JP2004234826A - Magnetic recording vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is a rewritable magnetic recording medium capable of rewriting at a large capacity and satisfying performance, reliability and a cost and which obviates the degradation in the crystal orientation growth properties of underlayers and magnetic layer by the influence of the gas released from a polymer film support object and can achieve good magnetic characteristics. <P>SOLUTION: The magnetic recording medium has the first underlayer 3 composed of a material selected from a nonmetallic element alone, a compound composed of only the nonmetallic element, and a compound compose of titanium and the nonmetallic element, the second underlayer 4 containing at least one element selected from the group consisting of chromium, titanium, iridium, platinum, palladium, ruthenium, rhodium, rhenium, osmium, cobalt, tungsten, vanadium, iron, and molybdenum and the magnetic layer comprised of a ferromagnetic alloy containing at least cobalt, platinum and chromium and a nonmagnetic material in this order on at least one surface of the nonmagnetic support object. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium for high-density recording used for recording digital information that can be reproduced using a high-sensitivity magnetoresistive head.

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 (magnetic layer) is formed on a mirror-polished ultra-smooth glass substrate, A flying height of 10 nm to 20 nm is realized. In the medium, the layer structure of CoPtCr magnetic layer / Cr underlayer is generally used. By forming the magnetic layer and the underlayer at a high temperature of 200 ° C. to 500 ° C., the CoPtCr is formed by the Cr underlayer. The easy magnetization direction of the magnetic system layer is controlled to be in the film plane. Further, segregation of Cr in the CoPtCr-based magnetic layer is promoted, and magnetic domains in the magnetic layer are separated. Due to such technological innovations as reducing the flying height of the head, improving the head structure, and improving the disk recording film, the surface recording density and recording capacity of the hard disk drive have increased dramatically in the last few years.

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, when it is used as a replaceable medium like a flexible disk or a rewritable optical disk, There is a high concern that a failure may occur due to impact or dust entrainment, and it cannot be used.
Further, when the high-temperature sputter deposition 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, and the production cannot be made 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 (magnetic layer) is formed by sputtering similar to that of a hard disk has been proposed. However, if a magnetic layer similar to that of a hard disk is formed on a polymer film, a high The thermal damage of the molecular film is large and it is difficult to put it into practical use. In addition, since a contact between the head and the medium is inevitable, a hard protective layer is indispensable. 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 made of a ferromagnetic metal alloy and a nonmagnetic oxide is used, CoPtCr deposited at a high temperature of 200 ° C. to 500 ° C. even when deposited at room temperature.
It has been found that magnetic properties almost equivalent to those of the magnetic system layer can be obtained. As such a ferromagnetic metal thin film made of a ferromagnetic metal alloy and a non-magnetic oxide, a so-called granular structure proposed for a hard disk can be used (for example, see Patent Documents 1 and 2).
However, even when the magnetic layer having such a granular structure is formed at room temperature, since heat is applied by the sputtering method, the gas component contained in the polymer film support is released, and as shown in FIG. In addition, the crystal growth properties of the magnetic layer and the like are significantly reduced. For this reason, it is difficult to control the crystal orientation, and sufficient characteristics have not been obtained yet.
On the other hand, 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-A-5-73880 Japanese Patent Laid-Open No. 7-311929

  Accordingly, an object of the present invention is to solve the above-mentioned problems, and is a large-capacity rewritable and replaceable magnetic recording medium satisfying performance, reliability, and cost. It is an object of the present invention to provide a magnetic recording medium capable of achieving good magnetic properties without lowering the crystal orientation growth of the underlayer and the magnetic layer due to the influence of the above.

As a result of intensive studies, the present inventor has achieved the above object by adopting the following configuration, and has achieved the present invention.
That is, the present invention is as follows.
(1) On at least one surface of the nonmagnetic support, a first underlayer made of a nonmetallic element alone, a compound composed of only a nonmetallic element, and a compound of titanium and a nonmetallic element, chromium, A second underlayer containing at least one element selected from the group consisting of titanium, iridium, platinum, palladium, ruthenium, rhodium, rhenium and osmium; and a ferromagnetic metal alloy containing at least cobalt, platinum and chromium And a magnetic layer made of a nonmagnetic substance in this order.

