JP2004362730A - Magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent corrosion resistance, sufficient mechanical strength, excellent smoothness, little cupping, and a good tape shape. <P>SOLUTION: The magnetic recording medium which has a magnetic layer 2 which is formed by a vacuum thin film forming technique on one major face of a long-sized nonmagnetic support 1 and has a shielding layer 4 which is deposited by a facing target sputtering process on another major face of the nonmagnetic support 1 and in which the absolute value of a/w is ≤0.05 when the cupping in a transverse direction is defined as (a) and the length of the width as w is provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium of a metal magnetic thin film type and a method for producing the same, and particularly to a magnetic recording medium having high corrosion resistance and hardness, excellent storage stability, and excellent flatness. is there.

In recent years, in the field of video tape recorders and the like, in order to achieve high image quality and high recording density, a metal material, a Co—Ni alloy, a Co—Cr alloy, a Co—CoO alloy are directly placed on a nonmagnetic support. There has been proposed a metal thin film type magnetic recording medium in which a magnetic layer such as a metal oxide is applied by using a vacuum thin film forming technique to form a magnetic layer.
As such a magnetic recording medium, for example, a high-band 8 mm video tape recorder, a vapor deposition tape for a digital video tape recorder, and the like have been put to practical use.

  Such a metal thin film type magnetic recording medium is excellent in coercive force and squareness ratio, and since the magnetic layer can be formed in an extremely thin layer, it has excellent electromagnetic conversion characteristics in a short wavelength region, and has a recording demagnetization and reproduction. The thickness loss at the time is extremely small. Further, unlike a coating type magnetic recording medium, since a binder which is a non-magnetic material is not mixed into a magnetic layer, there are various advantages such as a higher packing density of ferromagnetic metal fine particles.

  Further, as the demand for a magnetic recording medium such as a magnetic tape as a data streamer increases, it is required to further increase the recording density of the magnetic recording medium. Further, as a magnetic head used when reproducing recorded information, a magnetoresistive head (hereinafter, referred to as an MR head) has been applied instead of a conventional inductive head. Since the MR head can detect minute leakage magnetic flux from the magnetic layer with high sensitivity, the recording density can be improved.

  By the way, the MR head has a detection upper limit at which the sensitivity to the leakage magnetic flux is saturated, and cannot detect a leakage magnetic flux larger than the design of the MR head. Therefore, it is optimal to make the magnetic layer thickness of the magnetic recording medium thinner. It is necessary to make it.

  In general, in the magnetic recording tape system, when the deterioration of the magnetization amount of the tape is 16% or more, the deterioration amount is too large and a sufficient reproduction signal cannot be obtained, so that the deterioration of the tape magnetization amount is within 15%. The system is formed on the assumption of this.

However, as the thickness of the magnetic layer has been reduced, there has been a problem that when the magnetic recording medium is stored in a high-temperature and high-humidity environment, it is susceptible to deterioration due to corrosion.
Generally, in a magnetic recording medium such as a vapor-deposited tape, a protective layer made of diamond-like carbon (DLC) or the like is formed on the magnetic layer for the purpose of improving the corrosion resistance and running durability of the magnetic layer. Polyethylene terephthalate (PET), etc., which is widely used as a medium, has high permeability to oxygen and moisture, so that corrosion proceeds from the nonmagnetic support side in addition to the surface on which the DLC film is formed, and corrosion is likely to occur. Particularly in a thin-layer type magnetic recording medium, further improvement in corrosion resistance has been required.

Further, the recording density per unit length of the magnetic tape can be improved by developing a metal thin film type magnetic recording material or the like, but in a magnetic recording tape medium stored in a cassette or wound on a reel, It is desired to further improve the total recording capacity of one cassette or one reel.
In order to increase the total recording capacity, it is necessary to make the volume accommodated in one cassette or reel the same, and therefore, development for reducing the total thickness of the magnetic recording medium is being promoted.
As a method of reducing the total thickness of the magnetic recording medium, it is practical to reduce the thickness of the nonmagnetic support, which has the highest proportion of the thickness of the magnetic recording medium, and to reduce the thickness of the nonmagnetic support. Efforts are being made to make it thinner.

However, when the thickness of the non-magnetic support is reduced, the mechanical strength of the magnetic recording tape is inferior, for example, and the magnetic recording layer may be damaged due to the extension of the magnetic tape while the tape is running. Therefore, it is required to form a reinforcing layer that reinforces the mechanical strength that has been weakened by reducing the thickness of the nonmagnetic support.
This reinforcing layer is generally formed on a surface facing the magnetic layer with the non-magnetic support interposed therebetween, and has a thickness smaller than the thickness of the non-magnetic support, and is formed by reducing the thickness of the non-magnetic support. It is required to compensate for the lack of mechanical strength.

  Conventionally, there has been proposed a configuration in which a metal thin film such as a Cu film is formed on a nonmagnetic support by a known thin film forming technique such as an evaporation method or a sputtering method (for example, see Patent Document 1).

