magnetic recording media

Abstract

The main purpose of the present technology is to improve the reliability of magnetic recording tape by controlling the distribution of a binder in an underlayer.　The present technology provides a magnetic recording medium that comprises a magnetic layer, an underlayer, and a base layer in the stated order, the underlayer containing a chlorine-containing binder, and the thickness of a portion of the underlayer where the chlorine count number is at or above a threshold value being 130 nm or less. [Threshold value] = [average chlorine count number in underlayer] + 6 × [standard deviation obtained at calculation of average chlorine count number] The present technology also provides a magnetic recording medium that comprises a magnetic layer, an underlayer, and a base layer in the stated order, the underlayer containing a chlorine-containing binder, and the thickness of a portion of the underlayer where the chlorine count number is at or above the threshold value being 12% or less with respect to the thickness of the underlayer.

Description

[Technical Field]

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

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

[0003] Various technologies have been proposed for magnetic recording media. For example, Patent Document 1 below discloses a magnetic recording medium having a magnetic layer of 0.3 μm or less in thickness, containing at least an iron-atom-containing magnetic powder and a binder, on one or both sides of a non-magnetic support, wherein the magnetic recording medium satisfies S(Fe) / D(Fe)≧1.1, where S(Fe) is the average iron element content in the surface layer from the center of the magnetic layer and D(Fe) is the average iron element content in the deeper layer from the center of the magnetic layer.

[0004] Furthermore, Patent Document 2 listed below discloses a magnetic recording medium having a magnetic layer formed on a non-magnetic support by applying a magnetic paint containing at least a magnetic powder and a binder, wherein the magnetic layer is configured so that the constituent elements change in the depth direction of the magnetic layer, and the content ratio of carbon constituting the binder to the elements constituting the magnetic powder in the surface layer of the magnetic layer is 90 vol% or more, and the content ratio of carbon constituting the binder to the elements constituting the magnetic powder at a depth of 50 Å or more from the surface of the magnetic layer is 70 vol% or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-279619 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-100021 Summary of the Invention [Problem to be solved by the invention]

[0006] To manufacture a coated magnetic recording tape having a magnetic layer and an underlayer, a underlayer is formed on a base layer. A coating material for forming a magnetic layer is applied to form a base layer, and then a coating material for forming a magnetic layer is applied onto the base layer to form a magnetic layer. The main object of this technology is to improve the reliability of such magnetic recording tape. [Means for solving the problem]

[0007] This technology is a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; The thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 130 nm or less. A magnetic recording medium is provided. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count] The portion having a value equal to or greater than the threshold value may be present on the base layer side of the underlayer. The portion of the underlayer that is equal to or greater than the threshold may be present within 200 nm of the interface between the underlayer and the base layer. The portion of the underlayer that is equal to or greater than the threshold may be present within 130 nm of the interface between the underlayer and the base layer. The total thickness of the magnetic layer and the underlayer may be 1200 nm or less. The total thickness of the magnetic layer and the underlayer may be 1000 nm or less. The magnetic layer may have a thickness of 80 nm or less. The underlayer may have a thickness of 1120 nm or less. The underlayer may contain non-magnetic powder. The underlayer may include a lubricant. The average thickness t of the magnetic recording medium T may be 5.5 μm or less. The magnetic layer may include magnetic powder. The magnetic powder may include hexagonal ferrite, ε iron oxide, or Co-containing spinel ferrite. In addition, this technology: a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 12% or less of the thickness of the underlayer; A magnetic recording medium is also provided. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count] The present technology also provides a magnetic recording cartridge in which the magnetic recording medium is housed in a case while being wound around a reel. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the configuration of a magnetic recording medium according to a first embodiment. [Figure 2A] FIG. 2 is a diagram showing an example of the shape of a particle of magnetic powder. [Figure 2B] 1 is an example of a TEM photograph of a cross section of a sample. [Figure 2C] 10 is another example of a TEM photograph of a cross section of a sample. [Figure 3A] FIG. 2 is a schematic diagram showing the cross-sectional structure of a magnetic particle. [Figure 3B] FIG. 10 is a schematic diagram showing the cross-sectional structure of a magnetic particle in a modified example. [Figure 4A] FIG. 1 shows an example of a HAADF STEM image. [Figure 4B] FIG. 10 is a diagram for explaining a Cl Kα ray extraction region set for a HAADF STEM image. [Figure 4C] FIG. 10 is a diagram showing an example of plot data in which the net count number is plotted against the pixel position in the thickness direction. [Figure 4D] 1 is a diagram for explaining the net count number, and in particular, a diagram for explaining an example of a line where Kα rays are counted. [Figure 4E] FIG. 10 is a diagram showing an example of plot data in which the chlorine count after normalization is plotted against the position in the thickness direction. [Figure 5] FIG. 1 is a schematic diagram showing the configuration of a recording / reproducing device. [Figure 6] FIG. 10 is a cross-sectional view showing the configuration of a magnetic recording medium according to a modified example. [Figure 7] FIG. 2 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge. [Figure 8] FIG. 2 is a block diagram showing an example of the configuration of a cartridge memory. [Figure 9] FIG. 10 is an exploded perspective view showing an example of the configuration of a modified magnetic recording cartridge. [Figure 10] 1 is a plot of data of measurement results of chlorine count numbers in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] This technology will be described in the following order. 1. Description of this technology 2. First embodiment (1) Structure of magnetic recording medium (2) Explanation of each layer (3) Physical properties and structure (4) Manufacturing method of magnetic recording medium (5) Recording and playback device (6) Variations 3. Second embodiment (1) One embodiment of a magnetic recording cartridge (2) Modified magnetic recording cartridge 4. Working Example

[0011] In this specification, unless a measurement environment is specifically stated in the description of the measurement method, the measurement is performed in an environment of 25°C ± 2°C and 50% RH ± 5% RH.

[0012] 1. Description of this technology

[0013] As described above, in order to manufacture a coated magnetic recording tape, a primer layer is formed by applying a primer layer-forming paint onto a base layer, and then a magnetic layer-forming paint is applied onto the primer layer to form a magnetic layer. It has been found that applying the magnetic layer-forming paint results in uneven distribution of the binder contained in the primer layer in the thickness direction. It has also been found that uneven distribution of the binder in the underlayer affects the reliability of the magnetic recording tape. The uneven distribution of the binder causes the ratio of inorganic material to binder in the underlayer to become non-uniform across the thickness. Depending on the state of the uneven distribution, the reliability of the magnetic recording tape may decrease, increasing the likelihood of defects that require rewriting during the recording process. The present inventors have discovered that by controlling the distribution of the binder in the underlayer, the reliability of the magnetic recording tape can be improved.

[0014] That is, the magnetic recording medium of the present technology includes a magnetic layer, an underlayer, and a base layer in this order. The underlayer includes a chlorine-containing binder, and the underlayer includes a portion where the chlorine count is equal to or greater than the following threshold. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count] The chlorine count corresponds to the amount of chlorine-containing binder. The portion where the chlorine count is equal to or greater than the threshold value has a higher chlorine count than the other portions of the undercoat layer, and therefore contains more chlorine-containing binder than the other portions. In other words, the portion where the chlorine count is equal to or greater than the threshold value is the portion where the chlorine-containing binder is unevenly distributed. In the magnetic recording medium of the present technology, the width in the thickness direction of the portion where the thickness is equal to or greater than the threshold, i.e., the uneven distribution width, is controlled, thereby improving the reliability of the magnetic recording medium, for example, reliability during running for performing recording processing.

[0015] In one embodiment of the present technology, the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold may be, for example, 130 nm or less, preferably 125 nm or less, and more preferably 120 nm or less, 115 nm or less, 110 nm or less, 105 nm or less, 100 nm or less, 95 nm or less, or 90 nm or less. The thickness of the portion where the chlorine count is equal to or greater than the threshold means the length of the portion where the chlorine count is equal to or greater than the threshold in the thickness direction of the magnetic recording medium. The thickness of the portion may be, for example, 30 nm or more, 40 nm or more, or 50 nm or more. By ensuring that the thickness of the portion that is equal to or greater than the threshold falls within the above range, i.e., by ensuring that the uneven distribution width is small, the reliability of the magnetic recording medium can be improved, and for example, rewriting during recording processing can be prevented.

[0016] In another embodiment of the present technology, the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the threshold may be, for example, 12% or less of the thickness of the underlayer, preferably 11% or less, or even 10% or less, or 9% or less. Also in this embodiment, the thickness of the portion where the chlorine count is equal to or greater than the threshold means the length of the portion where the chlorine count is equal to or greater than the threshold in the thickness direction of the magnetic recording medium. The thickness of the portion may be, for example, 4% or more or 5% or more. By ensuring that the thickness of the portion that is equal to or greater than the threshold falls within the above range, i.e., by ensuring that the uneven distribution width is small, the reliability of the magnetic recording medium can be improved, and for example, rewriting during recording processing can be prevented.

[0017] Preferably, the portion of the underlayer having a magnetic recording medium thickness equal to or greater than the threshold value is located on the base layer side of the underlayer. For example, when the underlayer is divided into a magnetic layer side region and a base layer side region in the thickness direction of the magnetic recording medium, the portion of the underlayer having a magnetic recording medium thickness equal to or greater than the threshold value may be located in the base layer side region. More preferably, the portion of the underlayer having a thickness equal to or greater than the threshold may be located within 200 nm, preferably within 150 nm, and particularly preferably within 130 nm, 120 nm, 110 nm, or 100 nm of the interface between the underlayer and the base layer. In a particularly preferred embodiment, the portion having a thickness equal to or greater than the threshold may be located so as to contact the interface between the underlayer and the base layer. Controlling the position of the portion where the concentration is above the threshold, that is, the portion where the chlorine-containing binder is unevenly distributed, in this manner also contributes to improving the reliability of the magnetic recording medium.

[0018] In the underlayer, some of the chlorine-containing binder is adsorbed to the inorganic material contained in the underlayer, while others are present without being adsorbed to the inorganic material. The uneven distribution of the chlorine-containing binder described above is believed to be mainly due to the chlorine-containing binder not being adsorbed to the inorganic material. It is believed that controlling the uneven distribution of the chlorine-containing binder can improve the reliability of the magnetic recording medium. This will be explained in more detail below.

[0019] When the magnetic layer forming paint is applied, the solvent in the paint affects the distribution of the binder contained in the already formed base layer, and in particular affects the distribution of the binder that is present without being adsorbed to the inorganic material. Depending on the state of uneven distribution of the binder, there is a higher possibility that powder will fall off in the early stages of use of the magnetic recording medium, which may reduce the reliability of the magnetic recording medium. For example, when multiple reels of magnetic recording tape are run in one round trip or when full-surface recording is performed on multiple reels of magnetic recording tape, this can have an adverse effect on the reliability of the magnetic recording tape. By narrowing the range of uneven distribution of the chlorine-containing binder according to this technology, particularly by narrowing the range of uneven distribution of the chlorine-containing binder and making the uneven distribution of the chlorine-containing binder exist on the base layer side, the reliability of the magnetic recording medium can be improved, for example, the possibility of defects that require rewriting during the recording process can be reduced.

[0020] The improvement in reliability is believed to be due to the fact that the control of the uneven distribution allows the lubricant contained in the underlayer to be appropriately supplied to the surface of the magnetic recording medium. As described above, the uneven distribution is caused by the chlorine-containing binder not adsorbed to the inorganic material. The chlorine-containing binder not adsorbed to the inorganic material can block the pores that supply the lubricant to the surface, preventing the lubricant from being supplied to the surface of the magnetic recording medium. It is believed that by reducing the width of the uneven distribution, the range in which the chlorine-containing binder that is not adsorbed to the inorganic material is present is narrowed, thereby making it possible to appropriately supply the lubricant to the surface of the magnetic recording medium. Furthermore, by narrowing the width of the uneven distribution and having the uneven distribution exist in the base layer, it is possible to more effectively prevent the chlorine-containing binder from blocking pores and hindering the supply of lubricant. Furthermore, if the amount of chlorine-containing binder unevenly distributed on the base side is small, a certain amount of chlorine-containing binder that is not adsorbed to the inorganic material may also be present at the interface between the magnetic layer and the underlayer. In this case, too, there is a high possibility that the pores will be blocked by the chlorine-containing binder that is not adsorbed to the inorganic material. Therefore, the thickness of this portion is preferably at least 1 / 25 of the thickness of the underlayer, and more preferably at least 1 / 20 of the thickness of the underlayer.

[0021] The magnetic recording medium according to the present technology may preferably be a long magnetic recording medium, for example, a magnetic recording tape (particularly a long magnetic recording tape).

[0022] 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.

[0023] The average thickness (average total thickness) of the magnetic recording medium according to the present technology is t T may be, for example, 5.7 μm or less, preferably 5.6 μm or less, more preferably 5.5 μm or less, 5.4 μm or less, 5.3 μm or less, 5.2 μm or less, 5.1 μm or less, or 5.0 μm or less, and even more preferably 4.6 μm or less or 4.4 μm or less. Because the magnetic recording medium is so thin, for example, the length of tape wound into one magnetic recording cartridge can be made longer, thereby increasing the recording capacity per magnetic recording cartridge. The average thickness (average total thickness) t of the magnetic recording medium T The lower limit of t is not particularly limited, but for example, 3.5 μm≦t T is.

[0024] 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 80 nm or less, more preferably 70 nm or less, even more preferably 60 nm or less, 50 nm or less, and even more preferably 40 nm or less. m The lower limit of the average thickness of the magnetic layer is not particularly limited, but is preferably 30 nm or more. The method for measuring the average thickness of the magnetic layer will be explained below in 2.(3).

