JPH07161030A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in lubricating property and wear resistance and having good tribology performance. CONSTITUTION:This magnetic recording medium consists of a thin film magnetic layer, protective film and lubricant layer successively formed on a nonmagnetic substrate. The lubricant layer includes a layer of an aromatic compd. having several basic functional groups in the molecule and a layer of lubricant molecules having acid functional groups on one end of the molecule. The molecules of the lubricant of the lubricant layer having the two-layer structure are fixed to the surface of the magnetic recording medium by an electrostatic interaction with enough strength which does not cause aggregation or spin-off. Thereby, the obtd. medium has excellent lubricating property and wear resistance which realizes decrease in the head floating ting height and high recording density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a high recording density in which a lubricating layer which exhibits a lubricating function is formed by a thin film at a solid contact interface which slides at a high speed.

[0002]

2. Description of the Related Art A thin film magnetic recording medium is usually manufactured by depositing a magnetic metal or its alloy on a non-magnetic substrate by plating, vapor deposition or sputtering. In actual use, the magnetic head and the magnetic recording medium come into contact with each other at high speed and slide, so that the magnetic head may be damaged by wear or the magnetic characteristics may be deteriorated.

As a method for solving such a drawback, it has been proposed to provide a protective film or a lubricating layer on the magnetic layer to reduce static / dynamic friction during contact sliding as much as possible and improve wear resistance. ing. As the protective film, a carbonaceous film,
An oxide film, a nitrogen film, a boride film, etc. are used. A liquid lubricant or a solid lubricant is used as the lubricant, and generally, a perfluoropolyether compound which is a liquid lubricant is applied to the disk surface.

[0004]

When the magnetic recording medium is used, the disk medium is rapidly rotated and accelerated from a stopped state. Along with this, buoyancy is applied to the flying head slider and the head flies. When the power is cut off after use, the motor that rotates the disk medium stops, and the head and medium make contact at high speed and slide.

However, in recent years, in order to increase the areal recording density, it has been required to lower the flying height of the head and increase the speed of disk rotation, and the medium substrate tends to be smoother. It is very effective to provide a liquid lubricant film to reduce the dynamic friction coefficient, but as the liquid lubricant film is made thicker, a meniscus is formed between the head and the disk due to the surface tension of the liquid lubricant. It is known that the sticking phenomenon occurs. For this reason, it has been pointed out that the static friction coefficient increases, and the head is often inoperable while being stuck to the disk.

That is, as the substrate is made smoother in order to reduce the flying height of the head, the liquid lubricant has a serious drawback that the above adsorption phenomenon is very likely to occur, and the film is used to prevent the adsorption. When the thickness is reduced, there is a problem that sufficient durability cannot be obtained. In order to avoid these phenomena, it is proposed to introduce a functional group into the perfluoropolyether compound to improve the binding force of the molecule, or to fix the perfluoropolyether compound to the substrate by ultraviolet irradiation, Further, a solid lubricant that does not fundamentally form a meniscus is desired, and higher fatty acids and metal salts thereof have been proposed for some time.

As a method of introducing a functional group into a perfluoropolyether compound to improve the binding force of molecules, for example, a perfluoropolyether compound having amino groups at both ends and a perfluoropolyether having carboxyl groups at both ends are used. There has been proposed a method of forming a hydrogen bond network by mixing with a polyether compound (JP-A-5-205253). According to this method, an apparent molecular weight is increased due to hydrogen bonds between lubricant molecules, and scattering due to rotation of the disk is less likely to occur, but the hydrogen bond network formed in this case is three-dimensional. Therefore, like gels, molecules are connected three-dimensionally and their free movement is suppressed, so a thick film (about 100Å) must be used to obtain sufficient lubrication performance. However, if a thin film (50 Å or less) is used in response to the demand for a low flying height of the head, it is difficult to obtain sufficient lubricity because free movement of molecules is suppressed.
Further, for the purpose of fixing a perfluoropolyether compound having a carboxyl group or an acetyl group at both ends,
It has been proposed to provide a coating film of polyamide as a base on the protective film (JP-A-1-134714). However, since the polyamide as the base layer is a high molecular weight polymer, the thickness of the base layer is 50- Since 200Å is appropriate and the film thickness of the entire lubricating layer becomes large, it is difficult to realize a low flying height of the head.

