JPS63205813A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance and sustain wear resistance and lubricity and to improve reliability by providing an amorphous carbon film as a protective film of a thin type magnetic layer and forming a lubricating protective film molecular- bound with a straight chain org. compd. layer further thereon. CONSTITUTION:The amorphous carbon (a-C) film essentially consisting of carbon is formed on a magnetic layer consisting of a thin ferromagnetic material film and the lubricating protective film consisting of the straight chain compd. molecular-bound to the a-C film is further disposed thereon. The a a-C film is formed by a thermal cracking method of gaseous hydrogen, plasma cracking method, ion beam deposition method, etc., and the film thickness thereof is preferably about 30-2000Angstrom . The straight chain org. compd. layer molecular- bound to the surface of the a-C film is a straight chain hydrocarbon and the deriv. Thereof, satd. fatty acid and the thereof, etc., and has a vinyl group, allyl group, epoxy group, etc., at the terminal thereof. The film thickness thereof is preferably in a 10-200Angstrom range. The magnetic recording medium which has the good wear resistance and lubricity, excellent durability for a long period of time and high reliability and permits. high-density recording is obtd. by such constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium suitable for high-density recording, and particularly to a highly reliable magnetic recording medium with excellent durability.

[Conventional technology]

Thin-film magnetic recording media, which use a magnetic thin film made of a ferromagnetic metal, alloy, or oxide as a magnetic recording layer, are more efficient than conventional coated magnetic recording media, in which the magnetic recording layer is made by applying magnetic powder. It is well known that magnetic recording density can be further increased. Such thin film magnetic recording media are suitable for applications such as large capacity magnetic disks and high recording density magnetic tapes. However, the magnetic layer, which is the magnetic recording layer of current 1g film magnetic recording media, has weak mechanical strength and is easily worn out by the contact or sliding of the magnetic head during recording and reproduction, which causes noise and erroneous recording. Ta. In order to prevent this, a protective film is provided on the surface of the magnetic layer. As this protective film, for example, a polymer protective film formed by plasma polymerization as proposed in JP-A-59-154641, a lubricant solution as in JP-A-59-165235, etc. A protective film made by coating and drying, JP-A-59-
Examples include those in which an organic protective film is formed by vapor deposition, as disclosed in Japanese Patent No. 175030. All of the protective films formed by these methods have the effect of reducing wear on the magnetic layer and prolonging the life of the magnetic recording medium, but they do have the effect of reducing the running stability of the magnetic head and long-term stability in high-humidity environments. However, it has not yet reached the point where it fully satisfies the characteristics required at a practical level.

[Problem that the invention seeks to solve]

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

An object of the present invention is to improve the lubricity over time of an amorphous carbon film obtained by plasma decomposition or thermal decomposition of hydrocarbons, which has much better properties as a protective film than the protective films of the prior art described above. The object of the present invention is to provide a magnetic recording medium that prevents deterioration, has good wear resistance and lubricity over a long period of time, has excellent durability, is highly reliable, and is suitable for high-density recording.

[Means for solving the problem] The above purpose is to form an amorphous carbon film as a protective film for the magnetic layer, and to further molecularly bond an organic compound layer of a specific composition to the surface of this amorphous carbon film. This is achieved by

In an amorphous carbon film, active species generated by plasma decomposition or thermal decomposition of hydrocarbon gas are rapidly cooled and deposited on a solid surface, and active sites such as unreacted radicals and unsaturated bonds are deposited on the surface. It is thought that there are many By molecularly bonding an organic compound layer to this to inactivate it, it is possible to prevent oxygen and water vapor from reacting.

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

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

(2) An ion beam deposition method in which a hydrocarbon gas alone or mixed with other gases is ionized using an electron beam or hollow cathode discharge, and the resulting ions are extracted by an electric field and collided with a substrate to be deposited.

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

Hydrocarbon gases used when forming the amorphous carbon film of the present invention by plasma or heating CVD method, ion beam deposition method, etc. include methane, ethane, propane, butane, pentane, hexane, octane, etc. Saturated hydrocarbons, unsaturated hydrocarbons such as ethylene, propylene, butene, hexene, aromatic hydrocarbons such as benzene, toluene, xylene, styrene, ethylbenzene, fluoromethane, difluoromethane, trifluoromethane, tetrafluoromethane, difluoroethane, tetrafluoro Saturated or unsaturated halogen compounds such as ethylene, 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 200 mm, and even more preferably in the range of 50 to 500 mm. If it becomes thicker than this range, the spacing loss will increase and the magnetic conversion characteristics will deteriorate, which is undesirable, and if it becomes thin, the effect as a protective film will decrease, which is undesirable.

