magnetic recording media

Abstract

The purpose of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and runnability.　The present technology provides a magnetic recording medium that has a magnetic layer including magnetic powder, wherein: the average size of magnetic clusters measured on the basis of an MFM image on the surface of the magnetic layer is 1850 nm2 or less; the magnetic layer contains first particles having conductivity and second particles having a Mohs hardness of 7 or more; protrusions are formed on the surface of the magnetic layer side by the first particles and the second particles; the ratio (H1 / H2) of the average height (H1) of the protrusions formed by the first particles and the average height (H2) of the protrusions formed by the secondary particles is 2.00 or less.

Description

[Technical Field]

[0001] The present technology relates to magnetic recording media. [Background technology]

[0002] With the development of IoT, big data, and artificial intelligence, the amount of data collected and stored is increasing dramatically. Magnetic recording media are often used as a medium for recording large amounts of data.

[0003] Various technologies have been proposed for magnetic recording media. Patent Document 1 listed below describes a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder and a binder, in which the ferromagnetic powder is selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder and has an average particle size of 5 nm to 20 nm, the magnetic layer has a servo pattern, and the average area Sdc of magnetic clusters in a DC demagnetized state of the magnetic recording medium measured by a magnetic force microscope is 0.2×10 4 nm 2 Over 5.0 x 10 4 nm 2 A magnetic recording medium is disclosed in which the thickness is less than 1 / 2 mm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-140746 Summary of the Invention [Problem to be solved by the invention]

[0005] Advances in IoT utilization and big data analysis are increasing the amount of data being archived. This is in turn driving demand for increased capacity in the media used for archiving. Magnetic recording tape is also beginning to be used for archiving purposes, and there is a demand for even higher capacity than ever before.

[0006] One method for increasing the capacity of magnetic recording tape is to increase the areal recording density. Reducing the size of magnetic particles is one effective way to increase the areal recording density. However, as the size of magnetic particles decreases, it becomes more difficult to disperse them. Even if the magnetic particles are reduced in size, the electromagnetic conversion characteristics of the magnetic tape will not improve unless they are dispersed. Therefore, the size of magnetically independent magnetic clusters is important. In other words, it is desirable to optimize the dispersion of magnetic particles so that the average magnetic cluster size is small.

[0007] Furthermore, inorganic materials are added to magnetic recording tapes, for example, to improve their running properties. For example, to prevent an increase in frictional force while the magnetic recording tape is running, solid lubricant components (such as carbon particles that act as solid lubricants) are used. Furthermore, components with an abrasive effect (and even an anchoring effect) (such as particles with a high Mohs hardness, more specifically alumina) are used for magnetic head cleaning. It is conceivable that by including these two components in the magnetic layer of a magnetic recording tape, an increase in frictional force can be prevented and the magnetic head can be cleaned, thereby improving running properties. If the magnetic powder is dispersed so as not to magnetically aggregate, the inorganic materials may also become too dispersed and become embedded in the magnetic layer, reducing the effectiveness of the inorganic materials. Optimizing the dispersion of the magnetic particles in this way may improve electromagnetic conversion characteristics, but may also result in poor running performance. Conversely, optimizing the dispersion of the inorganic materials may result in insufficient dispersion of the magnetic particles, resulting in poor electromagnetic conversion characteristics.

[0008] The primary objective of this technology is to provide a magnetic recording tape with improved dispersion of magnetic particles and excellent running properties, and also to improve the electromagnetic conversion characteristics of the magnetic recording tape. [Means for solving the problem]

[0009] This technology is a magnetic layer containing magnetic powder; The average size of magnetic clusters measured based on the MFM image of the surface of the magnetic layer is 1850 nm 2 is as follows: the magnetic layer contains first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more, protrusions are formed on the surface of the magnetic layer side by the first particles and the second particles, the ratio (H1 / H2) of the average height H1 of the protrusions formed by the first particles to the average height H2 of the protrusions formed by the second particles is 2.00 or less; A magnetic recording medium is provided. The average height H1 may be 13.0 nm or less. The average height H1 may be 12.0 nm or less. The average height H1 may be 11.0 nm or less. The average height H2 may be 7.5 nm or less. The average height H2 may be 7.0 nm or less. The average height H2 may be 6.5 nm or less. The average size of the magnetic clusters is 1800 nm 2 It may be the following: The average size of the magnetic clusters is 1700 nm 2 It may be the following: The average size of the magnetic clusters is 1600 nm 2 It may be the following: The magnetic recording medium has an average thickness t T may be 5.1 μm or less. The magnetic recording medium may have a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less. The first particles may be carbon particles. The second particles may be inorganic particles. The number of protrusions formed by the first particles on the surface on the magnetic layer side is determined by the unit area (μm 2 ) may be 2.5 or less per The number of protrusions formed by the second particles on the surface on the magnetic layer side is determined by the unit area (μm 2 ) may be 2.0 or more per The magnetic layer may have an average thickness of 0.08 μm or less. The present technology also provides a magnetic recording medium having a magnetic layer containing magnetic powder, The average size of magnetic clusters measured based on the MFM image of the surface of the magnetic layer is 1850 nm 2 is as follows: The magnetic recording medium has a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less. A magnetic recording medium is also provided. The present technology also provides a magnetic recording cartridge in which the magnetic recording medium is housed in a case while being wound around a reel. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing the configuration of a magnetic recording medium according to a first embodiment. [Figure 2A] FIG. 2 is a diagram showing an example of the shape of a particle of magnetic powder. [Figure 2B] 1 is an example of a TEM photograph of a cross section of a sample. [Figure 2C] 10 is another example of a TEM photograph of a cross section of a sample. [Figure 3A] FIG. 2 is a schematic diagram showing the cross-sectional structure of a magnetic particle. [Figure 3B] FIG. 10 is a schematic diagram showing the cross-sectional structure of a magnetic particle in a modified example. [Figure 4A] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4B] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4C] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4D] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4E] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4F]FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4G] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4H] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 4I] FIG. 10 is a diagram for explaining image analysis processing of an MFM image. [Figure 5A] 1 is an image showing an example of a surface shape imaged by an AFM. [Figure 5B] FIG. 10 is a diagram showing an example of a protrusion analysis result obtained by AFM. [Figure 5C] FIG. 10 is a diagram showing an example of a protrusion height distribution measured by AFM. [Figure 6] This is an example of an FE-SEM image. [Figure 7] This is a composite image created by overlaying an AFM image and an FE-SEM image. [Figure 8] This is an enlarged view of a composite image obtained by superimposing an AFM image and an FE-SEM image. [Figure 9] FIG. 9 is a diagram showing an example of the results of an analysis of Line 1 in FIG. 8 by AFM. [Figure 10] FIG. 10 is a graph showing the change in standard deviation σPES over time. [Figure 11] FIG. 10 is a graph showing the change in standard deviation σPES over time. [Figure 12] FIG. 10 is a diagram showing the change over time in the standard deviation σPES, and a cross-sectional view schematically showing the change in the appearance of protrusions formed by carbon particles on the surface of the magnetic layer. [Figure 13A] 3A and 3B are diagrams illustrating examples of servo patterns in a servo band. [Figure 13B] FIG. 1 is a diagram for explaining a method for measuring PES. [Figure 13C] FIG. 10 is a diagram for explaining correction of movement in the width direction of the tape. [Figure 14] FIG. 1 is a schematic diagram showing the configuration of a recording / reproducing device. [Figure 15] FIG. 10 is a cross-sectional view showing the configuration of a magnetic recording medium according to a modified example. [Figure 16] FIG. 2 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge. [Figure 17] FIG. 2 is a block diagram showing an example of the configuration of a cartridge memory. [Figure 18] FIG. 10 is an exploded perspective view showing an example of the configuration of a modified magnetic recording cartridge. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments for carrying out the present technology will be described below. Note that the embodiments described below are representative embodiments of the present technology, and the scope of the present technology is not limited to these embodiments.

[0012] This technology will be described in the following order. 1. Description of this technology 2. First embodiment (1) Structure of magnetic recording medium (2) Explanation of each layer (3) Physical properties and structure (4) Manufacturing method of magnetic recording medium (5) Recording and playback device (6) Variations 3. Second embodiment (1) One embodiment of a magnetic recording cartridge (2) Modified magnetic recording cartridge 4. Working Example

[0013] In this specification, unless a measurement environment is specifically stated in the description of the measurement method, the measurement is performed in an environment of 25°C ± 2°C and 50% RH ± 5% RH.

[0014] 1. Description of this technology

[0015] This technology provides a magnetic recording medium having an average magnetic cluster size of a specific value or less and a ratio of the heights of the protrusions formed by two types of particles of a specific value or less. This magnetic recording medium has an improved dispersion state of the magnetic particles, but also exhibits the effects of the two types of particles, resulting in excellent running properties.

[0016] The magnetic recording medium according to the present technology has a magnetic layer containing magnetic powder, and the average size of magnetic clusters measured based on an MFM image of the surface of the magnetic layer is, for example, 1850 nm 2 or less, and more preferably 1800 nm 2 or less, and even more preferably 1750 nm 2 Below, 1700nm 2 Below, 1650nm 2 or below 1600nm 2 or less, and even 1550nm 2 Below 1500nm 2 The average magnetic cluster size of the magnetic layer of the magnetic recording medium according to the present technology is thus small, that is, the areal recording density is high. The lower limit of the average size of the magnetic clusters is not particularly limited, but is, for example, 500 nm 2 More than 600 nm, preferably 2 More preferably, 700 nm 2 Over 800nm 2 Over 900nm 2 or above 1000nm 2 By making the average magnetic cluster size equal to or greater than these values, the thermal stability of the magnetic recording medium is improved. The method for measuring the average size of the magnetic clusters will be explained below in 2.(3).

[0017] The magnetic layer also contains conductive first particles and second particles having a Mohs hardness of 7 or greater. The first particles are conductive and may function as a solid lubricant. The second particles may have a Mohs hardness of 7 or greater, thereby providing a polishing effect (and an anchoring effect). The first particles and the second particles form protrusions on the surface of the magnetic layer, and the ratio (H1 / H2) of the average height (H1) of the protrusions formed by the first particles to the average height (H2) of the protrusions formed by the second particles may be, for example, 2.00 or less, more preferably 1.95 or less, and even more preferably 1.90 or less, 1.85 or less, 1.80 or less, 1.75 or less, or 1.70 or less. When the magnetic recording medium has a protrusion average height ratio (H1 / H2) within the above numerical range, friction increase due to repeated runs is minimal, and the abrasive force against the head can be maintained appropriately. In a magnetic recording medium having a small average magnetic cluster size as described above, the ratio (H1 / H2) being within this range improves the dispersion of the magnetic particles in the magnetic layer, and the effects of the two types of particles are also exerted, resulting in excellent running properties.

[0018] The lower limit of the ratio of the average heights of the projections (H1 / H2) is not particularly limited, but may be, for example, 1.0 or more, preferably 1.1 or more, and more preferably 1.2 or more.

[0019] In the magnetic recording medium according to the present technology, the average height (H1) of the protrusions formed by the first particles may be, for example, 13.0 nm or less, preferably 12.0 nm or less, more preferably 11.5 nm or less, and even more preferably 11.0 nm or less, 10.5 nm or less, 10.0 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less. When the magnetic recording medium has an average height (H1) of the protrusions formed by the first particles within the above numerical range, the occurrence of an increase in friction due to multiple runs is reduced, and it is possible to maintain an appropriate abrasive force against the head. Furthermore, in order to improve the electromagnetic conversion characteristics, the average height (H1) of the protrusions is preferably 12.0 nm or less, more preferably 11.5 nm or less, even more preferably 11.0 nm or less, 10.5 nm or less, 10.0 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less.

[0020] The lower limit of the average height (H1) of the protrusions formed by the first particles is not particularly limited, but may be, for example, preferably 5.0 nm or more, more preferably 5.5 nm or more, and even more preferably 6.0 nm or more, thereby enabling the effects of adding the first particles to be more effectively exhibited.

[0021] In the magnetic recording medium according to the present technology, the average height (H2) of the protrusions formed by the second particles may be, for example, 8.0 nm or less, preferably 7.5 nm or less, more preferably 7.0 nm or less, and even more preferably 6.5 nm or less, 6.0 nm or less, 5.5 nm or less, or 5.3 nm or less. When the magnetic recording medium has an average height (H2) of the protrusions formed by the second particles within the above numerical range, friction increase due to repeated runs is reduced, and it is possible to maintain an appropriate abrasive force against the magnetic head. Furthermore, it is preferable that the average height (H2) of the protrusions is small, for example, 7.0 nm or less, from the viewpoint of improving electromagnetic conversion characteristics.

[0022] The lower limit of the average height (H2) of the protrusions formed by the secondary particles is not particularly limited, but may be, for example, preferably 2.0 nm or more, more preferably 2.5 nm or more, and even more preferably 3.0 nm or more, thereby enabling the effects of adding the secondary particles to be more effectively exhibited.

[0023] In a preferred embodiment of the present technology, the average height (H1) of the protrusions formed by the first particles is 12.0 nm or less, preferably 11.5 nm or less, more preferably 11.0 nm or less, 10.5 nm or less, 10.0 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less, and the average height (H2) of the protrusions formed by the second particles is 7.0 nm or less, preferably 6.5 nm or less, more preferably 6.0 nm or less, 5.5 nm or less, or 5.3 nm or less. When the average height of the protrusions formed by these two types of particles is within this numerical range, the effects of these particles are more effectively exerted, resulting in improved runnability. Furthermore, when the average height of the protrusions formed by these two types of particles is within this numerical range, the electromagnetic conversion characteristics are also improved.

[0024] Furthermore, the number of protrusions formed by the first particles on the surface on the magnetic layer side is determined based on the unit area (μm 2 ) may be, for example, 3.0 or less, preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, or 1.5 or less. The number is expressed as a number per unit area (μm 2 ) may be, for example, 0.3 or more, preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more. When the number is within the above range, the effect of the first particles is more effectively exhibited, contributing to improved running properties. Furthermore, when the number is within the above range, it also contributes to improved electromagnetic conversion characteristics.

[0025] Furthermore, the number of protrusions formed by the second particles on the surface on the magnetic layer side is determined based on the unit area (μm 2 ) may be, for example, 5.0 or less, preferably 4.0 or less, more preferably 3.9 or less, even more preferably 3.8 or less, 3.7 or less, 3.6 or less, or 3.5 or less. The number is expressed as a number per unit area (μm 2) may be, for example, 1.0 or more, preferably 1.5 or more, more preferably 1.7 or more, and even more preferably 2.0 or more. When the number is within the above range, the effect of the second particles is more effectively exhibited, contributing to improved running properties. Furthermore, when the number is within the above range, it also contributes to improved electromagnetic conversion characteristics.

[0026] The methods for measuring the average height (H1) of the protrusions formed by the first particles, the average height (H2) of the protrusions formed by the second particles, the ratio (H1 / H2) between them, and the number of these protrusions per unit area will be described below in 2.(3).

[0027] The magnetic recording medium according to the present technology is preferably a long magnetic recording medium, and may be, for example, a magnetic recording tape (particularly a long magnetic recording tape).

[0028] A magnetic recording medium according to the present technology may include a magnetic layer, a non-magnetic layer (underlayer), a base layer, and a back layer in this order, and may also include other layers in addition to these layers. The other layers may be selected appropriately depending on the type of magnetic recording medium. The magnetic recording medium may be a coating-type magnetic recording medium, that is, a magnetic recording medium manufactured by coating a base layer with a material (particularly a paint) that forms the other layers and then drying the coating.