The preferred embodiments of the present invention are listed below.
(2) On at least one surface of a non-magnetic support made of a flexible polymer, a non-metallic element alone, a compound consisting only of a non-metallic element, and a compound selected from a compound consisting of titanium and a non-metallic element. And a second lower layer containing at least one element selected from the group consisting of chromium, titanium, iridium, platinum, palladium, ruthenium, rhodium, rhenium, osmium, cobalt, tungsten, vanadium, iron and molybdenum. A magnetic recording medium comprising a base layer and a magnetic layer composed of a ferromagnetic metal alloy containing at least cobalt, platinum, and chromium and a nonmagnetic material in this order.
(3) The (1) or (2) above, wherein the non-metallic element of the first underlayer is one selected from C, Si, B, Te, As, Se, I, N, and O The magnetic recording medium described.
(4) The magnetic recording medium according to any one of (1) to (3), wherein the second underlayer crystal growth failure layer at the interface between the first underlayer and the second underlayer is 5 nm or less. .
(5) The magnetic recording medium according to any one of (1) to (4) above, wherein the surface roughness SRa on the surface of the magnetic recording medium having the magnetic layer is 3 nm or less.

The magnetic recording medium of the present invention includes a ferromagnetic metal thin film magnetic layer composed of a ferromagnetic metal alloy containing at least cobalt (Co), platinum (Pt), and chromium (Cr) and a nonmagnetic oxide. Recording at a high recording density as described above is possible, and the capacity can be increased.
Such a ferromagnetic metal thin film made of a ferromagnetic metal alloy containing Co, Pt, and Cr and a nonmagnetic oxide has a so-called granular structure proposed for a hard disk, and is disclosed in JP-A-5-73880 and JP-A-7. Those described in Japanese Patent No. 311929 can be used.
Furthermore, since the first underlayer of the magnetic recording medium of the present invention has an effect of shielding the gas released from the base and an effect of improving the crystal orientation of the second underlayer, it is regarded as a problem in a medium using a film base. The problem of the released gas can be solved.
By using such a first underlayer, a second underlayer, and a magnetic layer, conventional substrate heating becomes unnecessary, and good magnetic properties can be achieved even when the substrate temperature is room temperature. In addition, a magnetic recording medium that can solve the problem of gas released from the base can be obtained. For this reason, it is possible to provide not only glass substrates and Al substrates but also flat magnetic tapes and flexible disks that are resistant to contact recording without causing thermal damage even if the support is a polymer film. is there.

  In the magnetic recording medium of the present invention, a first underlayer and a second underlayer are provided on a nonmagnetic support, and a ferromagnetic metal alloy containing cobalt, platinum, and chromium and a nonmagnetic material are provided on the underlayer. By forming a magnetic layer that is composed, it has the effect of shielding the gas released from the support and improving the crystal orientation of the magnetic layer, and forming a magnetic layer with excellent characteristics on the flexible polymer support And high density recording is possible.

The magnetic recording medium of the present invention comprises a first lower layer comprising at least one surface of a nonmagnetic support selected from a single nonmetallic element, a compound composed of only a nonmetallic element, and a compound of titanium and a nonmetallic element. And a second underlayer containing at least one element selected from the group consisting of chromium, titanium, iridium, platinum, palladium, ruthenium, rhodium, rhenium, osmium, cobalt, tungsten, vanadium, iron, and molybdenum. Since a magnetic layer composed of a ferromagnetic metal alloy containing at least cobalt, platinum, and chromium and a nonmagnetic material is formed, the second underlayer and the magnetic layer are formed when a polymer film is used as a support. Crystal orientation growth of the second underlayer and magnetic layer by the gas released from the polymer film when formed by sputtering No reduction of, in which characteristics are excellent.
The magnetic recording medium of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing the layer structure of a magnetic recording medium according to an embodiment of the present invention.
The magnetic recording medium 1 of the present invention has the above-mentioned first underlayer 3, second underlayer 4 and magnetic layer 5 in this order on a nonmagnetic support 2, and if necessary on the magnetic layer 5 Can have a protective layer 6 or the like.

