JP7358965B2 - magnetic recording medium - Google Patents

Description

The present disclosure relates to magnetic recording media.

For example, with the development of IoT, big data, and artificial intelligence, the amount of data collected and stored has increased significantly. Magnetic recording media are often used as media for recording large amounts of data.

Various techniques have been proposed so far regarding magnetic recording media. For example, as a technology related to magnetic powder contained in a magnetic recording medium, Patent Document 1 below describes a magnetic powder formed by coating at least a magnetic paint containing ferromagnetic powder and a binder on a non-magnetic support. A magnetic recording medium having a layer, in which the magnetic layer contains a carboxyl group and at least one hydroxyl group in the molecule, and when there are two or more aromatic rings, the aromatic ring is a condensed ring. A magnetic recording medium characterized in that the compound is contained in an amount of 0.4 [parts by weight] to 10 [parts by weight] per 100 [parts by weight] of the above-mentioned ferromagnetic powder is disclosed.

Japanese Patent Application Publication No. 2002-373413

In order to increase the recording density of a magnetic recording medium, it is conceivable to reduce the particle volume of magnetic powder contained in the magnetic recording medium. Further, in order to improve the electromagnetic conversion characteristics, it is conceivable to make the particle volume of the magnetic powder smaller. However, as the particle volume of the magnetic powder becomes smaller, the thermal stability of the magnetic recording medium becomes worse.
Therefore, the main object of the present disclosure is to provide a magnetic recording medium that has excellent thermal stability even when the particle volume of magnetic powder is small.

The present disclosure provides a substrate;
a magnetic layer provided on the base and containing magnetic powder;
The average thickness of the magnetic layer is 90 nm or less,
The average aspect ratio of the magnetic powder is 1.0 or more and 3.0 or less,
The average particle volume of the magnetic powder is 2300 nm ³ or less,
The coercive force Hc1 in the vertical direction of the magnetic recording medium is 4500 Oe or less,
The coercive force Hc2 and the coercive force Hc1 in the longitudinal direction of the magnetic recording medium satisfy the relationship Hc2/Hc1≦0.8, and
The ratio Hrp/Hc1 of the residual magnetic force Hrp of the magnetic recording medium and the coercive force Hc1 measured using a pulsed magnetic field is 2.0 or less,
A tape-shaped magnetic recording medium is provided.
The average particle volume of the magnetic powder may be 2200 nm ³ or less.
The ratio Hrp/Hc1 may be 1.95 or less.
The ratio Hrp/Hc1 may be 1.90 or less.
The ratio Hrp/Hc1 may be 1.85 or less.
The magnetic powder may include hexagonal ferrite.
The hexagonal ferrite may include at least one of Ba and Sr.
The coercive force Hc2 in the longitudinal direction of the magnetic recording medium may be 2000 Oe or less.
The average thickness of the magnetic recording medium may be 5.6 μm or less.
The average thickness of the substrate may be 4.2 μm or less.
The average thickness of the magnetic layer may be 80 nm or less.
The coercive force Hc2 and the coercive force Hc1 may satisfy the relationship Hc2/Hc1≦0.7.
The coercive force Hc1 may be 500 Oe or more.
The magnetic recording medium may include an underlayer between the magnetic layer and the base,
The average thickness of the base layer may be 2.0 μm or less.
A back layer may be provided on the surface opposite to the surface on which the magnetic layer is provided among the two surfaces of the base,
The average thickness of the back layer may be 0.6 μm or less.
The average particle size of the magnetic powder may be 50 nm or less.
The present disclosure also provides the magnetic recording medium;
a communication unit that communicates with the recording/reproducing device;
storage section and
A control unit that stores information received from the recording/playback device via the communication unit in the storage unit, reads information from the storage unit in response to a request from the recording/playback device, and transmits the information to the recording/playback device via the communication unit. and,
The information includes adjustment information for adjusting the longitudinal tension of the magnetic recording medium. A tape cartridge is also provided.

1 is a cross-sectional view of a magnetic recording medium according to an embodiment of the present disclosure. FIG. 2A is a schematic diagram of the data band and servo band layout. FIG. 2B is an enlarged view of the data band. This is an example of a TEM photograph of a magnetic layer. FIG. 2 is a cross-sectional view showing the structure of magnetic particles. FIG. 7 is a cross-sectional view showing the configuration of magnetic particles in a modified example. It is a graph showing an example of an MH loop. This is an example of a residual magnetization curve. FIG. 1 is a schematic diagram of a recording/reproducing device. FIG. 2 is an exploded perspective view showing an example of the configuration of a cartridge. FIG. 2 is a block diagram showing an example of the configuration of a cartridge memory. FIG. 7 is a schematic diagram of a cross section of a modified example of a magnetic recording medium. FIG. 12A shows an MFM image when a data signal is recorded at wavelength λ. FIG. 12B shows an MFM image when a data signal is recorded at the shortest recording wavelength L'. It is a figure which shows the example of a magnetization curve and a residual magnetization curve.

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

The present disclosure will be described in the following order.
1. Description of the present disclosure 2. Embodiment (Example of coated magnetic recording medium)
(1) Structure of magnetic recording medium (2) Method of manufacturing magnetic recording medium (3) Recording and reproducing device (4) Cartridge (5) Effects (6) Modifications 3. Example

1. Description of this disclosure

The magnetic recording medium of the present disclosure has a magnetic layer containing magnetic powder having a specific particle volume, and has a coercive force Hc1 in the perpendicular direction, a ratio of coercive force Hc2 and coercive force Hc1 in the longitudinal direction Hc2/Hc1, And the ratio Hrp/Hc1 between the residual magnetic force Hrp and the coercive force Hc1 measured using a pulsed magnetic field is within a specific numerical range. As a result, the magnetic recording medium of the present disclosure has excellent electromagnetic conversion characteristics and excellent thermal stability. The thermal stability and residual magnetic force Hrp will be explained in more detail below.

As the particle volume of the magnetic powder contained in the magnetic recording medium becomes smaller, the recording density becomes higher and furthermore, the electromagnetic change characteristics can be improved. However, due to the smaller particle volume, the magnetization recorded in the magnetic recording medium (specifically the magnetic layer) is more likely to be lost by thermal energy, which can result in data signal attenuation. As described above, as the particle volume of the magnetic powder contained in the magnetic recording medium becomes smaller, the stability against heat (also referred to as thermal stability) of the magnetic recording medium may decrease.

Thermal energy applied to the magnetic recording medium from the storage environment during storage of the magnetic recording medium is considered not to have a large effect on the magnetic recording medium in the short term. However, it is assumed that the storage will last for a long period of time, and if the thermal energy is applied to the magnetic recording medium for a long period of time in the storage environment, there is a possibility that an unacceptable effect will be exerted on the magnetic recording medium. Therefore, in order to reduce signal attenuation due to the thermal energy as much as possible, it is desirable that the magnetic recording medium has higher thermal stability.

The present inventors investigated the thermal stability of magnetic recording media and found that by adjusting not only the conventionally known coercivity in the perpendicular and longitudinal directions, but also other indicators, better thermal stability could be achieved. It has been found that it is possible to obtain a magnetic recording medium having the following properties. The other index is the residual magnetic force Hrp.

The residual magnetic force Hrp will be explained below with reference to FIG. 13.
The coercive force Hc1 in the vertical direction is a conventionally used index, and in order to measure it, an MH loop (magnetization curve) is created based on the measurement results by, for example, a magnetometer. An example of an MH loop is shown in FIG. As shown in FIG. 13, the magnetic field at the position where the MH loop crosses the X axis (magnetic field) is the coercive force Hc1. The magnetic field sweep speed used for the measurements is slow.
The residual magnetic force Hrp, which was newly discovered by the present inventors as an index that can be used to improve thermal stability, is measured using a pulsed magnetic field, unlike the measurement of the coercive force Hc1. That is, the measurement is performed using a fast magnetic field sweep rate. In this measurement, a magnetization curve is created based on the amount of magnetization obtained using the pulsed magnetic field. This magnetization curve is called a residual magnetization curve. An example of a remanent magnetization curve is also shown in FIG. The magnetic field at the position where this residual magnetization curve crosses the X axis (magnetic field) is indicated by "Hrp" in FIG. 13, and this magnetic field is the residual magnetic force.
The present inventors have found that, more specifically, the ratio Hrp/Hc1 between the residual magnetic force Hrp and the coercive force Hc1 is within a specific numerical range by the small difference between the coercive force Hc1 and the residual magnetic force Hrp. It has been found that the thermal stability of the magnetic recording medium is improved by the following.
Note that the measurement of the residual magnetic force Hrp is performed using a high magnetic field sweep speed as described above. This fast magnetic field sweep speed is closer to the magnetic field applied in recording on a magnetic recording medium, compared to the slow magnetic field sweep speed used in measuring the coercive force Hc1. From this point of view as well, the residual magnetic force Hrp is considered to be a useful index.

The ratio Hrp/Hc1 of the residual magnetic force Hrp to the coercive force Hc1 of the magnetic recording medium of the present disclosure is 2.0 or less, more preferably 1.95 or less, even more preferably 1.90 or less, Even more preferably, it may be 1.85 or less. When the ratio Hrp/Hc1 is within the above numerical range, the magnetic recording medium of the present disclosure has excellent thermal stability, which can prevent signal attenuation during long-term storage, for example.
Furthermore, the average particle volume of the magnetic powder contained in the magnetic recording medium of the present disclosure may be 2300 nm ³ or less, more preferably 2200 nm ³ or less, even more preferably 2100 nm ³ or less, particularly preferably 2000 nm ^{3 or} less. . When the average particle volume is within the above numerical range, electromagnetic conversion characteristics are improved. Although the average particle volume of the magnetic powder contained in the magnetic recording medium of the present disclosure is thus extremely small, the magnetic recording medium of the present disclosure has excellent thermal stability as described above. Although it is difficult to achieve both electromagnetic conversion characteristics and thermal stability, the present disclosure makes it possible to improve both electromagnetic conversion characteristics and thermal stability.

The magnetic recording medium of the present disclosure includes a base and a magnetic layer provided on the base and containing magnetic powder, wherein the average thickness of the magnetic layer is 90 nm or less, and the average aspect ratio of the magnetic powder is 90 nm or less. The ratio is 1.0 or more and 3.0 or less. These improve electromagnetic conversion characteristics.

In the magnetic recording medium of the present disclosure, the coercive force Hc1 is 4500 Oe or less, and the coercive force Hc2 and the coercive force Hc1 in the longitudinal direction of the magnetic recording medium have a relationship of Hc2/Hc1≦0.8. satisfy. These also improve electromagnetic conversion characteristics.

The average thickness _tT of the magnetic recording medium of the present disclosure is preferably 5.6 μm or less, more preferably 5.3 μm or less, and even more preferably 5.2 μm or less, 5.0 μm or less, or 4.6 μm or less. It can be. The magnetic recording medium of the present disclosure may have a small overall thickness as described above. By reducing the total thickness of the magnetic recording medium of the present disclosure in this way, the length of the tape wound into one magnetic recording cartridge can be made longer, thereby increasing the recording capacity per one magnetic recording cartridge. can be increased. That is, according to the present disclosure, in addition to improving electromagnetic conversion characteristics and thermal stability, it is also possible to improve recording capacity.
The width of the magnetic recording medium according to the present disclosure may be, for example, between 5 mm and 30 mm, particularly between 7 mm and 25 mm, more particularly between 10 mm and 20 mm, even more particularly between 11 mm and 19 mm. The length of the tape-shaped magnetic recording medium according to the present disclosure can be, for example, 500 m to 1500 m. For example, the tape width according to the LTO8 standard is 12.65 mm and the length is 960 m.

The magnetic recording medium according to the present disclosure is tape-shaped, and can be, for example, a long magnetic recording tape. A tape-shaped magnetic recording medium according to the present disclosure may be housed in a magnetic recording cartridge, for example. More specifically, it may be housed in the magnetic recording cartridge in a state where it is wound around a reel within the cartridge.

In one preferred embodiment of the present disclosure, the magnetic recording medium of the present disclosure may include a magnetic layer, an underlayer, a substrate (also referred to as a base layer), and a back layer. These four layers may be stacked in this order. A magnetic recording medium according to the present disclosure may include other layers in addition to these layers. The other layers may be selected as appropriate depending on the type of magnetic recording medium. The magnetic recording medium according to the present disclosure can be, for example, a coated magnetic recording medium. Regarding the coating type magnetic recording medium, the following 2. This will be explained in more detail below.