[0029] The average thickness (average total thickness) of the magnetic recording medium according to the present technology is t T may be, for example, 5.7 μm or less, preferably 5.6 μm or less, more preferably 5.5 μm or less, 5.4 μm or less, 5.3 μm or less, 5.2 μm or less, 5.1 μm or less, or 5.0 μm or less, and even more preferably 4.6 μm or less or 4.4 μm or less. Because the magnetic recording medium is so thin, for example, the length of tape wound into one magnetic recording cartridge can be made longer, thereby increasing the recording capacity per magnetic recording cartridge. The average thickness (average total thickness) t of the magnetic recording medium TThe lower limit of t is not particularly limited, but for example, 3.5 μm≦t T is.

[0030] The average thickness t of the magnetic layer of the magnetic recording medium according to the present technology m The average thickness t of the magnetic layer is preferably 0.08 μm or less, more preferably 0.07 μm or less, even more preferably 0.06 μm or less, 0.05 μm or less, and even more preferably 0.04 μm or less. m Although there are no particular restrictions on the lower limit, it is preferably 0.03 μm or more. The method for measuring the average thickness of the magnetic layer will be explained below in 2.(3).

[0031] The average thickness of the nonmagnetic layer (also referred to as the underlayer) of the magnetic recording medium according to the present technology is preferably 1.2 μm or less, preferably 1.1 μm or less, more preferably 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less, and even more preferably 0.6 μm or less. The lower limit of the average thickness of the nonmagnetic layer is not particularly limited, but is preferably 0.2 μm or more, more preferably 0.3 μm or more. The method for measuring the average thickness of the nonmagnetic layer will be described below in Section 2.(3).

[0032] The average thickness of the base layer (also referred to as the substrate layer) of the magnetic recording medium according to the present technology can be preferably 4.5 μm or less, more preferably 4.2 μm or less, 4.0 μm or less, 3.8 μm or less, or 3.6 μm or less, and even more preferably 3.4 μm or less, 3.2 μm or less, or 3.0 μm or less. The lower limit of the average thickness of the base layer is not particularly limited, but can be, for example, 2.0 μm or more, preferably 2.5 μm or more. The method for measuring the average thickness of the base layer will be described below in 2.(3).

[0033] The average thickness of the back layer of the magnetic recording medium according to the present technology is preferably 0.6 μm or less, more preferably 0.5 μm or less, and even more preferably 0.4 μm or less, 0.3 μm or less, 0.25 μm or less, or 0.2 μm or less. The lower limit of the average thickness of the back layer is not particularly limited, but may be, for example, 0.1 μm or more, preferably 0.15 μm or more. The method for measuring the average thickness of the back layer will be described below in 2.(3).

[0034] The average particle volume of the magnetic powder contained in the magnetic recording medium of the present technology is, for example, 2200 nm 3 less than 2000 nm, preferably 3 or less, and more preferably 1900 nm 3 Below, 1800nm 3 Below, 1700nm 3 or below 1600nm 3 The average particle volume may be less than 500 nm. By having the average particle volume within the above numerical range, it becomes easier to adjust the average magnetic cluster size to a desired range. Furthermore, having the average particle volume within the above numerical range also contributes to improving electromagnetic conversion characteristics. The average particle volume of the magnetic powder is, for example, 500 nm 3 Above 700nm, especially 3 The method for measuring the average particle volume of the magnetic powder will be explained below in 2.(3).

[0035] A magnetic recording medium according to the present technology may have, for example, at least one data band and at least two servo bands. The number of data bands may be, for example, 2 to 10, particularly 3 to 6, and more particularly 4 or 5. The number of servo bands may be, for example, 3 to 11, particularly 4 to 7, and more particularly 5 or 6. These servo bands and data bands may be arranged, for example, so as to extend in the longitudinal direction of a long magnetic recording medium (particularly a magnetic recording tape), particularly so as to be substantially parallel. The data band and the servo band may be provided on the magnetic layer. An example of a magnetic recording medium having such a data band and servo band is a magnetic recording tape conforming to the LTO (Linear Tape-Open) standard. That is, the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO standard. For example, the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO8 standard or later (e.g., LTO9, LTO10, LTO11, or LTO12). The width of a long magnetic recording medium (particularly a magnetic recording tape) according to the present technology can be, for example, 5 mm to 30 mm, particularly 7 mm to 25 mm, more particularly 10 mm to 20 mm, and even more particularly 11 mm to 19 mm. The length of a long magnetic recording medium (particularly a magnetic recording tape) can be, for example, 500 m to 1500 m. For example, a tape conforming to the LTO8 standard has a width of 12.65 mm and a length of 960 m.

[0036] 2. First embodiment

[0037] (1) Structure of magnetic recording medium First, the configuration of a magnetic recording medium 10 according to the first embodiment will be described with reference to Fig. 1. The magnetic recording medium 10 is, for example, a magnetic recording medium that has been subjected to a perpendicular orientation treatment. As shown in Fig. 1, the magnetic recording medium 10 includes a long base layer (also referred to as a substrate) 11, a non-magnetic layer (also referred to as an underlayer) 12 provided on one major surface of the base layer 11, a magnetic layer (also referred to as a recording layer) 13 provided on the non-magnetic layer 12, and a back layer 14 provided on the other major surface of the base layer 11. Hereinafter, of the two major surfaces of the magnetic recording medium 10, the surface on which the magnetic layer 13 is provided will be referred to as the magnetic surface, and the surface opposite to the magnetic surface (the surface on which the back layer 14 is provided) will be referred to as the back surface.

[0038] The magnetic recording medium 10 has an elongated shape and runs longitudinally during recording and reproduction. The magnetic recording medium 10 may be configured to record signals at a minimum 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, and may be used, for example, in a recording and reproduction device whose minimum recording wavelength is within the above range. This recording and reproduction device may be equipped with a ring-type head as a recording head. The recording track width is, for example, 2 μm or less.

[0039] (2) Explanation of each layer

[0040] (base layer)

[0041] The base layer 11 can function as a support for the magnetic recording medium 10 and can be, for example, a flexible, long, non-magnetic substrate, particularly a non-magnetic film. The average thickness of the base layer 11 is, for example, preferably 4.5 μm or less, more preferably 4.2 μm or less, 4.0 μm or less, 3.8 μm or less, or 3.6 μm or less, and even more preferably 3.4 μm or less, 3.2 μm or less, or 3.0 μm or less. The lower limit of the average thickness of the base layer 11 can be determined, for example, from the viewpoint of film production limitations or the function of the base layer 11, and can be, for example, 2.0 μm or more, 2.2 μm or more, 2.4 μm or more, or 2.6 μm or more. The base layer 11 can include, for example, at least one of polyester resins, polyolefin resins, cellulose derivatives, vinyl resins, aromatic polyether ketone resins, and other polymer resins. When the base layer 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

[0042] The polyester resin may be, for example, one or a mixture of two or more of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate), and polyethylene bisphenoxycarboxylate. According to a preferred embodiment of the present technology, the base layer 11 may be formed from PET or PEN.

[0043] The polyolefin resin may be, for example, one or a mixture of two or more of PE (polyethylene) and PP (polypropylene).

[0044] The cellulose derivative may be, for example, one or a mixture of two or more of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate).

[0045] The vinyl resin may be, for example, one or a mixture of two or more of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0046] The aromatic polyetherketone resin may be, for example, one or a mixture of two or more of PEK (polyetherketone), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), and PEEKK (polyetheretherketoneketone). According to a preferred embodiment of the present technology, the base layer 11 may be formed from PEEK.

[0047] The other polymer resin may be, for example, one or a mixture of two or more 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, polyetherester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

[0048] (magnetic layer)

[0049] The magnetic layer 13 may be, for example, a perpendicular recording layer. The magnetic layer 13 contains magnetic powder. In addition to the magnetic powder, the magnetic layer 13 contains first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more. The magnetic layer 13 may further contain, for example, a binder. The magnetic layer 13 may further contain additives such as a lubricant and a rust inhibitor, as necessary.

[0050] The average thickness t of the magnetic layer 13 m The average thickness t of the magnetic layer 13 is preferably 0.08 μm or less, more preferably 0.07 μm or less, and even more preferably 0.06 μm or less, 0.05 μm or less, or 0.04 μm or less.m The lower limit of the average thickness t of the magnetic layer 13 is not particularly limited, but is preferably 0.03 μm or more. m Being within the above range contributes to improving the electromagnetic conversion characteristics.

[0051] The magnetic layer 13 is preferably a magnetic layer that is perpendicularly oriented. In this specification, perpendicular orientation means that the squareness ratio S1 measured in the longitudinal direction (travel direction) of the magnetic recording medium 10 is 35% or less. The magnetic layer 13 may be an in-plane oriented (longitudinal oriented) magnetic layer. That is, the magnetic recording medium 10 may be a horizontal recording type magnetic recording medium. However, from the viewpoint of achieving high recording density, a perpendicular orientation is more preferable.

[0052] (magnetic powder)

[0053] Examples of magnetic particles constituting the magnetic powder contained in the magnetic layer 13 include, but are not limited to, hexagonal ferrite, epsilon iron oxide (ε-iron oxide), Co-containing spinel ferrite, gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, and metals. The magnetic powder may be one of these or a combination of two or more of these. Preferably, the magnetic powder contains hexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite. More preferably, the magnetic powder is hexagonal ferrite. The hexagonal ferrite particularly preferably contains at least one of Ba and Sr. The ε-iron oxide particularly preferably contains at least one of Al and Ga. These magnetic particles may be appropriately selected by those skilled in the art based on factors such as the manufacturing method of the magnetic layer 13, the specifications of the tape, and the functions of the tape.

[0054] The shape of the magnetic particles depends on the crystal structure of the magnetic particles. For example, barium ferrite (BaFe) and strontium ferrite can be hexagonal plate-shaped. ε-iron oxide can be spherical. Cobalt ferrite can be cubic. Metal can be spindle-shaped. These magnetic particles are oriented during the manufacturing process of the magnetic recording medium 10.

[0055] 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, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may be, for example, 10 nm or more, preferably 12 nm or more.

[0056] The average aspect ratio of the magnetic powder may be, for example, 1.0 or more and 3.0 or less, or 1.0 or more and 2.9 or less.

[0057] (An embodiment in which the magnetic powder includes hexagonal ferrite)

[0058] According to a preferred embodiment of the present technology, the magnetic powder may include hexagonal ferrite, and more particularly, may include a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles"). The hexagonal ferrite is preferably a hexagonal ferrite having an M-type structure. The hexagonal ferrite has, for example, a hexagonal plate shape or a nearly hexagonal plate shape. The hexagonal ferrite may preferably include at least one of Ba, Sr, Pb, and Ca, more preferably at least one of Ba, Sr, and Ca. Specifically, the hexagonal ferrite may be, for example, one or a combination of two or more selected from barium ferrite, strontium ferrite, and calcium ferrite, and is particularly preferably barium ferrite or strontium ferrite. Barium ferrite may further include at least one of Sr, Pb, and Ca in addition to Ba. Strontium ferrite may further include at least one of Ba, Pb, and Ca in addition to Sr.

[0059] More specifically, hexagonal ferrites have the general formula MFe 12 O 19 The alloy may have 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.

[0060] 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, even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may be, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. For example, the average particle size of the magnetic powder may be 10 nm or more to 50 nm or less, 10 nm or more to 40 nm or less, 12 nm or more to 30 nm or less, 12 nm or more to 25 nm or less, or 15 nm or more to 22 nm or less. When the average particle size of the magnetic powder is the upper limit or less (e.g., 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.

[0061] When the magnetic powder contains hexagonal ferrite particles, the average aspect ratio of the magnetic powder is preferably 1.0 to 3.0, more preferably 1.0 to 2.9, and even more preferably 2.0 to 2.9. Having the average aspect ratio of the magnetic powder within the above range can suppress aggregation of the magnetic powder, and can also suppress the resistance applied to the magnetic powder when vertically orienting the magnetic powder in the process of forming the magnetic layer 13. This can improve the vertical orientation of the magnetic powder.

[0062] When the magnetic powder contains hexagonal ferrite particles, the average particle size and average aspect ratio of the magnetic powder can be determined as follows. First, the magnetic recording medium (hereinafter also referred to as "magnetic tape") housed in a magnetic recording cartridge is unwound, and a 50 mm section of the magnetic tape to be measured is cut out. For example, in the case of a magnetic recording cartridge 10A as shown in FIG. 19, the cut-out position may be 30 m longitudinally from the connection 221 between the magnetic tape T and the leader tape LT. Next, the magnetic tape to be measured is processed and thinned using a FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape facing the magnetic layer and the surface facing the back layer, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer. The thinning is performed along the length (longitudinal direction) of the magnetic tape. That is, the thinning process forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape.

[0063] The cross section of the obtained thin sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so that the entire magnetic layer is included in the thickness direction of the magnetic layer, and a TEM photograph is taken. TEM photographs are prepared in sufficient quantity to extract 50 particles from which the plate diameter DB and plate thickness DA (see Figure 2A) shown below can be measured.

[0064] In this specification, the size of a hexagonal ferrite particle (hereinafter referred to as "particle size") is defined as the plate diameter DB, which is the longest diameter of the plate surface or base, when the particle shape observed in the TEM photograph is plate-like or columnar (however, the thickness or height is smaller than the longest diameter of the plate surface or base), as shown in FIG. 2A. The thickness or height of the particle observed in the TEM photograph is defined as the plate thickness DA. When the plate surface or base of the particle observed in the TEM photograph is hexagonal, the longest diameter means the longest diagonal distance. When the thickness or height of a particle is not constant within a single particle, the thickness or height of the largest particle is defined as the plate thickness DA.

[0065] Next, 50 particles are selected from the TEM photograph based on the following criteria. Particles with parts outside the field of view of the TEM photograph are not measured, and only particles with a clear outline and that exist independently are measured. If particles overlap, those with a clear boundary between them and whose overall shape can be determined are measured as individual particles, but particles with unclear boundaries and whose overall shape cannot be determined are not measured as their shape cannot be determined.

[0066] Examples of TEM photographs are shown in Figures 2B and 2C. In these photographs, the particles indicated by arrows a and d are selected because their plate thickness (thickness or height) DA can be clearly confirmed. The plate thickness DA of each of the selected 50 particles is measured. The plate thicknesses DA thus obtained are simply averaged (arithmetic mean) to obtain the average plate thickness DA. ave Average plate thickness DA ave is the average particle plate thickness. Next, the plate diameter DB of each magnetic powder is measured. In order to measure the particle plate diameter DB, 50 particles whose particle plate diameter DB can be clearly confirmed are selected from the TEM photographs taken. For example, in these figures, the particles indicated by arrows b and c are selected because their plate diameter DB can be clearly confirmed. The plate diameter DB of each of the selected 50 particles is measured. The plate diameters DB thus determined are simply averaged (arithmetic average) to obtain the average plate diameter DB ave Average plate diameter DB aveis the average particle size.

[0067] When the magnetic powder comprises a powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 1800 nm 3 or less, and more preferably 1600 nm 3 or less, and more preferably 1400 nm 3 and even more preferably 1200 nm or less. 3 Below, 1100nm 3 or less than 1000 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 700 nm 3 It could be more than that.

[0068] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0069] The average particle volume of the magnetic powder can be calculated as follows: First, as described above in relation to the method for calculating the average particle size of the magnetic powder, the average plate thickness DA ave and average plate diameter DB ave Next, calculate the average particle volume V of the magnetic powder using the following formula:

[0070]

number

[0071] 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 a high-temperature, high-humidity environment. From this perspective, barium ferrite magnetic powder is preferred as the magnetic powder.

[0072] The average particle size of the barium ferrite magnetic powder is 22 nm or less, more preferably 10 nm or more and 20 nm or less, and even more preferably 12 nm or more and 18 nm or less.

