JPH0721857B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium suitable for high density recording, and more particularly to a highly reliable magnetic recording medium having excellent durability.

[Conventional technology]

A thin film magnetic recording medium using a magnetic thin film made of a metal, alloy or oxide having ferromagnetism as a magnetic recording layer is more conventional than a coating type magnetic recording medium in which magnetic powder is coated to form a magnetic recording layer. It is well known that the magnetic recording density is further increased. Such a thin film magnetic recording medium is suitable for applications such as a large capacity magnetic disk and a high recording density magnetic tape. However, since the magnetic layer, which is the magnetic recording layer of the thin-film magnetic recording medium, has low mechanical strength, it is easily worn by contact or sliding of the magnetic head during recording and reproduction, which causes noise and erroneous recording. . In order to prevent this, a protective film is provided on the surface of the magnetic layer. As this protective film, for example, Japanese Patent Laid-Open No.
A method for forming a polymer protective film by plasma polymerization as proposed in Japanese Patent Application Laid-Open No. 59-154641, etc.
Examples thereof include those in which a lubricant solution is applied and dried to form a protective film as in JP-A-59-165235, and those in which an organic protective film is formed by vapor deposition as in JP-A-59-175030. Each of the protective films formed by these methods has the effect of reducing wear of the magnetic layer and prolonging the life of the magnetic recording medium, but the stability of the magnetic head running and the long-term stability in a high humidity environment. It has not been possible to fully satisfy the required characteristics at a practical level.

[Problems to be solved by the invention]

As described above, the protective film according to the prior art has not sufficiently satisfied the necessary characteristics at a practical level such as stability of running of the magnetic head, wear resistance, corrosion resistance and reliability in a high humidity environment. Therefore, the inventors of the present invention have evaluated various protective films from the viewpoints of wear resistance and lubricity, and as a result, the amorphous carbon film obtained by plasma decomposition of hydrocarbon is It has been found that the above characteristics are far superior to those of the above-mentioned conventional protective film. However, it has been found that this amorphous carbon film has a drawback that it lacks long-term stability because its lubricity changes and deteriorates over time.

The object of the present invention is that the required properties as a protective film are far superior to those of the above-mentioned conventional protective films, and the lubricity of an amorphous carbon film obtained by plasma decomposition or thermal decomposition of hydrocarbons over time It is an object of the present invention to provide a magnetic recording medium that prevents deterioration, has excellent wear resistance and lubricity for a long period of time, has excellent durability, and is suitable for high-density recording with high reliability.

[Means for Solving Problems] The purpose is to form an amorphous carbon film as a protective film of a magnetic layer, and further to molecularly bond an organic compound layer of a specific composition to the surface of the amorphous carbon film. Is achieved by
Amorphous carbon film is a film in which active species generated by plasma decomposition or thermal decomposition of hydrocarbon gas are rapidly cooled and deposited on the solid surface, and active sites such as unreacted radicals and unsaturated bonds are deposited on the surface. Is considered to have many. It is possible to prevent oxygen and water vapor from reacting by inactivating the organic compound layer by molecularly bonding it to the organic compound layer.

Examples of the method for forming the amorphous carbon film include the following methods.

(1) A plasma CVD method in which a hydrocarbon gas alone or in a mixture with another gas is plasma decomposed and deposited. As a method for generating plasma, microwave discharge, high frequency discharge, direct current discharge or the like can be used. In either case, the substrate side to be deposited is set to a negative potential with respect to plasma,
When the positive ions collide with the deposited film at an energy of 0 eV or more, a hard and wear-resistant amorphous carbon film is obtained.

(2) An ion beam deposition method in which a hydrocarbon gas alone or in a mixture with another gas is ionized by an electron beam or a hollow cathode discharge, and the generated ions are extracted by an electric field to collide with a substrate to be deposited.

(3) A sputtering method in which graphite carbon is used as a target and is sputtered in an inert gas or hydrogen, and deposited on a substrate facing the target.

Amorphous carbon film of the present invention, by plasma or heating
The hydrocarbon gas used when forming by the CVD method or the ion beam deposition method is methane,
Saturated hydrocarbons such as ethane, propane, butane, pentane, hexane and octane, unsaturated hydrocarbons such as ethylene, propylene, butene and hexine, aromatic hydrocarbons such as benzene, toluene, xylene, styrene and ethylbenzene, fluoromethane, difluoromethane Saturated or unsaturated halogen compounds such as trifluoromethane, tetrafluoromethane, difluoroethane, tetrafluoroethylene, hexafluoropropylene, tetrafluorosilane, dichloroethylene and tetrachloroethane, alcohols,
Ketones, ethers, fatty acids and the like can be used alone or in combination.