2. Embodiment (Example of coated magnetic recording medium)

(1) Configuration of magnetic recording medium

First, with reference to FIG. 1, the configuration of a magnetic recording medium 10 according to an embodiment will be described. The magnetic recording medium 10 includes an elongated base 11, a base layer 12 provided on one main surface of the base 11, a magnetic layer 13 provided on the base layer 12, and the other main surface of the base 11. and a back layer 14 provided on the surface. Note that the base layer 12 and the back layer 14 are provided as necessary, and may be omitted.

The magnetic recording medium 10 has a long tape shape, and is run in the longitudinal direction during recording and reproduction. Note that the surface of the magnetic layer 13 is the surface on which the magnetic head runs. Preferably, the magnetic recording medium 10 is used in a recording/reproducing device that includes a ring-type head as a recording head. Note that in this specification, the term "perpendicular direction" refers to a direction perpendicular to the surface of the magnetic recording medium 10 (thickness direction of the magnetic recording medium 10), and the term "longitudinal direction" refers to a direction perpendicular to the surface of the magnetic recording medium 10. means the longitudinal direction (running direction).

(Base)
The base 11 is a nonmagnetic support that supports the underlayer 12 and the magnetic layer 13. The base 11 has a long film shape. The average thickness of the base body 11 is preferably 4.2 μm or less, more preferably 3.8 μm or less, and even more preferably 3.4 μm or less. When the average thickness of the base 11 is 4.2 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to a general magnetic recording medium. The average thickness of the base body 11 is preferably 3 μm or more, more preferably 3.2 μm or more. When the average thickness of the base body 11 is 3 μm or more, a decrease in strength of the base body 11 can be suppressed.

The average thickness of the base 11 is determined as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Subsequently, the layers of the sample other than the substrate 11 (ie, the underlayer 12, the magnetic layer 13, and the back layer 14) are removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample (substrate 11) is measured at five or more positions using a Mitutoyo laser holo gauge (LGH-110C) as a measuring device, and the measured values are simply averaged (arithmetic mean). Then, the average thickness of the base 11 is calculated. Note that the measurement position is randomly selected from the sample.

The base 11 includes, for example, at least one of polyesters, polyolefins, cellulose derivatives, vinyl resins, and other polymer resins. When the base body 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

Examples of polyesters include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p -oxybenzoate) and polyethylene bisphenoxy carboxylate.

The polyolefins include, for example, at least one of PE (polyethylene) and PP (polypropylene). The cellulose derivative includes, for example, at least one of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). The vinyl resin includes, for example, at least one of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

Other polymer resins include, for example, PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, e.g. Zylon (registered trademark)), polyether, PEK (polyetherketone), polyetherester, PES (polyethersulfone), PEI (polyetherimide), Contains at least one of PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).

(magnetic layer)
The magnetic layer 13 is a recording layer for recording signals. The magnetic layer 13 includes, for example, magnetic powder and a binder. The magnetic layer 13 may further contain at least one additive selected from a lubricant, an antistatic agent, an abrasive, a hardening agent, a rust preventive, nonmagnetic reinforcing particles, and the like, if necessary.

As shown in FIG. 2A, the magnetic layer 13 preferably has a plurality of servo bands SB and a plurality of data bands DB in advance. The plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic recording medium 10. A data band DB is provided between adjacent servo bands SB. A servo signal for tracking control of the magnetic head is written in advance in the servo band SB. User data is recorded in the data band DB.

The ratio R _S (=(S _SB /S)×100) of the total area S _SB of the servo band SB to the surface area S of the magnetic layer 13 is preferably 4.0% or less from the viewpoint of ensuring a high recording capacity. , more preferably 3.0% or less, even more preferably 2.0% or less. On the other hand, the ratio R _S of the total area S _SB of the servo band SB to the area S of the surface of the magnetic layer 13 is preferably 0.8% or more from the viewpoint of ensuring five or more servo tracks.

The ratio R _S of the total area S _SB of the servo band SB to the area S of the entire surface of the magnetic layer 13 is determined as follows. For example, the magnetic recording medium 10 is developed using a ferricolloid developer (Sigmarker Q, manufactured by Sigma High Chemical Co., Ltd.), and then the developed magnetic recording medium 10 is observed with an optical microscope to determine the servo band width W _SB and measure the number of servo bands SB. Next, the ratio R _S is determined from the following formula.
Ratio R _S [%] = (((servo band width W _SB )×(number of servo bands))/(width of magnetic recording medium 10))×100

The number of servo bands SB is preferably 5 or more, more preferably 5+4n (where n is a positive integer) or more, and even more preferably 9+4n or more. When the number of servo bands SB is 5 or more, it is possible to suppress the influence on servo signals due to dimensional changes in the width direction of the magnetic recording medium 10, and to ensure stable recording and reproducing characteristics with fewer off-tracks. The number of servo bands SB is not particularly limited, but is, for example, 33 or less.

The number of servo bands SB can be confirmed as follows. First, the surface of the magnetic layer 13 is observed using a magnetic force microscope (MFM) to obtain an MFM image. Next, the number of servo bands SB is counted using the MFM image.

From the viewpoint of ensuring high recording capacity, the servo bandwidth W _SB is preferably 95 μm or less, more preferably 60 μm or less, and even more preferably 30 μm or less. The servo bandwidth W _SB is preferably 10 μm or more. Manufacturing a recording head capable of reading servo signals with a servo bandwidth W _SB of less than 10 μm can be difficult.

The width of the servo band width _WSB is determined as follows. First, the surface of the magnetic layer 13 is observed using a magnetic force microscope (MFM) to obtain an MFM image. Next, the width of the servo band width _WSB is measured using the MFM image.

The magnetic layer 13 is configured to be able to form a plurality of data tracks Tk in the data band DB, as shown in FIG. 2B. From the viewpoint of ensuring high recording capacity, the data track width W is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. The data track width W is preferably 0.02 μm or more.

The data track width W is determined as follows. For example, the data recording pattern of the data band portion of the magnetic layer 13 on which data is recorded over the entire surface is observed using a magnetic force microscope (MFM) to obtain an MFM image. As the MFM, Dimension 3100 manufactured by Digital Instruments and its analysis software are used. The measurement area of the MFM image is 10 μm x 10 μm, and the 10 μm x 10 μm measurement area is divided into 512 x 512 (=262,144) measurement points. MFM measurements are performed on three 10 μm×10 μm measurement areas at different locations, that is, three MFM images are obtained. From the three MFM images obtained, track widths are measured at 10 locations using the analysis software attached to Dimension 3100, and the average value (simple average) is taken. The average value is the data track width W. The measurement conditions for the MFM are as follows: sweep speed: 1 Hz, chip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3.

In the magnetic layer 13, the minimum value L of the distance between magnetization reversals and the data track width W are preferably W/L≦200, more preferably W/L≦60, even more preferably W/L≦45, and particularly preferably W It is configured to be able to record data such that /L≦30. When the minimum value L of the distance between magnetization reversals is a constant value, and the minimum value L of the distance between magnetization reversals and the track width W are W/L>200 (that is, when the track width W is large), the track recording density increases. Therefore, there is a risk that sufficient recording capacity may not be secured. Furthermore, if the track width W is a constant value and the minimum value L of the distance between magnetization reversals and the track width W are W/L>200 (that is, when the minimum value L of the distance between magnetization reversals is small), the bit length becomes smaller and the linear recording density increases, but there is a risk that the SNR will deteriorate significantly due to the effect of spacing loss. Therefore, in order to suppress deterioration of SNR while ensuring recording capacity, it is preferable that W/L is in the range of W/L≦60 as described above. However, W/L is not limited to the above range, and may be W/L≦23 or W/L≦13. Although the lower limit value of W/L is not particularly limited, for example, 1≦W/L.

From the viewpoint of ensuring high recording capacity, the magnetic layer 13 has a minimum value L of the distance between magnetization reversals of preferably 55 nm or less, more preferably 53 nm or less, even more preferably 52 nm or less, 50 nm or less, 48 nm or less, or 44 nm or less. , particularly preferably 40 nm or less, so that data can be recorded. The lower limit of the minimum value L of the distance between magnetization reversals is preferably 20 nm or more in consideration of the magnetic particle size. The minimum value L of the distance between magnetization reversals is taken into consideration depending on the magnetic particle size.

The minimum value L of the distance between magnetization reversals is determined as follows. For example, the data recording pattern of the data band portion of the magnetic layer 13 on which data is recorded over the entire surface is observed using a magnetic force microscope (MFM) to obtain an MFM image. As the MFM, Dimension 3100 manufactured by Digital Instruments and its analysis software are used. The measurement area of the MFM image is 2 μm x 2 μm, and the 2 μm x 2 μm measurement area is divided into 512 x 512 (=262,144) measurement points. MFM measurements are performed on three 2 μm×2 μm measurement areas at different locations, that is, three MFM images are obtained. Fifty inter-bit distances are measured from the two-dimensional unevenness chart of the recording pattern of the obtained MFM image. The measurement of the distance between bits is performed using analysis software included with Dimension3100. A value that is approximately the greatest common divisor of the measured distances between 50 bits is set as the minimum value L of the distance between magnetization reversals. The measurement conditions are: sweep speed: 1 Hz, chip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3.

The average thickness of the magnetic layer 13 is preferably 90 nm or less, particularly preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. When the average thickness of the magnetic layer 13 is 90 nm or less, magnetization can be recorded uniformly in the thickness direction of the magnetic layer 13 when a ring-type head is used as a recording head. to Noise Ratio)).

The average thickness of the magnetic layer 13 is preferably 30 nm or more, more preferably 35 nm or more. When the average thickness of the magnetic layer 13 is 30 nm or more, output can be ensured when an MR type head is used as a reproducing head, so that electromagnetic conversion characteristics (for example, C/N) can be improved.

The average thickness of the magnetic layer 13 is determined, for example, as follows.
The magnetic recording medium 10 is processed into thin pieces by the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, by thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed.
The cross section of the obtained thinned sample is observed using a transmission electron microscope (TEM) under the following conditions to obtain a TEM image. Note that the magnification and acceleration voltage may be adjusted as appropriate depending on the type of device.
Equipment: TEM (H9000NAR manufactured by Hitachi)
Acceleration voltage: 300kV
Magnification: 100,000 times Next, the thickness of the magnetic layer 13 is measured at at least 10 positions in the longitudinal direction of the magnetic recording medium 10 using the obtained TEM image. The obtained measured values are simply averaged (arithmetic mean), and the obtained average value is defined as the average thickness [nm] of the magnetic layer 13. Note that the position where the measurement is performed is randomly selected from the test piece.

(Magnetic powder)

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

The shape of the magnetic particles depends on the crystal structure of the magnetic particles. For example, barium ferrite (BaFe) and strontium ferrite may have a hexagonal plate shape. ε iron oxide can be spherical. Cobalt ferrite can be cubic. The metal can be spindle-shaped. These magnetic particles are oriented during the manufacturing process of the magnetic recording medium 10.
The average particle size of the magnetic powder may preferably be 50 nm or less, more preferably 40 nm or less, even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size may be, for example, 10 nm or more, preferably 12 nm or more.
The average aspect ratio of the magnetic powder may be preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less.

(Embodiment in which the magnetic powder contains hexagonal ferrite)

According to a preferred embodiment of the present disclosure, the magnetic powder may include hexagonal ferrite, and more particularly, 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, hexagonal ferrite may have an average composition represented by the general formula MFe ₁₂ O ₁₉ . Here, M is, for example, at least one metal selected from Ba, Sr, Pb, and Ca, preferably at least one metal selected from Ba and Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb, and Ca. Furthermore, 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 another metal element.

When the magnetic powder includes powder of hexagonal ferrite particles, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 30 nm or less, 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm. It can be: The average particle size may be, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. For example, the average particle size of the magnetic powder may be from 10 nm to 50 nm, from 10 nm to 40 nm, from 12 nm to 30 nm, from 12 nm to 25 nm, or from 15 nm to 22 nm. When the average particle size of the magnetic powder is equal to or less than the above upper limit (e.g., 50 nm or less, particularly 30 nm or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high recording density magnetic recording medium 10. I can do it. When the average particle size of the magnetic powder is at least the above lower limit (for example, at least 10 nm, preferably at least 12 nm), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) are obtained. be able to.

When the magnetic powder includes powder of hexagonal ferrite particles, the average aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 2.0 or more. It may be 0 or more and 2.9 or less. By having the average aspect ratio of the magnetic powder within the above numerical range, agglomeration of the magnetic powder can be suppressed, and furthermore, when the magnetic powder is vertically aligned in the process of forming the magnetic layer 13, the resistance applied to the magnetic powder can be suppressed. can be suppressed. This can lead to improved vertical alignment of the magnetic powder.

