medium 10. First, the measuring device 210 will be described with reference to Fig. 6. The measuring device 210 includes a base 211, a support column 212, a light emitter 213, a light receiver 214, a support plate 215, five support members 216A to 216E, and a fixing portion 217.

[0098] Base 211 has a rectangular plate shape. Light receiver 214 is provided in the center of base 211. Support pillar 212 is erected adjacent to light receiver 214 at a position shifted from the center of base 211 toward one long side. Fixing portion 217 is provided on one short side of base 211.

[0099] A light emitter 213 is supported at the tip of the support column 212. The light emitter 213 and the light receiver 214 face each other. During measurement, the sample 10S supported by the support members 216A to 216E is placed between the facing light emitter 213 and the light receiver 214. The light emitter 213 and the light receiver 214 are connected to a PC (personal computer) not shown, and under the control of the PC, the width of the sample 10S supported by the support members 216A to 216E is measured and the measurement results are output to the PC.

[0100] A digital dimension measuring instrument LS-7000 manufactured by Keyence Corporation is incorporated into the light emitter 213 and the light receiver 214. The light emitter 213 irradiates the sample 10S supported by the support members 216A to 216E with linear light parallel to the width direction of the sample 10S. The light receiver 214 measures the width of the sample 10S by measuring the amount of light that is not blocked by the sample 10S.

[0101] A long, narrow rectangular support plate 215 is fixed at approximately half the height of the support column 212. The support plate 215 is supported so that its long sides are parallel to the main surface of the base 211. Five support members 216A to 216E are supported on one main surface of the support plate 215. The support members 216A to 216E have a cylindrical rod shape and support the back surface of the sample 10S (magnetic recording medium 10). All five support members 216A to 216E (especially their surfaces) are made of stainless steel SUS304, and their surface roughness Rz (maximum height) is 0.15 μm to 0.3 μm.

[0102] Here, the arrangement of the five support members 216A to 216E will be described with reference to FIG. 6. As shown in FIG. 6, the sample 10S is placed on the five support members 216A to 216E. The diameter of each of the five support members 216A to 216E is, for example, 7 mm. The distance d1 between support member 216A and support member 216B (particularly the distance between the central axes of these support members) is 20 mm. The distance d2 between support member 216B and support member 216C is 30 mm. The distance d3 between support member 216C and support member 216D is 30 mm. The distance d4 between support member 216D and support member 216E is 20 mm.

[0103] Furthermore, the three support members 216B to 216D are arranged so that the portions of the sample 10S resting between support members 216B, 216C, and 216D form a plane that is approximately perpendicular to the direction of gravity. Furthermore, support members 216A and 216B are arranged so that the sample 10S forms an angle of θ1 = 30° with respect to the approximately perpendicular plane between support members 216A and 216B. Furthermore, support members 216D and 216E are arranged so that the sample 10S forms an angle of θ2 = 30° with respect to the approximately perpendicular plane between support members 216D and 216E. Furthermore, of the five support members 216A to 216E, support member 216C is fixed so as not to rotate, but the other four support members 216A, 216B, 216D, and 216E are all rotatable.

[0104] Of support members 216A to 216E, support member 216C is located between light emitter 213 and light receiver 214 and is located approximately in the center between fixed portion 217 and the portion where a load is applied, and is provided with slit 216S. Light L is irradiated from light emitter 213 to light receiver 214 through slit 216S. The slit width of slit 216S is 1 mm, and light L can pass through slit 216S without being blocked by the frame of slit 216S.

[0105] When measuring the width of the sample 10S when each load is applied using the measuring device 210, first, the sample 10S is set in the measuring device 210. Specifically, one end of the long sample 10S is fixed by a fixing part 217. Next, the sample 10S is placed on five support members 216A to 216E. At this time, the back surface of the sample 10S is placed in contact with the five support members 216A to 216E.

[0106] Next, the measurement device 210 is placed in a chamber controlled to a constant temperature of 25°C and relative humidity of 50%, and a weight 233 for applying a 0.2 N load is attached to the other end of the sample 10S. The sample 10S is then kept in the above environment for at least two hours to allow the sample 10S to acclimate to the environment. After the two-hour storage period, the width of the sample 10S is measured. Specifically, with the 0.2 N load 218 attached, light L is irradiated from the light emitter 213 to the light receiver 214, and the width of the sample 10S with the load applied in the longitudinal direction is measured. This width measurement is performed when the sample 10S is not curled. Next, the weight for applying the 0.2 N load is changed to a weight for applying a 0.6 N load, and the width of the sample 10S is measured five minutes after the change. Finally, the weight for applying a 1.0 N load is changed to a weight for applying a 1.0 N load, and the width of the sample 10S is measured five minutes after the change.

[0107] (Temperature expansion coefficient α) The temperature expansion coefficient α of the magnetic recording medium 10 is preferably 3 [ppm / °C]≦α≦10 [ppm / °C]. When the temperature expansion coefficient α is in the above range, changes in the width of the magnetic recording medium 10 can be suppressed by adjusting the longitudinal tension of the magnetic recording medium 10 using a recording / reproducing device 30, which will be described later.

[0108] The temperature expansion coefficient α is calculated as follows. First, a sample 10S is prepared in the same manner as in the measurement of the dimensional change Δw, and the sample 10S is placed in the same measuring device 210 as in the measurement of the dimensional change Δw. Then, for example, to measure the temperature expansion coefficient α under a relative humidity environment of 10% RH, the measuring device 210 containing the sample 10S is placed in a chamber controlled to a constant temperature of 29°C and a relative humidity of 10%. Next, a load of 0.2 N is applied to the sample 10S in the longitudinal direction, and the sample 10S is kept in this environment for at least two hours to allow it to acclimate. Then, while maintaining the relative humidity at 10%, the temperature is changed in the order of 45°C, 29°C, and 10°C. The width of the sample 10S at 45°C and 10°C is measured, and the temperature expansion coefficient α is calculated using the following formula. The width measurement of the sample 10S at 29°C is performed to check for any abnormalities in the measurement (especially to confirm that the results of these three measurements are linear), and the measurement result is not used in the following formula.

number

[0109] (humidity expansion coefficient β) The humidity expansion coefficient β of the magnetic recording medium 10 is preferably β≦5 [ppm / % RH]. When the humidity expansion coefficient β is in the above range, the recording / reproducing device 30 can adjust the tension of the magnetic recording medium 10 in the longitudinal direction, thereby further suppressing changes in the width of the magnetic recording medium 10.

[0110] The humidity expansion coefficient β is calculated as follows. First, a sample 10S is prepared in the same manner as in the measurement of the dimensional change Δw, and the sample 10S is placed in the same measuring device 210 as in the measurement of the dimensional change Δw. Then, for example, to measure the humidity expansion coefficient β at a temperature of 10°C, the measuring device 210 containing the sample 10S is placed in a chamber controlled to a constant temperature of 10°C and a relative humidity of 24%. Next, a load of 0.2 N is applied to the sample 10S in the longitudinal direction, and the sample 10S is kept in this environment for at least two hours to allow it to acclimate. Then, while maintaining the temperature at 10°C, the relative humidity is changed in the order of 80%, 24%, and 10%, and the width of the sample 10S at 80% and 10% is measured, and the humidity expansion coefficient β is calculated using the following formula. The width measurement of the sample 10S at 24% humidity is performed to check for any abnormalities in the measurement (especially to confirm that the results of these three measurements are linear), and the measurement result is not used in the following formula.

number

[0111] (Friction coefficient ratio (μB / μA)) The magnetic recording medium 10 preferably has a friction coefficient ratio (μB / μA) of 1.0 to 2.0, more preferably 1.0 to 1.8, and even more preferably 1.0 to 1.6, between the dynamic friction coefficient μA between the magnetic head and surface 13S of magnetic layer 13 of magnetic recording medium 10 when a tension of 0.4 N is applied in the longitudinal direction of magnetic recording medium 10, and the dynamic friction coefficient μB between the magnetic head and surface 13S of magnetic layer 13 of magnetic recording medium 10 when a tension of 1.2 N is applied in the longitudinal direction of magnetic recording medium 10. Having the friction coefficient ratio (μB / μA) within the above numerical range reduces changes in the dynamic friction coefficient due to tension fluctuations during running, thereby stabilizing the running of magnetic recording medium 10.

[0112] The dynamic friction coefficients μA and μB for calculating the friction coefficient ratio (μB / μA) are determined as follows. First, as shown in FIG. 7, a ½-inch wide magnetic recording medium 10 is placed on two cylindrical guide rolls 91 and 92 with a diameter of 1 inch that are arranged parallel to and spaced apart from each other so that the surface 13S of the magnetic layer 13 comes into contact with them. The two guide rolls 91 and 92 are fixed in position relative to each other. FIG. 7 is a schematic diagram illustrating a method for measuring the dynamic friction coefficient.

[0113] Next, the magnetic recording medium 10 is brought into contact with a head block (for recording and reproduction) 93 mounted on an LTO5 drive so that the surface 13S of the magnetic layer 13 is in contact and the embrace angle θ1 [°] is 5.6°. One end of the magnetic recording medium 10 is held by a gripping jig 94 and connected to a movable strain gauge 95, and a weight 96 is suspended from the other end of the magnetic recording medium 10 to apply a tension T0 of 0.4 N. The head block 93 is fixed at a position where the embrace angle θ1 [°] is 5.6°. This also fixes the positional relationship between the guide rolls 91 and 92 and the head block 93.

[0114] Next, the magnetic recording medium 10 is slid 60 mm toward the movable strain gauge 95 at a speed of 10 mm / s relative to the head block 93 using the movable strain gauge 95. The output value (voltage) of the movable strain gauge 95 during this sliding is converted into T[N] based on the linear relationship between the output value and the load that has been acquired in advance (described later). T[N] is acquired 13 times from the start of the 60 mm sliding to the end of the sliding, and the 11 T[N] values ​​excluding the first and last two are simply averaged to obtain T ave [N] is obtained. Then, calculate the dynamic friction coefficient μA using the following formula.

number

[0115] The above-mentioned linear relationship is obtained as follows. That is, the output value (voltage) of the movable strain gauge 95 is obtained when a load of 0.4 N and a load of 1.5 N are applied to the movable strain gauge 95. From the obtained two output values ​​and the two loads, a linear relationship between the output value and the load is obtained. Using this linear relationship, the output value (voltage) from the movable strain gauge 95 during sliding is converted to T [N] as described above.

[0116] The dynamic friction coefficient μB is measured in the same manner as the dynamic friction coefficient μA, except that the tension T0 [N] applied to the other end is set to 1.2 N. From the dynamic friction coefficient μA and the dynamic friction coefficient μB measured as described above, the friction coefficient ratio (μB / μA) is calculated.

[0117] If the coefficient of dynamic friction between the surface 13S of the magnetic layer 13 and the magnetic head when the tension applied to the magnetic recording medium 10 is 0.6 N is μC, the ratio of the coefficient of dynamic friction μC(5) at the fifth run from the start of running to the coefficient of dynamic friction μC(1000) at the 1000th run from the start of running (μC(1000) / μC(5)) is preferably 1.0 to 1.9, more preferably 1.2 to 1.8. If the coefficient of friction ratio (μC(1000) / μC(5)) is 1.0 to 1.9, the change in the coefficient of dynamic friction due to multiple runs can be minimized, thereby stabilizing the running of the magnetic recording medium 10. Here, the magnetic head used is one that is compatible with the magnetic recording medium 10.

[0118] (Friction coefficient ratio (μC(1000) / μC(5))) The dynamic friction coefficient μC(5) and the dynamic friction coefficient μC(1000) for calculating the friction coefficient ratio (μC(1000) / μC(5)) can be calculated as follows.

[0119] Preferably, when the magnetic recording medium 10 is subjected to a tension of 0.6 N in the longitudinal direction and slid back and forth over a magnetic head five times, the kinetic friction coefficient μC(5) at the fifth stroke to the kinetic friction coefficient μC(1000) at the 1000th stroke over the magnetic head 1000 times has a friction coefficient ratio (μC(1000) / μC(5)) of 1.0 to 2.0, more preferably 1.0 to 1.8, and even more preferably 1.0 to 1.6. By keeping the friction coefficient ratio (μC(1000) / μC(5)) within the above range, it is possible to minimize changes in the kinetic friction coefficient over multiple runs, thereby stabilizing the running of the magnetic recording medium 10.