[Magnetic layer]
The magnetic layer formed in the magnetic recording medium of the present invention is a ferromagnetic thin film magnetic layer composed of a ferromagnetic metal alloy containing at least cobalt, platinum, and chromium and a nonmagnetic substance.
Since the magnetic recording medium of the present invention is provided with the magnetic layer, high recording density recording is possible like a hard disk, and the capacity of a removable magnetic recording medium can be increased. In addition, a ferromagnetic thin film magnetic layer made of a cobalt-containing ferromagnetic metal alloy and a nonmagnetic metal oxide has been proposed for hard disks, as disclosed in Japanese Patent Laid-Open Nos. 5-73880 and 7-311929. What was manufactured by the method similar to what was described can be used.

  The magnetic layer 5 is composed of a ferromagnetic metal alloy 7 containing at least cobalt, platinum, and chromium and a nonmagnetic substance 8. Although the ferromagnetic metal alloy 7 and the nonmagnetic substance 8 are apparently mixed, the ferromagnetic metal alloy 7 shown in the figure is a portion where the abundance of the ferromagnetic metal alloy is larger than the entire composition. The nonmagnetic material 8 is a portion where there are more nonmagnetic materials than the entire composition. Further, the portions where the ferromagnetic metal alloy is abundant are formed with an interval of 0.01 nm to 10 nm.

  The magnetic layer 5 in the magnetic recording medium of the present invention may be a so-called perpendicular magnetic recording film having an easy axis of magnetization in the direction perpendicular to the surface of the magnetic layer 5 or an in-plane magnetic recording film having an easy axis of magnetization in the horizontal direction. . The direction of the easy axis of magnetization can be controlled by the material, film formation conditions or crystal structure of the second underlayer 4 described later, and the composition and film formation conditions of the magnetic film.

  The magnetic layer 5 of the present invention desirably has a crystal growth reflecting the crystal orientation of the second underlayer 4 and forms a columnar structure as shown in FIG. With such a structure, the separation structure between the regions rich in the magnetic metal alloy is stabilized by the region rich in the nonmagnetic material, and a high coercive force can be achieved, and the portion rich in the ferromagnetic metal alloy can be magnetized. Since the amount increases, the output can be increased, and the dispersibility of the portion rich in the ferromagnetic metal alloy becomes uniform, so that the noise can be reduced.

  As a ferromagnetic metal alloy containing cobalt, platinum, and chromium, alloys of Co, Cr, Pt and elements such as Ni, Fe, B, Si, Ta, and Nb can be used. -Cr, Co-Pt-Cr-Ta, Co, Pt-Cr-B and the like are particularly preferable.

As non-magnetic substances (non-magnetic compounds), oxides, carbides, and nitrides such as Si, Zr, Ta, B, Ti, Al, Cr, Ba, Zn, Na, La, In, and Pb can be used. In view of characteristics, SiO _x is most preferable.

  The mixing ratio of the ferromagnetic metal alloy containing cobalt, platinum, and chromium and the nonmagnetic material is preferably in the range of ferromagnetic metal alloy: nonmagnetic material = 95: 5 to 80:20 (atomic ratio), 90 Is particularly preferably in the range of 10 to 85:15. If the amount of the ferromagnetic metal alloy is larger than this, the separation between the magnetic particles becomes insufficient, and the holding force may be reduced. On the other hand, if the amount is less than this, the amount of magnetization decreases, so that the signal output may be significantly reduced.