[0025] The average thickness of the underlayer (also referred to as the non-magnetic layer) of the magnetic recording medium according to the present technology can be preferably 1200 nm or less, preferably 1150 nm or less, 1120 nm or less, 1100 nm or less, more preferably 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, and even more preferably 600 nm or less. The lower limit of the average thickness of the underlayer is not particularly limited, but can be preferably 200 nm or more, more preferably 300 nm or more. The method for measuring the average thickness of the underlayer will be described below in 2.(3).

[0026] The average thickness of the base layer (also referred to as the substrate layer) of the magnetic recording medium according to the present technology can be preferably 4.5 μm or less, more preferably 4.2 μm or less, 4.0 μm or less, 3.8 μm or less, or 3.6 μm or less, and even more preferably 3.4 μm or less, 3.2 μm or less, or 3.0 μm or less. The lower limit of the average thickness of the base layer is not particularly limited, but can be, for example, 2.0 μm or more, preferably 2.5 μm or more. The method for measuring the average thickness of the base layer will be described below in 2.(3).

[0027] The average thickness of the back layer of the magnetic recording medium according to the present technology is preferably 0.6 μm or less, more preferably 0.5 μm or less, and even more preferably 0.4 μm or less, 0.3 μm or less, 0.25 μm or less, or 0.2 μm or less. The lower limit of the average thickness of the back layer is not particularly limited, but may be, for example, 0.1 μm or more, preferably 0.15 μm or more. The method for measuring the average thickness of the back layer will be described below in 2.(3).

[0028] The total thickness of the magnetic layer and underlayer of the magnetic recording medium according to the present technology is preferably 1200 nm or less, and may be, for example, 1100 nm or less, 1000 nm or less, or 900 nm or less, and may be, for example, 300 nm or more, particularly 400 nm or more.

[0029] A magnetic recording medium according to the present technology may have, for example, at least one data band and at least two servo bands. The number of data bands may be, for example, 2 to 10, particularly 3 to 6, and more particularly 4 or 5. The number of servo bands may be, for example, 3 to 11, particularly 4 to 7, and more particularly 5 or 6. These servo bands and data bands may be arranged, for example, so as to extend in the longitudinal direction of a long magnetic recording medium (particularly a magnetic recording tape), particularly so as to be substantially parallel. The data band and the servo band may be provided on the magnetic layer. An example of a magnetic recording medium having such a data band and servo band is a magnetic recording tape conforming to the LTO (Linear Tape-Open) standard. That is, the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO standard. For example, the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO8 standard or later (e.g., LTO9, LTO10, LTO11, or LTO12). The width of a long magnetic recording medium (particularly a magnetic recording tape) according to the present technology can be, for example, 5 mm to 30 mm, particularly 7 mm to 25 mm, more particularly 10 mm to 20 mm, and even more particularly 11 mm to 19 mm. The length of a long magnetic recording medium (particularly a magnetic recording tape) can be, for example, 500 m to 1500 m. For example, a tape conforming to the LTO8 standard has a width of 12.65 mm and a length of 960 m.

[0030] 2. First embodiment

[0031] (1) Structure of magnetic recording medium First, the configuration of a magnetic recording medium 10 according to the first embodiment will be described with reference to Fig. 1. The magnetic recording medium 10 is, for example, a magnetic recording medium that has been subjected to a perpendicular orientation process. As shown in Fig. 1, the magnetic recording medium 10 includes a long base layer (also referred to as a substrate) 11, 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 underlayer 12, and a back layer 14 provided on the other major surface of the base layer 11. Hereinafter, of the two major surfaces of the magnetic recording medium 10, the surface on which the magnetic layer 13 is provided will be referred to as the magnetic surface, and the surface opposite to the magnetic surface (the surface on which the back layer 14 is provided) will be referred to as the back surface.

[0032] The magnetic recording medium 10 has an elongated shape and runs longitudinally during recording and reproduction. The magnetic recording medium 10 may be configured to record signals at a minimum recording wavelength of preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less, and may be used, for example, in a recording and reproduction device whose minimum recording wavelength is within the above range. This recording and reproduction device may be equipped with a ring-type head as a recording head. The recording track width is, for example, 2 μm or less.

[0033] (2) Explanation of each layer

[0034] (base layer)

[0035] The base layer 11 functions as a support for the magnetic recording medium 10 and may be, for example, a flexible, long, non-magnetic substrate, particularly a non-magnetic film. The average thickness of the base layer 11 may be, for example, 4.5 μm or less, preferably 4.2 μm or less, more preferably 4.0 μm or less, 3.8 μm or less, or 3.6 μm or less, and even more preferably 3.4 μm or less, 3.2 μm or less, or 3.0 μm or less. The lower limit of the average thickness of the base layer 11 may be determined, for example, from the viewpoint of film production limitations or the function of the base layer 11, and may be, for example, 2.0 μm or more, 2.2 μm or more, 2.4 μm or more, or 2.6 μm or more. The base layer 11 may contain, for example, at least one of polyester resins, polyolefin resins, cellulose derivatives, vinyl resins, aromatic polyether ketone resins, and other polymer resins. When the base layer 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

[0036] The polyester resin may be, for example, one or a mixture of two or more of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate), and polyethylene bisphenoxycarboxylate. According to a preferred embodiment of the present technology, the base layer 11 may be formed from PET or PEN.

[0037] The polyolefin resin may be, for example, one or a mixture of two or more of PE (polyethylene) and PP (polypropylene).

[0038] 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).

[0039] The vinyl resin may be, for example, one or a mixture of two or more of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0040] 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.

[0041] The other polymer resin may be, for example, one or a mixture of two or more of PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, such as Zylon (registered trademark), polyether, polyetherester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

[0042] The base layer may be formed from a resin that does not contain chlorine, particularly a polyester resin that does not contain chlorine, although the base layer may also be formed from a resin that contains chlorine.

[0043] (magnetic layer)

[0044] The magnetic layer 13 may be, for example, a perpendicular recording layer. The magnetic layer 13 contains magnetic powder. The magnetic layer 13 may further contain a binder. The magnetic layer 13 may further contain non-magnetic particles. The magnetic layer 13 may further contain additives such as a lubricant and an anti-rust agent, as necessary.

[0045] The average thickness t of the magnetic layer 13m The average thickness t of the magnetic layer is preferably 80 nm or less, more preferably 70 nm or less, even more preferably 60 nm or less, 50 nm or less, and even more preferably 40 nm or less. m The lower limit of the average thickness t of the magnetic layer 13 is not particularly limited, but is preferably 30 nm or more. m Being within the above range contributes to improving the electromagnetic conversion characteristics.

[0046] The magnetic layer 13 is preferably a magnetic layer that is perpendicularly oriented. In this specification, perpendicular orientation means that the squareness ratio S1 measured in the longitudinal direction (travel direction) of the magnetic recording medium 10 is 35% or less. The magnetic layer 13 may be an in-plane oriented (longitudinal oriented) magnetic layer. That is, the magnetic recording medium 10 may be a horizontal recording type magnetic recording medium. However, from the viewpoint of achieving high recording density, a perpendicular orientation is more preferable.

[0047] (magnetic powder)

[0048] Examples of magnetic particles constituting the magnetic powder contained in the magnetic layer 13 include, but are not limited to, hexagonal ferrite, epsilon iron oxide (ε-iron oxide), Co-containing spinel ferrite, gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, and metals. The magnetic powder may be one of these or a combination of two or more of these. Preferably, the magnetic powder contains hexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite. More preferably, the magnetic powder is hexagonal ferrite. The hexagonal ferrite particularly preferably contains at least one of Ba and Sr. The ε-iron oxide particularly preferably contains at least one of Al and Ga. These magnetic particles may be appropriately selected by those skilled in the art based on factors such as the manufacturing method of the magnetic layer 13, the specifications of the tape, and the functions of the tape.

[0049] 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.

[0050] The average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may be, for example, 10 nm or more, preferably 12 nm or more.

[0051] 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.

[0052] (An embodiment in which the magnetic powder includes hexagonal ferrite)

[0053] According to a preferred embodiment of the present technology, the magnetic powder may include hexagonal ferrite, and more particularly, may include a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles"). The hexagonal ferrite is preferably a hexagonal ferrite having an M-type structure. The hexagonal ferrite has, for example, a hexagonal plate shape or a nearly hexagonal plate shape. The hexagonal ferrite may preferably include at least one of Ba, Sr, Pb, and Ca, more preferably at least one of Ba, Sr, and Ca. Specifically, the hexagonal ferrite may be, for example, one or a combination of two or more selected from barium ferrite, strontium ferrite, and calcium ferrite, and is particularly preferably barium ferrite or strontium ferrite. Barium ferrite may further include at least one of Sr, Pb, and Ca in addition to Ba. Strontium ferrite may further include at least one of Ba, Pb, and Ca in addition to Sr.

[0054] More specifically, hexagonal ferrites have the general formula MFe 12 O 19 The alloy may have an average composition represented by the formula: where M is, for example, at least one metal selected from Ba, Sr, Pb, and Ca, preferably at least one metal selected from Ba and Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb, and Ca. M may also be a combination of Sr and one or more metals selected from the group consisting of Ba, Pb, and Ca. In the above general formula, part of Fe may be substituted with another metal element.

[0055] When the magnetic powder contains hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may be, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. For example, the average particle size of the magnetic powder may be 10 nm or more to 50 nm or less, 10 nm or more to 40 nm or less, 12 nm or more to 30 nm or less, 12 nm or more to 25 nm or less, or 15 nm or more to 22 nm or less. When the average particle size of the magnetic powder is the upper limit or less (e.g., 50 nm or less, particularly 30 nm or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high-recording-density magnetic recording medium 10. When the average particle size of the magnetic powder is equal to or greater than the lower limit (for example, 10 nm or greater, preferably 12 nm or greater), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0056] When the magnetic powder contains hexagonal ferrite particles, the average aspect ratio of the magnetic powder is preferably 1.0 to 3.0, more preferably 1.0 to 2.9, and even more preferably 2.0 to 2.9. Having the average aspect ratio of the magnetic powder within the above range can suppress aggregation of the magnetic powder, and can also suppress the resistance applied to the magnetic powder when vertically orienting the magnetic powder in the process of forming the magnetic layer 13. This can improve the vertical orientation of the magnetic powder.

[0057] When the magnetic powder contains hexagonal ferrite particles, the average particle size and average aspect ratio of the magnetic powder can be determined as follows. First, the magnetic recording medium (hereinafter also referred to as "magnetic tape") housed in a magnetic recording cartridge is unwound, and a 50 mm section of the magnetic tape to be measured is cut out. For example, in the case of a magnetic recording cartridge 10A as shown in FIG. 19, the cut-out position may be 30 m longitudinally from the connection 221 between the magnetic tape T and the leader tape LT. Next, the magnetic tape to be measured is processed and thinned using a FIB method or the like. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape facing the magnetic layer and the surface facing the back layer, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer. The thinning is performed along the length (longitudinal direction) of the magnetic tape. That is, the thinning process forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape.

[0058] The cross section of the obtained thin sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so that the entire magnetic layer is included in the thickness direction of the magnetic layer, and a TEM photograph is taken. TEM photographs are prepared in sufficient quantity to extract 50 particles from which the plate diameter DB and plate thickness DA (see Figure 2A) shown below can be measured.

[0059] In this specification, the size of a hexagonal ferrite particle (hereinafter referred to as "particle size") is defined as the plate diameter DB, which is the longest diameter of the plate surface or base, when the particle shape observed in the TEM photograph is plate-like or columnar (however, the thickness or height is smaller than the longest diameter of the plate surface or base), as shown in FIG. 2A. The thickness or height of the particle observed in the TEM photograph is defined as the plate thickness DA. When the plate surface or base of the particle observed in the TEM photograph is hexagonal, the longest diameter means the longest diagonal distance. When the thickness or height of a particle is not constant within a single particle, the thickness or height of the largest particle is defined as the plate thickness DA.

[0060] Next, 50 particles are selected from the TEM photograph based on the following criteria. Particles with parts outside the field of view of the TEM photograph are not measured, and only particles with a clear outline and that exist independently are measured. If particles overlap, those with a clear boundary between them and whose overall shape can be determined are measured as individual particles, but particles with unclear boundaries and whose overall shape cannot be determined are not measured as their shape cannot be determined.

[0061] Examples of TEM photographs are shown in Figures 2B and 2C. In these photographs, the particles indicated by arrows a and d are selected because their plate thickness (thickness or height) DA can be clearly confirmed. The plate thickness DA of each of the selected 50 particles is measured. The plate thicknesses DA thus obtained are simply averaged (arithmetic mean) to obtain the average plate thickness DA. ave Average plate thickness DA ave is the average particle plate thickness. Next, the plate diameter DB of each magnetic powder is measured. In order to measure the particle plate diameter DB, 50 particles whose particle plate diameter DB can be clearly confirmed are selected from the TEM photographs taken. For example, in these figures, the particles indicated by arrows b and c are selected because their plate diameter DB can be clearly confirmed. The plate diameter DB of each of the selected 50 particles is measured. The plate diameters DB thus determined are simply averaged (arithmetic average) to obtain the average plate diameter DB ave Average plate diameter DB aveis the average particle size.

[0062] When the magnetic powder comprises a powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 1800 nm 3 or less, and more preferably 1600 nm 3 More preferably, 1400 nm or less. 3 and even more preferably 1200 nm or less. 3 Below, 1100nm 3 or less than 1000 nm 3 The average particle volume of the magnetic powder is preferably 500 nm 3 More preferably, 700 nm 3 It could be more than that.

