JP4325369B2 - Magnetic recording medium - Google Patents

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having a ferromagnetic metal thin film suitable for high density magnetic recording as a magnetic layer.

  In recent years, the magnetic recording density has been increased, and a magnetic tape capable of realizing a high surface recording density has been developed. In particular, as a metal thin film type magnetic tape, a high performance magnetic tape (hereinafter referred to as ME tape) using a cobalt-based obliquely deposited film as a magnetic layer and a diamond-based carbon protective film is an electromagnetic conversion characteristic, storage stability, and practical reliability. It is known to exhibit excellent properties such as properties. At present, the ME tape is used for a DV movie or the like which is a digital video recording device, and is also used as a data storage tape having a width of 8 mm.

  In the future, a recording / reproducing system having a high recording density applying a magnetoresistive head (hereinafter referred to as an MR head) technology used in a hard disk will be considered. As described above, there has been proposed a magnetic recording medium suitable for the MR head by optimizing the film thickness and the residual magnetization amount of the metal magnetic layer on the nonmagnetic substrate.

  The basic configuration of the magnetic recording medium 300 disclosed in Patent Document 1 is that a nonmagnetic substrate 301 is formed by sequentially forming a metal magnetic layer 302 and a protective layer 303 made of a ferromagnetic metal thin film on a nonmagnetic substrate 301 as shown in FIG. A back coat layer 304 is provided on the opposite surface of the metal magnetic layer 302, and the metal magnetic layer 302 having a controlled crystallinity in an oxygen-containing atmosphere is formed to a thickness of 20 to 120 nm, which is suitable for an MR head. High density magnetic recording medium.

  In order to make the MR head suitable, it is necessary to reduce the thickness of the metal magnetic layer 302 and improve the holding power. However, the reduced thickness of the metal magnetic layer 302 is applied to the protective layer 303 because the sheet resistance value is increased. When diamond-like carbon (hereinafter referred to as DLC) is formed by plasma CVD, it is difficult for a plasma discharge current to flow, and there is an essential problem that the film formation speed and / or film quality is lowered.

In order to solve the above-mentioned problems inherent in the magnetic recording medium 300 disclosed in Patent Literature 1, Patent Literature 2 discloses a configuration including a highly conductive metal layer between a nonmagnetic substrate and a metal magnetic layer. ing. That is, in the magnetic recording medium 400 disclosed in Patent Document 2, as shown in FIG. 4, a metal layer 402 is formed on a nonmagnetic substrate 401, and a metal magnetic layer 403 is formed on the metal layer 402. A DLC film 404 is provided on the metal magnetic layer 403, and a backcoat layer 405 is formed on the opposite surface of the nonmagnetic substrate 401 on which the metal layer 402 is formed. The metal layer 402 is a resistive metal layer having a lower resistance than the metal magnetic layer 403 by depositing a base metal material such as aluminum in an atmosphere into which a predetermined amount of oxygen gas is introduced. By providing it between the magnetic substrate 401 and the metal magnetic layer 403, the sheet resistance value of the thinned metal magnetic layer 403 becomes a combined resistance value with the metal layer 402, and thus the thickness of the metal layer 402 is thick. As a result, the plasma CVD deposition rate of the DLC film 404 is improved (results of 10 nm to 100 nm are shown, and the deposition rate of the DLC film 404 is improved as the film thickness increases), and the thin film metal magnetic layer 403 having the MR head suitability is obtained. The productivity of the magnetic recording medium provided with is improved.
Japanese Patent Application Laid-Open No. 11-203652 (paragraph numbers 0013 to 0019 and 0068 to 0090) JP 2003-16626 A (paragraph numbers 0021 to 023, 0025 to 0034, Table 1 and FIG. 1)

  As described above, it is required to reduce the thickness of the metal magnetic layer suitable for the MR head. However, when the metal magnetic layer is reduced in thickness, the resistance value of the metal magnetic layer increases, and the DLC protective film is formed. Speed and film quality are reduced. Therefore, when a metal layer is interposed between the nonmagnetic substrate and the metal magnetic layer, the combined resistance value of the metal layer and the metal magnetic layer is lowered, and the deposition rate of the DLC film formed on the metal magnetic layer is improved. However, crystal growth of the metal magnetic layer is promoted, and suitable magnetic properties cannot be obtained.

  Further, as disclosed in Patent Document 2, in the configuration in which the resistance value of the metal layer 402 formed by introducing oxygen during the film formation of the metal material is controlled to be lower than that of the metal magnetic layer 403, the DLC film 404 From the viewpoint of film formation speed, it is required to increase the thickness of the metal layer 402, and as a result of increasing the thickness of the metal layer 402, the metal layer 402 and the non-magnetic recording substrate 401 are stacked. There is a problem in that the metal magnetic layer 403 is thickened to prevent the magnetic recording medium from being thinned, and it takes time to form the metal layer 402 and the metal magnetic layer 403.

  Therefore, in view of the conventional problems related to the present invention, in order to protect a metal magnetic layer, a magnetic recording medium having an improved film forming speed and film quality of a protective layer formed on the metal magnetic layer is provided. Objective.

  The magnetic recording medium of the present invention includes a laminated structure in which a nonmagnetic conductive layer, a metal magnetic layer, and a protective layer are sequentially formed on one surface of a nonmagnetic substrate, and includes the nonmagnetic conductive layer and the metal magnetic layer. The nonmagnetic conductive layer at the interface includes oxygen.

