Magnetic recording medium

Abstract

The purpose of the present invention is to provide a magnetic recording medium with which it is possible to minimize a dimensional change in the width direction by having water vapor transmission be within a specific range. The present technology provides a tape-form magnetic recording medium, wherein: the medium comprises a magnetic layer, a non-magnetic layer, a base layer, and a back layer in the stated order; the magnetic layer and the non-magnetic layer are in contact, and the non-magnetic layer and the base layer are in contact; the average thickness of the magnetic recording medium is 5.74 μm or less; the Young's modulus of the base layer in the MD direction (longitudinal direction) is not more than 5.9 GPa; and the water vapor transmission of the magnetic recording medium, as measured according to Lyssy method, is not more than 2.93 g / m2 per day. The Young's modulus of the base layer in the MD direction (longitudinal direction) is not more than 5.3 GPa. The humidity expansion coefficient β at a temperature of 10°C is not more than 6.5 ppm / % RH.

Description

Technical Field

[0001] The present technology relates to a magnetic recording medium.

Background Art

[0002] In recent years, in next-generation magnetic tapes (magnetic recording media) that require high recording density, ensuring dimensional stability in the width direction has become important from the perspective of improving the reliability of the product. It is considered that the dimensional stability of the magnetic tape largely depends on the amount of deformation of the base film serving as the base material (base layer). As a major cause for the large dependence of the dimensional stability of the base film on the amount of deformation of the base film, it is presumed that environmental factors during storage of the base film account for a large part.

[0003] Some techniques for reducing the amount of dimensional deformation have been proposed so far. For example, in the magnetic tape medium disclosed in Patent Document 1 below, when the Young's modulus in the width direction of the non-magnetic support is X and the Young's modulus in the width direction of the back layer is Y, X is 850 kg / mm 2 or more, or when it is less than 850 kg / mm 2 X × Y is 6 × 10 5 or more, and when the Young's modulus in the width direction of the layer including the magnetic layer is Z, Y / Z is 6.0 or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The main object of the present technology is to provide a magnetic recording medium capable of suppressing dimensional deformation in the width direction.

Means for Solving the Problems

[0006] This technology relates to a tape-shaped magnetic recording medium, comprising a magnetic layer, a non-magnetic layer, a base layer, and a back layer in this order, wherein the magnetic layer and the non-magnetic layer are in contact, the non-magnetic layer and the base layer are in contact, the average thickness of the magnetic recording medium is 5.74 μm or less, the Young's modulus of the base layer in the MD direction (longitudinal direction) is 5.9 GPa or less, the water vapor transmission rate of the magnetic recording medium, measured according to the Lyssy method, is 2.93 g / m 2 ·day or less, and provides the magnetic recording medium. The water vapor transmission rate may be 2.00 g / m 2 ·day or less. The water vapor transmission rate may be 1.84 g / m 2 ·day or less. The water vapor transmission rate of the base layer, measured according to the Lyssy method, may be 7.57 g / m 2 ·day or less. The water vapor transmission rate of the base layer may be 4.00 g / m 2 ·day or less. The water vapor transmission rate of the base layer may be 3.00 g / m 2 ·day or less. The water vapor transmission rate of the base layer may be 2.19 g / m 2 ·day or less. The Young's modulus of the base layer in the MD direction (longitudinal direction) may be 5.3 GPa or less. The average thickness of the magnetic recording medium may be 5.60 μm or less. The average thickness of the magnetic recording medium may be 5.30 μm or less. The thickness of the non-magnetic layer may be 1.2 μm or less. The thickness of the base layer may be 4.5 μm or less. The thickness of the back layer may be 0.6 μm or less. The humidity expansion coefficient β at a temperature of 10 °C may be 6.5 ppm / %RH or less. The magnetic layer may contain magnetic powder. The magnetic layer and the non-magnetic layer may be vacuum thin films. The present technology provides a magnetic recording cartridge in which the magnetic recording medium is housed in a case in a state of being wound around a reel.

Brief Description of the Drawings

[0007]

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Embodiments for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments for carrying out the present technology will be described. Note that the embodiments described below show typical embodiments of the present technology, and the scope of the present technology is not limited only to these embodiments.

[0009] The present technology will be described in the following order. 1. Description of the present technology 2. First Embodiment (Example of a Coated Magnetic Recording Medium) (1) Configuration of the magnetic recording medium (2) Explanation of each layer (3) Physical properties and structure (4) Manufacturing method of the magnetic recording medium (5) Recording and reproducing apparatus (6) Modification example 3. Second Embodiment (Example of a Vacuum Thin Film Type Magnetic Recording Medium) (1) Configuration of the magnetic recording medium (2) Explanation of each layer (3) Physical properties and structure (4) Configuration of the sputtering apparatus (5) Manufacturing method of the magnetic recording medium (6) Modification example 4. Third Embodiment (Example of Vacuum Thin Film Type Magnetic Recording Medium) (1) Configuration of the magnetic recording medium (2) Explanation of each layer 5. One Embodiment of the Magnetic Recording Cartridge According to the Present Technology 6. Modification Example of the Magnetic Recording Cartridge According to the Present Technology 7. Examples

[0010] 1. Explanation of the Present Technology

[0011] In the next-generation magnetic recording tape that requires high recording density, it is important to ensure dimensional stability in the width direction. Dimensional deformation in the width direction of the magnetic recording tape is likely to occur especially when stored for a long time. Dimensional deformation in the width direction can cause phenomena that are not desirable for magnetic recording, such as the off-track phenomenon. The off-track phenomenon refers to the situation where the target track does not exist at the track position to be read by the magnetic head, or the magnetic head reads the wrong track position. The dimensional stability of the magnetic recording tape largely depends on the amount of deformation of the base film serving as the substrate. It is presumed that environmental factors when storing the base film largely account for the cause of the deformation of the base film.

[0012] Conventionally, in order to suppress dimensional deformation of the magnetic recording medium, techniques such as adding a layer for suppressing dimensional deformation of the magnetic recording medium have been performed.

[0013] The inventor has found that the parameter indicating the influence degree of environmental factors on the dimensional stability of the base film constituting the base layer is the humidity expansion coefficient β, and by specifying the water vapor transmission rate of the magnetic recording medium within a certain range, the humidity expansion coefficient β can be reduced, that is, the dimensional stability can be improved. Also, by specifying the water vapor transmission rate of the base film within a certain range, the humidity expansion coefficient β can be reduced, that is, the dimensional stability can be improved. That is, the magnetic recording medium according to the present technology has a water vapor transmission rate measured according to the Lyssy method of 2.93 g / m 2 ·day or less, preferably 2.00 g / m 2 ·day or less, more preferably 1.84 g / m 2 ·day or less, still more preferably 1.50 g / m 2 ·day or less. By the magnetic recording medium having a water vapor transmission rate within the above numerical range, it contributes to making it possible to suppress dimensional deformation in the width direction.

[0014] Also, the lower limit of the water vapor transmission rate is not particularly limited, but for example, it may be 0 g / m 2 ·day or more, preferably 0.2 g / m 2 ·day or more, more preferably 0.4 g / m 2 ·day or more. The measuring method of the water vapor transmission rate measured according to the Lyssy method will be described in (3) below.

[0015] The magnetic recording medium according to the present technology is preferably a long magnetic recording medium, and for example, it may be a magnetic recording tape (particularly a long magnetic recording tape).

[0016] The magnetic recording medium according to the present technology includes a magnetic layer, a non-magnetic layer, a base layer, and a back layer in this order, and in addition to these layers, may include other layers. The magnetic layer and the non-magnetic layer are in contact with each other, and the non-magnetic layer and the base layer are in contact with each other. The other layers may be appropriately selected according to the type of the magnetic recording medium. The magnetic recording medium may be, for example, a coating type magnetic recording medium or a vacuum thin film type magnetic recording medium. The coating type magnetic recording medium will be described in more detail in 2. below. The vacuum thin film type magnetic recording medium will be described in more detail in 3. below. For the layers included in the magnetic recording medium other than the above four layers, refer to these descriptions.

[0017] The base layer of the magnetic recording medium according to the present technology has a water vapor transmission rate measured according to the Lyssy method of preferably 7.57 g / m 2 ·day or less, more preferably 4.00 g / m 2 ·day or less, still more preferably 3.00 g / m 2 ·day or less, even more preferably 2.19 g / m 2 ·day or less. The lower limit of the water vapor transmission rate of the base layer is not particularly limited, but may be, for example, 0 g / m 2 ·day or more, preferably 0.2 g / m 2 ·day or more, more preferably 0.4 g / m 2 ·day or more. The method for measuring the water vapor transmission rate in the base layer is described in (3) of 2. below.

[0018] The base layer of the magnetic recording medium according to the present technology may have a TD direction (width direction) Young's modulus of preferably 9.0 GPa or more, more preferably 10.0 GPa or more, and still more preferably 11.0 GPa or more. By having the TD direction (width direction) Young's modulus within the above numerical range, it becomes possible to further suppress dimensional deformation in the width direction. The method for measuring the TD direction (width direction) Young's modulus in the base layer is described in (3) of 2. below.

[0019] The base layer of the magnetic recording medium according to the present technology may have an MD direction (longitudinal direction) Young's modulus of preferably 5.9 GPa or less, more preferably 5.3 GPa or less. By having the MD direction (longitudinal direction) Young's modulus of the magnetic recording medium within the above numerical range, it becomes possible to suppress dimensional deformation. The method for measuring the MD direction (longitudinal direction) Young's modulus in the base layer will be described in (3) of the following 2.

[0020] The average thickness of the magnetic recording medium according to the present technology may be preferably 5.74 μm or less, more preferably 5.60 μm or less, still more preferably 5.30 μm or less, and still more preferably 5.00 μm or less. Since the magnetic recording medium is thus thin, for example, the tape length wound in one magnetic recording cartridge can be made longer, and thereby the recording capacity per magnetic recording cartridge can be increased. The lower limit value of the average thickness of the magnetic recording medium is not particularly limited, but for example, 3.50 μm ≤ t T is satisfied.

[0021] The thickness of the non-magnetic layer of the magnetic recording medium according to the present technology may be preferably 1.2 μm or less, more preferably 1.0 μm or less, and still more preferably 0.8 μm or less. The method for measuring the thickness of the non-magnetic layer will be described in (3) of the following 2.

[0022] The thickness of the base layer of the magnetic recording medium according to the present technology may be preferably 4.5 μm or less, more preferably 4.2 μm or less, and still more preferably 3.6 μm or less. The method for measuring the thickness of the base layer will be described in (3) of the following 2.

[0023] The thickness of the back layer of the magnetic recording medium according to the present technology may be preferably 0.6 μm or less, more preferably 0.5 μm or less, and still more preferably 0.4 μm or less. The method for measuring the thickness of the back layer will be described in (3) of the following 2.

[0024] The magnetic recording medium according to the present technology may have a humidity expansion coefficient β at a temperature of 10°C of preferably 6.5 ppm / %RH or less, more preferably 6.0 ppm / %RH or less, and even more preferably 5.5 ppm / %RH or less. The humidity expansion coefficient β is presumed to have a correlation with the water vapor transmission rate described above. When the humidity expansion coefficient β at a temperature of 10°C is within the range of 6.5 ppm / %RH or less, the water vapor transmission rate of the magnetic recording medium can be reduced. That is, the dimensional deformation amount can be suppressed. The method for measuring the humidity expansion coefficient β will be described in (3) below. Further, the magnetic recording medium according to the present technology may have a humidity expansion coefficient β at a temperature of 35°C of preferably 8.0 ppm / %RH or less, more preferably 7.5 ppm / %RH or less, and even more preferably 7.0 ppm / %RH or less. The humidity expansion coefficient β is presumed to have a correlation with the water vapor transmission rate described above. When the humidity expansion coefficient β at a temperature of 35°C is within the range of 8.0 ppm / %RH or less, the water vapor transmission rate of the magnetic recording medium can be reduced. That is, the dimensional deformation amount can be suppressed. Furthermore, the magnetic recording medium according to the present technology may have a humidity expansion coefficient β at a temperature of 60°C of preferably 11.0 ppm / %RH or less, more preferably 10.0 ppm / %RH or less, and even more preferably 9.0 ppm / %RH or less. The humidity expansion coefficient β is presumed to have a correlation with the water vapor transmission rate described above. When the humidity expansion coefficient β at a temperature of 60°C is within the range of 11.0 ppm / %RH or less, the water vapor transmission rate of the magnetic recording medium can be reduced. That is, the dimensional deformation amount can be suppressed.

[0025] 2. First Embodiment (Example of Coated Magnetic Recording Medium)

[0026] (1) Configuration of Magnetic Recording Medium First, with reference to FIG. 1, the configuration of the magnetic recording medium 10 according to the first embodiment will be described. The magnetic recording medium 10 is, for example, a magnetic recording medium subjected to perpendicular orientation treatment. As shown in FIG. 1, it includes an elongated base layer (also referred to as a substrate) 11, an underlayer (non-magnetic layer) 12 provided on one main 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 main surface of the base layer 11. Hereinafter, among the two main surfaces of the magnetic recording medium 10, the surface on which the magnetic layer 13 is provided is referred to as the magnetic surface, and the surface on the opposite side of the magnetic surface (the surface on which the back layer 14 is provided) is referred to as the back surface.

[0027] The magnetic recording medium 10 has an elongated shape and travels in the longitudinal direction during recording and reproduction. Also, the magnetic recording medium 10 may be configured to be able 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. For example, it can be used in a recording and reproducing apparatus having a minimum recording wavelength within the above range. This recording and reproducing apparatus may include a ring head as a recording head. The recording track width is, for example, 2 μm or less.

[0028] (2) Explanation of each layer

[0029] (Base layer)

[0030] The base layer 11 can function as a support for the magnetic recording medium 10, and is, for example, a long non-magnetic substrate having flexibility, and particularly can be a non-magnetic film. The thickness of the base layer 11 can be, for example, preferably 4.5 μm or less, more preferably 4.2 μm or less, and even more preferably 3.6 μm or less. Note that the lower limit of the thickness of the base layer 11 can be determined, for example, from the viewpoint of the limit in film formation of the film or the function of the base layer 11. The base layer 11 can contain at least one of, for example, 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.

