JP2005339648A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is excellent in sliding durability in repeated high-speed travel and favorable in head contact, has less spacing loss and can cope with an AIT4 format. <P>SOLUTION: Loop stiffness SMD (unit: mN/8 mm) in the length direction of a magnetic recording medium having a metal magnetic thin film on a nonmagnetic support object (for example, a polyamide film) and the loop stiffness STD (unit: mN/8 mm) in the width direction is constituted so that all the following formulas can be satisfied. 1.0≤STD/SMD≤1.4... (1) 10.0<STD... (2) SMD+STD<29.0... (3) The surface roughness Ra of the metal magnetic thin film is 1.0 nm-3.0 nm, Rz is 10 nm-50 nm, the number of projections with projection height of 5 nm or more is 4 million-10 million/mm<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium for high-density recording, and more particularly to a magnetic recording medium that can support high-density recording for the AIT4 format.

  Conventionally, as a magnetic recording medium, a magnetic material such as an oxide magnetic powder or an alloy magnetic powder is dispersed on a nonmagnetic support in an organic binder such as a vinyl chloride-vinyl acetate copolymer, a polyester resin, or a polyurethane resin. A so-called coating-type magnetic recording medium is widely known which is manufactured by applying and drying a magnetic coating material.

  However, in recent years, in the field of video tape recorders and the like, there is a strong demand for higher image quality, higher density recording, longer recording time, and the like. Also, in the field of office computers such as minicomputers and personal computers, magnetic tapes for recording computer data (in order to achieve large recording capacity and miniaturization in conjunction with downsizing and increased information processing capabilities) There is a strong demand for improving the recording capacity of so-called tape streamers.

  In general, a magnetic tape has a structure in which a magnetic layer is provided on a nonmagnetic support made of a flexible material such as a synthetic resin, and in order to achieve the above-described improvement in recording capacity (volume recording capacity). It is said that an effective method is to increase the recording density of the magnetic layer itself by making the magnetic layer a ferromagnetic metal thin film and to reduce the total thickness of the magnetic tape. That is, as the magnetic tape, a vapor-deposited tape obtained by forming a metal magnetic thin film on a nonmagnetic support, that is, a so-called metal magnetic thin film type magnetic recording medium is effective.

  From this point of view, to meet the demand for high-density recording, a ferromagnetic material made of metal or an alloy such as Co—Ni is used for plating or vacuum thin film formation technology (vacuum deposition method, sputtering method, ion plating). For example, a magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film directly deposited on a nonmagnetic support has been put into practical use. For example, in the field of the video tape recorder and the like, there are a high-band 8 mm video tape recorder, a digital video tape recorder, a vapor deposition tape for 8 mm data storage format (AIT), and the like.

  Such a metal magnetic thin film type magnetic recording medium is excellent in coercive force, remanent magnetization, squareness ratio, etc., and not only has excellent electromagnetic conversion characteristics at a short wavelength, but also can be formed with a very thin magnetic layer, The thickness loss at the time of recording demagnetization and reproduction is small, it is not necessary to mix a binder that is a nonmagnetic material in the magnetic layer, so the packing density of the magnetic material can be increased, and a large magnetization can be obtained. Has a number of advantages.

  Further, in order to improve the electromagnetic conversion characteristics of the metal thin film type magnetic recording medium and obtain a larger output, when forming the magnetic layer of the magnetic recording medium, the magnetic layer is deposited obliquely, so-called The oblique vapor deposition has been proposed and put into practical use as a magnetic tape for high-quality VTR, digital VTR, and computer data storage.

  When a magnetic recording medium having the above-described advantages is put into practical use, fine protrusions with a uniform height are provided on the surface in order to maintain sliding resistance while keeping the spacing between the head and the magnetic layer small. The method of arranging in is taken. For example, by this method, a tape for DV mini or 8 mm data storage format (AIT) is realized.

  However, there is a demand for further improvement in recording capacity, that is, improvement in recording density, and a new response to higher recording density of metal magnetic thin film type magnetic recording media is required.

Conventionally, as a method corresponding to improvement of recording capacity and improvement of related characteristics, for example, the distribution of protrusion height and surface roughness of the surface of an aromatic polyamide film is specified, and output characteristics when used as a magnetic recording medium And methods for improving durability (running performance) have been proposed (see, for example, Patent Document 1 and Patent Document 2).
Alternatively, a method for improving the dropout of a magnetic recording medium by using a film mainly composed of para-oriented aromatic polyamide with controlled cross-sectional area of coarse protrusions of 0.27 μm or more and the number of contained per unit area is proposed. (For example, see Patent Document 3).

