JP2008033996A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium satisfying running durability and having effective corrosion resistance in a long term preservation even if the thickness of a protective layer is thin. <P>SOLUTION: In the magnetic recording medium 100 of a metal thin film type having a magnetic layer 2, a protective layer 3 mainly made of carbon and a lubricant layer 4 comprising a lubricant having a polar group on a non-magnetic supporting body 1, the protective layer 3 contains 0.5 to 50 at% metal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a so-called metal thin film type magnetic recording medium in which a metal magnetic thin film and a protective layer are formed on a nonmagnetic support, and more particularly to the structure of a carbon protective layer.

  Conventionally, as a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is placed 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 produced by applying and drying a magnetic coating material dispersed in a magnetic material.

  On the other hand, a ferromagnetic material made of metal or an alloy such as Co—Ni is made non-magnetic by vacuum thin film forming means (vacuum deposition method, sputtering method, ion plating method, etc.) due to the demand for high density recording. A magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film directly deposited on a support has been put into practical use.

  Such a so-called 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. Since there is little thickness loss at the time of recording demagnetization and reproduction, it is not necessary to mix a binder which is a nonmagnetic material in the magnetic layer, so that the packing density of the magnetic material can be increased, and a large magnetization can be obtained. Has a number of advantages.

  Furthermore, in order to improve the electromagnetic conversion characteristics of this type of magnetic recording medium and obtain a larger output, an oblique vapor deposition method using a vapor deposition apparatus 100 as shown in FIG. The mainstream of vapor-deposited magnetic tape. This evaporated magnetic tape has been put to practical use as a magnetic tape for high-quality VTR, digital VTR, data storage and the like.

By the way, in these magnetic recording media, a hard protective layer is formed on the surface of the magnetic layer, thereby ensuring durability against sliding with a magnetic head or the like. Examples of the hard protective layer include a carbon film, a quartz (SiO ₂ ) film, a zirconia (ZrO ₂ ) film, etc. Among them, a diamond-like carbon (DLC) film has high hardness and excellent protective effect. The deposition tape protective layer has become the mainstream. As a method for forming such a DLC film, there are a sputtering method and a CVD method.

  In the sputtering method, an inert gas such as Ar is ionized (plasmaized) using an electric field or a magnetic field, and the generated argon ions are accelerated to collide with a target. As a result, the atoms of the target are ejected by the kinetic energy of the argon ions, and the ejected atoms are deposited on the substrate facing the target to form a thin film.

  The CVD method (chemical vapor deposition method) uses the energy of plasma generated using an electric or magnetic field to cause a chemical reaction such as decomposition or synthesis to a raw material gas, and the reaction resulting from this chemical reaction. In this method, a thin film is formed by depositing a product on a substrate.

  In general, the electromagnetic conversion characteristics of a magnetic recording medium are evaluated by “CNR” which is the difference between “output” and “medium noise”, and a high output and low noise state is preferable. Among these, in order to increase the output, it is very important to reduce the distance (spacing) between the metal magnetic thin film and the recording head or reproducing head. The loss of recording / reproduction due to the spacing is called “spacing loss” and is expressed by the following equation (Equation 1). As the wavelength in recording / reproduction is shortened to improve the recording density, the spacing loss becomes more prominent.

      (Spacing loss) [dB] = (spacing loss coefficient) × (spacing) ÷ (recording / reproducing wavelength) (Equation 1)

The spacing loss coefficient in the vapor-deposited magnetic tape has been found to be about 90 to 130 by the inventors' investigation, and tentatively in the case of the shortest wavelength of 0.286 μm of AIT3 in the AIT (Advanced Intelligent Tape) format In the calculation, the following output change is expected.
・ 0.6-0.9dB with 2nm spacing
-1.3-1.8 dB with 4 nm spacing
・ 1.9-2.7 dB with 6 nm spacing

  Therefore, suppressing the spacing is an effective means for increasing the output and also an effective means for increasing the CNR.

  In the vapor-deposited magnetic tape, a hard carbon protective layer is formed on the surface of the magnetic layer, thereby ensuring durability against sliding with a magnetic head or the like. From the viewpoint of spacing loss, the thinner is preferable. However, when the protective layer is thin, sufficient sliding durability cannot be ensured. In the case of a thin protective layer, the low friction and high strength carbon protective layer is worn by sliding, and the time until the magnetic layer with high friction and low strength is exposed (sliding frequency) is accelerated. In addition, when the protective layer is made thinner, the corrosion resistance against the corrosive gas is deteriorated due to a decrease in surface coverage and an increase in gas permeation, which is also significant for data storage applications that require long-term storage. It is a problem.

