JP2005353140A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive magnetic recording medium of high capacity having high performance and high reliability, as the magnetic recording medium wherein a magnetic layer having at least a granular structure is formed on a non-magnetic substrate. <P>SOLUTION: The magnetic recording medium wherein the magnetic layer having at least the granular structure is formed on at least one surface of the non-magnetic substrate is characterized in that in TEM observation in the surface formed by cutting the magnetic layer in a direction parallel to the substrate, an average magnetic particle size in the magnetic layer is in the range of 3 to 8 nm and dispersion of the size is ≤3 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium.

  In recent years, with the spread of the Internet, the use form of computers has changed, such as processing of large-capacity moving image information and audio information using a personal computer. Accordingly, the storage capacity required for magnetic recording media such as hard disks is also increasing.

  In the hard disk device, the magnetic head slightly floats from the surface of the magnetic disk as the magnetic disk rotates, and performs magnetic recording without contact. For this reason, the magnetic disk is prevented from being damaged by the contact between the magnetic head and the magnetic disk. As the density increases, the flying height of the magnetic head is gradually reduced. By using a magnetic disk in which a magnetic recording layer or the like is formed on a mirror-polished ultra-smooth glass substrate, the current height is 10 nm to 20 nm. The flying height is realized. In the medium, a CoPtCr-based magnetic layer / Cr underlayer is generally used. By increasing the temperature to 200 ° C. to 500 ° C., the easy direction of magnetization of the CoPtCr-based magnetic layer is in-plane with the Cr underlayer. It is controlled to become. Further, segregation of Cr in the CoPtCr-based magnetic layer is promoted, and magnetic domains in the magnetic layer are separated. The surface recording density and recording capacity of hard disk devices have increased dramatically over the past few years due to such technological innovations as low head flying height, improved head structure and improved disk recording film.

  Increasing the amount of digital data that can be handled has created a need for recording and moving large volumes of data such as video data on a removable medium. However, since the hard disk has a hard substrate and the distance between the head and the disk is very small as described above, if it is used as a replaceable medium like a flexible disk or a rewritable optical disk, the impact during operation There is a high risk of malfunction due to entrapment of dust and dust, and it cannot be used.

  Further, when the high-temperature sputter film forming method is used in the production of the medium, not only the productivity is bad, but also the cost is increased at the time of mass production, so that it cannot be produced at a low cost.

On the other hand, a flexible disk is a polymer film with a flexible substrate and is a contact-recordable medium, so it has excellent interchangeability and can be produced at low cost. Is coated on a polymer film together with a polymer binder and an abrasive. Therefore, compared with a hard disk on which a magnetic film is formed by sputtering, the magnetic layer has poor high-density recording characteristics and is 1/10 that of a hard disk. Only the following recording density has been achieved.
Therefore, a ferromagnetic metal thin film type flexible disk in which the recording film is formed by the same sputtering method as that of the hard disk has been proposed. However, if a magnetic layer similar to the hard disk is formed on the polymer film, the heat of the polymer film Damage is great and practical application is difficult. For this reason, proposals have been made to use a highly heat-resistant polyimide or aromatic polyamide film as the polymer film, but these heat-resistant films are very expensive and difficult to put into practical use. If an attempt is made to form a magnetic film while the polymer film is cooled so as not to cause thermal damage to the polymer film, the magnetic properties of the magnetic layer become insufficient, making it difficult to improve the recording density.

  On the other hand, when a ferromagnetic metal thin film magnetic layer made of a ferromagnetic metal alloy and a nonmagnetic oxide or a Ru-based underlayer is used, the film is formed at a high temperature of 200 ° C. to 500 ° C. even when it is formed at room temperature. It has been found that magnetic properties almost equivalent to those of the coated CoPtCr magnetic layer can be obtained (see Patent Documents 1 and 2). Such a ferromagnetic metal thin film magnetic layer made of a ferromagnetic metal alloy and a nonmagnetic oxide has a so-called granular structure proposed for hard disks, and those described in Patent Document 3 and Patent Document 4 can be used. When a magnetic layer having a granular structure is used, as described in Patent Document 5, the size of magnetic particles in the magnetic layer can be reduced, and noise can be reduced. However, in higher density recording, improvement of S / N characteristics is a problem during recording / reproduction using a GMR head or the like.