The method for producing a magnetic recording medium of the present invention comprises:
A nonmagnetic conductive layer is formed on one main surface of the nonmagnetic substrate by vapor deposition, and an oxygen source of any of oxygen molecules, oxygen ions or active group oxygen is injected into the surface of the nonmagnetic conductive layer, and the oxygen source A metal magnetic layer is formed by vapor deposition on the conductive layer implanted with a gas, a voltage is applied between the plasma discharge electrode and the metal magnetic layer, and a carbon-based protective film is formed on the metal magnetic layer by plasma CVD. Composition to form,
Or
After forming a nonmagnetic conductive material on one main surface of the nonmagnetic substrate by vapor deposition, the nonmagnetic conductive material is vapor deposited in an oxygen source atmosphere of any of oxygen molecules, oxygen ions, or active oxygen. A conductive layer is formed, a metal magnetic layer is formed on the conductive layer by vapor deposition, a voltage is applied between the plasma discharge electrode and the metal magnetic layer, and a plasma CVD method is applied on the metal magnetic layer. To form a carbon-based protective film.

  The magnetic recording medium of the present invention has a laminated structure in which a nonmagnetic substrate, a nonmagnetic conductive layer, and a metal magnetic layer are sequentially stacked, and contains oxygen in the nonmagnetic conductive layer at the interface between the nonmagnetic conductive layer and the metal magnetic layer. As a result, a metal magnetic layer having excellent magnetic properties can be formed, and the deposition rate of a high-quality protective layer that protects the metal magnetic layer can be improved, thereby realizing high productivity. In addition, since the layer containing oxygen in the nonmagnetic conductive layer at the interface between the nonmagnetic conductive layer and the metal magnetic layer can increase the sheet resistance value of the nonmagnetic conductive layer and control the crystal growth of the metal magnetic layer, The magnetic properties of the magnetic layer can also be improved. Together, these have the effect of providing a high-density magnetic recording medium at low cost.

  The magnetic recording medium of the present invention includes a laminated structure in which a nonmagnetic conductive layer, a metal magnetic layer, and a protective layer are sequentially formed on one surface of a nonmagnetic substrate, and includes the nonmagnetic conductive layer and the metal magnetic layer. The nonmagnetic conductive layer at the interface is configured to contain oxygen, and the sheet resistance value of the metal magnetic film is increased by reducing the thickness of the metal magnetic layer in order to improve the holding power. However, the protective film is formed on the metal magnetic layer. When plasma is formed by plasma CVD, the plasma current flows preferentially in the nonmagnetic conductive layer provided between the metal magnetic layer and the nonmagnetic substrate, and as a result, the plasma discharge current easily flows. Control of crystal growth of the metal magnetic layer formed on the nonmagnetic conductive layer is possible by increasing the deposition rate and incorporating oxygen into the nonmagnetic conductive layer at the interface between the nonmagnetic conductive layer and the metal magnetic layer. To be able to Excellent metallic magnetic layer on the magnetic properties, and a magnetic recording medium which has achieved productivity and nonmagnetic protective layer having both the film quality can be realized.

  Further, when the combined transmittance of the nonmagnetic substrate and the laminated structure of the magnetic recording medium of the present invention has a configuration of 0.2% or more and 7% or less in a wavelength range of 600 nm to 800 nm, a tape-like magnetic The start / end detection on the recording medium can be reliably performed.

  In addition, when the film thickness of the nonmagnetic conductive layer of the magnetic recording medium of the present invention is 5 nm or more and 50 nm or less, it is possible to form a continuous film of the nonmagnetic conductive layer and to prevent the magnetic recording medium from being thinned. preferable.

  Further, when the sheet resistance value of the nonmagnetic conductive layer of the present invention is 3Ω / □ or more and 200Ω / □ or less, a metal magnetic layer exhibiting good magnetic properties can be formed by vapor deposition, and the metal magnetic layer When a protective layer is formed on the layer by vapor deposition, a protective film with high film quality and high film formation speed is obtained because the current caused by the voltage applied between the electrode and the metal magnetic layer easily flows to the nonmagnetic conductive layer. Can be formed.

  Further, when the light transmittance of the nonmagnetic conductive layer of the magnetic recording medium of the present invention is 1% to 50% in a wavelength range of 600 nm to 800 nm, the preferred film thickness of the nonmagnetic conductive layer and / It is preferable because a preferable sheet resistance value of the nonmagnetic conductive layer can be realized.

  In the method of manufacturing a magnetic recording medium of the present invention, when a nonmagnetic conductive layer is formed on a nonmagnetic substrate by vapor deposition, oxygen molecules are formed on the surface of the nonmagnetic conductive layer facing the nonmagnetic substrate after the nonmagnetic conductive layer is formed. In the structure of injecting an oxygen source of either oxygen ions or active group oxygen, or in an atmosphere of oxygen source of oxygen molecules, oxygen ions or active group oxygen after forming the nonmagnetic conductive layer by vapor deposition Therefore, the nonmagnetic conductive layer to which the oxygen source present at the interface between the nonmagnetic conductive layer and the metal magnetic layer is added is the metal magnetic layer. It is possible to easily manufacture a high-density magnetic recording medium that achieves both control of crystal growth and film formation speed and film quality of a protective film formed on the metal magnetic layer.