JP 2002-92860 A

  However, the technique disclosed in Patent Document 1 is intended only to supplement the mechanical strength of the non-magnetic support for a hard disk type medium, and further thins the magnetic layer in the future. In the case of producing a layered high-density recording type magnetic tape medium, it is not possible to reliably improve mechanical strength and at the same time prevent deterioration of magnetic properties due to corrosion.

Further, as described above, when a metal thin film such as a Cu film is formed on a non-magnetic support by a vacuum evaporation method or a parallel plate magnetron sputtering method, in order to sufficiently prevent corrosion, the metal thin film is relatively formed. Since the magnetic layer must be formed thick, the surface shape on the side of the magnetic layer becomes rough, and there is a possibility that a problem that a medium noise as a magnetic recording medium increases may occur.
Such a problem is caused when a giant magnetoresistive head (hereinafter, referred to as a GMR head), which has higher reproduction sensitivity and is more suitable for high-density recording at high frequencies, is applied as a reproduction head for a magnetic recording medium. Since the thickness of the magnetic layer needs to be further reduced, the problem becomes more serious.

In addition, since the thermal expansion coefficient of a metal material or a metal oxide material is different from the resin used for a non-magnetic support, the influence of the heat history generated in the vapor deposition process and the recoil argon in the parallel plate type magnetron sputtering method. There is a problem that so-called cupping or curling occurs due to the influence of the above.
If the cupping or curling of the magnetic tape exceeds a predetermined limit, for example, when used in a video tape recorder, the contact at the entrance-exit becomes worse, or the magnetic tape protrudes from the drum when it is wound around the drum. Interference with the magnetic head occurs, causing damage to the tape edge, or so-called head tapping. Therefore, the magnetic tape needs to have good flatness.

  In view of the above-mentioned problems, the present invention provides a magnetic recording medium having excellent corrosion resistance, sufficient mechanical strength, excellent smoothness, low cupping, and a good tape shape. It was decided to.

  According to the present invention, there is provided a magnetic recording medium in which a signal is reproduced in a sliding state with respect to a magnetoresistive magnetic head or a giant magnetoresistive magnetic head, wherein one main surface of a long nonmagnetic support is provided. On the other main surface of the non-magnetic support, there is a shield layer formed by a facing target sputtering method, and a magnetic layer formed by a vacuum thin film forming technique Where a is the width of the magnetic recording medium, and the absolute value of a / w is 0.05 or less.

  Further, the method of manufacturing a magnetic recording medium of the present invention comprises the steps of: forming a magnetic layer on one main surface of a long non-magnetic support by a vacuum thin film forming technique; A step of forming a shield layer by a facing target type sputtering method, wherein when the cupping in the width direction is a and the length of the width is w, the absolute value of a / w is 0.05 or less. It is to be.

  Further, in the present invention, a magnetic layer formed by a vacuum thin film forming technique is provided on one main surface of a long non-magnetic support, and a Young's modulus is provided on another main surface of the non-magnetic support. When a shield layer made of a metal of 60 GPa or more is formed by a facing target sputtering method, the shield layer has a film thickness of 30 nm to 600 nm, and the widthwise cupping is a and the width length is w. , A / w having an absolute value of 0.1 or less.

  Further, the method of manufacturing a magnetic recording medium of the present invention comprises the steps of: forming a magnetic layer on one main surface of a long non-magnetic support by a vacuum thin film forming technique; A step of forming a shield layer to a film thickness of 30 nm to 600 nm by a facing target type sputtering method using a metal having a Young's modulus of 60 GPa or more, wherein cupping in the width direction is a and width is w. In this case, the absolute value of a / w is set to 0.1 or less.

  According to the present invention, it is possible to obtain a high recording density type tape-shaped magnetic recording medium having excellent corrosion resistance, having sufficient mechanical strength, excellent in smoothness, and having a good tape shape with little cupping. Was.

  According to the present invention, a shield layer is formed on the main surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed by a facing target type sputtering method, a cupping in the width direction is a, and a width length is w. When the absolute value of a / w was defined, the tape shape became extremely good, and edge damage could be prevented reliably.

  Further, according to the present invention, since the shield layer is made of a silicon nitride film having a thickness of 2 nm or more and 400 nm or less, it is possible to achieve both excellent corrosion resistance and a good tape shape, extremely high weather resistance, and A magnetic recording medium having excellent electromagnetic conversion characteristics was obtained.

  Further, according to the method of the present invention, by applying the facing target type sputtering method, even if the shield layer is formed thick to secure sufficient corrosion resistance, excellent tape shape and flatness can be obtained, and edge damage can be obtained. Was effectively prevented.

  A specific embodiment of the magnetic recording medium of the present invention and a method of manufacturing the same will be described with reference to the drawings. In the following, an example of a magnetic tape of a system in which a signal is reproduced in a sliding state with respect to a magnetoresistive head or a giant magnetoresistive head will be described.

