Magnetic recording medium

Abstract

The objective of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics.　The present invention provides a magnetic recording medium including a magnetic layer containing a magnetic powder. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median value (Mean) of the magnetic force distribution is 0.18 or less, and the average magnetic cluster size measured on the basis of an MFM image of the surface on the magnetic layer side is 3300 nm2 or less.

Description

magnetic recording media

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

[0002] 2. Description of the Related Art 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 with a magnetic force microscope is 0.2×10 ４ nm ２ Above 5.0 x 10 ４ nm ２ A magnetic recording medium is disclosed in which the magnetic recording medium has a thickness of less than 1 / 2 mm.

[0004] Japanese Patent Application Laid-Open No. 2020-140746

[0005] Advances in IoT utilization and big data analysis are increasing the amount of data being archived. This is leading to 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 higher capacity than ever before.

[0006] One method for increasing the capacity of magnetic recording tape is to increase the areal recording density. For example, reducing the size of magnetic particles is one effective way to increase the areal recording density. Even reduced-size magnetic particles must have high magnetic properties. However, magnetic particles with high magnetic properties may not function magnetically as fine particles when made into tape due to magnetic agglomeration caused by particle size and magnetic agglomeration. In particular, magnetic particles with an average particle volume of 1300 nm ３ Uses magnetic powder of 25Gbit / in or more ２In magnetic recording media with these areal recording densities, in addition to variations in the magnetic properties of the magnetic powder, even if the magnetic powder is sufficiently dispersed in the applied coating, re-aggregation of the magnetic powder occurs during the tape production stage, preventing it from functioning as magnetically fine particles and resulting in inconsistent magnetic strength. If there is significant variation in the signal recording state during signal recording, there will also be significant variation in the magnetization transition region, which will become a source of noise. Therefore, it is important to reduce the size of agglomerates and magnetic variation.

[0007] The main objective of this technology is to provide a magnetic recording tape with excellent electromagnetic conversion characteristics. Furthermore, this technology aims to provide a magnetic recording tape with an areal recording density of 25 Gbit / in. ２ Another object of the present invention is to provide a magnetic recording tape having high electromagnetic conversion characteristics compatible with the above-mentioned high recording density.

[0008] The present technology provides a magnetic recording medium having a magnetic layer containing magnetic powder, wherein the ratio of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution (StDev / Mean) is 0.18 or less, and the average magnetic cluster size measured based on an MFM image of the surface of the magnetic layer is 3,300 nm. ２ The magnetic recording medium has a magnetic cluster average size of 3000 nm or less. The ratio StDev / Mean may be 0.16 or less. ２ or less. The magnetic powder may contain Ba atoms and Sr atoms. The magnetic powder may be barium ferrite magnetic powder. The magnetic powder may be a magnetic powder in which some of the Ba atoms (X) of the barium ferrite magnetic powder are substituted with Sr atoms (Y). The atomic ratio of Sr atoms (Y) / Ba atoms (X) of the magnetic powder may be less than 1. The magnetic powder may have an average particle volume of 1,300 nm ３ The magnetic powder may have an average particle volume of 1200 nm or less. ３ The magnetic powder may have an average particle volume of 1100 nm or less. ３The magnetic powder may be composite particles of ε-iron oxide and Co-containing spinel ferrite. The average total thickness may be 5.40 μm or less. The average total thickness may be 5.30 μm or less. The average total thickness may be 5.22 μm or less. The present technology also provides the magnetic recording medium, comprising a magnetic layer, an underlayer, and a base layer, in this order. The base layer may be formed from PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or PEEK (polyether ether ketone). The average thickness of the base layer may be 4.10 μm or less. The average thickness of the base layer may be 3.80 μm or more. The average thickness of the magnetic layer may be 0.08 μm or less. The average thickness of the underlayer may be 0.90 μm or less.

[0009] 1 is a cross-sectional view showing the configuration of a magnetic recording medium according to a first embodiment; FIG. 2 is a diagram showing an example of the shape of particles of magnetic powder; FIG. 3 is an example of a TEM photograph of a cross section of a sample; FIG. 4 is another example of a TEM photograph of a cross section of a sample; FIG. 5 is a diagram for explaining image analysis processing of an MFM image; FIG. 6 is a diagram for explaining image analysis processing of an MFM image; FIG. 7 is a diagram for explaining image analysis processing of an MFM image; FIG. 8 is a diagram for explaining image analysis processing of an MFM image; FIG. 9 is a diagram for explaining image analysis processing of an MFM image; FIG. 10 is a schematic diagram showing the configuration of a recording and reproducing device; FIG. 11 is a cross-sectional view showing the configuration of a magnetic recording medium in a modified example; FIG. 12 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge; FIG. 13 is a block diagram showing an example of the configuration of a cartridge memory; FIG. 14 is an exploded perspective view showing an example of the configuration of a modified magnetic recording cartridge;

[0010] 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.

[0011] The present technology will be described in the following order: 1. Description of the present technology 2. First embodiment (1) Configuration of magnetic recording medium (2) Description of each layer (3) Physical properties and structure (4) Manufacturing method of magnetic recording medium (5) Recording and reproducing device (6) Modified examples 3. Second embodiment (1) One embodiment of magnetic recording cartridge (2) Modified examples of magnetic recording cartridge 4. Examples

[0012] In this specification, unless a measurement environment is specifically stated in connection with the explanation of the measurement method, the measurement is performed in an environment of 25°C ± 2°C and 50% RH ± 5% RH.

[0013] 1. Description of the technology

[0014] This technology provides a magnetic recording medium having a ratio of the standard deviation of the magnetic force distribution to the median of the magnetic force distribution, StDev / Mean, that is equal to or less than a specific value, and an average magnetic cluster size that is equal to or less than a specific value. This magnetic recording medium can achieve high electromagnetic conversion characteristics that correspond to high recording densities, and also has a low frequency of partial reductions in the amplitude of reproduced signals (called "missing pulses"), resulting in a reduced error rate and improved reliability.

[0015] The magnetic recording medium according to the present technology has a magnetic layer containing magnetic powder, and the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution may be, for example, 0.18 or less, preferably 0.16 or less, more preferably 0.14 or less, and even more preferably 0.12 or less. By having the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution within the above numerical range, the magnetic force of the magnetic clusters varies little, the frequency of missing pulses is low, and the output is stable. The lower limit of the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution is not particularly limited, but may be, for example, preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more. The method for measuring the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution will be explained in 2.(3) below.

[0016] In the magnetic recording medium according to the present technology, the average size of magnetic clusters measured based on an MFM image of the surface of the magnetic layer side is, for example, 3300 nm ２ or less, preferably 3100 nm ２ Below, 3000nm ２ or less, more preferably 2900 nm ２ or less, more preferably 2700 nm ２ or less, even more preferably 2500 nm ２ The magnetic layer of the magnetic recording medium according to the present technology has such a small average magnetic cluster size, which means that the areal recording density is high. The lower limit of the average magnetic cluster size is not particularly limited, but may be, for example, 500 nm ２ More than 600 nm, preferably ２ More preferably, 700 nm ２ or more, 800 nm ２ or more, 900 nm ２ or more, or 1000 nm ２ The average magnetic cluster size may be equal to or greater than these values. 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 magnetic cluster size will be explained in 2.(3) below.

[0017] 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).

[0018] 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.

[0019] The average total thickness (average total thickness) t of the magnetic recording medium according to the present technology Ｔis preferably 5.40 μm or less, 5.30 μm or less, more preferably 5.22 μm or less, even more preferably 5.10 μm or less, 5.00 μm or less, and even more preferably 4.90 μm or less, 4.80 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 total thickness (average total thickness) t of the magnetic recording medium Ｔ The lower limit of t is not particularly limited, but for example, 3.50 μm≦t Ｔ is.

[0020] 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 The lower limit of the thickness is not particularly limited, but is preferably 0.03 μm or more. The method for measuring the average thickness of the magnetic layer will be explained in 2.(3) below.

[0021] The average thickness of the non-magnetic layer (also referred to as the underlayer) of the magnetic recording medium according to the present technology can be preferably 0.90 μm or less, 0.80 μm or less, more preferably 0.70 μm or less, 0.60 μm or less, 0.50 μm or less, or 0.45 μm or less, and even more preferably 0.40 μm or less. The lower limit of the average thickness of the non-magnetic layer is not particularly limited, but is preferably 0.20 μm or more, more preferably 0.30 μm or more. The method for measuring the average thickness of the non-magnetic layer will be explained in Section 2.(3) below.

[0022] The average thickness of the base layer (also referred to as the substrate layer) of the magnetic recording medium according to the present technology may be preferably 4.10 μm or less, more preferably 4.00 μm or less, 3.90 μm or less, 3.85 μm or less, or 3.80 μm or less, and even more preferably 3.75 μm or less, 3.70 μm or less. The lower limit of the average thickness of the base layer is not particularly limited, but may be, for example, preferably 3.40 μm or more, more preferably 3.50 μm or more. The method for measuring the average thickness of the base layer will be explained in Section 2. (3) below.