  Write-once and rewritable optical discs typified by DVD-R / RW have excellent interchangeability and are widespread because the head and the disc are not close to each other like a magnetic disc. However, the optical disk has a problem in that it is difficult to use a disk structure having recording surfaces on both sides like a magnetic disk advantageous for increasing the capacity because of the thickness and cost of the optical pickup. Furthermore, since the surface recording density is low and the data transfer speed is low as compared with the magnetic disk, it cannot be said that the performance is still sufficient when considering use as a rewritable large-capacity recording medium.

JP 2001-291230 A JP 2003-99918 A JP-A-5-73880 Japanese Patent Laid-Open No. 7-311929 JP 2003-178812 A

  As described above, high-capacity rewritable replaceable recording media are highly demanded, but none satisfy the performance, reliability, and cost.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to achieve high performance and high performance in a magnetic recording medium in which a magnetic layer having at least a granular structure is formed on a nonmagnetic substrate. An object of the present invention is to provide a high-capacity magnetic recording medium that is reliable and inexpensive.

Means for achieving the object is as follows.
(1) A magnetic recording medium in which a magnetic layer having at least a granular structure is formed on at least one surface of a nonmagnetic substrate, and in-plane TEM observation when the magnetic layer is cut in a direction parallel to the substrate An average magnetic particle size in the magnetic layer is in the range of 3 nm to 8 nm, and the dispersion is 3 nm or less.
(2) The magnetic recording medium according to (1), wherein the nonmagnetic substrate is a flexible polymer substrate.

  According to the present invention, a magnetic recording medium suitable for use in a high-density magnetic recording apparatus, having a small interaction between ferromagnetic materials, low noise, and high reliability can be provided at low cost.

Hereinafter, the present invention will be described in more detail.
Since the magnetic recording medium of the present invention includes at least a magnetic layer having a granular structure, high-density recording like a hard disk is possible even when film formation is performed at room temperature, and high capacity can be achieved.

  Further, by setting the average magnetic particle size in the magnetic layer in the range of 3 nm to 8 nm and the dispersion to 3 nm or less, the interaction between the magnetic particles is reduced, and a low noise medium that is important in high density recording is obtained. It becomes possible.

  The average magnetic particle size and dispersion in the magnetic layer can be controlled by controlling the crystal structure of the underlayer, the magnetic layer composition, the magnetic layer thickness, and the film formation conditions during film formation (eg, Ar pressure, input power, sputtering method, etc.) It becomes possible by controlling the above.

In the present invention, “cutting the magnetic layer in a direction parallel to the substrate” means slicing the magnetic layer in a direction parallel to the substrate with a thickness of 10 nm. Such a cutting method is known and can be performed using, for example, an ion milling method or an FIB method. Further, the location for cutting the magnetic layer is preferably a location within 15 nm from the surface of the magnetic layer in the thickness direction, and it is preferable to take out a slice piece having a thickness of 10 nm within this range. The sample thus obtained is observed in an in-plane TEM (transmission electron microscope), and the average magnetic particle size and dispersion are calculated from 100 magnetic particles as an equivalent circle diameter. In the present invention, the average magnetic particle size in the magnetic layer is in the range of 3 nm to 8 nm, preferably 4 nm to 8 nm, and the dispersion is 3 nm or less, preferably 2.5 nm or less.
FIG. 1 is a photograph of an in-plane TEM of the sample obtained as described above. From the 100 magnetic particles observed as shown in FIG. 1, the average magnetic particle size and dispersion are calculated as the equivalent circle diameter.

  By using such a magnetic layer and an underlayer, it is possible to obtain a magnetic recording medium having good S / N characteristics even when the substrate temperature is room temperature without the need for conventional substrate heating. Become. That is, it is possible to provide not only a glass substrate and an Al substrate but also a flat magnetic tape or flexible disk that is resistant to contact recording without causing thermal damage even if the substrate is a polymer film.