First, FIG. 1 shows a schematic sectional view of an example of the magnetic recording medium of the present invention.
In the magnetic recording medium 10, the magnetic layer 2, the protective layer 3, and the top coat layer 5 are formed on one main surface of the nonmagnetic support 1, and the shield layer 4 and the back coat layer 6 are formed on the other main surface. It has the structure which was done.

  As the non-magnetic support 1, any known material usually used as a substrate for a magnetic tape can be applied. For example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; and plastics such as polycarbonate, polyimide, polyamide, and polyamideimide.

A coating layer may be formed on the side of the non-magnetic support 1 on which the magnetic layer is formed, using a paint containing a binder resin, a filler and a surfactant. Strength can be increased.
As the binder resin, for example, an aqueous polyester resin, an aqueous acrylic resin, an aqueous polyurethane resin, or the like can be used. Examples of the filler include particles made of a heat-resistant polymer, silicon dioxide, calcium carbonate, and the like. The average particle diameter of the filler contained in the coating layer is preferably 5 to 30 nm, and the density of surface protrusions due to the filler is preferably about 500,000 to 30 million particles / mm ² , whereby good running durability and electromagnetic conversion characteristics are obtained. Is achieved.

A shield layer 4 is provided on the main surface of the nonmagnetic support 1 opposite to the surface on which the magnetic layer is formed.
The shield layer 4 will be described separately in the first embodiment and the second embodiment.
First, as a first embodiment, it is assumed that the shield layer 4 has a function of preventing corrosion due to permeation of oxygen and moisture from the nonmagnetic support 1 side. In this case, a preferable example of the shield layer 4 is a silicon nitride film having a thickness of 2 nm or more and 400 nm or less.
If the thickness of the shield layer 4 is less than 2 nm, sufficient coverage cannot be obtained, and the desired effect of improving corrosion resistance cannot be obtained. On the other hand, if the thickness of the shield layer 4 is greater than 400 nm, warpage in the width direction, that is, cupping increases, and it becomes impossible to secure a good head contact.

  As a method for forming the shield layer 4, a conventionally known magnetron sputtering apparatus having a configuration in which a target for film formation and the nonmagnetic support 1 are provided to face each other is used to form a sputtered film on the nonmagnetic support 1. However, according to such a method, there is a problem that warping occurs in the width direction of the tape, cupping becomes large, and head contact is deteriorated.

  Therefore, in the present invention, first, the amount of cupping of the magnetic tape is defined. When the cupping is a and the width of the magnetic tape is w, the absolute value of the ratio a / w of these values is 0. It is specified to be 1 or less, preferably 0.05 or less.

As described above, when the cupping is a and the width of the magnetic tape is w, in order to control the absolute value of the ratio a / w of these values as described above, the shield layer 4 must be formed by facing target sputtering. It has been found that it is preferable to form a film by a method.
In the facing target sputtering method, the object to be processed (the non-magnetic support 1) is not directly exposed to plasma as compared with a thin film formed by another sputtering method, so that the stress of the thin film can be kept low and cupping can be prevented. This has the advantage that a magnetic tape having a small and good shape can be obtained.

  When the shield layer 4 is formed as a layer having a function of preventing the occurrence of corrosion as described above, the material composition of the shield layer 4 is not limited to silicon nitride, but may be Co, Cu, Ni, Fe, Various metal materials such as Zr, Pt, Au, Ta, W, Ag, Al, Mn, Cr, Ti, V, Nb, and Mo, and compounds of these metal materials with oxygen and nitrogen are also applicable.

Next, a second embodiment will be described. In this example, it is assumed that the shield layer 4 has a function of mainly improving the mechanical strength of the magnetic tape medium.
In this case, the shield layer 4 having a thickness of 30 nm to 600 nm is formed on the surface on the side opposite to the magnetic layer 2 via the nonmagnetic support 1 by a facing target sputtering method using a metal having a Young's modulus of 60 GPa or more in a bulk state. To form
If the film thickness of the shield layer 4 is less than 30 nm, sufficient mechanical strength cannot be ensured. If the film thickness is more than 600 nm, warpage in the width direction of the tape, that is, cupping becomes large, which is not preferable. It is.

  As the material used for the shield layer 4, Al (Young's modulus in a bulk state: 70.4 GPa), Cu (127 GPa), Ag (81.1 GPa), Au (77.5 GPa), Cr (288 GPa), Ir (528 GPa) ), Mn (198 GPa), Mo (317.8 GPa), Nd (118.9 GPa), Ni (196 GPa), Pt (170 GPa), Ru (447 GPa), Ta (186 GPa), Ti (96.1 GPa), W ( Various metal materials such as 394 GPa) and Zn (99.2 GPa) can be used. Further, if the above-mentioned Young's modulus is 60 GPa or more, other alloy materials, compounds of a metal material and oxygen or nitrogen, and the like can be applied.

