JPH10105943A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium prevented from the generation of cupping and exhibiting high running stability by forming a back coat layer having a column structure, formed by controlling the structure to non- obliquely vapor deposit, on the surface opposite to a magnetic layer on a non- magnetic supporting body. SOLUTION: In the non-magnetic supporting body constituted so as to film- form a single layer of a metal cobalt magnetic layer with a prescribed thickness by obliquely vapor depositing on a PET film and to film-form a protective layer with a prescribed thickness thereon, the back coat layer is formed on the surface opposite to the magnetic layer of the non-magnetic supporting body. In such a case, gaseous oxygen is introduced under a prescribed condition at the time of film-forming the back coat layer on the non-magnetic supporting body on a cooling can roll. Further a fluorine based lubricant is applied as a lubricant layer with a prescribed thickness on both surfaces of the protective layer of the magnetic layer and the back coat layer. As a result, the back coat layer is formed from a thin film having a random structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deposition type magnetic recording medium, and more particularly to a back coat layer. More specifically, the present invention relates to a magnetic recording medium that can prevent cupping of a magnetic recording medium by controlling the structure of a thin film forming a back coat layer, and can maintain good running properties and head touch.

[0002]

2. Description of the Related Art Conventionally, a backcoat layer is formed on a surface of a nonmagnetic support opposite to a magnetic layer so as to have the following three functions. (1) By providing conductivity, adhesion of dust is prevented by an antistatic effect. (2) Running stability is obtained by controlling surface properties (coefficient of friction). (3) From the viewpoint of hardness and the like, the surface having the magnetic layer and the back surface having the back coat layer are balanced to prevent the occurrence of warpage.

[0003] As a method of forming the back coat layer, carbon having a particle size of 10 to 100 nm is dispersed in a binder (using a vinyl chloride-based, urethane-based, or nitrified cotton-based material alone or as a mixture), and the gravure method or the reverse method Conventionally, a method of applying a die coating method so that the thickness after drying becomes 0.4 to 1.0 μm, or a method of depositing a metal or metalloid in a vacuum vessel has been conventionally performed. In the method of forming the back coat layer by coating, the method (1) is based on the conductivity of carbon, the method (2) is controlled by controlling the particle size of carbon and a coating process, and the method (3) is based on a binder. And the control of the coating thickness satisfied each of them. However, due to the presence of the binder, the back coat layer could not obtain sufficient conductivity, and the magnetic layer was damaged because the medium had to be taken out to the atmosphere once when applying the back coat layer due to the influence of the solvent of the binder. There is a problem that the number of dropouts increases in the dropout inspection due to contamination, dirt, or adhesion of dust.

On the other hand, in the method of depositing a metal in a vacuum, the influence of the binder can be avoided, so that the conductivity of the back coat layer can be improved and the number of dropouts can be reduced. However, it is not possible to obtain sufficient conductivity when depositing a metalloid,
Also, when a metal is deposited, there have been problems in that the surface of the back coat layer becomes too smooth, it is difficult to provide the back coat layer with sufficient hardness, and the end face of the medium is deformed in a wavy manner. To solve the above problems, the present applicant has proposed a method of improving the conductivity of a back coat layer by vacuum-depositing a metalloid and an impurity in Japanese Unexamined Patent Publication No. Hei 7-1995.
Japanese Patent Application Laid-Open No. 98830/98 proposes that a back coat layer is made of two or more layers of metal or metalloid to impart appropriate surface properties and elasticity. Japanese Patent Application Laid-Open No. H8-1010 proposes that the back coat layer has sufficient hardness by forming
Japanese Patent Application Laid-Open No. Hei 8-102051 discloses a proposal in Japanese Patent Application Laid-Open No. Hei 8-102051 that a diamond-like carbon layer is formed on a back coat layer to suppress deformation of an end face of a magnetic recording medium.