  The thickness of the magnetic layer made of a mixture of a ferromagnetic metal alloy containing cobalt, platinum and chromium and a nonmagnetic substance is preferably in the range of 10 nm to 60 nm, more preferably 10 nm to 40 nm. If the thickness is greater than this, the noise may increase remarkably. Conversely, if the thickness is reduced, the output may be significantly reduced.

As a method for forming a magnetic layer made of a ferromagnetic metal alloy containing cobalt, platinum, and chromium and a nonmagnetic material, 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-quality thin film can be easily formed. As the sputtering method, either a DC sputtering method or an RF sputtering method can be used. As the sputtering method, a web sputtering apparatus or a single wafer sputtering apparatus for continuously forming a film on a continuous film can be used, but a web sputtering apparatus is preferably used.
Argon can be used as the gas used in the atmosphere during sputtering, but other rare gases may be used. A small amount of oxygen may be introduced to adjust the oxygen content and surface roughness of the nonmagnetic substance.

  In particular, in order to form a magnetic layer composed of a ferromagnetic metal alloy containing cobalt, platinum, and chromium and a nonmagnetic material by sputtering as in the present invention, a ferromagnetic metal alloy target and a nonmagnetic material target are used. It is possible to use these co-sputtering methods using seeds, but a homogeneous mixture of a ferromagnetic metal alloy and a nonmagnetic material that matches the composition ratio of the ferromagnetic metal alloy to be formed and the nonmagnetic material. When a target is used, a magnetic layer in which a ferromagnetic metal alloy is uniformly dispersed can be formed. Moreover, this mixture target can be produced by a hot press method or the like.

[First underlayer]
The first underlayer 3 in the magnetic recording medium of the present invention contains a nonmetallic element alone, a compound thereof (compound consisting only of a nonmetallic element), and a compound of titanium and a nonmetallic element.
As the nonmetallic element simple substance of the first underlayer, C, Si, and B are preferable. The mixture of nonmetallic elements is preferably a compound of an element selected from C, N, O, Si, B, Te, As, Se, and I. Among these nonmetallic elements, a compound selected from C, N, O, Si, and B is more preferable. Specific examples include Si and C, Si and O, Si and N, B and C, B and N, and B and O compounds.
As a compound of titanium and a nonmetallic element, a compound of Ti and C, Ti and N, Ti and O, Ti and B, or the like is preferable.
By forming these first underlayers, the gas released from the nonmagnetic support is shielded, so that the crystal growth properties of the second underlayer and magnetic layer thereon are improved.

  The thickness of the first underlayer is preferably 1 nm to 50 nm, particularly preferably 1 nm to 30 nm. When the thickness of the first underlayer is 50 nm or more, deformation and cracking of the support due to film stress are likely to occur and productivity is deteriorated. Conversely, when the thickness is 1 nm or less, the effect of shielding the released gas from the support is small, It does not contribute to the improvement of crystal growth properties of the second underlayer and the magnetic layer.

[Second base layer]
The second underlayer in the magnetic recording medium of the present invention comprises chromium (Cr), titanium (Ti), iridium (Ir), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), rhenium ( Re), osmium (Os), cobalt (Co), tungsten (W), vanadium (V), an alloy containing at least one element selected from the group consisting of iron (Fe) and molybdenum (Mo) Is.
Among these, from chromium (Cr), titanium (Ti), iridium (Ir), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), rhenium (Re) and osmium (Os). It is preferable to use an alloy containing 50 atomic% or more of at least one element from the group.
By using these second underlayers, the orientation of the magnetic layer can be improved, so that the recording characteristics are improved.

  The thickness of the second underlayer made of the alloy is preferably 1 nm to 50 nm, particularly preferably 1 nm to 35 nm. If the thickness is thicker than this, the productivity will deteriorate and noise during reading of recorded information may increase due to the enlargement of crystal grains. Conversely, if the thickness is thinner than this, the underlayer effect In some cases, the magnetic characteristics cannot be improved.