  If the shield layer 4 is formed by a parallel plate magnetron sputtering method, there is a problem that the cupping of the tape is further increased. Regarding the amount of cupping, when the warpage in the width direction of the tape, that is, the cupping is a, and the width of the magnetic tape is w, it is preferable to suppress the absolute value of the ratio a / w of these values to 0.1 or less. . This is because when the absolute value of a / w is 0.1 or more, the contact state between the tape and the head deteriorates.

  Therefore, in order to control the cupping of the tape as described above, the shield layer 4 is formed by the facing target sputtering method. In the facing target sputtering method, the object to be processed (the non-magnetic support 1) is not directly exposed to plasma as compared with a thin film formed by another sputtering method, so that the stress of the thin film can be kept low and cupping can be prevented. A small and good magnetic tape can be obtained.

  Next, the magnetic layer 2, the protective layer 3, the top coat layer 5, and the back coat layer 6 will be described as matters common to the first and second embodiments.

  The magnetic layer 2 is manufactured by a vacuum thin film forming technique. As a vacuum thin film forming technique, a ferromagnetic metal material is heated and evaporated under vacuum, and a vacuum deposition method of attaching the ferromagnetic metal material on the non-magnetic support, an ion plating method of evaporating the ferromagnetic metal material in a discharge, and argon are used. A so-called physical vapor deposition (PVD) method, such as a sputtering method in which glow discharge is caused in an atmosphere containing a main component and surface atoms of a target are beaten by generated argon ions, can be applied. it can.

  The vacuum evaporation method has the advantages of good film-forming properties, high productivity, and easy operation. The sputtering method can be easily produced and has good film formability. In addition, the ion plating method is easy to control in film formation and has good film formability.

Further, the magnetic recording medium of the present invention is applied to a recording / reproducing apparatus having an MR head or a GMR head, and has a magnetic layer for reducing noise and improving C / N (carrier / noise ratio). 2 is desirably formed in a very thin layer, particularly preferably 5 to 55 nm or less.
If the thickness of the magnetic layer 2 is less than 5 nm, for example, it may not be possible to obtain a sufficient reproduction output even if a high-sensitivity GMR head is used. This is because the recording density cannot be improved in some cases.

  As the ferromagnetic metal material for forming the magnetic layer 2, any known metal material or alloy for manufacturing a magnetic recording medium can be generally used. For example, ferromagnetic metals such as Co and Ni, Co-Ni-based alloys, Co-Fe-based alloys, Co-Ni-Fe-based alloys, Co-Cr-based alloys, Co-Pt-based alloys, and Co-Pt-B-based alloys , Co-Cr-Pt-based alloys, Co-Cr-Ta-based alloys, Co-Cr-Pt-Ta-based alloys, and the like, or these materials are formed in an oxygen atmosphere, and the film contains oxygen. Or a material in which one or more of these elements are added to these materials.

Further, Co-Pt-SiO ₂ , Co-Pt-Al ₂ obtained by simultaneously forming a film of these ferromagnetic materials and Al ₂ O ₃ , SiO ₂ , InO ₂ , ZrO _2, etc. which are insoluble. The magnetic layer 2 may be formed of a granular material such as O ₃ .

Note that the magnetic layer is not limited to a single layer, and may be a laminate of a plurality of magnetic layers.
Further, an intermediate layer (not shown) is formed between the non-magnetic support 1 and the magnetic layer 2 using a vacuum thin film forming technique for the purpose of miniaturizing the crystal grains of the magnetic layer and improving the orientation. May be. Examples of the material constituting the intermediate layer include metal materials such as Co, Cu, Ni, Fe, Zr, Pt, Au, Ta, W, Ag, Al, Mn, Cr, Ti, V, Nb, Mo, and Ru. And alloys of two or more of these, and compounds of this metal material with oxygen and nitrogen, and compounds such as SiO ₂ , silicon nitride, ITO (Indium Tin Oxide), In ₂ O ₃ , and ZrO.

It is desirable to form a protective layer 3 made of DLC or the like on the magnetic layer 2 in order to secure better running durability and corrosion resistance.
The same method as that for forming the shield layer 4 can be applied to the method for forming the protective layer 3. Further, it may be formed by a sputtering method, a physical film formation method (PVD method), a chemical vapor deposition method (CVD method), or the like.

Further, a back coat layer 6 is provided on the main surface opposite to the magnetic layer forming surface for the purpose of improving the running property of the magnetic recording medium and preventing static charge. The back coat layer 6 preferably has a thickness of 0.2 to 0.7 μm.
The back coat layer 6 is prepared by dispersing solid particles such as an inorganic pigment in a binder, kneading the mixture with an organic solvent selected according to the type of the binder, and adjusting the back coat layer paint. On the shield layer 4.