[0063] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0064] The average particle volume of the magnetic powder can be calculated as follows: First, as described above in relation to the method for calculating the average particle size of the magnetic powder, the average plate thickness DA ave and average plate diameter DB ave Next, calculate the average particle volume V of the magnetic powder using the following formula:

[0065]

number

[0066] 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.

[0067] 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.

[0068] When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness t m For example, the average thickness t [nm] of the magnetic layer 13 is preferably 90 nm or less, and more preferably 80 nm or less. m is 35 nm ≦ tm ≦ 90 nm, or 35 nm ≦ t m It may be ≦80 nm.

[0069] 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.

[0070] (Embodiment in which the magnetic powder contains ε-iron oxide)

[0071] According to another preferred embodiment of the present technology, the magnetic powder may preferably comprise a powder of nanoparticles containing ε-iron oxide (hereinafter referred to as "ε-iron oxide particles"). ε-iron oxide particles can achieve high coercivity even when they are fine particles. The ε-iron oxide contained in the ε-iron oxide particles preferably has a crystal orientation preferentially in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

[0072] The ε-iron oxide particles are spherical or nearly spherical, or cubic or nearly cubic. Because of the above-described shape of the ε-iron oxide particles, when used as magnetic particles, the contact area between particles in the thickness direction of the medium can be reduced, and aggregation between particles can be suppressed, compared to when hexagonal plate-shaped barium ferrite particles are used as magnetic particles. This improves the dispersibility of the magnetic powder, resulting in a better SNR.

[0073] The ε-iron oxide particles may have a core-shell structure. Specifically, as shown in Fig. 3A, the ε-iron oxide particles include a core 21 and a two-layer shell 22 provided around the core 21. The two-layer shell 22 includes a first shell 22a provided on the core 21 and a second shell 22b provided on the first shell 22a.

[0074] The core portion 21 contains ε-iron oxide. The ε-iron oxide contained in the core portion 21 preferably has ε-Fe2O3 crystals as a main phase, and more preferably is made of single-phase ε-Fe2O3.

[0075] The first shell portion 22a covers at least a portion of the periphery of the core portion 21. Specifically, the first shell portion 22a may cover a portion of the periphery of the core portion 21, or may cover the entire periphery of the core portion 21. From the viewpoint of ensuring sufficient exchange coupling between the core portion 21 and the first shell portion 22a and improving magnetic properties, it is preferable that the entire surface of the core portion 21 be covered.

[0076] The first shell portion 22a is a so-called soft magnetic layer and may include a soft magnetic material such as α-Fe, a Ni-Fe alloy, or an Fe-Si-Al alloy. The α-Fe may be obtained by reducing ε-iron oxide contained in the core portion 21.

[0077] The second shell portion 22b is an oxide coating serving as an anti-oxidation layer. The second shell portion 22b may contain α-iron oxide, aluminum oxide, or silicon oxide. The α-iron oxide may contain at least one iron oxide selected from Fe3O4, Fe2O3, and FeO. When the first shell portion 22a contains α-Fe (soft magnetic material), the α-iron oxide may be obtained by oxidizing the α-Fe contained in the first shell portion 22a.

[0078] The ε-iron oxide particles have the first shell portion 22a as described above, which ensures thermal stability, thereby maintaining a high coercivity Hc of the core portion 21 alone and / or adjusting the coercivity Hc of the ε-iron oxide particles (core-shell particles) as a whole to a coercivity Hc suitable for recording. Furthermore, the ε-iron oxide particles have the second shell portion 22b as described above, which prevents the ε-iron oxide particles from being exposed to air during and before the manufacturing process of the magnetic recording medium 10, which can lead to rust and other damage on the particle surface, thereby preventing deterioration of the properties of the ε-iron oxide particles. Therefore, deterioration of the properties of the magnetic recording medium 10 can be prevented.

[0079] As shown in Fig. 3B, the ε-iron oxide particles may have a shell portion 23 with a single layer structure. In this case, the shell portion 23 has the same structure as the first shell portion 22a. However, from the viewpoint of suppressing deterioration of the properties of the ε-iron oxide particles, it is more preferable that the ε-iron oxide particles have a shell portion 22 with a two-layer structure.

[0080] The ε-iron oxide particles may contain an additive instead of a core-shell structure, or may have a core-shell structure and contain an additive. In these cases, a portion of the Fe in the ε-iron oxide particles is substituted with the additive. By including an additive in the ε-iron oxide particles, the coercivity Hc of the entire ε-iron oxide particles can be adjusted to a coercivity Hc suitable for recording, thereby improving ease of recording. The additive includes a metal element other than iron, preferably at least one of Al (aluminum), Ga (gallium), In (indium), Co (cobalt), Mn (manganese), Zr (zirconium), Hf (hafnium), Cs (cesium), Ti (titanium), Sm (samarium), Nd (neodymium), Pr (praseodymium), and Tb (terbium).

[0081] Specifically, the ε-iron oxide containing additives is ε-Fe 2-x M x O3 crystal (wherein M is a metal element other than iron, preferably a trivalent metal element, more preferably one or more selected from the group consisting of Al, Ga, and In. x is, for example, 0 <x<1である。)である。

[0082] The average particle size (average maximum particle size) of the magnetic powder is preferably 22 nm or less, more preferably 8 nm to 22 nm, and even more preferably 12 nm to 22 nm. In the magnetic recording medium 10, the actual magnetization region is a region half the size of the recording wavelength. Therefore, a good SNR can be obtained by setting the average particle size of the magnetic powder to half the shortest recording wavelength or less. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high-recording-density magnetic recording medium 10 (e.g., a magnetic recording medium 10 configured to record signals at the shortest recording wavelength of 44 nm or less). On the other hand, when the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.

[0083] 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.

[0084] When the magnetic powder contains ε-iron oxide particles, the average particle size and average aspect ratio of the magnetic powder can be determined as follows. First, the magnetic recording medium to be measured is cut out as described above for the case where the magnetic powder contains hexagonal ferrite particles. The magnetic recording medium to be measured is processed into thin sections using a method such as FIB (Focused Ion Beam). When using the FIB method, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon film is formed on the magnetic layer side surface and back layer side surface of the magnetic recording medium by vapor deposition, and the tungsten thin film is further formed on the magnetic layer side surface by vapor deposition or sputtering. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium. In other words, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium.

[0085] 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.

[0086] Next, 50 particles whose particle shapes can be clearly confirmed are selected from the TEM photographs, and the long axis length DL and short axis length DS of each particle are measured. Here, the long axis length DL refers to the maximum distance between two parallel lines drawn from any angle so as to be tangent to the outline of each particle (the so-called maximum Feret diameter). On the other hand, the short axis length DS refers to the maximum length of the particle in the direction perpendicular to the long axis (DL) of the particle.

[0087] Next, the major axis lengths DL of the 50 measured particles were simply averaged (arithmetic mean) to obtain the average major axis length DL ave The average major axis length DL ave is the average particle size of the magnetic powder. The minor axis lengths DS of the 50 particles measured are simply averaged (arithmetic mean) to obtain the average minor axis length DS ave Then, calculate the average major axis length DL ave and mean minor axis length DS ave The average aspect ratio of the particles (DL ave / DS ave ) is found.

[0088] The average particle volume of the magnetic powder is preferably 1800 nm 3 or less, and more preferably 1600 nm 3 or less, and more preferably 1400 nm 3 and even more preferably 1200 nm or less. 3 Below, 1100nm 3 or less than 1000 nm 3 The average particle volume of the magnetic powder is preferably 500 nm or less. 3 More preferably, 700 nm 3 It could be more than that.

[0089] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0090] When the ε-iron oxide particles are spherical or nearly spherical, the average particle volume of the magnetic powder can be calculated as follows: First, the average major axis length DL is calculated in the same manner as in the above-mentioned method for calculating the average particle size of the magnetic powder. ave Next, calculate the average particle volume V of the magnetic powder using the following formula: V=(π / 6)×DL ave 3

[0091] 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.

[0092] The obtained thin film sample is observed using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 200 kV and a total magnification of 500,000 times to observe the cross section of the magnetic layer 13 in the thickness direction so as to include the entire magnetic layer 13, and a TEM photograph is obtained. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of apparatus.

[0093] Next, 50 particles with clear particle shapes are selected from the TEM photographs, and the side length DC of each particle is measured. The side lengths DC of the 50 measured particles are then simply averaged (arithmetic mean) to obtain the average side length DC ave Next, calculate the average side length DC aveUsing the following formula, the average particle volume of the magnetic powder, V ave (particle volume) is calculated. V ave =DC ave 3

[0094] The coercive force Hc of the ε iron oxide particles is preferably 2500 Oe or more, and more preferably 2800 Oe or more and 4200 Oe or less.

[0095] (An embodiment in which the magnetic powder includes Co-containing spinel ferrite)

[0096] According to yet another preferred embodiment of the present technology, the magnetic powder may include a powder of nanoparticles containing Co-containing spinel ferrite (hereinafter also referred to as "cobalt ferrite particles"). That is, the magnetic powder may be cobalt ferrite magnetic powder. The cobalt ferrite particles preferably have uniaxial crystal anisotropy. The cobalt ferrite magnetic particles have, for example, a cubic or nearly cubic shape. The Co-containing spinel ferrite may further include one or more elements selected from the group consisting of Ni, Mn, Al, Cu, and Zn in addition to Co.

[0097] Cobalt ferrite has an average composition represented by the following formula, for example. Co x M y FeO z (In the above formula, M is, for example, one or more metals selected from the group consisting of Ni, Mn, Al, Cu, and Zn. x is a value within the range of 0.4≦x≦1.0. y is a value within the range of 0≦y≦0.3, with the proviso that x and y satisfy the relationship (x+y)≦1.0. z is a value within the range of 3≦z≦4. A portion of Fe may be substituted with another metal element.)

[0098] 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.

[0099] When the magnetic powder contains cobalt ferrite particles, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm to 19 nm. Such a small average particle size of the magnetic powder allows for good electromagnetic conversion characteristics (e.g., SNR) to be obtained in a high-recording-density magnetic recording medium 10. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, allowing for better electromagnetic conversion characteristics (e.g., SNR). When the magnetic powder contains cobalt ferrite particles, the average aspect ratio and average particle size of the magnetic powder are determined in the same manner as when the magnetic powder contains ε-iron oxide particles.

[0100] The average particle volume of the magnetic powder is preferably 2000 nm 3 or less, and more preferably 1900 nm 3 or less, and more preferably 1800 nm 3 and even more preferably 1700 nm or less. 3 Below, 1600nm 3 or below 1500nm 3 The average particle volume of the magnetic powder is preferably 500 nm or less. 3 More preferably, 700 nm 3 It could be more than that.

[0101] When the average particle volume of the magnetic powder is equal to or less than the upper limit (for example, 2000 nm 3 When the average particle volume of the magnetic powder is equal to or greater than the lower limit (for example, 500 nm 3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

[0102] (binder)

[0103] The binder is preferably a resin having a structure in which a crosslinking reaction has been imparted to a polyurethane resin or a vinyl chloride resin. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin that is generally used in coating-type magnetic recording media 10.

[0104] 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.

[0105] Furthermore, a thermosetting resin or a reactive resin may be used as the binder, and examples of these include phenolic resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea-formaldehyde resin.

[0106] Furthermore, to improve the dispersibility of the magnetic powder, polar functional groups such as -SO3M, -OSO3M, -COOM, and P=O(OM)2 may be introduced into each of the binders described above, where M is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

[0107] Furthermore, the polar functional groups include -NR1R2 and -NR1R2R3 + X - Side chain type with terminal group of >NR1R2 + X - In the formula, R1, R2, and R3 are hydrogen atoms or hydrocarbon groups, and X - is a halogen ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. Polar functional groups include —OH, —SH, —CN, and epoxy groups.

[0108] In one embodiment of the present technology, the magnetic layer includes a chlorine-containing binder. The chlorine-containing binder may be a chlorine-containing resin. The chlorine-containing resin is a resin that contains a chlorine atom as at least one of the elements that constitute the resin. The chlorine-containing binder is, for example, a vinyl chloride resin. More specific examples of the chlorine-containing binder include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-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, vinylidene chloride-acrylonitrile copolymer, and synthetic rubber.

[0109] The content of the chlorine-containing binder in the magnetic layer may be, for example, 30 parts by weight or more, preferably 35 parts by weight or more, and more preferably 40 parts by weight or more, per 100 parts by weight of magnetic powder, and may be, for example, 70 parts by weight or less, preferably 65 parts by weight or less, and more preferably 60 parts by weight or less, per 100 parts by weight of magnetic powder.

[0110] The magnetic layer may further contain a chlorine-free binder in addition to the chlorine-containing binder. The chlorine-free binder may be a chlorine-free resin. The chlorine-free resin may include, for example, a polyurethane-based resin. The polyurethane-based resin is a polymer having a urethane bond (—NH—C(═O)—) and may be produced, for example, by a polyaddition reaction between an isocyanate compound and a diol compound. The polyurethane-based resin may be, for example, a urethane-modified copolymer polyester. The urethane-modified copolymer polyester may be a urethane-modified copolymer polyester having an aromatic polyester as a basic skeleton and a urethane component in the side chain, or a urethane-modified copolymer polyester containing an ester repeating unit and a urethane repeating unit in the basic skeleton.

[0111] The content of the chlorine-free binder in the magnetic layer may be, for example, 1 part by mass or more, preferably 2 parts by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of magnetic powder, and may be, for example, 10 parts by mass or less, preferably 9 parts by mass or less, more preferably 8 parts by mass or less, per 100 parts by mass of magnetic powder.