As a method for forming the first and second underlayers, a vacuum film formation 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, either a DC sputtering method or an RF sputtering method can be used. As the sputtering method, in the case of a flexible disk using a flexible polymer film as a support, a web sputtering apparatus that continuously forms a film on a continuous film is suitable. However, when an aluminum substrate or a glass substrate is used, a sheet is used. A mode sputtering device or a pass-through sputtering device can also be used.

  When the first and second underlayers are formed by sputtering, argon can be used as the sputtering gas, 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.

  In order to form an underlayer containing a plurality of elements by sputtering, a plurality of targets composed of each element target can be used, and these co-sputtering methods can be used. In order to produce a controlled and homogeneous film, it is preferable to use a composite target composed of all the elements used. This composite target can be produced by a hot press method or the like.

  The nonmagnetic support used in the magnetic recording medium of the present invention is not particularly limited, but is a flexible polymer made of a synthetic resin film capable of avoiding an impact when the magnetic head and the magnetic disk come into contact with each other. A support is preferably mentioned. Such synthetic resin films include aromatic polyimide, aromatic polyamide, aromatic polyamideimide, polyether ketone, polyethersulfone, polyetherimide, polysulfone, polyphenylene sulfide, polyethylene naphthalate, polyethylene terephthalate, polycarbonate, and triacetate cellulose. And a synthetic resin film made of a fluororesin or the like. In the present invention, since good recording characteristics can be achieved without heating the substrate, polyethylene terephthalate or polyethylene naphthalate, which has good surface properties and is easily available, is particularly preferable.

Moreover, you may use what laminated | stacked several synthetic resin films as a flexible polymer support body. By using a laminated film in which a plurality of sheets are laminated, it is possible to reduce warping and undulation caused by the flexible polymer support itself. As a result, the scratch resistance of the magnetic recording layer due to the collision of the surface of the magnetic recording medium with the magnetic head can be remarkably improved.
As a method of laminating a flexible film, roll laminating by a hot roll, flat laminating by flat plate hot press, dry laminating by applying an adhesive to the adhesive surface and laminating, or laminating using a pre-formed adhesive sheet Methods and the like. When an adhesive is used for lamination, a hot melt adhesive, a thermosetting adhesive, a UV curable adhesive, an EB curable adhesive, an adhesive sheet, an anaerobic adhesive, or the like can be used.

  The thickness of the flexible polymer support 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 flexible polymer support is less than 10 μm, stability during high-speed rotation may be reduced, and surface deflection may increase. On the other hand, if the thickness of the flexible polymer support is larger than 200 μm, the rigidity at the time of rotation becomes high, and it becomes difficult to avoid the impact at the time of contact, which may cause the magnetic head to jump.

Further, the stiffness of the flexible polymer support represented by the following formula, b = 10 mm a value for is ^{4.9MPa~19.6MPa (0.5kgf / mm 2 ~2.0kgf /} mm 2 ) In the range of 6.9 MPa to 14.7 MPa (0.7 kgf / mm ^{2 to} 1.5 kgf / mm ² ).

Flexible polymeric support waist strength of = Ebd ^3/12

  In this equation, E represents Young's modulus, b represents film width, and d represents film thickness.

  The surface of the flexible polymer support is preferably as smooth as possible in order to perform recording with a magnetic head. Unevenness on the surface of the support significantly reduces the signal recording / reproducing characteristics. Specifically, in the case of using an undercoat layer to be described later, the surface roughness measured by a light interference type surface roughness meter is 5 nm or less, preferably 2 nm or less, and the stylus roughness of the center plane average roughness SRa. The protrusion height measured by the meter is within 1 μm, preferably within 0.1 μm. In the case where no undercoat film is used, the surface roughness measured with an optical interference type surface roughness meter is within 3 nm, preferably within 1 nm, as the center plane average roughness SRa, and the protrusion measured with a stylus roughness meter The height is within 0.1 μm, preferably within 0.06 μm.