  Furthermore, the height of the abrasive (a ratio of the number of 15 nm to 30 nm with respect to the number less than 10 nm) of the coating type magnetic recording medium containing the abrasive in the magnetic layer, and the stiffness (with respect to the longitudinal direction) of the magnetic recording medium A method for improving head wear, dirt, and head contact has been proposed (for example, refer to Patent Document 4).

  In addition, the ratio of the stiffness (TDS) in the length direction to the stiffness (MDS) in the width direction (TDS / MDS) of the multilayer coating type magnetic recording medium is set to a specific region (0.8 to 1.2). A method for improving the mutual contact characteristic with respect to the head has been proposed. Here, each stiffness is expressed by an output (mV) obtained by pressing both ends of the magnetic recording medium cut to a predetermined size against the strain gauge at a constant speed (see, for example, Patent Document 5). .)

Japanese Patent No. 3047471 JP-A-10-114038 JP-A-11-106529 JP 2003-16629 A JP 2000-123355 A

According to Patent Documents 1 to 3, it is said that peeling of the magnetic layer, dropout, and the like are improved. However, only by specifying the projection height distribution on the surface, a higher density recording format (for example, AIT4). In some cases, it may not be able to sufficiently withstand high-speed sliding at a high transfer rate when used for formatting.
According to Patent Document 4, an improvement effect can be expected with respect to the head contact, but since it is a coating type, it cannot be said that the above conditions are met in the case of a metal thin film type magnetic recording medium of a high density recording format. Moreover, it is difficult to obtain sufficient surface smoothness and there is a limit in reducing the spacing loss.
Further, according to Patent Document 5, an improvement effect can be expected with respect to the head-per-layer of the multilayer coating type magnetic recording medium, but sufficient conditions are required in the case of the metal thin film type magnetic recording medium used in the above-described high-density recording format. However, it is difficult to obtain sufficient surface smoothness, and there is a limit to reducing the spacing loss.

  In order to meet future increases in recording density in metal thin-film magnetic recording media, for example, the AIT4 format with a recording capacity of 200 GB / winding, it is necessary to reduce the spacing loss by further smoothing the surface, and the high density. It is also necessary to improve the high-speed repetitive running property (sliding resistance) to the high transfer rate required in the recording format.

  The present invention has been made in view of the above prior art, and is a metal magnet that is excellent in sliding resistance in repeated high-speed running, has good head contact, has little spacing loss, and can be used for high-density recording (AIT4 format). An object is to provide a thin-film magnetic recording medium.

  As a result of intensive studies, the present inventors have reduced the contact pressure between the head and the surface of the tape by reducing the rigidity of the magnetic recording medium, thereby significantly improving the sliding resistance at high speeds and at the same time reducing the rigidity. In this case, good head contact can be achieved by balancing the rigidity in the tape length direction and width direction, and in combination with this, further spacing can be achieved by controlling the surface smoothness of the metal magnetic recording medium. The present inventors have found that the loss can be reduced and the above problems can be solved, and the present invention has been achieved.

That is, according to the present invention, in a magnetic recording medium having a metal magnetic thin film on a nonmagnetic support, a loop stiffness SMD in the length direction (unit: mN / 8 mm) and a loop stiffness STD in the width direction (unit: mN / 8 mm). However, the magnetic recording medium satisfies all of the following expressions.
1.0 ≦ STD / SMD ≦ 1.4 (1)
10.0 <STD (2)
SMD + STD <29.0 (3)

Here, the surface roughness Ra of the metal magnetic thin film is 1.0 nm to 3.0 nm, Rz is 10 nm to 50 nm, and the number of protrusions having a protrusion height of 5 nm or more is 4 million to 10 million pieces / mm ² . It is preferable to be.

  Furthermore, it is preferable that an aromatic polyamide film is used as the nonmagnetic support.

  The magnetic recording medium is preferably an AIT4 format magnetic tape.

According to the metal magnetic thin film type magnetic recording medium of the present invention, in a helical magnetic recording system, it is possible to obtain good per-head and repeated running durability of 20000 times or more, and a high recording density of 1.2 GB / inch ^2. It can be used as a magnetic recording medium for AIT4 format having
In addition, by controlling the surface smoothness of the medium, particularly the surface roughness Ra, Rz and the number of protrusions, the spacing loss between the metal magnetic thin film and the magnetic head can be further reduced, and higher density recording can be realized. it can.
Furthermore, if an aromatic polyamide film is used as the nonmagnetic support, the balance of loop stiffness is made suitable by excellent mechanical strength, and it is possible to realize a higher-density recording format.