  As the nonmagnetic substrate in the present invention, an Al substrate or a glass substrate can be used, but it is more preferable in terms of productivity to use a flexible polymer film. The magnetic recording medium of the present invention may be in the form of a tape or a flexible disk. A flexible disk using a flexible polymer film substrate has a structure in which a center hole is formed at the center, and is stored in a cartridge formed of plastic or the like. The cartridge is usually provided with an access window covered with a metallic shutter, and a magnetic head is introduced through the access window to record and reproduce signals on the flexible disk.

  Hereinafter, a flexible disk will be described, but the contents can be applied to an Al substrate, a hard disk using a glass substrate, and a magnetic tape using a flexible polymer film.

  A flexible disk has, for example, a base layer and a magnetic layer on both sides of a disk-shaped substrate made of a flexible polymer film, and further has an undercoat layer that improves surface properties and gas barrier properties, adhesion and Seed layer with functions such as gas barrier property and crystal orientation control of underlayer, underlayer for controlling crystal orientation of magnetic layer, magnetic layer, protective layer to protect magnetic layer from corrosion and wear, and running durability It is preferable that the lubricating layer for improving the property and the corrosion resistance is laminated in this order.

  The magnetic layer may be an in-plane magnetic recording film whose easy axis is oriented in the horizontal direction with respect to the substrate, or a perpendicular magnetic recording film that is oriented in the direction perpendicular to the substrate. The direction of the easy axis of magnetization can be controlled by the material and crystal structure of the underlayer, the composition of the magnetic film, and the film formation conditions.

  The magnetic layer has a granular structure and is also referred to as a granular magnetic layer. The granular magnetic layer is made of a ferromagnetic metal alloy and a nonmagnetic oxide. The granular structure is a structure in which a ferromagnetic metal alloy and a nonmagnetic oxide are mixed macroscopically, but microscopically, a ferromagnetic metal alloy fine particle is covered with a nonmagnetic oxide. In FIG. 1, the ferromagnetic metal alloy fine particles correspond to a black background, and the nonmagnetic oxide corresponds to a white background.

  The mixing ratio of the ferromagnetic metal alloy and the nonmagnetic oxide is preferably in the range of ferromagnetic metal alloy: nonmagnetic oxide (molar ratio) = 95: 5 to 80:20, and 90:10 to 85:15. It is particularly preferable that the range is If the amount of the ferromagnetic metal alloy is larger than this, the separation between the magnetic particles becomes insufficient, resulting in an increase in the size of the magnetic particles and a high noise medium. On the other hand, if the amount is smaller than this, the magnetic particle size can be reduced, but the amount of magnetization is reduced, so that the signal output is significantly reduced.

  The thickness of the magnetic layer is preferably 5 nm to 30 nm, more preferably 5 nm to 25 nm. By setting it within this range, it is possible to reduce the interaction between the magnetic particle columns, and to reduce the magnetic particle size, that is, to obtain a low noise medium.

As a method for forming the magnetic layer, a vacuum film forming method such as a vacuum deposition method or a sputtering method can be used. Among these, the sputtering method is suitable for the present invention because a good ultra-thin film can be easily formed. As the sputtering method, a DC sputtering method, an RF sputtering method, a DC pulse sputtering method, or the like can be used. Of these, RF sputtering and DC pulse sputtering are preferred in terms of magnetic particle size and dispersion control. As the sputtering method, a web sputtering apparatus for continuously forming a film on a continuous film is suitable, but a sheet-type sputtering apparatus and a passing-type sputtering apparatus used for manufacturing a hard disk can also be used.
A general argon gas can be used as a sputtering gas during sputtering, but other rare gases may be used. In order to avoid agglomeration of magnetic particles, a trace amount of oxygen gas may be introduced.

  In order to form a granular magnetic layer by sputtering, two types of ferromagnetic metal alloy target and nonmagnetic oxide target can be used, and these co-sputtering methods can be used. It is preferable to use an alloy target of a ferromagnetic metal alloy and a nonmagnetic oxide in order to improve the above and create a homogeneous film. This alloy target can be prepared by a hot press method or the like.

  The Ar pressure when forming the granular magnetic layer by sputtering is preferably 0.4 Pa or more and 10 Pa or less, and particularly preferably 1.0 Pa or more and 7 Pa or less. The higher the Ar pressure during film formation, the smaller the magnetic particle size and the better the dispersibility. On the other hand, if it is 10 Pa or more, the crystallinity of the magnetic particles, the adhesion of the film, and the film strength are lowered, so that not only sufficient magnetic properties cannot be obtained, but also a low-reliability medium.