When the magnetic powder includes powder of hexagonal ferrite particles, the average particle size and average aspect ratio of the magnetic powder are determined as follows.
First, the magnetic recording medium 10 to be measured is processed into a thin section by the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, by thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed.
The cross section of the obtained thin sample was examined using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies) at an accelerating voltage of 200 kV and a total magnification of 500,000 times, in the direction of the thickness of the magnetic layer 13. Observe the cross section so that it is included, and take a TEM photograph.
Next, from the TEM photograph taken, 50 particles are selected whose side faces face the observation surface and whose thickness can be clearly confirmed. For example, FIG. 3 shows an example of a TEM photograph. In FIG. 3, for example, the particles indicated by a and d are selected because their thickness can be clearly seen. The maximum plate thickness DA of each of the 50 selected particles is measured. The maximum plate thicknesses DA thus obtained are simply averaged (arithmetic mean) to obtain the average maximum plate thickness DA _ave .
Subsequently, the plate diameter DB of each magnetic powder is measured. In order to measure the plate diameter DB of the particles, 50 particles whose plate diameters can be clearly confirmed are selected from the taken TEM photographs. For example, in FIG. 3, the particles indicated by b and c are selected because their plate diameters can be clearly seen. The plate diameter DB of each of the 50 selected particles is measured. The average plate diameter DB _ave is obtained by simply averaging (arithmetic mean) the plate diameters DB obtained in this way. The average plate diameter DB _ave is the average particle size.
Then, the average aspect ratio (DB _ave /DA _ave ) of the particles is determined from the average maximum plate thickness DA _ave and the average plate diameter DB _ave .

When the magnetic powder includes powder of hexagonal ferrite particles, the average particle volume of the magnetic powder is preferably 2300 nm ³ or less, more preferably 2200 nm ³ or less, even more preferably 2100 nm ³ or less, particularly preferably 2000 nm ³ or less. sell. The average particle volume of the magnetic powder may be preferably 500 nm ³ or more, more preferably 700 nm ³ or more, and even more preferably 1000 nm ^{3 or} more.
When the average particle volume of the magnetic powder is equal to or less than the above upper limit (for example, 2300 nm ³ or less), good electromagnetic conversion characteristics (for example, SNR) can be obtained in the high recording density magnetic recording medium 10. When the average particle volume of the magnetic powder is at least the above lower limit (for example, 500 nm ³ or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

The average particle volume of magnetic powder is determined as follows. First, as described above regarding the method for calculating the average particle size of the magnetic powder, the average maximum plate thickness DA _ave and the average plate diameter DB _ave are determined. Next, the average volume V of the magnetic powder is determined using the following formula.

According to a particularly preferred embodiment of the present disclosure, the magnetic powder may be barium ferrite magnetic powder or strontium ferrite magnetic powder, more preferably barium ferrite magnetic powder. Barium ferrite magnetic powder includes magnetic particles of iron oxide having barium ferrite as a main phase (hereinafter referred to as "barium ferrite particles"). Barium ferrite magnetic powder has high reliability in data recording, with its coercive force not decreasing even in high-temperature and humid environments. From this point of view, barium ferrite magnetic powder is preferable as the magnetic powder.

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.

When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness t _m [nm] of the magnetic layer 13 is preferably 90 nm or less, more preferably 80 nm or less. For example, the average thickness t _m of the magnetic layer 13 may be 35 nm≦t _m ≦90 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 less. m or more and 270 kA/m or less.

(Embodiment in which the magnetic powder contains ε iron oxide)

According to another preferred embodiment of the present disclosure, the magnetic powder may preferably include powder of nanoparticles containing epsilon iron oxide (hereinafter referred to as "epsilon iron oxide particles"). Epsilon iron oxide particles can obtain high coercive force even in fine particles. The epsilon iron oxide contained in the epsilon iron oxide particles is preferably crystallized preferentially in the thickness direction (perpendicular direction) of the magnetic recording medium 10.

The ε iron oxide particles have a spherical or nearly spherical shape, or a cubic or almost cubic shape. Since the ε iron oxide particles have the shape described above, when ε iron oxide particles are used as the magnetic particles, the thickness of the medium is smaller than when hexagonal plate-shaped barium ferrite particles are used as the magnetic particles. The contact area between particles in the direction can be reduced, and aggregation of particles can be suppressed. Therefore, it is possible to improve the dispersibility of the magnetic powder and obtain a better SNR (Signal-to-Noise Ratio).

The ε iron oxide particles may have a core-shell structure. Specifically, as shown in FIG. 4, the ε iron oxide particles include a core portion 21 and a two-layer shell portion 22 provided around the core portion 21. The two-layer shell portion 22 includes a first shell portion 22a provided on the core portion 21 and a second shell portion 22b provided on the first shell portion 22a.

The core portion 21 contains ε iron oxide. The ε-iron oxide contained in the core portion 21 preferably has ε-Fe ₂ O ₃ crystal as its main phase, and more preferably consists of single-phase ε-Fe ₂ O ₃ .

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

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

The second shell portion 22b is an oxide film serving as an oxidation prevention layer. The second shell portion 22b may include alpha iron oxide, aluminum oxide, or silicon oxide. The α-iron oxide may include at least one type of iron oxide among, for example, Fe ₃ O ₄ , Fe ₂ O ₃ , and FeO. When the first shell portion 22a includes α-Fe (soft magnetic material), α-iron oxide may be obtained by oxidizing α-Fe contained in the first shell portion 22a.

Since the ε iron oxide particles have the first shell portion 22a as described above, thermal stability can be ensured, thereby maintaining the coercive force Hc of the core portion 21 alone at a large value and/or ε The coercive force Hc of the iron oxide particles (core-shell particles) as a whole can be adjusted to a coercive force Hc suitable for recording. Further, since the ε iron oxide particles have the second shell portion 22b as described above, the ε iron oxide particles are exposed to the air during the manufacturing process of the magnetic recording medium 10 and before that process, and the ε iron oxide particles are exposed to the particle surface. It is possible to suppress deterioration of the properties of the ε iron oxide particles due to occurrence of rust or the like. Therefore, deterioration of the characteristics of the magnetic recording medium 10 can be suppressed.

The ε iron oxide particles may have a single-layer shell portion 23, as shown in FIG. In this case, the shell portion 23 has the same configuration as the first shell portion 22a. However, from the viewpoint of suppressing the deterioration of the characteristics of the ε iron oxide particles, it is more preferable that the ε iron oxide particles have a shell portion 22 having a two-layer structure.

The ε iron oxide particles may contain an additive instead of having a core-shell structure, or may have a core-shell structure and contain an additive. In these cases, part of the Fe in the ε iron oxide particles is replaced by the additive. When the epsilon iron oxide particles contain an additive, the coercive force Hc of the entire epsilon iron oxide particles can be adjusted to a coercive force Hc suitable for recording, so that ease of recording can be improved. The additive is a metal element other than iron, preferably a trivalent metal element, more preferably one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In).
Specifically, the ε-iron oxide containing additives is a 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 Al , Ga, and In. x is, for example, 0<x<1).

The average particle size (average maximum particle size) 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 12 nm or more and 22 nm or less. In the magnetic recording medium 10, an area whose size is 1/2 of the recording wavelength becomes an actual magnetized area. Therefore, by setting the average particle size of the magnetic powder to less than half the shortest recording wavelength, a good SNR can be obtained. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic properties can be achieved in a high recording density magnetic recording medium 10 (for example, a magnetic recording medium 10 configured to be able to record signals at the shortest recording wavelength of 44 nm or less). Conversion characteristics (eg SNR) can be obtained. On the other hand, when the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

The average aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 1.0 or more and 2.5 or less. When the average aspect ratio of the magnetic powder is within the above numerical range, it is possible to suppress the agglomeration of the magnetic powder, and also to suppress the resistance applied to the magnetic powder when vertically aligning the magnetic powder in the process of forming the magnetic layer 13. be able to. Therefore, the vertical orientation of the magnetic powder can be improved.

When the magnetic powder contains ε iron oxide particles, the average particle size and average aspect ratio of the magnetic powder are determined as follows.
First, the magnetic recording medium 10 to be measured is processed into a thin section by the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, by thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed.
The cross section of the obtained thin sample was examined using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies) at an accelerating voltage of 200 kV and a total magnification of 500,000 times, in the direction of the thickness of the magnetic layer 13. Observe the cross section so that it is included, and take a TEM photograph.
Next, 50 particles whose shapes can be clearly confirmed are selected from the TEM photograph taken, and the long axis length DL and short axis length DS of each particle are measured. Here, the long axis length DL means the maximum distance between two parallel lines drawn from any angle so as to be in contact with the contour of each particle (so-called maximum Feret diameter). On the other hand, the short axis length DS means the maximum length of the particle in the direction orthogonal to the long axis (DL) of the particle.
Subsequently, the average long axis length DL _ave is determined by simply averaging (arithmetic mean) the long axis lengths DL of the 50 measured particles. The average major axis length DL _ave determined in this manner is defined as the average particle size of the magnetic powder. Further, the average short axis length DS _ave is determined by simply averaging (arithmetic mean) the short axis lengths DS of the 50 particles measured. Then, the average aspect ratio (DL _ave /DS _ave ) of the particles is determined from the average long axis length DL _ave and the average short axis length DS _ave .

The average particle volume of the magnetic powder may be preferably 2300 nm ³ or less, more preferably 2200 nm ³ or less, even more preferably 2100 nm ³ or less, particularly preferably 2000 nm ^{3 or} less. The average particle volume of the magnetic powder may be preferably 500 nm ³ or more, more preferably 700 nm ³ or more, and even more preferably 1000 nm ^{3 or} more.
When the average particle volume of the magnetic powder is equal to or less than the above upper limit (for example, 2300 nm ³ or less), good electromagnetic conversion characteristics (for example, SNR) can be obtained in the high recording density magnetic recording medium 10. When the average particle volume of the magnetic powder is at least the above lower limit (for example, 500 nm ³ or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

When the ε iron oxide particles have a spherical or nearly spherical shape, the average particle volume of the magnetic powder is determined as follows. First, the average major axis length DL _ave is determined in the same manner as the method for calculating the average particle size of the magnetic powder described above. Next, the average volume V of the magnetic powder is determined using the following formula.
V=(π/6)×DL _ave ³

When the ε iron oxide particles have a cubic shape, the average volume of the magnetic powder is determined as follows.
The magnetic recording medium 10 is processed into thin pieces by the FIB (Focused Ion Beam) method or the like. When using the FIB method, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, by thinning, a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10 is formed.
The obtained thin sample was examined using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies) at an accelerating voltage of 200 kV and a total magnification of 500,000 times so that the entire magnetic layer 13 was included in the thickness direction of the magnetic layer 13. Obtain a cross-sectional observation and obtain a TEM photograph. Note that the magnification and acceleration voltage may be adjusted as appropriate depending on the type of device.
Next, 50 particles whose shape is clear are selected from the TEM photograph taken, and the side length DC of each particle is measured. Next, the average side length DC _ave is determined by simply averaging (arithmetic mean) the side lengths DC of the 50 measured particles. Next, the average volume V _ave (particle volume) of the magnetic powder is determined from the following equation using the average side length DC _ave .
V _ave = DC _ave ³
The coercive force Hc of the ε iron oxide particles is preferably 2500 Oe or more, more preferably 2800 Oe or more and 4200 Oe or less.

(Embodiment in which the magnetic powder contains Co-containing spinel ferrite)

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

Cobalt ferrite has, for example, an average composition represented by the following formula (1).
C _x M _y Fe ₂ O _z ...(1)
(However, in formula (1), M is, for example, one or more metals selected from the group consisting of Ni, Mn, Al, Cu, and Zn. x is 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 3≦z≦ The value is within the range of 4. Part of Fe may be substituted with another metal element.)

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 2,500 Oe or more, more preferably 2,600 Oe or more and 3,500 Oe or less.

When the magnetic powder includes powder of cobalt ferrite particles, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 23 nm or less. When the average particle size of the magnetic powder is 25 nm or less, good electromagnetic conversion characteristics (for example, SNR) can be obtained in the high recording density magnetic recording medium 10. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained. When the magnetic powder includes powder of cobalt ferrite particles, the average aspect ratio and average particle size of the magnetic powder are determined in the same manner as when the magnetic powder includes ε iron oxide particles.