Hereinafter, an example of the magnetic recording medium of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view of a magnetic recording medium of the present invention.
This magnetic recording medium 100 has a magnetic layer 102 made of a metal magnetic thin film formed by a vacuum thin film forming technique on one main surface of a long nonmagnetic support 101, and a protective layer 103 is formed on the magnetic layer 102. The backcoat layer 104 is formed on the opposite side of the nonmagnetic support 101 from the magnetic layer 102. Usually, a predetermined fluorine-based lubricant is applied to both the surface layers of the magnetic layer 102 and the backcoat layer 104.

In the above configuration, for example, the main surface of the long nonmagnetic support 101 is provided with the magnetic layer 102 having a thickness of 140 to 220 nm (usually about 180 nm) formed by a vacuum thin film forming technique, and magnetically. A protective layer 103 made of diamond-like carbon having a thickness of 5 to 15 nm is provided on the layer 102.
Next, each constituent layer will be described in detail.

For the non-magnetic support 1, any known material that is usually used as a substrate of a magnetic recording medium can be applied. For example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide, polyetherimide and the like can be mentioned.
Among the nonmagnetic supports, polyester films, mainly PET films, have been conventionally used particularly for home video cassette tapes (for example, 8 mm tapes) and tape streamers for computer data backup. On the other hand, since the polyamide film has higher strength than the PET film, the thickness can be reduced, and it is desirable as a magnetic recording medium corresponding to long-time recording, large capacity, and the like. The thickness of the nonmagnetic support is usually 3.8 to 4.5 μm.
In the present invention, when adjusting and controlling the surface smoothness (surface roughness, number of protrusions) of the metal magnetic thin film as described later, fine protrusions are formed on the nonmagnetic support (base film) in advance, The surface property is suitably adjusted.

  Next, the metal magnetic material forming the magnetic layer 102 may be any material as long as it is normally applied to a magnetic tape. Examples thereof include ferromagnetic metals such as Fe, Co, Ni, and ferromagnetic alloys such as FeCo, CoNi, CoNiFe, CoCr, CoPt, CoPtB, CoCrPt, CoCrTa, CoCrPtTa, CoNiPt, FeCoNi, FeCoB, FeNiB, and FeCoNiCr.

  The magnetic layer 102 includes a vacuum evaporation method in which a metal magnetic material is heated and evaporated under vacuum and deposited on the nonmagnetic support 101, an ion plating method in which the metal magnetic material is evaporated in a discharge, and argon as a main component. The film can be formed into a thin film by a so-called PVD technique such as a sputtering method in which glow discharge is generated in an atmosphere and atoms on the target surface are beaten with argon ions.

In FIG. 2, the schematic block diagram of the continuous winding-type vapor deposition apparatus as an example of the apparatus used for film-forming of the magnetic layer 102 is shown.
In this vapor deposition apparatus 200, a feed roll 212 and a take-up roll 213 are provided in a vacuum chamber 211 that is evacuated from the exhaust ports 201 and 202, and a nonmagnetic support is provided therebetween. 101 runs sequentially.

  A cooling can 214 is provided between the feed roll 212 and the take-up roll 213 while the nonmagnetic support 101 travels. The cooling can 214 is provided with a cooling device (not shown) to suppress thermal deformation or the like due to a temperature rise of the nonmagnetic support 101.

  The nonmagnetic support 101 is sequentially fed from the feed roll 212, and further passed through the circumferential surface of the cooling can 214 and taken up by the take-up roll 213. A predetermined tension is applied to the non-magnetic support 101 by the guide rolls 215 and 216 so that the non-magnetic support 101 runs smoothly.

  A crucible 217 is provided in the vacuum chamber 211 below the cooling can 214, and the crucible is filled with a metal magnetic material 218. On the other hand, an electron gun 219 for heating and evaporating the metal magnetic material 218 filled in the crucible 217 is provided on the side wall of the vacuum chamber 211. The electron gun 219 is disposed at a position such that the electron beam B emitted from the electron gun 219 is applied to the metal magnetic material 218 in the crucible 217. Then, the metal magnetic material 218 evaporated by the irradiation of the electron beam B is deposited on the surface of the nonmagnetic support 101, and the magnetic layer 102 is formed.

  A shutter 220 is disposed between the cooling can 214 and the crucible 217 and in the vicinity of the cooling can 214 so as to cover a predetermined area of the nonmagnetic support 101 that runs on the peripheral surface of the cooling can 214. The metal magnetic material 218 evaporated by the shutter 220 is deposited obliquely on the nonmagnetic support 101 within a predetermined incident angle range. Reference numeral 222 denotes an adhesion preventing plate.