The input power for forming the granular magnetic layer by sputtering is preferably 1 W / cm ² or more and 100 W / cm ² or less, particularly preferably ² W / cm ² or more and 50 W / cm ^{2, and} has crystallinity and film adhesion. As well as ensuring, it is possible to prevent substrate deformation and generation of cracks in the sputtered magnetic layer.

  As the ferromagnetic metal alloy, alloys with elements such as Co, Cr, Pt, Ni, Fe, B, Si, Ta, Nb, and Ru can be used. However, in consideration of recording characteristics, Co—Pt—Cr, Co—Pt are considered. -Cr-Ta, Co-Pt-Cr-B, Co-Ru-Cr and the like are particularly preferable.

  As the nonmagnetic oxide, oxides such as Si, Zr, Ta, B, Ti, Al, Cr, Ba, Zn, Na, La, In, and Pb can be used, but SiOx is most preferable in consideration of recording characteristics.

  The underlayer is desirably provided for the purpose of controlling the crystal orientation of the magnetic layer and for the purpose of controlling the size and dispersion state of the magnetic particles in the magnetic layer. As such an underlayer, Ru, a Ru-based alloy, Cr, a Cr-based alloy, Ti, a Ti-based alloy, or the like can be used. Of these, a Ru or Ru-based alloy is preferable. Alloys containing other elements can also be used. By using such an underlayer, the orientation of the magnetic layer can be improved, so that the recording characteristics are improved. Also, the control of the magnetic particle size and dispersion state can be achieved by changing the film forming conditions for forming the underlayer.

  The thickness of the underlayer is preferably 5 nm to 200 nm, particularly preferably 5 nm to 100 nm. Within this range, the magnetic characteristics are improved, productivity is ensured, and the enlargement of crystal grains is suppressed, and the magnetic particle size in the magnetic layer formed immediately above can be reduced. In addition, since durability against stress applied during head-medium contact is ensured, running durability is ensured.

  As a method for forming the underlayer, a vacuum film forming method such as a vacuum deposition method or a sputtering method can be used. Among these, the sputtering method is suitable for the present invention because a good ultra-thin film can be easily formed. As the sputtering method, a known DC sputtering method, RF sputtering method, or the like can be used. In the case of a flexible disk having a flexible polymer film as a substrate, the sputtering method is preferably a web sputtering device that continuously forms a film on a continuous film, but is used when an Al substrate or a glass substrate is used. Such a sheet-type sputtering apparatus or a passing-type sputtering apparatus can also be used.

  A general argon gas can be used as a sputtering gas during the underlayer sputtering, but other rare gases may be used. Further, a trace amount of oxygen gas may be introduced for the purpose of controlling the lattice constant of the underlayer and for controlling the size of crystal grains in the underlayer.

  As Ar pressure at the time of forming a base layer by a sputtering method, 0.4 Pa or more and 10 Pa or less are preferable, and 1.0 Pa or more and 7 Pa or less are especially preferable. The higher the Ar pressure during film formation, the smaller the crystal grain size and the better the dispersibility. However, if the pressure is 10 Pa or more, the crystallinity of the sputtered particles, the adhesion of the film, and the film strength are lowered, so that the characteristics of the magnetic layer directly above cannot be improved, and the medium becomes unreliable.

  A seed layer may be provided directly under the underlayer for the purpose of improving the crystal orientation of the underlayer, controlling the crystal grain size and dispersibility of the underlayer, imparting conductivity, and the like.

As such a seed layer, it is desirable to use a Ti-based or W-based alloy, but other alloys may be used.

  The thickness of the seed layer is preferably 1 nm to 30 nm. By making it within this range, productivity is ensured, and enlargement of crystal grains is suppressed, so that the size of the magnetic particles in the underlayer and hence the magnetic layer can be reduced.

  As a method for forming the seed layer, a vacuum film-forming method such as a vacuum deposition method or a sputtering method can be used. Among these, a sputtering method can easily form a good ultra-thin film.