  Among the above-mentioned problems, a technique has been proposed for improving the corrosion problem by laminating a corrosion-resistant protective layer and a durable protective layer on the magnetic layer (see, for example, Patent Document 1). As a result, corrosion of the metal magnetic thin film as the magnetic layer is suppressed and the error rate can be improved, but the improvement in spacing loss is not sufficient.

JP-A-5-234059

  The present invention has been proposed in view of such a conventional situation, and even if the protective layer is thin and the film thickness is 14 nm or less, it satisfies running durability and is effective for corrosion resistance in long-term storage. An object of the present invention is to provide a simple magnetic recording medium.

  In order to solve the above-mentioned problems, the present invention provides a metal thin film type magnetism having a magnetic layer, a protective layer mainly composed of carbon, and a lubricating layer made of a lubricant having a polar group on a nonmagnetic support. A recording medium, wherein the protective layer contains 0.5 at% to 50 at% of a metal.

  Here, the nonmagnetic metal is preferably made of a single metal of Ti, W, or Cu or an alloy containing one or more metals selected from these metal groups.

  The protective layer preferably has a thickness of 2 to 14 nm.

  The thickness of the magnetic layer is preferably 20 to 300 nm.

  The lubricating layer is preferably coated with a fluorine-containing lubricant.

  Moreover, it is good to have a backcoat layer on the surface opposite to the magnetic layer forming surface of the nonmagnetic support.

  According to the magnetic recording medium of the present invention, by containing a predetermined metal in the protective layer mainly composed of carbon, the retention effect of the lubricant that constitutes the lubricating layer, for example, a fluorine-based lubricant is increased, and it is caused by repeated sliding. Reduction and depletion of fluorine-based lubricant is suppressed, and shuttle sliding durability is improved. As a result, the protective layer can be made thin, and a magnetic recording medium corresponding to a higher recording density can be provided. In addition, it is possible to provide a magnetic recording medium in which corrosion of the magnetic layer is suppressed by containing a noble metal that does not easily corrode in the protective layer.

The configuration of the magnetic recording medium according to the present invention will be described below.
FIG. 1 shows a schematic cross-sectional view of a magnetic recording medium prepared according to the present invention.
This magnetic recording medium 100 has a magnetic layer 2 produced by a vacuum thin film forming technique on one main surface of a long nonmagnetic support 1, and a protective layer 3 mainly composed of carbon is formed on the magnetic layer 2. The lubricant layer 4 formed of the lubricant having a polar group is formed on the protective layer 3. Details will be described below.

  As the nonmagnetic support 1, any of those conventionally used in metal magnetic thin film type magnetic recording media can be used. For example, polymer materials such as polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins, cellulose derivatives such as cellulose triacetate, polycarbonate resins, polyvinyl chloride resins, and polyamide resins can be used. In addition, prior to the formation of the magnetic thin film on these nonmagnetic supports, surface treatment and pretreatment should be performed for the purpose of facilitating adhesion, improving surface properties, coloring, antistatic, and imparting abrasion resistance. It may be.

  The metal magnetic material for forming the magnetic layer 2 may be any material as long as it is used for ordinary vapor deposition tapes. For example, a ferromagnetic metal such as Fe, Co, Ni, Fe—Co, etc. Co-Ni, Co-Cr, Co-Cr-Ta, Co-Cr-Pt, Co-Ni-Pt, Fe-Co-Ni, Fe-Co-B, Fe-Ni-B, Fe-Co-Ni -Ferromagnetic alloys such as Cr.

  The magnetic layer 2 is mainly composed of argon, a vacuum deposition method in which a metal magnetic material is heated and evaporated in vacuum and deposited on the nonmagnetic support 1, an ion plating method in which the metal magnetic material is evaporated in a discharge, and argon. It is a thin film formed by a so-called PVD technique such as a sputtering method in which glow discharge is caused in an atmosphere and atoms on the target surface are beaten with argon ions, and the film thickness is preferably 20 nm to 300 nm.