The average particle volume of the magnetic powder may be preferably 2300 nm ³ or less, more preferably 2200 nm ³ or less, even more preferably 2100 nm ³ or less, particularly preferably 2000 nm ^{3 or} less. The average particle volume of the magnetic powder may be preferably 500 nm ³ or more, more preferably 700 nm ³ or more, and even more preferably 1000 nm ^{3 or} more.
When the average particle volume of the magnetic powder is equal to or less than the above upper limit (for example, 2300 nm ³ or less), good electromagnetic conversion characteristics (for example, SNR) can be obtained in the high recording density magnetic recording medium 10. When the average particle volume of the magnetic powder is at least the above lower limit (for example, 500 nm ³ or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.

(binder)

As the binder, a resin having a structure in which a polyurethane resin, a vinyl chloride resin, or the like is subjected to a crosslinking reaction is preferable. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin commonly used in the coating type magnetic recording medium 10.

Examples of the binder include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer. , acrylic ester-vinyl chloride-vinylidene chloride copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-vinyl chloride copolymer, methacrylic ester-ethylene copolymer Polymers, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitro) One or a combination of two or more selected from (cellulose), styrene-butadiene copolymer, polyester resin, amino resin, and synthetic rubber may be used.

Moreover, a thermosetting resin or a reactive resin may be used as the binder. Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, and urea formaldehyde resins.

In addition, polar functional groups such as -SO ₃ M, -OSO ₃ M, -COOM, and P=O(OM) ₂ are introduced into each of the above-mentioned binders for the purpose of improving the dispersibility of the magnetic powder. You can leave it there. Here, M in the formula is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium.

Furthermore, examples of the polar functional group include side chain types having terminal groups of -NR1R2 and -NR1R2R3 ⁺ X ^- , and main chain types having >NR1R2 ⁺ X ^- . Here, in the formula, R1, R2, and R3 are each independently a hydrogen atom or a hydrocarbon group, and X ^- is, for example, a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. It is. Further, examples of the polar functional group include -OH, -SH, -CN, and epoxy group. The amount of these polar functional groups introduced into the binder is preferably 10 ^-1 to 10 ^-8 mol/g, more preferably 10 ^-2 to 10 ^-6 mol/g.

(lubricant)

The magnetic layer may include a lubricant. The lubricant may be, for example, one or more selected from fatty acids and/or fatty acid esters, and preferably contains both fatty acids and fatty acid esters. The fatty acid may preferably be a compound represented by the following general formula (1) or (2). For example, the fatty acid may include one or both of a compound represented by the following general formula (1) and a compound represented by the general formula (2).
Further, the fatty acid ester may preferably be a compound represented by the following general formula (3) or (4). For example, the fatty acid ester may include one or both of the compound represented by the following general formula (3) and the compound represented by the general formula (4).
The lubricant contains either or both of the compound represented by the general formula (1) and the compound represented by the general formula (2), the compound represented by the general formula (3), and the compound represented by the general formula (4). By including one or both of the compounds, it is possible to suppress an increase in the coefficient of dynamic friction due to repeated recording or reproduction of the magnetic recording medium.
CH ₃ (CH ₂ ) _k COOH...(1)
(However, in general formula (1), k is an integer selected from the range of 14 to 22, more preferably 14 to 18.)
CH ₃ (CH ₂ ) _n CH=CH (CH ₂ ) _m COOH...(2)
(However, in the general formula (2), the sum of n and m is an integer selected from the range of 12 to 20, more preferably 14 to 18.)
CH ₃ (CH ₂ ) _p COO (CH ₂ ) _q CH ₃ ...(3)
(However, in general formula (3), p is an integer selected from the range of 14 to 22, more preferably 14 to 18, and q is in the range of 2 to 5, more preferably 2 to 4. (It is an integer selected from the following range.)
CH ₃ (CH ₂ ) _r COO-(CH ₂ ) _s CH(CH ₃ ) ₂ ...(4)
(However, in the general formula (4), r is an integer selected from the range of 14 to 22, and s is an integer selected from the range of 1 to 3.)

Examples of the lubricant include esters of monobasic fatty acids with 10 to 24 carbon atoms and monohydric to hexahydric alcohols with 2 to 12 carbon atoms, mixed esters thereof, difatty acid esters, trifatty acid esters, etc. can be mentioned. Specific examples of the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, and stearic acid. Examples include octyl, isooctyl stearate, octyl myristate, and the like.

(Antistatic agent)
Examples of the antistatic agent include carbon black, natural surfactants, nonionic surfactants, and cationic surfactants.

(Abrasive)
Examples of polishing agents include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, and oxidized Acicular α made by dehydrating and annealing raw materials of titanium, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and magnetic iron oxide. Examples include iron oxide, and those surface-treated with aluminum and/or silica if necessary.

(hardening agent)
Examples of the curing agent include polyisocyanate. Examples of the polyisocyanate include aromatic polyisocyanates such as an adduct of tolylene diisocyanate (TDI) and an active hydrogen compound, and aliphatic polyisocyanates such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. Can be mentioned. The weight average molecular weight of these polyisocyanates is preferably in the range of 100 to 4,500.

(Rust preventive agent) Examples of the rust preventive agent include phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, heterocyclic compounds containing an oxygen atom, heterocyclic compounds containing a sulfur atom, and the like.

(Non-magnetic reinforcing particles)
Examples of non-magnetic reinforcing particles include 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), etc.

(base layer)
Underlayer 12 is a nonmagnetic layer containing nonmagnetic powder and a binder. The base layer 12 may further contain at least one additive selected from a lubricant, an antistatic agent, a hardening agent, a rust preventive, and the like, if necessary.

The average thickness of the base layer 12 is preferably 0.6 μm or more and 2.0 μm or less, more preferably 0.8 μm or more and 1.4 μm or less. Note that the average thickness of the underlayer 12 is determined in the same manner as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is adjusted as appropriate depending on the thickness of the base layer 12.
In a preferred embodiment of the present disclosure, an underlayer 12 is provided between the magnetic layer 13 and the base 11, and the average thickness of the underlayer 12 may be 2.0 μm or less.

(Non-magnetic powder)
The non-magnetic powder includes, for example, at least one of inorganic particle powder and organic particle powder. Further, the non-magnetic powder may include carbon powder such as carbon black. Note that one type of non-magnetic powder may be used alone, or two or more types of non-magnetic powder may be used in combination. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Examples of the shape of the non-magnetic powder include various shapes such as acicular, spherical, cubic, and plate-like, but are not limited to these shapes.

(binder)
The above description regarding the binder contained in the magnetic layer 13 also applies to the binder contained in the underlayer.

(Additive)
The above description regarding the lubricant, antistatic agent, hardening agent, and rust preventive agent contained in the magnetic layer 13 also applies to the lubricant, antistatic agent, hardening agent, and rust preventive agent contained in the underlayer.

(back layer)
Back layer 14 may include a binder and non-magnetic powder. The back layer 14 may further contain at least one additive selected from a lubricant, a curing agent, an antistatic agent, and the like, if necessary. The above description regarding the binder and nonmagnetic powder contained in the underlayer 12 also applies to the binder and nonmagnetic powder contained in the back layer.

The average particle size of the non-magnetic powder is preferably 10 nm or more and 150 nm or less, more preferably 15 nm or more and 110 nm or less. The average particle size of the non-magnetic powder is determined in the same manner as the average particle size of the magnetic powder described above. The non-magnetic powder may include non-magnetic powder having two or more particle size distributions.

The average thickness of the back layer 14 (also referred to as "average thickness t _b " or "t _b " in this specification) is preferably 0.6 μm or less. By having the average thickness t _b of the back layer 14 within the above range, even if the average thickness of the magnetic recording medium 10 is set to 5.6 μm or less, the thickness of the underlayer 12 and the base 11 can be kept thick, Thereby, running stability of the magnetic recording medium 10 within the recording/reproducing apparatus can be maintained. The lower limit of the average thickness _tb of the back layer 14 is not particularly limited, but is, for example, 0.2 μm or more.
In a preferred embodiment of the present disclosure, a back layer 14 is provided on the surface opposite to the surface on which the magnetic layer 13 is provided, of the two surfaces of the base 11, and the average thickness of the back layer 14 is may be 0.6 μm or less.

The average thickness t _b of the back layer 14 is determined as follows. First, the average thickness _tT of the magnetic recording medium 10 is measured. The method for measuring the average thickness _tT is as described herein below. Subsequently, the back layer 14 of the sample is removed using a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five or more positions using a laser holo gauge (LGH-110C) manufactured by Mitutoyo, and the measured values are simply averaged (arithmetic mean) to obtain the average value _tB. Calculate [μm]. Thereafter, the average thickness t _b [μm] of the back layer 14 is determined from the following formula. Note that the measurement position is randomly selected from the sample.
t _b [μm] = t _T [μm] - t _B [μm]

(Average thickness _tT of magnetic recording medium)

The average thickness of the magnetic recording medium 10 (also referred to as "average thickness t _T " or "t _T " in this specification is t _T ≦5.6 μm, more preferably 5.3 μm or less, and even more preferably can be 5.2 μm or less, 5.0 μm or less, or 4.6 μm or less. By having the average thickness t _T of the magnetic recording medium 10 within the above numerical range (for example, by t _T ≦5.6 μm) ), the recording capacity that can be recorded in one data cartridge can be increased compared to the conventional one.The lower limit of the average thickness _tT of the magnetic recording medium 10 is not particularly limited, but for example, 3.5 μm≦ _tT It is.

The average thickness _tT of the magnetic recording medium 10 is determined as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared and cut into a length of 250 mm to produce a sample. Next, the thickness of the sample is measured at five or more positions using a Mitutoyo Laser Hologage (LGH-110C) as a measuring device, and the measured values are simply averaged (arithmetic mean). The value t _T [μm] is calculated. Note that the measurement position is randomly selected from the sample.

(Coercive force Hc1 in the vertical direction)

The coercive force Hc1 in the vertical direction may be 4500 Oe or less, more preferably 3500 Oe or less, and even more preferably 3000 Oe or less, 2900 Oe or less, or 2850 Oe or less. A large coercive force Hc1 is preferable because it is less susceptible to thermal disturbances and demagnetizing fields, but if the coercive force Hc1 exceeds 4,500 Oe, there is a risk that saturation recording with the recording head will be difficult, resulting in areas that cannot be recorded. exists, noise increases, and as a result, electromagnetic conversion characteristics (for example, C/N) deteriorate.

The coercive force Hc1 in the vertical direction is preferably 500 Oe or more, more preferably 1000 Oe or more, and even more preferably 1500 Oe or more or 2000 Oe or more. When the coercive force Hc1 is equal to or greater than the above lower limit value, it is possible to suppress deterioration of electromagnetic conversion characteristics (for example, C/N) in a high-temperature environment due to the influence of thermal disturbance and the influence of a demagnetizing field.

The coercive force Hc1 in the vertical direction is determined as follows. First, three magnetic recording media 10 are stacked with double-sided tape, and then punched with a punch of φ6.39 mm to create a measurement sample. At this time, marking is performed using any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium can be recognized. Then, using a vibrating sample magnetometer (VSM), the M-H of the measurement sample (the entire magnetic recording medium 10) corresponding to the vertical direction ((thickness direction of the magnetic recording medium 10)) of the magnetic recording medium 10 is The loop is measured.Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off using acetone or ethanol, leaving only the substrate 11.Then, the obtained substrate 11 are stacked together with double-sided tape, and then punched out with a φ6.39 mm punch to form a background correction sample (hereinafter simply referred to as a correction sample).After that, VSM is used to form the base 11. The MH loop of the correction sample (substrate 11) corresponding to the vertical direction (thickness direction of the magnetic recording medium 10) is measured.

In measuring the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11), a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo was used. "Kata" is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, and average number of MHs: 20.

After the two MH loops are obtained, background correction is performed by subtracting the MH loop of the correction sample (substrate 11) from the MH loop of the measurement sample (the entire magnetic recording medium 10). Then, the MH loop after background correction is obtained. The measurement and analysis program attached to the "VSMP7-15" is used to calculate this background correction.

The vertical coercive force Hc1 is determined from the obtained background-corrected MH loop. Note that this calculation uses the measurement and analysis program attached to the "VSM-P7-15 type". Note that all of the above MH loop measurements are performed at 25°C. Further, it is assumed that "demagnetizing field correction" is not performed when measuring the MH loop in the direction perpendicular to the magnetic recording medium 10.