[0073] When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness t m For example, the average thickness t [nm] of the magnetic layer 13 is preferably 90 nm or less, and more preferably 80 nm or less. m is 35 nm ≦ tm ≦ 90 nm, or 35 nm ≦ t m It may be ≦80 nm.

[0074] Furthermore, the coercive force Hc1 measured in the thickness direction (perpendicular direction) of the magnetic recording medium 10 is preferably 2010 [Oe] or more and 3520 [Oe] or less, more preferably 2070 [Oe] or more and 3460 [Oe] or less, and even more preferably 2140 [Oe] or more and 3390 [Oe] or less.

[0075] (Embodiment in which the magnetic powder contains ε-iron oxide)

[0076] According to another preferred embodiment of the present technology, the magnetic powder may preferably comprise a powder of nanoparticles containing ε-iron oxide (hereinafter referred to as "ε-iron oxide particles"). ε-iron oxide particles can achieve high coercivity even when they are fine particles. The ε-iron oxide contained in the ε-iron oxide particles preferably has a crystal orientation preferentially in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

[0077] The ε-iron oxide particles are spherical or nearly spherical, or cubic or nearly cubic. Because of the above-described shape of the ε-iron oxide particles, when used as magnetic particles, the contact area between particles in the thickness direction of the medium can be reduced, and aggregation between particles can be suppressed, compared to when hexagonal plate-shaped barium ferrite particles are used as magnetic particles. This improves the dispersibility of the magnetic powder, resulting in a better SNR.

[0078] The ε-iron oxide particles may have a core-shell structure. Specifically, as shown in Fig. 3A, the ε-iron oxide particles 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.

[0079] The core portion 21 contains ε-iron oxide. The ε-iron oxide contained in the core portion 21 preferably has ε-Fe2O3 crystals as a main phase, and more preferably is made of single-phase ε-Fe2O3.

[0080] 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.

[0081] The first shell portion 22a is a so-called soft magnetic layer and may include 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.

[0082] The second shell portion 22b is an oxide coating serving as an anti-oxidation layer. The second shell portion 22b may contain α-iron oxide, aluminum oxide, or silicon oxide. The α-iron oxide may contain 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.

[0083] The ε-iron oxide particles have the first shell portion 22a as described above, which ensures thermal stability, thereby maintaining a high coercivity Hc of the core portion 21 alone and / or adjusting the coercivity Hc of the ε-iron oxide particles (core-shell particles) as a whole to a coercivity Hc suitable for recording. Furthermore, the ε-iron oxide particles have the second shell portion 22b as described above, which prevents the ε-iron oxide particles from being exposed to air during and before the manufacturing process of the magnetic recording medium 10, which can lead to rust and other damage on the particle surface, thereby preventing deterioration of the properties of the ε-iron oxide particles. Therefore, deterioration of the properties of the magnetic recording medium 10 can be prevented.

[0084] As shown in Fig. 3B, the ε-iron oxide particles may have a shell portion 23 with a single layer structure. In this case, the shell portion 23 has the same structure as the first shell portion 22a. However, from the viewpoint of suppressing deterioration of the properties of the ε-iron oxide particles, it is more preferable that the ε-iron oxide particles have a shell portion 22 with a two-layer structure.

[0085] The ε-iron oxide particles may contain an additive instead of a core-shell structure, or may have a core-shell structure and contain an additive. In these cases, 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 one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In).

[0086] Specifically, the ε-iron oxide containing additives is ε-Fe 2-x M x O3 crystal (wherein M is a metal element other than iron, preferably a trivalent metal element, more preferably one or more selected from the group consisting of Al, Ga, and In. x is, for example, 0 <x<1である。)である。

[0087] The average particle size (average maximum particle size) of the magnetic powder is preferably 22 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 SNR 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 44 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.

[0088] The average aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 1.0 or more and 2.5 or less. When the average aspect ratio of the magnetic powder is within the above range, 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.

[0089] When the magnetic powder contains ε-iron oxide particles, the average particle size and average aspect ratio of the magnetic powder can be determined as follows. First, the magnetic recording medium to be measured is cut out as described above for the case where the magnetic powder contains hexagonal ferrite particles. The magnetic recording medium to be measured is processed into thin sections using a method such as FIB (Focused Ion Beam). 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 back layer side surface of the magnetic recording medium 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. 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.

[0090] The cross section of the obtained thin film 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.

[0091] Next, 50 particles whose particle shapes can be clearly confirmed are selected from the TEM photographs, and the long axis length DL and short axis length DS of each particle are measured. Here, the long axis length DL refers to the maximum distance between two parallel lines drawn from any angle so as to be tangent to the outline of each particle (the so-called maximum Feret diameter). On the other hand, the short axis length DS refers to the maximum length of the particle in the direction perpendicular to the long axis (DL) of the particle.

[0092] Next, the major axis lengths DL of the 50 measured particles were simply averaged (arithmetic mean) to obtain the average major axis length DL ave The average major axis length DL ave is the average particle size of the magnetic powder. The minor axis lengths DS of the 50 particles measured are simply averaged (arithmetic mean) to obtain the average minor axis length DS ave Then, calculate the average major axis length DLave and mean minor axis length DS ave The average aspect ratio of the particles (DL ave / DS ave ) is found.

[0093] The average particle volume of the magnetic powder is preferably 1800 nm 3 or less, and more preferably 1600 nm 3 or less, and more preferably 1400 nm 3 and even more preferably 1200 nm or less. 3 Below, 1100nm 3 or less than 1000 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 700 nm 3 It could be more than that.

[0094] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0095] When the ε-iron oxide particles are spherical or nearly spherical, the average particle volume of the magnetic powder can be calculated as follows: First, the average major axis length DL is calculated in the same manner as in the above-mentioned method for calculating the average particle size of the magnetic powder. ave Next, calculate the average particle volume V of the magnetic powder using the following formula: V=(π / 6)×DL ave 3

[0096] When the ε-iron oxide particles have a cubic shape, the average particle volume of the magnetic powder can be determined as follows. The magnetic recording medium 10 is processed and thinned by a method such as FIB (Focused Ion Beam). When the FIB method is used, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. In other words, the thinning forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.

[0097] The obtained thin film 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 to observe the cross section of the magnetic layer 13 in the thickness direction so as to include the entire magnetic layer 13, and a TEM photograph is obtained. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of apparatus.

[0098] Next, 50 particles with clear particle shapes are selected from the TEM photographs, and the side length DC of each particle is measured. The side lengths DC of the 50 measured particles are then simply averaged (arithmetic mean) to obtain the average side length DC ave Next, calculate the average side length DC ave Using the following formula, the average particle volume of the magnetic powder, V ave (particle volume) is calculated. V ave =DC ave 3

[0099] The coercive force Hc of the ε iron oxide particles is preferably 2500 Oe or more, and more preferably 2800 Oe or more and 4200 Oe or less.

[0100] (An embodiment in which the magnetic powder includes Co-containing spinel ferrite)

[0101] According to yet another preferred embodiment of the present technology, the magnetic powder may include a powder of nanoparticles containing Co-containing spinel ferrite (hereinafter also referred to as "cobalt ferrite particles"). That is, the magnetic powder may be cobalt ferrite magnetic powder. The cobalt ferrite particles preferably have uniaxial crystal anisotropy. The cobalt ferrite magnetic particles have, for example, a cubic or nearly cubic shape. The Co-containing spinel ferrite may further include one or more elements selected from the group consisting of Ni, Mn, Al, Cu, and Zn in addition to Co.

[0102] Cobalt ferrite has an average composition represented by the following formula, for example. Co x M y FeO z (In the above formula, M is, for example, one or more metals 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, with the proviso that 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.)

[0103] The average particle size of the cobalt ferrite magnetic powder is preferably 21 nm or less, more preferably 19 nm or less.The coercive force Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe or more, more preferably 2600 Oe or more and 3500 Oe or less.

[0104] 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 to 19 nm. Such a small average particle size of the magnetic powder allows for good electromagnetic conversion characteristics (e.g., SNR) to 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, allowing for better electromagnetic conversion characteristics (e.g., SNR). When the magnetic powder contains cobalt ferrite particles, the average aspect ratio and average particle size of the magnetic powder are determined in the same manner as when the magnetic powder contains ε-iron oxide particles.

[0105] The average particle volume of the magnetic powder is preferably 2000 nm 3 or less, and more preferably 1900 nm 3 or less, and more preferably 1800 nm 3 and even more preferably 1700 nm or less. 3 Below, 1600nm 3 or below 1500nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 700 nm 3 It could be more than that.

[0106] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0107] (first particle)

[0108] The first particles are electrically conductive. The first particles may be fine particles primarily composed of carbon, preferably carbon particles, and examples of such carbon particles include carbon black. Examples of carbon black that can be used include Asahi #15 and #15HS from Asahi Carbon Co., Ltd. and Seast TA from Tokai Carbon Co., Ltd. Hybrid carbon, in which carbon is attached to the surface of silica particles, may also be used.

[0109] The average particle size (arithmetic mean value of particle diameters measured using an electron microscope) of the first particles (particularly carbon particles, for example, carbon black) may be, for example, 15 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. The average particle size may be, for example, 200 nm or less, preferably 180 nm or less, more preferably 150 nm or less, 130 nm or less, or 120 nm or less. The numerical range of the average particle size may be appropriately selected from these upper and lower limits, and may be, for example, 50 nm to 200 nm, preferably 50 nm to 180 nm, more preferably 50 nm to 150 nm, and even more preferably 50 nm to 130 nm. The nitrogen adsorption specific surface area of ​​the first particles (particularly carbon particles, for example, carbon black) is, for example, 5 m 2 / g~50m 2 / g, preferably 7m 2 / g~50m 2 / g, more preferably 10m 2 / g~50m 2 / g, and even more preferably 12m 2 / g~50m 2 / g. The iodine adsorption amount of the primary particles (particularly carbon particles, for example, carbon black) may be, for example, 5 mg / g to 50 mg / g, preferably 7 mg / g to 50 mg / g, more preferably 10 mg / g to 50 mg / g, and even more preferably 12 mg / g to 50 mg / g.

[0110] (second particle)

[0111] From the viewpoint of suppressing deformation due to contact with a magnetic head, the second particles may have a Mohs hardness of 7 or more, preferably 7.5 or more, more preferably 8 or more, and even more preferably 8.5 or more. From the viewpoint of suppressing head wear, the Mohs hardness of the second particles may be, for example, 10 or less, preferably 9.5 or less. That is, the second particles may be formed from a material having such a Mohs hardness. The second particles may preferably be inorganic particles. Examples of the second particles include α-alumina (the α-conversion rate may be, for example, 90% or more), β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and acicular α-iron oxide obtained by dehydrating and annealing magnetic iron oxide raw materials, optionally surface-treated with aluminum and / or silica, or diamond powder, or a combination of two or more of these. The second particles are preferably alumina particles such as α-alumina, β-alumina, and γ-alumina, or silicon carbide. These second particles may be acicular, spherical, cubic, or other shapes, but those with angular shapes are preferred because they have high abrasiveness, for example.

[0112] The average particle size (the arithmetic mean value of particle diameters measured using, for example, an electron microscope) of the second particles (particularly inorganic particles such as alumina) may be, for example, 15 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. The average particle size may be, for example, 200 nm or less, preferably 180 nm or less, more preferably 150 nm or less, 130 nm or less, or 120 nm or less. The numerical range of the average particle size may be appropriately selected from these upper and lower limits, and may be, for example, 50 nm to 180 nm, preferably 60 nm to 150 nm, and more preferably 60 nm to 120 nm. The second particles (particularly inorganic particles, such as alumina) may not be electrically conductive, i.e., the second particles may not have the same electrical conductivity as the first particles.

[0113] (Average height of protrusions formed by the first particles and the second particles)

[0114] The first particles and the second particles each form protrusions on the surface of the magnetic layer. The ratio (H1 / H2) of the average height (H1) of the protrusions formed by the first particles to the average height (H2) of the protrusions formed by the second particles may be, for example, 2.00 or less, more preferably 1.95 or less, and even more preferably 1.90 or less, 1.85 or less, 1.80 or less, 1.75 or less, or 1.70 or less. When the magnetic recording medium has an average protrusion height ratio (H1 / H2) within the above numerical range, friction increase (PES increase) due to multiple runs is reduced, contributing to the ability to appropriately maintain the abrasive force against the magnetic head.

[0115] The lower limit of the ratio of the average heights of the protrusions (H1 / H2) is not particularly limited, but may be, for example, preferably 1.00 or more, more preferably 1.10 or more, and even more preferably 1.20 or more.

[0116] The average height (H1) of the protrusions formed by the first particles may be, for example, 13.0 nm or less, preferably 12.0 nm or less, more preferably 11.5 nm or less, and even more preferably 11.0 nm or less, 10.5 nm or less, 10.0 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less. When the magnetic recording medium has an average height (H1) of the protrusions formed by the first particles within the above numerical range, the spacing between the magnetic head and the magnetic recording medium is reduced, friction increase due to multiple runs is reduced, and the abrasive force against the magnetic head can be maintained appropriately.

[0117] Furthermore, the lower limit of the average height (H1) of the protrusions formed by the primary particles is not particularly limited, but may be, for example, preferably 5.0 nm or more, more preferably 5.5 nm or more, and even more preferably 6.0 nm or more.

[0118] The average height (H2) of the protrusions formed by the second particles may be, for example, 8.0 nm or less, preferably 7.5 nm or less, more preferably 7.0 nm or less, and even more preferably 6.5 nm or less, 6.0 nm or less, 5.5 nm or less, or 5.3 nm or less. When the magnetic recording medium has an average height (H2) of the protrusions formed by the second particles within the above numerical range, the spacing between the magnetic head and the magnetic recording medium is reduced, the occurrence of friction increase due to multiple runs is reduced, and the abrasive force against the magnetic head can be maintained appropriately.

[0119] Furthermore, the lower limit of the average height (H2) of the protrusions formed by the secondary particles is not particularly limited, but may be, for example, preferably 2.0 nm or more, more preferably 2.5 nm or more, and even more preferably 3.0 nm or more.

[0120] (binder)

[0121] The binder is preferably a resin having a structure in which a crosslinking reaction has been imparted to a polyurethane resin or a vinyl chloride resin. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin that is generally used in coating-type magnetic recording media 10.

[0122] Examples of the binder 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, 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.

[0123] Furthermore, a thermosetting resin or a reactive resin may be used as the binder, and examples of such a resin include a phenolic resin, an epoxy resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea-formaldehyde resin.

[0124] 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 is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

[0125] Furthermore, the polar functional groups include -NR1R2 and -NR1R2R3 + X - Side chain type with terminal group of >NR1R2 + X - In the 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. Polar functional groups include —OH, —SH, —CN, and epoxy groups.

[0126] (additives)

[0127] 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.

[0128] (Nonmagnetic layer (base layer))

[0129] The non-magnetic layer (underlayer) 12 is a non-magnetic layer containing non-magnetic powder and a binder as its main components. The above description of the binder contained in the magnetic layer 13 also applies to the binder contained in the non-magnetic layer 12. The non-magnetic layer 12 may further contain at least one additive selected from the group consisting of first particles, a lubricant, a curing agent, and a rust inhibitor, as necessary.

[0130] The average thickness of the nonmagnetic layer 12 is preferably 1.2 μm or less, more preferably 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less, and even more preferably 0.6 μm or less. There is no particular lower limit to the average thickness of the nonmagnetic layer 12, but it is preferably 0.2 μm or more, and more preferably 0.3 μm or more.