[0031] The polyester resin may be, for example, one kind or a mixture of two or more kinds of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate), and polyethylene bisphenoxy carboxylate. According to a preferred embodiment of the present technology, the base layer 11 may be formed from PET or PEN.

[0032] The polyolefin resin may be, for example, one kind or a mixture of two or more kinds of PE (polyethylene) and PP (polypropylene).

[0033] The cellulose derivative may be, for example, one kind or a mixture of two or more kinds of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate).

[0034] The vinyl resin may be, for example, one kind or a mixture of two or more kinds of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0035] The aromatic polyether ketone resin may be, for example, one kind or a mixture of two or more kinds among PEK (polyether ketone), PEEK (polyether ether ketone), PEKK (polyether ketone ketone), and PEEKK (polyether ether ketone ketone). According to a preferred embodiment of the present technology, the base layer 11 may be formed of PEEK.

[0036] The other polymer resin may be, for example, one kind or a mixture of two or more kinds among PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, for example, Zylon (registered trademark)), polyether, polyether ester, PES (polyether sulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

[0037] (Magnetic layer)

[0038] The magnetic layer 13 may be, for example, a perpendicular recording layer. The magnetic layer 13 may contain magnetic powder. The magnetic layer 13 may further contain, for example, a binder and conductive particles in addition to the magnetic powder. The magnetic layer 13 may further contain additives such as a lubricant, an abrasive, and a rust preventive agent as necessary.

[0039] The thickness t of the magnetic layer 13 m is preferably 35 nm ≤ t m ≤ 120 nm, more preferably 35 nm ≤ t m ≤ 100 nm, and particularly preferably 35 nm ≤ t m ≤ 90 nm. That the thickness t of the magnetic layer 13 m is within the above numerical range contributes to the improvement of electromagnetic conversion characteristics.

[0040] The magnetic layer 13 is preferably a magnetic layer with perpendicular orientation. In this specification, perpendicular orientation means that the squareness ratio S1 measured in the longitudinal direction (running direction) of the magnetic recording medium 10 is 35% or less. Note that the magnetic layer 13 may be a magnetic layer with in-plane orientation (longitudinal orientation). That is, the magnetic recording medium 10 may be a horizontal recording type magnetic recording medium. However, perpendicular orientation is more preferable in terms of achieving high recording density.

[0041] (Magnetic powder)

[0042] Examples of the magnetic particles forming the magnetic powder contained in the magnetic layer 13 include, but are not limited to, epsilon-type iron oxide (ε-iron oxide), gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, hexagonal ferrite, barium ferrite (BaFe), Co ferrite, strontium ferrite, and metal. The magnetic powder may be one of these, or a combination of two or more. Particularly preferably, the magnetic powder may contain ε-iron oxide magnetic powder, barium ferrite magnetic powder, cobalt ferrite magnetic powder, or strontium ferrite magnetic powder. Note that ε-iron oxide may contain Ga and / or Al. These magnetic particles may be appropriately selected by those skilled in the art based on factors such as the manufacturing method of the magnetic layer 13, the tape specifications, and the tape functions.

[0043] The average particle size (average maximum particle size) D of the magnetic powder is preferably 22 nm or less, more preferably 8 nm or more and 22 nm or less, and even more preferably 10 nm or more and 20 nm or less.

[0044] The average particle size D of the above magnetic powder is determined as follows. First, the magnetic recording medium 10 to be measured is processed by a method such as the FIB (Focused Ion Beam) method to produce a thin slice, and the cross-section of the thin slice is observed by TEM. Next, 500 ε-iron oxide particles are randomly selected from the taken TEM photograph, and the maximum particle size d max of each particle is measured, and the maximum particle size d of the magnetic powdermax Determine the particle size distribution. Here, "maximum particle size d max " means the so-called maximum Feret diameter. Specifically, it refers to the maximum distance between two parallel lines drawn from all angles so as to be in contact with the contour of the ε-iron oxide particles. Then, from the obtained particle size distribution of the maximum particle size d max , determine the median diameter (50% diameter, D50) of the maximum particle size d max and use this as the average particle size (average maximum particle size) D of the magnetic powder.

[0045] The shape of the magnetic particles depends on the crystal structure of the magnetic particles. For example, BaFe and strontium ferrite can be hexagonal plate-shaped. ε-Iron oxide can be spherical. Cobalt ferrite can be cubic. The metal can be spindle-shaped. These magnetic particles are oriented in the manufacturing process of the magnetic recording medium 10.

[0046] According to one preferred embodiment of the present technology, the magnetic powder may preferably include a powder of nanoparticles containing ε-iron oxide (hereinafter referred to as "ε-iron oxide particles"). Even if the ε-iron oxide particles are fine particles, a high coercive force can be obtained. It is preferable that the ε-iron oxide contained in the ε-iron oxide particles is preferentially crystal-oriented in the thickness direction (vertical direction) of the magnetic recording medium 10.

[0047] The ε-iron oxide particles have a spherical or substantially spherical shape, or a cubic or substantially cubic shape. Since the ε-iron oxide particles have the above-mentioned shape, when the ε-iron oxide particles are used as magnetic particles, compared with the case where hexagonal plate-shaped barium ferrite particles are used as magnetic particles, the contact area between the particles in the thickness direction of the medium can be reduced, and the aggregation of the particles can be suppressed. Therefore, the dispersibility of the magnetic powder can be enhanced, and a better SNR (Signal-to-Noise Ratio) can be obtained.

[0048] The ε-iron oxide particles have a core-shell structure. Specifically, the ε-iron oxide particles include a core portion and a shell portion having a two-layer structure provided around the core portion. The shell portion having a two-layer structure includes a first shell portion provided on the core portion and a second shell portion provided on the first shell portion.

[0049] The core portion contains ε-iron oxide. The ε-iron oxide contained in the core portion preferably has ε-Fe 2 O 3 crystal as the main phase, and more preferably consists of single-phase ε-Fe 2 O 3 .

[0050] The first shell portion covers at least a part of the periphery of the core portion. Specifically, the first shell portion may partially cover the periphery of the core portion or may cover the entire periphery of the core portion. From the viewpoint of making the exchange coupling between the core portion and the first shell portion sufficient and improving the magnetic properties, it is preferable that the entire surface of the core portion is covered.

[0051] The first shell portion is a so-called soft magnetic layer and may contain a soft magnetic material such as α-Fe, Ni-Fe alloy, or Fe-Si-Al alloy. α-Fe may be obtained by reducing the ε-iron oxide contained in the core portion.

[0052] The second shell portion is an oxide film as an antioxidant layer. The second shell portion may contain α-iron oxide, aluminum oxide, or silicon oxide. α-iron oxide may contain, for example, at least one iron oxide of Fe 3 O 4 , Fe 2 O 3 , and FeO. When the first shell portion contains α-Fe (soft magnetic material), α-iron oxide may be obtained by oxidizing the α-Fe contained in the first shell portion.

[0053] By having the first shell portion as described above, the ε-iron oxide particles can ensure thermal stability, thereby maintaining a large coercive force Hc of the core portion alone and / or adjusting the coercive force Hc of the ε-iron oxide particles (core-shell type particles) as a whole to a coercive force Hc suitable for recording. Further, by having the second shell portion as described above, the ε-iron oxide particles can be prevented from being exposed to air during the manufacturing process of the magnetic recording medium 10 and before that process, and rust or the like can be prevented from occurring on the particle surface, thereby suppressing deterioration of the characteristics of the ε-iron oxide particles. Therefore, deterioration of the characteristics of the magnetic recording medium 10 can be suppressed.

[0054] The ε-iron oxide particles may have a shell portion having a single-layer structure. In this case, the shell portion has the same configuration as the first shell portion. However, from the viewpoint of suppressing deterioration of the characteristics of the ε-iron oxide particles, it is more preferable that the ε-iron oxide particles have a shell portion having a two-layer structure.

[0055] The ε-iron oxide particles may contain an additive instead of having a core-shell type structure, or may have a core-shell type structure and contain an additive. In these cases, a part of Fe of the ε-iron oxide particles is replaced with the additive. By the ε-iron oxide particles containing the additive, the coercive force Hc of the entire ε-iron oxide particles can be adjusted to a coercive force Hc suitable for recording, so that the ease of recording can be improved. The additive is one or more selected from the group consisting of metal elements other than iron, preferably trivalent metal elements, more preferably one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). Specifically, the ε-iron oxide containing the additive is ε-Fe 2-x M x O 3 crystal (where 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).

[0056] According to another preferred embodiment of the present technology, the magnetic powder may be barium ferrite (BaFe) magnetic powder. The barium ferrite magnetic powder includes magnetic particles of iron oxide having 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, the coercive force does not decrease even in a high-temperature and high-humidity environment. From such a viewpoint, the barium ferrite magnetic powder is preferable as the magnetic powder.

[0057] The average particle size of the barium ferrite magnetic powder is 50 nm or less, more preferably 10 nm or more and 40 nm or less, and even more preferably 12 nm or more and 25 nm or less.

[0058] When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the thickness t m [nm] of the magnetic layer 13 is preferably 35 nm ≦ t m ≦ 120 nm. Further, the coercive force Hc measured in the thickness direction (vertical direction) of the magnetic recording medium 10 is preferably 160 kA / m or more and 280 kA / m or less, more preferably 165 kA / m or more and 275 kA / m or less, and even more preferably 170 kA / m or more and 270 kA / m or less.

[0059] According to still another preferred embodiment of the present technology, the magnetic powder can be cobalt ferrite magnetic powder. The cobalt ferrite magnetic powder includes magnetic particles of iron oxide having cobalt ferrite as the main phase (hereinafter referred to as "cobalt ferrite magnetic particles"). The cobalt ferrite magnetic particles preferably have uniaxial anisotropy. The cobalt ferrite magnetic particles have, for example, a cubic shape or a substantially cubic shape. The cobalt ferrite is cobalt ferrite containing Co. The cobalt ferrite may further contain one or more selected from the group consisting of Ni, Mn, Al, Cu, and Zn in addition to Co.

[0060] The cobalt ferrite has, for example, an average composition represented by the following formula (1). Co x M y Fe 2O z ···(1) (However, in formula (1), M is one or more metals selected from the group consisting of, for example, Ni, Mn, Al, Cu, and Zn. x is a value within the range of 0.4 ≦ x ≦ 1.0. y is a value within the range of 0 ≦ y ≦ 0.3. However, x and y satisfy the relationship (x + y) ≦ 1.0. z is a value within the range of 3 ≦ z ≦ 4. A part of Fe may be substituted with other metal elements.)

[0061] The average particle size of the cobalt ferrite magnetic powder is preferably 25 nm or less, more preferably 23 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.)

[0062] According to still another preferred embodiment of the present technology, the magnetic powder may include a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as "hexagonal ferrite particles"). The hexagonal ferrite particles have, for example, a hexagonal plate shape or a substantially hexagonal plate shape. The hexagonal ferrite may preferably contain at least one of Ba, Sr, Pb, and Ca, more preferably at least one of Ba and Sr. Specifically, the hexagonal ferrite may be, for example, barium ferrite or strontium ferrite. Barium ferrite may further contain at least one of Sr, Pb, and Ca in addition to Ba. Strontium ferrite may further contain at least one of Ba, Pb, and Ca in addition to Sr.) More specifically, the hexagonal ferrite may have an average composition represented by the general formula MFe 12 O 19 Here, M is at least one metal of, for example, Ba, Sr, Pb, and Ca, preferably at least one metal of 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. Also, M may 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, a part of Fe may be substituted with other metal elements.) When the magnetic powder contains powder of hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 10 nm or more and 40 nm or less, and even more preferably 15 nm or more and 30 nm or less.

[0063] (Binder)

[0064] As the binder, a resin having a structure imparted with a crosslinking reaction, such as a polyurethane-based resin or a vinyl chloride-based resin, is preferable. However, the binder is not limited to these, and other resins may be appropriately blended according to 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 generally used in the coating-type magnetic recording medium 10.

[0065] Examples of the binder include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate ester-acrylonitrile copolymer, acrylate ester-vinyl chloride-vinylidene chloride copolymer, acrylate ester-vinylidene chloride copolymer, methacrylate ester-vinylidene chloride copolymer, methacrylate ester-vinyl chloride copolymer, methacrylate 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.

[0066] Also, as the binder, a thermosetting resin or a reactive resin may be used. Examples of these include phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin.

[0067] In addition, for each of the above-mentioned binders, for the purpose of improving the dispersibility of magnetic powder, -SO 3 M, -OSO 3 M, -COOM, P=O(OM) 2 and other polar functional groups may be introduced. Here, in the formula, M is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium.

[0068] Furthermore, examples of the polar functional group include side-chain types having a terminal group of -NR1R2, -NR1R2R3 + X - , and main-chain types of >NR1R2 + X - . Here, in the formula, R1, R2, and R3 are a hydrogen atom or a hydrocarbon group, and X - is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. In addition, examples of the polar functional group also include -OH, -SH, -CN, and an epoxy group.

[0069] (Additive)

[0070] The magnetic layer 13 may further contain, as non-magnetic reinforcing particles, 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 type or anatase type titanium oxide), and the like.

[0071] (Underlayer)

[0072] The underlayer 12 is a non-magnetic layer mainly containing non-magnetic powder and a binder. The description regarding the binder contained in the above-mentioned magnetic layer 13 also applies to the binder contained in the underlayer 12. The underlayer 12 may further contain at least one additive such as conductive particles, a lubricant, a curing agent, and a rust preventive agent, if necessary.

[0073] The thickness of the underlayer 12 can preferably be 1.2 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. Also, the lower limit of the thickness of the underlayer 12 is not particularly limited, but is preferably 0.2 μm or more, and more preferably 0.4 μm or more.

[0074] (Non-magnetic powder)

[0075] The non-magnetic powder contained in the underlayer 12 can contain, for example, at least one selected from inorganic particles and organic particles. One type of non-magnetic powder may be used alone, or two or more types of non-magnetic powder may be used in combination. The inorganic particles contain, for example, one or a combination of two or more selected from metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. More specifically, the inorganic particles can be, for example, one or two or more selected from iron oxyhydroxide, hematite, titanium oxide, and carbon black. Examples of the shape of the non-magnetic powder include various shapes such as needle-like, spherical, cubic, and plate-like, but are not particularly limited thereto.