[0112] (lubricant)

[0113] 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) or general chemical formula (4). For example, the fatty acid ester may contain either or both of the compound represented by the following general chemical formula (3) and the compound represented by the general chemical formula (4). The lubricant contains either or both of a compound represented by general chemical formula (1) and a compound represented by general chemical formula (2), and either or both of a compound represented by general chemical formula (3) and a compound represented by general chemical formula (4), thereby making it possible to suppress an increase in the dynamic friction coefficient of the magnetic recording medium due to repeated recording or reproduction.

[0114] CH3(CH2) k COOH (1) (However, in general chemical formula (1), k is an integer selected from the range of 14 or more and 22 or less, more preferably from the range of 14 or more and 18 or less.)

[0115] CH3(CH2) n CH=CH(CH2) m COOH (2) (However, in 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.)

[0116] CH3(CH2) p COO(CH2) q CH3···(3) (In 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.)

[0117] CH3(CH2) r COO-(CH2) s CH(CH3)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.)

[0118] Examples of the lubricant include esters of monobasic fatty acids having 10 to 24 carbon atoms with 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.

[0119] The content of the lubricant may be, for example, 1 part by mass or more, preferably 2 parts by mass or more, per 100 parts by mass of the magnetic powder, and may be, for example, 10 parts by mass or less, preferably 8 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the magnetic powder.

[0120] (additives)

[0121] 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.

[0122] In one embodiment of the present technology, the magnetic layer may contain first particles having electrical conductivity and second particles having a Mohs hardness of 7 or greater. The first particles and the second particles may form protrusions on the surface of the magnetic layer. For example, the first particles can prevent an increase in frictional force during magnetic recording tape running, and function as a solid lubricant component. Furthermore, the second particles can exert an abrasive effect (and even an anchor effect) for magnetic head cleaning. It is believed that including these two components in the magnetic layer of a magnetic recording tape can prevent an increase in frictional force and clean the magnetic head, thereby improving running performance.

[0123] The first particles are electrically conductive. The first particles may be fine particles primarily composed of carbon, preferably carbon particles, and examples of such carbon particles include carbon black. Examples of carbon black that can be used include Asahi #15 and #15HS from Asahi Carbon Co., Ltd. and Seast TA from Tokai Carbon Co., Ltd. Hybrid carbon, in which carbon is attached to the surface of silica particles, may also be used.

[0124] The average particle size (arithmetic mean value of particle diameters measured using an electron microscope) of the first particles (particularly carbon particles, for example, carbon black) may be, for example, 15 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. The average particle size may be, for example, 200 nm or less, preferably 180 nm or less, more preferably 150 nm or less, 130 nm or less, or 120 nm or less. The numerical range of the average particle size may be appropriately selected from these upper and lower limits, and may be, for example, 50 nm to 200 nm, preferably 50 nm to 180 nm, more preferably 50 nm to 150 nm, and even more preferably 50 nm to 130 nm. The nitrogen adsorption specific surface area of ​​the first particles (particularly carbon particles, for example, carbon black) is, for example, 5 m 2 / g~50m 2 / g, preferably 7m 2 / g~50m 2 / g, more preferably 10m 2 / g~50m 2 / g, and even more preferably 12m 2 / g~50m 2 / g. The iodine adsorption amount of the primary particles (particularly carbon particles, for example, carbon black) may be, for example, 5 mg / g to 50 mg / g, preferably 7 mg / g to 50 mg / g, more preferably 10 mg / g to 50 mg / g, and even more preferably 12 mg / g to 50 mg / g.

[0125] From the viewpoint of suppressing deformation due to contact with a magnetic head, the second particles may have a Mohs hardness of 7 or more, preferably 7.5 or more, more preferably 8 or more, and even more preferably 8.5 or more. From the viewpoint of suppressing head wear, the Mohs hardness of the second particles may be, for example, 10 or less, preferably 9.5 or less. That is, the second particles may be formed from a material having such a Mohs hardness. The second particles may preferably be inorganic particles. Examples of the second particles include α-alumina (the α-conversion rate may be, for example, 90% or more), β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and acicular α-iron oxide obtained by dehydrating and annealing magnetic iron oxide raw materials, optionally surface-treated with aluminum and / or silica, or diamond powder, or a combination of two or more of these. The second particles are preferably alumina particles such as α-alumina, β-alumina, and γ-alumina, or silicon carbide. These second particles may be acicular, spherical, cubic, or other shapes, but those with angular shapes are preferred because they have high abrasiveness, for example.

[0126] The average particle size (the arithmetic mean value of particle diameters measured using, for example, an electron microscope) of the second particles (particularly inorganic particles such as alumina) may be, for example, 15 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. The average particle size may be, for example, 200 nm or less, preferably 180 nm or less, more preferably 150 nm or less, 130 nm or less, or 120 nm or less. The numerical range of the average particle size may be appropriately selected from these upper and lower limits, and may be, for example, 50 nm to 180 nm, preferably 60 nm to 150 nm, and more preferably 60 nm to 120 nm. The second particles (particularly inorganic particles, such as alumina) may not be electrically conductive, i.e., the second particles may not have the same electrical conductivity as the first particles.

[0127] (base layer)

[0128] The underlayer 12 is a non-magnetic layer containing non-magnetic powder and a binder as its main components, and may further contain at least one additive selected from the group consisting of other particles, lubricants, hardeners, and rust inhibitors, as needed.

[0129] The average thickness of the underlayer 12 is preferably 1200 nm or less, preferably 1150 nm or less, 1120 nm or less, 1100 nm or less, more preferably 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, and even more preferably 600 nm or less. The lower limit of the average thickness of the underlayer is not particularly limited, but is preferably 200 nm or more, more preferably 300 nm or more.

[0130] (Non-magnetic powder)

[0131] The non-magnetic powder contained in the underlayer 12 includes, for example, at least one type selected from inorganic particles and organic particles, particularly at least one type selected from inorganic particles. One type of non-magnetic powder may be used alone, or two or more types of non-magnetic powders may be used in combination. The non-magnetic inorganic particles may be, for example, one or a combination of two or more types selected from metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. More specifically, the inorganic particles may be, for example, one or two or more types selected from iron oxide, aluminum oxide, carbon black, iron oxyhydroxide, hematite, titanium oxide, silicon oxide, titanium carbide, silicon carbide, diamond, and calcium carbonate. The shape of the non-magnetic powder may be, for example, acicular, spherical, cubic, plate-like, or other shapes, but is not particularly limited thereto.

[0132] In one embodiment of the present technology, the non-magnetic powder includes at least iron oxide, particularly acicular iron oxide. In this embodiment, the non-magnetic powder may further include carbon black and / or aluminum oxide.

[0133] The iron oxide (particularly, acicular iron oxide) may have an average major axis length of, for example, 0.01 μm or more, preferably 0.04 μm or more, and more preferably 0.07 μm or more, and may have an average major axis length of, for example, 0.5 μm or less, preferably 0.4 μm or less, and more preferably 0.3 μm or less.

[0134] The average particle size of the carbon black may be, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more, and may be, for example, 250 nm or less, preferably 150 nm or less, and more preferably 100 nm or less.

[0135] The carbon black content may be, for example, 15 parts by mass or more, preferably 20 parts by mass or more, and more preferably 25 parts by mass or more, per 100 parts by mass of the iron oxide, and the carbon black content may be, for example, 45 parts by mass or less, preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, per 100 parts by mass of the iron oxide.

[0136] The average particle size of the aluminum oxide may be, for example, 30 nm or more, preferably 40 nm or more, more preferably 60 nm or more, and may be, for example, 180 nm or less, preferably 150 nm or less, more preferably 120 nm or less.

[0137] The content of aluminum oxide may be, for example, 1 part by mass or more, preferably 2 parts by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of the iron oxide, and the content of aluminum oxide may be, for example, 10 parts by mass or less, preferably 9 parts by mass or less, more preferably 8 parts by mass or less, per 100 parts by mass of the iron oxide.

[0138] (binder)

[0139] The underlayer 12 contains a binder. The above description of the binder contained in the magnetic layer 13 also applies to the binder contained in the underlayer 12.

[0140] In the present technology, the underlayer contains at least a chlorine-containing binder. The chlorine-containing binder may be a chlorine-containing resin. The chlorine-containing resin is a resin that contains a chlorine atom as at least one of the elements constituting the resin. The chlorine-containing binder is, for example, a vinyl chloride resin. More specific examples of the chlorine-containing binder include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-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, vinylidene chloride-acrylonitrile copolymer, and synthetic rubber.

[0141] The underlayer contains a chlorine-containing binder adsorbed to the non-magnetic powder and a chlorine-containing binder not adsorbed to the non-magnetic powder. The distribution of the chlorine-containing binder not adsorbed to the non-magnetic powder in the underlayer is affected by the solvent contained in the magnetic layer-forming paint and the paint drying process during the magnetic layer-forming process in the manufacturing process of the magnetic recording medium. By controlling this distribution according to the present technology, the reliability of the magnetic recording medium can be improved.

[0142] The volume content of the chlorine-containing binder in the underlayer may be, for example, an amount equivalent to 20% by volume or more of the non-magnetic powder volume (particularly the total volume of the non-magnetic powder), preferably 30% by volume or more, more preferably 40% by volume or more, and may be, for example, an amount equivalent to 180% by volume or less of the non-magnetic powder volume (particularly the total volume of the non-magnetic powder), preferably 170% by volume or less, more preferably 160% by volume or less. For example, when the total volume of the non-magnetic powder is taken as 100, the volume of the chlorine-containing binder in the underlayer may be, for example, 20 to 180, preferably 30 to 170, and more preferably 40 to 160.

[0143] In one embodiment, the underlayer contains iron oxide as a non-magnetic powder. In this embodiment, the content of the chlorine-containing binder in the underlayer may be, for example, 20 parts by mass or more, preferably 25 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the iron oxide. The content may be, for example, 70 parts by mass or less, preferably 65 parts by mass or less, and more preferably 60 parts by mass or less, per 100 parts by mass of the iron oxide.

[0144] The underlayer may further contain a chlorine-free binder in addition to the chlorine-containing binder. The chlorine-free binder may be a chlorine-free resin. The chlorine-free resin may contain, for example, a polyurethane-based resin. The polyurethane-based resin is a polymer having a urethane bond (-NH-C(=O)-), and may be produced, for example, by a polyaddition reaction between an isocyanate compound and a diol compound. The polyurethane-based resin may be, for example, a urethane-modified copolymer polyester. The urethane-modified copolymer polyester has an aromatic polyester as a basic skeleton and urethane compounds in the side chains. Alternatively, the polyester may be a urethane-modified copolyester having an ester repeating unit and a urethane repeating unit in the basic skeleton.

[0145] The volume content of the chlorine-free binder in the underlayer may be, for example, an amount equivalent to 0% or more of the volume of the non-magnetic powder (particularly the total volume of the non-magnetic powder), preferably 10% or more, and more preferably 20% or more of the volume. Furthermore, the volume content may be, for example, an amount equivalent to 150% or less of the volume of the non-magnetic powder (particularly the total volume of the non-magnetic powder), preferably 140% or less, and more preferably 130% or less of the volume. The underlayer need not contain the chlorine-free binder. For example, when the total volume of the non-magnetic powder is taken as 100, the volume of the chlorine-containing binder in the underlayer may be, for example, 0 to 150, preferably 10 to 140, and more preferably 200 to 130.

[0146] In one embodiment, the underlayer contains iron oxide as a non-magnetic powder. In this embodiment, the content of the chlorine-free binder in the underlayer may be, for example, 0 parts by mass or more, preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the iron oxide. The content may be, for example, 30 parts by mass or less, preferably 25 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the iron oxide.

[0147] (lubricant)

[0148] The underlayer may contain a lubricant. The lubricant may be, for example, one or more selected from fatty acids and / or fatty acid esters, and the lubricant may preferably be a compound represented by general chemical formula (1) or (2), or general chemical formula (3) or (4) described above in relation to the magnetic layer. One or more of these compounds may be contained.

[0149] Examples of the lubricant include esters of monobasic fatty acids having 10 to 24 carbon atoms with 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.

[0150] The content of the lubricant in the underlayer may be, for example, 1 part by mass or more, preferably 1.5 parts by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of non-magnetic powder (100 parts by mass of total amount of non-magnetic powder). The content may be, for example, 12 parts by mass or less, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of non-magnetic powder (100 parts by mass of total amount of non-magnetic powder). The above numerical ranges may be applied, for example, when the non-magnetic powder contains iron oxide.

[0151] In one embodiment, the underlayer contains iron oxide as a nonmagnetic powder. In this embodiment, the content of the lubricant in the underlayer may be, for example, 2 parts by mass or more, preferably 2.5 parts by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of the iron oxide. The content may be, for example, 8 parts by mass or less, preferably 7 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of the iron oxide.

[0152] (Back layer)

[0153] The back layer 14 can contain a binder and a non-magnetic powder. The back layer 14 may also contain various additives such as a lubricant, a curing agent, and an antistatic agent as necessary. The above description of the binder and non-magnetic powder contained in the non-magnetic layer 12 also applies to the binder and non-magnetic powder contained in the back layer 14.

[0154] The average particle size of the inorganic particles contained in the back layer 14 is preferably 10 nm or more and 150 nm or less, and more preferably 15 nm or more and 110 nm or less. The average particle size of the inorganic particles is determined in the same manner as the average particle size D of the magnetic powder described above.