  An undercoat layer is preferably provided on the surface of the flexible polymer support in order to improve planarity and enhance gas barrier properties. Since the undercoat layer and the magnetic layer are 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 silicone resin, a fluorine resin, or the like is used. Can do. Thermosetting polyimide resins and thermosetting silicone resins are particularly preferable because they have a high smoothing effect. The thickness of the undercoat layer is preferably 0.1 μm to 3.0 μm. When another resin film is laminated on the support, an undercoat layer may be formed before the lamination process, or an undercoat layer may be formed after the lamination process.

  As the thermosetting polyimide resin, a polyimide resin obtained by thermally polymerizing an imide monomer having two or more terminal unsaturated groups in the molecule, such as bisallyl nadiimide (BANI manufactured by Maruzen Petrochemical Co., Ltd.) is preferable. Used for. 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 to the support and cured. In addition, this imide monomer can be used by dissolving in a general organic solvent, and is excellent in productivity and workability, has a low molecular weight, and its solution viscosity is low. High smoothing effect.

  As the thermosetting silicone resin, a silicone resin polymerized by a sol-gel method using a silicon compound having an organic group introduced as a raw material is preferably used. This silicone resin has a structure in which a part of the silicon dioxide bond is substituted with an organic group, and is greatly superior in heat resistance to silicone rubber and more flexible than a silicon dioxide film. Even if a resin film is formed on the support, cracks and peeling are unlikely to occur. Moreover, since the monomer used as a raw material can be directly applied and cured on the flexible polymer support, 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. The thermosetting silicone resin also has excellent gas barrier properties, and is a gas shield that shields the gas generated from the flexible polymer support during the formation of the magnetic layer and obstructs the crystallinity and orientation of the magnetic layer or underlayer. It is particularly suitable because of its high properties.

  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 flexible disk and improving the sliding characteristics. In addition, by providing the fine protrusions, the handleability of the flexible polymer support is improved. 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 microprotrusions is too high, the signal recording / reproduction characteristics deteriorate due to the spacing loss between the recording / reproducing head and the medium. If the microprotrusions are too low, the effect of improving the sliding characteristics 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 fine protrusions is too small, the effect of improving the sliding characteristics may be reduced. If the density is too large, high protrusions may increase due to an increase in aggregated particles and the recording / reproducing characteristics may deteriorate.
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.

  A protective layer 7 is preferably provided on the surface of the magnetic layer 5. The protective layer 7 is provided to prevent corrosion of the metal material contained in the magnetic layer 5, 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. It is done. The protective layer includes silica, alumina, titania, zirconia, oxides such as cobalt 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 diamond-like carbon (DLC) produced by a CVD method 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 recording layer side, corrosion resistance and durability can be achieved. It is possible to achieve a high level of compatibility.

On the protective layer, a lubricating layer is provided as necessary in order to improve running durability and corrosion resistance. A lubricant such as a hydrocarbon-based lubricant, a fluorine-based lubricant, and an extreme pressure additive is used for the lubricant layer.
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 include a perfluoromethylene-perfluoroethylene copolymer having a hydroxyl group at the molecular chain terminal (trade name: FOMBLIN Z-DOL, manufactured by Augmont).

  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

The above lubricants can be used alone or in combination. 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. Examples of rust inhibitors 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-mercaptobenzothiazole, tetrazaindene ring And nitrogen- and sulfur-containing heterocycles such as 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.

A method for producing a magnetic recording medium using a flexible polymer support will be described below.
FIG. 3 is a diagram illustrating a method for forming a magnetic layer on a flexible polymer support.
The film forming apparatus 11 has a vacuum chamber 12, and the tension of the flexible polymer support 14 wound from the winding roll 13 is adjusted by the tension adjusting rolls 15 </ b> A and 15 </ b> B to the film forming chamber 16. Sent.
In the film forming chamber 16, argon is supplied at a predetermined flow rate from the sputtering gas supply pipes 17 </ b> A to 17 </ b> D in a state where the pressure is reduced to a predetermined pressure reduction degree by a vacuum pump. The flexible polymer support 14 is allowed to come out of atoms for forming the underlayer from the target TA of the underlayer sputtering apparatus 19A while being wound around the film forming roll 18A provided in the film forming chamber 16. A film is formed on a flexible polymer support.