[0076] (Back layer)

[0077] The back layer 14 can contain a binder and non-magnetic powder. The back layer 14 may contain various additives such as a lubricant, a curing agent, and an antistatic agent as necessary. The explanations given for the binder and non-magnetic powder contained in the above-mentioned underlayer 12 also apply to the binder and non-magnetic powder contained in the back layer 14.

[0078] 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 above magnetic powder.

[0079] The thickness t of the back layer 14 b is preferably t b ≦0.6 μm. The thickness t of the back layer 14 bBy being within the above range, the thickness t of the magnetic recording medium 10 T is t T Even when it is set to ≦ 5.6 μm, the thicknesses of the underlayer 12 and the base layer 11 can be kept thick, and thereby the traveling stability of the magnetic recording medium 10 in the recording and reproducing apparatus can be maintained.

[0080] (3) Physical properties and structure

[0081] (Water vapor transmission rate of the magnetic recording medium)

[0082] The water vapor transmission rate refers to an index representing the amount of water vapor permeating through a 1 m 2 film substrate in 24 hours in grams. The unit is expressed as g / m 2 ·day. In other words, it can be used as an index indicating water vapor barrier properties. The lower this value, the lower the water vapor transmission rate, which means higher water vapor barrier performance.

[0083] In the magnetic recording medium according to this technology, the water vapor transmission rate means an index measured according to the Lyssy method. The Lyssy method is also referred to as the humidity sensor method.

[0084] In this technology, when measuring the water vapor transmission rate, first, prepare a sample holder (manufactured by SYSTECH) shown in FIGS. 17 and 18. FIG. 17 is a photograph of the front surface of the sample holder. FIG. 18 is a photograph of the back surface of the sample holder. As shown in FIG. 18, a circular white double-sided sheet WS with six holes opened on the back surface of the sample holder and a white double-sided sheet composed of other parts are adhered. FIG. 19 is a photograph showing a state where the circular white double-sided sheet WS with six holes opened is peeled off from the back surface of the sample holder shown in FIG. 18. First, as shown in FIG. 19, peel off the circular white double-sided sheet WS with six holes opened on the back surface of the sample holder from the back surface of the sample holder. Next, since the variation in the numerical values of the water vapor transmission rate in the longitudinal direction of the magnetic recording medium 10 is considered to be small, cut out a test piece by cutting a length of 14 cm from within the width of 12.65 mm of the magnetic recording medium 10 at an arbitrary position in the longitudinal direction of the magnetic recording medium 10. Attach the cut-out test piece to dust-free paper. Mark the test piece attached to the dust-free paper at intervals of 4 cm, 6 cm, and 4 cm respectively. Attach mending tape to each of the 4-cm interval part, 6-cm interval part, and 4-cm interval part of the test piece. Cut out samples of 4 cm in length, 6 cm in length, and 4 cm in length respectively from the test piece to which the mending tape is attached with a cutter. Next, place the cut-out 4-cm long sample with the magnetic layer facing down and carefully attach it to the part (1) on the back surface of the sample holder so that the two holes are completely covered. After attachment, cut the mending tape to an appropriate length. Cut off the remaining mending tape. Subsequently, place the 6-cm long sample with the magnetic layer facing down and carefully attach it to the part (2) on the back surface of the sample holder so that the two holes are completely covered. After attachment, cut the mending tape to an appropriate length. Cut off the remaining mending tape. Subsequently, place the remaining 4-cm long sample with the magnetic layer facing down and carefully attach it to the part (3) on the back surface of the sample holder so that the two holes are completely covered. After attachment, cut the mending tape to an appropriate length. Cut off the remaining mending tape.Figure 20 is a photograph showing a state in which a sample S is attached to each of the portions (1), (2), and (3) on the back surface of the sample holder. As shown in Figure 20, the six holes in the sample holder are completely covered by the sample S. Thereafter, a circular white double-sided sheet WS with the six peeled holes open is attached to the back surface of the sample holder. When attaching the circular white double-sided sheet WS to the back surface of the sample holder, the position of the hole of the circular white double-sided sheet WS is aligned with the sunken holes of the sample S attached to each of the portions (1), (2), and (3) on the back surface of the sample holder and then attached.

[0085] In this technology, the water vapor transmission rate is measured by the following procedure. A measuring device composed of a permeation cell having two chambers on the upper and lower sides of a test piece for a low humidity side and a high humidity side, a humidity sensor on the low humidity chamber side for detecting the amount of permeated water vapor as relative humidity, a pump for supplying dry air, and a drying cylinder is used. As such a measuring device, for example, the L80-5000 type water vapor transmission rate meter manufactured by Lyssy can be mentioned. When measuring the water vapor transmission rate, test water is stored in the high humidity chamber of the permeation cell. The low humidity chamber has a structure capable of accumulating the water vapor permeated through the test piece from the high humidity side, and a humidity sensor is installed on the upper part of this low humidity chamber. The permeation cell is configured to be maintained within a predetermined range of the test temperature by a temperature controller. After turning on the main power supply of the device, wait for 1 to 3 hours until the measurement temperature stabilizes, and then perform the measurement. When the device is placed in an environment maintained at a temperature of 25°C and a humidity of 50 to 60%, the measurement temperature is considered to be stable, and the measurement can be performed immediately after turning on the main power supply. The measurement of the water vapor transmission rate is automatically controlled by, for example, the device and performed by the following procedure. 1. Dry the low humidity chamber on the upper side of the test piece to a predetermined level in advance and close the valve. 2. The low humidity chamber is humidified to a predetermined level by the water vapor permeation of the test piece. 3. Measure the increase in relative humidity and measure the time required for the difference in the small relative humidity values set in two steps to change.

[0086] The specific operation procedures are as follows. The water vapor transmission rate meter (L80-5000 type manufactured by Lyssy) is placed stationary in a room maintained at a temperature of 25°C and a humidity of 50 - 60%. (1) Turn on the main switch of the power supply of the water vapor transmission rate meter (L80-5000 type manufactured by Lyssy), and turn on the switch on the front of the device. (2) After the device starts up, leave the device alone. After about 30 minutes, pour pure water into the water receiving part of the device. Input the operation parameters into the memory of the device. Specifically, press the MEMO key to enter the memory input mode, and press the SET key to input each operation parameter. Figure 23 is a printout of the input operation parameters. The parameters used in Figure 23 are as follows. Parameter 02: Permeability of the standard sample Parameter 03: Scale of UnderDry Parameter 04: Attribute of measurement (Normal +) Parameter 05: Upper limit value Parameter 06: Lower limit value Parameter 07: Relative humidity range Parameter 08: Permeability factor and temperature during calibration Parameter 09: Summary printout (ON or OFF) Parameter 10: Leakage amount of the equipment Parameter 11: Number of UNDERDRY CYCLES Parameter 12: TRENDMONITOR (ON or OFF) Parameter 14: Number of HUMIDITY COMP.CYCLES Parameter 16: Time base of the counter Parameter 19: Equilibrium tolerance value Parameter 20: Number of repetitions for average value calculation Parameter 21: Automatic start of the SAMPLE function Parameter 22: Total number of measurements Parameter 23: Sample identification name (for RS232C) Parameter 24: Client Name Parameter 25: Sample Name Parameter 30: Temperature (3) Turn the needle valve on the bottom plate of the silica gel cartridge counterclockwise one or two times, and then adjust the open valve to adjust the flow rate of the drying air for chamber purging so that the drying speed is 1 - 2 scales / second. To obtain reproducible results, adjust several times until the correct value is reached in the UNDER DRY cycle. Adjust the flow rate of this drying air according to the level of sample transmittance. When measuring a new series of samples for the first time, reduce the flow rate so that the overshoot of UNDER DRY is minimized. (4) Use 19μm PET (model number: 211113, manufactured by SYSTECH) as the standard sample. Figure 21 is a photograph of the surface of the standard sample holder. Figure 22 is a photograph of the back surface of the standard sample holder. In Figures 21 and 22, the standard sample S (19μm PET) is installed in the circular opening. Rotate the handwheel counterclockwise to open the measurement chamber, place the standard sample holder shown in Figures 21 and 22 into the device, and rotate the handwheel clockwise to close the measurement chamber. (5) After starting up the device for 8 hours, press the TEST STD key on the alphanumeric keyboard to start calibration. As shown in Figure 23, since the operation parameter 21 is set to ON, when equilibrium is reached, the device automatically ends calibration and starts measurement with the standard sample as the sample. The measurement temperature is 25°C and the measurement humidity is 50%. (6) When the average deviation of five consecutive measured values is within 3.8%, use the average value of these five points as the measured value and press the STOP key to end the measurement. The number of measurements is about 10 times. (7) Remove the standard sample from the device. (8) Rotate the handwheel counterclockwise to open the measurement chamber, and place the sample holder shown in Figures 17 and 18 into the device. (9) End the currently running measurement or data input using the STOP key. Press the MEMO key and sequentially check the currently set operation parameters to confirm that the operation parameters in MEMO are suitable for the measurement sample. Enter a new sample name and press the SAMPLE key to start the measurement. (10) When the average deviation of five consecutive measured values is within 3.8%, use the average value of these five points as the measured value and press the STOP key to end the measurement. Note that the number of measurements is approximately 10 times. (11) Remove the measurement sample from the device. (12) Insert a dummy sample holder into the device. (13) Turn off the switch on the front of the device and turn off the main switch of the power supply of the water vapor transmission rate meter (L80-5000 type, manufactured by Lyssy).

[0087] The water vapor transmission rate of the base layer 11 is obtained by first removing the underlayer 12, magnetic layer 13, and back layer 14 from the magnetic recording medium 10 to obtain the base layer 11. Using this base layer 11, it is determined by the method for measuring the water vapor transmission rate described in the method for measuring the water vapor transmission rate of the magnetic recording medium 10.

[0088] (Young's modulus of the magnetic recording medium)

[0089] The Young's modulus in the width direction (TD direction) and longitudinal direction (MD direction) of the magnetic recording medium 10 is measured using a tensile testing machine (AG-100D, manufactured by Shimadzu Corporation). First, prepare a measurement sample by cutting the magnetic recording medium 10 with a width of 1 / 2 inch to a length of 180 mm. Attach two jigs to the above tensile testing machine that can fix the measurement sample so as to cover the entire width thereof. Using the two jigs, chuck the two ends in the width direction of the measurement sample respectively. The distance between the chucks is 100 mm. After chucking the measurement sample, gradually apply stress to pull the measurement sample in the width direction. The pulling speed is 0.1 mm / min. From the change in stress and the amount of elongation at this time, the Young's modulus is calculated using the following formula.

Equation

[0090] (Young's modulus of the base layer)

[0091] The Young's modulus in the TD (width direction) and MD (longitudinal direction) of the base layer 11 is obtained as follows. First, the underlayer 12, the magnetic layer 13, and the back layer 14 are removed from the magnetic tape 10 to obtain the base layer 11. Using this base layer 11, the Young's modulus in the TD (width direction) and MD (longitudinal direction) is obtained.

[0092] (Thickness t of the magnetic recording medium T )

[0093] The thickness t of the magnetic recording medium 10 T is obtained as follows. First, a 1 / 2-inch-wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is made. Next, using a laser hologauge manufactured by Mitutoyo as a measuring device, the thicknesses at different locations of the sample are measured at 5 or more points, and their measured values are simply averaged (arithmetic mean) to calculate the average value t T [μm].

[0094] (Thickness of the non-magnetic layer)

[0095] The magnetic recording medium 10 is thinly processed perpendicular to its main surface to prepare a test piece, and the cross-section of the test piece is observed under the following conditions using a transmission electron microscope (TEM). Apparatus: TEM (H9000NAR manufactured by Hitachi, Ltd.) Accelerating voltage: 300 kV Magnification: 100,000 times Next, using the obtained TEM image, the thickness of the non-magnetic layer (underlayer) 12 was measured at at least 10 positions in the longitudinal direction of the magnetic recording medium 10, and then their measured values were simply averaged (arithmetic mean) to obtain the thickness (μm) of the non-magnetic layer (underlayer) 12.

[0096] (Thickness of the base layer)

[0097] The thickness of the base layer 11 can be obtained as follows. First, a 1 / 2-inch magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is made. Subsequently, the layers other than the base layer 11 of the sample are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a laser hologauge manufactured by Mitutoyo as a measuring device, the thickness of the sample (base layer 11) is measured at 5 or more positions, and their measured values are simply averaged (arithmetic mean) to obtain the thickness [μm] of the base layer 11.

[0098] (Thickness of the back layer)

[0099] The thickness t of the back layer 14 b is obtained as follows. First, a 1 / 2-inch wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is made. Next, using a laser hologauge manufactured by Mitutoyo as a measuring device, the thicknesses at 5 or more different locations of the sample are measured, and their measured values are simply averaged (arithmetic mean) to calculate the average value t T [μm]. Subsequently, after removing the back layer 14 of the sample with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid, the thicknesses at 5 or more different locations of the sample are measured again using the above laser hologauge, and their measured values are simply averaged (arithmetic mean) to calculate the average value t B [μm]. Then, the thickness t of the back layer 14 is obtained from the following formula b [μm]. t b [μm] = tT [μm] - t B [μm]

[0100] (Thickness t of the magnetic layer m )

[0101] Thickness t of the magnetic layer 13 m is obtained as follows. First, the magnetic recording medium 10 is thinly processed perpendicular to its main surface to produce a test piece, and the cross-section of the test piece is observed under the following conditions using a transmission electron microscope (TEM). Apparatus: TEM (H9000NAR manufactured by Hitachi, Ltd.) Accelerating voltage: 300 kV Magnification: 100,000 times Next, using the obtained TEM image, the thickness of the magnetic layer 13 is measured at at least 10 positions or more in the longitudinal direction of the magnetic recording medium 10, and then the measured values are simply averaged (arithmetic mean) to obtain the thickness t m of the magnetic layer 13 (nm).