(Coercive force Hc2 in longitudinal direction)

The coercive force Hc2 in the longitudinal direction is preferably 2000 Oe or less, more preferably 1900 Oe or less, even more preferably 1800 Oe or less. When the coercive force Hc2 in the longitudinal direction is 2000 Oe or less, the magnetization responds sensitively to the perpendicular magnetic field from the recording head, so that a good recording pattern can be formed.

The coercive force Hc2 in the longitudinal direction is preferably 1000 Oe or more. When the coercive force Hc2 in the longitudinal direction is 1000 Oe or more, demagnetization due to magnetic flux leakage from the recording head can be suppressed.

The above coercive force Hc2 is determined as follows.
First, three magnetic recording media 10 are stacked together using double-sided tape, and then punched with a punch of φ6.39 mm to prepare a measurement sample. At this time, marking is performed using any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic recording medium 10 can be recognized. Then, the MH loop of the measurement sample (the entire magnetic recording medium 10) corresponding to the longitudinal direction (running direction) of the magnetic recording medium 10 is measured using a vibrating sample magnetometer (VSM). Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off using acetone or ethanol, leaving only the base 11. Three sheets of the obtained substrate 11 are stacked together with double-sided tape, and then punched with a punch of 6.39 mm in diameter to produce a sample for background correction (hereinafter simply referred to as "sample for correction"). Thereafter, the MH loop of the correction sample (substrate 11) corresponding to the vertical direction of the substrate 11 (the vertical direction of the magnetic recording medium 10) is measured using the VSM.
In measuring the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11), a highly sensitive vibrating sample magnetometer "VSM-P7" manufactured by Toei Kogyo Co., Ltd. was used. -15 type” is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, and average number of MHs: 20.
After the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (substrate 11) are obtained, the MH loop of the measurement sample (the entire magnetic recording medium 10) is obtained. Background correction is performed by subtracting the MH loop of the correction sample (substrate 11), and the MH loop after background correction is obtained. The measurement and analysis program attached to the "VSM-P7-15 model" is used to calculate this background correction.
The coercive force Hc is determined from the obtained MH loop after background correction. Note that this calculation uses the measurement and analysis program attached to the "VSM-P7-15 type". Note that all of the above MH loop measurements are performed at 25°C. Further, it is assumed that "demagnetizing field correction" is not performed when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10.

(Hc2/Hc1)
The ratio Hc2/Hc1 of the coercive force Hc2 in the longitudinal direction and the coercive force Hc1 in the vertical direction is Hc2/Hc1≦0.8, preferably Hc2/Hc1≦0.75, more preferably Hc2/Hc1≦0.7, Even more preferably, the relationship Hc2/Hc1≦0.65 is satisfied, particularly preferably Hc2/Hc1≦0.6. When the coercive forces Hc1 and Hc2 satisfy the above relationship, the degree of vertical orientation of the magnetic powder can be increased. Therefore, it is possible to reduce the magnetization transition width and obtain a high-output signal during signal reproduction, so that electromagnetic conversion characteristics (for example, C/N) can be improved. Note that, as described above, when Hc2 is small, the magnetization reacts with high sensitivity to the perpendicular magnetic field from the recording head, so that a good recording pattern can be formed.

When the ratio Hc2/Hc1 is Hc2/Hc1≦0.8, it is particularly effective that the average thickness of the magnetic layer 13 is 90 nm or less. If the average thickness of the magnetic layer 13 exceeds 90 nm, when a ring-type head is used as a recording head, the lower region of the magnetic layer 13 (the region on the underlayer 12 side) will be magnetized in the longitudinal direction, and the magnetic layer 13 will be magnetized in the longitudinal direction. There is a risk that it will not be possible to magnetize uniformly in the thickness direction. Therefore, even if the ratio Hc2/Hc1 is set to Hc2/Hc1≦0.8 (that is, even if the degree of vertical orientation of the magnetic powder is increased), there is a possibility that the electromagnetic conversion characteristics (for example, C/N) cannot be improved. .

The lower limit value of Hc2/Hc1 is not particularly limited, but is, for example, 0.5≦Hc2/Hc1.

Note that Hc2/Hc1 represents the degree of vertical orientation of the magnetic powder, and the smaller Hc2/Hc1, the higher the degree of vertical orientation of the magnetic powder. The reason why Hc2/Hc1 is used as an index indicating the degree of vertical orientation of magnetic powder in this embodiment will be explained below.

Conventionally, the index (parameter) that generally indicates the degree of vertical orientation of magnetic powder is the squareness ratio SQ (= (Mr/Ms) x 100, where Mr (emu): residual magnetization, Ms (emu): saturation. magnetization) has been used. However, according to the findings of the present inventors, the squareness ratio SQ is less suitable than Hc2/Hc1 as an indicator of the degree of vertical orientation of magnetic powder for the following reasons.
(1) The squareness ratio SQ varies depending on the value of the coercive force Hc of the magnetic powder. For example, as shown in FIG. 6, when the coercive force Hc of the magnetic powder increases, the apparent squareness ratio SQ also increases.
(2) The squareness ratio SQ is affected by distortion of the MH loop due to overdispersion.

Therefore, in this embodiment, Hc2/Hc1 is used as an index that more appropriately indicates the degree of orientation of magnetic powder. Since the coercive forces Hc1 and Hc2 simply change depending on the orientation direction of the magnetic powder, Hc2/Hc1 is more suitable as an index indicating the degree of orientation of the magnetic powder.

(Residual magnetic force Hrp and ratio Hrp/Hc1)

In the magnetic recording medium of the present disclosure, the ratio Hrp/Hc1 of the residual magnetic force Hrp of the magnetic recording medium and the coercive force Hc1 in the perpendicular direction of the magnetic recording medium measured using a pulsed magnetic field is 2.0 or less, It is more preferably 1.95 or less, even more preferably 1.90 or less, particularly preferably 1.85 or less. By having the ratio Hrp/Hc1 within the above numerical range, the magnetic recording medium of the present disclosure has excellent thermal stability despite the small average particle volume of the magnetic powder.
The ratio Hrp/Hc1 may be, for example, 0 or more, 0.5 or more, or 1.0 or more.

Hc1 used for calculating the ratio Hrp/Hc1 is measured as described above.
Hrp used to calculate the ratio Hrp/Hc1 is determined as follows.
As a measurement sample, a sample similar to the sample used to calculate the coercive force Hc1 was prepared, and the residual magnetization curve was measured in the direction perpendicular to the film surface using a high-speed response characteristic evaluation device HR-PVSM20 manufactured by Hayama Corporation. You can get it like this.
First, a perpendicular magnetic field of about -3980 kA/m (-50 kOe) is applied to the measurement sample, and the magnetic field is returned to zero to create a residual magnetization state. Thereafter, a magnetic field of approximately 40.2 kA/m (approximately 505 Oe) is applied in the opposite direction to return it to zero and measure the amount of residual magnetization. The applied magnetic field at this time is a pulsed magnetic field with a pulse width on the order of 10 ⁻⁸ sec. Thereafter, a magnetic field that is approximately 40.2 kA/m larger than the previously applied magnetic field is applied and the measurement is repeated to return to zero, and the amount of residual magnetization is plotted against the applied magnetic field to create a DCD curve. The measured magnetic field is up to about 20 kOe. Note that background correction and demagnetizing field correction are not performed.
The measurement conditions are shown below.
Initial magnetization voltage: 220V (equivalent to -3980kA/m)
Measurement start voltage: 0V (equivalent to 0Oe)
Step voltage: 17.5V (equivalent to about 505Oe)
Maximum voltage: 350V (equivalent to 20kOe)
Lock-in amplifier waiting time: 10 seconds From the data obtained by the above measurements, a residual magnetization curve as shown in FIG. 7, for example, can be obtained. In order to obtain the residual magnetization curve from the data, phase correction is performed as necessary. The phase correction will be described later. Among the points forming the obtained residual magnetization curve, two points sandwiching the X-axis (two points closest to the X-axis) are connected with a straight line, and the point where the straight line intersects with the X-axis is calculated as Hrp.

The phase correction will be explained in more detail below.
The unit of magnetization is originally emu, but in the high-speed response characteristic evaluation device, the amount of magnetization in each applied magnetic field is output as voltage V, and the amount of magnetization (voltage V) in each applied magnetic field is , either positive or negative values are output as positive values. Therefore, correction according to the phase of each applied magnetic field is required. For this correction, phase information data included in the output result from the high-speed response characteristic evaluation device is used. Phase information data is also output for each applied magnetic field together with the amount of magnetization (voltage V) at each applied magnetic field.
If the phase information data of the amount of magnetization (voltage V) measured for a certain magnetic field is a negative value, it is necessary to multiply the measured amount of magnetization (voltage V) by "-1". The value obtained by multiplying the magnetization amount (voltage V) by "-1" is used to obtain the residual magnetization curve. The process of multiplying by "-1" is the phase correction.
On the other hand, if the phase information data of the amount of magnetization (voltage V) measured for a certain magnetic field is a positive value, there is no need to multiply the measured amount of magnetization (voltage V) by "-1", The measured magnetization amount (voltage V) is used as it is to obtain the residual magnetization curve.
Plot the magnetization after phase correction (multiplied by "-1") and the measured magnetization (not multiplied by "-1") obtained as above against the magnetic field. By doing so, a residual magnetization curve as shown in FIG. 7 is obtained.

(2) Method for manufacturing magnetic recording media

Next, a method for manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming a base layer is prepared by kneading and dispersing non-magnetic powder, a binder, etc. in a solvent. Next, a coating material for forming a magnetic layer is prepared by kneading and dispersing magnetic powder, a binder, and the like in a solvent. For preparing the coating material for forming the magnetic layer and the coating material for forming the base layer, the following solvents, dispersing devices, and kneading devices can be used, for example.

Examples of 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, methyl acetate, ethyl acetate, butyl acetate, and propyl acetate. , ester solvents such as 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, methylene chloride, ethylene chloride, Examples include halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, and chlorobenzene. These may be used alone or in an appropriate mixture.

As the kneading device used for preparing the above-mentioned paint, for example, a continuous twin-screw kneader, a continuous twin-screw kneader capable of diluting in multiple stages, a kneader, a pressure kneader, a roll kneader, etc. can be used. , but is not particularly limited to these devices. In addition, examples of dispersion equipment used in the above-mentioned paint preparation include roll mills, ball mills, horizontal sand mills, vertical sand mills, spike mills, pin mills, tower mills, pearl mills (for example, "DCP Mill" manufactured by Eirich, etc.), homogenizers, super Although a dispersion device such as a sonic dispersion machine can be used, the present invention is not particularly limited to these devices.

Next, the base layer 12 is formed by applying a base layer forming paint to one main surface of the base 11 and drying it. Subsequently, the magnetic layer 13 is formed on the base layer 12 by applying a magnetic layer forming paint onto the base layer 12 and drying it. Note that during drying, the magnetic powder is magnetically oriented in the thickness direction of the base 11 using, for example, a solenoid coil. Further, during drying, the magnetic powder may be magnetically oriented in the running direction (longitudinal direction) of the base 11 using, for example, a solenoid coil, and then the magnetic powder may be oriented in the thickness direction of the base 11. By performing such a magnetic field orientation treatment, the ratio Hc2/Hc1 can be lowered. Therefore, the degree of vertical orientation 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 11. As a result, a magnetic recording medium 10 is obtained.

The ratio Hc2/Hc1 is determined by, for example, the intensity of the magnetic field applied to the coating film of the coating material for forming the magnetic layer, the concentration of solid content in the coating material for forming the magnetic layer, the drying conditions of the coating film of the coating material for forming the magnetic layer (drying temperature and drying time) to the desired value. The strength of the magnetic field applied to the coating film is preferably at least two times and at most three times the coercive force of the magnetic powder. In order to further increase the ratio Hc2/Hc1, it is preferable to improve the dispersion state of the magnetic powder in the coating material for forming the magnetic layer. Furthermore, in order to further increase the ratio Hc2/Hc1, it is also effective to magnetize the magnetic powder before the magnetic layer forming paint enters the orientation device for orienting the magnetic powder in a magnetic field. Note that the above method for adjusting the ratio Hc2/Hc1 may be used alone or in combination of two or more.

The ratio Hrp/Hc1 can be controlled, for example, by adjusting the orientation conditions in the magnetic field orientation treatment and/or by adjusting the holding force of the magnetic powder. Further, the ratio Hrp/Hc1 can also be adjusted by changing the type of magnetic powder or the average particle volume, average aspect ratio, or average particle size of the magnetic powder.