  Hereinafter, an embodiment relating to a magnetic recording medium of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram for explaining an embodiment of the magnetic recording medium of the present invention, and FIG. 2 shows a schematic configuration of a plasma CVD apparatus of an embodiment for forming a protective film of the magnetic recording medium of the present invention. .

  In FIG. 1, a magnetic recording medium 100 includes a nonmagnetic substrate 101, a nonmagnetic conductive layer 102 formed on one surface of the nonmagnetic substrate 101, and a surface of the nonmagnetic conductive layer 102 that the nonmagnetic substrate 101 faces. An oxygen source addition layer 103, a metal magnetic layer 104 formed on the oxygen source addition layer 103, a protective layer formed on the metal magnetic layer 104, and a back coat layer 106 on the other surface of the nonmagnetic substrate 101. Prepare.

  Examples of the material applicable to the nonmagnetic substrate 101 include polymer films such as a polyethylene terephthalate film, a polyethylene naphthalate film, a polyamide film, and a polyimide film, and the thickness is generally 2 μm to 10 μm. In addition, these thin film films are dispersed and / or fixed with fine particles of an inorganic substance such as silicon dioxide and zinc oxide and an organic substance such as polyimide resin for the purpose of lowering the adhesion in a wound state. There are many.

  Examples of a material that can be applied to the nonmagnetic conductive layer 102 include aluminum, copper, tin, indium, antimony, zinc, magnesium, molybdenum, tungsten, tantalum, and titanium. It is formed by vapor deposition such as PVD such as Ting, or CVD such as laser CVD or plasma CVD, and reactive gases such as argon, xenon, and reactive gases such as nitrogen, oxygen, and hydrogen are introduced as needed. Is done.

  After the nonmagnetic conductive layer 102 is deposited, the oxygen source addition layer 103 exposes oxygen components such as oxygen molecules, oxygen ions, oxygen atoms, and oxygen radicals to the deposition chamber so that at least the outermost surface of the nonmagnetic conductive layer 102 is exposed. After the oxidized layer or the nonmagnetic conductive layer 102 is formed by vapor deposition, the material applied to the nonmagnetic conductive layer is deposited in an atmosphere having oxygen components such as oxygen molecules, oxygen ions, oxygen atoms, oxygen radicals, and the like. It is one of the layers having more oxygen components and / or oxidation components than the nonmagnetic conductive layer 102 formed, and has a function of increasing the sheet resistance value of the nonmagnetic conductive layer 102. The oxygen source addition layer 103 is an oxidized conductive material layer obtained by oxidizing either a material provided for the nonmagnetic conductive layer 102 or a conductive material other than a material provided for the nonmagnetic conductive layer 102. When oxygen is contained in the film formation process, the oxidation rate is higher than that of the nonmagnetic conductive layer 102. The injection thickness and / or injection amount for injecting the oxygen component by exposing the non-magnetic conductive layer to the non-magnetic conductive layer, the oxygen component amount introduced into the atmosphere having the oxygen component, and / or the deposited film thickness are non-magnetic. Although it differs depending on the material applied to the conductive layer and cannot be defined generally, the combined sheet resistance value of the nonmagnetic conductive layer 102 and the oxygen source addition layer 103 (hereinafter, the nonmagnetic conductive layer 102 and the oxygen source addition layer 103 are combined. The conductive layer is controlled to 3Ω / □ or more and 200Ω / □ or less from the magnetic properties of the metal magnetic layer 104 described later or the deposition rate and film quality of the protective layer 105. That is, when the synthetic sheet resistance value of the conductive layer is less than 3 Ω / □, it becomes difficult to flow current when forming the protective layer 105 under an applied voltage, the deposition rate is reduced, and not only productivity is deteriorated, but also protection. The film quality of the layer 105 also tends to deteriorate. If the composite sheet resistance value of the conductive layer exceeds 200Ω / □, it becomes difficult to control the crystal growth of the metal magnetic layer 104. For example, the coercive force and saturation magnetic flux density as a high-density magnetic layer suitable for MR head There is a tendency that the magnetic properties such as the product with the film thickness cannot be satisfied.

  The optimum film thickness of the conductive layer varies depending on the material applied to the nonmagnetic conductive layer 102, but is preferably 5 nm or more and 50 nm or less. If the thickness of the conductive layer is less than 5 nm, it is difficult to form a continuous conductive layer, and the sheet resistance value of the conductive layer tends to be abnormally high. The sheet resistance value of the layer 104 also increases, and as described above, the film quality and deposition rate of the protective layer decrease. When the thickness exceeds 50 nm, the total film thickness of the metal magnetic layer 104 described later is increased, and when the magnetic recording medium is applied to a tape, the volume after winding is increased, so that thinning is achieved. Can not do it. However, in the conductive layer of the present invention, when the oxygen content and the film thickness of the oxygen source addition layer 103 are the same, the sheet resistance value decreases as the film thickness increases, and the film quality and film formation of the protective film decrease as the sheet resistance value decreases. Since the speed can be improved, the upper limit of the thickness of the conductive layer may be, for example, about 70 nm from the viewpoint of forming the protective film. In addition, since the conductive layer is formed by vapor deposition, it is simple and accurate to manage the film thickness of the conductive layer by the light transmittance. Therefore, when the light transmittance of the conductive layer is controlled to 1% or more and 50% or less in a wavelength range of 600 nm to 800 nm, for example, the light transmittance is good regardless of the type of material applied to the nonmagnetic conductive layer 102. In addition, it is desirable to manage the wavelength that is applied to an actual DV device within the above-mentioned wavelength range (a wavelength of 700 nm is exclusively applied) because the detection accuracy of the start and end of the tape can be managed together. Moreover, since the color of the conductive material generally changes when oxidized, the film thickness management in the light transmittance measurement of the conductive film considering the actual use as a magnetic tape is measured including the oxygen source addition layer 103. To do.

