JP2003151122A - Magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in traveling durability and weather resistance and prevented from cupping. SOLUTION: The magnetic recording medium 1 has a magnetic layer 3, a functional layer 4 essentially comprising carbon and a lubricant layer 5 in this order on one face of a nonmagnetic support body 2 and has a cupping preventing layer 6 and a back coat layer 7 in this order on the other face of the support body 2. The cupping preventing layer 6 essentially comprises carbon to compensate the cupping effect of the functional layer 4 essentially comprising carbon which generates a convex state of the medium to the magnetic layer 3 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal magnetic thin film type magnetic recording medium and a method of manufacturing the same, more specifically,
The present invention relates to a magnetic recording medium in which cupping is prevented and a method for manufacturing the same.

[0002]

2. Description of the Related Art As the information society advances, there is a strong demand for higher density magnetic recording media. The metal magnetic thin film type magnetic recording medium does not include a binder in the magnetic layer unlike the coating type magnetic recording medium, and thus the medium has a large saturation magnetization and is suitable for high density recording.

In recent years, the magnetic layer in a magnetic recording medium has been remarkably thinned, and physical or chemical damage to the thinned magnetic layer has a great influence on the reliability of the medium. Regarding this point, in the magnetic recording medium of the metal magnetic thin film type, diamond-like carbon (DL) which is a harder film among carbon films on the magnetic layer is used.
By providing the film C) as a protective layer, physical or chemical damage is prevented, and appropriate running durability and weather resistance are maintained.

That is, referring to FIG. 1, a conventional metal magnetic thin film type magnetic recording medium (11) generally comprises a non-magnetic support.
Magnetic layer (13), DLC layer (14) and lubricant layer on one surface of (12)
(15) in this order, and a back coat layer (17) on the other surface of the non-magnetic support (12). The magnetic layer (13) is formed by the vapor deposition method, the DLC layer (14) is formed by the CVD method or the sputtering method, and the lubricant layer (15) is formed on the DLC layer (14) by the coating method. Further, the back coat layer (17) is formed by a coating method.

However, since the DLC film has a very strong compressive stress, in the above-mentioned layer structure, in the so-called longitudinal magnetic recording medium (11), a cupping (longitudinal magnetic field) which is convex on the magnetic layer (13) side of the medium is formed. (Curvature in the width direction of the recording medium) occurs.

The origin of the compressive stress of this DLC film is considered to be the growth pattern of the diamond structure, as described in Japanese Patent Laid-Open No. 4-132684. That is, as the diamond structure grows in an inversely tapered shape centering on the diamond nuclei captured on the substrate, compressive stress is formed / accumulated inside the film centering on the crystal grain boundaries as the growth progresses. Although the DLC film is not continuous, it also contains a diamond structure, so that a compressive stress is essentially generated. In addition, a DLC film containing more diamond structure will generate a stronger compressive stress.

As described above, the DLC film serves as a protective layer for the magnetic layer, but cupping occurs in the longitudinal magnetic recording medium due to the strong compressive stress of the DLC film. In the manufacturing process of a longitudinal medium, cupping causes instability in running and causes winding disorder and edge damage, which greatly affects product yield, recording / reproducing reliability, and running durability.

Japanese Patent No. 2638113, Japanese Patent Laid-Open No. 9-
In Japanese Patent No. 91681 and Japanese Patent Laid-Open No. 9-54935,
A magnetic recording medium having a DLC film on a magnetic layer is disclosed. However, none of these publications is sufficient to prevent cupping in a thin magnetic layer.

[0009]

Therefore, in a magnetic recording medium of a metal magnetic thin film type, a medium in which a DLC protective layer is provided on a magnetic layer so as to improve running durability and weather resistance and which does not cause cupping is desired. Be done. An object of the present invention is to provide a magnetic recording medium that is excellent in running durability and weather resistance and that prevents cupping, and a method for manufacturing the same.