  Further, when the magnetic layer 102 is deposited, oxygen gas is supplied to the surface of the nonmagnetic support 101 by the oxygen gas introduction pipe 221 provided through the side wall of the vacuum chamber 211, so that the magnetic layer The improvement of the magnetic characteristics, durability, and weather resistance of 102 is achieved.

  A protective layer 103 is formed on the magnetic layer 102 of the magnetic recording medium 100. The protective layer 103 is preferably formed using carbon as a base material in order to improve durability and corrosion resistance. .

  The protective layer 103 can be formed by a known vacuum film formation technique. For example, according to the CVD method in which a carbon compound is decomposed in plasma to form a film, the wear resistance, corrosion resistance, and surface coverage are reduced. In addition, a hard carbon called diamond-like carbon having a smooth surface shape and high electrical resistivity can be stably formed into a thickness of about 10 nm.

FIG. 3 shows a schematic configuration diagram of a continuous winding film forming apparatus as an example of an apparatus used for forming the protective layer 103, that is, a plasma CVD continuous film forming apparatus (CVD apparatus).
In this CVD apparatus 300, a feed roll 312 and a take-up roll 313 that rotate at a constant speed are provided in a vacuum chamber 311 that is made into a high vacuum state by an exhaust system 301 provided at the head. The non-magnetic support 101 on which the magnetic layer 102 is formed, that is, the object to be processed 320, sequentially travels from the roll 312 to the take-up roll 313.

  A counter electrode can 314 is provided in the middle of the workpiece 320 traveling from the feed roll 312 to the take-up roll 313. The counter electrode can 314 is provided so as to pull out the workpiece 320 downward in the figure, and is configured to rotate at a constant speed in the clockwise direction in the figure.

  The object 320 is sequentially fed from the feed roll 312, passes through the peripheral surface of the counter electrode can 314, and is taken up by the take-up roll 313. Guide rolls 315 and 316 are disposed between the feed roll 312 and the counter electrode can 314, and between the counter electrode can 314 and the take-up roll 313, respectively. Thus, the object to be processed 320 runs smoothly.

  A reaction tube 317 made of Pyrex (registered trademark) glass, plastic, or the like is provided in the vacuum chamber 311 below the counter electrode can 314. One end of the reaction tube 317 passes through the bottom of the vacuum chamber 311, and a film forming gas is introduced into the reaction tube 317 from this end. In addition, an electrode 318 made of a metal mesh or the like is attached to a middle portion in the reaction tube 317. The electrode 318 is connected to a DC power source 319 disposed outside, and a voltage of 500 to 2000 V is applied.

  In the CVD apparatus 300, glow discharge is generated between the electrode 318 and the counter electrode can 314 by applying a voltage to the electrode 318. Then, the film forming gas introduced into the reaction tube 317 is decomposed by the generated glow discharge, and is deposited on the object 320 to be processed, so that the protective layer 103 is formed.

As the carbon compound applied to the formation of the protective layer 103, any conventionally known materials such as hydrocarbons, ketones, and alcohols can be used. Further, during plasma generation, a gas for promoting the decomposition of the carbon compounds, Ar, H ₂ or the like may be introduced.
In addition, in order to improve the film hardness and corrosion resistance of diamond-like carbon, carbon may react with nitrogen and fluorine, and the diamond-like carbon film may be a single layer or a multilayer. Further, at the time of plasma generation, it is also possible to form a film in a state where a gas such as N ₂ , CHF ₃ , CH ₂ F ₂ or the like is used alone or appropriately mixed in addition to the carbon compound.

  The protective layer 103 is desirably formed to a thickness of 5 to 15 nm (usually about 10 nm). If it is formed thicker than 15 nm, the loss due to spacing increases, and if it is thinner than 5 nm, the wear resistance and corrosion resistance may deteriorate.

In addition to the carbon layer described above, any layer generally used as a protective layer of a metal magnetic thin film type magnetic recording medium can be applied as the layer forming the protective layer 103.
Examples thereof include Cr ₂ O ₃ , Al ₂ O ₃ , BN, Co oxide, MgO, SiO ₂ , Si ₃ O ₄ , SiN ₄ , ZrO ₂ , TiO ₂ , and TiC. The protective layer 103 may be a single layer film or a multilayer film.