[0120] The dynamic friction coefficient μC(5) and the dynamic friction coefficient μC(1000) for calculating the friction coefficient ratio (μC(1000) / μC(5)) can be calculated as follows. The magnetic recording medium 10 is connected to the movable strain gauge 71 in the same manner as the measurement method for the dynamic friction coefficient μA, except that the tension T0 [N] applied to the other end of the magnetic recording medium 10 is set to 0.6 N. The magnetic recording medium 10 is then slid 60 mm toward the movable strain gauge (forward movement) and 60 mm away from the movable strain gauge (return movement) relative to the head block 74 at 10 mm / s. This back-and-forth movement is repeated 1,000 times. Of these 1,000 back-and-forth movements, 13 strain gauge output values ​​(voltage) are obtained from the start to the end of the 60 mm movement on the fifth forward movement. These are converted to T [N] based on the linear relationship between the output value calculated as the dynamic friction coefficient μA and the load. The 11 values, excluding the first and last two, are simply averaged to calculate Tave [N]. The dynamic friction coefficient μC(5) is calculated using the following formula:

number

[0121] (Moisture content WA) As mentioned above, when the weight of the magnetic recording medium 10 is taken as 1, the moisture content (hereinafter referred to as moisture content WA) of the magnetic recording medium 10 after storage for 24 hours or more in an environment of 23°C and 45% RH is, for example, 0.64% by weight or less. This moisture content WA can be determined by the Karl Fischer method. Measurement of moisture content WA using the Karl Fischer method utilizes the specific reaction between water and an electrolyte (Karl Fischer reagent) primarily composed of iodide ions, sulfur dioxide, and alcohol in a titration cell in the presence of methanol. Measurement of moisture content WA is performed using a combination of a Mitsubishi Chemical Analytech "Trace Moisture Analyzer CA-200" and a "Moisture Vaporizer VA-230." That is, a moisture vaporizer VA-230 (hereinafter simply referred to as VA-230) is connected to a trace moisture analyzer CA-200 (hereinafter simply referred to as CA-200), and the sample is heated in a dry nitrogen gas stream to vaporize the moisture, which is then collected in an electrolyte. The iodine generated by electrolytic oxidation is subjected to a Karl Fischer reaction with the moisture in the sample, and the amount of electricity required until the iodine becomes excessive is measured to quantify the moisture content. The measurement conditions are as follows: Heating temperature: 150℃, Carrier gas type: nitrogen gas, Carrier gas flow rate: 250 ml / min Carrier gas pressure: 0.1Mpa or more and 0.2Mpa or less Reagent (anolyte): Aquamicron (registered trademark of Mitsubishi Chemical Corporation) AX, 150 ml Reagent (catholyte): Aquamicron (registered trademark of Mitsubishi Chemical Corporation) CXU, 10 ml Titration rate: 0.2μg / sec or less, Stirrer rotation speed: Set the adjustment knob to "3" Measurement environment: 23°C, 45% RH

[0122] Specifically, the moisture content WA of the magnetic recording medium 10 is measured as follows. 2 A sample of magnetic recording media of the same size was taken. The magnetic recording medium sample is then stored for at least 24 hours under the measurement environment (23°C, 45% RH), after which the magnetic recording medium sample is weighed. The weighed sample is immediately placed in a vial and the lid is closed. Next, it is confirmed that the liquid tank contains the above-mentioned anolyte and catholyte in the specified amounts. Next, the vial containing the sample is attached to the VA-230. Next, it is confirmed that the carrier gas pressure is at the specified value. Next, after turning on the power to the CA-200, the carrier gas flow rate is adjusted to the specified value by operating the flow rate control valve, and the heater heating temperature is set to the specified value. Next, the stirrer rotation speed adjustment knob is set to "3." Next, the [Titration] button on the CA-200 is pressed to dehydrate the inside of the electrolytic cell, making it ready for moisture content measurement. After confirming that the titration rate is below the specified value and that the heating temperature is at the specified value, press the [Start] button on the CA-200 to begin measuring the moisture content of the sample. Once the moisture content measurement is obtained, divide it by the weight of the sample that was previously weighed to obtain the moisture content, WA.

[0123] [1-3. Manufacturing Method of Magnetic Recording Medium 10] Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a base layer-forming paint is prepared by kneading and dispersing non-magnetic powder, binder, lubricant, etc. in a solvent. Next, a magnetic layer-forming paint is prepared by kneading and dispersing magnetic powder, binder, lubricant, etc. in a solvent. Next, a back layer-forming paint is prepared by kneading and dispersing binder, non-magnetic powder, etc. in a solvent. The following solvents, dispersing devices, and kneading devices can be used, for example, to prepare the magnetic layer-forming paint, base layer-forming paint, and back layer-forming paint.

[0124] Examples of solvents that can be 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.

[0125] Examples of kneading devices that can be used in preparing the above-mentioned coating materials include, but are not limited to, continuous twin-screw kneaders, continuous twin-screw kneaders capable of multi-stage dilution, kneaders, pressure kneaders, roll kneaders, etc. Furthermore, examples of dispersing devices that can be used in preparing the above-mentioned coating materials include, but are not limited to, roll mills, ball mills, horizontal sand mills, vertical sand mills, spike mills, pin mills, tower mills, pearl mills (e.g., the "DCP Mill" manufactured by Eirich), homogenizers, ultrasonic dispersers, etc.

[0126] Next, a base layer forming paint is applied to one main surface 11A of the substrate 11 and dried to form the base layer 12. Subsequently, a magnetic layer forming paint is applied to the base layer 12 and dried to form the magnetic layer 13 on the base layer 12. During drying, it is preferable to magnetically orient the magnetic powder in the thickness direction of the substrate 11, for example, using a solenoid coil. Alternatively, during drying, the magnetic powder may be magnetically oriented in the running direction (longitudinal direction) of the substrate 11, for example, using a solenoid coil, and then magnetically oriented in the thickness direction of the substrate 11. Such magnetic field orientation treatment can improve the degree of perpendicular orientation of the magnetic powder (i.e., squareness ratio S1). After the magnetic layer 13 is formed, a back layer forming paint is applied to the other main surface 11B of the substrate 11 and dried to form the back layer 14. This results in a magnetic recording medium 10.

[0127] 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 at least twice the coercive force of the magnetic powder. 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 powder in the magnetic layer-forming paint. To further increase the squareness ratio S1, it is also effective to magnetize the magnetic powder before the magnetic layer-forming paint enters an orientation device that magnetically orients the magnetic powder. The above methods for adjusting the squareness ratios S1 and S2 may be used alone or in combination.

[0128] The obtained magnetic recording medium 10 is then subjected to a calendering process to smooth the surface 13S of the magnetic layer 13. Next, the calendered magnetic recording medium 10 is wound up into a roll.

[0129] Finally, the magnetic recording medium 10 is cut to a predetermined width (for example, 1 / 2 inch width). In this way, the desired magnetic recording medium 10 is obtained.

[0130] The moisture content of the magnetic recording medium 10 after storage for 24 hours or more in an environment of 23° C. and 45% RH can be adjusted, for example, as follows. (A) In each drying step after applying each paint constituting the underlayer 12, magnetic layer 13, and back layer 14, the heating temperature and heating time are adjusted. (B) After the calendaring process and before cutting, the magnetic recording medium 10 is passed through a drying oven at 100° C. or higher (for example, 110° C.) to volatilize the moisture contained in the magnetic recording medium 10. (C) Before applying each coating material, the substrate 11 alone is run in a vacuum and then rewound onto another reel. (D) Before each coating is applied, the substrate 11 wound on the reel is stored in a vacuum for a predetermined time (for example, 24 hours). It is believed that by performing any of these processes (A) to (D), the moisture adsorbed inside the magnetic recording medium can be desorbed, and a binder, lubricant, etc. can be adsorbed in place of the desorbed portion, thereby adjusting the amount of moisture newly adsorbed into the magnetic recording medium.

[0131] [2-4. Recording / playback device 30] (Configuration of recording / playback device 30) Next, with reference to FIG. 8, the configuration of a recording / reproducing device 30 that records information on the above-mentioned magnetic recording medium 10 and reproduces information from the above-mentioned magnetic recording medium 10 will be described.

[0132] The recording / reproducing device 30 is configured to be able to adjust the tension applied to the magnetic recording medium 10 in the longitudinal direction. The recording / reproducing device 30 is also configured to be able to load a magnetic recording cartridge 1. For ease of explanation, the recording / reproducing device 30 is described here as being configured to be able to load one magnetic recording cartridge 1. However, in the present disclosure, the recording / reproducing device 30 may also be configured to be able to load multiple magnetic recording cartridges 1. As mentioned above, the magnetic recording medium 10 is tape-shaped, and may be, for example, a long magnetic recording tape. The magnetic recording medium 10 may be housed in a housing, for example, wound around a reel inside the magnetic recording cartridge 1. The magnetic recording medium 10 is configured to run in the longitudinal direction during recording and reproduction. The magnetic recording medium 10 may also be configured to be able to record signals at a shortest recording wavelength of preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less. For example, the magnetic recording medium 10 may be used in a recording / reproducing device 30 whose shortest recording wavelength is within the above range. The recording track width may be, for example, 2 μm or less.

[0133] The recording / playback device 30 is connected to information processing devices such as a server 41 and a personal computer (hereinafter referred to as "PC") 42 via a network 43, and is configured to be able to record data supplied from these information processing devices onto the magnetic recording medium cartridge 10A.

[0134] As shown in FIG. 8, the recording / playback device 30 includes a spindle 31, a reel 32, a drive unit 33, a drive unit 34, a plurality of guide rollers 35, a head unit 36, a communication interface (hereinafter referred to as I / F) 37, and a control device 38.

[0135] The spindle 31 is configured so that, for example, a magnetic recording cartridge 1 can be attached thereto. The magnetic recording cartridge 1 conforms to the LTO (Linear Tape Open) standard, and rotatably houses a single reel 3 around which a magnetic recording medium 10 is wound in a cartridge case 2. A V-shaped servo pattern is pre-recorded as a servo signal on the magnetic recording medium 10. The reel 32 is configured so that the leading end of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 1 can be fixed.

[0136] The drive unit 33 is a device that rotates the spindle 31. The drive unit 34 is a device that rotates the reel 32. When recording or reproducing data on the magnetic recording medium 10, the drive units 33 and 34 rotate the spindle 31 and the reel 32, respectively, thereby causing the magnetic recording medium 10 to run. The guide roller 35 is a roller that guides the running of the magnetic recording medium 10.

[0137] The head unit 36 ​​includes a plurality of recording heads for recording data signals on the magnetic recording medium 10, a plurality of reproducing heads for reproducing the data signals recorded on the magnetic recording medium 10, and a plurality of servo heads for reproducing the servo signals recorded on the magnetic recording medium 10. The recording heads may be, for example, ring-type heads, and the reproducing heads may be, for example, magnetoresistive magnetic heads, but the types of recording heads and reproducing heads are not limited to these.

[0138] The I / F 37 is for communicating with information processing devices such as a server 41 and a PC 42 , and is connected to a network 43 .

[0139] The control device 38 controls the entire recording / reproducing device 30. For example, in response to a request from the information processing device, such as the server 41 or the PC 42, the control device 38 records a data signal supplied from the information processing device onto the magnetic recording medium 10 using the head unit 36. In addition, in response to a request from the information processing device, such as the server 41 or the PC 42, the control device 38 reproduces the data signal recorded on the magnetic recording medium 10 using the head unit 36, and supplies the reproduced data signal to the information processing device.

[0140] (Operation of recording / playback device)

[0141] Next, the operation of the recording / reproducing device 30 having the above configuration will be described.

[0142] First, the magnetic recording cartridge 1 is loaded into the recording / reproducing device 30, the leading end of the magnetic recording medium 10 is pulled out and transported to the reel 32 via multiple guide rollers 35 and a head unit 36, and the leading end of the magnetic recording medium 10 is attached to the reel 32.