  The magnetic layer 2 may be a single-layer metal magnetic thin film formed by the above method or a multilayer film. Further, when the magnetic layer 2 is a multilayer film between the nonmagnetic support 1 and the magnetic layer 2, in order to improve the adhesion between each layer and control the coercive force, or the like, or An intermediate layer may be provided. Further, for example, the vicinity of the surface of the magnetic layer may be an oxide for improving the corrosion resistance.

FIG. 2 shows a schematic configuration diagram of an example of a vapor deposition apparatus 200 for forming the magnetic layer 2. In the present embodiment, in the vapor deposition apparatus 200 of FIG. 2, in the vapor deposition chamber 202 evacuated to 10 ⁻² Pa, the cobalt mass, which is the metal magnetic material 211 disposed in the crucible 210, is converted into an electron beam from the electron gun 212. Then, a cobalt metal magnetic thin film was deposited on the nonmagnetic support 1 having a width of 620 mm. In this vapor deposition apparatus 200, a feed roll 204 and a take-up roll 205 are provided in a vacuum chamber 201 that is evacuated from an exhaust port 203 to be in a vacuum state, and the nonmagnetic support 1 is interposed therebetween. It is designed to run sequentially.

  A cooling can 206 is provided between the feed roll 204 and the take-up roll 205 in the middle of the travel of the nonmagnetic support 1. The cooling can 206 is provided with a cooling device to suppress thermal deformation caused by a temperature rise of the nonmagnetic support 1.

  The nonmagnetic support 1 is sequentially fed from the feed roll 204, further passes through the peripheral surface of the cooling can 206, and is taken up by the take-up roll 205. Guide rolls 207 and 208 are provided between the feed roll 204 and the cooling can 206 and between the cooling can 206 and the take-up roll 205, respectively. A predetermined tension is applied to the nonmagnetic support 1 that runs from 206 to the take-up roll 205 so that the nonmagnetic support 1 runs smoothly.

  The vapor deposition chamber 202 is separated by a partition wall 209, and suppresses inflow of metal particles evaporated from the crucible 210 and an electron beam that is reflected and scattered. A crucible 210 is provided below the cooling can 206, and the crucible 210 is filled with a metal magnetic material 211. The crucible 210 has substantially the same width as the cooling can 206.

  On the other hand, an electron gun 212 for heating and evaporating the metal magnetic material 211 filled in the crucible 210 is attached to the side wall of the vapor deposition apparatus 200. The electron gun 212 is disposed at such a position that the electron beam emitted from the electron gun 212 is applied to the metal magnetic material 211 in the crucible 210. The metal magnetic material 211 evaporated by the electron beam is deposited as a magnetic layer 2 on the nonmagnetic support 1 that travels at a constant speed on the peripheral surface of the cooling can 206.

  A shutter 213 is disposed between the cooling can 206 and the crucible 210 and in the vicinity of the cooling can 206. The shutter 213 is formed so as to cover a predetermined area of the nonmagnetic support 1 that travels at a constant speed on the peripheral surface of the cooling can 206, and the metal magnetic material 211 evaporated by the shutter 213 is the nonmagnetic support. The body 1 is vapor-deposited obliquely within a predetermined angle range. Further, in the case of such vapor deposition, oxygen gas is supplied to the surface of the nonmagnetic support 1 through the oxygen gas inlet 214 provided through the side wall of the vapor deposition apparatus 200, and magnetic characteristics, durability and corrosion resistance are provided. Improvements are being made. The incident angle of vapor deposition is 90 to 45 degrees from the normal direction of the nonmagnetic support 1, and the feed rate of the nonmagnetic support 1 is changed to control the thickness of the vapor deposition layer. During vapor deposition, film formation is performed while oxygen gas is introduced from the oxygen gas introduction pipe 214 in order to control magnetic characteristics.

  The protective layer 3 is mainly composed of carbon and contains 0.5 at% or more and 50 at% or less of metal. The thickness of the protective layer 3 is preferably 2 to 14 nm.

  The metal contained in the protective layer 3 is, for example, a single metal of Mg, Al, Si, Ca, Ti, V, Cr, Mn, Zn, Ge, Zr, Nb, Mo, Sn, Ta, W, Pb, Bi Or the alloy containing the metal of 1 or 2 or more chosen from these metal groups is mentioned. Alternatively, from the viewpoint of improving corrosion resistance, a single metal of Cu, Ag, Au, or Pt or an alloy containing one or more metals selected from these metal groups can be used. Of these, a single metal of Ti, W, or Cu or an alloy containing one or more metals selected from these metal groups is preferable, and a nonmagnetic metal is more preferable.