Each constituent layer is formed as described above. The magnetic recording medium of the present invention has a loop stiffness SMD in the length direction (unit: mN / 8 mm) and a loop stiffness STD in the width direction (unit: mN / 8 mm). However, it satisfies all of the following expressions.
1.0 ≦ STD / SMD ≦ 1.4 (1)
10.0 <STD (2)
SMD + STD <29.0 (3)

Here, a method of measuring the loop stiffness in the present invention will be described.
FIG. 4 is an explanatory diagram showing a fixing jig and a sample shape when measuring loop stiffness. That is, a sample is first cut into a square of 8 mm × 8 mm. Next, as shown in FIG. 4, the length of the side in the direction to be measured is 4 mm outside the fixing jig, the sample end is overlapped with the fixing jig, and fixed with a double-sided adhesive tape.
Next, as shown in FIG. 5, the sample is formed into a loop shape, and a stylus having a triangular prism diameter connected to a strain gauge is pressed against the tip of the ring (loop) and pushed by 0.5 mm. Measure the force applied to the stylus. This force expressed in units of mN is defined as loop stiffness (mN / 8 mm). At this time, the tip of the stylus has a sufficiently acute angle and is regarded as a line contact.

In the above equation (1), when STD / SMD is smaller than 1.0 or larger than 1.4, the head hit becomes worse and the RF waveform fluctuation becomes larger.
Also, in the above equation (2), when STD is 10.0 or less, the loop stiffness in the width direction is too low, and the tape is likely to bend when the guide is touched during running, and edge damage is likely to occur. And repeated running durability deteriorates.
Further, in the above equation (3), when SMD + STD is 29.0 or more, the fine protrusions on the tape surface are worn by running, and the contact load between the head and the tape tends to increase, thereby hindering running.

  The loop stiffness SMD in the length direction and the loop stiffness STD in the width direction of the magnetic recording medium can be controlled by various methods such as changing the material and thickness of the film and adjusting the stretching method. .

Furthermore, in the magnetic recording medium of the present invention, the metal magnetic thin film has a surface roughness Ra (centerline average roughness) of 1.0 nm to 3.0 nm, an Rz (10 point average roughness) of 10 nm to 50 nm, and a protrusion height. It is preferable that the projections of 5 nm or more are 4 million to 10 million pieces / mm ² .
That is, when at least one of Ra, Rz, and the number of protrusions is a value lower than the predetermined range, the initial output is high, but drum tape sticking occurs and sufficient running durability is obtained. On the other hand, if at least one of Ra, Rz, and the protrusion has a value larger than the predetermined range, the output is reduced due to the spacing loss.
The surface roughness Ra (centerline average roughness) and Rz (10-point average roughness) are values measured using a surface roughness measuring instrument ET-30HK (Surfcorder manufactured by Kosaka Laboratories). The measurement of protrusion height shows the value measured by SPM (Nano Scope IV, Digital Instruments) Tapping AFM.

The fine protrusions necessary for satisfying the surface smoothness of the magnetic recording medium in the present invention are obtained by dispersing an inorganic filler (for example, SiO ₂ ) or a polymer filler in the film, and adjusting the size and amount of the internally added particles. It can be controlled by selecting. Although the PET film or PEN film to form a projection with a SiO ₂ filler, it is preferable to use a polymer filler to prevent aggregation in the case of polyamide film.
In order to obtain a magnetic recording medium having such a surface shape, the surface shape of the nonmagnetic support (base film) has a surface roughness Ra of 0.5 to 1.5 nm and Rz of 5 to 25 nm. Is preferred.

  Here, if an aromatic polyamide film is used as a non-magnetic support, running and durability are particularly excellent, and it is possible to minimize the spacing loss, and the wear resistance is also improved, resulting in high density. It is suitable as a magnetic recording medium for recording format (AIT4 format).

Next, the magnetic recording medium of the present invention will be described with specific examples and comparative examples.
Hereinafter, in this example, a polyamide film is used as the nonmagnetic support, but a film having a Young's modulus and thickness (for example, a PET film or a PEN film) having the same bending rigidity has the same effect. This is clear from the principle of the present invention, and the nonmagnetic support of the present invention is not limited to the polyamide film of the examples.

Examples 1-7, Comparative Examples 1-16
First, various polyamide films having different Young's moduli in the length direction and width direction and different thicknesses were prepared as nonmagnetic supports. Table 1 below shows the thickness and Young's modulus of the prepared polyamide film. On the surface side of each polyamide film on which the magnetic layer is formed, protrusions having a fine and uniform height are arranged, and in this example, the surface shape after forming the magnetic layer and the carbon protective film is as follows: The shape of the surface of the nonmagnetic support was adjusted so that the number of protrusions at a height of Ra = 2.0 nm, Rz = 30 nm, 5 nm or more was 7 million pieces / mm ² .