[0005]

It is desired to produce a high quality magnetic recording medium with high productivity in the future. However, in the method of forming the back coat layer by coating as described above, a sufficient conductivity is required. This is disadvantageous in that it is difficult to obtain the desired characteristics and the number of dropouts cannot be reduced. The surface property or hardness of the back coat layer was also improved by the above-mentioned proposal in the method of vapor deposition, but further suppression of cupping, improvement in running stability and head touch were desired, so the surface property of the back coat layer was further improved. Alternatively, improvement in hardness has been desired. In the future, the thickness of magnetic recording media will tend to be smaller in order to store more information in a container of a fixed size, and the magnetic layer and back coat layer formed on a non-magnetic support It has become necessary to make the recording medium have an appropriate hardness.
Therefore, in the present invention, in view of the conventional problems as described above, and for the future, in a magnetic recording medium having a magnetic layer formed by oblique deposition, by controlling the structure of the thin film forming the back coat layer It is an object of the present invention to provide a magnetic recording medium that can prevent occurrence of cupping and achieve high running stability.

[0006]

Means for Solving the Problems For this reason, the present inventors have:
In a magnetic recording medium with a magnetic layer having a column structure formed by oblique deposition, by forming a non-obliquely deposited back coat layer by controlling the structure on the surface opposite to the magnetic layer on the non-magnetic support The inventors have found that the above objects can be achieved, and have completed the present invention.

[0007] The back coat layer obtained by the present invention comprises:
Thin film or random structure with column structure formed on the surface opposite to the magnetic layer with column structure formed by oblique deposition on non-magnetic support and grown perpendicular to the surface of non-magnetic support Characterized by a thin film having In the present invention, a random structure means a structure having no specific structure such as a column structure. Here, the structural analysis of a plane parallel to the longitudinal direction of the non-magnetic support and perpendicular to the surface of the non-magnetic support is evaluated by observation with a transmission electron microscope (TEM) photograph or by electron beam diffraction. Further, the back coat layer is evaporated by irradiating a metal or metalloid with an electron beam in a vacuum chamber, and the metal or metalloid obtained by attaching the metal or metalloid on a nonmagnetic support or oxides, nitrides, Formed by carbide. Various metals can be attached as the back coat layer, but Al, Cu, Zn, Sn, N
i, Ag, etc. and their alloys are used.
Cu-Al alloys are preferred from the viewpoints of adhesion speed and stability after oxidation. Further, as the semimetal adhered as the back coat layer, Si, Ge, As, Sc, Sb, or the like is used, and Si is particularly preferable in terms of cost and adhesion speed. Furthermore, it is also preferable to perform any one of oxidation, nitridation, and carbonization simultaneously when depositing these metals or metalloids to form an oxide film, a nitride film, and a carbonized film. The thickness of the back coat layer is set to be smaller than the thickness of the magnetic layer by 2,000 mm in consideration of the rigidity of the magnetic layer formed on the surface of the nonmagnetic support opposite to the back coat layer. 2 than the thickness of
It is formed to have a thickness of 000 thick. The back coat layer may be formed on the non-magnetic support either before or after the formation of the magnetic layer and the protective layer on the non-magnetic support.

The non-magnetic support used in the present invention is preferably polyethylene terephthalate (PET) from the viewpoint of cost. However, in addition, use of polyesters such as polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate, polyvinyl chloride, polyimide, and aromatic polyamide. Can be. The thickness of these nonmagnetic supports is generally considered to be about 50 μm, but from the practical point of view, it is preferably 4.5 μm or less. It is preferably not more than 6.0 μm from the thickness of the body and the thickness of each layer.

In the present invention, the metal thin film type magnetic layer is formed by ordinary methods such as vapor deposition and sputtering. Examples of the magnetic material for forming the metal thin film type magnetic layer include ferromagnetic metal materials used for manufacturing a normal metal thin film type magnetic recording medium. For example, a ferromagnetic metal such as Co, Ni, and Fe, or Fe—Co, Fe—Ni, Co—Ni, and Fe—C
o-Ni, Fe-Cu, Co-Cu, Co-Au, Co
-Y, Co-La, Co-Pr, Co-Gd, Co-S
m, Co-Pt, Ni-Cu, Mn-Bi, Mn-S
b, Mn-Al, Fe-Cr, Co-Cr, Ni-C
and ferromagnetic alloys such as r-Fe-Co-Cr and Ni-Co-Cr. Particularly, from the viewpoint of the magnetic properties of the magnetic material used for the magnetic recording medium, at least one selected from a ferromagnetic alloy mainly composed of Co, Ni, and Fe and a nitride or carbide thereof is preferable. The durability can be improved by introducing an oxidizing gas at the time of vapor deposition to form an oxide layer on the surface of the magnetic layer. The magnetic layer formed by vapor deposition may be a single layer or a multilayer of two or more layers, but is preferably a multilayer for high-density recording, and a practical range of two to three layers is appropriate. It is preferable that the magnetic layer of the magnetic recording medium is formed on the non-magnetic support by oblique evaporation. The method of oblique deposition is not particularly limited, and follows a conventionally known method. The thickness of the metal thin-film magnetic layer is not limited, but is preferably 500 to 5000 °, and particularly preferably 800 to 3000 ° as a practical range. In the case of two layers, the lower layer is about 200 to 2000 ° and the upper layer is
The thickness is preferably about 0 to 1000 °, and in the case of three layers, the lower layer is preferably about 200 to 2000 °, the middle layer is about 200 to 2000 °, and the upper layer is about 100 to 1000 °.