The following method can be used to molecularly bond an organic compound layer to the surface of the amorphous carbon film of the present invention.

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

(2) The amorphous carbon film is subjected to plasma treatment to generate radicals on the surface, and then brought into contact with organic compound vapor to cause a reaction.

The organic compound is preferably one that easily bonds with radicals on the surface of the amorphous carbon film and is stable against oxygen and water. Moreover, those having lubricity are preferable. in particular.

Examples include (a) linear hydrocarbons and their derivatives, (b) saturated fatty acids and their esters, (c) compounds having a fluorinated alkyl group, (d) perfluoropolyethers and their derivatives, etc. . In particular, in order to increase the reactivity with surface radicals of the amorphous carbon film, it is more preferable to use a linear organic compound having a vinyl group, allyl group, epoxy group, halogen, etc. at the end.

Specific compounds of the linear hydrocarbons and their derivatives shown in (a) above include n-hexane, n-hebutane, n-octane, etc., and derivatives include 1-hexene, 1-heptene, 1- These include octene, 1-hexanol, 1-heptatool, and 1-octatool.

Examples of the saturated fatty acids and esters thereof shown in (b) above include n-caprylic acid, n-lauric acid, stearic acid, and methyl esters and ethyl esters thereof.

Examples of the compounds having a fluorinated alkyl group shown in (c) above include perfluoropropyl alcohol, perfluoro-1-butene, perfluorobutyl alcohol, and perfluorobutylic acid; The perfluoropolyethers and their derivatives have the general formula (OCF 2
CF +n (wherein, X represents F or CF, a group, and n represents 3-10.

) Preferably, it is an organic compound represented by

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 200, more preferably 20 to 100. This film thickness is 10
If the temperature is lower than that of human body, the stabilization of the amorphous carbon film and the provision of lubricity are insufficient.

If the number of people exceeds 200, the mechanical strength of the organic compound vapor is not very strong, so the organic compound layer is broken by sliding contact with a magnetic head, etc., and its effectiveness as a lubricating protective film is reduced, which is not preferable.

The magnetic layer of the magnetic recording medium in the present invention includes Fe, Co
A ferromagnetic thin film made of metals such as , Ni, or alloys or oxides containing these as main components can be used.

The magnetic recording medium of the present invention may have any shape such as tape, sheet, card, or disk, but tape shape is particularly preferred.

[Effect]

The organic compound that is molecularly bonded to the surface of the amorphous carbon film is
It not only stabilizes by reacting with active parts such as residual radicals on the surface of the amorphous carbon film, but also prevents moisture from adhering to the surface by introducing hydrophobic groups to the surface of the amorphous carbon film. As a result, changes in lubricity over time can be reduced. Further, since the organic compound layer that is molecularly bonded to the surface of the amorphous carbon film has good lubricity by itself, the coefficient of friction can be further reduced.

〔Example〕

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

(Example 1) A C0-Ni alloy was deposited to a thickness of 0.1 μm on a polyester film having a thickness of 10 μm to form a magnetic layer.

This film is used for internal electrode type high frequency (13,56MHz)
It is attached to the high frequency application side electrode of the plasma CVD equipment, and ethylene gas is introduced to control the inside of the reaction vessel to 0.005 Torr.
Adjusted to. Next, high frequency power of 200 W was applied to the electrode to generate plasma.

A 30 nm thick amorphous carbon film was formed in 1 minute. After stopping the plasma, the introduction of ethylene gas was immediately stopped and the inside of the reactor 1 was evacuated, and then 1-chlorooctane gas was introduced and left for about 2 hours.

Cut the magnetic tape prepared as above into a width of 8 mm.
The tape was run on a still testing machine using the same cylinder as the actual 8mm video machine, and the tape tension was examined by fixing the tape and rotating the cylinder. after that.

The tape was placed in a humidity chamber with a humidity of 90% and stored for one week, after which the tape tension was measured in the same manner as 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 tests as in Example 1 were conducted.