  Furthermore, it is desirable to form the top coat layer 5 by coating the outermost layer on the magnetic layer forming surface side or the main surface on the opposite side with a lubricant or a rust inhibitor.

The magnetic recording medium according to the present invention is suitable as a magnetic tape for a helical scan magnetic recording system using an MR reproducing head.
Here, the MR head is a read-only magnetic head that detects a signal from a magnetic recording medium using a magnetoresistance effect. Generally, MR heads are more suitable for high-density recording because they have higher sensitivity and higher reproduction output than inductive magnetic heads that perform recording and reproduction using electromagnetic induction. Therefore, higher density recording can be achieved by using an MR head as the reproducing magnetic head.

  The MR head includes, for example, a substantially rectangular MR element portion sandwiched by a pair of magnetic shields made of a soft magnetic material such as Ni-Zn polycrystalline ferrite via an insulator. A pair of terminals is led out from both ends of the MR element, and a sense current can be supplied to the MR element via these terminals.

  When reproducing a signal from the magnetic tape using the MR head, the magnetic tape is slid to the MR element. Then, a sense current is supplied to the MR element via terminals connected to both ends of the MR element while the magnetic tape is slid on the MR element, and a voltage change of the sense current is detected. When a sense current is supplied to the MR element while the magnetic tape is slid, the magnetization direction of the MR element changes according to the magnetic field from the magnetic tape, and the sense current and the magnetization direction supplied to the MR element are changed. And the relative angle changes. Then, the resistance value changes depending on the relative angle between the magnetization direction of the MR element and the direction of the sense current. For this reason, by making the current value of the sense current supplied to the MR element unit constant, a voltage change occurs in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic tape is detected, and the signal recorded on the magnetic tape is reproduced.

  In the MR head, the MR element formed in the MR element section may be any element exhibiting a magnetoresistance effect. For example, a larger magnetoresistance effect can be obtained by laminating a plurality of thin films. A so-called giant magnetoresistive element (GMR element) can also be used. The method of applying the bias magnetic field to the MR element may not be the SAL bias method, for example, a permanent magnet bias method, a shunt current bias method, a self-bias method, an exchange bias method, a barber pole method, a split element method, Various methods such as a servo bias method can be applied. The giant magnetoresistance effect and various bias methods are described in detail in, for example, "Magnetoresistance Head-Basic and Application-Translated by Kazuhiko Hayashi" published by Maruzen Co., Ltd.

Next, a method for manufacturing a magnetic recording medium will be described.
First, a long nonmagnetic support 1 is prepared, and desired fine irregularities are formed by forming a coating layer (not shown) on the surface.

Next, the shield layer 4 is formed on the main surface opposite to the magnetic layer formation surface by a facing target sputtering method.
The shield layer 4 is formed by, for example, generating a discharge in an atmosphere containing argon as a main component, hitting surface atoms of a target made of a predetermined film forming material with the generated argon ions, and performing sputtering.

  The film forming material is preferably silicon nitride in the case of the above-described first embodiment, and in addition, Co, Cu, Ni, Fe, Zr, Pt, Au, Ta, W, Ag, Al, Mn. , Cr, Ti, V, Nb, Mo and the like, and compounds of these metal materials with oxygen and nitrogen can also be applied.

  Further, in the case of the above-described second embodiment, the film-forming material is preferably a metal having a Young's modulus in a bulk state of 60 GPa or more, and Al, Cu, Ag, Au, Cr, Ir, Mn. , Mo, Nd, Ni, Pt, Ru, Ta, Ti, W, Zn and the like. If the Young's modulus is 60 GPa or more, other alloy materials, compounds of a metal material with oxygen or nitrogen, and the like can be applied.

The step of forming the shield layer 4 will be described with reference to FIG.
In the facing target type sputtering apparatus 20, targets 22 and 23 of film forming materials facing each other at a predetermined distance are arranged in a chamber 21 set under an argon gas atmosphere at a predetermined pressure. Magnetic field generating means 24 and 25 are provided along the respective circumferences.
When a predetermined potential is applied by a power supply 26 electrically connected to each of the targets 22 and 23, a vertical magnetic field is generated in the direction facing the targets, and surface atoms of the targets are knocked out. The shield layer 4 is formed on the non-magnetic support 1 which is arranged on the side of the space and is continuously transported.

Next, the magnetic layer 2 is formed on the main surface opposite to the surface on which the shield layer 4 is formed.
The magnetic layer 2 is formed by a vacuum thin film forming technique. Vacuum thin-film formation technology includes vacuum evaporation, in which a ferromagnetic metal material is heated and evaporated under vacuum, an ion plating method in which a ferromagnetic metal material is evaporated in a discharge, and in an atmosphere containing argon as a main component. A sputtering method in which surface atoms of a target are struck by argon ions generated by glow discharge, and the like, may be mentioned. As the ferromagnetic metal material for forming the magnetic layer 2, any of the above-mentioned known metal materials and alloys for producing a normal magnetic recording medium can be used.