[0102] (Humidity expansion coefficient β)

[0103] First, a 1 / 2-inch-wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample 10S is produced.

[0104] A measuring device shown in Fig. 2A incorporating a digital dimension measuring instrument LS-7000 manufactured by Keyence Corporation is prepared as a measuring device, and the sample 10S is set in this measuring device. Specifically, one end of the long sample (magnetic recording medium) 10S is fixed by the fixing portion 231. Next, as shown in Fig. 2A, the sample 10S is set on five substantially cylindrical and rod-shaped support members 232. The sample 10S is set on these support members such that its back surface contacts the five support members 232. All five support members 232 (especially their surfaces) are formed of stainless steel SUS304, and the surface roughness R Z (maximum height) is 0.15 μm to 0.3 μm.

[0105] The arrangement of the five bar-shaped support members 232 will be described with reference to FIG. 2B. As shown in FIG. 2B, the sample 10S is set on the five support members 232. Regarding the five support members 232, hereinafter, starting from the one closest to the fixing portion 231, they are referred to as the "first support member", the "second support member", the "third support member" (having the slit 232A), the "fourth support member", and the "fifth support member" (closest to the weight 233). The diameter of these five support members is 7 mm. The distance d 1 (particularly, the distance between the centers of these support members) between the first support member and the second support member is 20 mm. The distance d 2 between the second support member and the third support member is 30 mm. The distance d 3 between the third support member and the fourth support member is 30 mm. The distance d 4 between the fourth support member and the fifth support member is 20 mm. Also, these three support members are arranged such that the portion of the sample 10S set between the second support member, the third support member, and the fourth support member forms a plane substantially perpendicular to the gravitational direction. Further, the sample 10S forms an angle of θ 1 = 30° with respect to the substantially perpendicular plane between the first support member and the second support member, and the first support member and the second support member are arranged accordingly. Furthermore, the sample 10S forms an angle of θ 2 = 30° with respect to the substantially perpendicular plane between the fourth support member and the fifth support member, and the fourth support member and the fifth support member are arranged accordingly. Also, among the five support members 232, the third support member is fixed so as not to rotate, while the other four support members are all rotatable.

[0106] The sample 10S is held on the support member 232 so as not to move in the width direction of the sample 10S. Note that, among the support members 232, a slit 232A is provided in the support member 232 that is located between the light emitter 234 and the light receiver 235 and is positioned approximately at the center between the fixing portion 231 and the portion applying the load. Light L is irradiated from the light emitter 234 to the light receiver 235 through the slit 232A. The slit width of the slit 232A is 1 mm, and the light L can pass through the width without being blocked by the frame of the slit 232A.

[0107] The measuring device is housed in a chamber controlled to a constant environment of a temperature of 10°C and a relative humidity of 40%. Next, a load is applied in the longitudinal direction of the sample 10S, and the sample 10S is placed in the above environment for 6 hours. Then, while maintaining the temperature at 10°C, the relative humidity is changed in the order of 80%, 40%, and 10%, the widths of the sample 10S at 80%, 40%, and 10% are measured, and the humidity expansion coefficient β is obtained from the following formula. These measurements at the respective humidities are performed immediately after reaching each humidity. Note that the measurement at 40% humidity is performed to confirm whether any abnormality occurs in the measurement, and the measurement result is not used in the following formula. Note that in the case of a temperature of 35°C and in the case of a temperature of 60°C, the humidity expansion coefficient β is obtained under the same conditions as when measuring at a temperature of 10°C except for the temperature conditions. [Number] (However, in the formula, D(80%) and D(10%) respectively indicate the widths of the sample 10S at a relative humidity of 80% and 10%.)

[0108] (Thermal expansion coefficient α)

[0109] The temperature expansion coefficient α is obtained as follows. First, a sample 10S is prepared in the same manner as the measurement method of the humidity expansion coefficient β. After setting the sample 10S in the same apparatus as the measurement method of the humidity expansion coefficient β, the measuring apparatus is placed in a chamber controlled to a constant environment of a temperature of 35°C and a relative humidity of 10%. Next, a load is applied in the longitudinal direction of the sample 10S, and the sample 10S is placed in the above environment for 6 hours. Then, while maintaining a relative humidity of 10%, the temperature is changed in the order of 60°C, 35°C, and 10°C, the widths of the sample 10S at 60°C, 35°C, and 10°C are measured, and the temperature expansion coefficient α is obtained from the following formula. The measurements at these temperatures are performed 2 hours after reaching each temperature. Note that the measurement at a temperature of 35°C is performed to confirm whether any abnormality occurs in the measurement, and the measurement result is not used in the following formula. Note that in the case of a relative humidity of 40% and in the case of a relative humidity of 80%, except for the relative humidity conditions, the temperature expansion coefficient α is obtained under the same conditions as when measuring at a relative humidity of 10%. [Number] (However, in the formula, D(60°C) and D(10°C) respectively indicate the widths of the sample 10S at temperatures of 60°C and 10°C.)

[0110] (4) Method for manufacturing a magnetic recording medium

[0111] Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming a nonmagnetic layer (underlayer) is prepared by kneading and / or dispersing nonmagnetic powder, a binder, etc. in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and / or dispersing magnetic powder, a binder, etc. in a solvent. For the preparation of the paint for forming a magnetic layer and the paint for forming a nonmagnetic layer (underlayer), for example, the following solvents, dispersion devices, and kneading devices can be used.

[0112] Examples of the solvents used in the above paint preparation include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as methanol, ethanol, and propanol; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. One of these may be used, or a mixture of two or more may be used.

[0113] Examples of the kneading apparatuses used in the above paint preparation include kneading apparatuses such as a continuous twin-screw kneader, a continuously twin-screw kneader that can be diluted in multiple stages, a kneader, a pressure kneader, and a roll kneader, but are not particularly limited to these apparatuses. Examples of the dispersion apparatuses used in the above paint preparation include dispersion apparatuses such as a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (such as the "DCP mill" manufactured by Ehrlich), a homogenizer, and an ultrasonic disperser, but are not particularly limited to these apparatuses.

[0114] Next, a non-magnetic layer (underlayer) forming paint is applied to one main surface of the base layer 11 and dried to form an underlayer 12. Subsequently, a magnetic layer forming paint is applied to the underlayer 12 and dried to form a magnetic layer 13 on the underlayer 12. During drying, for example, a solenoid coil is used to magnetically orient the magnetic powder in the thickness direction of the base layer 11. Also, during drying, for example, after magnetically orienting the magnetic powder in the longitudinal direction (running direction) of the base layer 11 by a solenoid coil, it may be magnetically oriented in the thickness direction of the base layer 11. By performing such a magnetic orientation treatment, the ratio Hc2 / Hc1 of the holding force "Hc1" in the vertical direction to the holding force "Hc2" in the longitudinal direction can be lowered, and the vertical orientation degree of the magnetic powder can be improved. After forming the magnetic layer 13, a back layer 14 is formed on the other main surface of the base layer 11. Thereby, the magnetic recording medium 10 is obtained.

[0115] The ratio Hc2 / Hc1 is set to a desired value, for example, by adjusting the intensity of the magnetic field applied to the coating film of the magnetic layer forming paint, the concentration of the solid content in the magnetic layer forming paint, and the drying conditions (drying temperature and drying time) of the coating film of the magnetic layer forming paint. The intensity of the magnetic field applied to the coating film is preferably 2 times or more and 3 times or less the holding force of the magnetic powder. In order to further increase the ratio Hc2 / Hc1, it is also preferable to magnetize the magnetic powder at a stage before the magnetic layer forming paint enters the orientation device for magnetically orienting the magnetic powder. Note that the method for adjusting the ratio Hc2 / Hc1 may be used alone or in combination of two or more.

[0116] Thereafter, the obtained magnetic recording medium 10 is rewound around a large-diameter core and a curing treatment is performed. Finally, after performing a calendering treatment on the magnetic recording medium 10, it is cut to a predetermined width (for example, 1 / 2 inch width). Thus, the target elongated long magnetic recording medium 10 is obtained.

[0117] (5) Recording and reproducing apparatus

[0118] [Configuration of the recording and reproducing apparatus]

[0119] Next, with reference to FIG. 3, an example of the configuration of a recording and reproducing apparatus 30 that records and reproduces the magnetic recording medium 10 having the above-described configuration will be described.

[0120] The recording and reproducing apparatus 30 has a configuration capable of adjusting the tension applied in the longitudinal direction of the magnetic recording medium 10. Further, the recording and reproducing apparatus 30 has a configuration capable of loading the magnetic recording cartridge 10A. Here, for the sake of easy explanation, the case where the recording and reproducing apparatus 30 has a configuration capable of loading one magnetic recording cartridge 10A will be described, but the recording and reproducing apparatus 30 may have a configuration capable of loading a plurality of magnetic recording cartridges 10A. The recording and reproducing apparatus 30 is preferably a magnetic recording and reproducing apparatus of a timing servo system. The magnetic recording medium of the present technology is suitable for use in a magnetic recording and reproducing apparatus of a timing servo system.

[0121] The recording and reproducing apparatus 30 is connected to information processing apparatuses 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 the data supplied from these information processing apparatuses on the magnetic recording cartridge 10A. The shortest recording wavelength of the recording and reproducing apparatus 30 is preferably 100 nm or less, more preferably 75 nm or less, still more preferably 60 nm or less, and particularly preferably 50 nm or less.

[0122] As shown in FIG. 3, the recording and reproducing apparatus includes a spindle 31, a reel 32 on the recording and reproducing apparatus side, a spindle driving device 33, a reel driving device 34, a plurality of guide rollers 35, a head unit 36, a communication interface (hereinafter, I / F) 37, and a control device 38.

[0123] The spindle 31 is configured to be able to mount the magnetic recording cartridge 10A. The magnetic recording cartridge 10A complies with the LTO (Linear Tape Open) standard and rotatably houses a single reel 10C around which a magnetic recording medium 10 is wound in a cartridge case 10B. A U-shaped servo pattern is pre-recorded on the magnetic recording medium 10 as a servo signal. The reel 32 is configured to be able to fix the leading end of the magnetic recording medium 10 drawn out from the magnetic recording cartridge 10A. The present technology also provides a magnetic recording cartridge including a magnetic recording medium according to the present technology. In the magnetic recording cartridge, the magnetic recording medium may be wound around a reel, for example.

[0124] The spindle drive device 33 is a device that rotationally drives the spindle 31. The reel drive device 34 is a device that rotationally drives 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 rotationally drive the spindle 31 and the reel 32 to run the magnetic recording medium 10. The guide roller 35 is a roller for guiding the running of the magnetic recording medium 10.

[0125] 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. For example, a ring-type head can be used as the recording head, but the type of the recording head is not limited thereto.

[0126] The communication I / F 37 is for communicating with information processing devices such as the server 41 and the PC 42 and is connected to the network 43.

[0127] The control device 38 controls the entire recording and reproducing device 30. For example, the control device 38 records, by the head unit 36, the data signal supplied from the information processing device in accordance with the requests of information processing devices such as the server 41 and the PC 42 on the magnetic recording medium 10. Further, the control device 38 reproduces, by the head unit 36, the data signal recorded on the magnetic recording medium 10 in accordance with the requests of information processing devices such as the server 41 and the PC 42, and supplies it to the information processing device.

[0128] Also, the control device 38 detects a change in the width of the magnetic recording medium 10 based on the servo signal supplied from the head unit 36. Specifically, a plurality of C-shaped servo patterns are recorded as servo signals on the magnetic recording medium 10, and the head unit 36 can reproduce two different servo patterns simultaneously by two servo heads on the head unit 36 and obtain their respective servo signals. Using the relative position information between the servo pattern and the head unit obtained from this servo signal, the position of the head unit 36 is controlled so as to follow the servo pattern. At the same time, by comparing the waveforms of the two servo signals, the distance information between the servo patterns can also be obtained. By comparing the distance information between the servo patterns obtained at each measurement, the change in the distance between the servo patterns at each measurement can be obtained. By taking into account the distance information between the servo patterns at the time of servo pattern recording, the change in the width of the magnetic recording medium 10 can also be calculated. The control device 38 controls the rotational drive of the spindle drive device 33 and the reel drive device 34 based on the change in the distance between the servo patterns obtained as described above, or the calculated change in the width of the magnetic recording medium 10, and adjusts the longitudinal tension of the magnetic recording medium 10 so that the width of the magnetic recording medium 10 becomes a specified width or approximately the specified width. Thereby, the change in the width of the magnetic recording medium 10 can be suppressed.

[0129] [Operation of the Recording and Reproducing Device]

[0130] Next, the operation of the recording and reproducing device 30 having the above configuration will be described.

[0131] First, attach the magnetic recording cartridge 10A to the recording and reproducing apparatus 30, pull out the leading end of the magnetic recording medium 10, transfer it to the reel 32 via a plurality of guide rollers 35 and the head unit 36, and attach the leading end of the magnetic recording medium 10 to the reel 32.

[0132] Next, when an operation 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 travels from the reel 10C to the reel 32. As a result, while the magnetic recording medium 10 is being wound around the reel 32, the head unit 36 records information on the magnetic recording medium 10 or reproduces the information recorded on the magnetic recording medium 10.

[0133] When rewinding the magnetic recording medium 10 onto the reel 10C, the spindle 31 and the reel 32 are rotationally driven in the opposite direction to the above, so that the magnetic recording medium 10 travels from the reel 32 to the reel 10C. Also during this rewinding, the head unit 36 records information on the magnetic recording medium 10 or reproduces the information recorded on the magnetic recording medium 10.

[0134] (6) Modification

[0135] [Modification 1]

[0136] The magnetic recording medium 10 may further include a barrier layer 15 provided on at least one surface of the base layer 11 as shown in FIG. 4. The barrier layer 15 is a layer for suppressing dimensional deformation of the base layer 11 according to the environment. For example, as an example of the cause of the dimensional deformation, the hygroscopicity of the base layer 11 can be cited, and the barrier layer 15 can reduce the rate of moisture intrusion into the base layer 11. The barrier layer 15 contains a metal or a metal oxide. As the metal, for example, at least one of Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba, Pt, Au, and Ta can be used. As the metal oxide, for example, Al 2O 3 , CuO, CoO, SiO 2 , Cr 2 O 3 , TiO 2 , Ta 2 O 5 , and at least one of ZrO 2 can be used, and any of the metal oxides described above can also be used. Further, diamond-like carbon (DLC) or diamond can also be used.