[0143] Next, when an operating unit (not shown) is operated, spindle drive device 33 and reel drive device 34 are driven under the control of control device 38, and spindle 31 and reel 32 are rotated in the same direction so that magnetic recording medium 10 runs from reel 3 to reel 32. As a result, while magnetic recording medium 10 is wound onto reel 32, information is recorded on magnetic recording medium 10 or information recorded on magnetic recording medium 10 is reproduced by head unit 36.

[0144] When the magnetic recording medium 10 is rewound onto the reel 3, the spindle 31 and the reel 32 are rotated in the opposite direction to that described above, causing the magnetic recording medium 10 to run from the reel 32 to the reel 3. During this rewinding, the head unit 36 ​​also records information onto the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.

[0145] [2-5. Effects] As described above, in this embodiment, the magnetic recording medium 10 has an average thickness of 5.3 μm or less, and the environmental relative humidity at which the temperature expansion coefficient α of the magnetic recording medium 10 is 6.0 ppm / °C or more and 8.0 ppm / °C or less is set to be between 10% RH and 80% RH. Therefore, when the magnetic recording medium 10 is running in the recording / reproducing device 30, for example, the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made closer by adjusting the ambient relative humidity to an appropriate relative humidity between 10% RH and 80% RH. Therefore, even if the environmental temperature changes, the deformation amounts of the magnetic recording medium 10 and the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium 10 and the magnetic head is maintained. Therefore, when recording and reproducing data on the magnetic recording medium 10 while the magnetic recording medium 10 is running in the recording / reproducing device 30, for example, the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin. This allows for improved recording density in the magnetic recording medium 10.

[0146] In this embodiment, the environmental temperature at which the humidity expansion coefficient β of the magnetic recording medium 10 is between −3.0 ppm / °C and 3.0 ppm / °C is set to be between 10°C and 60°C. Therefore, for example, when the magnetic recording medium 10 is running in the recording / reproducing device 30, the humidity expansion coefficient of the magnetic recording medium 10 and the humidity expansion coefficient of the magnetic head can be made closer by adjusting the ambient temperature to an appropriate temperature between 10°C and 60°C. Therefore, even if the environmental humidity changes, the deformation amounts of the magnetic recording medium 10 and the magnetic head are approximately the same, and the relative positional relationship between the magnetic recording medium 10 and the magnetic head is maintained. Therefore, for example, when recording and reproducing data on the magnetic recording medium 10 while the magnetic recording medium 10 is running in the recording / reproducing device 30, the difference between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin. This allows for improved recording density on the magnetic recording medium 10.

[0147] [2-6. Modifications] (Variation 1) In the first embodiment described above, the ε-iron oxide particles 20 ( FIG. 4 ) having a two-layer shell portion 22 are exemplified. However, the magnetic recording medium of the present technology may also include ε-iron oxide particles 20A having a single-layer shell portion 23, as shown in FIG. 9 . The shell portion 23 in the ε-iron oxide particles 20A has a configuration similar to that of the first shell portion 22a. However, from the viewpoint of suppressing deterioration of characteristics, the ε-iron oxide particles 20 having the two-layer shell portion 22 described in the first embodiment are preferable to the ε-iron oxide particles 20A of Modification 1.

[0148] (Variation 2) In the magnetic recording medium 10 according to the embodiment described above, the ε-iron oxide particles 20 have a core-shell structure. However, the ε-iron oxide particles may contain an additive instead of the core-shell structure, or may have a core-shell structure and contain an additive. In this case, a portion of the Fe in the ε-iron oxide particles is substituted with the additive. By including an additive in the ε-iron oxide particles, the coercivity Hc of the entire ε-iron oxide particles 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 of Al (aluminum), Ga (gallium), and In (indium), and even more preferably at least one of Al and Ga.

[0149] Specifically, the ε-iron oxide containing the additive is an ε-Fe2-xMxO3 crystal (where M is a metal element other than iron, preferably a trivalent metal element, more preferably at least one of Al, Ga, and In, and even more preferably at least one of Al and Ga. x is, for example, 0 <x<1である。)である。

[0150] (Variation 3) The magnetic powder of the present disclosure may contain a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles") instead of a powder of ε-iron oxide particles. The hexagonal ferrite particles have, for example, a hexagonal plate shape or a nearly hexagonal plate shape. The hexagonal ferrite preferably contains at least one of Ba (barium), Sr (strontium), Pb (lead), and Ca (calcium), more preferably at least one of Ba and Sr. Specifically, the hexagonal ferrite may be, for example, barium ferrite or strontium ferrite. Barium ferrite may further contain at least one of Sr, Pb, and Ca in addition to Ba. Strontium ferrite may further contain at least one of Ba, Pb, and Ca in addition to Sr.

[0151] More specifically, hexagonal ferrites have the general formula MFe 12 O 19 The alloy has an average composition represented by the formula: where M is, for example, at least one metal selected from Ba, Sr, Pb, and Ca, preferably at least one metal selected from Ba and Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb, and Ca. M may also be a combination of Sr and one or more metals selected from the group consisting of Ba, Pb, and Ca. In the above general formula, part of Fe may be substituted with another metal element.

[0152] When the magnetic powder contains hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The average particle size of the magnetic powder is preferably 25 nm or less, 22 nm or less, 21 nm or less, or even more preferably 20 nm or less. The average particle size of the magnetic powder is, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. Therefore, the average particle size of the magnetic powder containing hexagonal ferrite particles can be, for example, 10 nm to 50 nm, 10 nm to 40 nm, 12 nm to 30 nm, 12 nm to 25 nm, or 15 nm to 22 nm. When the average particle size of the magnetic powder is below the upper limit (for example, 50 nm or less, particularly 30 nm or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high-recording-density magnetic recording medium 10. When the average particle size of the magnetic powder is equal to or greater than the lower limit (for example, 10 nm or greater, preferably 12 nm or greater), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0153] When the magnetic powder includes a powder of hexagonal ferrite particles, the average aspect ratio of the magnetic powder is preferably 1 or more and 3.5 or less, more preferably 1 or more and 3.1 or less, or 2 or more and 3.1 or less, and even more preferably 2 or more and 3 or less. By having the average aspect ratio of the magnetic powder within the above numerical range, aggregation of the magnetic powder can be suppressed, and further, the resistance applied to the magnetic powder when the magnetic powder is vertically oriented in the process of forming the magnetic layer 13 can be suppressed. This can lead to improved vertical orientation of the magnetic powder.

[0154] The average particle size and average aspect ratio of magnetic powder containing hexagonal ferrite particles are determined as follows. First, the magnetic recording medium 10 to be measured is thinned using a method such as FIB (Focused Ion Beam). The thinning is performed along the length (longitudinal direction) of the magnetic tape. The obtained thinned sample is observed in cross section in the thickness direction of the recording layer using a transmission electron microscope (Hitachi High-Technologies H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so as to include the entire recording layer. Next, 50 particles with their sides facing the observation surface are selected from the TEM photograph, and the maximum plate thickness DA of each particle is measured. The maximum plate thicknesses DA thus determined are simply averaged (arithmetic mean) to determine the average maximum plate thickness DAave. Next, the plate diameter DB of each magnetic powder is measured. Here, the plate diameter DB refers to the maximum distance between two parallel lines drawn from all angles so as to tangent to the outline of the magnetic powder (the so-called maximum Feret diameter). Next, the measured plate diameters DB are simply averaged (arithmetic averaged) to determine the average plate diameter DBave.Then, the average particle aspect ratio (DBave / DAave) is calculated from the average maximum plate thickness DAave and the average plate diameter DBave.

[0155] When the magnetic powder comprises a powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 400 nm 3 More than 1800nm 3 The average particle volume of the magnetic powder is 1800 nm or less. 3 When the average particle volume of the magnetic powder is 400 nm or less, it is possible to obtain good electromagnetic conversion characteristics (for example, SNR) required for a high-recording density magnetic recording medium 10. 3 If this is the case, for example, the thermal stability of the magnetic layer 13 is sufficiently ensured, and the recording state of the magnetic layer 13 is maintained in a good condition.

[0156] The average particle volume of the magnetic powder can be calculated as follows: First, the average maximum plate thickness DAave and the average maximum plate diameter DBave are calculated using the above-mentioned method for calculating the average particle size of the magnetic powder. Next, the average particle volume V of the magnetic powder is calculated using the following formula:

number

[0157] According to a particularly preferred embodiment of the present technology, the magnetic powder may be barium ferrite magnetic powder or strontium ferrite magnetic powder, and more preferably barium ferrite magnetic powder. The barium ferrite magnetic powder includes magnetic particles of iron oxide with barium ferrite as the main phase (hereinafter referred to as "barium ferrite particles"). The barium ferrite magnetic powder has high reliability in data recording, for example, because the coercive force does not decrease even in high-temperature and high-humidity environments. From this perspective, barium ferrite magnetic powder is preferred as the magnetic powder.

[0158] When magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness tm [nm] of magnetic layer 13 is preferably 35 nm≦tm≦100 nm, and particularly preferably 80 nm or less. Furthermore, the coercive force Hc measured in the thickness direction (perpendicular direction) of magnetic recording medium 10 is preferably 160 kA / m or more and 280 kA / m or less, more preferably 165 kA / m or more and 275 kA / m or less, and even more preferably 170 kA / m or more and 270 kA / m or less.

[0159] (Variation 4) The magnetic powder may contain a powder of nanoparticles containing Co-containing spinel ferrite (hereinafter referred to as "cobalt ferrite particles") instead of a powder of ε-iron oxide particles. The cobalt ferrite particles preferably have uniaxial anisotropy. The cobalt ferrite particles have, for example, a cubic or nearly cubic shape. The Co-containing spinel ferrite may further contain at least one of Ni, Mn, Al, Cu, and Zn in addition to Co.

[0160] The Co-containing spinel ferrite has an average composition represented by the following formula, for example. Co x M y FeO Z (In formula (1), M is, for example, at least one metal selected from the group consisting of Ni, Mn, Al, Cu, and Zn. x is a value within the range of 0.4≦x≦1.0. y is a value within the range of 0≦y≦0.3. However, x and y satisfy the relationship (x+y)≦1.0. z is a value within the range of 3≦z≦4. A portion of Fe may be substituted with another metal element.)

[0161] When the magnetic powder contains cobalt ferrite particles, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 23 nm or less. When the average particle size of the magnetic powder is 25 nm or less, good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high-recording-density magnetic recording medium 10. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained. When the magnetic powder contains cobalt ferrite particles, the average aspect ratio of the magnetic powder is the same as in the above-mentioned embodiment. The average particle size and average aspect ratio of the magnetic powder can also be calculated using the same calculation method as in the above-mentioned embodiment.

[0162] The average particle volume of the magnetic powder is preferably 15,000 nm 3 Less than 1000 nm, more preferably 3 More than 12000nm 3 The average particle volume of the magnetic powder is 15,000 nm or less. 3 When the average particle size of the magnetic powder is 25 nm or less, the same effect as when the average particle volume of the magnetic powder is 1000 nm or less can be obtained. 3 This provides the same effect as when the average particle size of the magnetic powder is 10 nm or more. The average particle volume of the magnetic powder is calculated in the same manner as in the first embodiment (the method for calculating the average particle volume when the ε iron oxide particles are cubic or nearly cubic).

[0163] The coercive force Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe or more, and more preferably 2600 Oe or more and 3500 Oe or less.

[0164] (Variation 5) The magnetic recording medium of this embodiment may further include a barrier layer 15 provided on at least one surface of the substrate 11, as in the magnetic recording medium 10A shown in FIG. 10 . The barrier layer 15 is a layer for suppressing dimensional changes of the substrate 11 in response to the environment. For example, one cause of such dimensional changes is the hygroscopicity of the substrate 11, and providing the barrier layer 15 can reduce the rate at which moisture penetrates the substrate 11. The barrier layer 15 includes, for example, a metal or a metal oxide. Examples of metals that can be used here include at least one of Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba, Pt, Au, and Ta. Examples of metal oxides that can be used include metal oxides containing one or more of the above metals. More specifically, for example, at least one of Al2O3, CuO, CoO, SiO2, Cr2O3, TiO2, Ta2O5, and ZrO2 can be used. The barrier layer 15 may also contain diamond-like carbon (DLC), diamond, or the like.