[0023] The average thickness of the back layer of the magnetic recording medium according to the present technology may be 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 explained in 2.(3) below.

[0024] The average particle volume of the magnetic powder contained in the magnetic recording medium of the present technology is preferably 1300 nm ３ Below, 1200nm ３ or less, more preferably 1100 nm ３ Less than 900 nm, more preferably ３ The average particle volume may be less than 500 nm. By having the average particle volume within the above range, it becomes easier to adjust the average magnetic cluster size to a desired range. Furthermore, having the average particle volume within the above range also contributes to improving electromagnetic conversion characteristics. The average particle volume of the magnetic powder is, for example, 500 nm ３ Above 600 nm, especially ３ The method for measuring the average particle volume of the magnetic powder will be explained in 2.(3) below.

[0025] 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 continuous 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 continuous magnetic recording medium (particularly a magnetic recording tape) can be, for example, 500 m to 1500 m. For example, the tape width according to the LTO8 standard is 12.65 mm and the length is 960 m.

[0026] 2. First embodiment

[0027] (1) Structure of the Magnetic Recording Medium First, the structure 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 the magnetic surface (the surface on which the back layer 14 is provided) will be referred to as the back surface.

[0028] The magnetic recording medium 10 has an elongated shape and runs in the longitudinal direction during recording and reproduction. The magnetic recording medium 10 may be configured to record signals at a shortest recording wavelength of preferably 60 nm or less, more preferably 55 nm or less, even more preferably 50 nm or less, and particularly preferably 45 nm or less, and may be used, for example, in a recording and reproduction device whose shortest 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.

[0029] (2) Explanation of each layer

[0030] (base layer)

[0031] 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 4.10 μm or less, more preferably 4.00 μm or less, and can be 3.90 μm or less, 3.85 μm or less, or 3.80 μm or less, and even more preferably 3.75 μm or less, or 3.70 μm or less. The lower limit of the average thickness of the base layer 11 can be determined, for example, from the perspective of film production limitations or the function of the base layer 11, and can be, for example, preferably 3.40 μm or more, more preferably 3.50 μm or more. The base layer 11 can include, for example, at least one of polyester-based resins, polyolefin-based resins, cellulose derivatives, vinyl-based 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.

[0032] The polyester-based 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.

[0033] The polyolefin resin may be, for example, one or a mixture of two or more of PE (polyethylene) and PP (polypropylene).

[0034] 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).

[0035] The vinyl resin may be, for example, one or a mixture of two or more of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0036] 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.

[0037] 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, e.g., Zylon (registered trademark), polyether, polyetherester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

[0038] (magnetic layer)

[0039] 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 may contain first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more. The magnetic layer 13 may also contain, for example, a binder. The magnetic layer 13 may further contain additives such as a lubricant and a rust inhibitor, as necessary.

[0040] 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, even more preferably 0.06 μm or less, 0.05 μm or less, and even more preferably 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.

[0041] 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 (running direction) of the magnetic recording medium 10 is 35% or less. The magnetic layer 13 may also be a magnetic layer that is in-plane oriented (longitudinal oriented). In other words, the magnetic recording medium 10 may be a horizontal recording type magnetic recording medium. However, from the viewpoint of achieving high recording density, perpendicular orientation is more preferable.

[0042] (Magnetic powder)

[0043] Examples of magnetic particles constituting the magnetic powder contained in the magnetic layer 13 include hexagonal ferrite, epsilon iron oxide (ε-iron oxide), Co-containing spinel ferrite, gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, and metal. The magnetic particles may be composite particles of hexagonal ferrite or ε-iron oxide and Co-containing spinel ferrite. The hexagonal ferrite may preferably be barium ferrite (BaFe). From the viewpoint of reducing the variation in magnetic powder size and obtaining high magnetic properties, the barium ferrite (BaFe) may particularly preferably be a magnetic powder in which some of the Ba atoms (X) are substituted with Sr atoms (Y). From the viewpoint of obtaining high magnetic properties, the atomic ratio of the number of Sr atoms (Y) to the number of Ba atoms (X) in the barium ferrite (BaFe) may be preferably less than 1, more preferably 0.9 or less, even more preferably 0.8 or less, and even more preferably 0.7 or less, and may be preferably 0.02 or more, more preferably 0.05 or more, and even more preferably 0.08 or more. That is, the barium ferrite (BaFe) may contain Ba atoms and Sr atoms. The ε-iron oxide may particularly preferably contain at least one of Al and Ga. The magnetic powder may include composite particles of hexagonal ferrite or ε-iron oxide and Co-containing spinel ferrite, and may further contain gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, metal, etc. 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 tape specifications, and the tape functions.

[0044] 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.

[0045] The average particle size of the magnetic powder is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 18 nm or less, 16 nm or less, 14 nm or less, 12 nm or less, or 10 nm or less. The average particle size may be, for example, 5 nm or more, preferably 7 nm or more.

[0046] 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.

[0047] (Embodiment in which the magnetic powder includes hexagonal ferrite)

[0048] According to a preferred embodiment of the present technology, the magnetic powder includes 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. From the viewpoint of suppressing glare of the magnetic powder size, the hexagonal ferrite preferably contains Ba and Sr, and further contains at least one of Pb and Ca, more preferably contains Ba and Sr, and may further contain Ca. Specific examples of the hexagonal ferrite include barium ferrite and strontium ferrite, and may further contain calcium ferrite, and barium ferrite or strontium ferrite is particularly preferred. Barium ferrite may contain Sr in addition to Ba and may further contain at least one of Pb and Ca. Strontium ferrite may contain Ba in addition to Sr and may further contain at least one of Pb and Ca.

[0049] More specifically, hexagonal ferrite has the general formula MFe １２ O １９ Here, M may be, for example, a combination of Ba and Sr, or may be a combination of this combination with at least one metal selected from Pb and Ca. In the above general formula, part of Fe may be substituted with another metal element.

[0050] When the magnetic powder contains hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 18 nm or less, 16 nm or less, 14 nm or less, 12 nm or less, or 10 nm or less. The average particle size may be, for example, 5 nm or more, preferably 7 nm or more. For example, the average particle size of the magnetic powder may be 7 nm or more to 30 nm or less, 7 nm or more to 20 nm or less, 7 nm or more to 18 nm or less, 7 nm or more to 16 nm or less, or 7 nm or more to 14 nm or less. When the average particle size of the magnetic powder is below the upper limit (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 above the lower limit (e.g., 10 nm or more, preferably 12 nm or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.

[0051] 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 1.0 to 2.5. By having the average aspect ratio of the magnetic powder within the above range, aggregation of the magnetic powder can be suppressed, and further, the resistance applied to the magnetic powder when the magnetic powder is vertically oriented in the process of forming the magnetic layer 13 can be suppressed. This can lead to improved vertical orientation of the magnetic powder.

[0052] 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 length 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 cutout 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 by FIB or other methods to thin it. 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.

[0053] 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 that the entire magnetic layer is included in the thickness direction of the magnetic layer, and a TEM photograph is taken. The number of TEM photographs prepared is sufficient to extract 50 particles from which the plate diameter DB and plate thickness DA (see Figure 2A) shown below can be measured.

[0054] 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 shape of the particle 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.

[0055] 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. When particles overlap, particles with a clear boundary between them and whose overall shape can be determined are measured as individual particles, but particles with an unclear boundary and whose overall shape cannot be determined are not measured, as their shape cannot be determined.

[0056] 2B and 2C show examples of TEM photographs. In these figures, the particles indicated by arrows a and d are selected because their plate thickness (thickness or height) DA can be clearly confirmed. The plate thickness DA of each of the selected 50 particles is measured. The plate thicknesses DA thus obtained are simply averaged (arithmetic mean) to obtain the average plate thickness DA. ａｖｅ Calculate the average plate thickness DA ａｖｅ is the average particle plate thickness. Next, the plate diameter DB of each magnetic powder is measured. In order to measure the plate diameter DB of the particles, 50 particles whose 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 diameter DBs thus determined are simply averaged (arithmetic averaged) to obtain the average plate diameter DB. ａｖｅ Average plate diameter DB ａｖｅ is the average particle size.

[0057] When the magnetic powder comprises a powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 1300 nm 3 or less, more preferably 1100 nm 3 More preferably, it is 900 nm or less. 3 and even more preferably 800 nm or less. 3 Below, 750nm 3 or less than 700 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 600 nm or more3 It could be more than that.

[0058] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 1300 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.

[0059] 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, the average particle volume V of the magnetic powder is calculated using the following formula:

[0060]

[0061] 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, by not losing its coercive force even in high-temperature and high-humidity environments. From this perspective, barium ferrite magnetic powder is preferred as the magnetic powder.

[0062] 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.

[0063] 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 ｍIt may be ≦80 nm.

[0064] 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.