[0010]

DISCLOSURE OF THE INVENTION As a result of intensive studies by the present inventors, in a magnetic recording medium in which a DLC protective layer is provided on a magnetic layer, a cupping prevention functional layer is provided on the backcoat layer side of a support. As a result, they have found that a magnetic recording medium that is excellent in running durability and weather resistance and does not cause cupping can be obtained, and has reached the present invention.
That is, in order to maintain the flatness of the medium by canceling the cupping action of the DLC protective layer formed on the magnetic layer on the one surface side of the support, which is convex on the magnetic layer side, the present invention provides DL as a cupping prevention function layer on the surface
It is based on forming a C layer.

The present invention has at least a magnetic layer, a functional layer containing carbon as a main component, and a lubricant layer in this order on one surface of the non-magnetic support, and on the other surface of the non-magnetic support, A magnetic recording medium having a cupping prevention functional layer and a back coat layer in this order. The present invention is the above-described magnetic recording medium, wherein the cupping prevention functional layer is provided so as to cancel the cupping action which is convex on the magnetic layer side of the medium by the functional layer containing carbon as a main component. The present invention is the above magnetic recording medium, wherein the cupping prevention functional layer is a layer containing carbon as a main component. The present invention is the above-mentioned magnetic recording medium, wherein the cupping prevention layer is a layer containing carbon as a main component and having a thickness of 0.01 μm or less.

The present invention is the above magnetic recording medium, wherein the magnetic layer is a metal thin film type magnetic layer. The present invention is the above magnetic recording medium, wherein the backcoat layer is formed by coating.

The present invention also provides a step of forming a magnetic layer on one surface of a non-magnetic support by a vapor deposition method, and a functional layer containing carbon as a main component on the magnetic layer by a CVD method or a sputtering method. And a step of forming a lubricant layer on the functional layer containing carbon as a main component by coating, and containing a carbon as a cupping-preventing functional layer on the other surface of the non-magnetic support as a main component. A method of manufacturing a magnetic recording medium, comprising: a step of forming a layer by a vapor phase film forming method; and a step of forming a back coat layer on the cupping prevention functional layer by coating.

According to the present invention, the cupping action which becomes convex on the magnetic layer side of the functional layer containing carbon as a main component on one surface of the non-magnetic support is canceled to maintain the flatness of the medium.
Manufacturing of the magnetic recording medium, wherein the layer containing carbon as the main component on the other surface of the non-magnetic support is formed under the same or similar conditions as the formation conditions of the functional layer containing carbon as the main component. Is the way.

The present invention comprises the steps of forming a magnetic layer on one surface of a non-magnetic support, forming a functional layer containing carbon as a main component on the magnetic layer by a CVD method or a sputtering method, and On the other surface of the magnetic support, carbon is mainly used as a cupping-preventing functional layer so as to cancel the cupping action that is convex on the magnetic layer side of the functional layer containing carbon as a main component and maintain the planarity of the medium. A method of manufacturing a magnetic recording medium, comprising the step of forming a component layer under the same or similar conditions as those of the functional layer containing carbon as the main component.

In the present invention, the functional layer containing carbon as a main component has a function of protecting the magnetic layer from physical damage and a function of preventing oxidation of the magnetic layer. Further, it has a function of improving lubricity, although it is weaker than the lubricant layer.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described with reference to FIGS. FIG. 2 is a sectional view showing an example of the layer structure of the magnetic recording medium of the present invention. In FIG. 2, the magnetic recording medium (1) comprises a magnetic layer (3), a carbon-based functional layer (4), and a lubricant layer on one surface of a non-magnetic support (2).
(5) in this order, and the cupping prevention functional layer (6) and the backcoat layer (7) in this order on the other surface of the non-magnetic support (2).

The material of the non-magnetic support (2) is not particularly limited, and polyethylene terephthalate (PET),
It is selected from polyester resins such as polyethylene naphthalate (PEN), polyamide resins such as aromatic polyamide, and olefin resins such as polyethylene and polypropylene. The thickness of the non-magnetic support is selected from 3 to 12 μm depending on the intended recording time, recording time and the like.