The test results of Example 1 and Comparative Example 1 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 during the continuous test of 1 hour or more. Further, even after storage in a humidity chamber (90% humidity), there was almost no change in tape tension, indicating good lubricating properties. On the other hand, in Comparative Example 1, it was found that the tape tension of the sample after storage in a humidity chamber increased over time, and the lubricity deteriorated over time.

(Example 2) A Co-Ni alloy was deposited to a thickness of 0.1 μm on a polyester film having a thickness of 10 μm to form a magnetic layer.

An amorphous carbon film was formed on this film by sputtering in an Ar gas atmosphere using graphite carbon as a target. Sputtering was performed using a planar magnetron type DC sputtering device, with a cathode voltage of -500V and a current of 2A. Further, the Ar gas pressure was set to 20 m Torr.

The tape on which the magnetic layer and 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. Ta.

After the plasma was stopped, the Ar gas was immediately stopped and the inside of the reactor was evacuated, and then a crucible containing stearic acid, which had been placed in the reactor in advance, was heated to generate stearic acid vapor. After holding the tape as it was for 10 minutes, 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 its characteristics did not change even after being stored in a humidity chamber for one week.

(Example 3) Both sides of an Al substrate for an 8-inch magnetic disk were anodized, and iron was sputtered and thermally oxidized in a mixed gas atmosphere of oxygen and Ar to form a γ-iron oxide film with a thickness of 0.15 μm. This substrate was placed in a vacuum container equipped with a magnetron type ion source, facing the ion source, and while a voltage of -500 V was applied to the substrate, methane gas was introduced into the ion source to generate ions. The generated ions were accelerated and collided with the substrate, forming an amorphous carbon film on the substrate. Next, ionization is stopped and low molecular weight perfluoropolyether molecules +C
F2-CF-〇+n, n=4-7) steamed CF.

Qi was introduced and held for 1 hour.

A CSS (contact start-stop) test was conducted in which a magnetic head was brought into contact with a magnetic disk manufactured using steam, the disk was rotated to lift the head into the air, and the disk was stopped again and the head was brought into contact. Ta. The result is.

No scratches appeared on the disc surface even after 30,000 repetitions.
No abrasion powder adhered to the head. This disc, 9
The same test was carried out after storage in a constant humidity chamber at o%RH for one week, and the test results were the same as above.

(Comparative Example 2) In Example 3, after forming the amorphous carbon film, the disk was taken out and subjected to a C8S test. After 30,000 repetitions,
Slight scratches were seen on the disk surface, and abrasion powder adhered to the head. Further, when the same test was performed after storing it in a humidity chamber at 90% RH for one week, wear e reached the magnetic layer after 20,000 cycles.

〔Effect of the invention〕

As explained 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,
Furthermore, thin-film magnetic recording media, which have a lubricating protective film on which a linear organic compound layer is molecularly bonded, have particularly good wear resistance and lubricity, and these necessary properties do not deteriorate over time. Therefore, a magnetic recording medium suitable for high-density recording that has excellent durability and reliability over a long period of time can be obtained.

Claims (1)

[Scope of 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 the amorphous carbon film further comprises: A magnetic recording medium characterized in that a lubricating protective film comprising a linear organic compound layer that is molecularly bonded to the amorphous carbon film is provided on the surface of the magnetic recording medium. 2. The amorphous carbon film was deposited on the magnetic layer by either hydrocarbon gas thermal decomposition method, plasma decomposition method, ion beam deposition method, or sputtering method using graphite carbon as a target. The magnetic recording medium according to claim 1, which is a magnetic recording medium. 3. The magnetic recording medium according to claim 1 or 2, wherein the thickness of the amorphous carbon film is in the range of 30 to 2000 Å. 4. The linear organic compound layer to be molecularly bonded to the amorphous carbon film is composed of linear hydrocarbons and their derivatives, saturated fatty acids and their esters, compounds having fluorinated alkyl groups, perfluoropolyethers and their derivatives. The magnetic recording medium according to any one of claims 1 to 3, characterized in that the magnetic recording medium comprises at least one type selected from among these. 5. The linear organic compound layer to be molecularly bonded to the amorphous carbon film is composed of a linear organic compound having at least one group selected from vinyl group, allyl group, epoxy group, and halogen at the end. A magnetic recording medium according to any one of claims 1 to 3, characterized in that: 6. Any one of claims 1 to 5, characterized in that the thickness of the linear organic compound layer that is molecularly bonded to the amorphous carbon film is in the range of 10 to 200 Å. The magnetic recording medium described in .