  In addition, as a method for providing the oxygen component of the oxygen source addition layer 103, for example, oxygen molecules are introduced into a glow discharge, arc discharge, sputtering atmosphere, or the like to be in an ionized, radicalized or generated group state, or the nonmagnetic conductive layer 102 is used. Ordinary techniques such as exposure of oxygen molecules may be used, and can be used together or selected as appropriate according to the amount of oxygen to be injected or contained. Note that the conductive material applied to the nonmagnetic conductive layer 102 and the material applied to the oxygen source addition layer 103 may be the same or different materials, but considering the deposition efficiency of the conductive layer Either the oxygen component is injected after the nonmagnetic conductive layer 102 is formed, or the film is formed in an atmosphere containing the oxygen component in the conductive material used for the nonmagnetic conductive layer 102, and the sheet resistance value of the conductive layer is managed. In this aspect, a relatively low resistance oxide such as tin oxide, indium oxide or zinc oxide or a relatively high resistance oxide such as aluminum oxide is appropriately laminated on the nonmagnetic conductive layer 102. Preferably, the conductive layer can be appropriately selected and used according to electrical characteristics required for the conductive layer.

  As the material applied to the metal magnetic layer 104, ferromagnetic metal such as Fe, Co, Ni, Fe-Co, Co-Ni, Co-O, Fe-Co-Ni, Fe-Cu, Co-Cu, Co-Au, Co-Pt, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr, Co-Ni-Cr, Co-Pt-Cr, Fe-Co-Ni-Cr, Mn-Bi, One or a plurality of materials selected from an alloy such as Mn—Al may be a single layer film or a multilayer film. For the metal magnetic layer 104, an oblique deposition method or a gradient deposition method in which the incident angle of the vapor of the material used for the metal magnetic layer 104 is continuously changed by a technique such as ion plating or sputtering is used. Thus, it can be formed as a perpendicular magnetization film. Note that an oxygen-containing metal magnetic film having high-efficiency electric / magnetic conversion characteristics can be formed by performing the vapor deposition in an oxygen atmosphere. It is to be noted that the film thickness control when the metal magnetic layer 104 is formed by vapor deposition is the simplest and most accurate with the light transmittance, similar to the formation of the conductive layer. For this reason, when managing the film thickness of the metal magnetic layer 104 by the light transmittance, it is managed by the method of managing the light transmittance of the metal magnetic layer 104 alone and the composite light transmittance of the conductive layer and the metal magnetic layer 104. However, when using a magnetic recording medium as a magnetic tape, it is also preferable to manage with a composite light transmittance since it also serves as a start / end detection test as described above. The measurement wavelength range is also set to any of 600 nm to 800 nm as in the conductive layer, and the light transmittance of the metal magnetic layer 104 alone in the wavelength range is preferably in the range of 10% to 60%. In particular, the transmittance loss in the protective layer 105, which will be described later, and the lubricant layer 107 applied as necessary is almost zero. Therefore, the measurement of the composite light transmittance almost shows the light transmittance itself of the magnetic tape in actual use. It can also be used to detect the position of the beginning and end of the tape in DV equipment. When this composite light transmittance exceeds 7%, it tends to be difficult to detect the difference in light transmittance between the leader tape and the magnetic tape. When the composite light transmittance is less than 0.2%, the thickness of the metal magnetic layer 104 can be controlled. The accuracy is inferior. For this reason, the composite light transmittance is preferably 0.2% to 7%, and more preferably 0.2% to 4%. Further, in order to obtain a magnetic recording medium having MR head suitability, it is desirable that the metal magnetic film 104 has a thickness in the range of 20 nm to 120 nm.

  The magnetic layer of the magnetic recording medium has a protective layer 105 that protects the metal magnetic layer 104 from the magnetic head so that the magnetic head slides and comes into contact with the magnetic layer to reproduce the information signal recorded or recorded on the magnetic layer. is required. On the other hand, in order to perform magnetic recording / reproducing with respect to the magnetic layer, it is necessary to optimize the magnetic gap as is well known. Therefore, the protective layer 105 that protects the metal magnetic layer 104 is required to have a thin film, high mechanical strength, and excellent physical properties. As the protective layer 105 that satisfies the above requirements, a carbon-based thin film is applied. Among them, a so-called diamond-like carbon (DLC) film containing a three-dimensional structure having a diamond structure has a moderately high film hardness, so that the magnetic recording medium is used. In addition to high reliability such as durability and storage stability, and high effect of suppressing damage such as wear of the magnetic head, it is widely applied. Such a protective layer 105 is formed by depositing a raw material containing carbon on the metal magnetic layer 104 by vapor deposition. In addition to a film formed only of carbon, nitrogen, oxygen, hydrogen, It may be a film containing one or more kinds of atoms selected from fluorine and boron. In order to form the protective layer 105 densely, field-applied vapor deposition that gives an electric charge to the raw material vapor is preferable, and plasma CVD is particularly preferable among them. The protective layer 105 shown in FIG. 1 has a single-layer structure, but can be applied to a multilayer structure formed by changing the composition, material, and / or vapor deposition method, for example. The thickness of the protective layer 105 is preferably 5 nm to 20 nm, and preferably 8 nm to 16 nm.