  Using each polyamide film shown in Table 1, according to the above-described embodiment of the present invention, each constituent layer was formed by the procedure shown in the following process flow and production conditions, and a magnetic recording medium (sample) was produced.

[Process flow and creation conditions]
(1) Formation of magnetic layer: vacuum vapor deposition method Using the vapor deposition apparatus shown in FIG. 1, a metal magnetic thin film was formed by depositing cobalt on a surface of a polyamide film having a thickness of 4 μm to a thickness of 180 nm. The degree of vacuum was about 10 ⁻³ Pa, and vapor deposition was performed in an oxygen atmosphere.
(2) Formation of Protective Layer: CVD Method Using the CVD apparatus shown in FIG. 2, the protective layer was formed by depositing carbon on the surface of the magnetic layer to a thickness of 10 nm by the CVD method. Ethylene was used as a source gas in forming the carbon protective film. The film was formed at a background vacuum of about 10 ⁻² Pa.
(3) Formation of back layer: coating method A coating liquid containing carbon as a pigment and polycarbonate as a binder is applied on the opposite side of the polyamide film to the magnetic layer forming side so that the thickness is 0.5 μm. Formed.
(4) Lubricant treatment on both surface layers: Application method A fluorine-based lubricant was applied to each surface of the magnetic layer and the backcoat layer. Alcohol was used as the solvent.
(5) Cutting of magnetic recording medium and incorporation into cartridge The above-prepared sample was cut into a width of 8 mm and wound around an AIT cartridge.

  The samples prepared as described above were subjected to loop stiffness evaluation (length direction and width direction), head-to-head evaluation (RF waveform fluctuation) by AIT4 drive, and repeated running durability evaluation under the following conditions.

<Loop stiffness evaluation>
The loop stiffness was measured in accordance with the sample shape and measurement method shown in FIGS. That is, the sample was cut into a square of 8 mm × 8 mm and fixed to a fixing jig in accordance with the direction (length direction or width direction) in which the sample was measured to form a loop-shaped ring. Next, a stylus with a triangular prism diameter was pressed against a loop-shaped ring and pushed in by 0.5 mm, and the force applied to the stylus at that time was measured with a connected strain gauge.

<Evaluation per head (RF waveform fluctuation)>
Regarding the waveform evaluation per head, measurement was performed under the following conditions using an AIT4 drive.
The number of heads of the AIT4 drive is 8 (4 recordings, 4 playbacks), and the rotational speed is 8500 rpm. Using this drive, a reproduction signal was read while writing a signal on an arbitrary part of the tape, and its RF waveform was evaluated. The RF waveform is ideally a rectangular wave, but fluctuates instead of a rectangular wave when the head contact is poor. Therefore, the difference between the maximum value and the minimum value of the RF waveform expressed in dB was evaluated as an index per head. In the determination, 1.0 dB or more was set as “x”, and less than 1.0 dB was set as “◯”.

<Repeated running durability evaluation>
Regarding repeated running durability evaluation, it was measured under the following conditions using an AIT4 drive.
Using the above-mentioned drive, a test was performed in which a 20 cm long section of the tape was reproduced after reading a signal (read after write), rewound to the start of the test section, and repeated while the signal was written again. The recording wavelength is 0.2 μm and the track pitch is 4 μm.
During the test, the output of the reproduction signal was monitored, and the number of repetitions until the 3 dB output dropped from the initial stage was evaluated as an indicator of running durability.
The test was performed up to 20,000 times as long as the output was normal. Furthermore, after running, the surface of the tape was observed, and it was visually inspected whether the end of the tape was deformed (edge damage). Further, whether or not the fine protrusions provided on the surface of the tape were worn was measured by an AFM (atomic force microscope), and when Rz was 6 nm or less, the protrusion wear was described as “present”. In addition, the judgment is “X” when the output is normal at 20,000 times, the edge damage “none”, the protrusion wear “none” is “◯”, and at least one of them is other than the above.
Table 2 below shows the evaluation results of the loop stiffness, head evaluation, and running durability evaluation.