A method of fixing a perfluoropolyether compound to a substrate by irradiation with ultraviolet rays (eg, H. Ohtani et.
al., Proceedings of Japan International Tribology
Conf., 1689 (1990).) Does not control at which position in the lubricant molecule the bond is formed, and forms a chemical bond everywhere between the lubricant molecule and the substrate or between the lubricant molecules. However, since the fixation of the lubricant molecules has a trade-off relationship with the lubrication performance, if the fixation is prioritized, satisfactory lubricity cannot be obtained.

On the other hand, solid lubricants such as higher fatty acids and metal salts thereof have a stable solid state at room temperature, and therefore, when applied on a disk, a part of the coating film is likely to crystallize and aggregate. was there. Especially when the substrate is smoothed, the tendency of aggregation is remarkable. If the agglomeration occurs, the coating thickness becomes non-uniform, which increases the possibility that the head and the disk come into direct contact with each other, and may cause the head to become dirty or the head to become unstable in flight. In order to prevent the solid lubricant from agglomerating and suppress the spin-off, it is necessary to effectively bond and bond the lubricant molecules to the substrate. As a measure for fixing the lubricant layer molecules to the substrate, a long chain alkyl group is a siloxane. Method of fixing by bonding (Japanese Patent Laid-Open No. 2-1037)
21, JP-A-2-103722). However, the method of fixing the lubricating layer by covalent bonding suppresses the movement of molecules, and the lubricity is insufficient. This is because fixing the lubricant has a trade-off relationship with the lubricating performance.

The fixing system is ideally a reversible fixing method in which the lubricant molecules interact with the substrate with sufficient strength to prevent agglomeration, and the fixing does not have a trade-off relationship with the lubricating performance. Target. The present invention aims to obtain a magnetic recording medium on which a lubricating layer is formed, which exhibits excellent lubricity even when it is a thin film, and in which lubricant molecules do not aggregate. It was achieved by designing.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having a lubricating layer which exhibits lubricity and wear resistance for a long period of time and which has no aggregation of lubricant molecules. The purpose is to provide a magnetic recording medium in which a thin film magnetic layer, a protective film and a lubricating layer are sequentially formed on a non-magnetic substrate, wherein the lubricating layer is an aromatic compound having a plurality of basic functional groups in its molecule. It is achieved by a magnetic recording medium characterized in that it comprises a layer of compounds and a layer of lubricant molecules having acidic functional groups only at one end.

The present invention will be described in detail below. Figure 1
1 shows a structure of a magnetic recording medium in which a magnetic layer 2, a protective film 3 and a lubricating layer are sequentially formed on a non-magnetic substrate 1. At least a part of the aromatic compound 5 in the lubricating layer is fixed to the surface of the protective film by binding its basic functional group with the acidic functional group 4 on the surface of the protective film, and the acidic functional group at the end of the lubricant molecule 6 is attached. Shows that the long chain skeleton of the lubricant molecule forms an ideal lubricating layer structure with the protective film surface facing upwards by binding with other basic functional groups of the aromatic compound. ing.

In forming the lubricating layer on the magnetic recording medium, an aluminum alloy plate or a glass substrate provided with a nickel-phosphorus layer formed by an electroless plating method is usually used as the non-magnetic substrate. A ceramic substrate, a resin substrate or the like can also be used. A thin film magnetic layer of cobalt, cobalt alloy, etc. is formed on a non-magnetic substrate,
It is formed by an electroless plating method, a sputtering method, or the like, directly or through an undercoat layer if necessary. The film thickness of the thin film magnetic layer is determined by the characteristics required for the magnetic recording medium, and is usually 200 to 1500Å. As the protective film, a carbonaceous film such as amorphous carbon or hydrogenated carbon is preferably used and is formed by a sputtering method, an ion plating method, a plasma polymerization method or the like, and usually 50 to 50
It is used with a film thickness of 500Å, preferably 100 to 300Å. When a hydrogenated carbon film is used as the carbonaceous film,
In order to enhance the bonding force with the lubricating layer, it is recommended to perform surface treatment by irradiating ultraviolet rays in an oxygen-containing gas atmosphere.