[0137] 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. The average thickness of the barrier layer 15 is obtained in the same manner as the average thickness t m of the magnetic layer 13. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the barrier layer 15.

[0138] [Modification Example 2]

[0139] The magnetic recording medium 10 may be incorporated into a library device. That is, the present technology also provides a library device including at least one magnetic recording medium 10. The library device has a configuration capable of adjusting the tension applied in the longitudinal direction of the magnetic recording medium 10, and may include a plurality of the recording and reproducing devices 30 described above.

[0140] [Modification Example 3]

[0141] The magnetic recording medium 10 may be subjected to a servo signal writing process by a servo writer. By adjusting the tension in the longitudinal direction of the magnetic recording medium 10 when the servo writer records a servo signal or the like, the width of the magnetic recording medium 10 can be kept constant or substantially constant. In this case, the servo writer may include a detection device for detecting 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.

[0142] 3. Second Embodiment (Example of Vacuum Thin-Film Type Magnetic Recording Medium)

[0143] (1) Configuration of Magnetic Recording Medium

[0144] The magnetic recording medium 110 according to the second embodiment is a long vertical magnetic recording medium. As shown in FIG. 5, it includes a film-shaped base layer 111, a soft magnetic underlayer (hereinafter referred to as "SUL") 112, a first seed layer 113A, a second seed layer 113B, a first underlayer 114A, a second underlayer 114B, and a magnetic layer 115. The SUL 112, the first and second seed layers 113A and 113B, the first and second underlayers 114A and 114B, and the magnetic layer 115 can be vacuum thin films such as layers formed by sputtering (hereinafter also referred to as "sputter layers").

[0145] The SUL 112, the first and second seed layers 113A and 113B, and the first and second underlayers 114A and 114B are provided between one main surface (hereinafter referred to as "surface") of the base layer 111 and the magnetic layer 115, and are laminated in the order of the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, and the second underlayer 114B in the direction from the base layer 111 to the magnetic layer 115. By providing a vacuum thin film such as a layer formed by sputtering (hereinafter also referred to as "sputter layer") on the surface of the base layer 111, the water vapor transmission rate of the base layer itself can be further reduced.

[0146] The magnetic recording medium 110 may further include a protective layer 116 provided on the magnetic layer 115 and a lubricating layer 117 provided on the protective layer 116 as needed. Also, the magnetic recording medium 110 may further include a back layer 118 provided on the other main surface (hereinafter referred to as "back surface") of the base layer 111 as needed.

[0147] Hereinafter, the longitudinal direction of the magnetic recording medium 110 (the longitudinal direction of the base layer 111) is referred to as the machine direction (MD). Here, the machine direction means the relative movement direction of the recording and reproducing head with respect to the magnetic recording medium 110, that is, the direction in which the magnetic recording medium 110 travels during recording and reproduction.

[0148] The magnetic recording medium 110 according to the second embodiment is suitable for use as a data archive storage medium whose demand is expected to increase more and more in the future. This magnetic recording medium 110 can achieve, for example, a areal recording density that is 10 times or more that of the current storage-type coated magnetic recording medium, that is, 50 Gb / in 2 or more areal recording density. When a general linear recording type data cartridge is configured using the magnetic recording medium 110 having such an areal recording density, a large-capacity recording of 100 TB or more per data cartridge becomes possible.

[0149] The magnetic recording medium 110 according to the second embodiment is suitable for use in a recording and reproducing apparatus (a recording and reproducing apparatus for recording and reproducing data) having a ring-type recording head and a giant magnetoresistive (GMR) type or tunneling magnetoresistive (TMR) type reproducing head. Further, it is preferable that a ring-type recording head is used as the servo signal writing head for the magnetic recording medium 110 according to the second embodiment. For example, a data signal is perpendicularly recorded on the magnetic layer 115 by a ring-type recording head. Also, for example, a servo signal is perpendicularly recorded on the magnetic layer 115 by a ring-type recording head.

[0150] (2) Explanation of each layer

[0151] (Base layer)

[0152] Regarding the base layer 111, the description of the base layer 11 in the first embodiment applies, so the description of the base layer 111 is omitted.

[0153] (SUL)

[0154] SUL112 includes a soft magnetic material in an amorphous state. The soft magnetic material includes, for example, at least one of Co-based materials and Fe-based materials. The Co-based material includes, for example, CoZrNb, CoZrTa, or CoZrTaNb. The Fe-based material includes, for example, FeCoB, FeCoZr, or FeCoTa.

[0155] SUL112 is a single-layer SUL and is provided directly on the base layer 111. The average thickness of SUL112 is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 30 nm or less.

[0156] The average thickness of SUL112 is determined by the same method as the method for measuring the average thickness of the magnetic layer 13 in the first embodiment. Note that the average thicknesses of the layers other than SUL112 (that is, the average thicknesses of the first and second seed layers 113A and 113B, the first and second underlayers 114A and 114B, and the magnetic layer 115) described later are also determined by the same method as the method for measuring the average thickness of the magnetic layer 13 in the first embodiment. However, the magnification of the TEM image is appropriately adjusted according to the thickness of each layer.

[0157] (The first and second seed layers)

[0158] The first seed layer 113A includes an alloy containing Ti and Cr and has an amorphous state. Further, this alloy may further contain O (oxygen). This oxygen may be impurity oxygen contained in trace amounts in the first seed layer 113A when the first seed layer 113A is formed by a film formation method such as a sputtering method.

[0159] Here, “alloy” means at least one of a solid solution, a eutectic, and an intermetallic compound containing Ti and Cr. “Amorphous state” means that a halo is observed by an X-ray diffraction or an electron beam diffraction method and the crystal structure cannot be specified.

[0160] The atomic ratio of Ti to the total amount of Ti and Cr contained in the first seed layer 113A is preferably in the range of 30 atomic % or more and 100 atomic % or less, more preferably 50 atomic % or more and 100 atomic % or less. When the atomic ratio of Ti is less than 30%, the (100) plane of the body-centered cubic (bcc) structure of Cr becomes oriented, and there is a risk that the orientation of the first and second underlayers 114A and 114B formed on the first seed layer 113A may deteriorate.

[0161] The atomic ratio of Ti is obtained as follows. While ion milling the magnetic recording medium 110 from the magnetic layer 115 side, depth direction analysis (depth profile measurement) of the first seed layer 113A by Auger Electron Spectroscopy (hereinafter referred to as "AES") is performed. Next, from the obtained depth profile, the average composition (average atomic ratio) of Ti and Cr in the film thickness direction is determined. Next, using the determined average compositions of Ti and Cr, the atomic ratio of Ti is determined.

[0162] When the first seed layer 113A contains Ti, Cr, and O, the atomic ratio of O to the total amount of Ti, Cr, and O contained in the first seed layer 113A is preferably 15 atomic % or less, more preferably 10 atomic % or less. When the atomic ratio of O exceeds 15 atomic %, TiO 2 crystals are formed, which may affect the crystal nucleation of the first and second underlayers 114A and 114B formed on the first seed layer 113A, and there is a risk that the orientation of the first and second underlayers 114A and 114B may deteriorate. The atomic ratio of O is obtained using the same analysis method as the atomic ratio of Ti.

[0163] The alloy contained in the first seed layer 113A may further contain an element other than Ti and Cr as an additive element. This additive element may be, for example, one or more elements selected from the group consisting of Nb, Ni, Mo, Al, and W.

[0164] The average thickness of the first seed layer 113A is preferably 2 nm or more and 15 nm or less, more preferably 3 nm or more and 10 nm or less.

[0165] The second seed layer 113B contains, for example, NiW or Ta and has a crystalline state. The average thickness of the second seed layer 113B is preferably 3 nm or more and 20 nm or less, more preferably 5 nm or more and 15 nm or less.

[0166] The first and second seed layers 113A and 113B do not have a crystal structure similar to the first and second underlayers 114A and 114B and are not seed layers provided for the purpose of crystal growth. Instead, they are seed layers that improve the perpendicular orientation of the first and second underlayers 114A and 114B due to their amorphous state.

[0167] (The first and second underlayers)

[0168] The first and second underlayers 114A and 114B preferably have the same crystal structure as the magnetic layer 115. When the magnetic layer 115 contains a Co-based alloy, the first and second underlayers 114A and 114B preferably contain a material having the same hexagonal close-packed (hcp) structure as the Co-based alloy, and the c-axis of the structure is preferably oriented in the direction perpendicular to the film surface (i.e., the film thickness direction). This is because it can enhance the orientation of the magnetic layer 115 and relatively well match the lattice constants between the second underlayer 114B and the magnetic layer 115. As the material having the hexagonal close-packed (hcp) structure, a material containing Ru is preferably used, specifically, Ru alone or a Ru alloy is preferable. As the Ru alloy, for example, Ru-SiO 2 , Ru-TiO 2 , and Ru-ZrO 2 and other Ru alloy oxides can be mentioned, and the Ru alloy may be any one of these.

[0169] As described above, similar materials can be used for the first and second underlayers 114A and 114B. However, the intended effects of the first and second underlayers 114A and 114B are different. Specifically, the second underlayer 114B has a film structure that promotes the granular structure of the magnetic layer 115 above it, and the first underlayer 114A has a film structure with high crystal orientation. In order to obtain such a film structure, it is preferable to use different film formation conditions such as sputtering conditions for the first and second underlayers 114A and 114B respectively.

[0170] The average thickness of the first underlayer 114A is preferably 3 nm or more and 15 nm or less, more preferably 5 nm or more and 10 nm or less. The average thickness of the second underlayer 114B is preferably 7 nm or more and 40 nm or less, more preferably 10 nm or more and 25 nm or less.

[0171] (Magnetic layer)

[0172] The magnetic layer (also referred to as the recording layer) 115 can be a perpendicular magnetic recording layer in which magnetic materials are vertically oriented. From the viewpoint of improving the recording density, the magnetic layer 115 is preferably a granular magnetic layer containing a Co-based alloy. This granular magnetic layer is composed of ferromagnetic crystal particles containing a Co-based alloy and a non-magnetic grain boundary (non-magnetic body) surrounding these ferromagnetic crystal particles. More specifically, this granular magnetic layer is composed of columns (columnar crystals) containing a Co-based alloy and non-magnetic grain boundaries (for example, oxides such as SiO 2 etc.) that surround these columns and magnetically separate each column. In this structure, a magnetic layer 115 having a structure in which each column is magnetically separated can be formed.

[0173] The Co-based alloy has a hexagonal close-packed (hcp) structure, and its c-axis is oriented in the direction perpendicular to the film surface (film thickness direction). As the Co-based alloy, it is preferable to use a CoCrPt-based alloy containing at least Co, Cr, and Pt. The CoCrPt-based alloy may further contain additional elements. Examples of the additional elements include one or more elements selected from the group consisting of Ni and Ta.

[0174] The non-magnetic grain boundary surrounding the ferromagnetic crystal particles contains a non-magnetic metal material. Here, the metal includes semi-metals. As the non-magnetic metal material, for example, at least one of metal oxides and metal nitrides can be used. From the viewpoint of more stably maintaining the granular structure, it is preferable to use a metal oxide. Examples of the metal oxide include metal oxides containing at least one or more elements selected from the group consisting of Si, Cr, Co, Al, Ti, Ta, Zr, Ce, Y, and Hf. Metal oxides containing at least Si oxide (i.e., SiO 2 ) are preferable. Specific examples of the metal oxide include SiO 2 , Cr 2 O 3 , CoO, Al 2 O 3 , TiO 2 , Ta 2 O 5 , ZrO 2 , and HfO 2 etc. Examples of the metal nitride include metal nitrides containing at least one or more elements selected from the group consisting of Si, Cr, Co, Al, Ti, Ta, Zr, Ce, Y, and Hf. Specific examples of the metal nitride include SiN, TiN, and AlN.

[0175] It is preferable that the CoCrPt-based alloy contained in the ferromagnetic crystal particles and the Si oxide contained in the non-magnetic grain boundary have the average composition shown in the following formula (1). This is because it can suppress the influence of the demagnetizing field and realize a saturation magnetization amount Ms that can ensure sufficient reproduction output, thereby realizing further improvement in recording and reproduction characteristics. (Co x Pty Cr 100-x-y ) 100-z -(SiO 2 ) z ···(1) (However, in formula (1), x, y, and z are respectively values within the ranges of 69 ≤ x ≤ 75, 10 ≤ y ≤ 16, and 9 ≤ z ≤ 12.)

[0176] The above composition can be obtained as follows. While ion milling the magnetic recording medium 110 from the magnetic layer 115 side, depth direction analysis of the magnetic layer 115 is performed by AES to obtain the average composition (average atomic ratio) of Co, Pt, Cr, Si, and O in the film thickness direction.

[0177] The average thickness t m [nm] of the magnetic layer 115 is preferably 9 nm ≤ t m ≤ 90 nm, more preferably 9 nm ≤ t m ≤ 20 nm, and even more preferably 9 nm ≤ t m ≤ 15 nm. By the average thickness t m of the magnetic layer 115 being within the above numerical range, the electromagnetic conversion characteristics can be improved.

[0178] (Protective layer)

[0179] The protective layer 116 contains, for example, a carbon material or silicon dioxide (SiO 2 ). From the perspective of the film strength of the protective layer 116, it is preferable to contain a carbon material. Examples of the carbon material include graphite, diamond-like carbon (DLC), or diamond, etc.

[0180] (Lubricating layer)

[0181] The lubricating layer 117 contains at least one kind of lubricant. The lubricating layer 117 may further contain various additives as required, such as rust inhibitors and the like. The lubricant has at least two carboxyl groups and one ester bond, and contains at least one kind of carboxylic acid compound represented by the following general formula (1). The lubricant may further contain lubricants of types other than the carboxylic acid compound represented by the following general formula (1). General formula (1):

Chemical formula

[0182] The above carboxylic acid compound is preferably represented by the following general formula (2) or (3). General formula (2):

Chemical formula

Chemical formula

[0183] The lubricant preferably contains one or both of the carboxylic acid compounds represented by the above general formulas (2) and (3).