[0131] (Non-magnetic powder)

[0132] The non-magnetic powder contained in the non-magnetic layer 12 may include, for example, at least one type selected from inorganic particles and organic particles. 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 may include, for example, one or a combination of two or more types selected from metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. More specifically, the inorganic particles may be, for example, one or two or more types selected from iron oxyhydroxide, hematite, titanium oxide, and carbon black. The shape of the non-magnetic powder may be, for example, acicular, spherical, cubic, plate-like, or other shapes, but is not particularly limited to these.

[0133] (Back layer)

[0134] The back layer 14 can contain a binder and a non-magnetic powder. The back layer 14 may also contain various additives such as a lubricant, a curing agent, and an antistatic agent as necessary. The above description of the binder and non-magnetic powder contained in the non-magnetic layer 12 also applies to the binder and non-magnetic powder contained in the back layer 14.

[0135] The average particle size of the inorganic particles contained in the 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 inorganic particles is determined in the same manner as the average particle size D of the magnetic powder described above.

[0136] The average thickness t of the back layer 14 b The average thickness t of the back layer 14 is preferably 0.6 μm or less, more preferably 0.5 μm or less, and even more preferably 0.4 μm or less, 0.3 μm or less, 0.25 μm or less, or 0.2 μm or less. b When the average thickness (average total thickness) t of the magnetic recording medium 10 is within the above range, T A TEven when the thickness is set to ≦5.7 μm, the average thickness of the nonmagnetic layer 12 and the base layer 11 can be kept large, thereby maintaining running stability within a recording / reproducing device for the magnetic recording medium 10. Furthermore, the lower limit of the average thickness of the back layer is not particularly limited, but can be, for example, 0.1 μm or more, and preferably 0.15 μm or more.

[0137] (3) Physical properties and structure

[0138] (average magnetic cluster size)

[0139] The average magnetic cluster size of the magnetic recording medium according to the present technology is, for example, 1850 nm 2 or less, and more preferably 1800 nm 2 or less, and even more preferably 1750 nm 2 Below, 1700nm 2 Below, 1650nm 2 or below 1600nm 2 or less, and even 1550nm 2 Below 1500nm 2 The average magnetic cluster size of the magnetic layer of the magnetic recording medium according to the present technology is thus small, that is, the areal recording density is high. The lower limit of the average size of the magnetic clusters is not particularly limited, but is, for example, 500 nm 2 More than 600 nm, preferably 2 More preferably, 700 nm 2 Over 800nm 2 Over 900nm 2 or above 1000nm 2 By making the average magnetic cluster size equal to or greater than these values, the thermal stability of the magnetic recording medium is improved.

[0140] The average magnetic cluster size is measured based on an MFM image of the surface of the magnetic recording medium on the side of the magnetic layer, using the following method.

[0141] First, a magnetic recording medium contained in a cartridge, such as cartridge 10A described below, is unwound, and a 1 cm x 1 cm square is cut out from the magnetic recording medium at a position 20 m longitudinally from the outside of the cartridge, from the area where data is recorded, and the cut-out portion is used as a measurement sample.

[0142] The surface of the measurement sample facing the magnetic layer is subjected to a DC erase treatment. The DC erase treatment is performed using a VSM (Vibrating Sample Magnetometer). The VSM may be a high-sensitivity vibrating sample magnetometer, model VSM-P7-15, manufactured by Toei Kogyo Co., Ltd. The measurement sample is placed in the VSM so that the magnetic surface of the measurement sample is parallel to the opposing coil of the VSM. An external magnetic field of 15 kOe is then applied perpendicular to the magnetic surface. The external magnetic field is then turned off, and a DC erased sample is obtained. In this manner, the DC erase process is performed.

[0143] Next, a 5 mm x 5 mm square was cut out from the center of the DC erased sample. The cut-out portion was observed using a magnetic force microscope (hereinafter also referred to as MFM). Three different locations were randomly selected from the cut-out portion, and MFM images were obtained for each of the three locations. In this way, three MFM images were obtained.

[0144] The MFM used to obtain the MFM images is a NanoScope IV Dimension 3100 manufactured by Digital Instruments and its analysis software. The cantilever used for the MFM is an SSS-MFMR (manufactured by NANOSENSORS, probe material: silicon single crystal coated with a magnetic film, cantilever length: 225 μm, tuned from 0 to 150 Hz). The measurement conditions for the MFM are as follows: <Measurement conditions> ScanSize:5μm×5μmNumber of Sample:512×512 Phase Detection Mode Lift Height: 20nm Filtering Process Flatten order:2 Planefit order XY:3 Sweep speed: 1Hz That is, the measurement area for obtaining the MFM image is set to 5 μm × 5 μm, and the 5 μm × 5 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. The 5 μm × 5 μm measurement area is measured by MFM under the measurement conditions described above to obtain an MFM image.

[0145] Three magnetic cluster size values ​​are obtained by performing the image analysis process described below on each of the three MFM images obtained, and the average magnetic cluster size is obtained by simply averaging the three magnetic cluster size values.

[0146] The image analysis process is performed using the image analysis software ImageJ (available from the National Institutes of Health) as follows. Specific operating procedures for the software are shown in parentheses for each step below. The image analysis process can also be said to measure the particle size distribution of the magnetic clusters, i.e., grain size analysis.

[0147] Step 1: Reading data ("File" → "Open") Open the image file of the MFM image to be analyzed.

[0148] Step 2: Scale adjustment ("Analyze" → "Set Scale") In the Set Scale window, set the scale as follows: Distance in pixels: 512 Known distance: 5 Pixel aspect ratio: 1.0 Unit of length: um After setting, click the OK button in the window. For example, as shown in FIG. 4A, after inputting into the Set Scale window, the OK button in the window is clicked.

[0149] Step 3: Crop the measurement image (Select "Rectangle" from the "Area Selection Tools" → Surround the MFM image → "Image" → "Crop") Use the rectangular selection tool to select a rectangle around the MFM image. The selected area is then cropped. For example, as shown in FIG. 4B, selecting the rectangular selection tool and then selecting and cropping a rectangle around the MFM image as shown by the white lines in FIG. 4C creates a window displaying the cropped MFM image as shown in FIG. 4D.

[0150] Step 4: Convert the image type ("Image" → "Type" → "8bit") The image type of the image cropped in step 3 is converted to an 8-bit grayscale image.

[0151] Step 5: Image smoothing ("Process" → "Smooth") The image converted to an 8-bit grayscale image in step 4 is subjected to a smoothing process to remove noise.

[0152] Step 6: Save (“Save”) The image after noise removal in step 5 is given an arbitrary name and saved in TIF format.

[0153] Step 7: Generate a histogram ("Analyze" → "Histogram") Generate a histogram of the image saved in step 6. This will display the Mean and StdDev. values ​​in the histogram window. For example, the histogram window shown in FIG. 4E is displayed, and the Mean value and StdDev. value are displayed in the window.

[0154] Step 8: Setting the threshold ("Image" → "Adjust" → "Threshold") Using the Mean and StdDev. values ​​displayed in step 7, the threshold is determined using the following formula. Note that the distribution in the histogram is assumed to be Gaussian (normal). Also, the standard deviation (StdDev. value) = root mean square (rms). [Threshold]=[Mean]+([StdDev.]×0.7) In the Threshold window, enter the determined threshold value as the minimum value (Min) and 255 as the maximum value (Max), and click the "Apply" button, which will display the binarized image. That is, the threshold range a for binarization is {[Mean]+([StdDev.]×0.7)}≦a≦255 The average area of ​​the positive electrode part in the image is calculated as follows: For example, enter the determined threshold value in the minimum (Min) input field in the Threshold window shown in Figure 4F, and click the "Apply" button to enter the maximum value. This will result in a binarized image as shown in Figure 4G.

[0155] Step 9: Particle size distribution calculation ("Analyze" → "Analyze Particles") A particle size distribution calculation process is performed on the binarized image obtained in step 8. The processing conditions for this calculation process are as follows: Size: 0-Infinity Circularity: 0.00-1.00 Show: Bare outlines Checking Summarize in the Analyze Particles window will display the Summary screen. The Summary screen displays the Count (number of particles), Total Area (total area), Average size (number of particles), Area Function (percentage of area occupied by particles), and Mean. Of these, the average magnetic cluster size is calculated using [Count] and [Total Area] using the following formula: [Magnetic cluster size value (nm 2 )]=[Total Area] / [Count]×10 6 For example, configure the settings in the Analyze Particles window as shown in Figure 4H and click the OK button. This will display the Summary screen as shown in Figure 4I. The magnetic cluster size value is calculated using the data in this screen.

[0156] The above image analysis process is performed on each of the three MFM images to obtain three magnetic cluster size values. The average magnetic cluster size is obtained by simply averaging the three magnetic cluster size values.

[0157] (Protrusion height)

[0158] As described below, the heights of the protrusions formed by the first particles and the second particles are measured by performing shape analysis of the same location on the measurement sample using an atomic force microscope (hereinafter referred to as an AFM) and component discrimination by image analysis of a field emission scanning electron microscope (hereinafter referred to as an FE-SEM) image taken by an FE-SEM, utilizing the brightness difference due to the difference in the amount of secondary electron emission of the first particles and the second particles. That is, the height of each protrusion can be measured using the AFM, and whether each protrusion is formed by the first particles or the second particles can be identified using the FE-SEM. A composite image can be obtained by overlaying the image obtained by the AFM of the same location and the image obtained by the FE-SEM of the certain region, and the type of particle forming each protrusion (whether it is the first particle or the second particle) can be associated with the height of each protrusion from the composite image. Below, we will explain how to measure the height of protrusions using AFM, how to identify the type of particles that form the protrusions using FE-SEM, and how to associate the height of the protrusions with the type of particles that form the protrusions.

[0159] (Method for measuring protrusion height using an atomic force microscope (AFM)) In the present technology, the height of the protrusions formed by the first particles and the second particles is determined as follows. First, a measurement sample is prepared by cutting out a portion of the magnetic recording medium 10 in the user data area (for example, 24 m or more from the leader pin) in an LTO cartridge to a size that can fit on the observation sample stage of the FE-SEM described below. Next, markings are made on the surface of the measurement sample, avoiding the center of the measurement sample. A method of marking may be employed in which a manipulator is used to scratch the surface of the magnetic recording medium 10 with a needle-shaped metal marker. Since the AFM scans the marked area with a probe, depending on the condition of the marked area, the tip of the probe may become contaminated, making it impossible to obtain an accurate shape image. Therefore, it is preferable to make the markings small and shallow to prevent contamination of the probe. Next, the shape of the area near the marking part on the surface of the measurement sample is analyzed by AFM. Since the marked marking part is recessed, alignment is performed so that the marking part is at the edge of the field of view as much as possible, and measurement is carried out at a field angle of 5 μm × 5 μm with AFM. Note that the protrusions on the periphery of the marking part are excluded from the measurement targets. As a specific procedure for the shape analysis, for example, first, a field angle of 10 μm × 10 μm including the marking part is measured, a reference part is determined for alignment, and then, in accordance with the reference part, the area without the marking part is measured at a field angle of 5 μm × 5 μm. The measurement conditions for the shape analysis are as described below. For each of the first particles and the second particles, when 20 or more particles can be identified in one field of view of AFM from one measurement sample, one field of view is measured with AFM. For each of the first particles and the second particles, when the number of particles that can be identified in one field of view of AFM is less than 20, a plurality (for example, 3 to 5) of fields of view are measured from one measurement sample. For each of the first particles and the second particles, 20 points identified as particles by binarization processing are secured, the 20 AFM measurement values are averaged, and the obtained average value is taken as the average height of the protrusions (the average height H1 of the protrusions formed by the first particles and the average height H2 of the protrusions formed by the second particles). Through the shape analysis, information regarding the surface shape, protrusion analysis, and height distribution of the protrusions can be obtained. FIG. 5A is an example of an image showing an example of the surface shape captured by AFM. FIG. 5B is a diagram showing an example of the protrusion analysis result by AFM. FIG. 5C is a diagram showing an example of the height distribution of the protrusions. Data such as the number of protrusions formed from the obtained information and the height of the protrusions formed by the particles can be obtained.

[0160] <AFM Measurement Conditions> Apparatus: AFM Dimension 3100 microscope (having a NanoscopeIV controller) (Digital Instruments, USA) Measurement mode: Tapping Tapping frequency during tuning: 200 - 400 kHz Cantilever: SNL-10 (manufactured by Bruker) Scan size: 5μm × 5μm Scan rate: 1Hz Scan line: 256

[0161] <Calculation method of reference plane when calculating protrusion height> Divide the AFM image into 256 × 256 (= 65,536) measurement points, measure the height Z(i) (i: measurement point number, i = 1 to 65,536) at each measurement point, and simply average (arithmetic mean) the measured heights Z(i) of each measurement point to obtain the average height (reference plane) Z ave (=(Z(1) + Z(2) + ··· + Z(65,536)) / 65,536). ("Height at measurement point" - "Reference plane height") corresponds to the height of each protrusion.

[0162] (Method for identifying the type of particles forming protrusions using FE - SEM) Image the region including the marking part of the measurement sample using a field emission scanning electron microscope (FE - SEM) under the FE - SEM measurement conditions described below to obtain a FE - SEM image. Figure A in Figure 6 is an example of a FE - SEM image. From the obtained FE - SEM image, utilize the luminance difference due to the difference in the secondary electron emission amounts of the first particles and the second particles respectively to identify the type of particles forming the protrusions. The image processing for this identification will be described later. Also, identify the positions of the protrusions formed by the first particles and the second particles respectively in the FE - SEM image.

[0163] <FE - SEM measurement conditions> Apparatus: HITACHI S - 4800 (manufactured by Hitachi High - Technologies Corporation) Field of view angle: 5.1μm × 3.8μm Acceleration voltage: 5kV Measurement magnification: 25000 times

[0164] The obtained FE-SEM image (Figure A in Figure 6) was binarized using the image processing software Image J under the two processing conditions described below. From the image obtained by binarization, information on the number of protrusions formed by each of the primary particles and secondary particles, the average area per protrusion, the total area of ​​the protrusions, and the diameter of the protrusions (Feret diameter) could be obtained. The number of protrusions per unit area for each of the first particle and the second particle can be calculated using the following formula. [Number of protrusions per unit area] = [Number of protrusions] ÷ [Area of ​​the area where the number of protrusions was obtained] In this calculation formula, the number of protrusions can be automatically obtained using image processing software Image J. In the binarization process, the conditions are changed as follows for the second particles with high brightness (white areas in A in FIG. 6) and the first particles with low brightness (black areas in A in FIG. 6).

[0165] <Binarization processing conditions for obtaining information about the first particle>

[0166] Software: Image J Ver 1.44p Binarization threshold: Threshold(0.65) Binarization target size: 0.002μm-infinity

[0167] <Binarization processing conditions for obtaining information about secondary particles>

[0168] Software: Image J Ver 1.44p Binarization threshold: Threshold(220,255) Binarization target size: 0.001μm-infinity

[0169] Figure 6B shows the position distribution of the protrusions formed by the secondary particles (alumina particles) after binarizing the FE-SEM image of Figure 6A under the binarization conditions for the secondary particles (alumina particles). For example, the following information about the secondary particles was obtained from the image obtained in Figure 6:

[0170] <Information about the obtained second particle>

[0171] Quantity: 58 Average area: 0.003μm 2 Total area: 0.198 μm 2 Feret diameter: 0.091 μm

[0172] Figure 6C is an image showing the position distribution of protrusions formed by the first particles (carbon black particles) obtained by binarizing the FE-SEM image of Figure 6A under the binarization conditions for the first particles (carbon black particles). For example, with regard to Figure 6, the following information about the first particles was obtained from the obtained image.