After the formation of the magnetic layer 2, a protective layer 3 made of, for example, a DLC film is formed on the magnetic layer 2. As a film forming method, for example, a plasma CVD method can be mentioned.
Further, the top coat layer 5 is formed by applying a perfluoropolyether-based lubricant, and if necessary, for example, a paint containing carbon is applied to form the back coat layer 6.

  The magnetic recording medium 10 manufactured by the method of the present invention has an absolute value of a / w of 0.1 or less, preferably 0.05 or less, where a is cupping in the width direction, and w is the length of the width. Identify something.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

(Experiment A)
[Example A1]
As the nonmagnetic support 1, a polyethylene terephthalate (PET) film having a thickness of 6.3 μm and a width of 150 mm was prepared.
A coating layer having a thickness of 5 nm was formed on the nonmagnetic support 1 on the side where the magnetic layer was formed. The coating layer is formed so that the protrusion density is about 1 × 10 ⁷ / mm ² by applying a coating prepared by stirring silica particles having a diameter of 10 nm to a water-soluble latex containing acrylic ester as a main component. did.
Next, a shield layer 4 made of a silicon nitride film was formed to a thickness of 2 nm on the surface opposite to the magnetic layer formation surface side by a facing target sputtering method. Specifically, the distance between the non-magnetic support 1 and the target is set to 15 mm, the non-magnetic support is transported at a feed rate of 10 m / min, and the silicon nitride (Si ₃ N ₄ ) target is sputtered. Then, a shield layer 4 made of a silicon nitride film having a thickness of 2 nm was formed.
Next, the magnetic layer 2 was formed on the surface opposite to the surface on which the shield layer was formed using a vacuum evaporation apparatus. Specifically, Co is applied as a metal magnetic material as a raw material, oxygen is introduced at 6.0 × 10 ⁻⁴ m ³ / min from an oxygen gas introduction tube, and an electron gun is used to irradiate an electron beam and heat the mixture. A Co-CoO-based magnetic layer was formed to a thickness of 50 nm by reactive vacuum deposition. At this time, the minimum incident angle of the Co-deposited particles was set to 45 ° and the maximum incident angle to 90 ° by the shutter.
Next, a protective layer 3 made of a DLC film was formed on the magnetic layer 2 to a thickness of 10 nm by a plasma CVD method.
Next, a topcoat layer 5 having a thickness of 2 nm was formed on the protective layer 3 using a perfluoropolyether-based lubricant.
In addition, in order to improve running durability, a back coat layer paint composed of carbon particles having an average particle diameter of 20 nm and a urethane resin is used as an inorganic pigment on the main surface opposite to the surface on which the magnetic layer 2 is formed. The back coat layer 6 was formed to a thickness of 0.5 μm by using a coating apparatus according to the method.
The raw magnetic tape produced as described above was cut into a width of 8 mm to prepare a magnetic tape as a sample.

[Example A2]
The shield layer 4 was formed to a thickness of 200 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Example A3]
The shield layer 4 was formed to a thickness of 300 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Example A4]
The shield layer 4 was formed to a thickness of 400 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Example A5]
Copper (Cu) was used as a film-forming target material, and the shield layer 4 was a Cu film having a thickness of 400 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Comparative Example A1]
No shield layer 4 was formed. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Comparative Example A2]
The shield layer 4 was formed to a thickness of 1 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Comparative Example A3]
The shield layer 4 was formed to a thickness of 450 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Comparative Example A4]
The shield layer 4 was formed to a thickness of 200 nm by using a magnetron sputtering apparatus 30 in which a target 32 and a nonmagnetic support 1 were arranged in a chamber 21 as shown in FIG. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

[Comparative Example A5]
Cu was applied as a target material, and the shield layer 4 was a Cu film having a thickness of 200 nm. Other conditions were the same as in Example A1 to produce a sample magnetic tape.

With respect to each sample magnetic tape produced as described above, the cupping and corrosion resistance of the magnetic tape were evaluated by the following methods.
(Evaluation of cupping)
The warp in the width direction of the magnetic tape, that is, the cupping was defined as a, and the width of the magnetic tape was defined as w, and the absolute value of the ratio a / w was calculated. The case where the absolute value of a / w was in the range of 0 to 0.05 was accepted.
Edge damage was evaluated in order to confirm the influence of magnetic tape cupping. Edge damage was evaluated by visually observing scratches generated at both ends in the width direction of the magnetic tape after repeating loading and unloading of the magnetic tape 100 times. The evaluation criteria were ○ when no edge damage was confirmed, and x when edge damage was confirmed.
(Evaluation of corrosion resistance)
Evaluation was made by measuring the magnetization deterioration rate of the magnetic layer after the corrosion test.
The magnetization deterioration rate was determined by measuring the magnetization amount (Ms ₀ : saturated magnetization) before standing and the magnetization amount (Ms ₁ ) after standing for 6 days in an environment of a temperature of 65 ° C. and a relative humidity of 90%. It was calculated using equation (1). If the magnetization deterioration rate was within 15%, it was regarded as acceptable.
Magnetization degradation rate (%) = [(Ms ₀ −Ms ₁ ) / Ms ₀ ] × 100 (1)

  Table 1 below shows the conditions for preparing the sample magnetic tapes of Examples A1 to A5 and Comparative Examples A1 to A5, and the results of the evaluation of cupping and corrosion resistance.