[0065] (Embodiment in which the magnetic powder contains ε-iron oxide)

[0066] 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 are hard magnetic particles that can achieve high coercivity even with fine particles. ε-iron oxide particles have a substantially spherical shape. Because the ε-iron oxide particles have the above-described shape, in the case of particles containing ε-iron oxide, the contact area between particles in the thickness direction of the magnetic tape MT can be reduced and aggregation between particles can be suppressed compared to when the particles include hexagonal ferrite particles that are plate-shaped (e.g., hexagonal plate-shaped) or columnar (e.g., hexagonal column-shaped) particles. This improves particle dispersibility and allows for even better electromagnetic conversion characteristics (e.g., SNR).

[0067] To suppress variations in magnetic properties, the ε-iron oxide particles may have a composite particle structure with spinel ferrite. More specifically, the ε-iron oxide particles include an ε-iron oxide portion and a soft magnetic portion or a magnetic portion having a higher saturation magnetization σs and a lower coercive force Hc than the ε-iron oxide (hereinafter referred to as the "soft magnetic portion, etc.").

[0068] The ε-iron oxide portion contains ε-iron oxide. The ε-iron oxide contained in the ε-iron oxide portion is ε-Fe ２ O ３ The crystal is preferably the main phase, and the single-phase ε-Fe ２ O ３ More preferably, it consists of:

[0069] The soft magnetic portion (the magnetic portion having a higher saturation magnetization σs than the ε-iron oxide and a lower coercive force Hc) is in contact with at least a portion of the ε-iron oxide. Specifically, the soft magnetic portion (the magnetic portion having a higher saturation magnetization σs than the ε-iron oxide and a lower coercive force Hc) may partially cover the ε-iron oxide or may completely cover the ε-iron oxide.

[0070] The soft magnetic portion (the magnetic portion having a higher saturation magnetization σs and a smaller coercive force Hc than ε-iron oxide) contains a soft magnetic material such as α-Fe, a Ni-Fe alloy, or an Fe-Si-Al alloy. α-Fe may be obtained by reducing ε-iron oxide contained in the ε-iron oxide portion.

[0071] The soft magnetic portion may be made of, for example, Fe. ３ O ４ , γ-Fe ２ O ３ , or spinel ferrite, etc.

[0072] By providing the ε-iron oxide particle with a portion having soft magnetic properties as described above, the coercive force Hc of the ε-iron oxide portion alone can be maintained at a high value to ensure thermal stability, while the coercive force Hc of the ε-iron oxide particle (composite particle) as a whole can be adjusted to a coercive force Hc suitable for recording.

[0073] The ε-iron oxide particles may contain an additive instead of the above-mentioned composite particle structure, or may have the above-mentioned composite particle structure and contain an additive. In this case, a portion of the Fe in the ε-iron oxide particles is substituted with the additive. By including an additive in the ε-iron oxide particles, the coercivity Hc of the ε-iron oxide particles as a whole can be adjusted to a coercivity Hc suitable for recording, thereby improving ease of recording. The additive is a metal element other than iron, preferably a trivalent metal element, more preferably at least one selected from the group consisting of Al, Ga, and In, and even more preferably at least one selected from the group consisting of Al and Ga.

[0074] Specifically, the ε-iron oxide containing additives is ε-Fe ２－ｘ M ｘ O ３crystal (wherein M is a metal element other than iron, preferably a trivalent metal element, more preferably at least one selected from the group consisting of Al, Ga, and In, and even more preferably at least one selected from the group consisting of Al and Ga; and x is, for example, 0<x<1).

[0075] The average particle size (average maximum particle size) of the magnetic powder is preferably 16 nm or less, more preferably 8 nm to 16 nm, and even more preferably 10 nm to 16 nm. In the magnetic recording medium 10, the actual magnetization region is a region half the size of the recording wavelength. Therefore, by setting the average particle size of the magnetic powder to less than half the shortest recording wavelength, a good SNR can be obtained. 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.

[0076] 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.

[0077] 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 focused ion beam (FIB) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon film is formed on the magnetic layer side surface and back layer side surface of the magnetic recording medium 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. 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.

[0078] 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.

[0079] Next, 50 particles whose particle shape can be clearly confirmed are selected from the TEM photograph, and the major axis length DL and minor axis length DS of each particle are measured. Here, the major axis length DL refers to the maximum distance between two parallel lines drawn from any angle so as to be tangent to the contour of each particle (so-called maximum Feret diameter). On the other hand, the minor axis length DS refers to the maximum length of the particle in the direction perpendicular to the major axis (DL) of the particle.

[0080] Next, the major axis lengths DL of the 50 particles were simply averaged (arithmetic mean) to obtain the average major axis length DL ave The average major axis length DL obtained in this way is ave is the average particle size of the magnetic powder. The minor axis lengths DS of the measured 50 particles are simply averaged (arithmetic mean) to obtain the average minor axis length DS ave Then, calculate the average major axis length DL ave and mean minor axis length DS aveFrom the average aspect ratio of the particles (DL ave / DS ave ) is required.

[0081] The average particle volume of the magnetic powder is preferably 1600 nm 3 or less, more preferably 1400 nm 3 or less, more preferably 1200 nm 3 and even more preferably 1000 nm or less. 3 Below, 900nm 3 or less, or 800 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 600 nm or more 3 It could be more than that.

[0082] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 1300 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.

[0083] 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, the average particle volume V of the magnetic powder is calculated using the following formula: V = (π / 6) × DL ave 3

[0084] 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.

[0085] 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 obtain a cross section of the magnetic layer 13 in the thickness direction, including the entire magnetic layer 13, to obtain a TEM photograph. The magnification and acceleration voltage may be adjusted appropriately depending on the type of apparatus.

[0086] Next, 50 particles whose particle shapes are clear are selected from the TEM photograph, and the side length DC of each particle is measured. Then, the side lengths DC of the measured 50 particles are simply averaged (arithmetic mean) to obtain the average side length DC ave Next, calculate the average side length DC ave Using the following formula, the average particle volume V of the magnetic powder is calculated. ave (particle volume) is calculated. ave = DC ave 3

[0087] The coercive force Hc of the ε-iron oxide particles is preferably 2500 Oe or more, and more preferably 3000 Oe or more and 4500 Oe or less.

[0088] (An embodiment in which the magnetic powder includes Co-containing spinel ferrite)

[0089] 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 approximately 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.

[0090] Cobalt ferrite has an average composition represented by the following formula, for example: Co ｘ M ｙ Fe ２ O 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. However, x and y satisfy the relationship (x+y)≦1.0. z is a value within the range of 3≦z≦4. A portion of Fe may be substituted with another metal element.)

[0091] 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.

[0092] When the magnetic powder contains cobalt ferrite particles, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 19 nm or less. Such a small average particle size of the magnetic powder enables 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, enabling better electromagnetic conversion characteristics (e.g., SNR) to be obtained. 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.

[0093] The average particle volume of the magnetic powder is preferably 1300 nm 3 or less, more preferably 1200 nm 3 or less, more preferably 1100 nm 3 and even more preferably 1000 nm or less. 3 Below, 990nm 3 or less, or 980 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 600 nm or more 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, 1300 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] (first particle)

[0096] 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 may 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.

[0097] 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) may be, for example, 5 m ２ / g to 50m ２ / g, preferably 7m ２ / g to 50m ２ / g, more preferably 10m ２ / g to 50m ２ / g, and even more preferably 12m ２ / g to 50m ２ The iodine adsorption amount of the first 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.

[0098] (Second particle)

[0099] 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 deformation due to contact with a magnetic head. The Mohs hardness of the second particles may be, for example, 10 or less, preferably 9.5 or less, from the viewpoint of suppressing head wear. That is, the second particles may be formed from a material having such a Mohs hardness. The second particles may preferably be inorganic particles. The second particles may be, for example, 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, or acicular α-iron oxide obtained by dehydrating and annealing a magnetic iron oxide raw material, 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, or γ-alumina, or silicon carbide. These second particles may be acicular, spherical, cubic, or other shapes, but those having corners in their shape are preferred because they have, for example, high abrasiveness.

[0100] The average particle size (the arithmetic mean value of particle diameters measured, for example, using an electron microscope) of the second particles (particularly inorganic particles, for example, alumina) may be, for example, 15 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. Furthermore, 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, for example, alumina) may not be electrically conductive. That is, the second particles may not have the electrical conductivity that the first particles have.

[0101] (Binder)

[0102] 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, etc. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required of the magnetic recording medium 10. There is no particular limitation on the resin to be blended, so long as it is a resin that is generally used in coating-type magnetic recording media 10.

[0103] 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.

[0104] 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.

[0105] In addition, in order to improve the dispersibility of the magnetic powder, each of the above-mentioned binders contains -SO ３ M, -OSO ３ M, -COOM, P=O(OM) ２ In the formula, M is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

[0106] Furthermore, the polar functional group is -NR1R2, -NR1R2R3 ＋ X － A side chain type having a 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. Examples of the polar functional group include —OH, —SH, —CN, and an epoxy group.

[0107] (Additives)

[0108] 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.