Based on the data obtained from the evaluation result per head, the relationship per head with respect to the stiffness in the length direction and the stiffness in the width direction is graphed in FIG. In the figure, ◯ indicates that the determination per head is “◯”, and ● indicates that the determination per head is “x”.
From FIG. 6, the relationship between the length direction value SMD of the loop stiffness and the width direction value STD is expressed by the following equation (1):
1.0 ≦ STD / SMD ≦ 1.4 (1)
When the above relationship is satisfied, the RF waveform fluctuation is less than 1.0 dB, indicating good head contact, and if it is outside this region, the RF waveform fluctuation is 1.0 dB or more, and the head contact is poor. This indicates that the head hitting is good when the balance between the longitudinal direction and the width direction of the stiffness of the tape is within a certain range.

Further, based on the data obtained from the results of the running durability evaluation, the relationship between the running durability with respect to the length direction stiffness and the width direction stiffness is graphed in FIG. In the figure, ◯ indicates that the running durability is determined as “◯”, and ● indicates that the traveling durability is determined as “×”.
From FIG. 7, the relationship between the length direction value SMD of the loop stiffness and the width direction value STD is expressed by the following equations (2) and (3):
10.0 <STD (2)
SMD + STD <29.0 (3)
It can be seen that when the above relationship is satisfied, the repeated running durability shows excellent durability of 20000 times or more.
On the other hand, when STD is 10.0 or less, that is, when the stiffness is weak, it can be seen that edge damage enters the tape and the durability is poor. This indicates that if the tape has low rigidity, the tape tends to buckle when contact with the guide or the like occurs during running. Further, when SMD + STD is 29.0 or more, that is, when the stiffness is strong, there is a tendency that fine protrusions on the surface of the tape are worn by running, and friction with the head and the drum becomes high, so that running is impossible. This is thought to be because the contact load between the head and the tape increases due to the high rigidity of the tape and the sliding resistance is poor.

From the above examples, it is clear that a magnetic recording medium having a smooth surface suitable for high-density recording has an appropriate stiffness range in order to ensure excellent head hitting and repeated running durability. It was. The range is a region where the loop stiffness SMD in the length direction (unit: mN / 8 mm) and the loop stiffness STD in the width direction (unit: mN / 8 mm) satisfy all of the following expressions.
1.0 ≦ STD / SMD ≦ 1.4 (1)
10.0 <STD (2)
SMD + STD <29.0 (3)
FIG. 8 shows SMD and STD regions that satisfy all of the above relational expressions (1), (2), and (3). In the figure, ◯ indicates that the judgment per head and repeated running durability are both “◯”, and ● indicates that the judgment per head and repeated running durability or both are “x”.

Example 8 (Experiments 1-19)
A magnetic recording medium sample (Experiment 1) was used with a process flow and production conditions similar to those of the above-mentioned Examples, using a polyamide film having a film thickness of 4 μm, a surface roughness Ra of 0.5 to 1.5 nm, and an Rz of 5 to 25 nm. To 19) were prepared.

That is, a magnetic layer made of cobalt having a thickness of 180 nm is formed on one main surface of a long nonmagnetic support by a vacuum thin film forming technique, and a diamond-like carbon protective layer having a thickness of 10 nm is formed on the magnetic layer by CVD. A back layer having a thickness of about 0.5 μm was applied and formed on the side opposite to the magnetic layer of the nonmagnetic support. Further, a fluorine-based lubricant was applied as an alcohol solution to each of the magnetic surface and the back surface.
The created sample was cut into a width of 8 mm and wound around an AIT cartridge.

  Here, when manufacturing each magnetic recording medium sample, the loop stiffness AMD in the length direction and the loop stiffness STD in the width direction were adjusted to be the same as those in the second embodiment.

Center line average roughness Ra (nm), 10-point average roughness Rz (nm), and protrusion height 5 nm based on the two-field average (30 μm × 30 μm) three-dimensional surface roughness of each magnetic recording medium sample of Experiments 1 to 19 Table 3 below shows the evaluation results of the number of projections (10,000 / mm ² ), running durability, and electromagnetic conversion characteristics.
The surface property of the magnetic recording medium was measured using a three-dimensional surface roughness measuring device ET-30HK (Kosaka Laboratory Surfcorder). The number of protrusions was measured using SPM (Nano Scope IV, Digital Instruments) Tapping AFM.

  About the sample created by the above, evaluation of the electromagnetic conversion characteristic (RF waveform: output) by AIT4 drive and evaluation of running durability by repeated running (shuttle mode) were performed under the following conditions, respectively.

<Evaluation of electromagnetic conversion characteristics by AIT4 drive (RF waveform)>
The number of heads of the used AIT drive is 8 (4 recordings, 4 playbacks), and the rotational speed is 8506 rpm. Using this drive, the reproduction signal was read while writing a signal on an arbitrary part of the tape, and the initial output was relatively evaluated from the RF waveform.