[0155] The average thickness t of the back layer 14 b The average thickness t of the back layer 14 is preferably 0.6 μm or less, more preferably 0.5 μm or less, and even more preferably 0.4 μm or less, 0.3 μm or less, 0.25 μm or less, or 0.2 μm or less. bWhen the average thickness (average total thickness) t of the magnetic recording medium 10 is within the above range, T A T Even when the thickness is set to ≦5.7 μm, the average thickness of the nonmagnetic layer 12 and the base layer 11 can be kept large, thereby maintaining running stability within a recording / reproducing device for the magnetic recording medium 10. Furthermore, the lower limit of the average thickness of the back layer is not particularly limited, but can be, for example, 0.1 μm or more, and preferably 0.15 μm or more.

[0156] (3) Physical properties and structure

[0157] (Thickness of the part of the base layer where the chlorine count is above the threshold)

[0158] The thickness of the portion of the underlayer 12 of the magnetic recording medium 10 where the chlorine count is equal to or greater than the threshold value described below is, for example, 130 nm or less, as described above. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count] The thickness of this portion is the thickness of a region where the chlorine count is equal to or greater than the threshold value, as determined by measuring the chlorine count across the thickness direction of the underlayer using a STEM (scanning transmission electron microscope). The thickness of the portion is measured as follows.

[0159] (Sample preparation method) To prepare a sample, a portion of a tape-shaped magnetic recording medium housed in a magnetic recording cartridge, extending approximately 20 m in the longitudinal direction of the tape from the outermost portion, is used. For example, a magnetic tape T housed in a cartridge such as the cartridge 10A described below is unwound, and a portion approximately 20 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT is used for sample preparation. Of this portion, a portion approximately central in the width direction of the magnetic tape T is cut out to a size appropriate for preparing a sample for STEM observation (e.g., a square of approximately 1 mm × 1 mm). Carbon deposition is applied to the surface of the cut sample, forming a carbon deposition film on the magnetic surface. The processed sample is introduced into a focused-ion beam (FIB) processing device equipped with a scanning electron microscope (SEM). From the processed sample, micro-samples of pieces appropriate for STEM observation (e.g., squares with sides of 10 μm to 50 μm) are obtained by the processing device. The micro-piece is fixed to the sample stage of the processing device and thinned. The thinning is performed so that the thickness of the micro-piece in the direction parallel to the magnetic surface is thick enough to transmit the electron beam used in STEM observation. In this way, a sample for STEM observation is prepared. The device and processing conditions for preparing the sample are as follows: [Device] Processing equipment: FEI Versa3D DualBeam [Processing conditions] Sample pretreatment: carbon deposition Ion species: gallium ions Acceleration voltage (voltage applied during rough drilling): 30 kV Final finishing voltage: 5kV Sample stage material: Mo

[0160] (Sample observation method) The STEM observation sample is observed and analyzed by EDX using the following STEM device under the following observation and analysis conditions, which will be described in detail later. [Device] STEM device: FEI TalosF200X (Schottky-FEG) EDX system: FEI Super-X EDX detector: Bruker windowless SDD detector (30 mm 2 , objective lens built-in type) 4 units [Observation conditions] Accelerating voltage: 200 kV Obtained image: BF STEM image (Bright Field: BF) HAADF STEM image (High Angle Annular Dark Field:HAADF) Camera length: 98mm Device display magnification: 57000x [Analysis conditions (conditions for mapping and line extraction in EDX analysis)] Accelerating voltage: 200 kV Device display magnification: 57000x Area analysis resolution: 800 pixels x 700 pixels (1 pixel corresponds to approximately 2.1 nm.) Moving average filter: 3 pixels Data Type: Net Count Cl Kα line extraction integrated width x thickness length: 700 pixels x 650 pixels Here, the "Cl Kα ray extraction integrated width" is the length of the side of a rectangle that defines the area where Cl Kα ray extraction is performed, and that is approximately parallel to the magnetic surface of the magnetic recording medium. The "length in the thickness direction" is the length of the side of a rectangle that defines the region where Cl Kα rays are extracted, the side being approximately parallel to the thickness direction of the magnetic recording medium. In this analysis, the Cl Kα net count at a certain position in the thickness direction of the magnetic recording medium corresponds to the Cl amount at that position. Therefore, the distribution of chlorine content can be determined based on the Cl Kα net count. Note that the energy of the characteristic Kα ray generated when Cl is irradiated with an electron beam is 2.62 keV.

[0161] Under the above observation conditions, an HAADF STEM image of the STEM observation sample was acquired in a direction parallel to the magnetic surface. An example of the acquired HAADF STEM image is shown in Figure 4A. As shown in the figure, the magnetic layer M and the underlayer U can be confirmed from the image. In this observation, the STEM cross-sectional photograph is checked to confirm that there are no parts in the cross section of the base layer that are clearly different from the normal state of the base layer. Such parts include, for example, coarse inorganic particles, voids, or undispersed binder, and the analysis is performed on a cross section that does not contain such parts.

[0162] By performing EDX analysis under the above analysis conditions, the distribution state of chlorine atoms at each position in the HAADF image can be identified. Specifically, this identification is performed by the following procedure.

[0163] (i) Setting the area for extracting chlorine counts in the acquired HAADF STEM image For example, in the HAADF image shown in FIG. 4A, as shown in FIG. 4B, the Kα ray extraction area A ex As shown in the figure, the Kα ray extraction region is a rectangle, particularly a rectangle. The length of one side of the rectangle in the horizontal direction is 700 pixels, which is the "Cl Kα ray extraction integrated width", that is, the length of the rectangular area where Cl Kα ray extraction is performed in a direction approximately horizontal to the magnetic surface of the magnetic recording medium. For example, in the same figure, the double-headed arrow L a The width indicated by is the Cl Kα ray extraction integrated width. The length of one side in the vertical direction of the rectangle is 650 pixels, which is the "length in the thickness direction" mentioned above. For example, in the same figure, b The length indicated by is the length in the thickness direction. As explained above with reference to Figure 4A, the magnetic layer and underlayer can be identified by visual observation of the HAADF image. The rectangle set as the Cl Kα ray extraction region is set so that the side corresponding to the Cl Kα ray extraction integrated width is approximately parallel to the visually identified magnetic layer surface, and the rectangle covers the carbon deposition film, the magnetic layer, the underlayer, and the base layer. Note that in actual settings, it is not necessary to draw white lines as shown in the figure.

[0164] (ii) Obtaining chlorine distribution data based on the results of the EDX analysis For each pixel position in the thickness direction, Cl Kα rays are counted over the entire Kα ray extraction integration width. For this counting, as shown in FIG. 4D, a line (Line X) approximately parallel to the magnetic surface is assumed for a pixel position X in the thickness direction. Cl Kα rays are counted over this entire line. The total number of counted Cl Kα rays is the net count. The net count number is calculated for all lines of pixel positions in the thickness direction. In this way, the net count number for each line of pixel positions, i.e., the net count number for each position in the thickness direction, is calculated. The calculated net counts are plotted against the pixel positions in the thickness direction to obtain a plot such as that shown in Figure 4C, where the "extraction position" on the horizontal axis corresponds to the pixel positions in the thickness direction.

[0165] (iii) Normalization The net count data obtained in (ii) above is normalized. Specifically, the total of the obtained net counts over the entire length in the thickness direction (i.e., the entire Kα ray extraction region) is normalized to 1. The value obtained by normalizing the net count at each pixel position is then used as the chlorine count.

[0166] (iv) Identification of the magnetic layer surface The fact that the carbon deposition film does not contain chlorine is utilized to identify the surface of the magnetic layer in the chlorine count extraction region. To identify the magnetic layer surface, first, the carbon deposition film portion is identified. The carbon deposition film portion can be roughly identified from the plot. For example, since the peak on the left side of the plot in Figure 4C corresponds to the magnetic layer portion, the portion to the left of the magnetic layer portion with a low net count is the carbon deposition film portion. Then, the average value (simple average value) of the net counts in the first 6 nm portion, where the net count starts from 0, is identified as the background value. Next, the position (pixel position in the thickness direction) in the plot generated in (ii) above where the net count exceeds the background value is recorded is taken as the position of the magnetic layer surface. For example, in Figure 4C, moving to the right from the 0 nm point on the extraction position axis, there is an extraction position data point where the background value is recorded. The extraction position of the data point immediately to the right of the extraction position data point is the position of the magnetic layer surface.

[0167] (v) Calculation of the average chlorine count and standard deviation in the base layer The average value and standard deviation of the chlorine count (value after normalization in (iii) above) in the range of 300 nm to 400 nm in the thickness direction from the surface of the magnetic layer specified in (iv) above are calculated. The average value is a simple average, and the standard deviation is calculated by the n-1 method. This average value is the "average chlorine count in the underlayer" in this specification, and this standard deviation is the "standard deviation obtained when calculating the average chlorine count" in this specification. 4E shows the data in which the chlorine counts after normalization are plotted against the position in the thickness direction. As shown in the figure, the range of 300 nm to 400 nm is used as the data range for calculating the average chlorine counts and standard deviation.

[0168] (vi) Calculation of threshold Using the "average chlorine count in the underlayer" calculated in (v) above and the "standard deviation obtained when calculating the average chlorine count," the threshold value is calculated according to the following formula. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count]

[0169] (vii) Identifying the thickness of the portion of the base layer where the chlorine count is equal to or greater than the threshold value. First, for each pixel position, a moving average value of the chlorine counts for 10 lines is calculated. The 10 lines are the line at the pixel position for which the moving average value is to be calculated, the lines at five pixel positions further toward the back layer than the pixel position, and the lines at four pixel positions further toward the magnetic surface than the pixel position. Moving further toward the base layer from the 300-400 nm range where the average chlorine count was calculated, the first position within the 6 nm where the moving average value is equal to or greater than the threshold is determined as the "starting point on the magnetic surface side of the portion where the chlorine count is equal to or greater than the threshold." An example of this starting point is shown in Figure 4E. Next, the interface between the underlayer and the base layer is identified. Moving further from the starting point toward the base layer, the chlorine count begins to decrease. Moving further toward the base layer, the first position where the chlorine count becomes lower than the "average chlorine count in the underlayer" is designated as the "interface between the underlayer and the base layer." An example of the location of this interface is also shown in Figure 4E. If the base layer is made of a material that does not contain chlorine, the position of the interface may be identified as the first position where the chlorine count becomes lower than the average chlorine count in the underlayer, as described above. On the other hand, it is also possible for the base layer to be made of a material that contains chlorine. In this case, if the chlorine count in the base layer differs from the net chlorine Kα count in the average portion of the underlayer, the position of the interface may be identified based on the difference. The length from the "starting point on the magnetic surface side of the part where the chlorine count is equal to or greater than the threshold" to the "interface between the underlayer and the base layer" determined as above is defined as the "thickness of the part of the underlayer where the chlorine count is equal to or greater than the threshold." An example of this part is also shown in Figure 4E.

[0170] (Other data obtained based on the above plot) Using the "thickness of the portion of the base layer where the chlorine count is equal to or greater than the threshold value" identified as above, the ratio of the thickness of the portion of the base layer where the chlorine count is equal to or greater than the threshold value to the thickness of the base layer can be obtained using the following formula. (Percentage (%) of the thickness of the portion of the base layer where the chlorine count is equal to or greater than the threshold value relative to the thickness of the base layer) = (Thickness of the portion of the base layer where the chlorine count is equal to or greater than the threshold value) / (Thickness of the base layer) × 100

[0171] Furthermore, as shown in Figure 4E, a peak corresponding to the magnetic layer can be seen on the left side of the plot. The maximum value of the chlorine counts in this peak is the "peak chlorine count in the magnetic layer."

[0172] (Average thickness of magnetic recording medium (average total thickness) t T )

[0173] Average thickness (average total thickness) t of the magnetic recording medium 10 T The average thickness t of the magnetic recording medium 10 may be, for example, 5.7 μm or less, preferably 5.6 μm or less, more preferably 5.5 μm or less, 5.4 μm or less, 5.3 μm or less, 5.2 μm or less, 5.1 μm or less, or 5.0 μm or less, and even more preferably 4.6 μm or less or 4.4 μm or less. T When the average thickness t of the magnetic recording medium 10 is 5.5 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to that of a general magnetic tape. T The lower limit is not particularly limited, but is, for example, 3.5 μm or more.

[0174] The average thickness t of the magnetic recording medium 10 (hereinafter also referred to as magnetic tape T)T is obtained as follows. First, the magnetic tape T housed in a cartridge such as the cartridge 10A described below is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT. Next, the thickness of the sample is measured at five positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t T The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape T.

[0175] (Average thickness of underlayer (non-magnetic layer))

[0176] The average thickness of the underlayer 12 is determined as follows. First, the magnetic tape T housed in a cartridge, such as the cartridge 10A described below, is unwound, and three samples of 250 mm are cut from the magnetic tape T at three locations, 10 m, 30 m, and 50 m from the connection 221 between the magnetic tape T and the leader tape LT, to prepare three samples. Next, each sample is thinned using a FIB method or other processing. When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM images described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape T facing the magnetic layer 13 and the surface facing the back layer 14, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 13. The thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.

[0177] The cross section of each of the obtained thinned samples is observed under a transmission electron microscope (TEM) under the following conditions. Apparatus: TEM (Hitachi H9000NAR) Accelerating voltage: 300 kV Magnification: 100,000x Next, using the obtained TEM image, the thickness of the underlayer 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 (nm) of the underlayer 12.

[0178] (average thickness of base layer)

[0179] The average thickness of the base layer 11 is determined as follows. First, the magnetic tape T housed in a cartridge such as the magnetic recording cartridge 10A described below is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT. In this specification, the "longitudinal direction" in the "longitudinal direction from the joint between the magnetic tape T and the leader tape LT" refers to the direction from one end on the leader tape LT side to the other end on the opposite side.