  For the purpose of improving adhesion and gas barrier properties, it is desirable to provide a gas barrier layer between the substrate and the underlayer.

  As such a gas barrier layer, a nonmetallic element alone or a mixture thereof, or a layer made of a compound of Ti and a nonmetallic element can be used. These materials are also resistant to stress during head-media contact.

  The thickness of the gas barrier layer is preferably 5 nm to 200 nm, particularly preferably 5 nm to 100 nm. By making it in this range, productivity is ensured and enlargement of crystal grains is suppressed, and the size of the magnetic particles in the underlayer and hence the magnetic layer can be reduced.

  As a method for forming the gas barrier layer, a vacuum film-forming method such as a vacuum deposition method or a sputtering method can be used. Among these, a sputtering method can easily form a good ultra-thin film.

  As described above, the substrate is preferably composed of a resin film having flexibility in order to avoid an impact when the magnetic head and the magnetic disk come into contact with each other. Examples of such resin films include aromatic polyimide, aromatic polyamide, aromatic polyamideimide, polyether ketone, polyether sulfone, polyether imide, polysulfone, polyphenylene sulfide, polyethylene naphthalate, polyethylene terephthalate, polycarbonate, and triacetate cellulose. And a resin film made of fluorine resin or the like. In the present invention, since good recording characteristics can be achieved without heating the substrate, polyethylene terephthalate or polyethylene naphthalate is particularly preferred from the viewpoint of cost and surface properties.

  Further, a substrate in which a plurality of resin films are laminated may be used. By using the laminate film, it is possible to reduce warpage and undulation caused by the substrate itself, and to significantly improve the scratch resistance of the magnetic layer.

  Examples of the laminating method include roll laminating using a heat roller, laminating using a flat plate heat press, dry laminating by applying an adhesive to the adhesive surface and laminating, and laminating using an adhesive sheet previously formed into a sheet shape. The type of the adhesive is not particularly limited, and a general hot melt adhesive, thermosetting adhesive, UV curable adhesive, EB curable adhesive, pressure-sensitive adhesive sheet, anaerobic adhesive, or the like may be used. Yes.

  The thickness of the substrate is 10 μm to 200 μm, preferably 20 μm to 150 μm, and more preferably 30 μm to 100 μm. If the thickness of the substrate is less than 10 μm, the stability during high-speed rotation is lowered and the surface blur increases. On the other hand, if the thickness of the substrate is greater than 200 μm, the rigidity at the time of rotation becomes high, and it becomes difficult to avoid an impact at the time of contact, and the magnetic head jumps.

The waist strength of the substrate represented by the following formula is preferably such that the value at b = 10 mm is in the range of 0.5 kgf / mm ^{2 to} 2.0 kgf / mm ² (4.9 to 19.6 MPa). 0.7 kgf / mm ^{2 to} 1.5 kgf / mm ² (6.86 to 14.7 MPa) is more preferable.
The waist of the board strength = Ebd ^3/12
In this equation, E represents Young's modulus, b represents film width, and d represents film thickness.

  The surface of the substrate is preferably as smooth as possible in order to perform recording with a magnetic head. Unevenness on the surface of the substrate significantly deteriorates the signal recording / reproducing characteristics. Specifically, when an undercoat layer described later is used, the surface roughness measured with an optical surface roughness meter is within 5 nm, preferably within 2 nm, with a center line average roughness Ra, and a stylus roughness meter. The height of the protrusion measured in step 1 is within 1 μm, preferably within 0.1 μm. When the undercoat film is not used, the surface roughness measured with an optical surface roughness meter is within 3 nm, preferably within 1 nm, as the centerline average roughness Ra, and the protrusion height measured with a stylus roughness meter Is within 0.1 μm, preferably within 0.06 μm.

  An undercoat layer is preferably provided on the surface of the substrate for the purpose of improving planarity and gas barrier properties. Since the magnetic layer is formed by sputtering or the like, the undercoat layer is preferably excellent in heat resistance. As the material of the undercoat layer, for example, a polyimide resin, a polyamideimide resin, a silicon resin, a fluorine resin, or the like can be used. . Thermosetting polyimide resins and thermosetting silicone resins are particularly preferred because they have a high smoothing effect. The thickness of the undercoat layer is preferably 0.1 μm to 3.0 μm. When laminating another resin film on the substrate, an undercoat layer may be formed before laminating, or an undercoat layer may be formed after laminating.