[0173] <Information about the first particle obtained>

[0174] Quantity: 55 Average area: 0.005μm 2 Total area: 0.262 μm 2 Feret diameter: 0.013 μm

[0175] (Method of Corresponding Protrusion Height to the Type of Particles That Form the Protrusions) The obtained AFM image is overlaid with the FE-SEM image before binarization to obtain a composite image. Using the composite image, the particles forming each protrusion are identified as either primary particles or secondary particles. For example, Figure 7C shows a composite image obtained by superimposing an AFM image (Figure 7B) and an FE-SEM image (Figure 7A) so that the positions of corresponding protrusions coincide. In Figure 7, the positions of the protrusions formed by the first particles P1 and the second particles P2, which are identified by the binarization process and which are present in the FE-SEM image (Figure 7A) before image synthesis, are marked with different marks so that they can be distinguished from each other. Similarly, the positions of the protrusions formed by the first particles (carbon black particles) P1 and the second particles (alumina particles) P2, which are identified by the binarization process and which are present in the AFM image (Figure 7B) before image synthesis, are marked with different marks so that they can be distinguished from each other. From this composite image obtained by superimposing the AFM image (Figure 7B) and the FE-SEM image (Figure 7A) so that the positions of corresponding protrusions coincide, it is possible to determine whether each protrusion is formed by the first particles P1 or the second particles P2. In addition, in Figure 7B, the marked area was measured with an AFM at a viewing angle of 10 μm × 10 μm, and then the area without the marking was measured at a viewing angle of 5 μm × 5 μm, so the marking is not present in the image.

[0176] Next, the height of each protrusion in the composite image is measured using AFM analysis software (Software version 5.12 Rev.B for Dimension 3100, manufactured by Veeco). As described above, the type of particle forming each protrusion (whether it is a first particle or a second particle) is identified, and therefore the identified particle type is associated with the measured height. For example, Fig. 8 is an enlarged view of a composite image obtained by superimposing an AFM image and an FE-SEM image. Fig. 9 is a diagram showing the results of AFM analysis (protrusion height measurement results) for Line 1 (Line 1) set at an arbitrary position in Fig. 8. As shown in Fig. 9, the heights of the protrusions formed by the first particles (carbon black particles) and second particles (alumina particles) present on Line 1 can be identified. In this way, the height of each protrusion can be identified from the composite image and the AFM analysis results.

[0177] (Average height of protrusions and average height ratio of protrusions)

[0178] From the information regarding the height of the protrusions obtained as described above, the average height of the protrusions formed by the first particles, the average height of the protrusions formed by the second particles, and the average height ratio of the protrusions are determined as described above.

[0179] (Average thickness of magnetic recording medium (average total thickness) t T )

[0180] Average thickness (average total thickness) t of the magnetic recording medium 10 T The average thickness t of the magnetic recording medium 10 may be, for example, 5.7 μm or less, preferably 5.6 μm or less, more preferably 5.5 μm or less, 5.4 μm or less, 5.3 μm or less, 5.2 μm or less, 5.1 μm or less, or 5.0 μm or less, and even more preferably 4.6 μm or less or 4.4 μm or less. T When the average thickness t of the magnetic recording medium 10 is 5.2 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to that of a general magnetic tape. T The lower limit is not particularly limited, but is, for example, 3.5 μm or more.

[0181] The average thickness t of the magnetic recording medium 10 (hereinafter also referred to as magnetic tape T) T is obtained as follows. First, the magnetic tape T housed in a cartridge such as the cartridge 10A described below is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT. Next, the thickness of the sample is measured at five positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t T The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape T.

[0182] (Average thickness of non-magnetic layer (underlayer))

[0183] The average thickness of the nonmagnetic layer 12 is determined as follows. First, the magnetic tape T housed in a cartridge, such as the cartridge 10A described below, is unwound, and three samples of 250 mm are cut from the magnetic tape T at three locations, 10 m, 30 m, and 50 m from the connection 221 between the magnetic tape T and the leader tape LT, to prepare three samples. Next, each sample is thinned using a FIB method or other method. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM images described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape T facing the magnetic layer 13 and the surface facing the back layer 14, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 13. The thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.

[0184] The cross section of each of the obtained thinned samples is observed under a transmission electron microscope (TEM) under the following conditions. Apparatus: TEM (Hitachi H9000NAR) Accelerating voltage: 300 kV Magnification: 100,000x Next, using the obtained TEM image, the thickness of the non-magnetic layer 12 is measured at at least 10 positions in the longitudinal direction of the magnetic tape T, and then the measured values ​​are simply averaged (arithmetic averaged) to obtain the average thickness (μm) of the non-magnetic layer 12.

[0185] (average thickness of base layer)

[0186] The average thickness of the base layer 11 is determined as follows. First, the magnetic tape T housed in a cartridge such as the magnetic recording cartridge 10A described below is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT. In this specification, the "longitudinal direction" in the "longitudinal direction from the joint between the magnetic tape T and the leader tape LT" refers to the direction from one end on the leader tape LT side to the other end on the opposite side.

[0187] Next, all layers of the sample other than the base layer 11 (i.e., the non-magnetic layer (underlayer) 12, the magnetic layer 13, and the back layer 14) are removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample (base layer 11) is measured at five positions, and the measured values ​​are simply averaged (arithmetic mean) to calculate the average thickness of the base layer 11. Note that the five measurement positions are selected randomly from the sample so that they are each different from the others in the longitudinal direction of the magnetic tape T.

[0188] (Average thickness of back layer t b )

[0189] The upper limit of the average thickness of the back layer 14 is preferably 0.6 μm or less. If the upper limit of the average thickness of the back layer 14 is 0.6 μm or less, the thicknesses of the nonmagnetic layer (underlayer) 12 and the base layer 11 can be kept thick even when the average thickness of the magnetic tape T is 5.6 μm or less, thereby maintaining running stability of the magnetic tape T within a recording / 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.

[0190] The average thickness t of the back layer 14 b can be calculated as follows: First, the average thickness (average total thickness) of the magnetic tape T is t T Measure the average thickness t TThe method for measuring the average total thickness is as described above. Next, the magnetic tape T housed in the cartridge 10A is unwound, and the magnetic tape T is cut into a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT to prepare a sample. Next, the back layer 14 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five positions using a Mitutoyo laser hologram (LGH-110C), and these measurements are simply averaged (arithmetic average) to obtain the average thickness t B Then, the average thickness t of the back layer 14 is calculated using the following formula: b The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape T. t b [μm]=t T [μm]-t B [μm]

[0191] (the average thickness of the magnetic layer t m )

[0192] The average thickness t of the magnetic layer 13 m is determined as follows. First, the magnetic tape T housed in the cartridge 10A is unwound, and three samples of 250 mm length are cut from the magnetic tape T at three positions, 10 m, 30 m, and 50 m from the joint 221 between the magnetic tape T and the leader tape LT, in the longitudinal direction. Each sample is then thinned using a FIB method or the like. When the FIB method is used, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape T facing the magnetic layer 13 and the surface facing the back layer 14, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 13. The thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.

[0193] The cross section of each obtained sliced ​​sample is observed under a transmission electron microscope (TEM) under the following conditions to obtain a TEM image of each sliced ​​sample. 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

[0194] Next, using the TEM image of each obtained sliced ​​sample, the thickness of the magnetic layer 13 is measured at 10 positions on each sliced ​​sample. The 10 measurement positions on each sliced ​​sample are randomly selected from the sample so that they are different positions in the longitudinal direction of the magnetic tape T. The measured values ​​of each obtained sliced ​​sample (thickness of the magnetic layer 13 at 30 points in total) are simply averaged (arithmetic average) to obtain an average value, which is the average thickness t of the magnetic layer 13. m Let [nm].

[0195] (Standard deviation of PES values ​​σPES)

[0196] The standard deviation σPES of the PES values ​​of the magnetic recording medium 10 according to the present technology may be 50 nm or less, preferably less than 50 nm, more preferably 40 nm or less, even more preferably 30 nm or less, and even more preferably 25 nm or less, when full volume tests are preferably performed 40 times. In this specification, the number of full volume tests is also referred to as the FV number. The PES (Position Error Signal) indicates the deviation (error) of the read position of the servo pattern in the width direction of the magnetic recording medium 10 when the servo pattern is reproduced (read) by the recording / reproducing device 30. In order to accurately adjust the tension in the longitudinal direction of the magnetic recording medium 10, it is preferable that the linearity of the servo band when the servo pattern is read by the recording / reproducing device 30 is as high as possible, that is, the standard deviation σPES of the PES value indicating the deviation of the read position is as low as possible. Since the standard deviation σPES of the PES value of the magnetic recording medium 10 of the present technology is a low value as described above, the linearity of the servo band is high and tension adjustment can be performed accurately.

[0197] FIG. 10 is a diagram showing the change over time in the standard deviation σPES of the PES values ​​as the magnetic tape runs. As shown in FIG. 10, if σPES is less than 50 nm when 40 full-volume tests are performed, no track misalignment occurs. FIG. 11 is a diagram showing the change over time in the standard deviation σPES of the PES values ​​as the magnetic tape runs. As shown in FIG. 11, if σPES is more than 50 nm when 40 full-volume tests are performed, frequent track misalignment occurs, causing the magnetic tape to stop running.

[0198] The top diagram in Figure 12 shows the change in standard deviation σPES over time as the magnetic tape runs. The bottom left diagram in Figure 12 is a cross-sectional view schematically illustrating the relationship between the magnetic head and the protrusions formed on the magnetic layer surface by the first particles (carbon particles) P1 and the protrusions formed on the magnetic layer surface by the second particles (alumina particles) P2 in region A (stable friction) where σPES in the top diagram is approximately constant. The dashed line in the diagram is a virtual line indicating contact between the protrusions formed on the magnetic layer surface by the first particles (carbon particles) P1 and the magnetic head surface. The bottom right diagram in Figure 12 is a cross-sectional view schematically illustrating the relationship between the magnetic head and the protrusions formed on the magnetic layer surface by the first particles (carbon particles) P1 and the protrusions formed on the magnetic layer surface by the second particles (alumina particles) P2 in region B (increasing friction) where σPES in the top diagram tends to increase. The dashed line in the diagram is a virtual line indicating contact between the protrusions formed on the magnetic layer surface by the first particles (carbon particles) P1 and the magnetic head surface.

[0199] As shown in Figure 12, the standard deviation σPES is almost constant in region A, but increases in region B. This is presumably because, in region A, the contact area between the protrusions formed by the first particles (carbon particles) P1 and the magnetic head surface is small and friction is constant, whereas in region B, as the magnetic tape runs, the first particles (carbon particles) P1 are worn down by the magnetic tape, the protrusions formed by the first particles (carbon particles) P1 gradually break down, the contact area between the protrusions formed by the first particles (carbon particles) P1 and the magnetic head surface increases, and friction increases.

[0200] Hereinafter, a method for measuring the standard deviation σPES will be described with reference to FIGS. 13A to 13C. The PES value is measured to determine the standard deviation σPES. To measure the PES value, a PES measurement head unit 300, such as that shown in FIG. 16B, is prepared. An LTO2 head (a head conforming to the LTO2 standard) manufactured by HPE (Hewlett Packard Enterprise) is used as the head unit 300. The head unit 300 has two head sections 300A and 300B arranged side by side along the longitudinal direction of the magnetic recording medium 10. Each head section includes a plurality of recording heads 340 for recording data signals on the magnetic recording medium 10, a plurality of reproducing heads 350 for reproducing the data signals recorded on the magnetic recording medium 10, and a plurality of servo heads 320 for reproducing the servo signals recorded on the magnetic recording medium 10. When the head unit 300 is used only for measuring the PES value, the recording head 340 and the reproducing head 350 do not necessarily have to be included in the head unit.

[0201] First, head unit 300 is used to reproduce (read) servo patterns in a predetermined servo band provided on magnetic recording medium 10. At this time, servo head 320 of head unit 300A and servo head 320 of head unit 300B sequentially face each servo pattern in the predetermined servo band, and these two servo heads 320 sequentially reproduce the servo patterns. At this time, the portion of the servo pattern recorded on magnetic recording medium 10 facing servo head 320 is read and output as a servo signal.

[0202] As shown in FIG. 13A, the PES value for each head part is calculated for each servo frame using the following formula:

number

[0203] The above difference (B a1 -A a1 ) indicates the time [sec] on the actual path between two corresponding servo patterns, servo pattern B1 and servo pattern A1. Similarly, other difference terms also indicate the time [sec] on the actual path between two corresponding servo patterns. These times are calculated from the time between timing signals obtained from the servo signal waveform and the tape running speed. In this specification, the actual path means the position where the servo signal read head actually runs on the servo signal. φ is the azimuth angle, which is determined by developing the magnetic recording medium 10 with a ferricolloid developer and using a universal tool microscope (TOPCON TUM-220ES) and a data processing device (TOPCON CA-1B).

[0204] In this technology, the standard deviation σPES of the PES values ​​is calculated using a servo signal that has been corrected for lateral tape movement. Furthermore, the servo signal is subjected to high-pass filtering to reflect the head tracking performance. In this technology, the standard deviation σPES is calculated using a signal obtained by performing the correction and high-pass filtering on the servo signal, and is known as the "written in PESσ." The method for measuring the standard deviation σPES of the PES values ​​will be described below.

[0205] First, the head 300 reads the servo signal from an arbitrary 1-meter range in the data recording area of ​​the magnetic recording medium 10. The signals acquired by the head units 300A and 300B are subtracted as shown in FIG. 13C to obtain a servo signal corrected for lateral tape movement. The corrected servo signal is then subjected to high-pass filtering. When the magnetic recording medium 10 is actually driven by a drive, the recording / reproducing head mounted on the drive is moved by an actuator across the width of the magnetic recording medium 10 to track the servo signal. Since the Written in PESσ is a noise value that takes into account the width-direction tracking ability of the head, the high-pass filtering is necessary. Therefore, although the high-pass filter is not particularly limited, it must be a function that can reproduce the width-direction tracking ability of the drive head. Using the signal obtained by the high-pass filtering, the PES value is calculated for each servo frame according to the above formula. The standard deviation of the PES values ​​calculated over the 1-meter range (Written in PESσ) is the standard deviation σPES of the PES values ​​in this technology.

[0206] (Squareness ratio in the vertical direction Rs2)

[0207] The squareness ratio Rs2 in the perpendicular direction (thickness direction) of the magnetic recording medium of the present technology can be preferably 65% ​​or more, more preferably 67% or more, and even more preferably 70% or more. When the squareness ratio Rs2 is 65% or more, the perpendicular orientation of the magnetic powder is sufficiently high, resulting in a superior SNR. Therefore, superior electromagnetic conversion characteristics can be obtained. Furthermore, the servo signal shape is improved, making it easier to control on the drive side. In this specification, a magnetic recording medium being perpendicularly oriented may mean that the squareness ratio Rs2 of the magnetic recording medium is within the above numerical range (for example, 65% or more).

[0208] The squareness ratio Rs2 in the vertical direction is found as follows. First, the magnetic tape T housed in the magnetic recording cartridge 10A is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT. The sample is punched out to 6.25 mm x 64 mm, and then folded in three to prepare a measurement sample of 6.25 mm x 8 mm. Then, the vertical squareness ratio Rs2 of the magnetic tape T is measured using a VSM. The MH hysteresis loop of the measurement sample (the entire magnetic tape T) corresponding to the perpendicular direction (thickness direction) is measured. Next, the coating films (underlayer 12, magnetic layer 13, back layer 14, etc.) are wiped off using acetone or ethanol, leaving only the base layer 11. The obtained base layer 11 is then punched out to 6.25 mm x 64 mm and folded in three to form a 6.25 mm x 8 mm sample for background correction (hereinafter simply referred to as the "correction sample"). Thereafter, the MH hysteresis loop of the correction sample (base layer 11) corresponding to the perpendicular direction of the base layer 11 (the perpendicular direction of the magnetic recording medium 10) is measured using a VSM.