[0109] (lubricant)

[0110] The magnetic layer may contain a lubricant. The lubricant may be, for example, one or more selected from fatty acids and / or fatty acid esters, and preferably contains both a fatty acid and a fatty acid ester. The fatty acid may preferably be a compound represented by the following general chemical formula (1) or general chemical formula (2). For example, the fatty acid may contain one or both of the compound represented by the following general chemical formula (1) and the compound represented by the general chemical formula (2). The fatty acid ester may preferably be a compound represented by the following general chemical formula (3), general chemical formula (4), or general chemical formula (5). For example, the fatty acid ester may contain any one of the compounds represented by the following general chemical formula (3), the compounds represented by the general chemical formula (4), and the compounds represented by the general chemical formula (5), or two or more selected from these. The lubricant contains either one or both of the compound represented by general chemical formula (1) and the compound represented by general chemical formula (2), and either one or two or more selected from the compound represented by general chemical formula (3), the compound represented by general chemical formula (4), and the compound represented by general chemical formula (5), thereby making it possible to suppress an increase in the dynamic friction coefficient of the magnetic recording medium due to repeated recording or reproduction.

[0111] CH ３ (CH ２ ) ｋCOOH (1) (wherein, in general chemical formula (1), k is an integer selected from the range of 14 to 22, more preferably from the range of 14 to 18.)

[0112] CH ３ (CH ２ ) ｎ CH=CH(CH ２ ) ｍ COOH (2) (In the general chemical formula (2), the sum of n and m is an integer selected from the range of 12 to 20, more preferably from the range of 14 to 18.)

[0113] CH ３ (CH ２ ) ｐ COO (CH ２ ) ｑ CH ３ ... (3) (In the general chemical formula (3), p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is an integer selected from the range of 2 or more and 5 or less, more preferably 2 or more and 4 or less.)

[0114] CH ３ (CH ２ ) ｒ COO-(CH ２ ) ｓ CH (CH ３ ) ２ ...(4) (In the general chemical formula (4), r is an integer selected from the range of 14 to 22, and s is an integer selected from the range of 1 to 3.)

[0115] CH ３ (CH ２ ) ｔ COO-(CH)(CH ３ ) CH ２ (CH ３ ) ｕ ...(5) (In general formula (5), t is an integer selected from the range of 14 to 22, and u is an integer selected from the range of 1 to 3.)

[0116] Examples of the lubricant include esters of monobasic fatty acids having 10 to 24 carbon atoms with any of monohydric to hexahydric alcohols having 2 to 12 carbon atoms, mixed esters thereof, di-fatty acid esters, tri-fatty acid esters, etc. Specific examples of the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, octyl myristate, etc. The magnetic layer may contain any one or more of these.

[0117] The content of the lubricant may be, for example, preferably 1 part by mass or more, more preferably 2 parts by mass or more, per 100 parts by mass of the magnetic powder, and may be, for example, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the magnetic powder.

[0118] (Nonmagnetic layer (base layer))

[0119] 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 hardener, and a rust inhibitor, as necessary.

[0120] 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, 0.7 μm or less, and even more preferably 0.6 μm or less. There is no particular limitation on the lower limit of 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.

[0121] (Non-magnetic powder)

[0122] 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 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.

[0123] (lubricant)

[0124] The nonmagnetic layer (underlayer) 12 may contain a lubricant. The lubricant may be, for example, one or more selected from fatty acids and / or fatty acid esters, and preferably contains both a fatty acid and a fatty acid ester. The fatty acid may preferably be a compound represented by the general chemical formula (1) or general chemical formula (2). For example, the fatty acid may contain one or both of the compound represented by the general chemical formula (1) and the compound represented by the general chemical formula (2). The fatty acid ester may preferably be a compound represented by the general chemical formula (3), general chemical formula (4), or general chemical formula (5). For example, the fatty acid ester may contain any one of the compounds represented by the general chemical formula (3), the compounds represented by the general chemical formula (4), and the compounds represented by the general chemical formula (5), or may contain two or more selected from these.

[0125] Examples of the lubricant include esters of monobasic fatty acids having 10 to 24 carbon atoms with any of monohydric to hexahydric alcohols having 2 to 12 carbon atoms, mixed esters thereof, di-fatty acid esters, tri-fatty acid esters, etc. Specific examples of the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, octyl myristate, etc. The magnetic layer may contain any one or more of these.

[0126] The content of the lubricant in the nonmagnetic layer 12 may be, for example, preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of nonmagnetic powder (100 parts by mass of total amount of nonmagnetic powder). Furthermore, the content may be, for example, preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of nonmagnetic powder (100 parts by mass of total amount of nonmagnetic powder). The above numerical ranges may be applied, for example, when the nonmagnetic powder contains iron oxide.

[0127] (Back layer)

[0128] The back layer 14 may 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.

[0129] 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 can be determined in the same manner as the average particle size D of the magnetic powder described above.

[0130] Average thickness t of the back layer 14 ｂThe 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 t Ｔ Even when the thickness is set to 5.7 μm or less, the average thickness of the nonmagnetic layer 12 and the base layer 11 can be kept large, thereby maintaining running stability within a recording and 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.

[0131] (3) Physical properties and structure

[0132] (Standard deviation of magnetic force distribution "StdDev.", median "Mean" and average size of magnetic clusters)

[0133] The ratio StdDev. / Mean of the standard deviation (StdDev.) of the magnetic force distribution to the median (Mean) of the magnetic force distribution of the magnetic recording medium according to the present technology may be, for example, 0.18 or less, preferably 0.16 or less, more preferably 0.14 or less, even more preferably 0.12 or less, and even more preferably 0.10 or less. By having the ratio StdDev. / Mean of the standard deviation (StdDev.) of the magnetic force distribution to the median (Mean) of the magnetic force distribution within the above-mentioned numerical range, the magnetic force of the magnetic clusters varies little, the frequency of missing pulses is low, and the output is stable. The lower limit of the ratio StdDev. / Mean of the standard deviation (StdDev.) of the magnetic force distribution to the median (Mean) of the magnetic force distribution is not particularly limited, but may be, for example, preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more.

[0134] The average magnetic cluster size of the magnetic recording medium according to the present technology is, for example, 3300 nm. ２ or less, preferably 3000 nm ２ or less, more preferably 2700 nm ２ or less, more preferably 2400 nm ２or less, even more preferably 2100 nm ２ The magnetic layer of the magnetic recording medium according to the present technology has such a small average magnetic cluster size, which means that the areal recording density is high. The lower limit of the average magnetic cluster size is not particularly limited, but may be, for example, 500 nm ２ More than 600 nm, preferably ２ More preferably, 700 nm ２ or more, 800 nm ２ or more, 900 nm ２ or more, or 1000 nm 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.

[0135] The standard deviation (StdDev.) of the magnetic force distribution, the median (Mean) of the magnetic force distribution, and the average size of the magnetic clusters are measured based on an MFM image of the surface of the magnetic recording medium on the side of the magnetic layer. The measurement methods are as follows.

[0136] First, a magnetic recording medium contained in a cartridge, such as cartridge 10A described below, is unwound, and three 1 cm x 1 cm squares are cut out from a 5 cm long area of ​​the magnetic recording medium where data is recorded, at a position approximately 10 m longitudinally from the outside of the cartridge, and the cut-out portions are used as measurement samples.

[0137] A DC erase process is performed on the magnetic layer side surface of the measurement sample. The DC erase process is performed using a VSM (Vibrating Sample Magnetometer, also known as a vibrating sample magnetometer). The VSM may be a high-sensitivity vibrating sample magnetometer VSM-P7-15 manufactured by Toei Kogyo Co., Ltd. The measurement sample is set in the VSM so that the magnetic surface of the measurement sample is perpendicular (facing) to the magnetic field generated by the opposing coil of the VSM. Then, a perpendicular external magnetic field of 15 kOe is applied to the magnetic surface. Thereafter, the external magnetic field is turned off, and a DC-erased sample is obtained. In this manner, the DC erase process is performed.

[0138] 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.

[0139] The MFM used to obtain the MFM image was a Bruker NanoScope IV Dimension ICON and its analysis software. The cantilever used for the MFM was an SSS-MFMR (NANOSENSORS, probe material: silicon single crystal coated with a magnetic film, cantilever length: 225 μm, tuned 0-150 Hz). The measurement conditions for the MFM were as follows: <Measurement Conditions> Scan Size: 5 μm × 5 μm Number of Samples: 512 × 512 Phase Detection Mode Lift Height: 20 nm Filtering Process Flatten Order: 2 Planefit Order XY: 3 Sweep Speed: 1 Hz In other words, the measurement area for obtaining the MFM image was 5 μm × 5 μm, and this 5 μm × 5 μm measurement area was 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.