  Hereinafter, a sputtering apparatus (FIG. 3) and a CVD (Chemical Vapor Deposition) apparatus (FIG. 4) for forming the protective layer 3 will be described. However, the protective layer film forming apparatus is not limited to this. .

FIG. 3 shows a schematic configuration diagram of a magnetron sputtering apparatus 300 as a film forming apparatus for the protective layer 3.
In this apparatus 300, a feed roll 304 that rotates at a constant speed and a take-up roll 305 are provided in a vacuum chamber 301 in which the inside is brought into a high vacuum state by an exhaust port 303 provided in the head. An object to be processed 501 in which a magnetic layer is deposited on the nonmagnetic support 1 is sequentially moved from the roll 304 to the take-up roll 305.

  A can 306 is provided in the middle of the object 501 traveling from the feed roll 304 to the take-up roll 305 side. The can 306 is provided so as to pull out the workpiece 501 downward in the drawing, and is configured to rotate at a constant speed in the clockwise direction in the drawing. In addition, a guide roll 307 and a guide roll 308 are disposed in the middle of the object to be processed 501 traveling from the feed roll 304 to the take-up roll 305, and a predetermined tension is applied to the object to be processed 501. The body 501 travels smoothly.

  The film formation chamber 302 is separated by a partition wall 309, and controls scattering particles and gas pressure during sputtering.

A target 310 is provided at a position facing the cooling can 306. The target 310 is made of carbon containing the metal. For example, a carbon target in which at least one kind of metal such as Ti, W, or Cu is mixed or embedded as the metal chip is used. These targets 310 are supported by a backing plate 311 constituting a cathode electrode. A magnet 312 that forms a magnetic field is disposed on the back surface of the backing plate 311. In the magnetron sputtering apparatus 300, when forming the carbon protective layer 3 containing metal, the inside of the film forming chamber 302 is depressurized to about 1 × 10 ⁻⁴ [Pa], and then the gas introduction pipe 314 is used. Ar gas is introduced to set the degree of vacuum to about 0.5 [Pa], for example.

  Then, while introducing Ar gas from the gas introduction pipe 314, the cooling can 306 is used as an anode, the backing plate 311 is used as a cathode, a voltage of about 600 V is applied using a power source 313, and a state where a current of about 40 A flows is maintained. . When this voltage is applied, the Ar gas is turned into plasma, and the ionized ions collide with the target 310, so that carbon and metal atoms are ejected from the target.

  At this time, since a magnetic field is formed in the vicinity of the target 310 by the magnet 312 disposed on the back surface of the backing plate 311, the ionized ions are concentrated in the vicinity of the target 310. The atoms ejected from these targets 310 adhere to the object 501 that travels along the outer peripheral surface of the cooling can 306. Thus, the to-be-processed object 502 in which the carbon protective layer 3 containing a metal was formed is wound around the winding roll 305.

  As the target, a metal chip may be disposed on the carbon target so that a desired concentration ratio is obtained as a protective layer after film formation, or a carbon in which metal is mixed from the beginning may be used.

FIG. 4 shows a schematic configuration diagram of a plasma CVD apparatus 400 as a film forming apparatus for the protective layer 3.
In this apparatus 400, a feed roll 404 that rotates at a constant speed and a take-up roll 405 are provided in a vacuum chamber 401 whose inside is brought into a high vacuum state by an exhaust port 403 provided in the head. An object to be processed 501 in which a magnetic layer is deposited on the nonmagnetic support 1 is sequentially moved from the roll 404 to the take-up roll 405.

  A can 406 is provided in the middle of the object 501 traveling from the feed roll 404 to the take-up roll 405 side. The can 406 is provided so as to pull out the workpiece 501 downward in the figure, and is configured to rotate at a constant speed in the clockwise direction in the figure. In addition, guide rolls 407 and 408 are arranged in the middle of the object to be processed 501 traveling from the feed roll 404 to the take-up roll 405 side, and a predetermined tension is applied to the object to be processed 501 so as to be processed 501. Is designed to run smoothly.

  In the film forming chamber 402, a reaction tube 410 made of Pyrex (registered trademark) glass, plastic, or the like is provided below the can 406. One end of the reaction tube 410 passes through the bottom of the film formation chamber 402, and a film formation gas is introduced into the reaction tube 410 from the gas introduction tube 411. In addition, an electrode 413 made of a metal mesh or the like is attached to the middle portion of the reaction tube 410. The electrode 413 is connected to a power source 412 provided outside, and a voltage of 0 to 3000 V is applied thereto.