The lubricant layer formed on the magnetic recording medium of the present invention comprises an aromatic compound having a plurality of basic functional groups in the molecule and a lubricant molecule having an acidic functional group only at one end on the protective film. Are sequentially laminated, and the ratio of the aromatic compound to the lubricant molecule is slightly different depending on the kinds of the aromatic compound and the lubricant molecule used, but is usually 1:
It is 10 to 5: 1, preferably 1: 5 to 2: 1.

The aromatic compound having a plurality of basic functional groups in the molecule has a skeleton of a monocyclic aromatic compound such as phenyl, a polycyclic aromatic compound such as naphthalene or biphenyl, or a heterocyclic compound, and an amino group or imino. A group in which a plurality of basic functional groups such as groups are substituted with a nucleus is used. It is desirable that three or more basic functional groups in the aromatic compound be present in the molecule in order to form a molecular group centered on the aromatic compound.
Further, when the molecular size of the aromatic compound is too large, the formed molecular population becomes large and the film thickness of the lubricating layer becomes large. Therefore, as the aromatic compound, the skeleton part excluding the basic functional group is used. The molecular weight is preferably 600 or less. This is approximately the molecular size corresponding to polycyclic aromatic compounds such as phthalocyanine.

As the lubricant molecule having an acidic functional group, higher fatty acid or the like is used. The long-chain molecular skeleton subsequent to the functional group is preferably a branched or straight-chain saturated or unsaturated higher aliphatic hydrocarbon chain having 8 or more carbon atoms, the higher chain containing an aromatic residue or a hetero atom. Aliphatic hydrocarbon chain,
Alternatively, a long-chain molecular skeleton in which some or all of the higher aliphatic hydrocarbon chains form a polyether chain, or the like, can be selected as long as it has a lubricating action regardless of the type of bond. In addition, when the number of basic functional groups of the aromatic compound is relatively small with respect to the molecular size (for example, less than 2 per aromatic ring), in order to form a denser lubricating layer, the lubricant molecule Preferably has a plurality of long-chain molecular skeletons.

In the lubricating layer formed on the magnetic recording medium of the present invention, the lubricant molecule is formed by the acidic functional group at the terminal,
Some of the basic functional groups in the aromatic compound that form a bond with the basic functional group in the aromatic compound due to electrostatic interaction and are not involved in the bonding with the lubricant molecule are By interacting with an acidic functional group or the like of the protective film to be attached, in cooperation with the interaction of the aromatic ring of the aromatic compound with the protective film, it works to enhance the binding force between the protective film and the lubricating layer. . If the lubricant molecules are prevented from crystallizing or agglomerating by the bond due to electrostatic interaction formed around the aromatic compound, and if the apparent molecular weight of the molecular group formed by the bond is a huge molecular weight like gel. No
Since the size of the molecular group formed around the aromatic compound is a size suitable for exhibiting lubricity, it has an appropriate degree of freedom as a molecular group and even a thin film of about several tens of liters Excellent lubrication performance can be realized.

In order to form a group of molecules suitable for expressing lubricity in the above-mentioned lubricating layer, it is important that the acidic functional group exists only at one end of the lubricant molecule. When the acidic functional group exists at both ends or in the middle of the lubricant molecular chain other than one end, it binds to other aromatic compounds at a distance from the aromatic compound located at the center of the molecular group. As a result, a three-dimensional gel-like network structure is obtained, resulting in impairing good lubricity.