[0180] Next, all layers of the sample other than the base layer 11 (i.e., the non-magnetic layer (underlayer) 12, the magnetic layer 13, and the back layer 14) are removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample (base layer 11) is measured at five positions, and the measured values ​​are simply averaged (arithmetic mean) to calculate the average thickness of the base layer 11. Note that the five measurement positions are selected randomly from the sample so that they are each different from the others in the longitudinal direction of the magnetic tape T.

[0181] (Average thickness of back layer t b )

[0182] The upper limit of the average thickness of the back layer 14 is preferably 0.6 μm or less. If the upper limit of the average thickness of the back layer 14 is 0.6 μm or less, the thickness of the underlayer (non-magnetic layer) 12 and the base layer 11 can be kept thick even when the average thickness of the magnetic tape T is 5.6 μm or less, thereby maintaining running stability of the magnetic tape T within a recording / reproducing device. The lower limit of the average thickness of the back layer 14 is not particularly limited, but is, for example, 0.2 μm or more.

[0183] The average thickness t of the back layer 14 b can be calculated as follows: First, the average thickness (average total thickness) of the magnetic tape T is t T Measure the average thickness t T The method for measuring the average total thickness is as described above. Next, the magnetic tape T housed in the cartridge 10A is unwound, and the magnetic tape T is cut into a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT to prepare a sample. Next, the back layer 14 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five positions using a Mitutoyo laser hologram (LGH-110C), and these measurements are simply averaged (arithmetic average) to obtain the average thickness t B Then, the average thickness t of the back layer 14 is calculated using the following formula: b The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape T. t b [μm]=t T [μm]-t B [μm]

[0184] (the average thickness of the magnetic layer t m )

[0185] The average thickness t of the magnetic layer 13 mis determined as follows. First, the magnetic tape T housed in the cartridge 10A is unwound, and three samples of 250 mm length are cut from the magnetic tape T at three positions, 10 m, 30 m, and 50 m from the joint 221 between the magnetic tape T and the leader tape LT, in the longitudinal direction. Each sample is then thinned using a FIB method or the like. When the FIB method is used, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape T facing the magnetic layer 13 and the surface facing the back layer 14, and the tungsten layer is further formed by vapor deposition or sputtering on the surface facing the magnetic layer 13. The thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning results in a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.

[0186] The cross section of each obtained sliced ​​sample is observed under a transmission electron microscope (TEM) under the following conditions to obtain a TEM image of each sliced ​​sample. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Apparatus: TEM (Hitachi H9000NAR) Accelerating voltage: 300 kV Magnification: 100,000x

[0187] 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].

[0188] (Squareness ratio in the vertical direction Rs2)

[0189] The squareness ratio Rs2 in the perpendicular direction (thickness direction) of the magnetic recording medium of the present technology can be preferably 65% ​​or more, more preferably 67% or more, and even more preferably 70% or more. When the squareness ratio Rs2 is 65% or more, the perpendicular orientation of the magnetic powder is sufficiently high, resulting in a superior SNR. Therefore, superior electromagnetic conversion characteristics can be obtained. Furthermore, the servo signal shape is improved, making it easier to control on the drive side. In this specification, a magnetic recording medium being perpendicularly oriented may mean that the squareness ratio Rs2 of the magnetic recording medium is within the above numerical range (for example, 65% or more).

[0190] The squareness ratio Rs2 in the vertical direction is determined as follows. First, the magnetic tape T housed in the magnetic recording 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. The sample is punched out to 6.25 mm x 64 mm and then folded in thirds to prepare a 6.25 mm x 8 mm measurement sample. Then, the MH hysteresis loop of the measurement sample (the entire magnetic tape T) corresponding to the vertical direction (thickness direction) of the magnetic tape T is measured using a VSM. Next, the coating films (the underlayer 12, the magnetic layer 13, the back layer 14, etc.) are wiped off using acetone or ethanol, leaving only the base layer 11. The obtained base layer 11 is then punched out to 6.25 mm x 64 mm and then folded in thirds to prepare a 6.25 mm x 8 mm sample for background correction (hereinafter simply referred to as the "correction sample"). Thereafter, the MH hysteresis loop of the correction sample (base layer 11) corresponding to the perpendicular direction of the base layer 11 (the perpendicular direction of the magnetic recording medium 10) is measured using the VSM.

[0191] The MH hysteresis loop of the measurement sample (the entire magnetic tape T) and the MH hysteresis loop of the correction sample (base layer 11) are measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Industry Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20. After obtaining the MH hysteresis loop of the measurement sample (the entire magnetic tape T) and the MH hysteresis loop of the correction sample (base layer 11), background correction is performed by subtracting the MH hysteresis loop of the correction sample (base layer 11) from the MH hysteresis loop of the measurement sample (the entire magnetic tape T), and the MH hysteresis loop after background correction is obtained. This background correction calculation is performed using the measurement and analysis program included with the "VSM-P7-15 model."

[0192] The saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the MH hysteresis loop after background correction are substituted into the following equation to calculate the squareness ratio Rs2 (%). Note that all of the above MH hysteresis loop measurements are performed at 25°C. Furthermore, no "demagnetizing field correction" is performed when measuring the MH hysteresis loop in the perpendicular direction to the magnetic tape T. Note that this calculation uses the measurement and analysis program included with the "VSM-P7-15 model." Squareness ratio Rs2(%)=(Mr / Ms)×100

[0193] (4) Manufacturing method of magnetic recording medium

[0194] Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming the underlayer (non-magnetic layer) is prepared by kneading and / or dispersing non-magnetic powder, a binder, etc. in a solvent. Next, a paint for forming the magnetic layer is prepared by kneading and / or dispersing magnetic powder, non-magnetic 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 underlayer (non-magnetic layer).

[0195] Examples of the solvents used in preparing the above-mentioned paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as methanol, ethanol, and propanol; and methyl acetate, acetic acid, and the like. Examples of suitable solvents include ester solvents such as ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. One of these may be used, or a mixture of two or more thereof may be used.

[0196] Examples of kneading devices that can be used in preparing the above-mentioned coating materials include, but are not limited to, continuous twin-screw kneaders, continuous twin-screw kneaders capable of multi-stage dilution, kneaders, pressure kneaders, and roll kneaders. Examples of dispersing devices that can be used in preparing the above-mentioned coating materials include, but are not limited to, bead mills, roll mills, ball mills, horizontal sand mills, vertical sand mills, spike mills, pin mills, tower mills, pearl mills (such as the "DCP Mill" manufactured by Eirich), homogenizers, and ultrasonic dispersers.

[0197] Next, a paint for forming an underlayer is applied to one main surface of the base layer 11 and dried to form the underlayer 12. Subsequently, a paint for forming a magnetic layer is applied to this underlayer 12 and dried to form the magnetic layer 13 on the non-magnetic layer 12.

[0198] The thickness and / or position of the portion where the chlorine count is above the threshold value below can be adjusted by adjusting the method for forming the magnetic layer and / or the base layer and / or the composition of the paint for forming the magnetic layer and / or the paint for forming the base layer. For example, the thickness and / or location of the portion where the chlorine count is equal to or greater than the threshold value can be adjusted by, for example, adjusting the drying temperature of the magnetic layer-forming paint and / or the undercoat layer-forming paint. For example, lowering the drying temperature will make the thickness wider, and conversely, increasing the drying temperature will make the thickness narrower and located closer to the base layer. Furthermore, the thickness and / or position of the above-mentioned portion can be adjusted by modifying the non-magnetic powder contained in the base layer coating material with a surface modifier. For example, the amount of binder adsorbed to the non-magnetic powder can be adjusted by modifying the surface with a surface modifier. Examples of such modifiers include polycarboxylic acids. Increasing the amount of adsorption can further narrow the above-mentioned thickness. Furthermore, the thickness and / or position of the portion can be adjusted by adjusting the time from when the base layer coating material dries to when the magnetic layer coating material is applied. For example, if this time is increased, the binder becomes less likely to move within the base layer when the magnetic layer coating material is applied, and the thickness becomes wider. Conversely, if this time is decreased, the binder becomes more likely to move within the base layer when the magnetic layer coating material is applied, and the thickness can be located closer to the base layer and narrower. The thickness of the portion can also be adjusted by the solids concentration of the magnetic layer-forming paint and / or the base layer-forming paint. For example, if the solids concentration of the magnetic layer-forming paint is high, the amount of solvent that penetrates into the base layer when the magnetic layer-forming paint is applied is reduced, resulting in a thicker portion. Conversely, if the solids concentration is low, the thickness of the portion is reduced. The thickness of the portion can also be adjusted by changing the ratio of non-magnetic powder to binder in the base layer coating material. For example, by increasing the amount of binder, the amount of binder that does not adhere to the non-magnetic powder increases, making the portion thicker. Conversely, by decreasing the amount of binder, the thickness of the portion can be made thinner.

[0199] During drying, the magnetic powder is magnetically oriented in the thickness direction of the base layer 11, for example, by a solenoid coil. Alternatively, during drying, the magnetic powder may be magnetically oriented in the longitudinal direction (running direction) of the base layer 11 by a solenoid coil, and then magnetically oriented in the thickness direction of the base layer 11. By performing such a magnetic field orientation process, the ratio Hc2 / Hc1 of the coercive force in the perpendicular direction "Hc1" to the coercive force in the longitudinal direction "Hc2" can be reduced, thereby improving the degree of perpendicular orientation of the magnetic powder. After forming the magnetic layer 13, a back layer 14 is formed on the other main surface of the base layer 11. This completes the magnetic recording medium 10.

[0200] The ratio Hc2 / Hc1 can be set to a desired value by, for example, adjusting the strength of the magnetic field applied to the coating film of the magnetic layer-forming paint, the concentration of solids in the magnetic layer-forming paint, and the drying conditions (drying temperature and drying time) for the coating film of the magnetic layer-forming paint. The strength of the magnetic field applied to the coating film is preferably between two and three times the cohesive strength of the magnetic powder. To further increase the ratio Hc2 / Hc1, it is also preferable to magnetize the magnetic powder before the magnetic layer-forming paint enters an orientation device that magnetically orients the magnetic powder. Note that the methods for adjusting the ratio Hc2 / Hc1 may be used alone or in combination of two or more.

[0201] The resulting magnetic recording medium 10 is then rewound around a large diameter core and hardened. Finally, the magnetic recording medium 10 is calendered and then cut to a predetermined width (e.g., 1 / 2 inch width). This completes the desired long, thin magnetic recording medium 10.

[0202] (5) Recording and playback device

[0203] [Configuration of recording / playback device]

[0204] Next, with reference to FIG. 5, 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.

[0205] The recording / reproducing device 30 may be configured to be able to adjust the tension applied to the magnetic recording medium 10 in the longitudinal direction. The recording / reproducing device 30 is also configured to be able to load a magnetic recording cartridge 10A. Here, for ease of explanation, a case will be described in which the recording / reproducing device 30 is configured to be able to load one magnetic recording cartridge 10A, but the recording / reproducing device 30 may also be configured to be able to load multiple magnetic recording cartridges 10A. The recording and reproducing device 30 is preferably a timing servo type magnetic recording and reproducing device, and the magnetic recording medium of the present technology is suitable for use in a timing servo type magnetic recording and reproducing device.

[0206] 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.

[0207] As shown in Figure 5, the recording and playback device includes a spindle 31, a reel 32 on the recording and playback device side, a spindle drive device 33, a reel drive device 34, multiple guide rollers 35, a head unit 36, a communication interface (hereinafter referred to as I / F) 37, and a control device 38.

[0208] The spindle 31 is configured so that a magnetic recording cartridge 10A can be attached thereto. The magnetic recording cartridge 10A conforms to the LTO (Linear Tape Open) standard, and rotatably accommodates a single reel 10C around which a magnetic recording medium 10 is wound in a cartridge case 10B. A V-shaped servo pattern is pre-recorded as a servo signal on the magnetic recording medium 10. The reel 32 is configured so that the leading end of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 10A can be fixed. The present technology also provides a magnetic recording cartridge including a magnetic recording medium according to the present technology. In the magnetic recording cartridge, the magnetic recording medium may be wound on a reel, for example, and may be housed in a case while wound on the reel.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] The control device 38 controls the entire recording / reproducing device 30. For example, in response to a request from the information processing device, such as the server 41 or the PC 42, the control device 38 records a data signal supplied from the information processing device onto the magnetic recording medium 10 using the head unit 36. In addition, in response to a request from the information processing device, such as the server 41 or the PC 42, the control device 38 reproduces the data signal recorded on the magnetic recording medium 10 using the head unit 36, and supplies the reproduced data signal to the information processing device.

[0213] The control device 38 also detects changes in the width of the magnetic recording medium 10 based on the servo signals supplied from the head unit 36. Specifically, multiple V-shaped servo patterns are recorded as servo signals on the magnetic recording medium 10, and the head unit 36 ​​simultaneously reproduces two different servo patterns using two servo heads on the head unit 36, thereby obtaining respective servo signals. Using relative position information between the servo patterns and the head unit obtained from these servo signals, the position of the head unit 36 ​​is controlled to track the servo patterns. At the same time, distance information between the servo patterns can be obtained by comparing the two servo signal waveforms. By comparing the distance information between the servo patterns obtained during each measurement, the change in the distance between the servo patterns at each measurement can be obtained. By adding the distance information between the servo patterns obtained during servo pattern recording to this, the change in the width of the magnetic recording medium 10 can also be calculated. Based on the change in the distance between the servo patterns obtained as described above or the calculated change in the width of the magnetic recording medium 10, the control device 38 controls the rotational drive of the spindle drive device 33 and the reel drive device 34, and adjusts the tension in the longitudinal direction of the magnetic recording medium 10 so that the width of the magnetic recording medium 10 becomes a specified width or approximately a specified width. This makes it possible to suppress changes in the width of the magnetic recording medium 10.