[0184] When a lubricant containing a carboxylic acid compound represented by the general formula (1) is applied to the magnetic layer 115 or the protective layer 116, etc., a lubricating action is exhibited due to the cohesive force between the fluorohydrocarbon groups or hydrocarbon groups Rf which are hydrophobic groups. When the Rf group is a fluorohydrocarbon group, it preferably has a total carbon number of 6 to 50 and the total carbon number of the fluorinated hydrocarbon group is 4 to 20. The Rf group may be, for example, a saturated or unsaturated linear, branched, or cyclic hydrocarbon group, but is preferably a saturated linear hydrocarbon group.

[0185] For example, when the Rf group is a hydrocarbon group, it is preferably a group represented by the following general formula (4). General formula (4):

Chemical formula

[0186] Also, when the Rf group is a fluorohydrocarbon group, it is preferably a group represented by the following general formula (5). General formula (5):

Chemical formula

[0187] The fluorinated hydrocarbon group may be concentrated at one position in the molecule as described above, or may be dispersed as in the following general formula (6), and -CF 3 and -CF 2 - not only, but also -CHF 2 and -CHF- etc. may be used. General formula (6):

Chemical formula

[0188] In General Formulas (4), (5), and (6), the reason for limiting the number of carbon atoms as described above is that when the number of carbon atoms (l, or the sum of m and n) constituting the alkyl group or fluorine-containing alkyl group is equal to or greater than the above lower limit, the length becomes appropriate, the cohesive force between hydrophobic groups is effectively exerted, a good lubricating action is exhibited, and the friction and wear durability are improved. Further, when the number of carbon atoms is equal to or less than the above upper limit, the solubility of the lubricant composed of the carboxylic acid-based compound in the solvent is kept good.

[0189] In particular, when the Rf group in General Formulas (1), (2), and (3) contains a fluorine atom, it is effective in reducing the friction coefficient and further improving the running performance. However, it is preferable to provide a hydrocarbon group between the fluorine-containing hydrocarbon group and the ester bond to separate them and ensure the stability of the ester bond to prevent hydrolysis.

[0190] Further, the Rf group may have a fluoroalkyl ether group or a perfluoropolyether group.

[0191] The R group in General Formula (1) may be absent, but when present, it is preferably a hydrocarbon chain having a relatively small number of carbon atoms.

[0192] Further, the Rf group or the R group may contain one or more elements selected from nitrogen, oxygen, sulfur, phosphorus, and halogen as constituent elements, and in addition to the functional groups described above, may further have a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, an ester bond, and the like.

[0193] The carboxylic acid-based compound represented by General Formula (1) is preferably at least one of the compounds shown below. That is, the lubricant preferably contains at least one of the compounds shown below. CF 3 (CF 2 )7 (CH 2 ) 10 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 3 (CH 2 ) 10 COOCH(COOH)CH 2 COOH C 17 H 35 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 2 OCOCH 2 CH(C 18 H 37 )COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 COOCH(COOH)CH 2 COOH CHF 2 (CF 2 ) 7 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 2 OCOCH 2 CH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 6 OCOCH 2 CH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 11 OCOCH 2 CH(COOH)CH 2COOH CF 3 (CF 2 ) 3 (CH 2 ) 6 OCOCH 2 CH(COOH)CH 2 COOH C 18 H 37 OCOCH 2 CH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 4 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 3 (CH 2 ) 4 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 3 (CH 2 ) 7 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 9 (CH 2 ) 10 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 (CH 2 ) 12 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 5 (CH 2 ) 10 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 CH(C9 H 19 )CH 2 CH=CH(CH 2 ) 7 COOCH(COOH)CH 2 COOH CF 3 (CF 2 ) 7 CH(C 6 H 13 )(CH 2 ) 7 COOCH(COOH)CH 2 COOH CH 3 (CH 2 ) 3 (CH 2 CH 2 CH(CH 2 CH 2 (CF 2 ) 9 CF 3 )) 2 (CH 2 ) 7 COOCH(COOH)CH 2 COOH

[0194] The carboxylic acid compound represented by the general formula (1) is soluble in a non-fluorine-based solvent with a low environmental load. For example, it has the advantage that operations such as coating, dipping, and spraying can be carried out using general-purpose solvents such as hydrocarbon solvents, ketone solvents, alcohol solvents, and ester solvents. Specifically, examples of the general-purpose solvents include solvents such as hexane, heptane, octane, decane, dodecane, benzene, toluene, xylene, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, diethyl ether, tetrahydrofuran, dioxane, and cyclohexanone.

[0195] When the protective layer 116 contains a carbon material, when the carboxylic acid compound is applied onto the protective layer 116 as a lubricant, two carboxyl groups which are polar bases of lubricant molecules and at least one ester bond group are adsorbed onto the protective layer 116, and a lubricating layer 117 with particularly good durability can be formed by the cohesive force between hydrophobic groups.

[0196] Note that the lubricant is not only held as the lubricating layer 117 on the surface of the magnetic recording medium 110 as described above, but may also be contained and held in layers such as the magnetic layer 115 and the protective layer 116 constituting the magnetic recording medium 110.

[0197] (Back layer)

[0198] Regarding the back layer 118, the description regarding the back layer 14 in the first embodiment applies.

[0199] (3) Physical properties and structure

[0200] All of the descriptions regarding the physical properties and structure described in (3) of 2. above also apply to the second embodiment. For example, the water vapor transmission rate, Young's modulus, and humidity expansion coefficient β measured for the magnetic recording medium 110 according to the Lyssy method may be the same as those in the first embodiment. Therefore, the description of the physical properties and structure of the magnetic recording medium of the second embodiment is omitted.

[0201] (4) Configuration of sputtering apparatus

[0202] Hereinafter, with reference to FIG. 6, an example of the configuration of a sputtering apparatus 120 used for manufacturing the magnetic recording medium 110 according to the second embodiment will be described. This sputtering apparatus 120 is a continuous winding type sputtering apparatus used for forming the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115. As shown in FIG. 6, the sputtering apparatus 120 includes a film formation chamber 121, a drum 122 which is a metal can (rotating body), cathodes 123a to 123f, a supply reel 124, a take-up reel 125, and a plurality of guide rollers 127a to 127c, 128a to 128c. The sputtering apparatus 120 is, for example, a DC (direct current) magnetron sputtering type apparatus, but the sputtering method is not limited to this method.

[0203] The film formation chamber 121 is connected to a vacuum pump (not shown) via an exhaust port 126, and the atmosphere inside the film formation chamber 121 is set to a predetermined degree of vacuum by this vacuum pump. Inside the film formation chamber 121, a drum 122 having a rotatable configuration, a supply reel 124, and a take-up reel 125 are arranged. Inside the film formation chamber 121, a plurality of guide rollers 127a to 127c for guiding the conveyance of the base layer 111 between the supply reel 124 and the drum 122 are provided, and a plurality of guide rollers 128a to 128c for guiding the conveyance of the base layer 111 between the drum 122 and the take-up reel 125 are provided. During sputtering, the base layer 111 unwound from the supply reel 124 is wound onto the take-up reel 125 via the guide rollers 127a to 127c, the drum 122, and the guide rollers 128a to 128c. The drum 122 has a cylindrical shape, and the long base layer 111 is conveyed along the cylindrical peripheral surface of the drum 122. The drum 122 is provided with a cooling mechanism (not shown), and during sputtering, it is cooled to about -20°C, for example. Inside the film formation chamber 121, a plurality of cathodes 123a to 123f are arranged facing the peripheral surface of the drum 122. Targets are set on these cathodes 123a to 123f, respectively. Specifically, targets for forming the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are set on the cathodes 123a, 123b, 123c, 123d, 123e, 123f, respectively. A plurality of types of films, namely the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115, are formed simultaneously by these cathodes 123a to 123f.

[0204] In the sputtering apparatus 120 having the above-described configuration, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 can be continuously formed by the Roll-to-Roll method.

[0205] (5) Method for manufacturing a magnetic recording medium

[0206] The magnetic recording medium 110 according to the second embodiment can be manufactured, for example, as follows.

[0207] First, using the sputtering apparatus 120 shown in FIG. 6, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are sequentially formed on the surface of the base layer 111. Specifically, the film formation is performed as follows. First, the film formation chamber 121 is evacuated to a predetermined pressure. Then, while introducing a process gas such as Ar gas into the film formation chamber 121, the targets set on the cathodes 123a to 123f are sputtered. As a result, the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 are sequentially formed on the surface of the traveling base layer 111.

[0208] The atmosphere in the film formation chamber 121 during sputtering is set, for example, to about 1×10 -5 Pa to 5×10 -5 Pa. The film thickness and characteristics of the SUL 112, the first seed layer 113A, the second seed layer 113B, the first underlayer 114A, the second underlayer 114B, and the magnetic layer 115 can be controlled by adjusting the tape line speed at which the base layer 111 is wound, the pressure of the process gas such as Ar gas introduced during sputtering (sputtering gas pressure), and the input power.

[0209] Next, a protective layer 116 is formed on the magnetic layer 115. As a method for forming the protective layer 116, for example, a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method can be used.

[0210] Next, a paint for forming the back layer is prepared by kneading and dispersing a binder, inorganic particles, a lubricant, etc. in a solvent. Next, the paint for forming the back layer is applied onto the back surface of the base layer 111 and dried, thereby forming the back layer 118 on the back surface of the base layer 111.

[0211] Next, for example, a lubricant is applied onto the protective layer 116 to form a lubricating layer 117. As the method for applying the lubricant, for example, various coating methods such as gravure coating and dip coating can be used. Next, if necessary, the magnetic recording medium 110 is cut to a predetermined width. Thus, the magnetic recording medium 110 shown in FIG. 5 is obtained.

[0212] (6) Modification

[0213] The magnetic recording medium 110 may further include an underlayer between the base layer 111 and the SUL 112. Since the SUL 112 has an amorphous state, it does not play a role in promoting the epitaxial growth of the layer formed on the SUL 112, but it is required not to disturb the crystal orientation of the first and second underlayers 114A and 114B formed on the SUL 112. For this purpose, it is preferable that the soft magnetic material has a fine structure in which columns are not formed. However, when the influence of the release of gas such as moisture from the base layer 111 is large, the soft magnetic material coarsens, and there is a risk of disturbing the crystal orientation of the first and second underlayers 114A and 114B formed on the SUL 112. In order to suppress the influence of the release of gas such as moisture from the base layer 111, as described above, it is preferable to provide an underlayer containing an alloy containing Ti and Cr and having an amorphous state between the base layer 111 and the SUL 112. As a specific configuration of this underlayer, the same configuration as the first seed layer 113A of the second embodiment can be adopted.

[0214] The magnetic recording medium 110 may not include at least one of the second seed layer 113B and the second underlayer 114B. However, from the viewpoint of improving the SNR, it is more preferable to include both the second seed layer 113B and the second underlayer 114B.

[0215] The magnetic recording medium 110 may be provided with an APC-SUL (Antiparallel Coupled SUL) instead of a single-layer SUL.

[0216] 4. Third Embodiment (Example of Vacuum Thin Film Type Magnetic Recording Medium)

[0217] (1) (Configuration of Magnetic Recording Medium)

[0218] As shown in FIG. 7, the magnetic recording medium 130 according to the third embodiment includes a base layer 111, an SUL 112, a seed layer 131, a first underlayer 132A, a second underlayer 132B, and a magnetic layer 115. In the third embodiment, the same parts as those in the second embodiment are denoted by the same reference numerals and the description thereof is omitted.

[0219] The SUL 112, the seed layer 131, the first and second underlayers 132A and 132B are provided between one main surface of the base layer 111 and the magnetic layer 115, and are laminated in the order of the SUL 112, the seed layer 131, the first underlayer 132A, and the second underlayer 132B from the base layer 111 toward the magnetic layer 115.

[0220] (2) (Description of Each Layer)

[0221] (Seed Layer)

[0222] The seed layer 131 contains Cr, Ni, and Fe, has a face-centered cubic lattice (fcc) structure, and is preferentially oriented such that the (111) plane of this face-centered cubic structure is parallel to the surface of the base layer 111. Here, preferential orientation means a state in which the diffraction peak intensity from the (111) plane of the face-centered cubic lattice structure is larger than the diffraction peaks from other crystal planes in the θ-2θ scan of the X-ray diffraction method, or a state in which only the diffraction peak intensity from the (111) plane of the face-centered cubic lattice structure is observed in the θ-2θ scan of the X-ray diffraction method.

[0223] From the perspective of SNR improvement, the intensity ratio of X-ray diffraction of the seed layer 131 is preferably 60 cps / nm or more, more preferably 70 cps / nm or more, and even more preferably 80 cps / nm or more. Here, the intensity ratio of X-ray diffraction of the seed layer 131 is a value (I / D (cps / nm)) obtained by dividing the intensity I (cps) of X-ray diffraction of the seed layer 131 by the average thickness D (nm) of the seed layer 131.

[0224] Cr, Ni, and Fe included in the seed layer 131 preferably have an average composition represented by the following formula (2). Cr X (Ni Y Fe 100-Y ) 100-X ···(2) (However, in formula (2), X is in the range of 10 ≦ X ≦ 45, and Y is in the range of 60 ≦ Y ≦ 90.) When X is within the above range, the (111) orientation of the face-centered cubic lattice structure of Cr, Ni, and Fe is improved, and a better SNR can be obtained. Similarly, when Y is within the above range, the (111) orientation of the face-centered cubic lattice structure of Cr, Ni, and Fe is improved, and a better SNR can be obtained.

[0225] The average thickness of the seed layer 131 is preferably 5 nm or more and 40 nm or less. By setting the average thickness of the seed layer 131 within this range, the (111) orientation of the face-centered cubic lattice structure of Cr, Ni, and Fe can be improved, and a better SNR can be obtained. The average thickness of the seed layer 131 is obtained in the same manner as the magnetic layer 13 in the first embodiment. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the seed layer 131.