Thereafter, the obtained magnetic recording medium 10 is re-wound around a large-diameter core and subjected to a hardening process. Finally, the magnetic recording medium 10 is calendered and then cut into a predetermined width (for example, 1/2 inch width). Through the above steps, the desired elongated magnetic recording medium 10 is obtained.

(3) Recording and reproducing device

[Configuration of recording/playback device]

Next, with reference to FIG. 8, an example of the configuration of the recording and reproducing apparatus 30 that performs recording and reproducing of the magnetic recording medium 10 having the above-described configuration will be described.

The recording/reproducing device 30 has a configuration that can adjust the tension applied to the magnetic recording medium 10 in the longitudinal direction. Furthermore, the recording/reproducing device 30 has a configuration in which a magnetic recording cartridge 10A can be loaded therein. Here, for ease of explanation, a case will be described in which the recording/reproducing device 30 has a configuration in which one magnetic recording cartridge 10A can be loaded. It may have a configuration in which 10A can be loaded.

The recording and reproducing device 30 is connected to an information processing device such as a server 41 and a personal computer (hereinafter referred to as "PC") 42 via a network 43, and stores data supplied from these information processing devices on a magnetic recording cartridge. It is configured to be able to record at 10A. The shortest recording wavelength of the recording/reproducing device 30 is preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, particularly preferably 50 nm or less.

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

The spindle 31 is configured such that the magnetic recording cartridge 10A can be attached thereto. The magnetic recording cartridge 10A complies with the LTO (Linear Tape Open) standard, and has a cartridge case 10B rotatably housing a single reel 10C on which the magnetic recording medium 10 is wound. A V-shaped servo pattern is recorded in advance on the magnetic recording medium 10 as a servo signal. The reel 32 is configured to be able to fix the leading end of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 10A.

The spindle drive device 33 is a device that rotationally drives the spindle 31. The reel drive device 34 is a device that rotates the reel 32. When recording or reproducing data on the magnetic recording medium 10, the spindle drive device 33 and the reel drive device 34 rotate the spindle 31 and the reel 32, thereby causing the magnetic recording medium 10 to run. . The guide roller 35 is a roller for guiding the running of the magnetic recording medium 10.

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 data signals recorded on the magnetic recording medium 10 , and a plurality of reproducing heads for reproducing data signals recorded on the magnetic recording medium 10 . and a plurality of servo heads for reproducing recorded servo signals. For example, a ring-type head can be used as the recording head, but the type of recording head is not limited to this.

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.

The control device 38 controls the entire recording/reproducing device 30 . For example, the control device 38 records data signals supplied from the information processing devices, such as the server 41 and the PC 42, on the magnetic recording medium 10 using the head unit 36. Furthermore, in response to requests from information processing devices such as the server 41 and the PC 42, the control device 38 reproduces data signals recorded on the magnetic recording medium 10 using the head unit 36, and supplies the reproduced data signals to the information processing devices.

[Operation of recording/playback device]

Next, the operation of the recording/reproducing apparatus 30 having the above configuration will be explained.

First, the magnetic recording cartridge 10A is mounted on the recording/reproducing device 30, the leading end of the magnetic recording medium 10 is pulled out, and the leading end of the magnetic recording medium 10 is transferred to the reel 32 via the plurality of guide rollers 35 and the head unit 36. Attach it to the reel 32.

Next, when an operation section (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, so that the magnetic recording medium 10 is run from the reel 10C toward the reel 32. The spindle 31 and reel 32 are rotated in the same direction. Thereby, while the magnetic recording medium 10 is wound onto the reel 32, the head unit 36 records information on the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.

Further, 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 is run 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 information recorded on the magnetic recording medium 10.

(4) Cartridge

[Cartridge configuration]

The present disclosure also provides a magnetic recording cartridge (also referred to as a tape cartridge) that includes a magnetic recording medium according to the present disclosure. In the magnetic recording cartridge, the magnetic recording medium may be wound around a reel, for example. The magnetic recording cartridge includes, for example, a communication section that communicates with a recording and reproducing device, a storage section, and a storage section that stores information received from the recording and reproducing device via the communication section; The recording apparatus may further include a control section that reads information from the storage section and transmits the information to the recording/reproducing device via the communication section in response to a request. The information may include adjustment information for adjusting the tension applied in the longitudinal direction of the magnetic recording medium. The adjustment information may include, for example, widthwise dimension information at multiple positions in the longitudinal direction of the magnetic recording medium. The dimensional information in the width direction is obtained from dimensional information at the time of manufacturing the magnetic recording medium (initial period after manufacturing) and/or during recording and/or reproducing processing of the magnetic recording medium, which will be described below in [Cartridge memory configuration]. may be dimension information.

With reference to FIG. 9, an example of the configuration of a cartridge 10A including the magnetic recording medium 10 having the above-described configuration will be described.

FIG. 9 is an exploded perspective view showing an example of the configuration of the cartridge 10A. The cartridge 10A is a magnetic recording medium cartridge compliant with the LTO (Linear Tape-Open) standard, and a magnetic tape (tape-shaped magnetic recording medium ) 10 wound thereon, 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 lower shell 212A and an upper shell 212B. A sliding door 217 that straddles and opens and closes the tape outlet 212C provided in the cartridge case 10B, a door spring 218 that urges the slide door 217 to the closed position of the tape outlet 212C, and a write protector that prevents erroneous erasure. 219 and a cartridge memory 211. The reel 10C is approximately disk-shaped with an opening in the center, and is composed of a reel hub 213A and a flange 213B made of a hard material such as plastic. A leader pin 220 is provided at one end of the magnetic tape 10.

Cartridge memory 211 is provided near one corner of cartridge 10A. When the cartridge 10A is loaded into the recording/reproducing device 30, the cartridge memory 211 faces a reader/writer (not shown) of the recording/reproducing device 30. The cartridge memory 211 communicates with the recording/reproducing device 30, specifically with a reader/writer (not shown), using a wireless communication standard based on the LTO standard.

[Cartridge memory configuration]

An example of the configuration of the cartridge memory 211 will be described with reference to FIG. 10.

FIG. 10 is a block diagram showing an example of the configuration of cartridge memory 211. As shown in FIG. The cartridge memory 211 includes an antenna coil (communication unit) 331 that communicates with a reader/writer (not shown) according to a prescribed communication standard, and generates and rectifies the radio waves received by the antenna coil 331 using induced electromotive force. A rectifier/power supply circuit 332 that generates power; a clock circuit 333 that also generates a clock using induced electromotive force from the radio waves received by the antenna coil 331; and a clock circuit 333 that generates a clock using induced electromotive force; A controller (controller) consists of a detection/modulation circuit 334 that modulates the signal to be transmitted, and a logic circuit for discriminating commands and data from the digital signals extracted from the detection/modulation circuit 334 and processing them. section) 335, and a memory (storage section) 336 for storing 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 form a resonant circuit.

The memory 336 stores information related to the cartridge 10A. Memory 336 is non-volatile memory (NVM). The storage capacity of memory 336 is preferably about 32 KB or more. For example, if the cartridge 10A complies with the LTO-9 standard or the LTO-10 standard, the memory 336 has a storage capacity of approximately 32 KB.

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 a cartridge memory compliant with the LTO standard before LTO8 (hereinafter referred to as "conventional cartridge memory"), and is used for storing information compliant with the LTO standard before LTO8. It is an area. Information conforming to the LTO standard before LTO8 includes, for example, manufacturing information (for example, the unique number of the cartridge 10A, etc.), usage history (for example, the number of tape withdrawals (Thread Count), etc.).

The second storage area 336B corresponds to an extended storage area with respect to the storage area of a conventional cartridge memory. The second storage area 336B is an area for storing additional information. Here, the additional information refers to information related to the cartridge 10A that is not specified in LTO standards prior to LTO8. Examples of the additional information include tension adjustment information, management ledger data, index information, thumbnail information of moving images stored on the magnetic tape 10, but are not limited to these data. The tension adjustment information includes the distance between adjacent servo bands (distance between servo patterns recorded on adjacent servo bands) when data is recorded on the magnetic tape 10. The distance between adjacent servo bands is an example of width-related information related to the width of the magnetic tape 10. 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".

Memory 336 may have multiple banks. In this case, some of the banks may constitute the first storage area 336A, and the remaining banks may constitute the second storage area 336B. Specifically, for example, if the cartridge 10A is compliant with the LTO-9 standard or the LTO-10 standard, the memory 336 has two banks with a storage capacity of approximately 16 KB, and the memory 336 has two banks with a storage capacity of approximately 16 KB. One of the banks may constitute the first storage area 336A, and the other bank may constitute the second storage area 336B.

The antenna coil 331 induces an induced voltage by electromagnetic induction. The controller 335 communicates with the recording/reproducing device 30 via the antenna coil 331 according to a prescribed communication standard. Specifically, for example, mutual authentication, command transmission/reception, data exchange, etc. are performed.

The controller 335 stores information received from the recording/reproducing device 30 via the antenna coil 331 in the memory 336. The controller 335 reads information from the memory 336 in response to a request from the recording/reproducing device 30 and transmits the information to the recording/reproducing device 30 via the antenna coil 331 .

(5) Effect

In the magnetic recording medium 10, the average thickness of the magnetic layer 13 is 90 nm or less, the average aspect ratio of the magnetic powder contained in the magnetic layer 13 is 1.0 or more and 3.0 or less, and the average particle volume of the magnetic powder is 2300 nm ³ or less, furthermore, the coercive force Hc1 in the vertical direction of the magnetic recording medium 10 is 4500 Oe or less, and the coercive force Hc2 in the longitudinal direction of the magnetic recording medium 10 and the coercive force Hc1 are Hc2/Hc1≦0.8. The following relationship is satisfied, and the ratio Hrp/Hc1 between the residual magnetic force Hrp of the magnetic recording medium 10 and the coercive force Hc1 measured using a pulsed magnetic field is 2.0 or less. Thereby, the magnetic recording medium 10 has excellent both electromagnetic conversion characteristics and thermal stability.

(6) Modification example

(Modification 1)

The magnetic recording medium 10 may further include a barrier layer 15 provided on at least one surface of the base 11, as shown in FIG. The barrier layer 15 is a layer for suppressing dimensional changes in the base 11 depending on the environment. For example, one example of the cause of the dimensional change is the hygroscopicity of the base 11, and by providing the barrier layer 15, the speed at which moisture enters the base 11 can be reduced. Barrier layer 15 includes, for example, metal or metal oxide. Examples of metals include Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba, Pt, At least one of Au and Ta can be used. As the metal oxide, for example, a metal oxide containing one or more of the above metals can be used. More specifically, for example, _at least one of Al2O3, CuO, CoO, _SiO2 , _Cr2O3 , _TiO2 , _{Ta2O5 ,} and _ZrO2 can be used. Further, the barrier layer 15 may include diamond-like carbon (DLC), diamond, or the like.

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 determined in the same manner as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is adjusted as appropriate depending on the thickness of the barrier layer 15.

(Modification 2)

The magnetic recording medium 10 may be incorporated into a library device. That is, the present disclosure also provides a library device including at least one magnetic recording medium 10. The library device has a configuration that can adjust the tension applied in the longitudinal direction of the magnetic recording medium 10, and may include a plurality of the recording/reproducing devices 30 described above.

3. Example

EXAMPLES Hereinafter, the present disclosure will be specifically described with reference to Examples, but the present disclosure is not limited to these Examples.

In this example, the average thickness of the base film (substrate), the average thickness of the magnetic layer, the average thickness of the underlayer, the average thickness of the back layer, the average thickness of the magnetic tape (magnetic recording medium), the average aspect ratio of the magnetic powder, The average particle size of the magnetic powder, the average particle volume of the magnetic powder, the coercive force Hc1 of the magnetic tape in the vertical direction, the coercive force Hc2 of the magnetic tape in the longitudinal direction, and the residual magnetic force Hrp are as described in the above embodiment. It was determined by the measurement method.

[Example 1]
(Preparation process of paint for forming magnetic layer)
A paint for forming a magnetic layer was prepared as follows. First, a first composition having the following composition was kneaded using an extruder. Next, the kneaded first composition and the second composition having the following composition were added to a stirring tank equipped with a disperser for preliminary mixing. Subsequently, the mixture was further mixed in a sand mill and filtered to prepare a coating material for forming a magnetic layer.

(First composition)
Magnetic powder: 100 parts by mass Vinyl chloride resin (cyclohexanone solution 30% by mass): 60 parts by mass (degree of polymerization 300, Mn = 10000, polar group OSO ₃ K = 0.07 mmol/g, secondary OH = 0.3 mmol /g)
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)
In addition, as the magnetic powder, those shown in Table 1 were used.