A magnetic layer (3) is provided on one surface of the non-magnetic support (2).
Is formed by a vapor phase film forming method such as vapor deposition or ion plating. As the magnetic material, Co or an alloy containing Co, for example, Co—Ni, Co—Cr, Fe—Co—Ni, C
o-Pt, Co-Fe, etc. are used. In vapor-phase film formation such as vapor deposition, alloys with similar boiling points are used, and multiple vapor depositions with different boiling points are performed. On the other hand, in the case of sputtering or the like, the film is formed with the metal or alloy as it is. For tape-shaped media, oblique vapor phase film formation is performed.

The deposition of the magnetic layer is carried out by
After evacuating to about 0 ^-5 Torr, the magnetic material is melted by an electron gun, and when the whole magnetic material is melted, the non-magnetic support is run along the cooled main roller (cooling can) and the main roller. Starts vapor deposition at the department. At this time, in order to control the magnetic characteristics, an oxidizing gas selected from oxygen, ozone, and nitrous oxide may be introduced into the magnetic layer. For the longitudinal medium, oblique film formation is performed, and the column angle is set to 20 to 50 degrees with respect to the non-magnetic support. On the other hand, in the vertical medium, the crucible is located right below the can, and the opening of the mask is ± 10 degrees or less.

The magnetic layer has a single-layer or multi-layer structure. The thickness of the magnetic layer is about 0.01 to 0.5 μm.

A functional layer (4) (DLC film) containing carbon as a main component is formed on the magnetic layer (3) by a CVD method or a sputtering method. Although there is no problem with the sputtering method, the CVD method that can form a film at high speed is preferable. As the gas used in the CVD method, a gaseous substance such as methane, ethane, propane, butane, ethylene, propylene, and acetylene at room temperature and normal pressure is easy to use, or a liquid raw material may be used.

The gas described above is introduced into the reaction system, a high frequency is applied to create a plasma state, and vapor phase film formation is performed. Specifically, it is provided with a feeding roller, a winding roller, a main roller having plasma-polymerizing partially cylindrical surface-shaped (section arc-shaped) electrode plates facing each other with a gap, and a pass roller if necessary. In a chamber (vacuum chamber), a raw fabric (a roll of a non-magnetic support on which a ferromagnetic metal is vapor-deposited) is placed on a feeding roller, and after exhausting to a pressure lower than 10 ^-5 Torr, a hydrocarbon is discharged. Plasma polymerization is carried out while introducing a predetermined amount of gas so that the reaction pressure becomes 1 to 10 ^-2 Torr. The amount to be introduced depends on the size of the chamber and is appropriately determined as necessary.

The high frequency is not particularly limited, but 1 kHz to
Discharge of about 1 MHz is stable and easy to use. If the frequency is lower than 1 kHz, it is difficult to form a film for a long time, and
It is difficult to obtain a hard film at a frequency higher than z. As a range that is easy to use, 50 kHz to 450 kHz is desirable. The thickness of the film containing carbon as a main component is 2 to
20 nm thick is used, preferably 5-10 nm
It is a degree. If it is thinner than 2 nm, the function of the protective film does not appear, while if it is thicker than 20 nm, there is a problem in terms of spacing loss.

Since it is difficult to apply a lubricant on the DLC film, a post-treatment may be performed after the DLC film is formed. The post-treatment is preferably performed using oxygen or a gas containing oxygen,
For example, oxygen, air, carbon dioxide gas or the like is used. For the post-treatment, a method that is not much different from that used when the DLC film is formed is easy to use. The frequency in the post-treatment is preferably 1 kHz to 40 MHz as in the case of forming the DLC film, and particularly 50 kHz to 1
If it is 3.56 MHz, the effect is likely to be exhibited.

A lubricant layer (5) is formed by coating on the functional layer (4) containing carbon as a main component. As the lubricant, a lubricant containing fluorine, a hydrocarbon-based ester, or a mixture thereof is used.