  In this CVD apparatus, a glow discharge is generated between the electrode 413 and the can 406 by applying a voltage to the electrode 413. Then, the film forming gas introduced into the reaction tube 410 is decomposed by the generated glow discharge, and is deposited on the object to be processed 501 to form the protective layer 3.

As the film forming gas applied to the formation of the protective layer 3, any conventionally known material such as hydrocarbon, ketone, and alcohol can be used. Further, Ar, H ₂ or the like may be introduced as a gas for promoting the decomposition of the carbon compound during plasma generation. 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. In addition, when generating plasma, a film such as N ₂ , CHF ₃ , CH ₂ F _2, or the like, in addition to a carbon compound, may be used alone or in an appropriately mixed state.

  The protective layer 3 containing a metal is formed by mixing a metal-containing gas with a carbon-based gas using the raw materials shown below with respect to the carbon-based gas and performing CVD using the mixed gas.

As raw materials for generating metal-containing gas, halogen-based metal materials such as TiCl ₄ and WF ₆ , Ca (DPM) ₂ , Ca (DPM) ₂ , Ti (Oi-Pr) ₂ (DPM) ₂ , Ti (Ot-Am ) ₂ (TMOD) ₂ , TiO (DPM) ₂ , Cr (DPM) ₃ , Mn (DPM) ₃ , Zn (DPM) ₂ , Zr (DPM) ₄ , Zr (DIBM) ₄ , Nb (OEt) ₄ (DPM) ), Ta (OEt) ₄ (DPM), Pb (DPM) ₂ , Bi (O-Tol) ₃ , Cu (DPM) ₂ , Cu (IBPM) ₂ , Cu (DIBM) _2, etc. can be used. It is not limited.

  When the protective layer 3 containing the metal is formed too thick, the loss due to spacing increases. When the protective layer 3 is too thin, the durability and the corrosion resistance decrease. Therefore, the protective layer 3 is preferably formed to a thickness of 2 nm to 14 nm.

  The lubricant layer 4 is formed by applying a lubricant having a polar group on the protective layer 3 in order to reduce friction with a guide roll, a rotating drum, a head, and the like. A conventionally known material can be used as the lubricant, but a fluorine-based lubricant is particularly preferable.

  In the magnetic recording medium 100 of the present invention, a backcoat layer 5 having a thickness of 0.1 to 0.7 μm is formed on the side of the nonmagnetic support 1 opposite to the surface on which the magnetic layer 2 is formed as necessary. Also good. In this case, as the material for forming the backcoat layer 5, conventionally known materials such as nonmagnetic pigments and resin binders can be appropriately used. The magnetic recording medium 100 of the present invention is assumed to be used in a helical scan recording / reproducing system, but is not limited to this system.

Next, the magnetic recording medium 100 of the present invention will be described with specific examples. However, the magnetic recording medium of the present invention is not limited to the following examples.
<Example 1>
(1) Sample Preparation A polyethylene terephthalate (PET) film having a thickness of 6 μm is prepared as the nonmagnetic support 1 of the magnetic recording medium 100 shown in FIG. 1, and the magnetic layer 2 is formed on the nonmagnetic support 1 as shown in FIG. It was created under the following conditions using the vapor deposition apparatus 200 shown in FIG.
(Deposition conditions)
-Film forming material: Co 100 wt%
-Incident angle: 45 ° to 90 °
-Introducing gas: oxygen gas-Magnetic layer thickness: 150 nm

Next, the protective layer 3 containing metal was formed using the plasma CVD apparatus 400 shown in FIG. 4 under the following conditions.
(CVD conditions)
Introducing gas: Ethylene / argon / TiCl ₄ mixed gasTiCl ₄ flow rate: 2 sccm
・ Reaction tube pressure: 30 Pa
-Input voltage: + 1.2kV
-Film thickness of protective layer: 8nm

  Next, the lubricant layer 4 was formed using a fluorine-based lubricant, the carbon-based backcoat layer 5 was formed, and finally, the sample was cut into a width of 8 mm to obtain a sample of the tape-like magnetic recording medium 100.