  FIG. 2 is a diagram illustrating the configuration of a plasma CVD apparatus that can be applied to the magnetic recording medium of the present invention. The plasma CVD apparatus 200 includes a tape-shaped magnetic recording medium precursor (magnetic recording medium only of the metal magnetic layer 104) 203 wound around a feeding roller 202 provided in a chamber maintained at a predetermined high vacuum by a vacuum pump 201. Then, the magnetic recording medium 206 on which the protective layer 105 is formed is taken up by the take-up roller 205 through the film forming roller 204. Sub rollers 207 and 208 for adjusting tension and meandering are provided between the feeding roller 202 and the film forming roller 204 and between the film forming roller 204 and the take-up roller 205, respectively. The magnetic recording medium precursor 203 forms a magnetic recording medium 206 by forming a protective layer 105 at a position where the plasma discharge tube 209 faces. In the plasma discharge tube 209, for example, a raw material gas obtained by mixing a carbon source such as methane gas or hexane gas and an introduction gas such as argon at a predetermined ratio is introduced into the plasma discharge tube 211 through the introduction tube 210, and plasma discharge is performed. Between the electrode 209 and the metal magnetic layer 104 of the magnetic recording medium precursor 203, for example, a voltage of a power source 212 in which a 900V DC power source is superimposed on an AC power source having a frequency of 20 kHz effective value 800V is applied. In the figure, a voltage is applied from the power source 212 to the sub-rollers 207 and 208 via the plasma discharge electrode 211, the magnetic recording medium precursor 203, and the magnetic recording medium 206. A current flowing between the sub rollers 207 and 208 is referred to as a plasma current.

  In view of the current path of the plasma current, the current preferentially flows through a portion having a low resistance value, and the thickness of the metal magnetic layer 104 is about several tens of nm as described above. Then, the conductive layer having a much lower sheet resistance value preferentially flows in the plane direction than the metallic magnetic layer 104 having a higher sheet resistance value. When the plasma current is uniform and flows a lot, the applied voltage can be increased, and the film quality of the protective layer 105 (in this case, the DLC film) is dense and the film formation speed is high. Since the magnetic recording medium precursor 203 and the magnetic recording medium 206 sequentially move along the film forming roller 204, the contact portion between the sub roller 207 and the magnetic recording medium precursor 203 and the sub roller 208 and the magnetic recording medium 206 Since both the contact locations change, the metal magnetic layer 104 having a high sheet resistance value is not destroyed. On the other hand, in the magnetic recording medium that does not include the conductive layer described in Patent Document 1 and the like, the current path is only the metal magnetic layer 302 having a high sheet resistance value. Due to the high sheet resistance value of the layer 302, heat paths or current paths that flow intensively in the metal magnetic layer 302 are formed unevenly with respect to the film surface direction. The problem of melting or tearing the substrate 301 can be overcome.

  A back coat layer 106 is formed on the other surface of the nonmagnetic substrate 101 of the magnetic recording medium 206 on which such a protective layer 105 is formed, if necessary. The back coat layer 106 is a dispersion obtained by mixing a predetermined amount of a binder having a solvent solubility such as a polyester resin and a solid lubricant such as carbon, talc, boron fluoride, and the like. In general, wet coating is performed, but a solid lubricant such as carbon or silicon oxide may be formed into a dry film by a technique such as vapor deposition. The film thickness is generally about 0.2 μm to 1 μm, and it is sufficient that the back surface of the tape can be given slidability when sandwiched with a magnetic head such as a DV device. Furthermore, in order to further add the surface lubricity of the protective layer 105 on the protective layer 105, for example, a lubricating layer 107 coated with a fluorine-based lubricant or the like may be provided on the outermost surface. When the lubricating layer 107 is formed by wet coating, the lubricant is absorbed by the protective layer 105 and the like, and the film thickness that appears as the lubricating layer 107 is about 0.05 nm to 50 nm when converted from the wet coating solution. The magnetic recording medium 100 shown in FIG. 1 shows a configuration including the backcoat layer 106 and the lubricating layer 107, but as described above, the backcoat layer 106 and the lubricating layer 107 are not essential.