[0209] The MH hysteresis loop of the measurement sample (the entire magnetic tape T) and the MH hysteresis loop of the correction sample (base layer 11) are measured using a high-sensitivity vibration sample magnetometer "VSM-P7-15" manufactured by Toei Industry 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. After obtaining the MH hysteresis loop of the measurement sample (the entire magnetic tape T) and the MH hysteresis loop of the correction sample (base layer 11), background correction is performed by subtracting the MH hysteresis loop of the correction sample (base layer 11) from the MH hysteresis loop of the measurement sample (the entire magnetic tape T), and the MH hysteresis loop after background correction is obtained. This background correction calculation is performed using the measurement and analysis program included with the "VSM-P7-15 model."

[0210] The saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the MH hysteresis loop after background correction are substituted into the following equation to calculate the squareness ratio Rs2 (%). Note that all of the above MH hysteresis loop measurements are performed at 25°C. Furthermore, no "demagnetizing field correction" is performed when measuring the MH hysteresis loop in the perpendicular direction to the magnetic tape T. Note that this calculation uses the measurement and analysis program included with the "VSM-P7-15 model." Squareness ratio Rs2(%)=(Mr / Ms)×100

[0211] (Coercive force Hc)

[0212] The coercive force Hc in the perpendicular direction (thickness direction) of the magnetic recording medium 10 may be preferably 160 kA / m or more, more preferably 165 kA / m or more, and even more preferably 170 kA / m or more. By having the coercive force Hc be equal to or greater than this lower limit, excellent thermal stability can be obtained even when the average magnetic cluster size is small as described above. The coercive force Hc may be preferably 300 kA / m or less, more preferably 290 kA / m or less, and even more preferably 280 kA / m or less, 275 kA / m or less, or 270 kA / m or less. When the coercive force Hc is equal to or less than such an upper limit, recording processing by a magnetic head can be performed satisfactorily. Thus, the present technology has a magnetic layer containing magnetic powder, and the average magnetic cluster size measured based on an MFM image of the surface of the magnetic layer is 1850 nm. 2 The present invention also provides a magnetic recording medium having a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less. This magnetic recording medium has excellent electromagnetic conversion characteristics and is also excellent from the viewpoint of recording processing by a magnetic head.

[0213] The coercive force Hc is determined as follows. First, three magnetic recording media 10 are stacked with double-sided tape and then punched out with a φ6.39 mm punch to prepare a measurement sample. At this time, markings are made with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be identified. Then, 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 is measured using a vibrating sample magnetometer (VSM). Next, the coating films (underlayer 12, magnetic layer 13, back layer 14, etc.) are wiped off using acetone or ethanol, leaving only the base layer 11. Then, three of the obtained base layers 11 are stacked with double-sided tape and then punched out with a φ6.39 mm punch to prepare a sample for background correction (hereinafter simply referred to as the "correction sample"). Thereafter, the MH loop of the correction sample (base layer 11) corresponding to the perpendicular direction of the base layer 11 (perpendicular direction of the magnetic recording medium 10) is measured using the VSM. The MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (base layer 11) are measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Industry 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. After obtaining the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (base layer 11), background correction is performed by subtracting the MH loop of the correction sample (base layer 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10), thereby obtaining the MH loop after background correction. This background correction calculation is performed using the measurement and analysis program included with the "VSM-P7-15 model." 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.

[0214] (4) Manufacturing method of magnetic recording medium

[0215] Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming a non-magnetic layer (underlayer) is prepared by kneading and / or dispersing non-magnetic powder, a binder, etc. in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and / or dispersing magnetic powder, first particles, second particles, a binder, etc. in a solvent. The following solvents, dispersing devices, and kneading devices can be used, for example, to prepare the paint for forming a magnetic layer and the paint for forming a non-magnetic layer (underlayer).

[0216] Examples of solvents that can be used in preparing the coating material include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol-based solvents such as methanol, ethanol, and propanol; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; ether-based solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbon-based solvents such as benzene, toluene, and xylene; and halogenated hydrocarbon-based solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These solvents may be used singly or in combination.

[0217] 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, and roll kneaders. Examples of dispersing devices that can be used in preparing the above-mentioned coating materials include, but are not limited to, bead mills, roll mills, ball mills, horizontal sand mills, vertical sand mills, spike mills, pin mills, tower mills, pearl mills (such as the "DCP Mill" manufactured by Eirich), homogenizers, and ultrasonic dispersers.

[0218] In a preferred embodiment, the magnetic layer-forming coating material is used to produce a magnetic recording medium having the above-mentioned characteristics regarding the average size of magnetic clusters (for example, the average size is 1850 nm 2 and a characteristic regarding the first particles and the second particles (for example, a characteristic regarding the ratio H1 / H2 being 2.00 or less). For this preparation, for example, the processing conditions (e.g., type of apparatus, time, etc.) for kneading and / or dispersing the magnetic powder and the first and second particles may be adjusted. In one embodiment, a bead mill may be used as the apparatus for the dispersion treatment. The bead diameter may be appropriately selected by those skilled in the art depending on the particle size to be dispersed. Furthermore, by adjusting the dispersion time, it is possible to adjust the coating material to achieve the above characteristics. For example, the average magnetic cluster size can be reduced by extending the time for the dispersion treatment of the magnetic powder. The dispersion time (particularly the actual dispersion time) may be, for example, 30 minutes to 3 hours, preferably 30 minutes to 2 hours. The dispersion time may be appropriately adjusted by those skilled in the art depending on, for example, the type of particles. For this preparation, the content of the magnetic powder, the content of the first particles, and the content of the second particles may be adjusted, for example. For example, when a magnetic powder with a smaller average particle volume is used, the content of the first particles and / or the second particles can be reduced to make the dispersion state of these particles more appropriate, and thereby the height of the protrusions formed by these particles can be adjusted to an appropriate value. The content of the first particles may be, for example, 1 to 15 parts by mass, preferably 2 to 10 parts by mass, per 100 parts by mass of the magnetic powder. The content of the second particles may also be, for example, 1 to 15 parts by mass, preferably 2 to 10 parts by mass, per 100 parts by mass of the magnetic powder. The content of each particle may be appropriately selected by a person skilled in the art from within these numerical ranges.

[0219] In a particularly preferred embodiment, the dispersion treatment of the magnetic powder in the solvent and the dispersion treatment of the first particles and the second particles in the solvent are carried out separately. By separately carrying out the dispersion treatment of the magnetic powder and the dispersion treatment of the inorganic material in this manner, the dispersion state of these materials can be appropriately adjusted, making it easier to achieve the above-mentioned features. In this embodiment, a bead mill may be used as the device for the dispersion treatment. The bead diameter may be appropriately selected by those skilled in the art depending on the particle size to be dispersed. The dispersion time (particularly the actual dispersion time) may be, for example, 30 minutes to 3 hours, preferably 30 minutes to 2 hours. The dispersion time may be appropriately adjusted by those skilled in the art depending on, for example, the type of particles. Achieving these features can lead to improvements in the electromagnetic conversion characteristics and / or running performance of the magnetic recording medium. To adjust the dispersion state, for example, the dispersion time and / or the amount of each component may be adjusted.

[0220] That is, the manufacturing method includes a step of preparing a paint for forming a magnetic layer, and this step may include a first dispersion step of dispersing the magnetic powder in a solvent, and a second dispersion step of dispersing the first particles and the second particles in the solvent. In the first dispersion step, a first composition is obtained in which the magnetic powder is dispersed in a solvent (particularly a binder-containing solvent, for example, a resin-containing solvent). In the second dispersion step, a second composition is obtained in which the first particles and the second particles are dispersed in a solvent (particularly a binder-containing solvent, for example, a resin-containing solvent). The magnetic layer-forming paint preparation step includes a mixing step of mixing the first composition and the second composition. In this mixing step, other compositions (particularly binder-containing solvents, for example, resin-containing solvents) may also be mixed. By this mixing step, the magnetic layer-forming paint is produced.

[0221] In another embodiment, the magnetic layer-forming coating preparation process may include a first dispersion process for dispersing the magnetic powder in a solvent, a second dispersion process for dispersing the first particles in a solvent, and a third dispersion process for dispersing the second particles in a solvent. In this manner, the dispersion process of the magnetic powder, the dispersion process of the first particles, and the dispersion process of the second particles may be performed separately. Even in this embodiment, the dispersion state of these materials can be appropriately adjusted, making it easier to achieve the above-described characteristics. Furthermore, achieving these characteristics can lead to improved electromagnetic conversion characteristics and / or improved running performance of the magnetic recording medium. Even in this embodiment, the dispersion state may be adjusted by adjusting, for example, the dispersion time and / or the amount of each component.

[0222] Next, a nonmagnetic layer (underlayer) forming paint is applied to one main surface of the base layer 11 and dried to form the nonmagnetic layer 12. Subsequently, a magnetic layer forming paint is applied to the nonmagnetic layer 12 and dried to form the magnetic layer 13 on the nonmagnetic layer 12. During drying, the magnetic powder is magnetically oriented in the thickness direction of the base layer 11, for example, using a solenoid coil. Alternatively, during drying, the magnetic powder may be magnetically oriented in the longitudinal direction (running direction) of the base layer 11 using a solenoid coil, and then magnetically oriented in the thickness direction of the base layer 11. Such magnetic field orientation treatment can reduce the ratio Hc2 / Hc1 of the coercivity in the perpendicular direction (Hc1) to the coercivity in the longitudinal direction (Hc2), thereby improving the degree of perpendicular orientation of the magnetic powder. After the magnetic layer 13 is formed, a back layer 14 is formed on the other main surface of the base layer 11. This completes the magnetic recording medium 10.

[0223] The ratio Hc2 / Hc1 can be set to a desired value 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) for the coating film of the magnetic layer-forming paint. The strength of the magnetic field applied to the coating film is preferably between two and three times the cohesive strength of the magnetic powder. To further increase the ratio Hc2 / Hc1, it is also preferable to magnetize the magnetic powder before the magnetic layer-forming paint enters an orientation device that magnetically orients the magnetic powder. Note that the methods for adjusting the ratio Hc2 / Hc1 may be used alone or in combination of two or more.

[0224] The resulting magnetic recording medium 10 is then rewound around a large diameter core and hardened. Finally, the magnetic recording medium 10 is calendered and then cut to a predetermined width (e.g., 1 / 2 inch width). This completes the desired long, thin magnetic recording medium 10.

[0225] (5) Recording and playback device

[0226] [Configuration of recording / playback device]

[0227] Next, with reference to FIG. 14, an example of the configuration of a recording / reproducing device 30 that performs recording and reproducing on the magnetic recording medium 10 having the above configuration will be described.

[0228] The recording / reproducing device 30 may be 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 10A. Here, for ease of explanation, a case will be described in which the recording / reproducing device 30 is configured to be able to load one magnetic recording cartridge 10A, but the recording / reproducing device 30 may also be configured to be able to load multiple magnetic recording cartridges 10A. The recording and reproducing device 30 is preferably a timing servo type magnetic recording and reproducing device, and the magnetic recording medium of the present technology is suitable for use in a timing servo type magnetic recording and reproducing device.

[0229] The recording / reproducing 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 cartridge 10A. The shortest recording wavelength of the recording / reproducing device 30 is 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.

[0230] As shown in Figure 14, the recording and playback device includes a spindle 31, a reel 32 on the recording and playback device side, a spindle drive device 33, a reel drive device 34, multiple guide rollers 35, a head unit 36, a communication interface (hereinafter referred to as I / F) 37, and a control device 38.

[0231] The spindle 31 is configured so that a magnetic recording cartridge 10A can be attached thereto. The magnetic recording cartridge 10A conforms to the LTO (Linear Tape Open) standard, and rotatably accommodates a single reel 10C around which a magnetic recording medium 10 is wound in a cartridge case 10B. 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 10A can be fixed. The present technology also provides a magnetic recording cartridge including a magnetic recording medium according to the present technology. In the magnetic recording cartridge, the magnetic recording medium may be wound on a reel, for example, and may be housed in a case while wound on the reel.

[0232] The spindle drive device 33 is a device that rotates the spindle 31. The reel drive device 34 is a device that rotates the reel 32. When recording or reproducing data on the magnetic recording medium 10, the spindle drive device 33 and the reel drive device 34 rotate the spindle 31 and the reel 32, thereby running the magnetic recording medium 10. The guide roller 35 is a roller that guides the running of the magnetic recording medium 10.

[0233] 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. A ring-type head can be used as the recording head, for example, but the type of recording head is not limited to this.

[0234] The communication 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.

[0235] 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.

[0236] The control device 38 also detects changes in the width of the magnetic recording medium 10 based on the servo signals supplied from the head unit 36. Specifically, multiple V-shaped servo patterns are recorded as servo signals on the magnetic recording medium 10, and the head unit 36 ​​simultaneously reproduces two different servo patterns using two servo heads on the head unit 36, thereby obtaining respective servo signals. Using relative position information between the servo patterns and the head unit obtained from these servo signals, the position of the head unit 36 ​​is controlled to track the servo patterns. At the same time, distance information between the servo patterns can be obtained by comparing the two servo signal waveforms. By comparing the distance information between the servo patterns obtained during each measurement, the change in the distance between the servo patterns at each measurement can be obtained. By adding the distance information between the servo patterns obtained during servo pattern recording to this, the change in the width of the magnetic recording medium 10 can also be calculated. Based on the change in the distance between the servo patterns obtained as described above or the calculated change in the width of the magnetic recording medium 10, the control device 38 controls the rotational drive of the spindle drive device 33 and the reel drive device 34, and adjusts the tension in the longitudinal direction of the magnetic recording medium 10 so that the width of the magnetic recording medium 10 becomes a specified width or approximately a specified width. This makes it possible to suppress changes in the width of the magnetic recording medium 10.

[0237] [Recording / playback device operation]

[0238] Next, the operation of the recording / reproducing device 30 having the above configuration will be described.

[0239] First, the magnetic recording cartridge 10A 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 a plurality of guide rollers 35 and a head unit 36, and the leading end of the magnetic recording medium 10 is attached to the reel 32.

[0240] Next, when an operating unit (not shown) is operated, the spindle drive device 33 and the reel drive device 34 are driven under the control of the control device 38, and the spindle 31 and the reel 32 are rotated in the same direction so that the magnetic recording medium 10 runs from the reel 10C toward the reel 32. As a result, the magnetic recording medium 10 is wound onto the reel 32, while the head unit 36 ​​records information onto the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.

[0241] When rewinding the magnetic recording medium 10 onto the reel 10C, the spindle 31 and the reel 32 are rotated in the opposite direction to the above, causing the magnetic recording medium 10 to run from the reel 32 to the reel 10C. 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.

[0242] (6) Variations

[0243] [Variation 1]

[0244] As shown in FIG. 15, the magnetic recording medium 10 may further include a barrier layer 15 disposed on at least one surface of the base layer 11. The barrier layer 15 is a layer for suppressing dimensional deformation of the base layer 11 due to environmental factors. For example, one cause of dimensional deformation is the hygroscopicity of the base layer 11, and the barrier layer 15 can reduce the rate at which moisture penetrates the base layer 11. The barrier layer 15 includes a metal or a metal oxide. Examples of metals that can be used 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 at least one of Al2O3, CuO, CoO, SiO2, Cr2O3, TiO2, Ta2O5, and ZrO2, as well as oxides of any of the above metals. Diamond-like carbon (DLC) or diamond can also be used.