(2) Sample evaluation The following evaluation was performed about the obtained sample.
(I) Metal content in the protective layer The metal content in the protective layer 3 was measured with an X-ray photoelectron spectrometer (ESCA, manufactured by SHIMAZU). Specifically, the photoelectron detection intensity (A) in a standard sample of 100% carbon (carbon) and the photoelectron detection intensity (B) in a standard sample of 100% contained metal (for example, Ti) are measured and measured. In the relative protective layer of the sample to be measured by obtaining the carbon abundance ratio (a / A) and the Ti abundance ratio (b / B) from the photoelectron detection intensity (carbon: a, Ti: b) of the target sample, respectively. The metal content of was calculated.

(Ii) Shuttle durability (number of shuttles)
In order to evaluate the sliding durability of the sample, the atmosphere in the thermostatic chamber was controlled at a temperature of 25 ° C. and a relative humidity of 50%, and a commercially available AIT3 deck (manufactured by Sony Corporation; trade name SDX-700C) Were repeatedly slid (shuttle). The time when the reproduction output fell 3 dB from the initial output was defined as the number of sliding ends. Although the shuttle durability is judged, if the number of shuttle times exceeds 30000 passes, there is no problem as a product, and if it exceeds 50000 passes, the protective film may be further thinned, which is a promising level for next-generation products. .

(Iii) Electromagnetic conversion characteristics of inductive head reproduction After recording an information signal at a recording wavelength of 0.286 μm on each sample magnetic tape using a commercially available AIT3 deck (manufactured by Sony Corporation; product name SDX-700C), Reproduction was performed with an inductive head, and the output level and CNR were measured. When the magnetic tape of Comparative Example 1 described later is used as a reference (reference value (± 0 dB)), the CNR level is −1.5 dB or less compared to the reference, so that practically sufficient recording / reproduction characteristics can be obtained. I can't get it.

(Iv) Remaining amount of lubricant due to sliding First, the amount of lubricant in the sample in the initial state was measured using an X-ray photoelectron spectrometer (ESCA, manufactured by SHIMAZU), and this tape was applied to a SUS pin with a diameter of 90 mm. A frictional sliding test was performed for 1000 passes by winding at an angle of ° and repeatedly going back and forth with a load of 10 gf.
After completion of the friction test, the amount of lubricant on the tape was again measured using an X-ray photoelectron spectrometer (ESCA, manufactured by SHIMAZU), and the remaining amount of lubricant was determined by the following equation.
(Remaining amount) (%) = (Lubricant amount after sliding) ÷ (Lubricant amount in the initial state)

<Examples 2 to 9>
In Example 1, the TiCl ₄ flow rates were 4 sccm (Example 2), 8 sccm (Example 3), 20 sccm (Example 4), 40 sccm (Example 5), 80 sccm (Example 6), and 120 sccm (Example 7), respectively. ), 160 sccm (Example 8), 200 sccm (Example 9), and otherwise, a sample of the magnetic recording medium 100 was obtained in the same manner as in Example 1.

<Comparative Examples 1-4>
In Example 1, the flow rate of TiCl ₄ was set to 0 sccm (Comparative Example 1), 1 sccm (Comparative Example 2), 240 sccm (Comparative Example 3), and 280 sccm (Comparative Example 4), respectively. A sample of the recording medium was obtained.

<Comparative Examples 5 and 6>
In Comparative Example 1, the thickness of the protective layer was 4 nm (Comparative Example 5) and 6 nm (Comparative Example 6), respectively. Otherwise, a sample of the magnetic recording medium was obtained in the same manner as Comparative Example 1.

  Table 1 shows the evaluation results of the above samples. The amount of lubricant remaining after sliding was measured for Example 4 and Comparative Example 1.

(Influence of protective layer thickness)
<Examples 10 to 15>
In Example 4, the thickness of the protective layer 3 is 2 nm (Example 10), 4 nm (Example 11), 6 nm (Example 12), 10 nm (Example 13), 12 nm (Example 14), 14 nm ( A sample of the magnetic recording medium 100 was obtained in the same manner as in Example 4 except that the film formation rate was changed so that Example 15) was obtained.

<Comparative Examples 7 and 8>
In Example 4, the film formation rate was changed so that the thickness of the protective layer 3 was 1 nm (Comparative Example 7) and 16 nm (Comparative Example 8), respectively. Otherwise, the magnetic recording was performed in the same manner as in Example 4. A media sample was obtained.