  As the thermosetting polyimide resin, for example, polyimide obtained by thermal polymerization of an imide monomer having two or more terminal unsaturated groups in the molecule, such as bisallyl nadiimide “BANI” manufactured by Maruzen Petrochemical Co., Ltd. Resins are preferably used. Since this imide monomer can be thermally polymerized at a relatively low temperature after being applied to the surface of the support in the monomer state, the monomer as a raw material can be directly applied on the substrate and cured. In addition, this imide monomer can be used by being dissolved in a general-purpose solvent. It has excellent productivity and workability, has a low molecular weight, and its solution viscosity is low. Is expensive.

  As the thermosetting silicon resin, a silicon resin polymerized by a sol-gel method using a silicon compound having an organic group introduced as a raw material is preferably used. This silicon resin has a structure in which a part of the silicon dioxide bond is substituted with an organic group, and has a heat resistance significantly higher than that of silicon rubber, and also has a flexibility higher than that of a silicon dioxide film, and thus a flexible film. Even if a resin film is formed on the substrate, cracks and peeling are unlikely to occur. Moreover, since the monomer used as a raw material can be directly applied and cured on the substrate, a general-purpose solvent can be used, the wraparound of the unevenness is good, and the smoothing effect is high. Furthermore, since the condensation polymerization reaction proceeds from a relatively low temperature by adding a catalyst such as an acid or a chelating agent, it can be cured in a short time, and a resin film can be formed using a general-purpose coating apparatus. Thermosetting silicone resins are particularly suitable because they have excellent gas barrier properties, and have high gas barrier properties that shield gases that hinder the crystallinity and orientation of the magnetic layer or underlayer generated from the substrate when the magnetic layer is formed.

  The surface of the undercoat layer is preferably provided with minute protrusions (textures) for the purpose of reducing the true contact area between the magnetic head and the magnetic disk and improving the sliding characteristics. Moreover, the handling property of the support is improved by providing the fine protrusions. As a method for forming the fine protrusions, a method of applying spherical silica particles, a method of forming an organic protrusion by applying an emulsion, and the like can be used. However, in order to ensure the heat resistance of the undercoat layer, the spherical silica particles are applied. Thus, it is preferable to form minute protrusions.

The height of the microprojections is preferably 5 nm to 60 nm, and more preferably 10 nm to 30 mm. If the height of the minute protrusion is too high, the recording / reproducing characteristics of the signal deteriorate due to the spacing loss between the recording / reproducing head and the medium, and if the minute protrusion is too low, the effect of improving the sliding characteristic is reduced. The density of minute projections is preferably from 0.1 to 100 pieces / [mu] m ^2, more preferably 1 to 10 / [mu] m ^2. If the density of the microprojections is too small, the effect of improving the sliding characteristics is reduced. If the density is too large, high projections are increased due to an increase in aggregated particles, and the recording / reproducing characteristics are deteriorated.

  In addition, the fine protrusions can be fixed to the support surface using a binder. It is preferable to use a resin having sufficient heat resistance for the binder, and as the resin having heat resistance, a solvent-soluble polyimide resin, a thermosetting polyimide resin, or a thermosetting silicone resin should be used. Is particularly preferred.

  The protective layer is provided to prevent corrosion of the metal material contained in the magnetic layer, to prevent wear due to pseudo contact or contact sliding between the magnetic head and the magnetic disk, and to improve running durability and corrosion resistance. The protective layer includes silica, alumina, titania, zirconia, oxides such as Co oxide and nickel oxide, nitrides such as titanium nitride, silicon nitride and boron nitride, carbides such as silicon carbide, chromium carbide and boron carbide, graphite, Materials such as carbon such as amorphous carbon can be used.

  As the protective layer, a hard film having a hardness equal to or higher than that of the magnetic head material, which is less likely to cause seizure during sliding and has a stable effect, is preferable because of excellent sliding durability. . At the same time, those having few pinholes are more preferred because they have excellent corrosion resistance. As such a protective film, a hard carbon film called DLC (diamond-like carbon) produced by a CVD method, an ion beam method, an ECR sputtering method, an ECR-CVD method, or the like can be given.