[0165] The average thickness of the barrier layer 15 is preferably 20 nm or more and 1000 nm or less, and more preferably 50 nm or more and 1000 nm or less. The average thickness of the barrier layer 15 is determined in the same manner as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is adjusted appropriately depending on the thickness of the barrier layer 15.

[0166] (Variation 6) The magnetic recording medium 10 according to the embodiment described above may be used in a library device. In this case, the library device may include a plurality of recording / reproducing devices 30 according to the embodiment described above.

[0167] 3. Second embodiment (example of magnetic recording cartridge including sputter-type magnetic recording medium) [3-1. Configuration of Magnetic Recording Cartridge 1] The magnetic recording cartridge 1 of this embodiment is the same as the magnetic recording cartridge 1 described in the first embodiment above, except that it includes a sputtered magnetic recording medium 110 instead of the coated magnetic recording medium 10.

[0168] 3-2. Configuration of the magnetic recording medium 110 FIG. 11 schematically illustrates an example cross-sectional configuration of a magnetic recording medium 110. The magnetic recording medium 110 is a long perpendicular magnetic recording medium and has a laminated structure in which multiple layers are stacked as shown in FIG. 11. Specifically, the magnetic recording medium 110 includes a long tape-shaped substrate 111, a first seed layer 113A, a second seed layer 113B, a first underlayer 114A, a second underlayer 114B, and a magnetic layer 115, in that order. Here, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 can be sputtered films formed by a sputtering method, for example.

[0169] The magnetic recording medium 110 may further include a protective film 116 and a lubricating layer 117, in that order, on the magnetic layer 115. The magnetic recording medium 110 may also include a back layer 118 provided on the second major surface of the substrate 111. The magnetic recording medium 110 may also include a soft magnetic underlayer (SUL) 112 provided on the first major surface of the substrate 111.

[0170] Hereinafter, the longitudinal direction of the magnetic recording medium 110 (the longitudinal direction of the substrate 111) is referred to as the machine direction (MD). Here, the machine direction refers to the direction of relative movement of the recording and reproducing head with respect to the magnetic recording medium 110, i.e., the direction in which the magnetic recording medium 110 runs during recording and reproducing.

[0171] The magnetic recording medium 110 is suitable for use as a storage medium for data archives, a field recording density of which is expected to increase in the future. The magnetic recording medium 110 has an areal recording density of 50 Gb / inch, which is 10 times or more that of current coated magnetic recording media for storage. 2 When a general linear recording type data cartridge is constructed using a magnetic recording medium 110 having such a high areal recording density, a large capacity of 100 TB or more can be recorded per magnetic recording cartridge.

[0172] The magnetic recording medium 110 can be suitably used in a recording / reproducing device (a recording / reproducing device for recording and reproducing data) having a ring-type recording head and a giant magnetoresistive (GMR) or tunneling magnetoresistive (TMR) type reproducing head. The magnetic recording medium 110 preferably uses a ring-type recording head as a servo signal write head. A data signal is perpendicularly recorded on the magnetic layer 115 by, for example, a ring-type recording head. A servo signal is perpendicularly recorded on the magnetic layer 115 by, for example, a ring-type recording head.

[0173] For the magnetic recording medium 110, similarly to the magnetic recording medium 10, it is preferable that the environmental relative humidity be between 10% and 80% RH so that the temperature expansion coefficient α of the magnetic recording medium 110 is between 6.0 ppm / °C and 8.0 ppm / °C. In particular, it is preferable that the temperature expansion coefficient α at a relative humidity of 10% RH, the temperature expansion coefficient α at a relative humidity of 40% RH, and the temperature expansion coefficient α at a relative humidity of 80% RH are all between 4.5 ppm / °C and 9.5 ppm / °C. Furthermore, it is preferable that the environmental temperature be between 10°C and 60°C so that the humidity expansion coefficient β of the magnetic recording medium 110 is between -3.0 ppm / °C and 3.0 ppm / °C.

[0174] Furthermore, when the weight of the magnetic recording medium 110 is taken as 1, the moisture content of the magnetic recording medium 110 is preferably, for example, 0.2% by weight or more and 0.64% by weight or less. The moisture content of the magnetic recording medium 110 is particularly preferably 0.3% by weight or less. The moisture content of the magnetic recording medium 110 is the same as the moisture content of the magnetic recording medium 10 of the first embodiment. That is, the moisture content of the magnetic recording medium 110 refers to the moisture content of the magnetic recording medium 110 in a stabilized state in an environment at a temperature of 23°C and a relative humidity of 45% RH. This does not refer to the moisture content of a magnetic recording medium that has been temporarily dried in a special environment, such as a high-temperature vacuum environment. It refers to the moisture content of the magnetic recording medium 110 that has been placed in an environment at a temperature of 23°C and a relative humidity of 45% RH for at least 24 hours. The average thickness of the magnetic recording medium 110 is, for example, 4.0 μm to 5.3 μm, particularly preferably 4.0 μm to 5.3 μm. The total surface area of ​​the magnetic recording medium 110 wound on the reel 3 of the magnetic recording cartridge 1 is, for example, 6.3 m 2 More than 25m 2 less than 12m, more preferably 2 More than 25m 2 less than 15m, and even more preferably 2 More than 25m 2 It is preferable that the total surface area of ​​the magnetic recording medium 110 be equal to or less than the total surface area of ​​the magnetic recording medium 110. The length of the magnetic recording medium 110 wound around the reel 3 of the magnetic recording cartridge 1 is, for example, 1000 m. The total surface area of ​​the magnetic recording medium 110 here is essentially the same as the total surface area of ​​the magnetic recording medium 10. In other words, the total surface area of ​​the magnetic recording medium 110 does not include the area of ​​the surface on the side of the substrate 111 on which the back layer 118 is provided, but refers to the sum of the areas of the surfaces on the side of the substrate 111 on which the magnetic layer 115 is provided. Specifically, it is calculated by multiplying the total length of the magnetic recording medium 110 included in the magnetic recording cartridge 1 by the width of the magnetic recording medium 110. The total surface area of ​​the magnetic recording medium 110 here does not include the area of ​​the surface of the magnetic recording medium 110 corresponding to the region where the magnetic layer 115 is not formed.

[0175] (Base 111) The substrate 111 may have substantially the same configuration as the substrate 11 in the magnetic recording medium 10 of the first embodiment, and therefore a detailed description of the substrate 111 will be omitted.

[0176] (SUL112) The SUL 112 includes a soft magnetic material in an amorphous state. The soft magnetic material includes, for example, at least one of a Co-based material and an Fe-based material. The Co-based material includes, for example, CoZrNb, CoZrTa, or CoZrTaNb. The Fe-based material includes, for example, FeCoB, FeCoZr, or FeCoTa.

[0177] The SUL 112 has, for example, a single-layer structure and is provided directly on the substrate 111. The average thickness of the SUL 112 is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 30 nm or less. The average thickness of the SUL 112 can be determined, for example, using the same method as that used to measure the average thickness of the magnetic layer 13 in the first embodiment. The average thicknesses of the layers other than the SUL 112, i.e., the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115, can also be determined using the same method as that used to measure the average thickness of the magnetic layer 13.

[0178] (First seed layer 113A, second seed layer 113B) The first seed layer 113A includes an alloy containing Ti and Cr and has an amorphous material. The alloy may further contain O (oxygen). This oxygen may be impurity oxygen contained in trace amounts in the first seed layer 113A when the first seed layer 113A is formed by a film formation method such as sputtering. The alloy here refers to at least one of a solid solution, a eutectic, and an intermetallic compound containing Ti and Cr. The amorphous state means that a halo is observed by X-ray diffraction or electron beam diffraction, and the crystal structure of the material constituting the first seed layer 113 cannot be identified.

[0179] The atomic ratio of Ti to the total amount of Ti and Cr contained in first seed layer 113A is preferably 30 atomic % or more and less than 100 atomic %, more preferably 50 atomic % or more and less than 100 atomic %. If the atomic ratio of Ti is less than 30%, the (100) plane of the body-centered cubic lattice (bcc) structure of Cr will become oriented, which may reduce the orientation of first underlayer 114A and second underlayer 114B formed on first seed layer 113A.

[0180] The atomic ratio of Ti is determined as follows. While ion milling the magnetic recording medium 110 from the magnetic layer 115 side, a depth profile analysis (depth profile measurement) of the first seed layer 113A is performed by Auger Electron Spectroscopy (AES). Next, the average composition (average atomic ratio) of Ti and Cr in the film thickness direction is determined from the obtained depth profile. Next, the atomic ratio of Ti is determined using the determined average composition of Ti and Cr.

[0181] When first seed layer 113A contains Ti, Cr, and O, the atomic ratio of O to the total amount of Ti, Cr, and O contained in first seed layer 113A is preferably 15 atomic % or less, more preferably 10 atomic % or less. If the atomic ratio of O exceeds 15 atomic %, TiO crystals are generated, which may affect the crystal nucleation of first underlayer 114A and second underlayer 114B formed on first seed layer 113A, and may reduce the orientation of first underlayer 114A and second underlayer 114B. The atomic ratio of O is determined using the same analytical method as for the atomic ratio of Ti.

[0182] The alloy contained in first seed layer 113A may further contain an element other than Ti and Cr as an additional element, which may be, for example, one or more elements selected from the group consisting of Nb, Ni, Mo, Al, and W.

[0183] The average thickness of first seed layer 113A is preferably 1 nm or more and 15 nm or less, and more preferably 1 nm or more and 10 nm or less.

[0184] Second seed layer 113B contains, for example, NiW or Ta, and is in a crystalline state. The average thickness of second seed layer 113B is preferably 2 nm or more and 20 nm or less, and more preferably 3 nm or more and 15 nm or less.

[0185] The first seed layer 113A and the second seed layer 113B are not seed layers provided for the purpose of crystal growth of the first underlayer 114A and the second underlayer 114B, but are seed layers that improve the vertical orientation of the first underlayer 114A and the second underlayer 114B.

[0186] (First Underlayer 114A and Second Underlayer 114B) The first underlayer 114A and the second underlayer 114B preferably have a crystal structure similar to that of the magnetic layer 115. When the magnetic layer 115 contains a Co-based alloy, the first underlayer 114A and the second underlayer 114B preferably contain a material with a hexagonal close-packed (hcp) structure similar to that of the Co-based alloy, with the c-axis of the structure oriented perpendicular to the film surface (i.e., in the film thickness direction). This is because it enhances the orientation of the magnetic layer 115 and can relatively well match the lattice constants of the second underlayer 114B and the magnetic layer 115. As the material with the hexagonal close-packed (hcp) structure, a material containing Ru is preferably used, specifically Ru alone or a Ru alloy. Examples of Ru alloys include Ru alloy oxides such as Ru-SiO2, Ru-TiO2, and Ru-ZrO2, and the Ru alloy may be any one of these. In addition to the above, materials having a hexagonal close-packed (hcp) structure that constitute the first underlayer 114A and the second underlayer 114B include, for example, Co (100-y) Cr y (However, the range is 35≦y≦45.) Co-based alloys such as [Co (100-y) Cr y ](100-z) (MO2) z (where y is within the range of 35≦y≦45, z is within the range of 10, and M is Si or Ti).

[0187] As described above, the first underlayer 114A and the second underlayer 114B can be made of the same material. However, the intended effects of the first underlayer 114A and the second underlayer 114B are different. Specifically, the second underlayer 114B has a film structure that promotes the granular structure of the magnetic layer 115 that is the layer thereover, while the first underlayer 114A has a film structure that has high crystalline orientation. To achieve such a film structure, it is preferable to use different film formation conditions, such as sputtering conditions, for the first underlayer 114A and the second underlayer 114B.

[0188] The average thickness of the first underlayer 114A is preferably 3 nm to 15 nm, more preferably 5 nm to 10 nm. The average thickness of the second underlayer 114B is preferably 7 nm to 100 nm, more preferably 40 nm to 80 nm.

[0189] (magnetic layer) The magnetic layer (also referred to as the recording layer) 115 can be a perpendicular magnetic recording layer in which the magnetic material is perpendicularly oriented. From the viewpoint of improving recording density, the magnetic layer 115 is preferably a granular magnetic layer containing a Co-based alloy. This granular magnetic layer is composed of ferromagnetic crystal grains containing a Co-based alloy and nonmagnetic grain boundaries (nonmagnetic materials) surrounding the ferromagnetic crystal grains. More specifically, this granular magnetic layer is composed of columns (columnar crystals) containing a Co-based alloy and nonmagnetic grain boundaries (e.g., oxides such as SiO2) surrounding the columns and magnetically separating them. This structure allows the magnetic layer 115 to be configured so that each column is magnetically separated.