Next, atoms for forming the magnetic layer are released from the target TB in which the ferromagnetic metal alloy and the nonmagnetic material are uniformly dispersed in the film forming roll 18A on the film-forming underlayer, which is mounted on the magnetic layer sputtering apparatus 19B. A magnetic layer is formed on the underlayer.
Next, in a state where the surface on which the magnetic layer is formed is moved while being wound around the film forming roll 18B, atoms for forming the underlayer jump out from the target TC of the underlayer sputtering apparatus 19C, and the flexible polymer support The side opposite to the surface on which the magnetic layer was previously formed is formed. Further, on the film forming roll 18B, atoms for forming the magnetic layer are released from the target TD in which the ferromagnetic metal alloy and the nonmagnetic material that are mounted on the magnetic layer sputtering apparatus 19D are uniformly dispersed, and the magnetic layer is formed on the underlayer. It is formed.

Through the above steps, the magnetic layers are formed on both surfaces of the flexible polymer support and wound by the winding roll.
In the above description, the method of forming the magnetic layer on both surfaces of the flexible polymer support has been described. However, it is also possible to form the magnetic layer only on one surface by the same method.
After forming the magnetic layer, a protective layer including diamond-like carbon is formed on the magnetic layer by a CVD method.

FIG. 4 is a diagram for explaining an example of a CVD apparatus using high-frequency plasma applicable to the present invention.
The flexible polymer support 32 on which the magnetic layer 31 is formed is unwound from the roll 33, and the bias voltage is supplied from the bias power source 35 to the magnetic layer 31 by the pass roller 34 and wound around the film forming roll 36. Run.
On the other hand, the raw material gas 37 containing hydrocarbon, nitrogen, noble gas, etc. is a carbon containing nitrogen, noble gas on the metal thin film on the film forming roll 36 by the plasma generated by the voltage applied from the high frequency power supply 38. A protective film 39 is formed and wound on the winding roll 40. Also, greater adhesion can be ensured by cleaning the surface of the magnetic film by glow treatment with a rare gas or hydrogen gas before the carbon protective film is formed. Further, the adhesion can be further enhanced by forming a silicon intermediate layer or the like on the surface of the magnetic layer.

The present invention will be explained more specifically with reference to the following examples. However, the scope of the present invention is of course not limited by these examples.
[Example 1]
Gravure an undercoat solution consisting of 3-glycidoxypropyltrimethoxysilane, phenyltriethoxysilane, hydrochloric acid, aluminum acetylacetonate, and ethanol on a polyethylene naphthalate (PEN) film with a thickness of 63 μm and surface roughness Ra = 1.4 nm After coating by a coating method, drying and curing were performed at 100 ° C. to prepare an undercoat layer made of a silicone 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 . The undercoat layer was formed on both sides of the PEN film. A PEN film on which an undercoat layer is formed is used as an original fabric, and the original fabric is installed in a sputtering apparatus, and the film is transported in close contact with a water-cooled can (film forming roll). On the undercoat layer, a DC magnetron sputtering method is used. A first underlayer made of C with a thickness of 30 nm, a second underlayer made of Ru with a thickness of 25 nm, a CoPtCr alloy (Co: Pt: Cr = 70: 20: 10 atomic ratio): SiO ₂ = 88: 12 A magnetic layer having a composition of (atomic ratio) was formed with a thickness of 20 nm.

The first underlayer, the second underlayer, and the magnetic layer were formed on both sides of the film. Next, this raw material is set in a web-type CVD apparatus, and nitrogen is added at a ratio of C: H: N = 62: 29: 7 mol by RF plasma CVD using ethylene gas, nitrogen gas, and argon gas as reaction gases. A DLC protective film was formed with a thickness of 10 nm. At this time, a bias of −500 V was applied to the magnetic layer. This protective layer was also formed on both sides of the 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 film. Next, a 3.5 inch sized 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.
The characteristics of the obtained flexible disk were evaluated by the evaluation method shown below, and the results are shown in Table 2.