(Second composition)
Vinyl chloride resin: 1.1 parts by mass (resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
n-Butyl stearate: 2 parts by mass Methyl ethyl ketone: 121.3 parts by mass Toluene: 121.3 parts by mass Cyclohexanone: 60.7 parts by mass

Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) and 2 parts by mass of myristic acid were added as curing agents to the magnetic layer forming paint prepared as described above. did.

(Preparation process of paint for base layer formation)
A paint for forming a base layer was prepared as follows. First, a third composition having the following composition was kneaded using an extruder. Next, the kneaded third composition and the fourth composition having the following composition were added to a stirring tank equipped with a disper for preliminary mixing. Subsequently, the mixture was further mixed in a sand mill and filtered to prepare a paint for forming a base layer.

(Third composition)
Acicular 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)

(Fourth composition)
Polyurethane resin UR8200 (manufactured by Toyobo): 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

Finally, 4 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 to the base layer forming paint prepared as described above. did.

(Preparation process of paint for back layer formation)
A paint for forming a back layer was prepared as follows. A paint for forming a back layer was prepared by mixing the following raw materials in a stirring tank equipped with a disperser and filtering the mixture.
Carbon black (manufactured by Asahi Co., Ltd., product name: #80): 100 parts by mass Polyester polyurethane: 100 parts by mass (manufactured by Nippon Polyurethane Co., Ltd., product name: N-2304)
Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass

(Film forming process)
Using the paint produced as described above, a magnetic tape having a medium configuration 1 as shown in Table 2 below was produced in the following manner. First, a long PEN film (base film) having an average thickness of 4.0 μm was prepared as a support. Next, a base layer forming paint was applied on one main surface of the PEN film and dried to form a base layer having an average thickness of 1.1 μm on one main surface of the PEN film. Next, a magnetic layer forming paint was applied onto the underlayer and dried to form a magnetic layer having an average thickness of 80 nm on the underlayer. In addition, when drying the paint for forming the magnetic layer, the magnetic powder was magnetically oriented in the thickness direction of the PEN film using a solenoid coil. Specifically, the magnetic powder was once magnetically oriented in the running direction (longitudinal direction) of the PEN film using a solenoid coil, and then the magnetic powder was oriented in the thickness direction of the PEN film. Further, the drying conditions (drying temperature and drying time) of the paint for forming the magnetic layer were adjusted, and the coercive force Hc1 in the vertical direction and the coercive force Hc2 in the longitudinal direction were set as shown in Table 1.

Subsequently, a back layer forming paint was applied onto the other main surface of the PEN film on which the underlayer and magnetic layer were formed, and dried to form a back layer having an average thickness of 0.4 μm. Then, the PEN film on which the underlayer, magnetic layer, and back layer were formed was subjected to a curing treatment. Thereafter, a calender treatment was performed to smooth the surface of the magnetic layer.

(Cutting process)
The magnetic tape obtained as described above was cut into 1/2 inch (12.65 mm) width pieces. As a result, a long magnetic tape having an average thickness of 5.6 μm was obtained. The residual magnetic force Hrp of the obtained magnetic tape was measured and found to be 5000 Oe.

(Writing servo signals and data signals)
Servo signals and data signals were written on the long magnetic tape obtained as described above in the following manner. First, five servo bands having a servo band width _WSB of 96 μm were formed by writing servo signals on a magnetic tape using a servo writer. Note that by writing the servo signals, a V-shaped magnetic pattern row was formed in each servo band.

Next, a data signal was written in the data band between the servo bands using a recording/reproducing device. At this time, the recording and reproducing apparatus was controlled so that the recording track width W was 2.9 μm and the recording wavelength λ was a single recording wavelength of 0.208 μm. Note that the recording wavelength λ [nm] of the data signal is four times the minimum value L [nm] (=0.052 μm) of the distance between magnetization reversals when recorded at the shortest recording wavelength (that is, the shortest recording wavelength L' =2×L, and the recording wavelength λ=(twice the length of L'). A ring head with a gap length of 0.2 μm was used as the recording head.

Here, the reason why the recording wavelength λ is twice the shortest recording wavelength L' is as follows. That is, in a recording/reproducing system using a short wavelength, the C/N is generally the output/noise ratio when recording/reproducing at a recording wavelength twice the shortest recording wavelength. Further, the C/N at twice the recording wavelength has a higher correlation with the error rate than the C/N at the shortest recording wavelength. Furthermore, when C/N measurement is performed at the shortest recording wavelength, depending on the wavelength characteristics of the recording and reproducing system, tape noise may be hidden by the system noise of the recording and reproducing system, and the noise characteristics of the medium may not be reflected correctly. Especially in the case of high linear recording density recording, the noise characteristics of the media are often not reflected correctly.

The minimum value L of the distance between magnetization reversals and the data track width W were determined as follows. First, the surface of the magnetic layer 13 was observed using a magnetic force microscope (MFM), and an MFM image was obtained. A and B in FIG. 12 show an example of the MFM image. Next, from the acquired MFM image, the dimensions of the magnetization pattern array in the width direction of the magnetic tape were measured, and the track width was determined as W [nm]. Further, the distance between bright areas or the distance between dark areas in the longitudinal direction of the magnetic tape was defined as λ [nm]. Thereafter, half the value of λ[nm] was set as L'[nm], and further half of L'[nm] was set as L[nm].

[Examples 2 to 7]
The magnetic powder was changed to have the average aspect ratio, average particle size, and average particle volume as shown in Table 1, and the average thickness, Hc1, Hc2, and Hrp of the magnetic layer were changed as shown in Table 1. A magnetic tape was obtained in the same manner as in Example 1 except for the following changes.

[Example 8]
A magnetic tape was obtained in the same manner as in Example 4, except that the medium configuration of the magnetic tape was changed to Medium Configuration 2 shown in Table 2, and the average thickness of the magnetic layer was changed to 80 nm. The Hrp of the obtained magnetic tape was 4920 Oe.

[Example 9]
A magnetic tape was obtained in the same manner as in Example 2, except that the medium configuration of the magnetic tape was changed to Media Configuration 3 shown in Table 2.

[Example 10]
A magnetic tape was obtained in the same manner as in Example 6, except that the medium configuration of the magnetic tape was changed to Media Configuration 4 shown in Table 2.

[Example 11]
A magnetic tape was obtained in the same manner as in Example 6, except that the medium configuration of the magnetic tape was changed to medium configuration 5 shown in Table 2, and the average thickness of the underlayer was changed to 1.0 μm.

[Example 12]
A magnetic tape was obtained in the same manner as in Example 7, except that the medium configuration of the magnetic tape was changed to medium configuration 6 shown in Table 2, and the average thickness of the underlayer was changed to 1.0 μm.

[Example 13]
A magnetic tape was obtained in the same manner as in Example 4 except that Hc1, Hc2, and Hrp were changed as shown in Table 1. ,

[Example 14]
A magnetic tape was obtained in the same manner as in Example 4, except that the average thickness of the magnetic layer was changed to 80 nm, and Hc1, Hc2, and Hrp were changed as shown in Table 1. ,

[Example 15]
A magnetic tape was obtained in the same manner as in Example 7 except that Hc1, Hc2, and Hrp were changed as shown in Table 1.

[Example 16]
The magnetic powder was changed to epsilon iron oxide having the average aspect ratio, average particle size, and average particle volume as shown in Table 1, and Hc1, Hc2, and Hrp were changed as shown in Table 1. A magnetic tape was obtained in the same manner as in Example 1 except for the following.

[Example 17]
The magnetic powder was changed to epsilon iron oxide having the average aspect ratio, average particle size, and average particle volume as shown in Table 1, and Hc1, Hc2, and Hrp were changed as shown in Table 1. A magnetic tape was obtained in the same manner as in Example 1 except for the following.

[Comparative example 1]
The magnetic powder was changed to have the average aspect ratio, average particle size, and average particle volume as shown in Table 1, and the average thickness, Hc1, and Hrp of the magnetic layer were changed as shown in Table 1. A magnetic tape was obtained in the same manner as in Example 1 except for this.

[Comparative example 2]
A magnetic tape was obtained in the same manner as in Example 4, except that the average thickness of the magnetic layer was changed as shown in Table 1.

[Comparative example 3]
A magnetic tape was obtained in the same manner as in Example 1, except that the average thickness of the magnetic layer, Hc1, Hc2, and Hrp were changed as shown in Table 1.

[Comparative example 4]
A magnetic tape was obtained in the same manner as in Example 1, except that Hc1, Hc2, and Hrp were changed as shown in Table 1.

[Comparative example 5]
A magnetic tape was obtained in the same manner as in Example 5, except that Hc1, Hc2, and Hrp were changed as shown in Table 1.

[Comparative example 6]
The magnetic powder was changed to have the average aspect ratio, average particle size, and average particle volume as shown in Table 1, and the average thickness, Hc1, and Hrp of the magnetic layer were changed as shown in Table 1. A magnetic tape was obtained in the same manner as in Example 1 except for this.

The magnetic tapes of Examples 1 to 15 and Comparative Examples 1 to 6 obtained as described above were evaluated for signal attenuation and electromagnetic conversion characteristics (C/N) after 10 years. These evaluation methods are described below.

(Signal attenuation after 10 years)

For the samples of each Example and each Comparative Example, the amount of signal attenuation after 10 years was determined as follows. Specifically, "Tape Head Tester (hereinafter referred to as THT)" manufactured by Micro Physics was used. For the recording/playback head, we used the one installed in the IBM tape drive "TS1140" as is. For the measurements, a magnetic tape serving as a magnetic recording medium was cut into a length of 90 cm, formed into a ring shape with the recording layer on the back side, and then both ends of the magnetic tape were joined on the back side of the magnetic tape with adhesive tape. Further, a silver tape was pasted adjacent to the joint to detect the tape rotation position. After the ring-shaped magnetic tape was attached to the THT, it was rotated at a speed of 2 m/sec.

Next, a 10 MHz signal generated using a signal generator "ARBITRARY WAVEFORM GENERATOR AWG2021" manufactured by Tektronix was recorded on the magnetic tape for one rotation of the entire length of the tape using the optimum recording current. Following recording, the signals recorded on the tape were continuously played back from the next round, and the playback output was measured using a spectrum analyzer "8591E" manufactured by Hewlett Packard. The settings of the spectrum analyzer at this time were RBW: 1 MHz, VBW: 1 MHz, SWP: 500 msec, point: 400, and zero span mode. The measurement was performed only for 0.4 seconds between the "recording parts" excluding the "near the tape joints" where sufficient recording was not performed, and the average value Y of the reproduction output during this period was calculated. Measurement was performed for each round of the tape, and the average value Y of the reproduction output for each round was taken as the average value Y(t) of the reproduction output for the elapsed time from the end of signal recording (t=0). Measurement was performed up to t=100 sec, and timely transmitted to the connected personal computer for recording.

The above measurement flow was performed four times using the same magnetic tape, and the Y(t) values obtained from each measurement were averaged at the same elapsed time t to form a sequence of Y _ave (t). The obtained Y _ave (t) was plotted on a graph with the Y axis and the elapsed time t on the X axis, and an approximate curve was created from this graph using logarithmic approximation. The amount of signal attenuation after 10 years was calculated using the obtained approximate curve.

(C/N)

"Tape Head Tester (hereinafter referred to as THT)" manufactured by Micro Physics was used. As the recording/reproducing head, the recording/reproducing head installed in the IBM tape drive "TS1140" was used as is. For the measurements, a magnetic tape serving as a magnetic recording medium was cut into a length of 90 cm, formed into a ring shape with the recording layer on the back side, and then both ends of the magnetic tape were joined on the back side of the magnetic tape with adhesive tape. Further, a silver tape was pasted adjacent to the joint to detect the tape rotation position. After the ring-shaped magnetic tape was attached to the THT, it was rotated at a speed of 2 m/sec.

First, we acquired the magnetic tape playback signal. The conditions for acquiring the reproduced signal are shown below. signal: single recording frequency (10MHz)
Recording current: optimal recording current

Next, the reproduced signal was taken in by a spectrum analyzer, and the reproduced output value of 10 MHz and the average value of noise of 10 MHz±1 MHz were measured, and the difference between them was defined as C/N. The results are shown in Table 1 as relative values assuming that the C/N of Comparative Example 1 is 0 dB. Note that when the C/N is 1.5 dB or more, a medium that can withstand short wavelengths and narrow track densities can be realized.