Further, since the bond fixing the lubricant molecules to the solid surface is a reversible bond mode called electrostatic interaction, it has a great feature that it self-repairs even if the lubricant film is broken by impact. The lubricating layer of the present invention has not only excellent lubricity but also excellent durability. Suppression of aggregation can be achieved by using a covalent bond such as a siloxane bond, but because the bonding mode is irreversible,
Once fractured, the bond at that portion cannot be restored, and the portion from which the lubricant has been once removed loses lubricity thereafter, resulting in insufficient durability.

In the magnetic recording medium of the present invention, not only the lubricant molecules in the lubricating layer form a group of molecules in a very small unit to prevent large crystallization and aggregation, but as shown in FIG. Since a minute concavo-convex is formed on the surface of the lubricating layer by the group of molecules, the frictional resistance becomes smaller due to the reduction of the contact area between the head and the lubricating layer, and the degree of freedom of each molecule in the group of molecules makes the monomolecular film It exhibits excellent lubricity with a very thin film thickness.

To form a lubricating layer on the protective film, an aromatic compound having a plurality of basic functional groups in the molecule is attached to the protective film to form a layer of the aromatic compound, and then a lubricant molecule is formed. It is done by stacking layers. The formation of each layer is
It is carried out by immersing the disk in a solution of an aromatic compound or a lubricant molecule, and a method of forming a coating by contacting the disk surface with a tape or the like impregnated with the solution under a load, to form a pad on the disk surface. A method of applying while rotating or a spray method can be used. The concentration of the solution varies depending on the type of aromatic compound or lubricant molecule and the type of solvent, but is usually 0.1 to
Used at 5 g / l. Further, by applying heat treatment or the like to the applied lubricating layer, it is possible to effectively form a bond and more firmly fix the lubricating layer to the protective film.

The formation of the aromatic compound layer on the protective film is as follows.
This can be confirmed, for example, by rinsing the disc with a solvent. As the solvent, it is preferable to use the same solvent as the solution used when laminating the lubricant molecule layer in the next step. If the underlayer of the aromatic compound is fixed on the disk without being lost even after rinsing with a solvent, a layer of lubricant molecules may be laminated on the layer of the aromatic compound to form a two-layer structure. it can.

The thickness of the aromatic compound layer is preferably 5 to 30 Å, the lubricant molecule layer is preferably 10 to 40 Å, and the total thickness of the lubricating layer is preferably 15 to 60 Å.

[0024]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 A magnetic disk having a diameter of 3.5 inches, in which a chromium underlayer (2000 Å), a magnetic thin film of cobalt alloy (400 Å) and a carbon protective film (300 Å) were formed on a smooth aluminum alloy substrate by a diamino method, was used. After immersing in a methanol solution containing benzidine at a concentration of 1 mmol / l and then withdrawing, a uniform coating film having a thickness of 18Å was formed on the surface of the disk. The film thickness was measured by ellipsometry. When the disk was dipped in a chloroform solution for 5 minutes and then pulled up at a speed of 2 mm / sec, the thickness of the coating film was hardly changed, and it was confirmed that diaminobenzidine was fixed on the protective film.

The disc on which diaminobenzidine was fixed was treated with β- (N, N-diheptadecylaminocarbonyl).
A lubricating layer having a thickness of 31 Å was formed by immersing in a chloroform solution containing propionic acid at a concentration of 2 mmol / l, pulling it up, and baking at 130 ° C. for 1 hour. Lubricating performance and cohesiveness tests were conducted on the disks having a lubricating layer. As a test of the lubrication performance, a thin film head was used to perform a continuous sliding test under the conditions of a load of 9.5 gf and a sliding linear velocity of 0.32 m / sec (radius 30 mm, 100 rpm), and the frictional force was measured. As the cohesiveness test, the disks were left in an environment of temperature 25 ° C. and humidity 40% and at temperature 60 ° C. and humidity 80% for the period described in Table 1, and observed for coagulation and crystal formation with an optical microscope. The results are shown in Table 1.

Two kinds of discs having a layer of diaminobenzidine (underlayer) and a layer of β- (N, N-diheptadecylaminocarbonyl) propionic acid were prepared by the same method as described above. The underlayer thickness and the total lubricating layer thickness of each disk were 22Å and 60Å and 7Å and 28Å, respectively. When these discs were rinsed with a chloroform solution, the thickness of the remaining coating film was 21Å and 8Å. From the above results, it was confirmed that the lubricating layer of this example had a two-layer structure in which a layer of lubricant molecules was formed on the base layer of diaminobenzidine.