The lubricant has, for example, R ¹ as a basic structure.
It is represented by -A-R ² . _{^{Wherein, R 1: CF 3 (CF}} 2) n -, CF 3 (CF 2) n (C
_{H 2) m -, CH 3} (CH 2) l -, or a H, A: -COO -, - O-, or -COOCH (C _l H
_2l + 1) CH ₂ is _{^{COO-, R 2: CF 3 (}} CF 2) n -, CF 3 (CF 2) n (C
H ₂ ) _m −, CH ₃ (CH ₂ ) ₁ −, or H. However, unlike R ¹ and R ² , n = 7 to 17 and m = 1 to
Those satisfying 3, 1 = 7 to 30 are preferable. Furthermore, R
^{If 1} and / or R ² is a straight chain, the lubricating effect is large. When n is less than 7, the water repellency effect is low, and when n is greater than 17, a blocking phenomenon occurs between the lubricant and the non-magnetic support or the back coat layer, and the friction is not lowered. Of these, a lubricant containing fluorine is particularly preferable. Further, two or more kinds of such lubricants may be mixed.

These lubricants are used as ketones, hydrocarbons,
A coating liquid is prepared by dissolving it in a solvent such as alcohols. Examples of the ketones include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, cyclohexanone, diethyl ketone and the like. Hydrocarbons include hexane, heptane, octane, nonane, decane,
Examples include normal type of andecan and dodecane, and iso type. Examples of alcohols include methanol, ethanol, propanol, and isopropanol.
The prepared coating liquid is applied onto a film containing carbon as a main component and dried to form a lubricant layer. The thickness of the lubricant layer cannot be measured accurately, but is set to about several nm. The amount of lubricant is adjusted according to the concentration of the coating liquid.

On the other surface of the non-magnetic support (2), a layer containing carbon as a main component (6) (DLC as a cupping prevention layer).
The film is formed in the same manner as in the functional layer (4) containing carbon as a main component. By providing a layer containing carbon as the main component on the other surface of the non-magnetic support (2), a cupping action by the functional layer containing carbon as the main component (4) that is convex on the magnetic layer (3) side of the medium Can be canceled and cupping can be prevented.

The prevention of cupping will be described with reference to FIG. FIG. 3 shows a magnetic layer (3) in a longitudinal magnetic recording medium (1), a functional layer containing carbon as a main component (4), a layer containing carbon as a cupping-preventing functional layer (6), and a back coat layer. FIG. 7 is a cross-sectional view in the width direction that conceptually shows the effect of (7) on the cupping of each layer. Therefore, the layers are depicted separated.

The functional layer (4) containing carbon as a main component is a magnetic layer.
(3) A DLC film vapor-deposited on top of the DLC film, which has a cupping action of being convex on the magnetic layer (3) side by compressive stress.
On the other hand, the carbon-based layer (6) as the cupping prevention layer is a DLC film formed on the lower surface of the support (2) in a vapor phase.
It is a film, and has a cupping action of being convex on the back coat layer (7) side due to compressive stress. In this way, the cupping action which is convex on the magnetic layer (3) side by the functional layer (4) containing carbon as a main component is canceled. Therefore, the carbon-based layer (6) preferably has a thickness equal to or similar to that of the carbon-based functional layer (4), and is the same as the carbon-based functional layer (4). Alternatively, it is preferable that the film is formed under similar conditions.

More specifically, the magnetic layer (3) formed by vapor deposition is weaker than the DLC film, but the back coat layer
(7) It has a cupping action that is convex on the side. The back coat layer (7) formed by coating described below is DLC.
It is weaker than the film, but has a cupping action to make it convex on the magnetic layer (3) side. Therefore, the layer containing carbon as the main component (6) as the cupping prevention layer is the layer (3), (4),
The thickness is preferably 0.01 μm or less so that the cupping effect of (6) and (7) is well neutralized and the flatness of the medium is maintained. Carbon-based layers (6)
More preferable thickness of 0.001 μm to 0.09 μm
Is.

A back coat layer (7) is formed by coating on a layer (6) containing carbon as a main component as a cupping prevention function layer. DLC film prior to coating the back coat layer (7)
(6) After the formation, the same post-treatment as described above may be performed.