[0214] [Recording / playback device operation]

[0215] Next, the operation of the recording / reproducing device 30 having the above configuration will be described.

[0216] 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.

[0217] 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.

[0218] When rewinding the magnetic recording medium 10 onto the reel 10C, the spindle 31 and the reel 32 are rotated in the opposite direction to the above, causing the magnetic recording medium 10 to run from the reel 32 to the reel 10C. During this rewinding, the head unit 36 ​​also records information onto the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.

[0219] (6) Variations

[0220] [Variation 1]

[0221] As shown in FIG. 6, the magnetic recording medium 10 may further include a barrier layer 15 disposed on at least one surface of the base layer 11. The barrier layer 15 is a layer for suppressing dimensional deformation of the base layer 11 due to environmental factors. For example, one cause of dimensional deformation is the hygroscopicity of the base layer 11, and the barrier layer 15 can reduce the rate at which moisture penetrates the base layer 11. The barrier layer 15 includes a metal or a metal oxide. Examples of metals that can be used include at least one of Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba, Pt, Au, and Ta. Examples of metal oxides that can be used include at least one of Al2O3, CuO, CoO, SiO2, Cr2O3, TiO2, Ta2O5, and ZrO2, as well as oxides of any of the above metals. Diamond-like carbon (DLC) or diamond can also be used.

[0222] 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.

[0223] [Variation 2]

[0224] 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.

[0225] [Variation 3]

[0226] 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.

[0227] 3. Second embodiment (1) One embodiment of a magnetic recording cartridge

[0228] [Cartridge configuration]

[0229] The present technology also provides a magnetic recording cartridge (also called a tape cartridge) including a magnetic recording medium according to the present technology. In the magnetic recording cartridge, the magnetic recording medium may be wound around a reel, for example. The magnetic recording cartridge may include, for example, a communication unit that communicates with a recording / reproducing device, a storage unit, and a control unit that stores information received from the recording / reproducing device via the communication unit in the storage unit, and reads information from the storage unit and transmits it to the recording / reproducing device via the communication unit in response to a request from the recording / reproducing device. The information may include adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction.

[0230] An example of the configuration of a magnetic recording cartridge 10A equipped with a magnetic recording medium T having the above-described configuration will be described with reference to FIG.

[0231] 16 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge 10A. The magnetic recording cartridge 10A is a magnetic recording cartridge that complies with the LTO (Linear Tape-Open) standard, and includes a cartridge case 10B made up of a lower shell 212A and an upper shell 212B, a reel 10C around which a magnetic tape (a tape-like magnetic recording medium) T is wound, a reel lock 214 and a reel spring 215 for locking the rotation of the reel 10C, a spider 216 for unlocking the locked state of the reel 10C, a slide door 217 that straddles the lower shell 212A and the upper shell 212B and opens and closes a tape pull-out opening 212C provided in the cartridge case 10B, a door spring 218 that biases the slide door 217 to a closed position of the tape pull-out opening 212C, a write protect 219 for preventing accidental erasure, and a cartridge memory 211. The reel 10C is generally disk-shaped with an opening in the center, and is composed of a reel hub 213A made of a hard material such as plastic and a flange 213B. A leader tape LT is connected to one end of the magnetic tape T. A leader pin 220 is provided at the tip of the leader tape LT.

[0232] 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.

[0233] [Cartridge memory configuration]

[0234] An example of the configuration of the cartridge memory 211 will be described with reference to FIG.

[0235] 8 is a block diagram showing an example of the configuration of the cartridge memory 211. The cartridge memory 211 includes an antenna coil (communication unit) 331 that communicates with a reader / writer (not shown) using a specified communication standard, a rectification / power circuit 332 that generates power by using induced electromotive force from radio waves received by the antenna coil 331 and rectifying it, a clock circuit 333 that generates a clock from the radio waves received by the antenna coil 331 using induced electromotive force, a detection / modulation circuit 334 that detects the radio waves received by the antenna coil 331 and modulates the signal to be transmitted by the antenna coil 331, a controller (control unit) 335 that is composed of logic circuits and the like for identifying and processing commands and data from the digital signal extracted from the detection / modulation circuit 334, and a memory (storage unit) 336 that stores information. The cartridge memory 211 also includes a capacitor 337 connected in parallel to the antenna coil 331, and the antenna coil 331 and capacitor 337 form a resonant circuit.

[0236] The memory 336 stores information related to the magnetic recording cartridge 10A. The memory 336 is a nonvolatile memory (NVM). The memory 336 preferably has a storage capacity of approximately 32 KB or more. For example, if the magnetic recording cartridge 10A conforms to the next-generation LTO format standard or later, the memory 336 has a storage capacity of approximately 32 KB.

[0237] The memory 336 has a first memory area 336A and a second memory area 336B. The first memory area 336A corresponds to the memory area of ​​a cartridge memory (hereinafter referred to as a "conventional cartridge memory") that conforms to the LTO standard prior to LTO8, and is an area for storing information that conforms to the LTO standard prior to LTO8. Information that conforms to the LTO standard prior to LTO8 includes, for example, manufacturing information (such as a unique number for the magnetic recording cartridge 10A), usage history (such as the number of times the tape has been pulled out (Thread Count)), etc.

[0238] The second memory area 336B corresponds to an extended memory area for the memory area of ​​a conventional cartridge memory. The second memory area 336B is an area for storing additional information. Here, additional information refers to information related to the magnetic recording cartridge 10A that is not specified in the LTO standard prior to LTO8. Examples of additional information include, but are not limited to, tension adjustment information, management ledger data, index information, and thumbnail information of videos stored on the magnetic tape T. The tension adjustment information includes the distance between adjacent servo bands (the distance between servo patterns recorded on adjacent servo bands) when data is recorded on the magnetic tape T. The distance between adjacent servo bands is an example of width-related information related to the width of the magnetic tape T. The distance between servo bands will be described in detail later. In the following description, the information stored in the first memory area 336A may be referred to as "first information," and the information stored in the second memory area 336B may be referred to as "second information."

[0239] The memory 336 may have multiple banks. In this case, some of the multiple banks may constitute the first storage area 336A, and the remaining banks may constitute the second storage area 336B. Specifically, for example, if the magnetic recording cartridge 10A conforms to the next-generation or later LTO format standard, the memory 336 may have two banks with a storage capacity of approximately 16 KB, and one of the two banks may constitute the first storage area 336A, and the other bank may constitute the second storage area 336B.

[0240] 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.

[0241] 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.

[0242] (2) Modified magnetic recording cartridge

[0243] [Cartridge configuration]

[0244] 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. 9.

[0245] 9 is an exploded perspective view showing an example of the configuration of a two-reel type cartridge 421. Cartridge 421 includes an upper half 402 made of synthetic resin, a transparent window member 423 that fits into and is fixed to a window 402a opened in the top surface of upper half 402, a reel holder 422 that is fixed to the inside of upper half 402 and prevents reels 406 and 407 from floating up, a lower half 405 that corresponds to upper half 402, reels 406 and 407 that are stored in a space formed when upper half 402 and lower half 405 are combined, magnetic tape MT1 wound around reels 406 and 407, a front lid 409 that closes a front opening formed when upper half 402 and lower half 405 are combined, and a back lid 409A that protects magnetic tape MT1 exposed in this front opening.

[0246] The reel 406 includes a lower flange 406b having a cylindrical hub portion 406a in the center around which the magnetic tape MT1 is wound, an upper flange 406c having approximately the same size as the lower flange 406b, and a reel plate 411 sandwiched between the hub portion 406a and the upper flange 406c. The reel 407 has the same configuration as the reel 406.

[0247] The window member 423 is provided with mounting holes 423a at positions corresponding to the reels 406 and 407, respectively, for assembling reel holders 422, which are reel holding means for preventing these reels from floating up. The magnetic tape MT1 is the same as the magnetic tape T in the first embodiment.

[0248] The present technology can also employ the following configuration. [1] a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; The thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 130 nm or less. Magnetic recording media. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count] [2] The magnetic recording medium according to [1], wherein the portion having a value equal to or greater than the threshold value is present on the base layer side of the underlayer. [3] The magnetic recording medium according to [1] or [2], wherein the portion of the underlayer where the density is equal to or greater than the threshold value is within 200 nm of the interface between the underlayer and the base layer. [4] The magnetic recording medium according to any one of [1] to [3], wherein the portion of the underlayer that is equal to or greater than the threshold value is present within 130 nm from the interface between the underlayer and the base layer. [5] The magnetic recording medium according to any one of [1] to [4], wherein the total thickness of the magnetic layer and the underlayer is 1200 nm or less. [6] The magnetic recording medium according to any one of [1] to [5], wherein the total thickness of the magnetic layer and the underlayer is 1000 nm or less. [7] The magnetic recording medium according to any one of [1] to [6], wherein the thickness of the magnetic layer is 80 nm or less. [8] The magnetic recording medium according to any one of [1] to [5] and [7], wherein the underlayer has a thickness of 1120 nm or less. [9] The magnetic recording medium according to any one of [1] to [8], wherein the underlayer contains non-magnetic powder.

[10] The magnetic recording medium according to any one of [1] to [9], wherein the underlayer contains a lubricant.

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

[10] , wherein the thickness is 5.5 μm or less.

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

[11] , wherein the magnetic layer contains magnetic powder.

[13] The magnetic recording medium according to

[12] , wherein the magnetic powder contains hexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite.

[14] a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 12% or less of the thickness of the underlayer; Magnetic recording media. [Threshold value] = [average chlorine count in the base layer] + 6 × [standard deviation obtained when calculating the average chlorine count]

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

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

[0249] 4. Working Example

[0250] 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.

[0251] Magnetic tapes were obtained as described in the following Comparative Examples 1 to 3 and Examples 1 to 3.

[0252] [Comparative Example 1]

[0253] (Preparation process of paint for forming magnetic layer) The magnetic layer-forming paint was prepared as follows. First, a first composition having the following formulation was kneaded using an extruder. Next, the kneaded first composition and a second composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Next, further mixing was performed using a Dynomill and filtering was performed to prepare the magnetic layer-forming paint.

[0254] (First composition) Barium ferrite (BaFe 12 O 19 ) Magnetic powder (hexagonal plate shape, average aspect ratio 3.0, average particle volume 1600nm 3 ):100 parts by mass Vinyl chloride resin (cyclohexanone solution 30% by mass): 50 parts by mass (Degree of polymerization: 300, Mn=10,000, contains polar groups OSO3K=0.07 mmol / g and secondary OH=0.3 mmol / g.) Aluminum oxide powder: 5 parts by mass (α-Al2O3, average particle size 0.1 μm)

[0255] (Second composition) Carbon black: 2 parts by mass (manufactured by Tokai Carbon Co., Ltd., product name: Seest TA) Polyurethane resin (resin solution: polyurethane resin content 30% by mass, cyclohexanone content 70% by mass): 5.56 parts by mass (Polyurethane resin: number average molecular weight Mn = 25,000, Tg 110°C) n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 121.3 parts by mass Toluene: 121.3 parts by mass Cyclohexanone: 60.7 parts by mass

[0256] Finally, 3.3 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) and 2 parts by mass of stearic acid were added as a curing agent to the magnetic layer-forming coating material prepared as described above.

[0257] (Preparation process of paint for forming base layer) A third composition having the following formulation was kneaded using an extruder. Next, the kneaded third composition and a fourth composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Next, using a bead mill ECM-PRO (Shinmaru Enterprises Co., Ltd.), mixing was carried out at a circulation flow rate of 1000 L / h for 100 minutes, followed by filtering to prepare a coating material for forming a primer layer.

[0258] (Third composition) Acicular iron oxide powder: 100 parts by mass (α-Fe2O3, average major axis length 0.15μm) Aluminum oxide powder: 5 parts by mass (α-Al2O3, average particle size 80 nm, manufactured by Sumitomo Chemical Co., Ltd., product name: HIT82, Mohs hardness: 9) Vinyl chloride resin: 55.6 parts by mass (Resin solution: 30% resin by mass, 70% cyclohexanone by mass)

[0259] (4th composition) Carbon black: 30 parts by mass (Average particle size 20nm) Polyurethane resin UR8200 (manufactured by Toyobo): 18.5 parts by weight n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 223.0 parts by mass Toluene: 223.0 parts by mass Cyclohexanone: 49.6 parts by mass

[0260] Finally, 2 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation) and 2 parts by mass of myristic acid were added as a curing agent to the coating material for forming an undercoat layer prepared as described above.

[0261] (Preparation process of paint for forming back layer) The paint for forming the back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the paint for forming the back layer: Carbon black (manufactured by Asahi Corporation, product name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (Nippon Polyurethane Co., Ltd., product name: N-2304) Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass Polyisocyanate (product name: Coronate L, manufactured by Tosoh Corporation): 10 parts by mass

[0262] (Film forming process) Using the coating material prepared as described above, a magnetic tape was prepared as follows.

[0263] First, a long PEN film (base film) with an average thickness of 4.00 μm was prepared as a support for the base layer of the magnetic tape. Next, a primer layer-forming paint was applied to one main surface of the PEN film and dried to form a primer layer on one main surface of the PEN film so that the average thickness of the final product would be 1120 nm. Next, a magnetic layer-forming paint was applied to the primer layer and dried to form a magnetic layer on the primer layer so that the average thickness of the final product would be 80 nm. Furthermore, the magnetic layer was subjected to a vertical orientation treatment using a solenoid coil.