For the purpose of improving the durability and corrosion resistance of the magnetic recording medium, a protective layer of a high hardness thin film can be provided on the magnetic layer and the back coat layer. Such a protective layer is made of a non-magnetic material such as carbide, nitride, or oxide such as diamond-like carbon, boron carbide, silicon carbide, boron nitride, silicon nitride, silicon oxide, or aluminum oxide. The film is formed by the PVD method.

A lubricating layer made of a suitable lubricant may be formed on the protective layer on the magnetic layer and the back coat layer or on the protective layer on the magnetic layer and the protective layer on the back coat layer. The lubricating layer may be formed by applying a solution obtained by dissolving a lubricant in an appropriate solvent, or may be formed by spraying the lubricant in a vacuum. As the lubricant, a fluorine-based lubricant such as perfluoropolyether is preferable from the viewpoint of lubricating property in either application or spraying. For example, the molecular weight of perfluoropolyether is 2,000 to 5,
000 are preferred. The amount of the lubricant to be applied or sprayed is determined as appropriate depending on the use of the magnetic recording medium and the type of the lubricant.
It is about.

[0012]

FIG. 1 shows an example of a vapor deposition apparatus 1 suitable for producing a magnetic recording medium according to the present invention. Here, a vacuum chamber 2 connected to a vacuum evacuation device (not shown), a cooling can roll 3 provided in the vacuum chamber 2, and a nonmagnetic support 4 such as a PET film running on the cooling can roll 3. Unwinding roll 5 and take-up roll 6 are provided. A crucible 7 is disposed vertically below the rotation axis of the cooling can roll 3 as an evaporation source, and a back coat forming material such as C
A u-Al alloy is accommodated. An electron gun 8 is arranged in the vacuum chamber 2 and irradiates the crucible 7 with an electron beam to evaporate the Cu-Al alloy in the crucible 7. Between the crucible 7 and the cooling can roll 3, a deposition preventing plate 9 for limiting the incident range of the Cu—Al alloy vapor from the crucible 7 evaporated by the electron beam toward the cooling can roll 3 to the non-magnetic support 4. And 9 'are arranged. Further, nozzles 10 and 1 for supplying oxygen gas are provided between the deposition-preventing plates 9 and 9 ′ and the cooling can roll 3.
0 'is arranged.

The manufacture of a magnetic recording medium according to the present invention using such a vapor deposition apparatus 1 is as follows. That is, after the inside of the vacuum chamber 2 is evacuated to a predetermined degree by the vacuum exhaust device, the non-magnetic support 4 is run from the unwinding roll 5 onto the cooling can roll 3. At this time, the non-magnetic support may be either a magnetic layer and a protective layer formed on the magnetic layer in advance, or a non-magnetic support having no magnetic layer formed thereon. The electron gun 8 irradiates the crucible 7 with an electron beam, melts and evaporates the Cu-Al alloy in the crucible 7, and performs vapor deposition on the nonmagnetic support 4. This is done in the presence of oxygen supplied from nozzles 10 and 10 '. The non-magnetic support 4 thus treated is wound on a take-up roll 6. Thereafter, if necessary, a protective layer is formed on the back coat layer. Further, immediately after the protective layer has been formed on the magnetic layer and the magnetic layer in advance, immediately after the protective layer is formed on the magnetic layer or on the magnetic layer, if not.
If necessary, a lubricating layer is formed on the magnetic layer, on the back coat layer, on the protective layer on the magnetic layer, and on the protective layer on the back coat layer. As described above, the lubricating layer is formed by applying a fluorine-based lubricant in the air or spraying it in a vacuum. After the necessary layers have been formed,
Slitting, entanglement, cassette incorporation, and the like are performed by a general method.