  The protective layer can be formed by laminating two or more types of thin films having different properties. For example, by providing a hard carbon protective film for improving sliding characteristics on the surface side and providing a nitride protective film such as silicon nitride for improving corrosion resistance on the magnetic layer side, the corrosion resistance and durability are high. It becomes possible to achieve both dimensions.

  On the protective layer, a lubricating layer is provided in order to improve running durability and corrosion resistance. For the lubricating layer, known lubricants such as hydrocarbon lubricants, fluorine lubricants, and extreme pressure additives are used.

  Hydrocarbon lubricants include carboxylic acids such as stearic acid and oleic acid, esters such as butyl stearate, sulfonic acids such as octadecyl sulfonic acid, phosphate esters such as monooctadecyl phosphate, stearyl alcohol, oleyl alcohol And the like, carboxylic acid amides such as stearamide, and amines such as stearylamine.

Examples of the fluorine-based lubricant include a lubricant in which part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group. Perfluoropolyether groups include perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , perfluoroisopropylene oxide polymer (CF ( CF ₃ ) CF ₂ O) _n or a copolymer thereof. Specific examples thereof include a perfluoromethylene-perfluoroethylene copolymer having a hydroxyl group at the molecular weight terminal (trade name “FOMBLIN Z-DOL” manufactured by Augmont Co., Ltd.).

  Extreme pressure additives include phosphate esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphates such as trilauryl trithiophosphite, dibenzyl disulfide And sulfur-based extreme pressure agents such as

These lubricants can be used alone or in combination, and a solution obtained by dissolving a lubricant in an organic solvent can be used for the surface of the protective layer by spin coating, wire bar coating, gravure coating, dip coating, etc. What is necessary is just to apply | coat to a protective layer surface by a vacuum evaporation method. The coating amount of the lubricant is preferably ^{1~30mg / m 2, 2~20mg / m} 2 is particularly preferred.

Moreover, in order to further improve corrosion resistance, it is preferable to use a rust inhibitor together. Antirust agents include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives in which an alkyl side chain is introduced into the mother nucleus, benzothiazole, 2-mercapton benzothiazole, tetrazaindene Examples thereof include nitrogen- and sulfur-containing heterocycles such as ring compounds and thiouracil compounds and derivatives thereof. These rust preventives may be mixed with a lubricant and applied on the protective layer, or may be applied on the protective layer before applying the lubricant, and the lubricant may be applied thereon. As an application quantity of a rust preventive agent, 0.1-10 mg / m < ² > is preferable and 0.5-5 mg / m < ² > is especially preferable.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited by the following example.

Example 1
Gravure an undercoat solution consisting of 3-glycidoxypropyltrimethoxysilane, phenyltriethoxysilane, hydrochloric acid, aluminum acetylacetonate and ethanol on a polyethylene naphthalate film with a thickness of 63 μm and surface roughness Ra = 1.4 nm as a substrate. After coating by a coating method, drying and curing were performed at 100 ° C. to prepare an undercoat layer made of a silicon resin having a thickness of 1.0 μm. A coating liquid obtained by mixing a silica sol having a particle diameter of 25 nm and the above-described undercoat liquid was applied on the undercoat layer by a gravure coating method, and protrusions having a height of 15 nm were formed on the undercoat layer at a density of 10 pieces / μm ² . This undercoat layer was formed on both sides of the substrate film. Next, this web is installed in a web sputtering apparatus, and the film is conveyed while adhering to a water-cooled can, and a gas barrier layer made of C is formed on the undercoat layer by a DC magnetron sputtering method with a thickness of 20 nm. After forming a base layer made of Ru with a thickness of 20 nm under an Ar pressure of 3.0 Pa, a magnetic layer made of (Co ₇₀ —Pt ₂₀ —Cr ₁₀ ) ₈₈ — (SiO ₂ ) ₁₂ was used. It was formed with a thickness of 20 nm under 5 Pa conditions. The gas barrier layer, underlayer and magnetic layer were formed on both sides of the substrate film. Next, this raw fabric is set in a web type protective layer film forming apparatus, and C: H: N = 62: 29: 7 mol ratio by an ion beam deposition method using ethylene gas, nitrogen gas, and argon gas as reaction gases. A nitrogen-added DLC protective film made of 5 nm in thickness was formed. This protective layer was also formed on both sides of the substrate film. Next, a gravure coating solution obtained by dissolving a perfluoropolyether lubricant having a hydroxyl group at the molecular terminal on the surface of the protective layer (FOMBLIN Z-DOL manufactured by Augmont) in a fluorine lubricant (HFE-7200 manufactured by Sumitomo 3M) This was applied by a method to form a 1 nm thick lubricating layer. This lubricating layer was also formed on both sides of the substrate film. Next, a 3.7 inch size disk was punched out from the original fabric, tape burnished, and then incorporated into a resin cartridge (for Zip 100 manufactured by Fuji Photo Film Co., Ltd.) to produce a flexible disk.