  Table 2 shows the results of evaluating the metal content in the protective layer, shuttle durability (shuttle frequency), and electromagnetic conversion characteristics of inductive head regeneration for the above samples.

(Influence of magnetic layer thickness)
<Examples 16 to 21>
In Example 4, the thickness of the magnetic layer 2 was 20 nm (Example 16), 35 nm (Example 17), 50 nm (Example 18), 100 nm (Example 19), 150 nm (Example 20), 200 nm ( A sample of the magnetic recording medium 100 was obtained in the same manner as in Example 4 except that the vapor deposition film formation rate was changed to be Example 21) and 300 nm (Example 21).

<Comparative Examples 9 and 10>
In Example 4, the vapor deposition rate was changed so that the film thickness of the magnetic layer 2 was 15 nm (Comparative Example 9) and 400 nm (Comparative Example 10), respectively. Otherwise, the magnetic recording was performed in the same manner as in Example 4. A media sample was obtained.

With respect to the above samples, the metal content in the protective layer, shuttle durability (shuttle frequency), electromagnetic conversion characteristics of inductive head reproduction, and electromagnetic conversion characteristics of anisotropic magnetoresistive head (AMR head) reproduction were evaluated. The electromagnetic conversion characteristics of AMR head reproduction were evaluated as follows.
(Electromagnetic conversion characteristics of AMR head playback)
An AMR head for a commercially available digital video camera recorder “MicroMV” (manufactured by Sony Corporation; product name DCR-IP7) is mounted on an AIT3 deck (manufactured by Sony Corporation; product name SDX-700C). After recording an information signal at a recording wavelength of 0.22 μm, it was reproduced by an AMR head and the output level and CNR were measured. Here, when the CNR level is −1.5 dB or less compared to the reference when the magnetic tape of Comparative Example 1 is used as a reference (reference value (± 0 dB)), practically sufficient recording / reproduction characteristics are obtained. I can't. Further, the inductive head and the head using the magnetoresistive effect such as the AMR head and the GMR head have different optimum magnetic layer thickness ranges, and it is not necessary to satisfy the excellent CNR in both reproducing heads.

  The above evaluation results are shown in Table 3.

Next, examples in which the protective layer 3 is formed by using Cu, Ti, W, Ti—W as the contained metal by sputtering will be described below.
<Example 22>
A polyethylene terephthalate (PET) film having a thickness of 6 μm is prepared as the nonmagnetic support 1 of the magnetic recording medium 100 shown in FIG. 1, and the magnetic layer 2 is formed on the nonmagnetic support 1 by the vapor deposition apparatus shown in FIG. 200 was used under the following conditions.
(Deposition conditions)
-Film forming material: Co 100 wt%
-Incident angle: 45 ° to 90 °
-Introducing gas: oxygen gas-Magnetic layer thickness: 150 nm

Next, the protective layer 3 containing metal was formed using the magnetron sputtering apparatus 300 shown in FIG. 3 under the following conditions. Here, a target in which a predetermined number of chips made of metal having a length of 5 mm, a width of 5 mm, and a thickness of 1 mm were embedded in the surface of a rectangular carbon target was used.
(Sputtering conditions)
・ Introduction gas: Argon ・ Target: Carbon + Cu chips ・ Number of Cu chips: 2 ・ Input voltage: 500 V
-Carbon protective layer thickness: 8nm

  Next, the lubricant layer 4 was formed using a fluorine-based lubricant, the carbon-based backcoat layer 5 was formed, and finally, the sample was cut into a width of 8 mm to obtain a sample of the tape-like magnetic recording medium 100.

<Examples 23 to 30>
In Example 22, the number of Cu chips embedded in the carbon target was 4 (Example 23), 8 (Example 24), 20 (Example 25), 40 (Example 26), and 80 (Example). Example 27), 120 pieces (Example 28), 160 pieces (Example 29), 200 pieces (Example 30), and the sample of the magnetic recording medium 100 was obtained in the same manner as in Example 22 except that.

<Comparative Examples 11-14>
In Example 22, the number of Cu chips embedded in the carbon target was 0 (Comparative Example 11), 1 (Comparative Example 12), 240 (Comparative Example 13), and 280 (Comparative Example 14), respectively. A magnetic recording medium sample was obtained in the same manner as in Example 22.