[0245] The average thickness of the barrier layer 15 is preferably 20 nm or more and 1000 nm or less, more preferably 50 nm or more and 1000 nm or less. m However, the magnification of the TEM image is adjusted appropriately depending on the thickness of the barrier layer 15.

[0246] [Variation 2]

[0247] The magnetic recording medium 10 may be incorporated into a library device. That is, the present technology also provides a library device equipped with at least one magnetic recording medium 10. The library device has a configuration capable of adjusting the tension applied to the magnetic recording medium 10 in the longitudinal direction, and may be equipped with a plurality of the above-described recording / reproducing devices 30.

[0248] [Variation 3]

[0249] The magnetic recording medium 10 may be subjected to a servo signal writing process by a servo writer. The servo writer can maintain the width of the magnetic recording medium 10 constant or approximately constant by adjusting the tension in the longitudinal direction of the magnetic recording medium 10 during recording of the servo signal. In this case, the servo writer can include a detection device that detects the width of the magnetic recording medium 10. The servo writer can adjust the tension in the longitudinal direction of the magnetic recording medium 10 based on the detection result of the detection device.

[0250] 3. Second embodiment (1) One embodiment of a magnetic recording cartridge

[0251] [Cartridge configuration]

[0252] The present technology also provides a magnetic recording cartridge (also called a tape cartridge) including a magnetic recording medium according to the present technology. In the magnetic recording cartridge, the magnetic recording medium may be wound around a reel, for example. The magnetic recording cartridge may include, for example, a communication unit that communicates with a recording / reproducing device, a storage unit, and a control unit that stores information received from the recording / reproducing device via the communication unit in the storage unit, and reads information from the storage unit and transmits it to the recording / reproducing device via the communication unit in response to a request from the recording / reproducing device. The information may include adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction.

[0253] An example of the configuration of a magnetic recording cartridge 10A equipped with a magnetic recording medium T having the above-described configuration will be described with reference to FIG.

[0254] 16 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge 10A. The magnetic recording cartridge 10A is a magnetic recording cartridge that complies with the LTO (Linear Tape-Open) standard, and includes a cartridge case 10B made up of a lower shell 212A and an upper shell 212B, a reel 10C around which a magnetic tape (a tape-like magnetic recording medium) T is wound, a reel lock 214 and a reel spring 215 for locking the rotation of the reel 10C, a spider 216 for unlocking the locked state of the reel 10C, a slide door 217 that straddles the lower shell 212A and the upper shell 212B and opens and closes a tape pull-out opening 212C provided in the cartridge case 10B, a door spring 218 that biases the slide door 217 to a closed position of the tape pull-out opening 212C, a write protect 219 for preventing accidental erasure, and a cartridge memory 211. The reel 10C is generally disk-shaped with an opening in the center, and is composed of a reel hub 213A made of a hard material such as plastic and a flange 213B. A leader tape LT is connected to one end of the magnetic tape T. A leader pin 220 is provided at the tip of the leader tape LT.

[0255] The cartridge memory 211 is provided near one corner of the magnetic recording cartridge 10A. When the magnetic recording cartridge 10A is loaded into the recording / reproducing device 80, the cartridge memory 211 faces a reader / writer (not shown) of the recording / reproducing device 80. The cartridge memory 211 communicates with the recording / reproducing device 30, specifically the reader / writer (not shown), using a wireless communication standard that complies with the LTO standard.

[0256] [Cartridge memory configuration]

[0257] An example of the configuration of the cartridge memory 211 will be described with reference to FIG.

[0258] 17 is a block diagram showing an example of the configuration of the cartridge memory 211. The cartridge memory 211 includes an antenna coil (communication unit) 331 that communicates with a reader / writer (not shown) using a specified communication standard, a rectification / power circuit 332 that generates power by using induced electromotive force from radio waves received by the antenna coil 331 and rectifying it, a clock circuit 333 that generates a clock from the radio waves received by the antenna coil 331 using induced electromotive force, a detection / modulation circuit 334 that detects the radio waves received by the antenna coil 331 and modulates the signal to be transmitted by the antenna coil 331, a controller (control unit) 335 that is composed of logic circuits and the like for identifying and processing commands and data from the digital signal extracted from the detection / modulation circuit 334, and a memory (storage unit) 336 that stores information. The cartridge memory 211 also includes a capacitor 337 connected in parallel to the antenna coil 331, and the antenna coil 331 and capacitor 337 form a resonant circuit.

[0259] The memory 336 stores information related to the magnetic recording cartridge 10A. The memory 336 is a nonvolatile memory (NVM). The memory 336 preferably has a storage capacity of approximately 32 KB or more. For example, if the magnetic recording cartridge 10A conforms to the next-generation LTO format standard or later, the memory 336 has a storage capacity of approximately 32 KB.

[0260] The memory 336 has a first memory area 336A and a second memory area 336B. The first memory area 336A corresponds to the memory area of ​​a cartridge memory (hereinafter referred to as a "conventional cartridge memory") that conforms to the LTO standard prior to LTO8, and is an area for storing information that conforms to the LTO standard prior to LTO8. Information that conforms to the LTO standard prior to LTO8 includes, for example, manufacturing information (such as a unique number for the magnetic recording cartridge 10A), usage history (such as the number of times the tape has been pulled out (Thread Count)), etc.

[0261] The second memory area 336B corresponds to an extended memory area for the memory area of ​​a conventional cartridge memory. The second memory area 336B is an area for storing additional information. Here, additional information refers to information related to the magnetic recording cartridge 10A that is not specified in the LTO standard prior to LTO8. Examples of additional information include, but are not limited to, tension adjustment information, management ledger data, index information, and thumbnail information of videos stored on the magnetic tape T. The tension adjustment information includes the distance between adjacent servo bands (the distance between servo patterns recorded on adjacent servo bands) when data is recorded on the magnetic tape T. The distance between adjacent servo bands is an example of width-related information related to the width of the magnetic tape T. The distance between servo bands will be described in detail later. In the following description, the information stored in the first memory area 336A may be referred to as "first information," and the information stored in the second memory area 336B may be referred to as "second information."

[0262] The memory 336 may have multiple banks. In this case, some of the multiple banks may constitute the first storage area 336A, and the remaining banks may constitute the second storage area 336B. Specifically, for example, if the magnetic recording cartridge 10A conforms to the next-generation or later LTO format standard, the memory 336 may have two banks with a storage capacity of approximately 16 KB, and one of the two banks may constitute the first storage area 336A, and the other bank may constitute the second storage area 336B.

[0263] The antenna coil 331 induces an induced voltage by electromagnetic induction. The controller 335 communicates with the recording / reproducing device 80 using a specified communication standard via the antenna coil 331. Specifically, for example, mutual authentication, sending and receiving of commands, or data exchange is performed.

[0264] The controller 335 stores information received from the recording / reproducing device 80 via the antenna coil 331 in the memory 336. In response to a request from the recording / reproducing device 80, the controller 335 reads information from the memory 336 and transmits it to the recording / reproducing device 80 via the antenna coil 331.

[0265] (2) Modified magnetic recording cartridge

[0266] [Cartridge configuration]

[0267] In the above-described embodiment of the magnetic recording cartridge, the magnetic tape cartridge is described as a one-reel type cartridge, but the magnetic recording cartridge of the present technology may also be a two-reel type cartridge. That is, the magnetic recording cartridge of the present technology may have one or more (e.g., two) reels on which the magnetic tape is wound. Below, an example of a magnetic recording cartridge of the present technology having two reels will be described with reference to FIG. 18 .

[0268] 18 is an exploded perspective view showing an example of the configuration of a two-reel type cartridge 421. Cartridge 421 includes an upper half 402 made of synthetic resin, a transparent window member 423 fitted into and fixed to a window 402a opened in the top surface of upper half 402, a reel holder 422 fixed to the inside of upper half 402 to prevent reels 406 and 407 from floating up, a lower half 405 corresponding to upper half 402, reels 406 and 407 stored in a space formed when upper half 402 and lower half 405 are combined, magnetic tape MT1 wound on reels 406 and 407, a front lid 409 that closes a front opening formed when upper half 402 and lower half 405 are combined, and a back lid 409A that protects magnetic tape MT1 exposed in this front opening.

[0269] The reel 406 includes a lower flange 406b having a cylindrical hub portion 406a in the center around which the magnetic tape MT1 is wound, an upper flange 406c having approximately the same size as the lower flange 406b, and a reel plate 411 sandwiched between the hub portion 406a and the upper flange 406c. The reel 407 has the same configuration as the reel 406.

[0270] The window member 423 is provided with mounting holes 423a at positions corresponding to the reels 406 and 407, respectively, for assembling reel holders 422, which are reel holding means for preventing these reels from floating up. The magnetic tape MT1 is the same as the magnetic tape T in the first embodiment.

[0271] The present technology can also employ the following configuration. [1] a magnetic layer containing magnetic powder; The average size of magnetic clusters measured based on the MFM image of the surface of the magnetic layer is 1850 nm 2 is as follows: the magnetic layer contains first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more, protrusions are formed on the surface of the magnetic layer side by the first particles and the second particles, the ratio (H1 / H2) of the average height H1 of the protrusions formed by the first particles to the average height H2 of the protrusions formed by the second particles is 2.00 or less; Magnetic recording media. [2] The magnetic recording medium according to [1], wherein the average height H1 is 13.0 nm or less. [3] The magnetic recording medium according to [1], wherein the average height H1 is 12.0 nm or less. [4] The magnetic recording medium according to [1], wherein the average height H1 is 11.0 nm or less. [5] The magnetic recording medium according to any one of [1] to [4], wherein the average height H2 is 7.5 nm or less. [6] The magnetic recording medium according to any one of [1] to [4], wherein the average height H2 is 7.0 nm or less. [7] The magnetic recording medium according to any one of [1] to [4], wherein the average height H2 is 6.5 nm or less. [8] The average size of the magnetic clusters is 1800 nm 2 The magnetic recording medium according to any one of [1] to [7] below. [9] The average size of the magnetic clusters is 1700 nm 2 The magnetic recording medium according to any one of [1] to [7] below.

[10] The average size of the magnetic clusters is 1600 nm 2 The magnetic recording medium according to any one of [1] to [7] below.

[11] The magnetic recording medium has an average thickness t T The magnetic recording medium according to any one of [1] to

[10] , wherein the thickness is 5.1 μm or less.

[12] The magnetic recording medium according to any one of [1] to

[11] , wherein the magnetic recording medium has a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less.

[13] The magnetic recording medium according to any one of [1] to

[12] , wherein the first particles are carbon particles.

[14] The magnetic recording medium according to any one of [1] to

[13] , wherein the second particles are inorganic particles.

[15] The number of protrusions formed by the first particles on the surface on the magnetic layer side is determined by the unit area (μm 2 The magnetic recording medium according to any one of [1] to

[14] , wherein the number of particles per one of the plurality of particles is 2.5 or less.

[16] The number of protrusions formed by the second particles on the surface on the magnetic layer side is determined by the unit area (μm 2 The magnetic recording medium according to any one of [1] to

[15] , wherein the number of particles per one of the plurality of particles is 2.0 or more.

[17] The magnetic recording medium according to any one of [1] to

[16] , wherein the average thickness of the magnetic layer is 0.08 μm or less.

[18] a magnetic layer containing magnetic powder; The average size of magnetic clusters measured based on the MFM image of the surface of the magnetic layer is 1850 nm 2 is as follows: The magnetic recording medium has a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less. Magnetic recording media.

[19] A magnetic recording cartridge in which the magnetic recording medium according to any one of [1] to

[18] is housed in a case in a state where it is wound around a reel.

[0272] 4. Working Example

[0273] The present technology will be described in more detail below with reference to examples, but the present technology is not limited to these examples. Note that the values ​​of various parameters appearing in these examples were determined by the measurement methods described above unless otherwise specified.

[0274] 4-1. Evaluation of the effect of the average size of magnetic clusters on electromagnetic conversion characteristics

[0275] [Example 1] (Preparation process of paint for forming magnetic layer) The coating material for forming the magnetic layer was prepared as follows. First, a first composition having the following formulation was kneaded using an extruder to obtain it. Then, a second composition having the following formulation was stirred using a disperser to obtain it. That is, the dispersion process of the magnetic powder and the dispersion process of the first and second particles were carried out separately. Next, the obtained first and second compositions and a third composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, further sand mill mixing was carried out and filtering was carried out to prepare the coating material for forming the magnetic layer.

[0276] (First composition) Magnetic powder (hexagonal ferrite with M-type structure, composition: Ba-Ferrite, shape: plate-like hexagonal particles, average particle volume: 1680 nm 3 ):100 parts by mass Vinyl chloride resin (cyclohexanone solution 30% by mass): 45 parts by mass (Degree of polymerization 300, Mn=10000, polar group OSO3K=0.07mmol / g, Contains secondary OH = 0.3mmol / g.

[0277] (Second composition) Aluminum oxide powder: 7.5 parts by mass (α-Al2O3, average particle size 80 nm, manufactured by Sumitomo Chemical Co., Ltd., product name: HIT82, Mohs hardness: 9) Carbon black: 2.0 parts by mass (Average particle size 70 nm, manufactured by Tokai Carbon Co., Ltd., product name: Seest TA) The vinyl chloride resin (cyclohexanone solution 30% by mass): 8.8 parts by mass

[0278] (Third composition) Vinyl chloride resin: 1.6 parts by mass (Cyclohexanone solution 30% by mass resin) 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

[0279] Finally, 2 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 curing agents to the magnetic layer-forming coating material prepared as described above.

[0280] (Preparation process of paint for forming base layer) The paint for forming the primer layer was prepared as follows. First, the fourth composition having the following formulation was kneaded using an extruder. Next, the kneaded fourth composition and the fifth composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, further mixing was performed using a sand mill and filtering was performed to prepare the paint for forming the primer layer.

[0281] (4th composition) Acicular iron oxide powder: 100 parts by mass (α-Fe2O3, average major axis length 0.15μm) Aluminum oxide powder: 5 parts by mass (α-Al2O3, average particle size 80 nm, manufactured by Sumitomo Chemical Co., Ltd., product name: HIT82, Mohs hardness: 9) Vinyl chloride resin: 55.6 parts by mass (Resin solution: 30% resin by mass, 70% cyclohexanone by mass) Carbon black: 10 parts by mass (Average particle size 20nm)

[0282] (5th 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

[0283] Finally, 2 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) and 2 parts by mass of myristic acid were added as a curing agent to the coating material for forming an undercoat layer prepared as described above.

[0284] (Preparation process of paint for forming back layer) The paint for forming the back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the paint for forming the back layer: Carbon black (manufactured by Asahi Corporation, product name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (Nippon Polyurethane Co., Ltd., product name: N-2304) Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass Polyisocyanate (product name: Coronate L, manufactured by Tosoh Corporation): 10 parts by mass

[0285] (Film forming process) Using the coating material prepared as described above, a magnetic tape was prepared as follows.

[0286] First, a long PEN film (base film) with an average thickness of 4.00 μm was prepared as a support for the base layer of the magnetic tape. Next, a primer layer-forming paint was applied to one main surface of the PEN film and dried to form a primer layer on one main surface of the PEN film so that the average thickness of the final product would be 1.00 μm. Next, a magnetic layer-forming paint was applied to the primer layer and dried to form a magnetic layer on the primer layer so that the average thickness of the final product would be 80 nm. Furthermore, the magnetic layer was subjected to a vertical orientation treatment using a solenoid coil.