[0140] By performing the image analysis process described below on each of the three obtained MFM images, the ratio of the standard deviation (StdDev.) of the three magnetic force distributions to the median (Mean) of the magnetic force distributions, StdDev. / Mean, and three magnetic cluster size values ​​are obtained. By simply averaging the three ratios, StdDev. / Mean, and the three magnetic cluster size values, the average value of the ratio of the standard deviation (StdDev.) of the magnetic force distributions to the median (Mean) of the magnetic force distributions, StdDev. / Mean, and the average magnetic cluster size are obtained.

[0141] The image analysis process is performed using image analysis software Image-J (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.

[0142] Step 1: Reading data ("File" → "Open") Open the image file of the MFM image to be analyzed.

[0143] Step 2: Adjusting the scale (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. 3A, after inputting the data into the Set Scale window, click the OK button in the window.

[0144] Step 3: Crop the measurement image (Among the "Area Selection Tools," select "Rectangle" → surround the MFM image → "Image" → "Crop") The MFM image is selected using a rectangular selection tool. The selected area is then cropped. For example, as shown in FIG. 3B, the rectangular selection tool is selected, and a rectangle is selected around the MFM image as indicated by the white line in FIG. 3C. Then, by cropping, a window displaying the cropped MFM image is generated, as shown in FIG. 3D.

[0145] Step 4: Converting the image type ("Image" → "Type" → "8bit") The image type of the image cropped in step 3 is converted to an 8-bit grayscale image.

[0146] 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.

[0147] Step 6: Save ("Save") The image after noise removal in step 5 is given an arbitrary name and saved in TIF format.

[0148] Step 7: Generate histogram ("Analyze" → "Histogram") The image saved in step 6 is used as brightness information, and the maximum value of either the S or N signal is processed as brightness 0 using the image analysis software Image-J to generate a histogram (256 divisions). This displays the Mean (median) value and StdDev. (standard deviation) value in the histogram window. The StdDev. / Mean is also calculated. For example, the histogram window shown in Figure 3E is displayed, and the Mean and StdDev. values ​​are displayed in this window.

[0149] 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.] x 0.7) In the Threshold window, enter the determined threshold as the minimum value (Min) and 255 as the maximum value (Max), and click the "Apply" button. This will display the binarized image. That is, the threshold range a for binarization is set to {[Mean] + ([StdDev.] x 0.7)} ≦ a ≦ 255, and the average area of ​​the positive polarity portion in the image is calculated. For example, enter the determined threshold value in the minimum value (Min) input field in the Threshold window shown in Fig. 3F, and click the "Apply" button to enter the maximum value, thereby obtaining a binarized image as shown in Fig. 3G.

[0150] Step 9: Calculate particle size distribution ("Analyze" → "Analyze Particles") The binary image obtained in step 8 is subjected to particle size distribution calculation processing. The processing conditions for this calculation processing are as follows: Size: 0-Infinity Circularity: 0.00-1.00 Show: Bare outlines Checking Summarize in the Analyze Particles window displays the Summary screen. The Summary screen displays 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, [Count] and [Total Area] are used to calculate the magnetic cluster size 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 3H and click the OK button. This will display the Summary screen as shown in Figure 3I. The magnetic cluster size value is calculated using the data in this screen.

[0151] The above image analysis process is performed on each of the three MFM images to obtain three magnetic cluster size values, which are then simply averaged to obtain the average magnetic cluster size.

[0152] (Average thickness (average total thickness) of the magnetic recording medium) t Ｔ )

[0153] The average thickness t of the magnetic recording medium 10 (hereinafter also referred to as magnetic tape T) Ｔis 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.

[0154] (Average thickness of non-magnetic layer (underlayer))

[0155] 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 length 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 processed by FIB or other methods to thin it down. 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 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.

[0156] The cross section of each obtained thinned sample is observed using a transmission electron microscope (TEM) under the following conditions: Apparatus: TEM (Hitachi H9000NAR), Acceleration voltage: 300 kV, Magnification: 100,000x. Next, using the obtained TEM image, the thickness of the nonmagnetic 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 nonmagnetic layer 12.

[0157] (average thickness of base layer)

[0158] 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 toward the other end on the opposite side.

[0159] 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 with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample (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.

[0160] (Average thickness of the back layer t ｂ )

[0161] Average thickness t of the back layer 14 ｂ is calculated as follows: First, the average thickness (average total thickness) t of the magnetic tape T is calculated. 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, using a laser hologram gauge (LGH-110C) manufactured by Mitutoyo Corporation, the thickness of the sample is measured at five positions, and these measurements are simply averaged (arithmetic mean) 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. ｂ [μm] = t Ｔ [μm]-t Ｂ [μm]

[0162] (Average thickness of the magnetic layer t ｍ )

[0163] 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 250 mm samples are cut from the magnetic tape T at positions 10 m to 20 m, 30 m to 40 m, and 50 m to 60 m from one end of the outer periphery of the magnetic tape T in the longitudinal direction, respectively. Each sample is then processed and thinned by FIB or other methods. 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.

[0164] The cross section of each obtained thinned sample was observed under the following conditions using a transmission electron microscope (TEM) to obtain a TEM image of each thinned sample. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Device: TEM (H9000NAR manufactured by Hitachi, Ltd.) Acceleration voltage: 300 kV Magnification: 100,000 times

[0165] 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].

[0166] (Ba / Sr ratio of magnetic powder)

[0167] The average thickness t of the magnetic layer 13 ｍ The cross section of each thinned sample used for measuring the average thickness t ｍ The sliced ​​samples are observed under the same conditions as in the measurement of step 1, and a TEM image of each sliced ​​sample is obtained. Next, EDX measurement is performed on the magnetic layer 13 portion of each sliced ​​sample to determine the Ba / Sr element ratio. The element ratios of Ba and Sr are determined for each of the three sliced ​​samples, and the average value is taken as the Ba / Sr ratio.

[0168] (Squareness ratio Rs2 in the vertical direction)

[0169] 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, thereby obtaining a better SNR. Therefore, better electromagnetic conversion characteristics can be obtained. In addition, the servo signal shape is improved, making it easier to control on the drive side. In this specification, the 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).

[0170] The squareness ratio Rs2 in the perpendicular direction is determined as follows. First, the magnetic tape T housed in the magnetic recording cartridge 10A is unwound, and a 250 mm sample is cut from the magnetic tape T at a position 30 m longitudinally from the joint 221 between the magnetic tape T and the leader tape LT. This sample is then punched out to 6.25 mm x 64 mm and folded in thirds to create a 6.25 mm x 8 mm measurement sample. The M-H hysteresis loop of the measurement sample (the entire magnetic tape T) corresponding to the perpendicular direction (thickness direction) of the magnetic tape T is then measured using a VSM. Next, the coatings (underlayer 12, magnetic layer 13, back layer 14, etc.) are wiped off using acetone or ethanol, leaving only the base layer 11. The resulting base layer 11 is then punched out to 6.25 mm x 64 mm and folded in thirds to create 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 (perpendicular direction of the magnetic recording medium 10) is measured using a VSM.

[0171] A high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Industry Co., Ltd. was used to measure the M-H hysteresis loop of the measurement sample (the entire magnetic tape T) and the M-H hysteresis loop of the correction sample (base layer 11). The measurement conditions were: 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, and number of MH averages: 20. After the M-H hysteresis loop of the measurement sample (the entire magnetic tape T) and the M-H hysteresis loop of the correction sample (base layer 11) were obtained, background correction was performed by subtracting the M-H hysteresis loop of the correction sample (base layer 11) from the M-H hysteresis loop of the measurement sample (the entire magnetic tape T), and a background-corrected M-H hysteresis loop was obtained. The background correction calculation is carried out using the measurement and analysis program attached to the "VSM-P7-15 model."

[0172] The saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the obtained M-H hysteresis loop after background correction are substituted into the following formula to calculate the squareness ratio Rs2 (%). Note that all of the above M-H hysteresis loop measurements are performed at 25°C. Also, no "demagnetizing field correction" is performed when measuring the M-H hysteresis loop in the perpendicular direction to the magnetic tape T. Note that this calculation uses the measurement and analysis program attached to the "VSM-P7-15 model." Squareness ratio Rs2 (%) = (Mr / Ms) x 100

[0173] (Coercive force Hc)

[0174] The coercive force Hc in the perpendicular direction (thickness direction) of the magnetic recording medium 10 may be preferably 190 kA / m or more, more preferably 200 kA / m or more, and even more preferably 220 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 350 kA / m or less, more preferably 330 kA / m or less, and even more preferably 310 kA / m or less, 300 kA / m or less, or 290 kA / m or less. By having the coercive force Hc be equal to or less than this upper limit, recording processing by a magnetic head can be sufficiently performed. 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 magnetic layer side surface is 1850 nm. ２ The present invention also provides a magnetic recording medium having a coercive force Hc in the perpendicular direction of 200 kA / m or more and 350 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.