<Example 31>
In Example 22, the chip embedded in the carbon target was a Ti chip (vertical 5 mm × horizontal 5 mm × thickness 1 mm), the number of Ti chips was 30, and the rest of the magnetic recording medium 100 was performed in the same manner as in Example 22. A sample was obtained.

<Example 32>
In Example 22, the chip embedded in the carbon target is a W chip (vertical 5 mm × horizontal 5 mm × thickness 1 mm), the number of W chips is 50, and other than that, the magnetic recording medium 100 is the same as in Example 22. A sample was obtained.

<Example 33>
In Example 22, the chip embedded in the carbon target is a TiW chip (vertical 5 mm × horizontal 5 mm × thickness 1 mm), the number of TiW chips is 40, and other than that, the magnetic recording medium 100 is the same as in Example 22. A sample was obtained.

For the above samples, the metal content in the protective layer, shuttle durability (number of shuttles), electromagnetic conversion characteristics of inductive head regeneration, and SO ₂ corrosion resistance were evaluated. Incidentally, SO ₂ Evaluation of corrosion resistance Example 22-30 were performed for Comparative Example 11 to 14 as follows.
(SO ₂ corrosion resistance)
As an evaluation of the magnetization deterioration in the SO ₂ gas environment, the change in the amount of magnetization of a sample stored for 50 hours in an environment of a gas test apparatus (SO ₂ gas concentration = 0.5 ppm, 30 ° C., 80% RH) was measured. The saturation magnetization of the sample was measured using VSM, and the magnetization deterioration rate was calculated using the following formula (Formula 2). In Equation 2, the magnetization deterioration rate is 50% when the amount of magnetization of the Co magnetic layer after storage in the SO ₂ gas environment is reduced by half, and the magnetization deterioration rate is 100% when the magnetization rate after storage is reduced to zero. Here, those with a magnetization deterioration rate of less than 20% were evaluated as good, and those with 20% or more were evaluated as impossible.
(Magnetic deterioration rate φs) (%) = ((magnetization amount before storage) − (magnetization amount after storage)) / (magnetization amount before storage) (Equation 2)

  The above evaluation results are shown in Table 4.

It is sectional drawing which shows the structure of the magnetic-recording medium based on this invention. It is the schematic which shows the structure of the vapor deposition apparatus used for manufacture of the magnetic-recording medium of this invention. It is the schematic which shows the structure of the magnetron sputtering apparatus used for manufacture of the magnetic-recording medium of this invention. It is the schematic which shows the structure of the plasma CVD apparatus used for manufacture of the magnetic recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Magnetic layer, 3 ... Protective layer, 4 ... Lubrication layer, 5 ... Backcoat layer, 100 ... Magnetic recording medium, 200 ... Vapor deposition apparatus, 201, 301, 401 ... vacuum chamber, 202 ... vapor deposition chamber, 203, 303, 403 ... exhaust port, 204, 304, 404 ... feed roll, 205, 305, 405 ... Winding roll, 206, 306, 406 ... cooling can, 207, 208, 307, 308, 407, 408 ... guide roll, 209, 309, 409 ... partition, 210 ... crucible, 211 ... Metal magnetic material, 212 ... Electron gun, 213 ... Shutter, 214 ... Oxygen gas introduction pipe, 300 ... Magnetron sputtering apparatus, 302, 402 ... Deposition chamber, 310 ...・ Target 3 DESCRIPTION OF SYMBOLS 1 ... Backing plate, 312 ... Magnet, 313, 412 ... Power source, 314, 411 ... Gas introduction pipe, 400 ... Plasma CVD apparatus, 410 ... Reaction tube, 413 ... Discharge electrode, 501, 502... Target object, 502

Claims (6)

A metal thin film type magnetic recording medium having a magnetic layer, a protective layer mainly composed of carbon, and a lubricating layer made of a lubricant having a polar group on a nonmagnetic support,
The magnetic recording medium, wherein the protective layer contains 0.5 at% to 50 at% of metal.   2. The magnetic recording medium according to claim 1, wherein the metal is a single metal of Ti, W, or Cu or an alloy containing one or more metals selected from these metal groups.   The magnetic recording medium according to claim 1, wherein the protective layer has a thickness of 2 to 14 nm.   The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 20 to 300 nm.   The magnetic recording medium according to claim 1, wherein the lubricant layer is coated with a lubricant containing fluorine.   The magnetic recording medium according to claim 1, further comprising a backcoat layer on a surface opposite to the magnetic layer forming surface of the nonmagnetic support.

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