Table 1 below shows the magnetic properties and evaluation results of the magnetic tapes of Examples 1 to 15 and Comparative Examples 1 to 6. Table 2 below shows details of each medium configuration.

The following can be seen from Tables 1 and 2.

In all of the magnetic tapes of Examples 1 to 15, the signal attenuation after 10 years was −1.0 dB or more, even though the average particle volume of the magnetic powder was 2300 nm ³ or less. Therefore, the magnetic tapes of Examples 1 to 15 all had excellent thermal stability despite the small average particle volume of the magnetic powder. Further, all of the magnetic tapes of Examples 1 to 15 had a C/N of 1.5 dB or more and had excellent electromagnetic conversion characteristics. These results show that the magnetic recording medium of the present disclosure has excellent electromagnetic conversion characteristics and thermal stability.

From the comparison between Example 3 and Comparative Example 1, it is clear that the average aspect ratio of the magnetic powder is 3.0 or less and the average particle volume of the magnetic powder is 2300 nm ³ or less to increase the C/N by 1.5 dB or more. It can be seen that it is contributing to this.
A comparison between Example 4 and Comparative Example 2 shows that the average thickness of the magnetic layer of 90 nm or less contributes to achieving a C/N of 1.5 dB or more.
From the comparison between Example 1 and Comparative Example 3, it can be seen that the C/N is 1.5 dB or more when Hc1 and Hc2 satisfy the relationship of Hc2/Hc1≦0.8.
From the comparison between Example 1 and Comparative Example 4, it can be seen that Hc1 of 4500 Oe or less contributes to making the C/N 1.5 dB or more.
From these comparisons, it is found that the average aspect ratio of the magnetic powder is 3.0 or less, the average particle volume is 2300 nm ^or less, the average thickness of the magnetic layer is 90 nm or less, and that Hc2 and Hc1 are equal to Hc2/Hc1. It can be seen that satisfying the relationship of ≦0.8 and that Hc1 is 4500 Oe or less brings about an improvement in electromagnetic conversion characteristics.
However, as shown in Comparative Examples 5 and 6, even if these requirements are met, the signal attenuation after 10 years is lower than -1.0 dB, and excellent thermal stability may not be obtained. I understand.
Here, looking at Example 5 and Comparative Example 5, it is found that Hrp/Hc1 of 2.0 or less contributes to reducing the amount of signal attenuation after 10 years, that is, thermal stability It can be seen that this results in an improvement in
Further, Hrp/Hc1 is also 2.0 or less in other examples, and in these examples, the signal attenuation after 10 years is -1.0 dB or more. Regarding Comparative Example 6, Hrp/Hc1 is over 2.0, and the signal attenuation after 10 years is lower than -1.0 dB. These results also indicate that Hrp/Hc1 of 2.0 or more improves thermal stability.
As described above, the average aspect ratio and average particle volume of the magnetic powder, the average thickness of the magnetic layer, the ratio Hc2/Hc1, and Hc1 are within specific numerical ranges, and furthermore, Hrp/Hc1 is 2.0. It can be seen that the magnetic recording medium has excellent electromagnetic conversion characteristics and thermal stability when the following conditions are satisfied.

In Examples 7 and 12, Hrp/Hc1 is 1.98, and in this case, the signal attenuation after 10 years is -0.95 dB. On the other hand, in other examples, Hrp/Hc1 is lower and the evaluation result of the amount of signal attenuation after 10 years is better. From these results, in order to further improve thermal stability, Hrp/Hc1 is more preferably 1.95 or less, even more preferably 1.90 or less, and particularly preferably 1.85 or less. . For example, it can be seen that by setting Hrp/Hc1 to 1.85 or less, the signal attenuation after 10 years can be set to -0.50 dB or more.

Examples 1 to 7 and Examples 13 to 15 are different from Examples 8 to 12 in the medium configuration of the magnetic tape. For example, the W/L of media configurations 2 to 6 is smaller than that of media configuration 1. Furthermore, the average thickness of the magnetic tapes in media configurations 3 to 6 is smaller than those in media configurations 1 and 2. Further, the number of servo tracks in media configurations 4 to 6 is greater than that in media configurations 1 to 3.
As shown in Examples 1 to 15, excellent electromagnetic conversion characteristics and thermal stability were obtained with magnetic tapes having such different media configurations. Therefore, it can be seen that the effects of the present disclosure can be achieved by magnetic tapes having various media configurations.

Although the embodiments and examples of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and examples, and various modifications based on the technical idea of the present disclosure are possible. It is.

For example, the configurations, methods, processes, shapes, materials, numerical values, etc. mentioned in the above-mentioned embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and values may be used as necessary. Numerical values etc. may also be used. Further, the chemical formulas of compounds, etc. are representative ones, and as long as they are general names of the same compound, they are not limited to the stated valency, etc.

Further, the configurations, methods, processes, shapes, materials, numerical values, etc. of the embodiments and examples described above can be combined with each other without departing from the gist of the present disclosure.

Furthermore, in this specification, a numerical range indicated using "~" indicates a range that includes the numerical values written before and after "~" as the minimum value and maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit or lower limit of the numerical range of one step may be replaced with the upper limit or lower limit of the numerical range of another step. The materials exemplified herein can be used alone or in combination of two or more, unless otherwise specified.

Note that the present disclosure can also have the following configuration.
[1] Base and
a magnetic layer provided on the base and containing magnetic powder;
The average thickness of the magnetic layer is 90 nm or less,
The average aspect ratio of the magnetic powder is 1.0 or more and 3.0 or less,
The average particle volume of the magnetic powder is 2300 nm ³ or less,
The coercive force Hc1 in the vertical direction of the magnetic recording medium is 4500 Oe or less,
The coercive force Hc2 and the coercive force Hc1 in the longitudinal direction of the magnetic recording medium satisfy the relationship Hc2/Hc1≦0.8, and
The ratio Hrp/Hc1 of the residual magnetic force Hrp of the magnetic recording medium and the coercive force Hc1 measured using a pulsed magnetic field is 2.0 or less,
A tape-shaped magnetic recording medium.
[2] The magnetic recording medium according to [1], wherein the magnetic powder has an average particle volume of 2200 nm ³ or less.
[3] The magnetic recording medium according to [1] or [2], wherein the ratio Hrp/Hc1 is 1.95 or less.
[4] The magnetic recording medium according to [1] or [2], wherein the ratio Hrp/Hc1 is 1.90 or less.
[5] The magnetic recording medium according to [1] or [2], wherein the ratio Hrp/Hc1 is 1.85 or less.
[6] The magnetic recording medium according to any one of [1] to [5], wherein the magnetic powder contains hexagonal ferrite.
[7] The magnetic recording medium according to [6], wherein the hexagonal ferrite contains at least one of Ba and Sr.
[8] The magnetic recording medium according to any one of [1] to [7], wherein the magnetic recording medium has a coercive force Hc2 of 2000 Oe or less in the longitudinal direction.
[9] The magnetic recording medium according to any one of [1] to [8], wherein the average thickness of the magnetic recording medium is 5.6 μm or less.
[10] The magnetic recording medium according to any one of [1] to [9], wherein the average thickness of the substrate is 4.2 μm or less.
[11] The magnetic recording medium according to any one of [1] to [10], wherein the magnetic layer has an average thickness of 80 nm or less.
[12] The magnetic recording medium according to any one of [1] to [11], wherein the coercive force Hc2 and the coercive force Hc1 satisfy the relationship Hc2/Hc1≦0.7.
[13] The magnetic recording medium according to any one of [1] to [12], wherein the coercive force Hc1 is 500 Oe or more.
[14] An underlayer is provided between the magnetic layer and the base,
The average thickness of the base layer is 2.0 μm or less,
The magnetic recording medium according to any one of [1] to [13].
[15] A back layer is provided on the surface opposite to the surface on which the magnetic layer is provided of the two surfaces of the base,
The average thickness of the back layer is 0.6 μm or less,
The magnetic recording medium according to any one of [1] to [14].
[16] The magnetic recording medium according to any one of [1] to [15], wherein the magnetic powder has an average particle size of 50 nm or less.
[17] The tape-shaped magnetic recording medium according to any one of [1] to [16];
a communication unit that communicates with the recording/reproducing device;
storage section and
A control unit that stores information received from the recording/playback device via the communication unit in the storage unit, reads information from the storage unit in response to a request from the recording/playback device, and transmits the information to the recording/playback device via the communication unit. and,
The information includes adjustment information for adjusting the tension applied in the longitudinal direction of the magnetic recording medium. Tape Cartridge.

10 Magnetic recording medium 11 Substrate (base layer)
12 Base layer 13 Magnetic layer 14 Back layer

Claims (22)

A base body;
a magnetic layer provided on the base and containing magnetic powder;
The average thickness of the magnetic layer is 80 nm or less,
The average aspect ratio of the magnetic powder is 1.0 or more and 2.8 or less,
The average particle volume of the magnetic powder is 2000 nm ³ or less,
The substrate is PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate). and at least one of polyethylene bisphenoxy carboxylate,
The coercive force Hc1 in the vertical direction of the magnetic recording medium is 3000 Oe or less, and the average thickness is 5.6 μm or less ,
The coercive force Hc2 and the coercive force Hc1 in the longitudinal direction of the magnetic recording medium satisfy the relationship Hc2/Hc1≦ 0.75 , and
The ratio Hrp/Hc1 of the residual magnetic force Hrp of the magnetic recording medium and the coercive force Hc1 measured using a pulsed magnetic field is 2.0 or less,
A tape-shaped magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder includes hexagonal ferrite, and the hexagonal ferrite includes at least one of Ba and Sr. The magnetic recording medium according to claim 1 or 2 , wherein the ratio Hrp/Hc1 is 1.95 or less. The magnetic recording medium according to claim 1, wherein the ratio Hrp/Hc1 is 1.90 or less . The magnetic recording medium according to claim 1, wherein the ratio Hrp/Hc1 is 1.85 or less . The magnetic recording medium according to any one of claims 1 to 5 , wherein the coercive force Hc2 in the longitudinal direction of the magnetic recording medium is 2000 Oe or less . The magnetic recording medium according to any one of claims 1 to 6 , wherein the average thickness of the magnetic recording medium is 5.3 μm or less . The magnetic recording medium according to any one of claims 1 to 6 , wherein the average thickness of the magnetic recording medium is 5.2 μm or less . The magnetic recording medium according to any one of claims 1 to 6 , wherein the average thickness of the magnetic recording medium is 5.0 μm or less . The magnetic recording medium according to any one of claims 1 to 9 , wherein the average thickness of the substrate is 4.2 μm or less. The magnetic recording medium according to any one of claims 1 to 9 , wherein the average thickness of the substrate is 3.8 μm or less . The magnetic recording medium according to any one of claims 1 to 9 , wherein the average thickness of the substrate is 3.4 μm or less . The magnetic recording medium according to any one of claims 1 to 12 , wherein the average thickness of the magnetic layer is 70 nm or less . The magnetic recording medium according to any one of claims 1 to 12 , wherein the average thickness of the magnetic layer is 60 nm or less . The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic layer is 50 nm or less . 16. The magnetic recording medium according to claim 1 , wherein the coercive force Hc2 and the coercive force Hc1 satisfy the relationship Hc2/Hc1≦0.7 . An underlayer is provided between the magnetic layer and the base,
The magnetic recording medium according to any one of claims 1 to 16 , wherein the average thickness of the underlayer is 0.8 μm or more and 1.4 μm or less . Of the two surfaces of the base, a back layer is provided on the surface opposite to the surface on which the magnetic layer is provided,
The magnetic recording medium according to any one of claims 1 to 17, wherein the average thickness of the back layer is 0.6 μm or less. The magnetic recording medium according to any one of claims 1 to 18, wherein the average particle size of the magnetic powder is 15 nm or more and 22 nm or less. The magnetic recording medium according to claim 1, wherein the coercive force Hc2 and the coercive force Hc1 satisfy the relationship Hc2/Hc1≦0.65. The magnetic recording medium according to claim 1, wherein the coercive force Hc2 and the coercive force Hc1 satisfy the relationship Hc2/Hc1≦0.60. A tape-shaped magnetic recording medium according to any one of claims 1 to 21,
a communication unit that communicates with the recording/reproducing device;
storage section and
A control unit that stores information received from the recording/playback device via the communication unit in the storage unit, reads information from the storage unit in response to a request from the recording/playback device, and transmits the information to the recording/playback device via the communication unit. and,
A tape cartridge, wherein the information includes adjustment information for adjusting tension applied in the longitudinal direction of the magnetic recording medium.