[0175] 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 6.39 mm diameter punch to prepare a measurement sample. At this time, markings are made with any nonmagnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be identified. Then, an M-H 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. Three of the obtained base layers 11 are then stacked with double-sided tape and then punched out with a 6.39 mm diameter punch to prepare a sample for background correction (hereinafter simply referred to as a "correction sample"). Thereafter, the M-H loop of the correction sample (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. A high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Industry Co., Ltd. is used to measure the M-H loop of the measurement sample (the entire magnetic recording medium 10) and the M-H loop of the correction sample (base layer 11). The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20. After obtaining the M-H loop of the measurement sample (the entire magnetic recording medium 10) and the M-H loop of the correction sample (base layer 11), background correction is performed by subtracting the M-H loop of the correction sample (base layer 11) from the M-H loop of the measurement sample (the entire magnetic recording medium 10), thereby obtaining the M-H loop after background correction. The measurement and analysis program included with the "VSM-P7-15" is used for this background correction calculation. The coercive force Hc is determined from the obtained M-H loop after background correction. Note that the measurement and analysis program included with the "VSM-P7-15" is used for this calculation.It should be noted that all of the above MH loop measurements are performed at 25° C. Furthermore, when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10, "demagnetizing field correction" is not performed.

[0176] (4) Manufacturing method of magnetic recording medium

[0177] 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 a non-magnetic powder, a binder, etc. in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and / or dispersing a 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 the magnetic layer and the paint for forming the non-magnetic layer (underlayer).

[0178] 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. One of these may be used, or a mixture of two or more of them may be used.

[0179] Examples of kneading devices that can be used in preparing the above-mentioned coating material 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 material 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.

[0180] 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 ratio StDev / Mean of the standard deviation (StDev) to the median (Mean) of the magnetic force distribution (for example, the ratio StDev / Mean is 0.18 or less) and the average size of the magnetic clusters (for example, the average size is 1850 nm ２The coating composition is prepared to have the following characteristics: (i.e., the characteristics of being less than or equal to the above). For this preparation, for example, the processing conditions (e.g., the type of apparatus, time, etc.) for kneading and / or dispersing the magnetic powder, the first particles, and the 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 one skilled in the art depending on the particle size to be dispersed. Furthermore, the coating material for achieving the above characteristics can be adjusted by adjusting the dispersion time. For example, the average magnetic cluster size can be reduced by extending the dispersion treatment time 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 one skilled in the art depending on, for example, the type of particle. Furthermore, for this preparation, for example, the content of the magnetic powder, the content of the first particles, and the content of the second particles may be adjusted. For example, when using a magnetic powder with a smaller average particle volume, the dispersion state of these particles can be made more appropriate by reducing the content of the first particles and / or the second particles, thereby making it possible to adjust the height of the protrusions formed by these particles 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 one skilled in the art from within these numerical ranges.

[0181] 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 performed separately. By performing the dispersion treatment of the magnetic powder and the dispersion treatment of the inorganic material separately in this manner, the dispersion state of these materials can be appropriately adjusted, making it easier to achieve the above-mentioned characteristics. In this embodiment, a bead mill may be used as the device for the dispersion treatment. The bead diameter may be appropriately selected by a person 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 a person skilled in the art depending on, for example, the type of particles. Achieving these characteristics 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.

[0182] That is, the manufacturing method includes a magnetic layer-forming paint preparation step, which 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 the mixing step, another composition (particularly a binder-containing solvent, for example, a resin-containing solvent) may also be mixed. The magnetic layer-forming paint is produced by the mixing step.

[0183] 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 carried out 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 improvements in the electromagnetic conversion characteristics and / or 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.

[0184] 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 results in a magnetic recording medium 10.

[0185] 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) of the coating film of the magnetic layer-forming paint. The strength of the magnetic field applied to the coating film is preferably between two and three times the cohesive force 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.

[0186] 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 elongated magnetic recording medium 10.

[0187] (5) Recording and playback device

[0188] [Configuration of recording / playback device]

[0189] Next, with reference to FIG. 4, 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.

[0190] The recording and 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 and 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 and reproducing device 30 is configured to be able to load one magnetic recording cartridge 10A, but the recording and 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. The magnetic recording medium of the present technology is suitable for use in a timing servo type magnetic recording and reproducing device.

[0191] 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.

[0192] As shown in Figure 4, 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, a plurality of guide rollers 35, a head unit 36, a communication interface (hereinafter referred to as I / F) 37, and a control device 38.

[0193] The spindle 31 is configured to allow attachment of a magnetic recording cartridge 10A. 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 on the magnetic recording medium 10 as a servo signal. The reel 32 is configured to be able to fix the leading end of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 10A. The present technology also provides a magnetic recording cartridge including a magnetic recording medium according to the present technology. Within the magnetic recording cartridge, the magnetic recording medium may be wound around a reel, for example, and may be housed in a case while wound around the reel.

[0194] 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.

[0195] 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.

[0196] 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 .

[0197] The control device 38 controls the entire recording / reproducing device 30. For example, in response to a request from an information processing device such as a server 41 or a 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 a 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.

[0198] 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 on the magnetic recording medium 10 as servo signals, 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 this 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 taking into account the distance information between the servo patterns when the servo patterns were recorded, the change in the width of the magnetic recording medium 10 can also be calculated. The control device 38 controls the rotational drive of the spindle drive device 33 and the reel drive device 34 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, 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.

[0199] [Operation of recording / playback device]

[0200] Next, the operation of the recording / reproducing apparatus 30 having the above configuration will be described.

[0201] 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.

[0202] 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.

[0203] When the magnetic recording medium 10 is rewound onto the reel 10C, the spindle 31 and the reel 32 are rotated in the opposite direction to that described above, causing the magnetic recording medium 10 to run from the reel 32 to the reel 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.

[0204] (6) Modified Example

[0205] [Modification 1]

[0206] As shown in FIG. 5 , the magnetic recording medium 10 may further include a barrier layer 15 provided 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 depending on the environment. For example, one example of a 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 into the base layer 11. The barrier layer 15 includes a metal or a metal oxide. As the metal, for example, 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 can be used. As the metal oxide, for example, Al ２ O ３ , CuO, CoO, SiO ２ , Cr ２ O ３ , TiO ２ , Ta ２ O ５ , and ZrO ２At least one of the above can be used, or any of the oxides of the above metals can be used. Diamond-like carbon (DLC) or diamond can also be used.

[0207] 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.

[0208] [Modification 2]

[0209] 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.

[0210] [Modification 3]

[0211] 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.

[0212] [Modification 4]

[0213] The magnetic recording medium 10 may be subjected to recording and reproduction by a recording and reproduction device. The recording and reproduction device can correct width variations of the magnetic recording medium 10 by adjusting the tilt of a recording and reproduction head of a drive in accordance with width variations of the magnetic recording medium 10. The reproduction device can adjust the tilt of the recording and reproduction head of the drive.

[0214] 3. Second Embodiment (1) One embodiment of a magnetic recording cartridge

[0215] [Cartridge configuration]

[0216] The present technology also provides a magnetic recording cartridge (also referred to as a tape cartridge) including a magnetic recording medium according to the present technology. Within 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.

[0217] An example of the configuration of a magnetic recording cartridge 10A equipped with the magnetic recording medium T having the above-described configuration will be described with reference to FIG.

[0218] 6 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 conforms to 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 and a flange 213B made of a hard material such as plastic. 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.

[0219] 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.

[0220] [Cartridge memory configuration]

[0221] An example of the configuration of the cartridge memory 211 will be described with reference to FIG.

[0222] 7 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 rectifying and generating electricity from radio waves received by the antenna coil 331 using induced electromotive force, 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 determining commands and data from the digital signal extracted from the detection / modulation circuit 334 and processing them, 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.

[0223] The memory 336 stores information related to the magnetic recording cartridge 10A. The memory 336 is a non-volatile 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.

[0224] 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") of the LTO standard prior to LTO8, and is an area for storing information compliant with the LTO standard prior to LTO8. Information compliant with the LTO standard prior to LTO8 includes, for example, manufacturing information (such as a unique number of the magnetic recording cartridge 10A), usage history (such as the number of times the tape has been pulled out (Thread Count)), etc.

[0225] 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 moving images 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 recording data 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. Details of the distance between servo bands will be described later. In the following description, the information stored in the first memory area 336A will sometimes be referred to as "first information," and the information stored in the second memory area 336B will sometimes be referred to as "second information."

[0226] The memory 336 may have multiple banks. In this case, some of the multiple banks may constitute a first storage area 336A, and the remaining banks may constitute a 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, with one of the two banks constituting the first storage area 336A and the other bank constituting the second storage area 336B.

[0227] 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.

[0228] 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.

[0229] (2) Modified Magnetic Recording Cartridge

[0230] [Cartridge configuration]

[0231] 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. 8 .

[0232] 8 is an exploded perspective view showing an example of the configuration of a two-reel type cartridge 421. The cartridge 421 comprises 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 the upper half 402, a reel holder 422 fixed to the inside of the upper half 402 to prevent the reels 406 and 407 from floating up, a lower half 405 corresponding to the upper half 402, the reels 406 and 407 stored in the space formed when the upper half 402 and lower half 405 are combined, the magnetic tape MT1 wound on the reels 406 and 407, a front lid 409 closing the front opening formed when the upper half 402 and lower half 405 are combined, and a back lid 409A protecting the magnetic tape MT1 exposed in this front opening.