Hereinafter, the present invention will be described in detail with specific examples. In the following examples and comparative examples, a polyethylene terephthalate film with a film thickness of 6.3 μm is applied as a nonmagnetic substrate, the nonmagnetic conductive layer is formed by sputtering copper, and the oxygen source added layer is formed by a nonmagnetic conductive layer. After that, the surface of the nonmagnetic conductive layer is oxidized by oxygen passed through the glow discharge, and the metal magnetic layer is formed by electron beam evaporation in an oxygen atmosphere using oblique deposition technique, and then In the plasma CVD apparatus shown in FIG. 2, methane gas and argon gas are mixed in equal amounts, and a total gas pressure of 13.3 Pa is applied to the plasma discharge electrode and a voltage obtained by superimposing a 900 V DC power supply on a 20 kHz effective value 800 V AC power supply. Glow discharge is generated, the speed of the film forming roller 204 is adjusted to form a DLC film on the metal magnetic layer so as to have a thickness of 10 nm, and the fluorine-containing carbon is formed on the protective layer. The phosphate-based lubricant was 4nm applied wet terms by wet coating to obtain a magnetic recording medium, and a magnetic recording tape was slit thereafter 1/4 inch wide. The film thicknesses of the nonmagnetic conductive layer (that is, the conductive layer) and the metal magnetic layer including the oxygen source addition layer were controlled by measuring the light transmittance of 700 nm independently.
Example 1
By controlling the light transmittance of the conductive layer to 10%, a film thickness of 30 nm and a sheet resistance value of 9Ω / □ are laminated on the metal magnetic film by controlling the light transmittance of 90 nm, 70 nm and 50 nm on the conductive layer. Sample Nos. 1, 2 and 3 were prepared and the influence of the film thickness of the metal magnetic layer was verified.
(Example 2)
The light transmittance of the conductive layer is controlled to 6%, 10%, and 45%, respectively, the film thickness is 6 nm, 10 nm, and 45 nm, and the sheet resistance value is 180Ω / □, 120Ω / □, and 4Ω / □, respectively. Sample numbers 4, 5, and 6 were prepared by laminating 90 nm by controlling the metal magnetic layer with light transmittance, and the film thickness and sheet resistance dependency of the conductive layer were verified.
(Comparative Example 1)
In order to verify the presence or absence of a conductive layer as a comparison with Example 1, Sample No. 1 ′ having a film thickness of 90 nm was produced by directly controlling the metal magnetic layer with a light transmittance on a nonmagnetic substrate.
(Comparative Example 2)
In order to verify the presence or absence of an oxidation source addition layer as a comparison with Example 1, a film thickness of 30 nm was formed by controlling the light transmittance of the conductive layer to 10%, and on the conductive layer not subjected to oxidation treatment, Sample number 2 ′ was prepared by laminating 90 nm by controlling the metal magnetic layer with light transmittance. Since the conductive layer was not oxidized, the sheet resistance value was 8Ω / □.
(Comparative Example 3)
As a comparison with Example 2, in order to verify the dependency of the film thickness of the conductive layer and the sheet resistance value, the light transmittance of the conductive layer was controlled to 60% and 0.6%, respectively, the film thickness was 4 nm and 45 nm, and the sheet Sample numbers 3 ′ and 4 ′ were prepared by laminating a metal magnetic layer by 90 nm on conductive layers having resistance values of 300Ω / □ and 2Ω / □, respectively, by controlling the light transmittance. The oxidation treatment of the conductive layer to the oxygen source addition layer was performed under exactly the same conditions as in Example 2.

  The configuration of each of the 10 samples is shown in (Table 1). In (Table 1), 10 samples each of sample numbers 1 to 6 and sample numbers 1 ′ to 4 ′ are prepared, and the measurement results of the composite sheet resistance value and the composite transmittance of the conductive layer and the metal magnetic layer are shown. Average values are also noted.

  Ten samples of each of the above 10 samples are kept as the deposition speed at which a DLC film can be formed to 10 nm, still resistance as an evaluation of the DLC film quality, detection of the start and end when mounted on a DV device, and appropriateness of the MR head. Evaluation of magnetic force and electrical / magnetic conversion characteristics (product of saturation magnetic flux density and film thickness) was listed as an evaluation item. The results of each evaluation item are shown in (Table 2).

  For evaluation of still resistance, each sample was wound around a friction member made of stainless steel (SUS420J2, surface roughness 0.2S, outer diameter 6 mm) at a winding angle of 90 °, and unwound and wound under the condition of a tension of 20 gf. The take-up was repeated 100 times, the tensions on the unwinding side and the winding side were measured, and the dynamic friction coefficient was calculated from the ratio of the winding-side tension to the unwinding-side tension based on Euler's equation. The initial dynamic friction coefficient was the first value.

  In addition, the start / end detection is performed by incorporating each sample into a commercially available DV cassette and running on the DV deck, and detecting the transmittance between the leader tape and the magnetic tape based on the light transmittance at a wavelength of 700 nm. evaluated.

  From Table 2, it is clear that the sample numbers 1 to 6 according to the examples are superior to the sample numbers 1 'to 4' according to the comparative example. Hereinafter, the configuration of each sample and each evaluation item will be considered in detail.

  First, regarding the presence or absence of a conductive layer provided between the non-magnetic substrate and the metal magnetic layer, sample numbers 1 and 4 to 6 are sample number 1 over all of the DLC film deposition rate, dynamic friction coefficient, and start / end detection. 'It is clear from (Table 2) that it is superior. That is, since the film thickness of the metal magnetic layer of all the samples is 90 nm, the sheet resistance value of the metal magnetic layer is assumed to be constant, but the deposition rate of the DLC film of sample number 1 ′ is Although the initial value was almost the same as the dynamic friction coefficient, it was remarkably deteriorated after 100 times. This is due to the fact that Sample No. 1 ′ is not provided with a conductive layer, and therefore the combined sheet resistance value (labeled as the resistance value) of the conductive layer and the metal magnetic layer (indicated in the table as conductive layer / magnetic layer). However, it is assumed that this is because the DLC film formation rate is slow and the DLC film quality is low and the DLC film cannot withstand the still test. On the other hand, in Sample Nos. 1 and 4 to 6, it was found that the deposition rate of the DLC film was uniformly high and the productivity was greatly improved, and the coefficient of dynamic friction was 0.01 to at most in the evaluation of still resistance. Since it only stays at 0.04, it can be seen that it has high film-forming properties and high film quality. In addition, since the composite transmittance of the conductive layer of sample No. 1 ′ and the metal magnetic layer (in the table, referred to as “transmissivity”, referred to as “composite transmittance”) is as high as 15.0%. Since it could not be detected, it was impossible to run on the actual DV deck applied to the evaluation, and in the configuration without the conductive layer, the metal magnetic layer having a thickness of at least 90 nm lacked the concealability, so it is necessary to increase the thickness. It is assumed that there is a possibility of lack of proper MR head when the metal magnetic layer is thickened.