  As shown in Table 1 above, when the shield layer 4 made of a silicon nitride film is formed by the facing target sputtering method, and the cupping in the width direction is a and the length of the width is w, the absolute value of a / w However, in the magnetic tapes of Examples A1 to A5, the edge damage was not confirmed, the flatness of the tape was good, and the magnetization deterioration rate was within 15%. And showed good corrosion resistance.

  In Comparative Example A1, since the shield layer 4 was not formed, practically sufficient corrosion resistance was not obtained, and the magnetization deterioration rate deteriorated.

  In Comparative Example A2, since the shield layer 4 was too thin, sufficient corrosion resistance was not obtained, and the magnetization deterioration rate was deteriorated.

  In Comparative Example A3, the shield layer 4 was too thick, and the absolute value of a / w exceeded 0.05, causing edge damage.

  In Comparative Example A4, since the shield layer 4 was formed by using the magnetron sputtering apparatus 30 in which the target 32 and the object 1 were arranged to face each other as shown in FIG. It exceeded 0.05, causing edge damage.

  In Comparative Example A5, since the shield layer 4 was formed of a Cu film by using a magnetron sputtering apparatus 30 in which the target 32 and the object 1 were arranged to face each other as shown in FIG. The absolute value exceeded 0.05, causing edge damage.

  Further, comparing Example A5 with Comparative Example A5, the absolute value of a / w is set to 0.05 or less when the facing target type sputtering method is applied, even if the shield layer 4 is formed of a thick Cu film. It was found that the tape shape could be improved. That is, according to the method of the present invention, it was found that both excellent corrosion resistance and reduction of edge damage were achieved.

(Experiment B)
[Example B1]
As a nonmagnetic support, a polyethylene terephthalate (PET) film having a thickness of 4.5 μm and a width of 150 mm was prepared.
First, a coating layer having a thickness of 5 nm was formed on the magnetic layer forming surface side of the non-magnetic support 1. The coating layer was formed by applying a silica particle having a diameter of 10 nm to a water-soluble latex containing an acrylic ester as a main component so as to have a density of about 1 × 10 ⁷ particles / mm ² .

Next, the magnetic layer 2 was formed using an evaporation apparatus. The magnetic metal material as a raw material was Co, oxygen was introduced at 6.0 × 10 ⁻⁴ m ³ / min from an oxygen gas introduction tube, and the electron gun was irradiated with an electron beam and heated. -A CoO-based magnetic layer was formed to a thickness of 50 nm. At this time, the minimum incident angle of the Co-deposited particles was adjusted to 45 ° and the maximum incident angle to 90 ° by the shutter.

Next, a protective layer 3 made of DLC (diamond-like carbon) was formed on the magnetic layer 2. The protective layer 3 was formed to have a thickness of 10 nm by a plasma CVD method.
Next, a 30-nm-thick shield layer 4 was formed on the surface of the non-magnetic support 1 opposite to the surface on which the magnetic layer 2 was formed by using a facing film sputtering method using Al as a film-forming material.
Specifically, using the facing target type sputtering apparatus 20 shown in FIG. 2, the distance between the nonmagnetic support and the target was set to 15 mm, and the continuous film was transported at a feed speed of 5 m / min. Then, an Al target was sputtered to form a shield layer 4 made of Al.

Next, on the surface opposite to the surface on which the magnetic layer 2 is formed, that is, on the surface on which the shield layer 4 is formed, a back made of carbon particles having an average particle diameter of 20 nm as an inorganic pigment and urethane resin is used to obtain running durability. Using a coating material for coating, a back coat layer 6 was formed to a thickness of 0.5 μm using a coating device based on a direct gravure method.
Next, a perfluoropolyether-based lubricant was applied on the protective layer 3 to form a top coat layer 5 having a thickness of 2 nm.
Finally, the material was cut into a width of 8 mm to obtain a sample tape. This was used as a sample of Example B1.

[Examples B2 to B5, Comparative Examples B1 to B4]
For Examples B2 to B5 and Comparative Examples B1 to B4, magnetic tape media were manufactured according to the following Table 2 by changing the film thickness of the shield layer 4, the film forming material, and the film forming method.
Other manufacturing conditions are the same as in Example B1.