[0233] 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 a similar configuration to the reel 406.

[0234] The window member 423 has mounting holes 423a for assembling reel holders 422, which are reel holding means for preventing these reels from floating up, at positions corresponding to the reels 406 and 407. The magnetic tape MT1 is the same as the magnetic tape T in the first embodiment.

[0235] The present technology can also employ the following configuration: [1] A magnetic recording medium having a magnetic layer containing magnetic powder, wherein the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution is 0.18 or less, and the average size of magnetic clusters measured based on an MFM image of the surface of the magnetic layer side is 3,300 nm. ２ [2] The magnetic recording medium according to [1], wherein the ratio StDev / Mean is 0.16 or less. [3] The average magnetic cluster size is 3000 nm. ２[4] The magnetic recording medium according to [1] or [2], wherein the magnetic powder contains Ba atoms and Sr atoms. [5] The magnetic recording medium according to any one of [1] to [3], wherein the magnetic powder is barium ferrite magnetic powder. [6] The magnetic recording medium according to [5], wherein the magnetic powder is barium ferrite magnetic powder in which some of the Ba atoms (X) are substituted with Sr atoms (Y). [7] The magnetic recording medium according to [6], wherein the atomic ratio of Sr atoms (Y) / Ba atoms (X) in the magnetic powder is less than 1. [8] The magnetic powder has an average particle volume of 1,300 nm ３ [9] The magnetic recording medium according to any one of [1] to [7], wherein the magnetic powder has an average particle volume of 1200 nm or less. ３

[10] The magnetic recording medium according to any one of [1] to [7], wherein the magnetic powder has an average particle volume of 1100 nm or less. ３

[11] The magnetic recording medium according to any one of [1] to [7], wherein the magnetic powder is composite particles of ε-iron oxide and Co-containing spinel ferrite.

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

[11] , wherein the average total thickness is 5.40 μm or less.

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

[11] , wherein the average total thickness is 5.30 μm or less.

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

[11] , wherein the average total thickness is 5.22 μm or less.

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

[14] , wherein the magnetic recording medium comprises a magnetic layer, an underlayer, and a base layer in this order.

[16] The magnetic recording medium according to

[15] , wherein the base layer is formed from PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or PEEK (polyether ether ketone).

[17] The magnetic recording medium according to

[15] or

[16] , wherein the average thickness of the base layer is 4.10 μm or less.

[18] The magnetic recording medium according to any one of

[15] to

[17] , wherein the average thickness of the base layer is 3.80 μm or more.

[19] The magnetic recording medium according to any one of

[15] to

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

[20] The magnetic recording medium according to any one of

[15] to

[19] , wherein the average thickness of the underlayer is 0.90 μm or less.

[21] The magnetic recording medium according to any one of

[15] to

[20] , wherein the underlayer contains non-magnetic powder.

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

[21] , wherein the magnetic recording medium contains a lubricant.

[23] A magnetic recording medium comprising: a case; and a reel housed in the case and wound with a magnetic recording medium, wherein the magnetic recording medium has a magnetic layer containing magnetic powder, wherein the ratio StDev / Mean of the standard deviation (StDev) of a magnetic force distribution to the median (Mean) of the magnetic force distribution is 0.18 or less, and the average size of magnetic clusters measured based on an MFM image of the surface of the magnetic layer side is 3,300 nm. ２ A magnetic recording cartridge, which is:

[0236] 4. Working Example

[0237] 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.

[0238] 4-1. Evaluation of the effect of the average size of magnetic clusters on electromagnetic conversion characteristics

[0239] [Example 1] (Preparation process of magnetic layer-forming paint) A magnetic layer-forming paint was prepared as follows. First, a first composition having the following formulation was kneaded using an extruder. Next, the kneaded first composition, the second composition having the following formulation, and the third composition having the following formulation were added to a stirring tank equipped with a disperser, and 180.0 parts by mass of methyl ethyl ketone, 90.0 parts by mass of toluene, and 180.0 parts by mass of cyclohexanone were added, followed by premixing. Next, further mixing was performed using a Dynomill, and filtering was performed to prepare a magnetic layer-forming paint.

[0240] (First composition) Barium ferrite (Ba 0.9 Sr 0.1 Fe １２ O １９ ) Magnetic powder (hexagonal plate shape, average particle volume 1000 nm ３ Vinyl chloride resin (cyclohexanone solution 30% by mass): 35 parts by mass (degree of polymerization 300, Mn = 10,000, containing polar groups OSOK = 0.07 mmol / g and secondary OH = 0.3 mmol / g) Polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 10 parts by mass (polyurethane resin: number average molecular weight Mn = 25,000, Tg = 110°C)

[0241] (Second composition) Aluminum oxide powder: 3.0 parts by mass (α-Al2O3, average particle size 0.1 μm) Vinyl chloride resin (cyclohexanone solution 30% by mass): 3.0 parts by mass (degree of polymerization 300, Mn = 10,000, contains polar groups OSOK = 0.07 mmol / g and secondary OH = 0.3 mmol / g) Cyclohexanone: 10.0 parts by mass Mixed for 10 hours using a paint shaker

[0242] (Third composition) Carbon black: 2.0 parts by mass (manufactured by Tokai Carbon Co., Ltd., product name: Seast S, arithmetic mean particle size 70 nm) Vinyl chloride resin (cyclohexanone solution 30% by mass): 4.0 parts by mass (degree of polymerization 300, Mn = 10,000, contains polar groups OSOK = 0.07 mmol / g and secondary OH = 0.3 mmol / g) Cyclohexanone: 18.5 parts Mixed for 10 hours using a paint shaker

[0243] Finally, 1.8 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) and 2.0 parts by mass of stearic acid were added as a curing agent to the magnetic layer-forming coating material prepared as described above.

[0244] (Preparation process of paint for forming base layer) The paint for forming base layer was prepared as follows. First, the fourth composition having the following formulation was kneaded using an extruder. Next, the kneaded fourth composition and the fifth composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, further mixing was performed using a Dynomill and filtering was performed to prepare the paint for forming base layer.

[0245] (Fourth composition) Acicular iron oxide powder: 100 parts by mass (α-Fe2O3, average major axis length 0.15 μm) Vinyl chloride resin: 50 parts by mass (cyclohexanone solution 30% by mass) (degree of polymerization 300, Mn=10,000, contains polar groups OSOK=0.07 mmol / g and secondary OH=0.3 mmol / g) Aluminum oxide powder: 3 parts by mass (α-Al ２ O ３ , average particle size 0.1 μm)

[0246] (Fifth composition) Carbon black: 30 parts by mass (manufactured by Asahi Carbon Co., Ltd., product name: #80) Polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 50 parts by mass (polyurethane resin: number average molecular weight Mn = 25,000, Tg = 70°C) n-butyl stearate: 2 parts by mass Methyl ethyl ketone: 110 parts by mass Toluene: 80 parts by mass Cyclohexanone: 110 parts by mass

[0247] Finally, 1.5 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) and 1.5 parts by mass of stearic acid were added as a curing agent to the paint for forming the undercoat layer prepared as described above.

[0248] (Preparation process of paint for forming back layer) The paint for forming back layer was prepared as follows. The following raw materials were mixed in a stirring tank equipped with a disperser and filtered to prepare the paint for forming back layer. Carbon black (manufactured by Asahi Corporation, trade name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (manufactured by Nippon Polyurethane Co., Ltd., trade name: N-2304) Methyl ethyl ketone: 250 parts by mass Toluene: 150 parts by mass Cyclohexanone: 250 parts by mass Polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation): 10 parts by mass

[0249] (Film Forming Step) Using the coating material prepared as described above, a magnetic tape was prepared as described below.

[0250] 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, with an average thickness of 0.80 μm in the final product. Next, a magnetic layer-forming paint was applied to the primer layer and dried to form a magnetic layer on the primer layer, with an average thickness of 0.07 μm in the final product. The magnetic layer was then subjected to a vertical orientation treatment using a solenoid coil.

[0251] Next, a back layer-forming coating material was applied to the other main surface of the PEN film on which the underlayer and magnetic layer had been formed, and then dried to form a back layer with an average thickness of 0.35 μm in the final product. The PEN film on which the underlayer, magnetic layer, and back layer had been formed was then subjected to a curing treatment. After that, a calendering treatment was performed to smooth the surface of the magnetic layer.

[0252] (Cutting Step) The magnetic tape obtained as described above was cut into 1 / 2 inch (12.65 mm) widths, thereby obtaining a long magnetic tape.

[0253] 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 parallel rows in the longitudinal direction at known intervals (hereinafter referred to as "the known intervals between pre-recorded magnetic pattern rows").

[0254] The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.16, and the average magnetic cluster size was 2915 nm ２ The results are shown in Table 1.