[Examples 2 to 16, Comparative Examples 1 to 4]
A flexible disk was produced in the same manner as in Example 1 except that the composition of the first underlayer and the second underlayer was as shown in Table 1.
The characteristics of the obtained flexible disk were evaluated by the evaluation method shown below, and the results are shown in Table 2.

(Evaluation methods)
1. Magnetic properties The coercive force Hc was measured with a sample vibration magnetometer (VSM) to obtain magnetic properties.
2. Film thickness of defective layer of second underlayer by cross-sectional TEM In the cross-sectional TEM photograph, a layer from the interface between the second underlayer and its lower layer to a portion showing a columnar structure in the second underlayer The film thickness was evaluated.
3. Surface roughness (SRa)
Using SPA-500 manufactured by Seiko Instruments Inc., surface roughness (SRa) was determined by applying tilt correction from an area of about 500 nm square in the AFM contact mode.

  As can be seen from the results in Table 2, the flexible disk of the example which is the magnetic recording medium of the present invention has excellent magnetic properties, the crystal growth failure layer thickness of the second underlayer is 5 nm or less, and the surface roughness is also good. On the other hand, the flexible disk in the comparative example without the first underlayer or using Ti has the magnetic characteristics, the film thickness of the defective crystal growth layer of the second underlayer, and the surface roughness. It was unsatisfactory in either.

It is a cross-sectional schematic diagram which shows the layer structure of the magnetic recording medium of this invention. It is a cross-sectional schematic diagram which shows the layer structure of the conventional magnetic recording medium. It is a figure explaining the outline | summary of the manufacturing method and manufacturing apparatus of the magnetic-recording medium of this invention. It is a figure explaining an example of the CVD apparatus using the applicable high frequency plasma in order to form a protective layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Nonmagnetic polymer support body 3 1st base layer 4 2nd base layer 5 Magnetic layer 6 Protective layer 7 Ferromagnetic metal alloy 8 Nonmagnetic substance 10 Single layer base layer 11 Film-forming apparatus 12 Vacuum chamber 13 Volume Stock roll 14 Flexible polymer support 15A, 15B Tension adjusting roll 16 Film forming chambers 17A, 17B, 17C, 17D Sputtering gas supply pipes 18A, 18B Film forming rolls 19A, 19B, 19C, 19D Underlayer sputtering apparatus TA, TB, TC, TD Target 31 Magnetic layer 32 Flexible polymer support 33 Roll 34 Pass roller 35 Bias power supply 36 Film forming roll 37 Raw material gas 38 High frequency power supply 39 Carbon protective film 40 Winding roll

Claims (2)

  A first underlayer made of at least one surface of a nonmagnetic support made of a nonmetallic element alone, a compound made of only a nonmetallic element, or a compound of titanium and a nonmetallic element; and chromium, titanium, iridium A second underlayer containing at least one element selected from the group consisting of platinum, palladium, ruthenium, rhodium, rhenium and osmium, and a ferromagnetic metal alloy containing at least cobalt, platinum and chromium and nonmagnetic A magnetic recording medium having a magnetic layer made of a substance in this order.   A first underlayer made of at least one surface of a non-magnetic support made of a flexible polymer and made of a non-metal element alone, a compound made of only a non-metal element, and a compound of titanium and a non-metal element And a second underlayer containing at least one element selected from the group consisting of chromium, titanium, iridium, platinum, palladium, ruthenium, rhodium, rhenium, osmium, cobalt, tungsten, vanadium, iron and molybdenum, A magnetic recording medium comprising: a ferromagnetic metal alloy containing at least cobalt, platinum, and chromium; and a magnetic layer composed of a nonmagnetic material in this order.