[0190] The Co-based alloy has a hexagonal close-packed (hcp) structure, with its c-axis oriented perpendicular to the film surface (film thickness direction). The Co-based alloy is preferably a CoCrPt-based alloy containing at least Co, Cr, and Pt. The CoCrPt-based alloy may further contain an additive element. The additive element may be, for example, one or more elements selected from the group consisting of Ni, Ta, etc.

[0191] The non-magnetic grain boundaries surrounding the ferromagnetic crystal grains contain a non-magnetic metal material. Here, metal includes semi-metal. For example, at least one of a metal oxide and a metal nitride can be used as the non-magnetic metal material, and from the viewpoint of maintaining the granular structure more stably, it is preferable to use a metal oxide. Examples of metal oxides include metal oxides containing at least one element selected from the group consisting of Si, Cr, Co, Al, Ti, Ta, Zr, Ce, Y, and Hf, and metal oxides containing at least Si oxide (i.e., SiO2) are preferred. Specific examples of metal oxides include SiO2, Cr2O3, C Examples of the metal nitride include SiN, TiN, and AlN. Examples of the metal nitride include SiN, TiN, and AlN.

[0192] It is preferable that the CoCrPt alloy contained in the ferromagnetic crystal grains and the Si oxide contained in the non-magnetic grain boundaries have an average composition as shown in the following formula (1), because this can suppress the influence of the demagnetizing field and realize a saturation magnetization Ms that can ensure sufficient reproduction output, thereby further improving the recording and reproduction characteristics. (CoxPtyCr100-xy)100-z-(SiO2)z···(1) (In formula (1), x, y, and z are values ​​within the ranges of 69≦x≦75, 10≦y≦16, and 9≦z≦12, respectively.)

[0193] The above composition can be determined as follows: While ion milling the magnetic recording medium 110 from the magnetic layer 115 side, depth direction analysis of the magnetic layer 115 is performed by AES to determine the average composition (average atomic ratio) of Co, Pt, Cr, Si, and O in the film thickness direction.

[0194] The average thickness tm [nm] of the magnetic layer 115 is preferably 9 nm≦tm≦90 nm, more preferably 9 nm≦tm≦20 nm, and even more preferably 9 nm≦tm≦15 nm. When the average thickness tm of the magnetic layer 115 is within the above range, the electromagnetic conversion characteristics can be improved.

[0195] The magnetic powder in the magnetic layer 115 formed by sputtering has an average particle volume of 350 nm 3 More than 1800nm 3 It is desirable that the average particle volume of the magnetic powder in the magnetic layer 115 is determined by first exposing the surface of the magnetic layer 115 by etching and observing the surface using a TEM. From the observed image, the diameter R115 of the magnetic particles on the surface of the magnetic layer 115 is measured. Next, a cross section of the magnetic layer 115 is formed using, for example, an FIB, and the thickness t115 of the magnetic layer 115 is measured from the image of the cross section obtained using the TEM. The particle volume is then determined using the following formula: (particle volume) = ((R115) / 2) 2 ×π×(t115) This is repeated at several points, and the average value of the particle volumes is calculated.

[0196] (protective layer) The protective layer 116 includes, for example, a carbon material or silicon dioxide (SiO2), and preferably includes a carbon material from the viewpoint of the film strength of the protective layer 116. Examples of the carbon material include graphite, diamond-like carbon (DLC), and diamond.

[0197] (lubricating layer) The lubricating layer 117 contains at least one type of lubricant. The lubricating layer 117 may further contain various additives, such as a rust inhibitor, as necessary. The lubricant has at least two carboxyl groups and one ester bond and contains at least one type of carboxylic acid compound represented by the following general formula (1). The lubricant may further contain a type of lubricant other than the carboxylic acid compound represented by the following general formula (1). General formula (1): [ka] (In the formula, Rf is an unsubstituted or substituted, saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group, Es is an ester bond, and R is, although it may be absent, an unsubstituted or substituted, saturated or unsaturated hydrocarbon group.)

[0198] The carboxylic acid compound is preferably one represented by the following general formula (2) or (3). General formula (2): [ka] (In the formula, Rf is an unsubstituted or substituted, saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group.) General formula (3): [ka] (In the formula, Rf is an unsubstituted or substituted, saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group.)

[0199] The lubricant preferably contains one or both of the carboxylic acid compounds represented by the above general formulas (2) and (3).

[0200] When a lubricant containing a carboxylic acid compound represented by general formula (1) is applied to magnetic layer 115 or protective layer 116, a lubricating effect is exhibited due to the cohesive force between the hydrophobic fluorine-containing hydrocarbon groups or hydrocarbon groups Rf. When the Rf group is a fluorine-containing hydrocarbon group, it preferably has a total of 6 to 50 carbon atoms and a total of 4 to 20 carbon atoms in the fluorinated hydrocarbon group. The Rf group may be, for example, a saturated or unsaturated linear, branched, or cyclic hydrocarbon group, but is preferably a saturated linear hydrocarbon group.

[0201] For example, when the Rf group is a hydrocarbon group, it is desirable that it is a group represented by the following general formula (4). General formula (4): [ka] (However, in general formula (4), l is an integer selected from the range of 8 to 30, more preferably 12 to 20.)

[0202] Furthermore, when the Rf group is a fluorine-containing hydrocarbon group, it is preferably a group represented by the following general formula (5). General formula (5): [ka] (In the general formula (5), m and n are integers independently selected from the following ranges: m=2 to 20, n=3 to 18, and more preferably m=4 to 13, n=3 to 10.)

[0203] The fluorohydrocarbon groups may be concentrated at one location within the molecule as described above, or may be dispersed as shown in the following general formula (6), and may be -CF3 or -CF2-, or may be -CHF2 or -CHF-, etc. General formula (6): [ka] (However, in general formulas (5) and (6), n1+n2=n, and m1+m2=m.)

[0204] The reason for limiting the number of carbon atoms in the general formulas (4), (5), and (6) as above is that if the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (l or the sum of m and n) is equal to or greater than the lower limit, the length becomes appropriate, the cohesive force between the hydrophobic groups is effectively exerted, good lubricating action is exhibited, and friction and wear resistance are improved. On the other hand, if the number of carbon atoms is equal to or less than the upper limit, the solubility of the lubricant composed of the carboxylic acid compound in the solvent is maintained good.

[0205] In particular, when the Rf groups in the general formulae (1), (2), and (3) contain a fluorine atom, this is effective in reducing the coefficient of friction and further improving running performance, etc. However, it is preferable to provide a hydrocarbon group between the fluorine-containing hydrocarbon group and the ester bond to separate the fluorine-containing hydrocarbon group from the ester bond, thereby ensuring the stability of the ester bond and preventing hydrolysis.

[0206] The Rf group may also have a fluoroalkyl ether group or a perfluoropolyether group.

[0207] The R group in general formula (1) may not be present, but if present, it is preferably a hydrocarbon chain with a relatively small number of carbon atoms.

[0208] Furthermore, the Rf group or the R group contains one or more elements selected from nitrogen, oxygen, sulfur, phosphorus, and halogen as constituent elements, and may further have a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, an ester bond, or the like in addition to the functional groups described above.

[0209] Specifically, the carboxylic acid compound represented by general formula (1) is preferably at least one of the compounds shown below. That is, the lubricant preferably contains at least one of the compounds shown below. CF3(CF2)7(CH2) 10 COOCH(COOH)CH2COOH CF3(CF2)3(CH2) 10 COOCH(COOH)CH2COOH C 17 H 35 COOCH(COOH)CH2COOH CF3(CF2)7(CH2)2OCOCH2CH(C 18 H 37 )COOCH(COOH)CH2COOH CF3(CF2)7COOCH(COOH)CH2COOH CHF2(CF2)7COOCH(COOH)CH2COOH CF3(CF2)7(CH2)2OCOCH2CH(COOH)CH2COOH CF3(CF2)7(CH2)6OCOCH2CH(COOH)CH2COOH CF3(CF2)7(CH2) 11 OCOCH2CH(COOH)CH2COOH CF3(CF2)3(CH2)6OCOCH2CH(COOH)CH2COOH C 18 H 37 OCOCH2CH(COOH)CH2COOH CF3(CF2)7(CH2)4COOCH(COOH)CH2COOH CF3(CF2)3(CH2)4COOCH(COOH)CH2COOH CF3(CF2)3(CH2)7COOCH(COOH)CH2COOH CF3(CF2)9(CH2) 10 COOCH(COOH)CH2COOH CF3(CF2)7(CH2) 12 COOCH(COOH)CH2COOH CF3(CF2)5(CH2) 10 COOCH(COOH)CH2COOH CF3(CF2)7CH(C9H 19 )CH2CH=CH(CH2)7COOCH(COOH)CH2COOH CF3(CF2)7CH(C6H 13 )(CH2)7COOCH(COOH)CH2COOH CH3(CH2)3(CH2CH2CH(CH2CH2(CF2)9CF3))2(CH2)7COOCH(COOH)CH2COOH

[0210] The carboxylic acid compound represented by general formula (1) is soluble in non-fluorinated solvents that have a low environmental impact, and has the advantage that it can be applied by coating, immersion, spraying, etc. using general-purpose solvents such as hydrocarbon solvents, ketone solvents, alcohol solvents, and ester solvents. Specific examples of the general-purpose solvents include hexane, heptane, octane, decane, dodecane, benzene, toluene, xylene, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, diethyl ether, tetrahydrofuran, dioxane, and cyclohexanone.

[0211] When the protective layer 116 contains a carbon material, applying the above-mentioned carboxylic acid compound as a lubricant onto the protective layer 116 causes two carboxyl groups and at least one ester bond group, which are the polar bases of the lubricant molecule, to be adsorbed onto the protective layer 116, and the cohesive force between the hydrophobic groups allows the formation of a particularly durable lubricating layer 117.

[0212] In addition, the lubricant may not only be retained as a lubricating layer 117 on the surface of the magnetic recording medium 110 as described above, but may also be contained and retained in layers such as the magnetic layer 115 and protective layer 116 that constitute the magnetic recording medium 110.

[0213] (Back layer) The back layer 118 can have the same configuration as the back layer 14 in the first embodiment.

[0214] The explanations regarding the physical properties of magnetic recording medium 10 and the methods for measuring them described in the first embodiment also apply to the physical properties of magnetic recording medium 110 of this embodiment and the methods for measuring them. For example, the average thickness of magnetic recording medium 110 and the methods for measuring it are the same as the average thickness of magnetic recording medium 10. The same applies to parameters representing other physical properties, such as coercive force Hc, squareness ratio, and moisture content WA.

[0215] [3-3. Configuration of the sputtering equipment] An example of the configuration of a sputtering apparatus 120 used in manufacturing the magnetic recording medium 110 will be described below with reference to FIG. 12. The sputtering apparatus 120 is a continuous winding sputtering apparatus used to form the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115. As shown in FIG. 12, the sputtering apparatus 120 includes a film formation chamber 121, a drum 122 which is a metal can (rotating body), cathodes 123a-123f, a supply reel 124, a take-up reel 125, and a plurality of guide rollers 127a-127c and 128a-128c. The sputtering apparatus 120 is, for example, a DC (direct current) magnetron sputtering type apparatus, but the sputtering type is not limited to this type.