Example 2
In Example 1, a flexible disk was produced in the same manner as in Example 1 except that the magnetic layer was formed by a 100 kHz-DC pulse sputtering method with an Ar pressure of 3.5 Pa and a thickness of 20 nm.

Example 3
A flexible disk was produced in the same manner as in Example 1 except that the base layer was formed with a thickness of 20 nm under the Ar pressure: 4.0 Pa condition in Example 1.

Example 4
A hard disk was formed in the same manner as in Example 1 except that a 3.7-inch glass substrate that had been mirror-polished was used as the substrate in Example 1. However, the sputtering apparatus was not a web type, a sheet format was used, no undercoat was applied, and it was not incorporated into the cartridge.

Comparative Example 1
A flexible disk was produced in the same manner as in Example 1 except that the base layer and the magnetic layer were formed with a thickness of 20 nm under the Ar pressure: 0.2 Pa condition in Example 1.

Comparative Example 2
A flexible disk was manufactured in the same manner as in Example 1 except that the base layer was formed to 60 nm and the magnetic layer was formed to 40 nm in Example 1.

Evaluation The following evaluation was performed on the various magnetic recording media obtained above.
(1) Average magnetic particle size and dispersion of magnetic particles The magnetic layer was sliced with a thickness of 10 nm in a direction parallel to the substrate. This slicing was performed using an ion milling method. The location where the magnetic layer was cut was sliced within 15 nm from the surface of the magnetic layer in the thickness direction, specifically, from the position of 10 nm toward the thickness direction from the surface of the magnetic layer to the location of 10 nm toward the substrate. . The sample thus obtained was observed by in-plane TEM, and the average magnetic particle size and dispersion were calculated from 100 magnetic particles as the equivalent circle diameter.
(2) Recording / reproducing characteristics Using a GMR head having a reproducing track width of 0.25 μm and a reproducing gap of 0.09 μm, recording / reproducing is performed at a linear recording density of 400 kFCI, and a reproduction signal / noise (S / N) ratio and noise characteristics are obtained. It was measured. At this time, the rotational speed was 4200 rpm and the radial position was 35 mm. In addition, the S / N value and Noise value showed the increase / decrease from the value on the basis of the value in Example 1.
The results are shown in Table 1.

  As can be seen from the above results, the flexible disk and hard disk of the present invention achieve low noise characteristics during high-density recording / reproduction with a GMR head due to the reduction in average magnetic particle size and dispersion value. On the other hand, in Comparative Examples 1 and 2, although the output is slightly increased, the noise characteristics are greatly degraded, and sufficient S / N characteristics are not obtained in the high-density recording / reproducing system using the GMR head.

It is a photograph of in-plane TEM of a measurement sample.

Claims (2)

  In a magnetic recording medium in which a magnetic layer having at least a granular structure is formed on at least one surface of a nonmagnetic substrate, the magnetic layer in the in-plane TEM observation when the magnetic layer is cut in a direction parallel to the substrate A magnetic recording medium, wherein the average magnetic particle size in the layer is in the range of 3 nm to 8 nm and the dispersion is 3 nm or less.   The magnetic recording medium according to claim 1, wherein the nonmagnetic substrate is a flexible polymer substrate.

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