The thickness of the amorphous carbon film provided as a protective film for the magnetic layer of the present invention is preferably in the range of 30 to 2000Å, and more preferably 50 to 500Å. If the thickness exceeds this range, the spacing loss becomes large and the magnetic conversion characteristics deteriorate, which is not preferable, and if the thickness becomes thin, the effect as a protective film decreases, which is not preferable.

The following methods are available as means for molecularly bonding the organic compound layer to the surface of the amorphous carbon film of the present invention.

(1) After forming an amorphous carbon film by a plasma CVD method or an ion beam deposition method, the reaction container is filled with an organic compound vapor to react active points such as radicals remaining on the film surface with the organic compound.

(2) The amorphous carbon film is plasma-treated to generate radicals on the surface, and then exposed to an organic compound vapor to cause a reaction.

It is preferable that the organic compound be capable of easily binding to radicals on the surface of the amorphous carbon film and stable to oxygen and water. Further, those having lubricity are preferable. Specifically, (a) straight-chain hydrocarbons and their derivatives, (b) saturated fatty acids, and their esters, (c) compounds having a fluorinated alkyl group, (d) perfluoropolyethers and their derivatives. , And so on. In particular, a linear organic compound having a vinyl group, an allyl group, an epoxy group, a halogen or the like at the terminal is more preferable in order to increase the reactivity with the surface radicals of the amorphous carbon film.

Specific compounds of the linear hydrocarbons and their derivatives shown in (a) above include, for example, n-hexane, n-heptane, n-octane, and the like, and derivatives such as 1-hexene, 1-heptene, 1-octene. , 1-hexanol, 1-heptanol, 1-octanol, etc., and saturated fatty acids and their esters shown in (b) above include n-caprylic acid, n-lauric acid, stearic acid, and their methyl groups. Examples of the compound having a fluorinated alkyl group shown in (c) above include perfluoropropyl alcohol, perfluoro-1-butene, perfluorobutyl alcohol, perfluorobutyric acid and the like. In addition, the perfluoropolyethers shown in (d) above and their The conductor of the general formula, (In the formula, X represents an F or CF ₃ group, and n represents 3 to 10.) It is preferable that the organic compound is represented by the following formula.

The thickness of the organic compound layer formed on the surface of the amorphous carbon film of the present invention is preferably in the range of 10 to 200Å, more preferably in the range of 20 to 100Å. If this film thickness is less than 10Å, the stabilization and lubricity of the amorphous carbon film are insufficient, and if it exceeds 200Å, the mechanical strength of the organic compound itself is not so strong, so Sliding contact breaks the organic compound layer and reduces the effect as a lubricity protective film, which is not preferable.

For the magnetic layer of the magnetic recording medium of the present invention, a ferromagnetic thin film made of a metal such as Fe, Co, or Ni, or an alloy or oxide containing them as a main component can be used.

The shape of the magnetic recording medium of the present invention may be a tape, a sheet, a card, a disk or the like, but the tape shape is particularly preferable.

[Action]

The organic compound that is molecularly bonded to the surface of the amorphous carbon film is
It reacts with active parts such as residual radicals on the surface of the amorphous carbon film to stabilize it, and also introduces hydrophobic groups to the surface of the amorphous carbon film to prevent water from adhering to the surface. As a result, the change in lubricity with time can be reduced. Further, the layer of the organic compound that is molecularly bonded to the surface of the amorphous carbon film has good lubricity by itself, so that the friction coefficient can be further reduced.

〔Example〕

 An example of the present invention will be described below in more detail.

(Example 1) The thickness of a Co-Ni alloy on a polyester film having a thickness of 10 μm
0.1 μm was vapor-deposited to form a magnetic layer. This film was attached to the high frequency application side electrode of the internal electrode type high frequency (13.56 MHz) plasma CVD apparatus, and ethylene gas was introduced to adjust the inside of the reaction vessel to 0.005 Torr. Next, apply high frequency power to the electrodes
00 W was applied to generate plasma. A 30 nm thick amorphous carbon film was formed in 1 minute. After stopping the plasma,
Immediately after the introduction of ethylene gas was stopped and the inside of the reactor was evacuated, 1-chlorooctane gas was introduced and left for about 2 hours.

Cut the magnetic tape produced as described above to a width of 8 mm,
The tape was fixed on a still tester using the same cylinder as the actual machine of 8 mm video, and the cylinder was rotated to examine the tape tension. Then, the tape was put in a constant humidity chamber having a humidity of 90%, stored for 1 week, and then the tape tension was measured by the same method as described above.

(Comparative Example 1) After forming a magnetic layer and an amorphous carbon film on a polyester film in the same manner as in Example 1, the film was immediately taken out into the atmosphere, and the same test as in Example 1 was performed.

The test results of Example 1 and Comparative Example 1 described above are shown in Table 1.