[0216] The film formation chamber 121 is connected to a vacuum pump (not shown) via an exhaust port 126, and the atmosphere inside the film formation chamber 121 is set to a predetermined vacuum level by this vacuum pump. A rotatable drum 122, a supply reel 124, and a take-up reel 125 are arranged inside the film formation chamber 121. A plurality of guide rollers 127a to 127c are provided inside the film formation chamber 121 to guide the transport of the base layer 111 between the supply reel 124 and the drum 122, and a plurality of guide rollers 128a to 128c are provided inside the film formation chamber 121 to guide the transport of the base layer 111 between the drum 122 and the take-up reel 125. During sputtering, the base layer 111 unwound from the supply reel 124 is wound onto the take-up reel 125 via the guide rollers 127a to 127c, the drum 122, and the guide rollers 128a to 128c. The drum 122 has a cylindrical shape, and the long base layer 111 is transported along the cylindrical circumferential surface of the drum 122. The drum 122 is provided with a cooling mechanism (not shown), and is cooled to, for example, about −20° C. during sputtering. Inside the film formation chamber 121, multiple cathodes 123a to 123f are arranged facing the circumferential surface of the drum 122. Targets are set on each of these cathodes 123a to 123f. Specifically, targets for forming the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are set on the cathodes 123a, 123b, 123c, 123d, 123e, and 123f, respectively. These cathodes 123a to 123f simultaneously deposit multiple types of films, namely, SUL 112, first seed layer 113A, second seed layer 113B, first underlayer 114A, second underlayer 114B, and magnetic layer 115.

[0217] In the sputtering apparatus 120 having the above-described configuration, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 can be successively deposited by the roll-to-roll method.

[0218] 3-4. Manufacturing Method of Magnetic Recording Medium 110 The magnetic recording medium 110 can be manufactured, for example, as follows.

[0219] First, using the sputtering apparatus 120 shown in FIG. 12, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are sequentially deposited on the surface of the base layer 111. Specifically, the deposition is performed as follows. First, the deposition chamber 121 is evacuated to a predetermined pressure. Then, while a process gas such as Ar gas is introduced into the deposition chamber 121, the targets set on the cathodes 123a to 123f are sputtered. As a result, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are sequentially deposited on the surface of the traveling base layer 111.

[0220] The atmosphere in film formation chamber 121 during sputtering is set to, for example, about 1×10 Pa to 5×10 Pa. The film thickness and characteristics of SUL 112, first seed layer 113A, second seed layer 113B, first underlayer 114A, second underlayer 114B, and magnetic layer 115 can be controlled by adjusting the tape line speed for winding base layer 111, the pressure of process gas such as Ar gas introduced during sputtering (sputtering gas pressure), input power, etc.

[0221] Next, the protective layer 116 is formed on the magnetic layer 115. The protective layer 116 can be formed by, for example, chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0222] Next, a coating material for forming the back layer is prepared by kneading and dispersing a binder, inorganic particles, a lubricant, etc. in a solvent. Next, the coating material for forming the back layer is applied to the rear surface of the base layer 111 and dried, thereby forming the back layer 118 on the rear surface of the base layer 111.

[0223] Next, for example, a lubricant is applied onto the protective layer 116 to form a lubricating layer 117. Various methods, such as gravure coating and dip coating, can be used to apply the lubricant. Next, if necessary, the magnetic recording medium 110 is cut to a predetermined width. In this manner, the magnetic recording medium 110 shown in FIG. 11 is obtained.

[0224] [3-5. Effects] In this embodiment, the magnetic recording medium 110 has an average thickness of 5.3 μm or less, and the environmental relative humidity at which the temperature expansion coefficient α of the magnetic recording medium 110 is 6.0 ppm / ° C. or more and 8.0 ppm / ° C. or less is set to be between 10% RH and 80% RH. Therefore, the same effects as those of the magnetic recording medium 10 of the first embodiment can be expected.

[0225] [3-6. Modifications] The magnetic recording medium 110 may further include an underlayer between the substrate 111 and the SUL 112. Because the SUL 112 is amorphous, it does not promote epitaxial growth of layers formed on the SUL 112. However, the SUL 112 is required not to disturb the crystalline orientation of the first underlayer 114A and the second underlayer 114B formed on the SUL 112. To achieve this, it is preferable for the soft magnetic material to have a fine structure that does not form columns. However, if the release of gases such as moisture from the substrate 111 has a significant effect, the soft magnetic material may coarsen, potentially disturbing the crystalline orientation of the first underlayer 114A and the second underlayer 114B formed on the SUL 112. To suppress the effect of the release of gases such as moisture from the substrate 111, it is preferable to provide an underlayer that contains an alloy containing Ti and Cr and is amorphous between the substrate 111 and the SUL 112, as described above. As a specific configuration of this underlayer, the same configuration as that of the first seed layer 113A can be adopted.

[0226] The magnetic recording medium 110 does not necessarily have to include at least one of the second seed layer 113B and the second underlayer 114B, but from the viewpoint of improving the SNR, it is more preferable to include both the second seed layer 113B and the second underlayer 114B.

[0227] The magnetic recording medium 110 may be provided with an APC-SUL (Antiparallel Coupled SUL) instead of the SUL 112 having a single-layer structure.

[0228] <4. Example> The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0229] In the following examples and comparative examples, the temperature expansion coefficient α, humidity expansion coefficient β, average thickness of the substrate, average thickness of the magnetic recording medium, arithmetic mean roughness Ra of the surface of the magnetic layer, and average particle volume of the magnetic powder are values ​​determined by the measurement method described in the above-mentioned embodiment.

[0230] [Example 1] A magnetic recording medium as Example 1 was obtained as follows.

[0231] (Preparation process of paint for forming magnetic layer) The magnetic layer-forming paint was prepared as follows. First, a first composition having the following formulation was kneaded using an extruder. Next, the kneaded first composition and a second composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, further sand mill mixing was performed and filtering was carried out to prepare the magnetic layer-forming paint.

[0232] (First composition) Barium ferrite nanoparticle powder (average particle volume V is 1600nm 3 ):100 parts by mass Vinyl chloride resin (30% by mass in cyclohexanone solution): 52.0 parts by mass (degree of polymerization 300, Mn=10,000, contains polar groups OSOK=0.07 mmol / g and secondary OH=0.3 mmol / g) ·Aluminum oxide powder: 5 parts by mass (α-Al2O3, average particle size 0.2μm) Carbon black: 2 parts by weight (manufactured by Tokai Carbon Co., Ltd., product name: Seest TA)

[0233] (Second composition) Vinyl chloride resin: 3.7 parts by mass (resin solution: resin content 30% by mass, cyclohexanone 70% by mass) n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 121.3 parts by mass Toluene: 121.3 parts by mass Cyclohexanone: 60.7 parts by mass

[0234] Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) and 2 parts by mass of myristic acid were added as a curing agent to the magnetic layer-forming coating material prepared as described above.

[0235] (Preparation process of paint for forming base layer) The paint for forming the primer layer was prepared as follows. First, the third composition having the following composition was kneaded using an extruder. Next, the kneaded third composition and the fourth composition having the following composition were added to a stirring tank equipped with a disperser and premixed. Subsequently, further mixing was performed using a sand mill and filtering was performed to prepare the paint for forming the primer layer.

[0236] (Third composition) ·Acicular iron oxide powder: 100 parts by mass (α-Fe2O3, average major axis length 0.15μm) Vinyl chloride resin: 55.6 parts by mass (resin solution: 30% by mass resin, 70% by mass cyclohexanone) Carbon black: 10 parts by weight (average particle size 20 nm)

[0237] (4th composition) Polyurethane resin UR8200 (manufactured by Toyobo): 18.5 parts by weight n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 108.2 parts by mass Toluene: 108.2 parts by mass Cyclohexanone: 18.5 parts by mass

[0238] Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) as a curing agent and 2 parts by mass of myristic acid were added to the coating material for forming the undercoat layer prepared as described above.

[0239] (Preparation process of paint for forming back layer) The coating material for forming a back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the coating material for forming a back layer. Carbon black (manufactured by Asahi Carbon Co., Ltd., product name: #80): 100 parts by weight Polyester polyurethane: 100 parts by weight (Nippon Polyurethane Co., Ltd., product name: N-2304) Methyl ethyl ketone: 500 parts by weight Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass

[0240] (Film forming process) Using the coating material prepared as described above, an underlayer with an average thickness of 0.6 μm and a magnetic layer with an average thickness tm of 90 nm were formed on a polymer film substrate as follows. The polymer film used was a PEN (polyethylene naphthalate) film with an average thickness of 4.4 μm. First, a coating material for forming an underlayer was applied to the polymer film and dried, forming an underlayer on the polymer film. Next, a coating material for forming a magnetic layer was applied to the underlayer and dried, forming a magnetic layer on the underlayer. During drying of the coating material for forming a magnetic layer, a solenoid coil was used to magnetically orient the magnetic powder in the thickness direction of the film. The application time of the magnetic field to the coating material for forming a magnetic layer was adjusted to set the squareness ratio S2 in the thickness direction (perpendicular direction) of the magnetic recording medium to 65%.

[0241] Next, a back layer with an average thickness tb of 0.25 μm was applied to the polymer film on which the underlayer and magnetic layer were formed and dried. The polymer film on which the underlayer, magnetic layer, and back layer were formed was then subjected to a curing process. Subsequently, a calendering process was performed to smooth the surface of the magnetic layer. The calendering conditions (temperature) were adjusted so that the interlayer friction coefficient μ between the magnetic surface and the back surface was approximately 0.5, and then the film was subjected to a second curing process, resulting in a magnetic recording medium with an average thickness tT of 5.2 μm.

[0242] (Cutting process) The magnetic recording medium obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining the desired long magnetic recording medium (average thickness 5.2 μm) as Example 1.

[0243] The magnetic recording media obtained in Example 1 had a temperature expansion coefficient α of 3.2 ppm / °C (10% RH), 5.1 ppm / °C (40% RH), and 7.5 ppm / °C (80% RH), a humidity expansion coefficient β of 7.3 ppm / % RH (10°C), 8.6 ppm / % RH (35°C), and 10.4 ppm / % RH (60°C), and the surface roughness Ra of the magnetic layer was 1.8 nm. The measurement results of the characteristic values ​​of these magnetic recording media are shown in Table 1. The configuration of the magnetic recording media is also shown in Table 2.

[0244] [Table 1]

[0245] [Table 2]

[0246] Furthermore, the temperature expansion coefficient α is also shown in FIG. 13, and the humidity expansion coefficient β is also shown in FIG.

[0247] The indicators P, Q, R, and Q+R shown in Table 1 are all parameters related to the amount of variation in the track width dimension of the magnetic recording medium relative to the magnetic head due to changes in the temperature and humidity environment, i.e., the amount of variation in the width of the magnetic recording medium when based on the position of the magnetic head; the smaller the value, the smaller the amount of variation in width.

[0248] Specifically, the index P is expressed by the following formula. P = 50[℃] × |(CTH) - (CTP)| Here, CTH represents the temperature expansion coefficient of the magnetic head that performs recording and reproduction on this magnetic recording medium, and CTP represents the temperature expansion coefficient (ppm / °C) of the magnetic recording medium that is closest to the temperature expansion coefficient (ppm / °C) of the magnetic head among the temperature expansion coefficients of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH. The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C to 8.0 ppm / °C, for example 7.0 ppm / °C, in a relative humidity environment of 10% RH to 80% RH.

[0249] When the number of servo bands SB on the magnetic recording medium is 5, it is desirable that the index P be 70 ppm or less. This is because, for example, as shown in Table 3, when the number of servo bands SB on the magnetic recording medium is 5, the data band width is 2868 μm, and if the index P is 70 ppm or less, the variation in the width of the magnetic recording medium relative to the position of the magnetic head can be kept to 0.1 μm or less. In other words, when the number of servo bands SB on the magnetic recording medium is 5, if the index P is 70 ppm or less, the off-track margin can be reduced to 0.1 μm, which can contribute to improving the recording density. In Example 1, the index P is 0 ppm. Therefore, according to the magnetic recording medium of Example 1, it was found that when the number of servo bands SB is 5 or less, the variation in the width of the magnetic recording medium due to the temperature and humidity environment can be kept to 0.1 μm or less.

[0250] [Table 3]

[0251] [Example 2] A magnetic recording medium as Example 2 was obtained as follows.