  Next, regarding the presence or absence of the oxygen source addition layer provided in the conductive layer, when the sample numbers 1 and 1 ′ are compared, the DLC film deposition rate and the still resistance evaluation items are the same, so the DLC film has the same degree. The sample No. 1 ′ showed a decrease from the viewpoint of coercive force. It is assumed that in Sample No. 1 ′, the surface in contact with the metal magnetic layer was not oxidized, so that control of crystal growth of the ferromagnetic metal material in the metal magnetic layer was limited, and the crystal grains became larger. Is done. Therefore, if a conductive layer or metal layer having good conductivity is provided between the nonmagnetic substrate and the metal magnetic layer, good results can be obtained from the viewpoint of the DLC film. From the viewpoint of the coercive force required for such magnetic recording media, the oxygen source addition layer can exhibit the crystal controllability of the ferromagnetic metal material.

  Next, regarding the influence of the film thickness of the conductive layer, the film thickness of the conductive layer increases in the order of sample numbers 3 ′, 4, 5, 1, 6, 4 ′, and the combined resistance value and composite transmittance are accordingly increased. It can be seen from Table 1 that both show a tendency opposite to the change in film thickness. When the results of (Table 1) and the results of (Table 2) are collated, the thickness of the metal magnetic layer is 90 nm and the entire sample is constant, so the coercive force is almost the same and there is no difference. In Sample No. 3 ′ where the layer thickness is thin, the sheet resistance value of the conductive layer is as high as 300Ω / □, so the combined resistance value is equivalently as high as 150Ω / □, and the film formation speed and quality of the DLC film are the other five. Compared to, a decrease was observed, and since the composite transmittance was as high as 9.0%, the start / end could not be detected. In contrast, sample No. 4 has a good DLC film deposition rate, and its film quality is within the allowable range of 0.04 in the coefficient of dynamic friction in the still resistance test, and the start / end detection by the actual DV deck is also possible. It has been detected without problems. From this, if the composite transmittance is 7% or less, it is possible to detect the start and end of the actual DV deck, and the conductive layer sheet resistance value of around 180Ω / □ is the main factor of the combined resistance value 110Ω / □. If so, satisfactory characteristics can be obtained over all the evaluation items of the DLC film deposition rate, film quality, still resistance, start / end detection, and coercive force. In view of the numerical values of the conductive layer and the conductive layer / magnetic layer in (Table 1) of Sample Nos. 4 and 3 ′ and the evaluation results in (Table 2), the sheet resistance value of the conductive layer is 200Ω / □. Hereinafter, it is assumed that the thickness of the conductive layer is 5 nm or more and the light transmittance is 50% or less.

  On the other hand, in the sample No. 4 ′ where the thickness of the conductive layer is 65 nm, which is the thickest, the sheet resistance value of the conductive layer is as low as 2Ω / □, so the combined resistance value is equivalently as low as 2Ω / □. As shown in 2), the film formation rate of the DLC film, the film quality of the DLC film, the start / end detection and the coercive force are all good, but the composite transmittance is 0.1%. In terms of production management of the metal magnetic layer, it is disadvantageous for thinning the magnetic tape because it is almost in the vicinity of the limit value of film thickness management and the conductive layer is as thick as 65 nm. On the other hand, in Sample No. 6, the thickness of the conductive layer is 45 nm, the sheet resistance value of the conductive layer is 4Ω / □, and the combined resistance value is equivalently lower than that of Sample No. 4 ′. Satisfactory results have been obtained for all the evaluation items shown in (Table 2). However, the composite transmittance of Sample No. 6 is 0.3%, and the light transmittance is higher than the limit of the thickness control of the metal magnetic layer in the production of the magnetic recording medium. Can be provided, and thinning as a magnetic tape is more effective than Sample No. 4 ′. In light of the fact that the light transmittance at the film thickness control limit of the metal magnetic layer is about 0.1% as described above, if the thickness is about 5 nm thicker than the conductive layer of sample number 6 and is about 50 nm, the metal Even if the magnetic layer is formed to a thickness of about 90 nm, for example, the light transmittance is expected to be about 0.2%. In view of the results of Sample Nos. 6 and 4 ′, the light transmittance of the conductive layer at that time is about 1%, Since the sheet resistance value is assumed to be about 3Ω / □, it can be assumed to be the limit value of the conductive layer.