<Evaluation of running durability>
Using a magnetic tape having a tape length of 30 m, the running durability was evaluated by the AIT drive. The recording wavelength is 0.2 μm, the track pitch is 4 μm, and the driving is repeated up to 20000 times in the short shuttle mode shown in FIG. As evaluated.

  Table 3 below shows the results of evaluation of electromagnetic conversion characteristics (output) and running durability by the AIT4 drive. Table 3 shows the centerline average roughness Ra, 10-point average roughness Rz, and the number of protrusions having a protrusion height of 5 nm or more. Also shown.

From the above experimental results, in Experiments 1 to 4, that is, the number of protrusions having a center line average roughness Ra, a 10-point average roughness Rz, and a protrusion height of 5 nm or more, Ra is smaller than 1.0 nm or Rz is 10 nm. If the number of protrusions is less than 4 million pieces / mm ² or at least one of them, the initial output is high, but drum tape sticking occurs and sufficient running durability is achieved. Was not obtained.
In addition, in Experiments 12 to 19, that is, in the number of protrusions having a center line average roughness Ra, a 10-point average roughness Rz, and a protrusion height of 5 nm or more, whether Ra is larger than 3.0 nm or Rz is larger than 50 nm, It was found that when the number of protrusions is greater than 10 million pieces / mm ² or at least one of them corresponds, the running durability is high but the output is reduced due to spacing loss.
On the other hand, in Experiments 5 to 11, that is, center line average roughness Ra, 10-point average roughness Rz, and the number of protrusions having a protrusion height of 5 nm or more, Ra is in the range of 1.0 to 3.0 nm, and Rz is 10 to 10. When the number of protrusions was adjusted and controlled within the range of 50 nm and the range of 4 million to 10 million pieces / mm ² , both electromagnetic conversion characteristics and running durability could be achieved.

It is a schematic sectional drawing of an example of the magnetic recording medium of this invention. It is a schematic block diagram which shows an example of the apparatus used for forming the magnetic layer in FIG. It is a schematic block diagram which shows an example of the apparatus used for forming the protective layer in FIG. It is explanatory drawing which shows the fixing jig and sample shape in the case of measuring the loop stiffness in this invention. It is explanatory drawing which shows the measuring method of the loop stiffness in this invention. It is a graph which shows the relationship of the quality per head with respect to the length direction stiffness and the width direction stiffness based on the evaluation data in the Example of this invention. It is a graph which shows the relationship of the quality of driving | running | working durability with respect to the length direction stiffness and the width direction stiffness based on the evaluation data in the Example of this invention. It is a graph which shows the area | region which satisfies both the head contact | abutting with respect to the length direction stiffness and the width direction stiffness, and running durability based on the evaluation data in the Example of this invention. It is a figure which shows the short shuttle mode of the repeated driving | running | working applied in the driving | running | working durability evaluation in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Magnetic recording medium, 101 Nonmagnetic support body, 102 Magnetic layer, 103 Protective layer, 104 Backcoat layer, 200 Deposition apparatus, 201, 202 Exhaust port, 211 Vacuum chamber, 212 Feed roll, 213 Winding roll, 214 Cooling can 215, 216 Guide rolls, 217 crucible, 218 Metal magnetic material, 219 Electron gun, 220 Shutter, 221 Oxygen gas introduction tube, 222 Depositing plate, B Electron gun, 300 CVD apparatus, 301 Exhaust system, 311 Vacuum chamber, 312 Feed roll, 313 Winding roll, 314 Counter electrode can, 315, 316 Guide roll, 317 Reaction tube, 318 electrode, 319 DC power supply, 320 Object to be processed

Claims (4)

In a magnetic recording medium having a metal magnetic thin film on a nonmagnetic support, the lengthwise loop stiffness SMD (unit: mN / 8 mm) and the widthwise loop stiffness STD (unit: mN / 8 mm) are all expressed by the following formulas: A magnetic recording medium characterized by satisfying
1.0 ≦ STD / SMD ≦ 1.4 (1)
10.0 <STD (2)
SMD + STD <29.0 (3) The metal magnetic thin film has a surface roughness Ra of 1.0 nm to 3.0 nm, Rz of 10 nm to 50 nm, and protrusions having a protrusion height of 5 nm or more of 4 million to 10 million pieces / mm ^2. The magnetic recording medium according to claim 1.   The magnetic recording medium according to claim 1, wherein an aromatic polyamide film is used as the nonmagnetic support. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is an AIT4 format magnetic tape.

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