[0255] [Example 2] Magnetic powder was barium ferrite (Ba 0.55 Sr 0.45 Fe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1000 nm ３ A magnetic tape was obtained in the same manner as in Example 1, except that the magnetic tape was changed to 0.18. A magnetic recording cartridge was then obtained using the magnetic tape in the same manner as in Example 1. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.18, and the average magnetic cluster size was 3291 nm. ２ It was.

[0256] [Example 3] Magnetic powder was barium ferrite (Ba 0.98 Sr 0.02 Fe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1200 nm ３A magnetic tape was obtained in the same manner as in Example 1, except that the magnetic tape was changed to 0.17. A magnetic recording cartridge was then obtained using the magnetic tape in the same manner as in Example 1. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.17, and the average magnetic cluster size was 3295 nm. ２ It was.

[0257] [Comparative Example 1] Magnetic powder was barium ferrite (BaFe12O19) magnetic powder (hexagonal plate shape, average particle volume 1600 nm 3 A magnetic tape was obtained in the same manner as in Example 1, except that the base layer was changed to a 4.2 μm thick PEN film, the magnetic layer thickness was 0.06 μm, and the underlayer thickness was 0.60 μm. Then, using this magnetic tape, a magnetic recording cartridge was obtained in the same manner as in Example 1. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.21, and the average magnetic cluster size was 3459 nm. ２ It was.

[0258] Comparative Example 2: Magnetic powder was barium ferrite (BaFe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1600 nm ３ ) and the Dynomill mixing time was increased by 1.2 times, 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 ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.20, and the average magnetic cluster size was 3366 nm ２ It was.

[0259] Comparative Example 3: Magnetic powder was barium ferrite (BaFe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1600 nm ３A magnetic tape was obtained in the same manner as in Example 1, except that the thickness of the magnetic layer was changed to 0.08 μm, the thickness of the underlayer was changed to 0.90 μm, and the total thickness was changed to 5.58 μm. The magnetic tape was then used to obtain a magnetic recording cartridge in the same manner as in Example 1. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.19, and the average magnetic cluster size was 3,300 nm. ２ It was.

[0260] [Comparative Example 4] Magnetic powder was barium ferrite (Ba 0.98 Sr 0.02 Fe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1200 nm ３ ) and the Dynomill mixing time was increased by 0.9 times, 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 ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.16, and the average magnetic cluster size was 3371 nm ２ It was.

[0261] Comparative Example 5: Magnetic powder was barium ferrite (BaFe 12 O 19 ) Magnetic powder (hexagonal plate shape, average particle volume 1000 nm ３ A magnetic tape was obtained in the same manner as in Example 1, except that the magnetic tape was changed to 0.19. A magnetic recording cartridge was then obtained using the magnetic tape in the same manner as in Example 1. The ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the obtained magnetic tape to the median (Mean) of the magnetic force distribution was 0.19, and the average magnetic cluster size was 3327 nm. ２ It was.

[0262] [Evaluation of Electromagnetic Conversion Characteristics] The electromagnetic conversion characteristics of the magnetic tape housed in each of the magnetic recording cartridges manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 were evaluated. The evaluation was carried out as follows.

[0263] First, a loop tester (Microphysics) was used to obtain a playback signal from the magnetic tape. The playback signal acquisition conditions are as follows: Head: GMR Head speed: 1.85 m / s Signal: Single recording frequency 10 MHz (2T half Nyquist frequency) Recording current: Optimum recording current

[0264] 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.

[0265] [Evaluation of Tape Quality] The quality of the magnetic tape housed in each of the magnetic recording cartridges manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 was evaluated. The quality of the magnetic tape was evaluated based on the number of missing pulses in accordance with JISx-6175. The evaluation was carried out as follows.

[0266] A magnetic recording cartridge containing each magnetic tape (total length 500 m) of the Examples and Comparative Examples was loaded into a Mountain Engineering II MTS Transport 2'x3' deck. Recording was then performed on the magnetic tape in the magnetic recording cartridge at a single recording frequency of 20 MHz (2T half-Nyquist frequency) while sliding the LT09 magnetic head of the drive against the magnetic layer surface at a running speed of 3.7 m / s. The playback signal during playback was input to an external AD (Analog / Digital) converter, and a missing pulse was detected when the playback signal output dropped 16.5 dB below the normal output (average output of a 2T signal (180,000 bits)). The number of missing pulses per meter of one track was counted. A magnetic tape with a missing pulse count of 30 or less per meter was deemed to have high practical reliability.

[0267]

[0268] From the results shown in Examples 1 to 3 in Table 1, the ratio StDev / Mean of the standard deviation (StDev) of the magnetic force distribution of the magnetic tape to the median (Mean) of the magnetic force distribution was 0.18 or less, and the average magnetic cluster size was 3,300 nm. ２ It is believed that by keeping the value below this, the electromagnetic conversion characteristics are improved, the number of missing pulses is small, and the variation in magnetic force is reduced.

[0269] Furthermore, the results shown in Table 1 reveal the following.

[0270] As shown in Comparative Examples 1 and 2, StDev / Mean exceeds 0.18, and the average magnetic cluster size is 3300 nm. ２ As shown in Comparative Example 3, when the average size of the magnetic clusters is 3300 nm or more, there are many missing pulses and the electromagnetic conversion characteristics SNR is also poor. ２ As shown in Comparative Example 4, the average size of the magnetic clusters is 3300 nm, and the StDev / Mean ratio exceeds 0.18, which causes variations in the magnetic force of the magnetic clusters and results in an increase in the number of missing pulses. ２If the SNR exceeds 100%, the electromagnetic conversion characteristic SNR is poor.

[0271] A comparison between Comparative Example 2 and Comparative Example 4 shows that, if the average magnetic cluster size is approximately the same, the smaller the StDev / Mean, the less variation there is in the magnetic force of the magnetic clusters, resulting in a more stable output and better electromagnetic conversion characteristics SNR. A comparison between Example 1 and Comparative Example 4 shows that even if StDev / Mean is small, as the average magnetic cluster size increases, noise increases and the electromagnetic conversion characteristics SNR deteriorate. The results of Comparative Examples 1 to 5 show that as StDev / Mean increases, variation occurs in the magnetic force of the magnetic clusters, resulting in more missing pulses, and as the average size of the magnetic clusters increases, this effect becomes even worse.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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 the numerical ranges described in stages in this specification, the upper limit or lower limit of a numerical range in a certain stage may be replaced with the upper limit or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in this specification may be used alone or in combination of two or more types.

[0276] 10 magnetic recording medium 11 base layer 12 underlayer 13 magnetic layer 14 back layer

Claims

1. A magnetic recording medium having a magnetic layer containing magnetic powder, wherein the ratio of the standard deviation (StDev) of the magnetic force distribution to the median (Mean) of the magnetic force distribution (StDev / Mean) is 0.18 or less, and the average magnetic cluster size measured based on an MFM image of the magnetic layer side surface is 3,300 nm. ２ A magnetic recording medium comprising:

2. The magnetic recording medium according to claim 1, wherein the ratio StDev / Mean is 0.16 or less.

3. The average size of the magnetic clusters is 3000 nm. ２ 2. The magnetic recording medium according to claim 1, wherein:

4. The magnetic recording medium according to claim 1, wherein the magnetic powder contains Ba atoms and Sr atoms.

5. The magnetic recording medium according to claim 1, wherein said magnetic powder is barium ferrite magnetic powder.

6. The magnetic recording medium according to claim 5, wherein the magnetic powder is barium ferrite magnetic powder in which some of the Ba atoms (X) are substituted with Sr atoms (Y).

7. The magnetic recording medium according to claim 6, wherein the atomic ratio of Sr atoms (Y) to Ba atoms (X) in said magnetic powder is less than 1.

8. The magnetic powder has an average particle volume of 1,300 nm ３ 2. The magnetic recording medium according to claim 1, wherein:

9. The magnetic powder has an average particle volume of 1200 nm ３ 2. The magnetic recording medium according to claim 1, wherein:

10. The magnetic powder has an average particle volume of 1100 nm ３ 2. The magnetic recording medium according to claim 1, wherein:

11. The magnetic recording medium according to claim 1, wherein the magnetic powder is a composite particle of ε-iron oxide and Co-containing spinel ferrite.

12. The magnetic recording medium according to claim 1, having an average total thickness of 5.40 μm or less.

13. The magnetic recording medium according to claim 1, having an average total thickness of 5.30 μm or less.

14. The magnetic recording medium according to claim 1, having an average total thickness of 5.22 μm or less.

15. The magnetic recording medium of claim 1, comprising, in that order, a magnetic layer, an underlayer, and a base layer.

16. The magnetic recording medium according to claim 15, wherein the base layer is formed from PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or PEEK (polyether ether ketone).

17. The magnetic recording medium according to claim 15, wherein the average thickness of the base layer is 4.10 μm or less.

18. The magnetic recording medium according to claim 15, wherein the average thickness of the base layer is 3.80 μm or more.

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

20. The magnetic recording medium according to claim 15, wherein the average thickness of said underlayer is 0.90 μm or less.