  Sample Nos. 4, 5, 1 and 6 are samples in which the metal magnetic layer has the same thickness and the thickness of the conductive layer is changed, but the transmission of the conductive layer depends on the thickness of the conductive layer. The ratio and the sheet resistance value are also changed, and equivalently, the combined resistance value and the composite transmittance value are also changed. The sample obtained favorable results over all the evaluation items from (Table 2). From this, it is understood that the above ranges are appropriate for the upper limit value and the lower limit value of the film thickness, light transmittance, sheet resistance value, combined resistance value, and composite transmittance of the conductive layer described above. Accordingly, the numerical range of each component in the magnetic recording medium of the present invention is that the film thickness of the conductive layer is 5 nm or more and 50 nm or less, the sheet resistance value of the conductive layer is 3Ω / □ or more and 200Ω / □ or less, and the conductive layer has a wavelength. The light transmittance measured with light of 700 nm is optimally 1% to 50%, and the composite transmittance measured at wavelength 700 nm is optimally 0.2% to 7%. In addition, since the material of the conductive layer and the material of the metal magnetic layer applied in the present invention do not have a specific absorption range in the wavelength range of 600 nm to 800 nm, in this example, measurement was performed using a wavelength of 700 nm. However, when the wavelength range is 600 nm or more and 800 nm or less, the light transmittance and the composite transmittance shown in (Table 1) hardly change.

  Further, in each of sample numbers 1 to 3, the thickness of the conductive layer is kept constant at 30 nm, the light transmittance and the sheet resistance value of the conductive layer are equivalently the same, and the thickness of the metal magnetic layer is changed to the same sample. This is the case. Although the composite transmittance varies with the thickness of the metal magnetic layer, the combined resistance is almost directly affected by the sheet resistance of the conductive layer because the sheet resistance of the conductive layer is as low as 9Ω / □. It was almost the same value. The film thickness of the metal magnetic layer is selected from a film thickness range having MR head suitability. Since the combined resistance value and the composite transmittance value in (Table 1) are within the above-described ranges, good results are obtained over the DLC film deposition rate, DLC film quality, and start / end detection. (Table 2). What should be noted in sample numbers 1 to 3 is the product of coercive force and saturation magnetic flux density and film thickness. In order to ensure the proper MR head, the smaller the value of the product of the saturation magnetic flux density and the coating film pressure, which is one of the indicators of the electrical / magnetic conversion characteristics, is better. It is assumed that the metal magnetic layer is preferably thin. If the thickness of the metal magnetic layer is reduced, the plasma current becomes difficult to flow in the process of forming the protective layer as described above. However, since the present invention includes a conductive layer, mass production is possible even if the thickness of the metal magnetic layer is reduced. There is no problem with sex. In addition, in the technique disclosed in Patent Document 2, that is, a configuration in which a resistive metal layer is interposed between the nonmagnetic substrate and the metal magnetic layer, resistance is required to achieve a practical protective layer deposition rate. A film thickness of about 100 nm is required only for the thickness of the metal layer, but by applying the conductive layer having the oxygen source addition layer of the present invention, the film thickness of the laminated structure of the conductive layer and the metal magnetic layer can be reduced. It has been found that both a protective layer that can withstand practical use at about 100 nm and excellent magnetic properties can be achieved.

  The present invention can greatly improve the production efficiency of a magnetic recording medium capable of recording / reproducing information signals at high density, and can provide a magnetic recording medium that can be applied to MR heads and higher density recording heads.

Sectional drawing in one Embodiment of the magnetic-recording medium of this invention Schematic configuration diagram of one vapor deposition apparatus for forming a protective layer of a magnetic recording medium of the present invention Sectional drawing explaining an example of the conventional magnetic recording medium Sectional drawing explaining the other example of the conventional magnetic recording medium

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Nonmagnetic board | substrate 102 Conductive layer 103 Oxygen source addition layer 104 Metal magnetic layer 105 Protective layer 106 Backcoat layer 107 Lubricant layer

Claims (7)

A laminated structure in which a nonmagnetic conductive layer, a metal magnetic layer, and a protective layer are sequentially formed on one surface of the nonmagnetic substrate; and the nonmagnetic conductive layer at the interface between the nonmagnetic conductive layer and the metal magnetic layer A magnetic recording medium containing oxygen. 2. The magnetic recording medium according to claim 1, wherein a composite light transmittance of the nonmagnetic substrate and the laminated structure in a wavelength range of 600 nm to 800 nm is 0.2% to 7%. The magnetic recording medium according to claim 1, wherein the conductive layer has a thickness of 5 nm to 50 nm. The magnetic recording medium according to claim 1, wherein the conductive layer has a sheet resistance value of 3Ω / □ or more and 200Ω / □ or less. 3. The magnetic recording medium according to claim 1, wherein the light transmittance of the conductive layer in a wavelength range of 600 nm to 800 nm is 1% to 50%. Forming a nonmagnetic conductive layer on one main surface of the nonmagnetic substrate by vapor deposition;
Injecting an oxygen source of oxygen molecules, oxygen ions, or active group oxygen into the surface of the nonmagnetic conductive layer,
Forming a metal magnetic layer on the conductive layer injected with the oxygen source by vapor deposition;
A method for manufacturing a magnetic recording medium, wherein a voltage is applied between a plasma discharge electrode and the metal magnetic layer, and a carbon-based protective film is formed on the metal magnetic layer by a plasma CVD method. After forming a nonmagnetic conductive material on one main surface of the nonmagnetic substrate by vapor deposition, the nonmagnetic conductive material is vapor deposited in an oxygen source atmosphere of any of oxygen molecules, oxygen ions, or active oxygen. Forming the formed conductive layer,
A metal magnetic layer is formed on the conductive layer by vapor deposition,
A method for manufacturing a magnetic recording medium, wherein a voltage is applied between a plasma discharge electrode and the metal magnetic layer, and a carbon-based protective film is formed on the metal magnetic layer by a plasma CVD method.

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