[0014]

【Example】

Example 1 A single metal cobalt magnetic layer was formed on a 4.5 μm-thick PET film in advance by oblique deposition at 1800 °, and 100 nm of diamond-like carbon was formed thereon as a protective layer.
Å A non-magnetic support on which a film was formed was prepared. A back coat layer was formed on this non-magnetic support by using the apparatus shown in FIG. 1 on the surface of the non-magnetic support opposite to the magnetic layer. After the inside of the vacuum chamber 2 was evacuated to 2 × 10 ⁻⁵ Torr, the Cu—Al alloy in the crucible 7 was irradiated with an electron gun 8 at an output of 30 kW to form an evaporation atmosphere. The non-magnetic support 4 was run on the cooling can roll 3 at a speed of 10 m / min to form a back coat layer. At this time, oxygen gas was introduced from the nozzles 10 and 10 'at 200 SCCM. Further, both surfaces of the protective layer and the back coat layer were coated with a fluorine-based lubricant so that the thickness of each of the lubricant layers was 30 °, thereby forming a lubricant layer. 8 obtained
It was cut to a width of 8 mm and loaded into a cassette to produce an 8 mm video cassette. The structure of the cross section and the structure of the back coat layer of the obtained magnetic recording medium are as shown in FIG. 3B according to a TEM photograph or electron beam diffraction. The back coat layer is formed of a thin film having a random structure. It had been. The thickness of the back coat layer was 2000 mm.

Example 2 A back coat layer was formed on the same non-magnetic support as used in Example 1 by changing the conditions. Using the apparatus of FIG. 1, a back coat layer was formed on the surface of the non-magnetic support opposite to the magnetic layer. 2 × 10 ⁻⁵ Torr in the vacuum chamber 2
After evacuating to a vacuum, the electron gun 8 was used to irradiate the Cu-Al alloy in the crucible 7 with an electron beam at an output of 30 kW to form an evaporation atmosphere. Non-magnetic support 4 on cooling can roll 3
Was run at a speed of 10 m / min to form a back coat layer. At this time, oxygen gas was introduced from the nozzles 10, 10 'and 11 at 50 SCCM. Further, both surfaces of the protective layer and the back coat layer were coated with a fluorine-based lubricant so that the thickness of each of the lubricant layers was 30 °, thereby forming a lubricant layer. The obtained one was cut into a width of 8 mm and loaded into a cassette to produce an 8 mm video cassette. The structure of the cross section and the structure of the back coat layer of the obtained magnetic recording medium were TE
According to the M-photograph or the electron beam diffraction, as shown in FIG. 3A, the back coat layer was formed of a thin film having a vertical structure. The thickness of the back coat layer is 1900Å
Met.

Example 3 The back coat forming material was changed from Cu-Al alloy to Al, and the back coat layer was formed on the same non-magnetic support as in Example 1 using the apparatus of FIG. 1 under the same conditions as in Example 1. Was formed to produce an 8 mm video cassette. The structure of the cross section and the structure of the back coat layer of the obtained magnetic recording medium are as follows:
According to the TEM photograph or the electron beam diffraction, as shown in FIG. 3B, the back coat layer was formed of a thin film having no structure. The thickness of the back coat layer is 25
It was 00 $.