For each of the sample magnetic tapes produced as described above, the cupping of the tape and the damage after running the tape were evaluated. The evaluation results are shown in Table 2 below.
The cupping was evaluated by calculating the ratio a / w of these values when the warpage in the width direction of the magnetic tape, that is, the cupping was a and the width was w.
Evaluation of the tape damage was performed by repeating the loading and unloading of the magnetic tape 100 times and then visually observing the scratches generated on the magnetic tape. In the evaluation, ○ indicates no damage and X indicates damage.

  As shown in Table 2 above, the magnetic tapes of Examples B1 to B5 in which a shield layer 4 having a thickness of 30 nm to 600 nm was formed by a facing target sputtering method using a metal having a Young's modulus of 60 GPa or more as a film forming material, a / w ratio) was 0.1 or less, and excellent results were obtained for the evaluation of tape damage.

On the other hand, the magnetic tape of Comparative Example B1 in which the film thickness of the shield layer 4 was 20 nm had a good cupping of 0.1 or less and a good shape, but did not give a practically good evaluation for tape damage.
In the magnetic tape of Comparative Example B2 in which the film thickness of the shield layer 4 was 700 nm, the cupping was 0.1 or more, and no favorable evaluation of tape damage was obtained.

The magnetic tape of Comparative Example B3, in which the shield layer 4 was formed using a parallel-plate magnetron sputtering method as the film forming method, had a cupping of 0.1 or more, deteriorated the tape shape, and obtained a practically good evaluation of tape damage. Did not.
Further, with respect to the magnetic tape of Example B4 in which the shield layer 4 was formed by applying bismuth having a Young's modulus of less than 60 GPa in the bulk state to the film forming material, the cupping was 0.1 or less, and a good shape was obtained. However, no practically good evaluation was obtained for the tape damage.

1 shows a schematic sectional view of the magnetic recording medium of the present invention. FIG. 1 is a schematic configuration diagram of a facing target sputtering apparatus for forming a shield layer. FIG. 1 shows a schematic configuration diagram of a conventional magnetron sputtering apparatus.

Explanation of reference numerals

1 Non-magnetic support, 2 Magnetic layer, 3 Protective layer, 4 Shield layer, 5
Top coat layer, 6 Back coat layer, 10 Magnetic recording medium, 20 Counter target sputtering apparatus, 21 Chamber, 22, 23 Target, 2
4, 25 ... magnetic field generating means, 26 ... power supply, 30 ... magnetron sputtering device, 32 ... target

Claims (7)

A magnetic recording medium in which signal reproduction is performed in a sliding state with respect to a magnetoresistive head or a giant magnetoresistive head,
On one main surface of a long non-magnetic support, having a magnetic layer formed by a vacuum thin film forming technique,
On the other main surface of the non-magnetic support, having a shield layer formed by a facing target sputtering method,
A magnetic recording medium wherein the absolute value of a / w is 0.05 or less, where cupping in the width direction is a and length of the width is w.   2. The magnetic recording medium according to claim 1, wherein the shield layer is made of a silicon nitride film having a thickness of 2 nm or more and 400 nm or less. A method of manufacturing a magnetic recording medium in which a signal is reproduced in a sliding state using a magnetoresistive magnetic head or a giant magnetoresistive magnetic head,
Forming a magnetic layer on one main surface of a long non-magnetic support by a vacuum thin film forming technique;
Forming a shield layer on the other main surface of the nonmagnetic support by a facing target sputtering method,
A method of manufacturing a magnetic recording medium, wherein when the cupping in the width direction is a and the length of the width is w, the absolute value of a / w is 0.05 or less.   2. The magnetic recording medium according to claim 1, wherein the shield layer is made of a metal having a Young's modulus of 60 GPa or more, and has a thickness of 30 nm or more and 600 nm or less.   4. The method according to claim 3, wherein the shield layer is formed of a metal having a Young's modulus of 60 GPa or more and a film thickness of 30 nm or more and 600 nm or less. A magnetic recording medium in which signal reproduction is performed in a sliding state with respect to a magnetoresistive head or a giant magnetoresistive head,
On one main surface of a long non-magnetic support, having a magnetic layer formed by a vacuum thin film forming technique,
On the other main surface of the non-magnetic support, has a shield layer made of metal having a Young's modulus of 60 GPa or more and formed by a facing target sputtering method,
The shield layer has a thickness of 30 nm to 600 nm,
A magnetic recording medium wherein the absolute value of a / w is 0.1 or less, where cupping in the width direction is a and width is w. A method of manufacturing a magnetic recording medium in which a signal is reproduced in a sliding state using a magnetoresistive magnetic head or a giant magnetoresistive magnetic head,
Forming a magnetic layer on one main surface of a long non-magnetic support by a vacuum thin film forming technique;
Forming a shield layer to a thickness of 30 nm to 600 nm on the other main surface of the nonmagnetic support by using a metal having a Young's modulus of 60 GPa or more by a facing target sputtering method,
A method of manufacturing a magnetic recording medium, wherein when the cupping in the width direction is a and the length of the width is w, the absolute value of a / w is 0.1 or less.

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