[0252] (SUL film formation process) First, a PEN film having an average thickness of 4.0 μm was prepared as a substrate, and a CoZrNb layer having an average thickness of 10 nm was formed as an SUL on the surface of the PEN film under the following film formation conditions. Coating method: DC magnetron sputtering method Target: CoZrNb target Gas type: Ar Gas pressure: 0.1 Pa

[0253] (First seed layer formation process) Next, a TiCr layer having an average thickness of 5 nm was formed as a first seed layer on the CoZrNb layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: TiCr target ·Ultimate vacuum level: 5×10-5Pa Gas type: Ar Gas pressure: 0.5Pa

[0254] (Second seed layer formation process) Next, a NiW layer having an average thickness of 10 nm was formed as a second seed layer on the TiCr layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: NiW target ·Ultimate vacuum level: 5×10-5Pa Gas type: Ar Gas pressure: 0.5Pa

[0255] (First Underlayer Forming Process) Next, a Ru layer having an average thickness of 10 nm was formed as a first underlayer on the NiW layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: Ru target Gas type: Ar Gas pressure: 0.5Pa

[0256] (Second Underlayer Forming Process) Next, a Ru layer having an average thickness of 20 nm was formed as a second underlayer on the Ru layer under the following film-forming conditions: The film was formed. Sputtering method: DC magnetron sputtering method Target: Ru target Gas type: Ar Gas pressure: 1.5Pa

[0257] (Magnetic layer deposition process) Next, a (CoCrPt)-(SiO2) layer with an average thickness of 9 nm was formed as a magnetic layer on the Ru layer under the following film formation conditions. Coating method: DC magnetron sputtering method Target: (CoCrPt)-(SiO2) target Gas type: Ar Gas pressure: 1.5Pa

[0258] (Protective layer deposition process) Next, a carbon layer having an average thickness of 5 nm was formed as a protective layer on the magnetic layer under the following film formation conditions. Coating method: DC magnetron sputtering method Target: Carbon target Gas type: Ar Gas pressure: 1.0Pa

[0259] (Lubrication layer formation process) Next, a lubricant was applied onto the protective layer to form a lubricating layer.

[0260] (Back layer deposition process) Next, a back layer coating material was applied to the surface of the substrate opposite the magnetic layer and dried to form a back layer with an average thickness tb of 0.3 μm, thereby obtaining a magnetic recording medium with an average thickness tT of 4.4 μm.

[0261] (Cutting process) The magnetic recording medium obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining the desired long magnetic recording medium (average thickness 4.4 μm) as Example 2.

[0262] As shown in Table 1, Figures 13 and 14, the magnetic recording medium obtained in Example 2 had a temperature expansion coefficient α of 4.9 ppm / °C (10% RH), 5.3 ppm / °C (40% RH), and 6.0 ppm / °C (80% RH), a humidity expansion coefficient β of -0.6 ppm / % RH (10°C), -0.8 ppm / % RH (35°C), and 0.1 ppm / % RH (60°C), and the surface roughness Ra of the magnetic layer was 2.6 nm.

[0263] Specifically, the index Q shown in Table 1 is expressed by the following formula. Q = 50[℃] × |(CTH) - (CTQ)| Here, CTH represents the temperature expansion coefficient of the magnetic head that records and reproduces data on this magnetic recording medium, and CTQ represents the temperature expansion coefficient of the magnetic recording medium that deviates most from the temperature expansion coefficient of the magnetic head in a relative humidity environment of 10% RH or more and 80% RH or less.

[0264] When the index Q is, for example, 140 ppm or less, to ensure an off-track margin of 0.1 μm during recording and reproduction operations, the number of servo bands SB on the magnetic recording medium needs to be 9 or more, as shown in Table 4. When the number of servo bands SB on the magnetic recording medium is 9, the data band width is 1386 μm, so if the index Q is 140 ppm or less, the variation in the width of the magnetic recording medium will be 0.1 μm or less.

[0265] [Table 4]

[0266] In addition, the index R shown in Table 1 is specifically expressed by the following formula. R = 70[%RH] × |(CHH) - (CHR)| Here, CHH represents the humidity expansion coefficient [ppm / %RH] of the magnetic head that records and plays back on this magnetic recording medium, and CHR represents the humidity expansion coefficient [ppm / %RH] of the magnetic recording medium that deviates most from the humidity expansion coefficient of the magnetic head in a temperature environment of 10°C or higher and 60°C or lower.

[0267] When the index R is, for example, 280 ppm or less, to ensure an off-track margin of 0.1 μm during recording and reproduction operations, the number of servo bands SB on the magnetic recording medium needs to be 17 or more, as shown in Table 5. When the number of servo bands SB on the magnetic recording medium is 17, the data band width is 691 μm, so if the index R is 280 ppm or less, the variation in the width of the magnetic recording medium will be 0.1 μm or less.

[0268] [Table 5]

[0269] Furthermore, when the absolute value |Q+R| of the index Q+R shown in Table 1 is, for example, 200 ppm or less, to ensure an off-track margin of 0.1 μm during recording and reproduction operations, the number of servo bands SB on the magnetic recording medium needs to be 13 or more, as shown in Table 6. When the number of servo bands SB on the magnetic recording medium is 13, the data band width is 938 μm, so if the absolute value of the index Q+R is 200 ppm or less, the variation in the width of the magnetic recording medium will be 0.1 μm or less.

[0270] [Table 6]

[0271] In Example 2, the index P is 50 ppm, the index Q is 105 ppm, the index R is 56 ppm, and the absolute value of the index Q+R is 161 ppm. Therefore, according to the magnetic recording medium of Example 2, it was found that if the number of servo bands SB is 17 or less, the fluctuation in the width of the magnetic recording medium due to the temperature and humidity environment can be suppressed to 0.1 μm or less.

[0272] [Example 3] A magnetic recording medium with an average thickness of 4.4 μm was fabricated using SPALTAN (a registered trademark of Toray Industries, Inc.), a PET film containing a high Tg material with an average thickness of 4.0 μm, as the polymer film substrate. A magnetic recording medium of Example 3 was obtained in the same manner as Example 2, except for the above points. As shown in Table 1, Figures 13 and 14, the temperature expansion coefficient α of the magnetic recording medium of Example 3 was 8.0 ppm / °C (10% RH), 8.5 ppm / °C (40% RH), and 9.1 ppm / °C (80% RH), the humidity expansion coefficient β was -4.0 ppm / % RH (10°C), -3.8 ppm / % RH (35°C), and -3.2 ppm / % RH (60°C), and the surface roughness Ra of the magnetic layer was 2.8 nm.

[0273] In Example 3, the index P was 50 ppm, the index Q was 105 ppm, the index R was 280 ppm, and the absolute value of the index Q+R was 385 ppm. Therefore, according to the magnetic recording medium of Example 3, it was found that if the number of servo bands SB is 9 or less, the fluctuation in the width of the magnetic recording medium due to the temperature and humidity environment can be suppressed to 0.1 μm or less.

[0274] [Example 4] A magnetic recording medium with an average thickness of 5.2 μm was fabricated using a PEN film with an average thickness of 4.8 μm as the polymer film substrate. A magnetic recording medium of Example 4 was obtained in the same manner as Example 2, except for the above points. As shown in Table 1, Figures 13 and 14, the temperature expansion coefficient α of the magnetic recording medium of Example 4 was 6.9 ppm / °C (10% RH), 7.5 ppm / °C (40% RH), and 8.1 ppm / °C (80% RH), the humidity expansion coefficient β was -3.6 ppm / % RH (10°C), -3.3 ppm / % RH (35°C), and -2.9 ppm / % RH (60°C), and the surface roughness Ra of the magnetic layer was 1.2 nm.

[0275] In Example 4, the index P was 5 ppm, the index Q was 55 ppm, the index R was 252 ppm, and the absolute value of index Q+R was 307 ppm. Therefore, with the magnetic recording medium of Example 4, in a constant humidity environment, the index P was 5 ppm, so the temperature change in width could be made approximately equal to the temperature change of the magnetic head, and width fluctuations of the magnetic recording medium due to the temperature and humidity environment could be virtually eliminated. Furthermore, since the index Q was 55 ppm in a constant temperature environment, even in a variable humidity environment, even in a system with five servo bands (e.g., a linear servo type recording / reproducing device operating with a format having five servo bands), width fluctuations of the magnetic recording medium within the data band width could be suppressed to 0.1 μm or less. Therefore, the magnetic recording medium of Example 4 can be fully compatible with systems with five servo bands SB. In this case, the magnetic recording medium of Example 4 can be compatible with all systems with five or more servo bands SB. Furthermore, in an environment where both temperature and humidity change, the absolute value of the index Q+R is 307 ppm, so in a system with 13 servo bands SB, the variation in the width of the magnetic recording medium within the range of the data band width can be suppressed to 0.15 μm or less. Therefore, the magnetic recording medium of Example 4 can be used in any system that has 13 or more servo bands SB and that can tolerate a variation of 0.15 μm or less.

[0276] [Comparative Example 1] A polymer film substrate was made of SPALTAN (a registered trademark of Toray Industries, Inc.) with an average thickness of 4.6 μm, and the vinyl chloride resin (30% by mass of cyclohexanone solution) in the first composition was 46.3 parts by mass, forming an underlayer with an average thickness of 0.8 μm, thereby producing a magnetic recording medium with an average thickness of 5.6 μm. Except for the above points, a magnetic recording medium was obtained as Comparative Example 1 in the same manner as in Example 1 above.

[0277] Comparative Example 2 A PEN film with an average thickness of 3.6 μm was used as the polymer film substrate, an underlayer was formed to an average thickness of 1.2 μm, and a back layer was formed to an average thickness of 0.6 μm, to produce a magnetic recording medium with an average thickness of 5.2 μm. Except for the above points, a magnetic recording medium was obtained as Comparative Example 2 in the same manner as in Example 1 above.

[0278] Comparative Example 3 A polymer film substrate was made of SPALTAN (registered trademark of Toray Industries, Inc.) with an average thickness of 4.0 μm, an underlayer was formed to an average thickness of 1.2 μm, and a back layer was formed to an average thickness of 0.6 μm, producing a magnetic recording medium with an average thickness of 5.6 μm. Except for the above points, a magnetic recording medium was obtained as Comparative Example 3 in the same manner as in Example 1 above.

[0279] Comparative Example 4 A PET film with an average thickness of 5.3 μm was used as the polymer film substrate, and a magnetic recording medium with an average thickness of 5.7 μm was produced. Except for the above points, a magnetic recording medium was obtained as Comparative Example 4 in the same manner as in Example 2 above.

[0280] Comparative Example 5 A magnetic recording medium having an average thickness of 4.4 μm was produced using an aramid film having an average thickness of 4.0 μm as the polymer film substrate. Except for the above points, a magnetic recording medium was obtained as Comparative Example 5 in the same manner as in Example 2.

[0281] Comparative Example 6 A PEN film having an average thickness of 4.4 μm was used as the polymer film substrate, and the magnetic powder in the first composition had an average particle volume V of 2500 nm 3 ) Barium ferrite nano A magnetic recording medium having an average thickness of 5.6 μm was produced by forming an underlayer using a powder of particles to have an average thickness of 0.8 μm and a back layer to have an average thickness of 0.3 μm. Except for the above points, a magnetic recording medium was obtained as Comparative Example 6 in the same manner as in Example 1.

[0282] [evaluation] The magnetic recording media obtained in the above manner in Examples 1 to 4 all had an index P of 70 ppm or less. Therefore, it was found that in the magnetic recording media in Examples 1 to 4, if the number of servo bands SB is at least 5 or less, the variation in width of the magnetic recording media relative to the position of the magnetic head, which is caused by the temperature and humidity environment, can be suppressed to 0.1 μm or less.

[0283] In contrast, in Comparative Examples 1 and 6, the average thickness of the magnetic recording medium was 5.6 μm, so the length of the magnetic recording medium that could be housed in one magnetic recording cartridge was insufficient compared to Examples 1 to 4, where the average thickness of the magnetic recording medium was 5.3 μm or less, resulting in a lower recording capacity per magnetic recording cartridge. Also, in each of the magnetic recording media of Comparative Examples 2 to 5, the index P was 70 ppm or less, which revealed that the variation in the width of the magnetic recording medium relative to the position of the magnetic head caused by the temperature and humidity environment was greater compared to the magnetic recording media of the Examples.

[0284] The present disclosure has been specifically described above by giving embodiments and modifications thereof, but the present disclosure is not limited to the above embodiments, and various modifications are possible.

[0285] For example, the configurations, methods, steps, shapes, materials, and numerical values, etc., described in the above-described embodiments and their modified examples are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values, etc., may be used as needed. Specifically, the magnetic recording medium of the present disclosure may include components other than the substrate, underlayer, magnetic layer, back layer, and barrier layer. Furthermore, the chemical formulas of compounds, etc., are representative, and are not limited to the valences, etc., described as long as they are general names of the same compounds.