For the back coat layer, a back coat paint is prepared using a material and a solvent selected from carbon black, inorganic pigments (such as calcium carbonate), nitrocellulose, phenoxy resin, urethane resin, polyester resin and vinyl chloride resin. Then, the prepared coating material is applied on the other surface of the non-magnetic support and dried to form. As the solvent, methyl ethyl ketone, toluene, cyclohexanone or the like can be used. The thickness of the back coat layer is 0.1 to
0.7 μm, particularly 0.3 to 0.5 μm is preferable. The vapor deposition type magnetic recording medium is manufactured as described above.

[0035]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples.

[Example] A 100% Co 100% magnetic layer having a total thickness of 0.2 μm was formed on one surface of a PEN (polyethylene naphthalate) support having a thickness of 4.5 μm in the same direction 2 by vapor deposition.
Layers were formed. Onto the magnetic layer, ethylene was introduced and a predetermined discharge frequency (50 kHz) was applied to form a plasma polymerized hard carbon film (DLC film) with a thickness of 0.01 μm. D
Post treatment (plasma treatment) for fixing the lubricant to the LC film was performed using O ₂ gas. Post-processed DLC
A lubricant coating solution was applied onto the film by a die nozzle method and dried to form a lubricant layer. The lubricant coating liquid contains the following fluorine-containing compound of succinic acid derivative and fluorine-containing compound of aliphatic ester in the same weight so that the total lubricant concentration becomes 0.5% by weight: MEK / hexane / ethanol = 1
It was a solution dissolved in a mixed solvent of / 2/7.

On the other surface of the support, ethylene was introduced,
A predetermined discharge frequency (50 kHz) was applied to form a plasma polymerized hard carbon film (DLC film) with a thickness of 0.01 μm. Post-treatment (plasma treatment) was performed on the DLC film using O ₂ gas. A backcoat layer dispersion having the following composition was applied onto the post-treated DLC film by a die nozzle method so as to have a thickness after drying of 0.4 μm and dried to form a backcoat layer.

The obtained raw fabric on which each layer has been formed is DVC (1
It was cut into a width of / 4 inch) to obtain a magnetic tape sample.
The magnetic layer has a coercive force (Hc) of 118.5 A / m (150
0 Oe), saturation magnetic flux density (Bs) = 0.55 T (550
0G). The cupping of magnetic tape samples was measured.

(Lubricant) HOOCCH (C ₁₄ H ₂₉ ) CH ₂ COOCH ₂ CH ₂ (CF ₂ ) ₇ CF ₃ CH ₃ (C ₁₆ H ₃₂ ) COOCH ₂ CH ₂ (CF ₂ ) ₇ CF ₃ (Backcoat layer Composition of coating liquid) Carbon black (particle size 80 nm) 10 parts by weight Carbon black (particle size 20 nm) 40 parts by weight Calcium carbonate (particle size 70 nm) 50 parts by weight Nc (nitrocellulose) 40 parts by weight (Asahi Kasei Kogyo KK (BTH1 / 2S) Polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 60 parts by weight Methyl ethyl ketone 800 parts by weight Toluene 640 parts by weight Cyclohexanone 160 parts by weight Polyisocyanate (solid content 50%) 40 parts by weight (Nippon Polyurethane Industry Co .: Coronate L) )

[Comparative Example] A magnetic tape sample was prepared in the same manner as in Example except that the DLC film was not formed on the other surface of the support and the back coat layer was directly formed on the other surface of the support. did. The cupping of magnetic tape samples was measured.

(Method of measuring cupping) A magnetic tape sample having a length of 150 mm, as shown in FIG. 4, has a magnetic layer side face up, and two fulcrums provided at a horizontal position with a center distance of 35 mm. (p) (p) is symmetrically applied, and 0.3g is applied to each of the left and right ends of the tape (w) (w)
did. The deformation thickness (mm) at the midpoint of the tape in the left-right direction in this state was measured by the light-shielding width of laser light. The value of this deformation thickness (mm) was used as the cupping measurement value.