[0226] (The first and second underlayers)

[0227] The first underlayer 132A contains Co and O having a face-centered cubic lattice structure and has a columnar (columnar crystal) structure. In the first underlayer 132A containing Co and O, an effect (function) almost the same as that of the second underlayer 132B containing Ru can be obtained. The concentration ratio of the average atomic concentration of O to the average atomic concentration of Co ((average atomic concentration of O) / (average atomic concentration of Co)) is 1 or more. When the concentration ratio is 1 or more, the effect of providing the first underlayer 132A is improved, and a better SNR can be obtained.

[0228] From the viewpoint of improving SNR, the columnar structure is preferably inclined. The direction of the inclination is preferably the longitudinal direction of the long magnetic recording medium 130. The reason why the longitudinal direction is preferred is as follows. The magnetic recording medium 130 according to the present embodiment is a so-called magnetic recording medium for linear recording, and the recording track is parallel to the longitudinal direction of the magnetic recording medium 130. Further, the magnetic recording medium 130 according to the present embodiment is also a so-called perpendicular magnetic recording medium. From the viewpoint of recording characteristics, it is preferable that the crystal orientation axis of the magnetic layer 115 is in the vertical direction. However, due to the influence of the inclination of the columnar structure of the first underlayer 132A, the crystal orientation axis of the magnetic layer 115 may be inclined. In the magnetic recording medium 130 for linear recording, due to the relationship with the head magnetic field during recording, a configuration in which the crystal orientation axis of the magnetic layer 115 is inclined in the longitudinal direction of the magnetic recording medium 130 can reduce the influence on the recording characteristics due to the inclination of the crystal orientation axis compared to a configuration in which the crystal orientation axis of the magnetic layer 115 is inclined in the width direction of the magnetic recording medium 130. In order to incline the crystal orientation axis of the magnetic layer 115 in the longitudinal direction of the magnetic recording medium 130, it is preferable that the inclination direction of the columnar structure of the first underlayer 132A is the longitudinal direction of the magnetic recording medium 130 as described above.

[0229] The inclination angle of the column structure is preferably greater than 0° and equal to or less than 60°. In the range where the inclination angle is greater than 0° and equal to or less than 60°, since the change in the tip shape of the columns included in the first underlayer 132A is large and almost in the shape of a triangular mountain, the effect of the granular structure is enhanced, the noise is reduced, and the SNR tends to improve. On the other hand, when the inclination angle exceeds 60°, since the change in the tip shape of the columns included in the first underlayer 132A is small and it is difficult to become almost in the shape of a triangular mountain, the low-noise effect tends to fade.

[0230] The average particle size of the column structure is 3 nm or more and 13 nm or less. When the average particle size is less than 3 nm, since the average particle size of the column structure included in the magnetic layer 115 becomes small, there is a risk that the ability to retain recording will decrease with current magnetic materials. On the other hand, when the average particle size is 13 nm or less, noise can be suppressed and a better SNR can be obtained.

[0231] The average thickness of the first underlayer 132A is preferably 10 nm or more and 150 nm or less. When the average thickness of the first underlayer 132A is 10 nm or more, the (111) orientation of the face-centered cubic lattice structure of the first underlayer 132A is improved, and a better SNR can be obtained. On the other hand, when the average thickness of the first underlayer 132A is 150 nm or less, an increase in the particle size of the columns can be suppressed. Therefore, noise can be suppressed and a better SNR can be obtained. The average thickness of the first underlayer 132A is determined in the same manner as the magnetic layer 13 in the first embodiment. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the first underlayer 132A.

[0232] The second underlayer 132B preferably has the same crystal structure as the magnetic layer 115. When the magnetic layer 115 contains a Co-based alloy, the second underlayer 132B preferably contains a material having a hexagonal close-packed (hcp) structure similar to that of the Co-based alloy, and the c-axis of the structure is oriented in a direction perpendicular to the film surface (i.e., the film thickness direction). This is because it can enhance the orientation of the magnetic layer 115 and relatively well match the lattice constants between the second underlayer 132B and the magnetic layer 115. As the material having a hexagonal close-packed structure, a material containing Ru is preferably used, and specifically, Ru alone or a Ru alloy is preferred. Examples of the Ru alloy include Ru alloy oxides such as Ru-SiO 2 , Ru-TiO 2 or Ru-ZrO 2 .

[0233] The average thickness of the second underlayer 132B may be thinner than that of the underlayer (e.g., an underlayer containing Ru) in a general magnetic recording medium, and for example, it can be set to 1 nm or more and 5 nm or less. Since the seed layer 131 and the first underlayer 132A having the above-described configuration are provided under the second underlayer 132B, a good SNR can be obtained even if the average thickness of the second underlayer 132B is as thin as described above. Note that the average thickness of the second underlayer 132B is obtained in the same manner as the magnetic layer 13 in the first embodiment. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the second underlayer 132B.

[0234] 5. An embodiment of the magnetic recording cartridge according to the present technology

[0235] [Configuration of the cartridge]

[0236] The present technology also provides a magnetic recording cartridge (also referred to as a tape cartridge) including a magnetic recording medium according to the present technology. 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 and reproducing apparatus, a storage unit, and a control unit that stores information received from the recording and reproducing apparatus via the communication unit in the storage unit, and reads out information from the storage unit in response to a request from the recording and reproducing apparatus and transmits the information to the recording and reproducing apparatus via the communication unit. The information may include adjustment information for adjusting the tension applied in the longitudinal direction of the magnetic recording medium.

[0237] With reference to FIG. 8, an example of the configuration of a magnetic recording cartridge 10A including a magnetic recording medium T having the above-described configuration will be described.

[0238] FIG. 8 is an exploded perspective view showing an example of the configuration of the magnetic recording cartridge 10A. The magnetic recording cartridge 10A is a magnetic recording cartridge compliant with the LTO (Linear Tape-Open) standard. Inside a cartridge case 10B composed of a lower shell 212A and an upper shell 212B, there are provided a reel 10C around which a magnetic tape (tape-shaped 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 releasing the locked state of the reel 10C, a slide door 217 for opening and closing a tape outlet 212C provided in the cartridge case 10B across the lower shell 212A and the upper shell 212B, a door spring 218 for biasing the slide door 217 to the closed position of the tape outlet 212C, a write protect 219 for preventing accidental erasure, and a cartridge memory 211. The reel 10C has a substantially disk shape with an opening at the center, and is composed of a reel hub 213A and a flange 213B made of a hard material such as plastic. A leader pin 220 is provided at one end of the magnetic tape T.

[0239] The cartridge memory 211 is provided near one corner of the magnetic recording cartridge 10A. In a state where the magnetic recording cartridge 10A is loaded into the recording and reproducing apparatus 80, the cartridge memory 211 faces a reader / writer (not shown) of the recording and reproducing apparatus 80. The cartridge memory 211 communicates with the recording and reproducing apparatus 30, specifically a reader / writer (not shown), according to a wireless communication standard compliant with the LTO standard.

[0240] [Configuration of Cartridge Memory]

[0241] With reference to FIG. 9, an example of the configuration of the cartridge memory 211 will be described.

[0242] FIG. 9 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) according to a specified communication standard, a rectification / power supply circuit 332 that generates power by generating and rectifying an induced electromotive force from the radio wave received by the antenna coil 331 to generate a power supply, a clock circuit 333 that generates a clock using the induced electromotive force from the radio wave received by the antenna coil 331, a detection / modulation circuit 334 that performs detection of the radio wave received by the antenna coil 331 and modulation of the signal transmitted by the antenna coil 331, a controller (control unit) 335 composed of a logic circuit or the like that discriminates commands and data from the digital signal extracted from the detection / modulation circuit 334 and processes them, and a memory (storage unit) 336 that stores information. Further, the cartridge memory 211 includes a capacitor 337 connected in parallel to the antenna coil 331, and the antenna coil 331 and the capacitor 337 constitute a resonance circuit.

[0243] The memory 336 stores information related to the magnetic recording cartridge 10A and the like. The memory 336 is a non-volatile memory (NVM). The storage capacity of the memory 336 is preferably about 32 KB or more. For example, when the magnetic recording cartridge 10A complies with the LTO format standard after the next generation, the memory 336 has a storage capacity of about 32 KB.

[0244] The memory 336 has a first storage area 336A and a second storage area 336B. The first storage area 336A corresponds to the storage area of the cartridge memory of the LTO standard before LTO8 (hereinafter referred to as "conventional cartridge memory"), and is an area for storing information compliant with the LTO standard before LTO8. Information compliant with the LTO standard before LTO8 is, for example, manufacturing information (such as the unique number of the magnetic recording cartridge 10A), usage history (such as the thread count), etc.

[0245] The second storage area 336B corresponds to an extended storage area for the storage area of the conventional cartridge memory. The second storage area 336B is an area for storing additional information. Here, the additional information means information related to the magnetic recording cartridge 10A that is not defined by the LTO standard before LTO8. Examples of the additional information include tension adjustment information, management ledger data, index information, or thumbnail information of the video stored on the magnetic tape T, but are not limited to these data. The tension adjustment information includes the distance between adjacent servo bands (the distance between servo patterns recorded on adjacent servo bands) when recording data on the magnetic tape T. The distance between adjacent servo bands is an example of width-related information related to the width of the magnetic tape T. Details of the distance between servo bands will be described later. In the following description, the information stored in the first storage area 336A may be referred to as "first information", and the information stored in the second storage area 336B may be referred to as "second information".

[0246] The memory 336 may have a plurality of banks. In this case, a first storage area 336A may be constituted by some of the plurality of banks, and a second storage area 336B may be constituted by the remaining banks. Specifically, for example, when the magnetic recording cartridge 10A conforms to the LTO format standard after the next generation, the memory 336 has two banks having a storage capacity of about 16 KB, and the first storage area 336A is constituted by one of the two banks, and the second storage area 336B may be constituted by the other bank.

[0247] The antenna coil 331 induces an induced voltage by electromagnetic induction. The controller 335 communicates with the recording and reproducing apparatus 80 via the antenna coil 331 in accordance with a specified communication standard. Specifically, for example, mutual authentication, transmission and reception of commands, or exchange of data is performed.

[0248] The controller 335 stores the information received from the recording and reproducing apparatus 80 via the antenna coil 331 in the memory 336. The controller 335 reads out the information from the memory 336 in response to a request from the recording and reproducing apparatus 80, and transmits it to the recording and reproducing apparatus 80 via the antenna coil 331.

[0249] 6. Modification example of the magnetic recording cartridge according to the present technology

[0250] [Configuration of cartridge]

[0251] In the above-described embodiment of the magnetic recording cartridge, the case where the magnetic tape cartridge is a one-reel type cartridge has been described. However, the magnetic recording cartridge of the present technology may be a two-reel type cartridge. That is, the magnetic recording cartridge of the present technology may have one or a plurality (for example, two) of reels around which the magnetic tape is wound. Hereinafter, an example of the magnetic recording cartridge of the present technology having two reels will be described with reference to FIG. 10.

[0252] FIG. 10 is an exploded perspective view showing an example of the configuration of a 2-reel type cartridge 421. The cartridge 421 includes an upper half 402 made of synthetic resin, a transparent window member 423 that is fitted and fixed to a window portion 402a opened on the upper surface of the upper half 402, a reel holder 422 that is fixed inside the upper half 402 to prevent the reels 406 and 407 from rising, a lower half 405 corresponding to the upper half 402, reels 406 and 407 housed in a space formed by combining the upper half 402 and the lower half 405, a magnetic tape MT1 wound around the reels 406 and 407, a front lid 409 that closes the front side opening formed by combining the upper half 402 and the lower half 405, and a back lid 409A that protects the magnetic tape MT1 exposed at this front side opening.

[0253] The reel 406 includes a lower flange 406b having a cylindrical hub portion 406a around which the magnetic tape MT1 is wound at the center, an upper flange 406c having substantially 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.

[0254] The window member 423 is provided with mounting holes 423a for assembling a reel holder 422, which is a reel holding means for preventing the reels 406 and 407 from rising, at positions corresponding to the reels 406 and 407. The magnetic tape MT1 is the same as the magnetic tape T in the first embodiment.

[0255] The present technology can also adopt the following configuration. [1] A tape-shaped magnetic recording medium, comprising a magnetic layer, a non-magnetic layer, a base layer, and a back layer in this order, wherein the magnetic layer and the non-magnetic layer are in contact with each other, the non-magnetic layer and the base layer are in contact with each other, the average thickness of the magnetic recording medium is 5.74 μm or less, the Young's modulus in the MD direction (longitudinal direction) of the base layer is 5.9 GPa or less, The water vapor transmission rate of the magnetic recording medium measured according to the Lyssy method is 2.93 g / m 2 ·day or less, said magnetic recording medium. [2] The water vapor transmission rate is 2.0 g / m 2 ·day or less, the magnetic recording medium according to [1]. [3] The water vapor transmission rate is 1.84 g / m 2 ·day or less, the magnetic recording medium according to [1]. [4] The water vapor transmission rate of the base layer measured according to the Lyssy method is 7.57 g / m 2 ·day or less, the magnetic recording medium according to any one of [1] to [3]. [5] The water vapor transmission rate of the base layer is 4.00 g / m 2 ·day or less, the magnetic recording medium according to any one of [1] to [3]. [6] The water vapor transmission rate of the base layer is 3.00 g / m 2 ·day or less, the magnetic recording medium according to any one of [1] to [3]. [7] The water vapor transmission rate of the base layer is 2.19 g / m 2 ·day or less, the magnetic recording medium according to any one of [1] to [6]. [8] The Young's modulus in the MD direction (longitudinal direction) of the base layer is 5.3 GPa or less, the magnetic recording medium according to any one of [1] to [7]. [9] The average thickness of the magnetic recording medium is 5.60 μm or less, the magnetic recording medium according to any one of [1] to [8].

[10] The average thickness of the magnetic recording medium is 5.30 μm or less, the magnetic recording medium according to any one of [1] to [8].

[11] The thickness of the nonmagnetic layer is 1.2 μm or less, the magnetic recording medium according to any one of [1] to

[10] .

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

[11] , wherein the thickness of the base layer is 4.5 μm or less.

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

[12] , wherein the thickness of the back layer is 0.6 μm or less.