[0286] Furthermore, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments and their modified examples can be combined with one another without departing from the spirit of the present disclosure.

[0287] In addition, in the numerical ranges described in stages in this specification, the upper limit or lower limit of a numerical range in a certain stage may be replaced with the upper limit or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more.

[0288] Furthermore, in the above embodiment, the magnetic recording cartridge 1 is described in which one reel 3 is provided in one cartridge case 2, but the present disclosure is not limited thereto. For example, as in the magnetic recording cartridge 1A shown in FIG. 15 , two reels 3A and 3B may be provided in one cartridge case 2A, and the magnetic recording medium 10 may be reciprocated between the reel 3A and the reel 3B. Note that the cartridge case 2A may be provided with guide rollers 4A and 4B, as necessary, to guide the running of the magnetic recording medium 10. The reel 3A is driven to rotate by, for example, a spindle 31A in a recording / reproducing device, and the reel 3B is driven to rotate by a spindle 31B in the recording / reproducing device. In the magnetic recording cartridge 1A, the magnetic recording medium 10 moves from, for example, a state where it is wound on the reel 3A to, for example, the reel 3B, as the rotation of the spindle 31A and the rotation of the spindle 31B are linked in the recording / reproducing device. Thereafter, the spindles 31A and 31B rotate in opposite directions, so that the magnetic recording medium 10 moves from a state in which it is wound around the reel 3B to a state in which it is wound around the reel 3A.

[0289] As described above, the magnetic recording medium according to one embodiment of the present disclosure has an average thickness of 5.3 μm or less, and is configured to have an environmental relative humidity between 10% and 80% RH such that the temperature expansion coefficient α of the magnetic recording medium 10 is 6.0 ppm / °C or more and 8.0 ppm / °C or less. Therefore, even if the environmental temperature changes, the amount of deformation of the magnetic recording medium 10 and the amount of deformation of the magnetic head are approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained. This is advantageous for improving recording density. Note that the effects of the present disclosure are not limited to these, and may be any of the effects described in this specification. Furthermore, the present technology may have the following configurations. (1) A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% and 80% RH, there is an environmental relative humidity where the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less. Magnetic recording media. (2) The thermal expansion coefficients at a relative humidity of 10%, 40%, and 80% are all between 4.5 ppm / °C and 9.5 ppm / °C. The magnetic recording medium according to (1) above. (3) Between 10°C and 60°C, there is an environmental temperature where the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C. The magnetic recording medium according to (1) or (2) above. (4) The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 5, and the following conditional expression (1) is satisfied: The magnetic recording medium according to any one of (1) to (3) above. P=50[℃]×|(CTH)-(CTP)|≦70[ppm] ……(1) however, P: First index CTH: Temperature expansion coefficient of magnetic head CTP: The thermal expansion coefficient of a magnetic recording medium in a relative humidity environment of 10% RH to 80% RH that is closest to the thermal expansion coefficient of a magnetic head. (5) The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less. The magnetic recording medium according to (4) above. (6) The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 9, and the following conditional expression (2) is satisfied: The magnetic recording medium according to any one of (1) to (5) above. Q=50[℃]×|(CTH)-(CTQ)|≦140[ppm] ……(2) however, Q: Second indicator CTH: Thermal expansion coefficient of magnetic head [ppm / ℃] CTQ: The thermal expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the thermal expansion coefficient of the magnetic head that deviates most from the thermal expansion coefficient of the magnetic recording medium [ppm / °C] (7) The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less. The magnetic recording medium according to (6) above. (8) The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 17, and the following conditional expression (3) is satisfied: The magnetic recording medium according to (3) above. R=70[%RH]×|(CHH)-(CHR)|≦280[ppm] ……(3) however, R: The third index CHH: Humidity expansion coefficient of magnetic head [ppm / %RH] CHR: Humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10°C to 60°C, the humidity expansion coefficient [ppm / %RH] that is the most deviated from the humidity expansion coefficient of the magnetic head. (9) The humidity expansion coefficient of the magnetic head is -0.5 ppm / °C or more and 0.5 ppm / °C or less in a temperature environment of 10°C or more and 60°C or less. The magnetic recording medium according to (8) above. (10) The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 13, and the following conditional expressions (4) to (6) are satisfied: The magnetic recording medium according to (3) above. Q=50[℃]×|(CTH)-(CTQ)|≦140[ppm] ……(4) R=70[%RH]×|(CHH)-(CHR)|≦280[ppm] ……(5) |Q+R|≦200[ppm] ……(6) however, Q: Second indicator CTH: Thermal expansion coefficient of magnetic head [ppm / ℃] CTQ: The temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH or more and 80% RH or less, which is the temperature expansion coefficient [ppm / °C] that deviates most from the temperature expansion coefficient of the magnetic head. R: The third index CHH: Humidity expansion coefficient of magnetic head [ppm / %RH] CHR: Humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10°C to 60°C, the humidity expansion coefficient [ppm / %RH] that is the most deviated from the humidity expansion coefficient of the magnetic head. (11) the temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less, The humidity expansion coefficient of the magnetic head is -0.5 ppm / °C or more and 0.5 ppm / °C or less in a temperature environment of 10°C or more and 60°C or less. The magnetic recording medium according to (10) above. (12) The average thickness of the magnetic recording medium is 5.1 μm or less. The magnetic recording medium according to any one of (1) to (11) above. (13) The average thickness of the substrate is 4.0 μm or more and 4.4 μm or less. The magnetic recording medium according to any one of (1) to (12) above. (14) A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10° C. and 60° C., there is an environmental temperature at which the humidity expansion coefficient of the magnetic recording medium 10 is −3.0 ppm / ° C. or more and 3.0 ppm / ° C. or less. Magnetic recording media. (15) Case and a reel housed in the case and wound with a magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% and 80% RH, there is an environmental relative humidity where the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less. Magnetic recording cartridge. (16) Case and a reel housed in the case and wound with a magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10°C and 60°C, there is an environmental temperature where the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C. Magnetic recording cartridge. (17) a spindle onto which a magnetic recording medium can be mounted; a drive device that drives the spindle; a magnetic head for recording and reproducing data on the magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% and 80% RH, there is an environmental relative humidity where the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less. Recording and playback device. (18) The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less. The recording and reproducing device according to (17) above. (19) a spindle onto which a magnetic recording medium can be mounted; a drive device that drives the spindle; a magnetic head for recording and reproducing data on the magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10°C and 60°C, there is an environmental temperature where the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C. Recording and playback device.

[0290] This application claims priority based on Japanese Patent Application No. 2020-186855, filed on November 9, 2020, with the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0291] Those skilled in the art will recognize that various modifications, combinations, subcombinations, and variations may occur depending on design requirements and other factors, and are intended to be within the scope of the appended claims and their equivalents.

Claims

1. A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 5, and the following conditional expression (1) is satisfied: Magnetic recording media. P = 50 [℃] × | (CTH) - (CTP) | ≦70 [ppm] ... (1) however, P: First index CTH: Temperature expansion coefficient of the magnetic head CTP: The temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the temperature expansion coefficient that is closest to the temperature expansion coefficient of the magnetic head.

2. The thermal expansion coefficient in a relative humidity environment of 10% RH, the thermal expansion coefficient in a relative humidity environment of 40% RH, and the thermal expansion coefficient in a relative humidity environment of 80% RH are all 4.5 ppm / °C or more and 9.5 ppm / °C or less.

2. The magnetic recording medium according to claim 1.

3. Between 10°C and 60°C, there is an environmental temperature at which the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C.

2. The magnetic recording medium according to claim 1.

4. The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less.

2. The magnetic recording medium according to claim 1.

5. A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 9, and the following conditional expression (2) is satisfied: Magnetic recording media. Q = 50 [℃] × | (CTH) - (CTQ) | ≦140 [ppm] ... (2) however, Q: Second indicator CTH: Temperature expansion coefficient of the magnetic head [ppm / °C] CTQ: the temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the temperature expansion coefficient that deviates most from the temperature expansion coefficient of the magnetic head [ppm / °C]

6. The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less.

6. The magnetic recording medium according to claim 5.

7. A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, Between 10°C and 60°C, there is an environmental temperature at which the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C, The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 17, and the following conditional expression (3) is satisfied: Magnetic recording media. R = 70 [%RH] × | (CHH) - (CHR) | ≦280 [ppm] ... (3) however, R: Third index CHH: Humidity expansion coefficient of magnetic head [ppm / % RH] CHR: humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10° C. to 60° C., the humidity expansion coefficient [ppm / % RH] that is the value that deviates most from the humidity expansion coefficient of the magnetic head.

8. The humidity expansion coefficient of the magnetic head is -0.5 in a temperature environment of 10°C to 60°C. 5 ppm / °C or more and 0.5 ppm / °C or less 8. The magnetic recording medium according to claim 7.

9. A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, Between 10°C and 60°C, there is an environmental temperature at which the humidity expansion coefficient of the magnetic recording medium is between -3.0 ppm / °C and 3.0 ppm / °C, The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 13, and the following conditional expressions (4) to (6) are satisfied: Magnetic recording media. Q = 50 [℃] × | (CTH) - (CTQ) | ≦ 140 [ppm] ... (4) R = 70 [%RH] × | (CHH) - (CHR) | ≦280 [ppm] ... (5) |Q+R|≦200[ppm]...(6) however, Q: Second indicator CTH: Temperature expansion coefficient of the magnetic head [ppm / °C] CTQ: the temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the temperature expansion coefficient that deviates most from the temperature expansion coefficient of the magnetic head [ppm / °C] R: Third index CHH: Humidity expansion coefficient of magnetic head [ppm / % RH] CHR: humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10° C. to 60° C., the humidity expansion coefficient [ppm / % RH] that is the value that deviates most from the humidity expansion coefficient of the magnetic head.

10. The temperature expansion coefficient of the magnetic head is 10% RH or more and 80% RH or less. 6.0 ppm / °C or more and 8.0 ppm / °C or less, The humidity expansion coefficient of the magnetic head is -0.5 ppm / °C or more and 0.5 ppm / °C or less in a temperature environment of 10°C or more and 60°C or less.

10. The magnetic recording medium according to claim 9.

11. The average thickness of the magnetic recording medium is 5.1 μm or less.

2. The magnetic recording medium according to claim 1.

12. The average thickness of the substrate is 4.0 μm or more and 4.4 μm or less.

2. The magnetic recording medium according to claim 1.

13. Case and a reel housed in the case and wound with a magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, The magnetic recording medium is one on which recording and reproduction are performed by a magnetic head, The number of servo bands is 5, and the following conditional expression (1) is satisfied: Magnetic recording cartridge. P = 50 [℃] × | (CTH) - (CTP) | ≦70 [ppm] ... (1) however, P: First index CTH: Temperature expansion coefficient of the magnetic head CTP: The temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the temperature expansion coefficient that is closest to the temperature expansion coefficient of the magnetic head.

14. a spindle onto which a magnetic recording medium can be mounted; a drive device that drives the spindle; a magnetic head for recording and reproducing data on the magnetic recording medium; Equipped with The magnetic recording medium is A tape-shaped magnetic recording medium having an average thickness of 5.3 μm or less, a substrate; a magnetic layer provided on the substrate; and Between 10% RH and 80% RH, there is an environmental relative humidity at which the thermal expansion coefficient of the magnetic recording medium is 6.0 ppm / °C or more and 8.0 ppm / °C or less, The number of servo bands is 5, and the following conditional expression (1) is satisfied: Recording and playback device. P = 50 [℃] × | (CTH) - (CTP) | ≦70 [ppm] ... (1) however, P: First index CTH: Temperature expansion coefficient of the magnetic head CTP: The temperature expansion coefficient of the magnetic recording medium in a relative humidity environment of 10% RH to 80% RH, which is the temperature expansion coefficient that is closest to the temperature expansion coefficient of the magnetic head.

15. The temperature expansion coefficient of the magnetic head is 6.0 ppm / °C or more and 8.0 ppm / °C or less in a relative humidity environment of 10% RH or more and 80% RH or less.

15. The recording / reproducing apparatus according to claim 14.

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