As shown in Table 1, in Example 1, the tape tension was low and good lubricity was exhibited, and there was almost no change in the tape tension even in the test for one week or longer continuously. In addition, even after storage in a constant humidity chamber (humidity 90%), there was almost no change in tape tension, indicating good lubrication characteristics. On the other hand, in Comparative Example 1, it was found that the tape tension increased with time and the lubricity deteriorated with time in the sample stored in the constant humidity tank.

(Example 2) A Co film having a thickness of 10 μm was coated with a Co—Ni alloy.
0.1 μm was vapor-deposited to form a magnetic layer. Amorphous carbon film was formed on this film by sputtering graphite carbon in Ar gas atmosphere. For the sputtering, a planar magnetron type DC sputtering device was used, and the cathode voltage was -500V and the current was 2A. Also, the Ar gas pressure is 20 mTor
It was r.

The tape on which the magnetic layer and the amorphous carbon film were formed as described above was placed in a reactor of a high frequency plasma generator having parallel plate electrodes, and Ar gas was introduced at 0.5 Torr to generate plasma for 2 minutes. Immediately after the plasma was stopped, Ar gas was stopped, the inside of the reactor was evacuated, and the crucible containing stearic acid, which had been placed in the reactor in advance, was heated to generate stearic acid vapor. After holding for 10 minutes as it was, the tape was taken out and subjected to a still tester in the same manner as in Example 1 to examine the tape tension. As a result, the tape tension was low as in Example 1, and the characteristics did not change even after storage in a constant humidity tank for 1 week.

(Example 3) Both sides of an Al substrate for an 8-inch magnetic disk were anodized, and iron was sputtered in a mixed gas atmosphere of oxygen and Ar and thermally oxidized to form a γ-iron oxide film having a thickness of 0.15 μm. This substrate was placed in a vacuum container equipped with a magnetron type ion source so as to face the ion source, and methane gas was introduced into the ion source while applying a voltage of -500 V to the substrate to generate ions. The generated ions were accelerated and collided with the substrate to form an amorphous carbon film on the substrate. Next, the ionization is stopped and the low molecular weight perfluoropolyether molecule The steam of n = 4 to 7) was introduced, and it was kept as it was for 1 hour.

Conduct a CSS (contact start stop) test that repeats the cycle of contacting a magnetic disk with a magnetic disk manufactured like steam, rotating the disk to levitate the head, stopping the disk again and contacting the head It was As a result, scratches did not occur on the disk surface even after repeating 30,000 times, and no abrasion powder adhered to the head.
This disk was stored in a 90% RH constant humidity tank for 1 week and then subjected to the same test, but the test result was the same as above.

Comparative Example 2 In Example 3, the disk was taken out after forming the amorphous carbon film, and the CSS test was performed. After repeating 30,000 times, a slight sliding mark was observed on the disk surface, and abrasion powder adhered to the head. The same test was carried out after storing it in a humidity chamber of 90% RH for 1 week, and the magnetic layer was abraded after 20,000 cycles. Has reached.

〔The invention's effect〕

As described in detail above, a protective film of an amorphous carbon film containing carbon as a main component is formed on the magnetic layer according to the present invention,
Further, a thin film magnetic recording medium having a lubricity protective film having a linear organic compound layer molecularly bonded thereon has particularly good wear resistance and lubricity, and does not cause deterioration of those necessary characteristics with time. Therefore, it is possible to obtain a magnetic recording medium which is excellent in durability over a long period of time and which is suitable for high-density recording with high reliability.

Claims (6)

[Claims] 1. In a magnetic recording medium having a ferromagnetic thin film as a magnetic layer, an amorphous carbon film containing carbon as a main component is formed on the magnetic layer, and further the surface of the amorphous carbon film is formed. A magnetic recording medium provided with a lubricity protective film comprising a linear organic compound layer which is molecularly bonded to the amorphous carbon film. 2. An amorphous carbon film is deposited on a magnetic layer by a pyrolysis method of hydrocarbon gas, a plasma decomposition method, an ion beam deposition method, or a sputtering method targeting graphite carbon. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium. 3. The magnetic recording medium according to claim 1 or 2, wherein the film thickness of the amorphous carbon film is in the range of 30 to 2000Å. 4. A straight-chain organic compound layer to be molecularly bonded to an amorphous carbon film, a straight-chain hydrocarbon and its derivative, saturated fatty acid and its ester, a compound having a fluorinated alkyl group, perfluoropolyether and The magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic recording medium comprises at least one selected from derivatives thereof. 5. The linear organic compound layer to be molecularly bonded to the amorphous carbon film has a linear organic compound having at least one group selected from a vinyl group, an allyl group, an epoxy group and a halogen at a terminal. The magnetic recording medium according to any one of claims 1 to 3, which is composed of a compound. 6. The film thickness of the linear organic compound layer to be molecularly bonded to the amorphous carbon film is in the range of 10 to 200Å, any of claims 1 to 5 inclusive. 2. A magnetic recording medium according to item 1.