[0264] 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 0.30 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.Then, a calendering treatment was performed to smooth the surface of the magnetic layer.

[0265] (Cutting process) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm), thereby obtaining a long magnetic tape.

[0266] The 1 / 2 inch wide magnetic tape was wound around a reel provided in a cartridge case to obtain a multi-wrap 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 the pre-recorded magnetic pattern rows").

[0267] As explained in "(3) Physical Properties and Structure" in Section 2 above, various values ​​relating to chlorine distribution, such as the chlorine count in the underlayer and the thickness of the portion where the chlorine count is above the threshold, were measured for the magnetic recording cartridge. The results of these measurements are shown in Table 1 below and Figure 10. As shown in the table, the average chlorine count C in the underlayer was ave The standard deviation σ was 0.063. Therefore, the threshold (C ave 10, the plot indicated by the square markers is the measurement result of the chlorine count number in Comparative Example 1. The thickness of the part of the underlayer that was equal to or greater than the threshold was 143 nm. The part that was equal to or greater than the threshold was in contact with the interface between the underlayer and the base layer, i.e., it was within 200 nm of the interface. Furthermore, the ratio of the "thickness of the portion equal to or greater than the threshold value" to the "thickness of the underlayer" was 12.8%. In addition, the peak chlorine count in the magnetic layer (maximum chlorine count in the magnetic layer) C mp is 5.393, and the peak chlorine count C in the magnetic layer mp " / "Average chlorine count in the base layer C ave " was 4.64.

[0268] Comparative Example 2 A magnetic tape was obtained in the same manner as in Comparative Example 1, except that the thicknesses of the magnetic layer and underlayer were changed to 60 nm and 640 nm, respectively. Also, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1. For this magnetic recording cartridge, various values ​​related to chlorine distribution were measured in the same way as in Comparative Example 1. The measurement results are shown in Table 1 and FIG. 10, as in Comparative Example 1. In FIG. 10, the plot indicated by the triangular markers is the measurement result of the chlorine count number in Comparative Example 2.

[0269] Comparative Example 3 A magnetic tape was obtained in the same manner as in Comparative Example 1, except that the drying temperature applied when drying the primer layer-forming paint applied to one main surface of the PEN film was lower than that in Comparative Example 1. Also, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1. The magnetic recording cartridge was measured for various values ​​relating to chlorine distribution in the same manner as in Comparative Example 1. The measurement results are shown in Table 1, as in Comparative Example 1. Furthermore, in comparison with Comparative Example 1, the thickness of the portion above the threshold value increases by lowering the drying temperature, which shows that the thickness can be adjusted by adjusting the drying temperature.

[0270] [Example 1] A magnetic tape was obtained in the same manner as in Comparative Example 1, except that the treatment time in the bead mill in the step of preparing the base layer-forming paint was extended by 1.2 times compared to Comparative Example 1. Also, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1. For this magnetic recording cartridge, various values ​​related to chlorine distribution were measured in the same manner as in Comparative Example 1. The measurement results are shown in Table 1 and FIG. 10, as in Comparative Example 1. In FIG. 10, the plot indicated by the dark gray circular markers is the measurement result of the chlorine count number in Example 1.

[0271] Average chlorine count in the base layer C ave is 1.100 and the standard deviation σ is 0.040, so the threshold (C ave +6σ) was 1.340. The thickness of the part of the underlayer that was equal to or greater than the threshold was 85 nm. The part that was equal to or greater than the threshold was in contact with the interface between the underlayer and the base layer, that is, it was within 150 nm, particularly 100 nm, from the interface. Furthermore, the ratio of the "thickness of the portion equal to or greater than the threshold value" to the "thickness of the underlayer" was 7.6%. In addition, the peak chlorine count in the magnetic layer (maximum chlorine count in the magnetic layer) C mp is 6.506, and the peak chlorine count C in the magnetic layer mp " / "Average chlorine count in the base layer C ave " was 5.91.

[0272] As described above, extending the processing time in the bead mill improves the dispersion of the components in the coating material, allowing more chlorine-containing binder to bond to the inorganic material. Furthermore, when the magnetic layer-forming coating material is applied, the solvent contained in the magnetic layer-forming coating material penetrates into the base layer, causing the chlorine-containing binder that is not bonded to the inorganic material in the base layer to migrate toward the base layer. As described above, since more chlorine-containing binder is bonded to the inorganic material, the amount of migrated chlorine-containing binder is reduced. Therefore, it is believed that the thickness (and its proportion) of the portion above the threshold in Example 1 is smaller than the thickness (and its proportion) of the portion above the threshold in Comparative Example 1.

[0273] [Example 2] A magnetic tape was obtained in the same manner as in Example 1, except that the thicknesses of the magnetic layer and underlayer to be formed were changed to 70 nm and 880 nm, respectively, and the drying temperature after application of the magnetic layer-forming paint was made higher than in Example 1. Furthermore, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Example 1. For this magnetic recording cartridge, various values ​​related to chlorine distribution were measured in the same manner as in Comparative Example 1. The measurement results are shown in Table 1 and FIG. 10, as in Comparative Example 1. In FIG. 10, the plot indicated by the light gray circular markers is the measurement result of the chlorine count number in Example 2.

[0274] Average chlorine count in the base layer C ave is 1.071 and the standard deviation σ is 0.039, so the threshold (C ave +6σ) was 1.305. The thickness of the part of the underlayer that was equal to or greater than the threshold was 77 nm. The part that was equal to or greater than the threshold was in contact with the interface between the underlayer and the base layer, i.e., it was within 150 nm, particularly 100 nm, from the interface. Furthermore, the ratio of the "thickness of the portion equal to or greater than the threshold value" to the "thickness of the underlayer" was 8.8%. In addition, the peak chlorine count in the magnetic layer (maximum chlorine count in the magnetic layer) C mp is 7.956, and the peak chlorine count C in the magnetic layer mp " / "Average chlorine count in the base layer C ave " was 7.43.

[0275] When the magnetic layer-forming paint is applied to the base layer, the solvent in the magnetic layer-forming paint penetrates into the base layer, and the soaked solvent also moves toward the base layer. As described above, by making the base layer thinner and increasing the drying temperature, the evaporation rate of the solvent in the magnetic layer-forming paint increases. Increasing the evaporation rate causes the soaked solvent to move toward the magnetic surface, thereby reducing the amount of chlorine-containing binder remaining on the base layer side. Therefore, it is believed that the thickness (and its proportion) of the portion above the threshold in Example 2 is even smaller than the thickness (and its proportion) of the portion above the threshold in Example 1.

[0276] [Example 3] A magnetic tape was obtained in the same manner as in Comparative Example 1, except that the treatment time in the bead mill in the step of preparing the base layer-forming paint was extended by 1.1 times compared to Comparative Example 1. Also, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1.

[0277] Average chlorine count in the base layer C ave is 1.110 and the standard deviation σ is 0.052, so the threshold (C ave +6σ) was 1.422. The thickness of the part of the underlayer that was equal to or greater than the threshold was 121 nm. The part that was equal to or greater than the threshold was in contact with the interface between the underlayer and the base layer, that is, it was within 150 nm, particularly 130 nm, from the interface. Furthermore, the ratio of the "thickness of the portion equal to or greater than the threshold value" to the "thickness of the underlayer" was 10.8%. In addition, the peak chlorine count in the magnetic layer (maximum chlorine count in the magnetic layer) C mpis 6.675, and the peak chlorine count C in the magnetic layer mp " / "Average chlorine count in the base layer C ave " was 6.01.

[0278] As in Comparative Example 1, various values ​​relating to the chlorine distribution were measured for this magnetic recording cartridge. As described in Example 1, extending the treatment time in the bead mill improves the dispersion of the components in the coating material, resulting in more chlorine-containing binder bonding to the inorganic material. Because more chlorine-containing binder is bonded to the inorganic material, as described above, the amount of chlorine-containing binder that migrates to the base layer during application of the magnetic layer-forming coating material is reduced. Therefore, the thickness (and its proportion) of the portion above the threshold in Example 1 is thought to be smaller than the thickness (and its proportion) of the portion above the threshold in Comparative Example 1. Furthermore, a comparison with Example 1 reveals that the thickness of the portion above the threshold is reduced by further improving the dispersion. Therefore, it can be seen that the thickness can be adjusted by adjusting the dispersion.

[0279] [Reliability assessment] The reliability of the magnetic tape housed in each cartridge was evaluated using the magnetic recording cartridges manufactured in Comparative Examples 1 to 3 and Examples 1 to 3. The evaluation was carried out as follows.

[0280] The magnetic recording cartridge of Comparative Example 1 was inserted into the LTO8 drive immediately after the cleaning tape had been run, and one round trip of recording processing was performed after the insertion. This operation was performed on multiple magnetic recording cartridges of Comparative Example 1. The above-mentioned recording process was carried out sequentially on 25 magnetic recording cartridges, and if the recording process on any of the cartridges ran without any problems, the reliability was judged to be "good." If rewrites occurred twice at any point before the recording process for 25 volumes was completed, the reliability was determined to be "poor." The number of volumes in which rewrites occurred twice was also recorded. The evaluation results for each magnetic tape are shown in Table 1 below.

[0281] [Table 1]

[0282] As shown in Table 1, for the magnetic tapes of Examples 1 to 3, when one round trip was performed on a 25-volume magnetic recording cartridge, no second rewrite occurred for any of the magnetic recording cartridges. On the other hand, for the magnetic tapes of Comparative Examples 1 to 3, a second rewrite occurred on the 17th, 10th, and 13th volumes of the magnetic recording cartridge, respectively. These results demonstrate that the magnetic recording medium according to the present technology and the magnetic recording cartridge in which the magnetic recording medium is housed have improved reliability during running.

[0283] The results shown in Table 1 indicate that reliability during running is improved by reducing the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the threshold. The results shown in the same table indicate that reliability during running of the magnetic tape is improved by making the thickness of the portion where the chlorine count is equal to or greater than the threshold, for example, 130 nm or less, 125 nm or less, or 123 nm or less, more preferably 120 nm or less, 110 nm or less, 100 nm or less, or 90 nm or less.

[0284] The results shown in Table 1 also show that reliability during running is improved by reducing the proportion of the thickness of the underlayer where the chlorine count is equal to or greater than the threshold. The results shown in the same table suggest that reliability during running of the magnetic tape can be improved by, for example, setting the proportion of the thickness of the portion where the chlorine count is equal to or greater than the threshold to 12% or less, 11.5% or less, or 11% or less, more preferably 10% or less, 9.5% or less, or 9% or less.

[0285] 10, the portion of the underlayer that is equal to or greater than the threshold is located on the base layer side, for example, within 400 nm, 300 nm, 200 nm, or 150 nm of the interface between the underlayer and the base layer. Comparison between the examples and the comparative examples reveals that the portion is preferably located within 130 nm or 125 nm of the interface between the underlayer and the base layer, more preferably within 120 nm, 110 nm, 100 nm, or 90 nm. The presence of the portion in such an area of ​​the underlayer is also believed to contribute to improving the reliability of the magnetic tape during running.

[0286] Furthermore, from the results shown in Table 1, it is preferable that the peak chlorine count C mp is, for example, 6.4 or more, or 6.5 or more. Also, preferably, the "peak chlorine count number C in the magnetic layer" is mp " / "Average chlorine count in the base layer C ave " is, for example, 5.5 or greater, or 5.7 or greater.

[0287] 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.

[0288] 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.

[0289] 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.

[0290] Furthermore, in this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more types. [Explanation of symbols]

[0291] 10 Magnetic recording media 11 Base Layer 12 Base layer 13 Magnetic layer 14 Back layer

Claims

1. a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; The thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 130 nm or less. Magnetic recording media. [Threshold value] = [average chlorine count in the underlayer] + 6 × [standard deviation obtained when calculating the average chlorine count]

2. 2. The magnetic recording medium according to claim 1, wherein the portion having a value equal to or greater than the threshold value is present on the base layer side of the underlayer.

3. 2. The magnetic recording medium according to claim 1, wherein the portion of the underlayer that is equal to or greater than the threshold value is present within 200 nm of the interface between the underlayer and the base layer.

4. 2. The magnetic recording medium according to claim 1, wherein the portion of the underlayer that is equal to or greater than the threshold value is present within 130 nm of the interface between the underlayer and the base layer.

5. 2. The magnetic recording medium according to claim 1, wherein the total thickness of the magnetic layer and the underlayer is 1200 nm or less.

6. 2. The magnetic recording medium according to claim 1, wherein the total thickness of the magnetic layer and the underlayer is 1000 nm or less.

7. 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic layer is 80 nm or less.

8. 2. The magnetic recording medium according to claim 1, wherein the underlayer has a thickness of 1120 nm or less.

9. The magnetic recording medium according to claim 1 , wherein the underlayer contains non-magnetic powder.

10. The magnetic recording medium of claim 1 , wherein the underlayer contains a lubricant.

11. The average thickness t of the magnetic recording medium Ｔ 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 5.5 [mu]m or less.

12. The magnetic recording medium according to claim 1 , wherein the magnetic layer contains magnetic powder.

13. The magnetic recording medium according to claim 12, wherein the magnetic powder comprises hexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite.

14. a magnetic layer, an underlayer, and a base layer in this order; the underlayer comprises a chlorine-containing binder; the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold is 12% or less of the thickness of the underlayer; Magnetic recording media. [Threshold value] = [average chlorine count in the underlayer] + 6 × [standard deviation obtained when calculating the average chlorine count]

15. 10. A magnetic recording cartridge comprising the magnetic recording medium according to claim 1 wound around a reel and housed in a case.

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