Example 2 A disk similar to that of Example 1 was prepared by adding 1 part of diaminobenzidine.
After soaking in a methanol solution containing a concentration of mmol / l,
By pulling up, a uniform coating film having a thickness of 8Å was formed on the surface of the disk. When the disc was rinsed with a chloroform solution, it was confirmed that the film thickness of the coating film was almost unchanged and diaminobenzidine was fixed on the protective film.

A disk having diaminobenzidine fixed thereto was subjected to a dipping method to form a uniform lubricating layer having a thickness of 24Å by using a chloroform solution containing stearic acid at a concentration of 2 mmol / l. With respect to the disk on which the lubricating layer was formed, the lubrication performance and cohesiveness were tested in the same manner as in Example 1. The results are shown in Table 1.

By the same method as described above, disks each having a diaminobenzidine layer (underlayer) and a stearic acid layer formed by 7Å and 24Å, respectively, were produced. When this disk was rinsed with a chloroform solution, the thickness of the remaining coating film was 9Å. From the above results, it was confirmed that the lubricating layer of this example had a two-layer structure in which a layer of lubricant molecules was formed on the base layer of diaminobenzidine.

Comparative Example 1 A chloroform solution containing β- (N, N-diheptadecylaminocarbonyl) propionic acid at a concentration of 1 mmol / l was used to dip the surface of a disk similar to that of Example 1 by the dipping method. A 28 Å lubricating film was formed. With respect to the disk on which the lubricating film was formed, the lubrication performance and cohesiveness were tested in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 Using a chloroform solution containing stearic acid at a concentration of 3 mmol / l, a lubricating film having a thickness of 16 Å was formed on the surface of the same disc as in Example 1 by the dipping method. With respect to the disk on which the lubricating film was formed, the lubrication performance and cohesiveness were tested in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 Using a chloroform solution containing diaminobenzidine at a concentration of 1 mmol / l, a lubricating film having a thickness of 21 Å was formed as in Example 1. With respect to the disk on which the lubricating film was formed, the lubrication performance and cohesiveness were tested in the same manner as in Example 1. The results are shown in Table 1.

[0033]

[Table 1]

[0034]

EFFECTS OF THE INVENTION According to the present invention, a thin film (almost a monomolecular film thickness) has excellent lubricity and wear resistance, and moreover it is possible to maintain the lubricant molecules for a long time without agglomerating. It is possible to obtain a magnetic recording medium having a high recording density, which is reliable and has a long term, and which has a lubricating layer capable of achieving the above.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view of a magnetic recording medium of the present invention.

[Explanation of symbols]

 1 Nonmagnetic Substrate 2 Magnetic Layer 3 Protective Film 4 Acidic Functional Group on Protective Film Surface 5 Aromatic Compound Having Basic Functional Group 6 Lubricant Molecule Having Acidic Functional Group at Terminal

Claims (5)

[Claims] 1. A magnetic recording medium in which a thin film magnetic layer, a protective film and a lubricating layer are sequentially formed on a non-magnetic substrate, wherein the lubricating layer has an aromatic compound having a plurality of basic functional groups in its molecule. Recording medium and a layer of lubricant molecules having an acidic functional group only at one end thereof 2. The magnetic recording according to claim 1, wherein the aromatic compound has three or more amino groups or imino groups as basic functional groups, and the skeleton portion excluding the basic functional groups has a molecular weight of 600 or less. Medium 3. The magnetic recording medium according to claim 1, wherein the lubricant molecule has a carboxyl group as an acidic functional group at the terminal and has 8 or more carbon atoms. 4. The protective film is a carbonaceous film.
Magnetic recording medium according to any one of 5. The magnetic recording medium according to claim 1, wherein the thickness of the aromatic compound layer is 5 to 30 Å.