[0287] Next, a back layer-forming coating material was applied to the other main surface of the PEN film on which the undercoat layer and magnetic layer were formed, and then dried to form a back layer with an average thickness of 0.50 μm in the final product.The PEN film on which the undercoat layer, magnetic layer, and back layer were formed was then subjected to a curing treatment.Then, a calendering treatment was performed to smooth the surface of the magnetic layer.

[0288] (Cutting process) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining a long magnetic tape.

[0289] The 1 / 2-inch-wide magnetic tape was wound around a reel provided inside a cartridge case to obtain a magnetic recording cartridge. A servo signal was recorded on the magnetic tape using a servo track writer. The servo signal consisted of a series of V-shaped magnetic patterns, and the magnetic patterns were pre-recorded in two or more rows parallel to the longitudinal direction at known intervals (hereinafter referred to as "the known intervals between pre-recorded magnetic pattern rows").

[0290] The average magnetic cluster size of the obtained magnetic tape was 1690 nm as shown in Table 1 below. 2 It was.

[0291] [Example 2] A magnetic tape was obtained in the same manner as in Example 1, except that the thickness of the magnetic layer, the thickness of the underlayer, and the thickness of the back layer were changed to 75 nm, 0.70 μm, and 0.40 μm, respectively, and that no perpendicular orientation treatment was performed. Then, using this magnetic tape, a magnetic recording cartridge was obtained in the same manner as in Example 1. The average magnetic cluster size of the obtained magnetic tape was 1702 nm, as shown in Table 1 below. 2 It was.

[0292] [Comparative Example 1] A magnetic tape was obtained in the same manner as in Example 1, except that the composition was changed as shown in Table 1, such as using a magnetic powder having a smaller average particle volume than the magnetic powder used in Example 1, and that in preparing the coating material for forming the magnetic layer, a dispersion treatment was carried out on a single composition containing the magnetic powder, aluminum oxide powder, and carbon black, rather than separating it into a first composition and a second composition. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using this magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1880 nm. 2 It was. The average particle volume of the magnetic powder used in Comparative Example 1 was smaller than that of the magnetic powder used in Example 1, but the average magnetic cluster size of the magnetic tape of Comparative Example 1 was larger than that of the magnetic tape of Example 1. One reason for this is thought to be that in preparing the coating material for forming the magnetic layer, the dispersion treatment was carried out on a single composition without dividing it into a first composition and a second composition, which reduced the degree of dispersion of the magnetic powder.

[0293] Comparative Example 2 The average particle volume (1700 nm) was slightly larger than that of the magnetic powder used in Example 1. 3 A magnetic tape was obtained in the same manner as in Example 1, except that the composition was changed as shown in Table 1, such as using a magnetic powder having the formula (I), and the time for dispersing the first composition and the second composition in preparing the coating material for forming the magnetic layer was shortened. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1944 nm. 2 It was. The average magnetic cluster size of the magnetic tape of Comparative Example 2 was larger than that of the magnetic tape of Example 1. This is thought to be partly due to the shorter dispersion treatment time for the first composition and the second composition in the preparation of the coating material for forming the magnetic layer.

[0294] Comparative Example 3 The average particle volume (965 nm) was smaller than that of the magnetic powder used in Example 1. 3 A magnetic tape was obtained in the same manner as in Example 1, except that the composition was changed as shown in Table 1, such as by using a magnetic powder having the following properties: 1) A magnetic tape was obtained in the same manner as in Example 1, and a magnetic recording cartridge was obtained using the magnetic tape in the same manner as in Example 1. The average magnetic cluster size of the obtained magnetic tape was 2210 nm. 2 It was. The average magnetic cluster size of the magnetic tape of Comparative Example 3 was larger than that of the magnetic tape of Example 1. One reason for this is thought to be that the average particle volume of the magnetic powder was too small, so the magnetic powder was not dispersed well during the preparation of the coating material for forming the magnetic layer.

[0295] Comparative Example 4 A magnetic tape was obtained in the same manner as in Example 1, except that the thickness of the magnetic layer, the thickness of the underlayer, and the thickness of the back layer were changed to 85 nm, 1.10 μm, and 0.45 μm, respectively, and that the perpendicular orientation treatment was not performed. Then, using this magnetic tape, a magnetic recording cartridge was obtained in the same manner as in Example 1. The average magnetic cluster size of the obtained magnetic tape was 1882 nm. 2 It was. The average magnetic cluster size of the magnetic tape of Comparative Example 4 was larger than that of the magnetic tapes of Examples 1 and 2. This is thought to be partly due to changes in the layer structure (for example, making the magnetic layer thicker).

[0296] [Evaluation of electromagnetic conversion characteristics] The electromagnetic conversion characteristics of the magnetic tape housed in each cartridge were evaluated using the magnetic recording cartridges manufactured in Examples 1 and 2 and Comparative Examples 1 to 4. The evaluation was carried out as follows.

[0297] First, a loop tester (manufactured by Microphysics) was used to obtain a playback signal from the magnetic tape. The conditions for obtaining the playback signal are as follows: head:GMR Head speed: 1.85m / s signal: Single recording frequency 10MHz (2T half Nyquist frequency) Recording current: Optimum recording current

[0298] Next, the playback signal was captured using a spectrum analyzer with a span of 0 to 20 MHz (resolution bandwidth = 100 kHz, VBW = 30 kHz). The peak of the captured spectrum was then taken as the signal amount S, and the floor noise excluding the peak was integrated from 3 MHz to 20 MHz to obtain the noise amount N. The ratio S / N of the signal amount S to the noise amount N was calculated as the SNR (Signal-to-Noise Ratio). The calculated SNR was then converted into a relative value (dB) based on the SNR of Example 1 as the reference media. The evaluation results of the electromagnetic conversion characteristics of each magnetic tape are also shown in Table 1.

[0299] [Table 1]

[0300] From the results shown in Table 1, it can be seen that the electromagnetic conversion characteristics are improved by making the average size of the magnetic clusters smaller. 2 Below 1800 nm, preferably 2 or less, and even more preferably 1750 nm 2 Below, 1700nm 2 Below, 1650nm 2 or below 1600nm 2 It is believed that the electromagnetic conversion characteristics are improved by satisfying the following conditions.

[0301] Furthermore, from the results shown in Table 1, even if the average particle volume of the magnetic powder is small (for example, 1453 nm in Comparative Example 1), 3 and 965 nm in Comparative Example 3 3) It is also clear that the electromagnetic conversion characteristics deteriorate when the average magnetic cluster size is too large.

[0302] 4-2. Evaluation of the effect of protrusions formed by the first particles and the second particles on electromagnetic conversion characteristics

[0303] Reducing the average magnetic cluster size can affect the state of the inorganic particles, particularly the state of the protrusions formed by the inorganic material on the surface of the magnetic layer. Therefore, an evaluation was conducted to assess this effect. Specifically, the following magnetic tapes were prepared. In addition to the magnetic tapes of Examples 1 and 2 described above, the magnetic tapes of Examples 3 to 7 and Comparative Examples 5 and 6 described below were also prepared. The height of the protrusions formed by the inorganic particles was measured for these tapes, and the running performance of these magnetic tapes was evaluated.

[0304] [Example 3] Average particle volume is approximately 1050 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder of 0.01g was used, the amount of alumina added was reduced, and the thicknesses of the magnetic layer, underlayer, and back layer were changed. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1490 nm as shown in Table 2 below. 2 It was.

[0305] [Example 4] Average particle volume is approximately 1100 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder of 0.01g was used, the amount of alumina added was reduced, and the thicknesses of the magnetic layer, underlayer, and back layer were changed. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1431 nm as shown in Table 2 below. 2 It was.

[0306] [Example 5] Average particle volume is approximately 1400 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder of 100% was used and the dispersion time was extended. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1450 nm as shown in Table 2 below. 2 It was.

[0307] [Example 6] Average particle volume is approximately 1400 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder having the formula (I) was used and the thicknesses of the substrate layer and back layer were changed. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1682 nm as shown in Table 2 below. 2 It was.

[0308] [Example 7] Average particle volume is approximately 1050 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that a magnetic powder of the formula (I) was used and the thicknesses of the magnetic layer, underlayer, and back layer were changed. Then, a magnetic recording cartridge was obtained in the same manner as in Example 1 using the magnetic tape. The average magnetic cluster size of the obtained magnetic tape was 1510 nm as shown in Table 2 below. 2 It was.

[0309] Comparative Example 5 Except for reducing the amount of alumina added and changing the thickness of the back layer, a magnetic tape was obtained in the same manner as in Example 1. Then, using this magnetic tape, a magnetic recording cartridge was obtained in the same manner as in Example 1. The average magnetic cluster size of the obtained magnetic tape was 1706 nm, as shown in Table 2 below. 2 It was.

[0310] Comparative Example 6 A magnetic tape was prepared in which the average particle volume of the magnetic powder was large and the average magnetic cluster size was large. The average magnetic cluster size of the magnetic tape was 2470 nm, as shown in Table 2 below. 2 It was.

[0311] [Evaluation of electromagnetic conversion characteristics] The electromagnetic conversion characteristics of the magnetic tape housed in each cartridge were evaluated using the magnetic recording cartridges manufactured in Examples 1 to 7 and Comparative Examples 5 and 6. The evaluation was carried out as described in 4-1 above.

[0312] [Evaluation of driving performance] Using the magnetic recording cartridges manufactured in Examples 1 to 7 and Comparative Examples 5 and 6, the running properties of the magnetic tape housed in each cartridge were evaluated. The evaluation of the running properties was carried out by measuring the standard deviation σPES as described in 4-1 above. The evaluation criteria for the running properties based on the standard deviation σPES are as follows: σPES is 50nm or less within 40FV number: Good runnability σPES over 50nm within 40FV number: poor runnability

[0313] The measurement results for each tape and the evaluation results for electromagnetic conversion characteristics and running properties are shown in Table 2. Note that "-" in the table means that the measurement was not performed.

[0314] [Table 2]

[0315] The results shown in Table 2 reveal the following:

[0316] Comparing the magnetic tapes of Examples 1 and 2 with Comparative Example 5, the average height H1 of the protrusions formed by the first particles (carbon black) and the average height H2 of the protrusions formed by the second particles (Al2O3) When the ratio of the average protrusion height H2 (H1 / H2) is, for example, 2.0 or less, more preferably 1.95 or less, and even more preferably 1.90 or less, 1.85 or less, 1.80 or less, 1.75 or less, or 1.70 or less, the standard deviation σPES becomes low, i.e., the runnability is good. Furthermore, as described above, Examples 1 and 2 have a small average magnetic cluster size, which results in excellent electromagnetic conversion characteristics. These results show that in magnetic tapes with small average magnetic cluster sizes, good runnability can be achieved by controlling the ratio between the average height H1 of the protrusions formed by the first particles and the average height H2 of the protrusions formed by the second particles. In Comparative Example 6, in which the average magnetic cluster size was large and the ratio (H1 / H2) was large, the evaluation results for electromagnetic conversion characteristics were also poor, and the running properties were also poor.

[0317] Furthermore, by comparing Examples 1 and 2 with Examples 3 to 5, it is possible to further improve the electromagnetic conversion characteristics while maintaining good running properties by making the ratio (H1 / H2) 2.0 or less and further reducing the average magnetic cluster size. Therefore, in order to obtain even better electromagnetic conversion characteristics, the average magnetic cluster size is more preferably 1700 nm. 2 Below, 1650nm 2 or below 1600nm 2 or less, and even 1550nm 2 Below 1500nm 2 It is preferable that:

[0318] Furthermore, by comparing Examples 1 and 2 with Examples 6 and 7, it can be seen that by setting the ratio (H1 / H2) to 2.0 or less, the running properties are good, but depending on the values ​​of the average height H1 of the protrusions formed by the first particles and the average height H2 of the protrusions formed by the second particles, which are involved in the ratio, the electromagnetic conversion characteristics may be degraded. From these results, in order to obtain good electromagnetic conversion characteristics, the average height H1 of the protrusions formed by the first particles is preferably 12.0 nm or less, more preferably 11.5 nm or less, and even more preferably 11.0 nm or less, 10.5 nm or less, 10.0 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less. Furthermore, in order to obtain good electromagnetic conversion characteristics, the average height H2 of the protrusions formed by the second particles is preferably 7.0 nm or less, more preferably 6.5 nm or less, and even more preferably 6.0 nm or less, 5.5 nm or less, or 5.3 nm or less. Thus, the magnetic cluster size is small (e.g., 1850 nm 2 For a magnetic tape having a ratio (H1 / H2) of 1 / 2 or less (as described below), it is believed that good electromagnetic conversion characteristics can be obtained more reliably by adjusting the average height H1 and average height H2 involved in the ratio in addition to the ratio (H1 / H2).

[0319] Although the embodiments and examples of the present technology have been specifically described above, the present technology is not limited to the above-described embodiments and examples, and various modifications based on the technical ideas of the present technology are possible.

[0320] For example, the configurations, methods, steps, shapes, materials, and numerical values, etc., given in the above-described embodiments and examples are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values, etc., may be used as necessary. Furthermore, the chemical formulas of compounds, etc., are representative, and are not limited to the valences, etc., given as long as they are general names of the same compounds.

[0321] Furthermore, the configurations, methods, processes, shapes, materials, numerical values, and the like of the above-described embodiments and examples can be combined with each other without departing from the spirit of the present technology.

[0322] Furthermore, in this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more types. [Explanation of symbols]

[0323] 10 Magnetic recording media 11 Base Layer 12 Base layer 13 Magnetic layer 14 Back layer

Claims

1. a magnetic layer containing magnetic powder; The average size of magnetic clusters measured based on the MFM image of the surface of the magnetic layer side is 1850 nm ２ is as follows: the magnetic layer contains first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more, protrusions are formed on the surface of the magnetic layer side by the first particles and the second particles, The average height H of the protrusions formed by the first particles １ and the average height H of the protrusions formed by the second particles ２ The ratio (H １ / H ２ ) is 2.00 or less, Magnetic recording media.

2. The average height H １ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 13.0 nm or less.

3. The average height H １ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 12.0 nm or less.

4. The average height H １ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 11.0 nm or less.

5. The average height H ２ 2. The magnetic recording medium according to claim 1, wherein the thickness is 7.5 nm or less.

6. The average height H ２ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 7.0 nm or less.

7. The average height H ２ 2. The magnetic recording medium according to claim 1, wherein the thickness is 6.5 nm or less.

8. The average size of the magnetic clusters is 1800 nm ２ 2. The magnetic recording medium according to claim 1, wherein:

9. The average size of the magnetic clusters is 1700 nm ２ 2. The magnetic recording medium according to claim 1, wherein:

10. The average size of the magnetic clusters is 1600 nm ２ 2. The magnetic recording medium according to claim 1, wherein:

11. The average thickness t of the magnetic recording medium Ｔ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 5.1 [mu]m or less.

12. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a coercive force Hc in the perpendicular direction of 165 kA / m or more and 300 kA / m or less.

13. 2. The magnetic recording medium according to claim 1, wherein the first particles are carbon particles.

14. The magnetic recording medium according to claim 1 , wherein the second particles are inorganic particles.

15. The number of protrusions formed by the first particles on the surface on the magnetic layer side is determined by the unit area (μm ２ 2. The magnetic recording medium according to claim 1, wherein the number of particles per one particle is 2.5 or less.

16. The number of protrusions formed by the second particles on the surface on the magnetic layer side is determined by the unit area (μm ２ 2. The magnetic recording medium according to claim 1, wherein the number of particles per one particle is 2.0 or more.

17. 2. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic layer is 0.08 [mu]m or less.

18. A magnetic recording cartridge comprising the magnetic recording medium according to any one of claims 1 to 17, wound around a reel and housed in a case.

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