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

[13] , wherein the humidity expansion coefficient β at a temperature of 10 °C is 6.5 ppm / %RH or less.

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

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

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

[14] , wherein the magnetic layer and the non-magnetic layer are vacuum thin films.

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

[16] is housed in a case in a state of being wound around a reel.

[0256] 7. Examples

[0257] Hereinafter, the present technology will be specifically described by way of examples, but the present technology is not limited to only these examples.

[0258] In the following examples and comparative examples, the water vapor transmission rate of the magnetic tape, the Young's modulus of the magnetic tape, the thickness t T of the non-magnetic layer (underlayer), the thickness of the base layer, the thickness of the back layer, and the thickness t m of the magnetic layer, and the humidity expansion coefficient β are values obtained by the measurement methods described in the first embodiment.

[0259] [Example 1] (Step of preparing a coating material for forming a magnetic layer) A coating material for forming a magnetic layer was prepared as follows. First, a first composition having the following formulation was kneaded with an extruder. Next, the kneaded first composition and a second composition having the following formulation were added to a stirring tank equipped with a disperser and premixed. Subsequently, sand mill mixing was further performed and filter treatment was performed to prepare a coating material for forming a magnetic layer.

[0260] (First Composition) Magnetic powder (hexagonal ferrite having an M-type structure, composition: Ba-Ferrite, average particle volume: 1600 nm3): 100 parts by mass Vinyl chloride resin (30 mass% cyclohexanone solution): 60 parts by mass (Degree of polymerization 300, Mn = 10000, OSO as a polar group 3 K = 0.07 mmol / g, contains 0.3 mmol / g of secondary OH.) Aluminum oxide powder: 5 parts by mass (α-Al 2 O 3 , average particle size 0.2 μm) Carbon black: 2 parts by mass (Manufactured by Tokai Carbon Co., Ltd., product name: Seast TA)

[0261] (Second Composition) Vinyl chloride resin: 1.1 parts by mass (Resin solution: 30 mass% resin, 70 mass% cyclohexanone) 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

[0262] Finally, to the magnetic layer-forming paint prepared as described above, 2 parts by mass of polyisocyanate (product name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and 2 parts by mass of myristic acid were added as curing agents.

[0263] (Preparation Process of Underlayer-Forming Paint) The underlayer-forming paint was prepared as follows. First, the third composition with the following formulation was kneaded with an extruder. Next, the kneaded third composition and the fourth composition with the following formulation were added to a stirring tank equipped with a disper for preliminary mixing. Subsequently, further sand mill mixing was performed, followed by filter treatment to prepare the underlayer-forming paint.

[0264] (Composition No. 3) Needle-shaped iron oxide powder: 100 parts by mass (α-Fe 2 O 3 , average major axis length 0.15 μm) Vinyl chloride resin: 55.6 parts by mass (Resin solution: resin content 30% by mass, cyclohexanone 70% by mass) Carbon black: 10 parts by mass (Average particle size 20 nm)

[0265] (Composition No. 4) Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.): 18.5 parts by mass n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 108.2 parts by mass Toluene: 108.2 parts by mass Cyclohexanone: 18.5 parts by mass

[0266] Finally, to the primer-forming paint prepared as described above, 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 curing agents.

[0267] (Process for preparing the back layer-forming paint) The back layer-forming paint was prepared as follows. The following raw materials were mixed in a stirring tank equipped with a disper, and subjected to filter treatment to prepare the back layer-forming paint. Carbon black (manufactured by Asahi Co., Ltd., trade name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name: N-2304) Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass Polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation): 10 parts by mass

[0268] (Film-forming process) Using the paint produced as described above, a magnetic tape was produced as described below.

[0269] First, as a support for the base layer of the magnetic tape, a PEN film (base film) having a long shape and an average thickness of 4.0 μm was prepared. Next, a paint for forming an underlayer was applied onto one main surface of the PEN film and dried, thereby forming an underlayer on one main surface of the PEN film such that the average thickness when it becomes a final product is 1.25 μm. Next, a paint for forming a magnetic layer was applied onto the underlayer and dried, thereby forming a magnetic layer on the underlayer such that the average thickness when it becomes a final product is 0.08 μm.

[0270] Subsequently, a paint for forming a back layer was applied onto the other main surface of the PEN film on which the underlayer and the magnetic layer were formed and dried, thereby forming a back layer such that the average thickness when it becomes a final product is 0.58 μm. Then, a curing treatment was performed on the PEN film on which the underlayer, the magnetic layer, and the back layer were formed. Thereafter, a calendering treatment was performed to smooth the surface of the magnetic layer.

[0271] (Cutting step) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm). Thereby, a magnetic tape having a long shape was obtained. The obtained magnetic tape had a water vapor transmission rate of 1.84 g / m 2 ·day, a humidity expansion coefficient β at a temperature of 10 °C of 3.23 ppm / %RH, a tape TD Young's modulus of 12.4 GPa, and an average thickness t of the magnetic tape T was 5.74 μm.

[0272] [Example 2] Example 1 was different in that the base layer thickness was set to 3.60 μm, the back layer thickness was set to 0.50 μm, and the average thickness t of the magnetic tape T was set to 5.29 μm, and a magnetic tape was obtained in the same manner as in Example 1. The water vapor transmission rate of the magnetic tape was 2.93 g / m 2· day, the humidity expansion coefficient β at a temperature of 10 °C is 5.66 ppm / %RH, the tape TD Young's modulus is 8.9 GPa, and the average thickness t of the magnetic tape T was 5.29 μm.

[0273] [Comparative Example 1] Different from Example 1, a magnetic tape was obtained in the same manner as in Example 1 except that the average thickness t of the magnetic tape T was 5.65 μm. The water vapor transmission rate of the magnetic tape was 3.22 g / m 2 · day, the humidity expansion coefficient β at a temperature of 10 °C was 6.12 ppm / %RH, and the TD Young's modulus of the magnetic tape was 9.9 GPa.

[0274] [Comparative Example 2] Different from Example 1, a magnetic tape was obtained in the same manner as in Example 1 except that the back layer thickness was set to 0.50 μm and the average thickness t of the magnetic tape T was 5.23 μm. The water vapor transmission rate of the magnetic tape was 6.36 / m 2 · day, the humidity expansion coefficient β at a temperature of 10 °C was 10.12 ppm / %RH, and the TD Young's modulus of the magnetic tape was 6.77 GPa.

[0275] [Example 3] (Film formation process of SUL) First, a CoZrNb layer (SUL) with an average thickness of 100 nm was formed on the surface of a long polymer film as a non-magnetic support (base layer) under the following film formation conditions. Note that a PEN film was used as the polymer film. Film formation method: DC magnetron sputtering method Target: CoZrNb target Gas type: Ar Gas pressure: 0.1 Pa

[0276] (Film formation process of the first seed layer) Next, a TiCr layer (the first seed layer) with an average thickness of 3 nm was formed on the CoZrNb layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: TiCr target Reached vacuum degree: 5×10 -5 Pa Gas species: Ar Gas pressure: 0.5 Pa

[0277] (Film formation process of the second seed layer) Next, an NiW layer (second seed layer) with an average thickness of 10 nm was formed on the TiCr layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: NiW target Reached vacuum degree: 5×10 -5 Pa Gas species: Ar Gas pressure: 0.5 Pa

[0278] (Film formation process of the first underlayer) Next, an Ru layer (first underlayer) with an average thickness of 10 nm was formed on the NiW layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: Ru target Gas species: Ar Gas pressure: 0.5 Pa

[0279] (Film formation process of the second underlayer) Next, an Ru layer (second underlayer) with an average thickness of 20 nm was formed on the Ru layer under the following film formation conditions. Sputtering method: DC magnetron sputtering method Target: Ru target Gas species: Ar Gas pressure: 1.5 Pa

[0280] (Film formation process of the magnetic layer) Next, an (CoCrPt)-(SiO 2 ) layer (magnetic layer) with an average thickness of 14 nm was formed on the Ru layer under the following film formation conditions. Film formation method: DC magnetron sputtering method Target: (CoCrPt)-(SiO 2 ) target Gas type: Ar Gas pressure: 1.5 Pa

[0281] (Film formation process of protective layer) Next, a carbon layer (protective layer) with an average thickness of 5 nm was formed on the magnetic layer under the following film formation conditions. Film formation method: DC magnetron sputtering method Target: Carbon target Gas type: Ar Gas pressure: 1.0 Pa

[0282] (Film formation process of lubricating layer) Next, a lubricant was applied on the protective layer to form a lubricating layer. The total thickness of the sputtered film on the base layer was 45 nm.

[0283] (Film formation process of back layer) Next, a back layer forming paint was applied to the surface opposite to the magnetic layer and dried to form a back layer with an average thickness t b of 0.3 μm. As a result, a magnetic tape with an average thickness t T of 4.0 μm was obtained.

[0284] (Cutting process) The magnetic tape obtained as described above was cut into a width of 1 / 2 inch (12.65 mm).

[0285] The magnetic tape obtained as described above had a water vapor transmission rate of 0.06 g / m 2 ·day, and the water vapor transmission rate of the base layer (PEN film) alone was 2.97 g / m 2 ·day, and the water vapor transmission rate could be reduced by about 98%.

[0286] Table 1 shows the configurations and evaluation results of the magnetic tapes of Examples 1 to 2 and Comparative Examples 1 to 2.

[0287]

Table 1

[0288] In addition, each symbol in Table 1 represents the following measured values. t T : Thickness of the magnetic tape (unit: μm) β: Humidity expansion coefficient of the magnetic tape (unit: ppm / %RH) t m : Average thickness of the magnetic layer (unit: nm) t b : Average thickness of the back layer (unit: μm) Also, the measured values in the table are values rounded off at the lower digit.

[0289] [Relationship between water vapor transmission rate and humidity expansion coefficient β]

[0290] The relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the humidity expansion coefficient β at a temperature of 10°C are shown in FIG. 11. Also, the relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the humidity expansion coefficient β at a temperature of 35°C are shown in FIG. 12. Furthermore, the relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the humidity expansion coefficient β at a temperature of 60°C are shown in FIG. 13.

[0291] [Relationship between water vapor transmission rate and temperature expansion coefficient α]

[0292] The relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the temperature expansion coefficient α at a relative humidity of 10% are shown in FIG. 14. Also, the relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the temperature expansion coefficient α at a relative humidity of 40% are shown in FIG. 15. Furthermore, the relationships between the water vapor transmission rates of the magnetic tapes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 and the temperature expansion coefficient α at a relative humidity of 80% are shown in FIG. 15.

[0293] From the results shown in Table 1, the following can be understood.

[0294] The magnetic tapes of Examples 1 to 2 all had a water vapor transmission rate of the magnetic tape of 3.2 g / m 2 ·day or less, and a humidity expansion coefficient β at 10 °C of 6.00 ppm / %RH or less, and were excellent in dimensional stability in the width direction.

[0295] From the results shown in FIGS. 8 to 10, it can be seen that the water vapor transmission rate and the humidity expansion coefficient β of the magnetic tape have a correlation with R 2 being 0.8 or more in any temperature environment. That is, it can be seen that as the water vapor transmission rate decreases, the humidity expansion coefficient contributing to dimensional stability decreases, and the dimensional stability is further improved.

[0296] As described above, the embodiments and examples of the present technology have been specifically described. However, the present technology is not limited to the above-described embodiments and examples, and various modifications based on the technical idea of the present technology are possible.

[0297] For example, the configurations, methods, processes, shapes, materials, and numerical values etc. given in the above-described embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values etc. may be used as necessary. Also, chemical formulas such as compounds are representative, and as long as they are common names of the same compound, they are not limited to the valences etc. described.

[0298] Also, the configurations, methods, processes, shapes, materials, and numerical values etc. of the above-described embodiments and examples can be combined with each other as long as they do not deviate from the gist of the present technology.

[0299] Also, in this specification, the numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value respectively. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value of a certain step's numerical range may be replaced with the upper limit value or the lower limit value of another step's numerical range. The materials exemplified in this specification can be used alone or in combination of two or more as long as not particularly specified.

Description of Reference Numerals

[0300] 10 Magnetic recording medium 11 Base layer 12 Underlayer 13 Magnetic layer 14 Back layer

Claims

1. A tape-shaped magnetic recording medium, comprising: a magnetic layer, a non-magnetic layer, a base layer, and a back layer in this order, wherein the magnetic layer and the non-magnetic layer are in contact with each other, the non-magnetic layer and the base layer are in contact with each other, the average thickness of the magnetic recording medium is 5.74 μm or less, the Young's modulus in the MD direction (longitudinal direction) of the base layer is 5.9 GPa or less, The water vapor transmission rate of the magnetic recording medium, measured according to the Lyssy method, is 2.93 g / m ２ ·day or less, and and the humidity expansion coefficient β at a temperature of 10°C is 6.5 ppm / %RH or less.

2. The water vapor transmission rate is 2.00 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

3. The water vapor transmission rate is 1.84 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

4. The water vapor transmission rate of the base layer, measured according to the Lyssy method, is 7.57 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

5. The water vapor transmission rate of the base layer is 4.00 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

6. The water vapor transmission rate of the base layer is 3.00 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

7. The water vapor transmission rate of the base layer is 2.19 g / m ２ ・day or less, the magnetic recording medium according to claim 1.

8. The magnetic recording medium according to claim 1, wherein the Young's modulus in the MD direction (longitudinal direction) of the base layer is 5.3 GPa or less.

9. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic recording medium is 5.60 μm or less.

10. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic recording medium is 5.30 μm or less.

11. The magnetic recording medium according to claim 1, wherein the thickness of the non-magnetic layer is 1.2 μm or less.

12. The magnetic recording medium according to claim 1, wherein the thickness of the base layer is 4.5 μm or less.

13. The magnetic recording medium according to claim 1, wherein the thickness of the back layer is 0.6 μm or less.

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

15. The magnetic recording medium according to claim 1, wherein the magnetic layer and the non-magnetic layer are vacuum thin films.

16. A magnetic recording cartridge, wherein the magnetic recording medium according to claim 1 is housed in a case in a state of being wound around a reel.

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