The tape sample of the example had a measured cupping value of 0 mm, and the tape sample of the comparative example had a measured cupping value of 0.8 mm (convex to the magnetic layer side).

[0043]

According to the present invention, in a magnetic recording medium in which a DLC protective layer is provided on a magnetic layer, a cupping prevention function layer is provided on the backcoat layer side of a support, whereby running durability and weather resistance are improved. Provided are a magnetic recording medium which is excellent in heat resistance and does not cause cupping, and a manufacturing method thereof. That is, according to the present invention, both protection of the thin film magnetic layer and maintenance of the medium shape can be achieved. The method of forming the cupping-preventing functional layer on the backcoat layer side of the support according to the present invention is very effective for further thinning of the medium in the future.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a layer structure of a conventional magnetic recording medium.

FIG. 2 is a cross-sectional view showing a layer configuration example of a magnetic recording medium of the present invention.

FIG. 3 is a cross-sectional view in the width direction conceptually showing the effect of each layer on the cupping in the longitudinal magnetic recording medium for explaining the cupping prevention in the present invention.

FIG. 4 is an explanatory diagram of a cupping measurement method.

[Explanation of symbols]

(1): Magnetic recording medium (2): Support (3): Magnetic layer (4): Functional layer containing carbon as a main component (5): Lubricant layer (6): Cupping prevention layer (7): Back coat layer

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 5/851 G11B 5/851 F term (reference) 5D006 AA02 AA05 CC01 CC03 5D112 AA07 AA08 BC01 BC05 BD01 BD02 FA01 FA04 FA09

Claims (9)

[Claims] 1. A non-magnetic support having at least a magnetic layer, a functional layer containing carbon as a main component and a lubricant layer in this order on one surface of the non-magnetic support, and preventing cupping on the other surface of the non-magnetic support. A magnetic recording medium having a functional layer and a back coat layer in this order. 2. The magnetic recording according to claim 1, wherein the cupping-preventing functional layer is provided so as to cancel a cupping action which is convex on the magnetic layer side of the medium by the functional layer containing carbon as a main component. Medium. 3. The magnetic recording medium according to claim 1, wherein the cupping prevention functional layer is a layer containing carbon as a main component. 4. The cupping prevention functional layer has a thickness of 0.01 μm.
A layer containing carbon as a main component and having the following thickness:
4. The magnetic recording medium according to any one of 3. 5. The magnetic recording medium according to claim 1, wherein the magnetic layer is a metal thin film type magnetic layer. 6. The magnetic recording medium according to claim 1, wherein the back coat layer is formed by coating. 7. A step of forming a magnetic layer on one surface of a non-magnetic support by a vapor deposition method, and a step of forming a functional layer containing carbon as a main component on the magnetic layer by a CVD method or a sputtering method. A step of forming a lubricant layer on the functional layer containing carbon as a main component by coating, and a layer containing carbon as a main component as a cupping-preventing functional layer on the other surface of the non-magnetic support in a vapor phase. A method of manufacturing a magnetic recording medium, comprising a step of forming by a film forming method and a step of forming a back coat layer on the cupping prevention functional layer by coating. 8. A non-magnetic support having a functional layer containing carbon as a main component on one surface of the non-magnetic support is canceled so as to cancel the cupping action which is convex toward the magnetic layer side and maintains the flatness of the medium. The method for manufacturing a magnetic recording medium according to claim 7, wherein the layer containing carbon as a main component on the other surface is formed under the same or similar conditions as the formation conditions of the functional layer containing carbon as a main component. . 9. A step of forming a magnetic layer on one surface of a non-magnetic support, a step of forming a functional layer containing carbon as a main component on the magnetic layer by a CVD method or a sputtering method, and the non-magnetic support. On the other surface of the body, carbon is used as the main component of the cupping-preventing functional layer so as to cancel the cupping action which is convex on the magnetic layer side of the functional layer containing carbon as the main component and keeps the flatness of the medium. And a step of forming the layer under the same or similar conditions as those of the functional layer containing carbon as a main component.