COMPARATIVE EXAMPLE 1 In the same manner as in Example 1, a single magnetic layer of metal cobalt was formed on a 4.5 μm thick PET film by oblique vapor deposition.
A non-magnetic support was prepared by forming a film of the thickness of 00 and then forming a film of diamond-like carbon thereon as the protective layer by the thickness of 100. A back coat layer was formed on the non-magnetic support by using the apparatus shown in FIG. 4 on the surface of the non-magnetic support opposite to the magnetic layer. After the inside of the vacuum chamber 12 was evacuated to 2 × 10 ⁻⁵ Torr, the Cu—Al alloy in the crucible 17 was irradiated with an electron gun 18 at an output of 30 kW to form an evaporation atmosphere. The non-magnetic support 14 was run on the cooling can roll 13 at a speed of 10 m / min to form a back coat layer. At this time, oxygen gas was supplied from the nozzle 20 for 200 SC.
Introduced in CM. Further, both surfaces of the protective layer and the back coat layer were coated with a fluorine-based lubricant so that the thickness of the lubricating layer became 30 °, respectively, to form a lubricating layer. The obtained one was cut into a width of 8 mm and loaded into a cassette to produce an 8 mm video cassette. According to the TEM photograph or the electron beam diffraction, the back coat layer of the obtained magnetic recording medium was
It was formed from a thin film having a mixed structure of a random structure and a column structure. The thickness of the back coat layer is 2
000Å.

Performance Evaluation The envelope characteristics of the output waveforms of the magnetic recording media obtained in Examples and Comparative Examples were measured by using a device modified from a commercially available 8 mm VTR device. Although the envelope characteristic waveform as shown in FIG. 2A is ideal, the waveform is actually chipped as shown in FIG. Here, the envelope characteristic was obtained by subtracting, from the 100%, the higher chipping rate of the front chipping or the rear chipping at the time of measurement.

The running performance of the magnetic recording media obtained in the examples and comparative examples was evaluated based on the coefficient of friction. The coefficient of friction is measured as follows. That is, temperature 2
At a temperature of 0 ° C. and a humidity of 50% RH, a magnetic tape is wound around a SUS pin having a diameter of 2 mm and a surface roughness of 0.2 S by 90 ° with a tension of 0.1 N from the unwinding side.
The tape is fed at a speed of 18.8 mm / s. The tension is also measured on the winding side, and the friction with the friction pin is calculated from the ratio with the tension on the unwinding side according to Euler's equation to determine the friction coefficient of the magnetic recording medium. Table 1 shows the results.

[0020]

[Table 1]

[0021]

According to the present invention, a magnetic recording medium which can achieve better head touch because cupping of the support can be prevented can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an apparatus that can be used for manufacturing a magnetic recording medium of the present invention.

FIG. 2 is a model diagram showing a missing rate of an envelope waveform.

FIG. 3 is a model diagram showing a cross-sectional structure of a magnetic recording medium obtained by the present invention.

FIG. 4 is a schematic view of an apparatus used for manufacturing a conventional magnetic recording medium.

[Explanation of symbols]

 1, 41 Vacuum evaporation device 2, 42 Vacuum chamber 3, 43 Cooling can roll 4 Non-magnetic support 5, 45 Unwind roll 6, 46 Take-up roll 7, 47 Crucible 8, 48 Electron gun 9, 9 ', 49, 49 'Deposition plate 10, 10', 11, 50 Nozzle

Claims (9)

[Claims] 1. A magnetic recording medium having a magnetic layer having a single or two or more column structure formed on a non-magnetic support by oblique vapor deposition, a vacuum is applied to the surface of the non-magnetic support opposite to the magnetic layer. A magnetic recording medium having a back coat layer formed by film formation and made of a thin film having a non-oblique column structure. 2. The magnetic recording medium according to claim 1, wherein the back coat layer is formed of a thin film having a column structure grown perpendicular to the surface of the non-magnetic support. 3. The magnetic recording medium according to claim 1, wherein the back coat layer is made of a thin film having a random structure. 4. The method according to claim 1, wherein the back coat layer is a metal or metalloid, or is one of an oxide, a nitride, and a carbide of the metal or metalloid. Magnetic recording medium. 5. The metal constituting the back coat layer is A
The magnetic recording medium according to claim 4, wherein the magnetic recording medium further comprises l. 6. The film thickness Tbc of the back coat layer and the film thickness Tm of the magnetic layer have a relationship represented by the following equation.
The magnetic recording medium according to any one of claims 1 to 5, wherein Tbc = Tm ± 2000Å 7. The magnetic recording medium according to claim 1, wherein a lubricating layer exists on the back coat layer. 8. The magnetic recording medium according to claim 1, wherein a protective layer and a lubricating layer are present on the back coat layer. 9. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic support is 4.5 μm or less, and the total thickness of the magnetic recording medium is 6.0 μm or less.
The magnetic recording medium according to any one of claims 1 to 8, wherein