JPH0766529B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention is a so-called magnetic thin film formed on a non-magnetic support as a magnetic layer by a technique such as vacuum thin film forming technology such as vacuum deposition or sputtering. The present invention relates to a ferromagnetic metal thin film type magnetic recording medium.

[Outline of Invention]

The present invention relates to a magnetic recording medium comprising a ferromagnetic metal thin film formed as a magnetic layer on a non-magnetic support, and a ferromagnetic metal thin film as a magnetic layer is lubricated with a perfluoroalkylcarboxylic acid ester and a sulfur-based extreme pressure agent. The purpose of the present invention is to provide a magnetic recording medium which is adhered as an agent, exhibits excellent running properties, wear resistance, and durability under all conditions of use, and continues to have these lubricating effects.

[Conventional technology]

Conventionally, γ-on a non-magnetic support has been used as a magnetic recording medium.
Fe ₂ O _3, containing _{Co γ-Fe 2 O 3,} Fe 3 O 4, containing Co Fe ₃ O
₄ , γ-Fe ₂ O ₃ and Fe ₃ O ₄ Bertride Compounds, Co-containing Bertride Compounds, Oxide Ferromagnetic Powders such as CrO ₂ or Alloy Magnetic Properties Containing Fe, Co, Ni, etc. as Main Components A coating type magnetic recording medium prepared by coating and drying a magnetic coating material in which a powder magnetic material such as a powder is dispersed in an organic binder such as a vinyl chloride-vinyl acetate copolymer, polyester resin or polyurethane resin Widely used.

On the other hand, with the increasing demand for high-density magnetic recording, co-magnetic metal materials such as Co-Ni alloys are coated with polyester by plating or vacuum thin film forming technology (vacuum evaporation method, sputtering method, ion plating method, etc.). Directly deposited on a non-magnetic support such as a film or polyimide film,
A so-called ferromagnetic metal thin film type magnetic recording medium has been proposed,
It is getting attention. This ferromagnetic metal thin film type magnetic recording medium is not only excellent in coercive force and squareness ratio and excellent in electromagnetic conversion characteristics at short wavelengths, but it is also possible to make the thickness of the magnetic layer extremely thin so that recording demagnetization is possible. Also, there are various advantages such as a remarkably small thickness loss at the time of reproduction and an increase in the packing density of the magnetic material because it is not necessary to mix an organic binder which is a non-magnetic material in the magnetic layer.

However, in the above-mentioned ferromagnetic metal thin film type magnetic recording medium, since the smoothness of the magnetic layer surface is extremely good,
The substantial contact area becomes large, the adhesion phenomenon (so-called sticking) easily occurs, the friction coefficient becomes large, and the like, and there are many defects in durability and running property, and improvement thereof is a major issue. In general, a magnetic recording medium must be placed in a high-speed relative motion with a magnetic head in the process of recording / reproducing a magnetic signal, and at that time, the running must be performed smoothly and in a stable state. Further, it is preferable that wear and damage due to contact with the magnetic head be as small as possible.

Therefore, for example, it has been attempted to improve the durability and the running property by applying a lubricant to the surface of the magnetic layer of the magnetic recording medium, that is, the surface of the ferromagnetic metal thin film to form a protective film.

[Problems to be solved by the invention]

By the way, when the protective film is formed by applying the lubricant as described above, the protective film exhibits good adhesion to the ferromagnetic metal thin film which is the magnetic layer and exhibits a high lubricating effect. Is required. Further, these adhesion and lubricating effect must be excellent under high temperature and high humidity conditions such as in tropical regions and subtropical regions, and under low temperature conditions such as cold regions.

However, the operating temperature range of the lubricants that have been widely used in the past is limited, and in particular, many of them solidify or freeze at a low temperature such as 0 to -5 ° C, so that the lubricating effect should be sufficiently exhibited. I couldn't. Furthermore, there is a problem that the lubricant is gradually scraped off by the magnetic head due to the insufficient adhesion of the lubricant to the ferromagnetic metal thin film, and the effect is rapidly reduced.

Therefore, it is an object of the present invention to provide a magnetic recording medium that maintains adhesion and lubricity under any use conditions and that has a long-lasting lubrication effect.

[Means for Solving Problems] The inventors of the present invention have earnestly studied that they do not achieve the above-mentioned object, and as a result, have a long-chain alkyl group or a double bond in the ester portion of perfluoroalkylcarboxylic acid. By combining a perfluoroalkylcarboxylic acid ester into which an alkyl group, or any of branched alkyl groups is introduced, and a sulfur-based extreme pressure agent, an excellent lubricating action is exhibited as compared with the case of using it alone, At the same time, the inventors have found that it is possible to expand the operating temperature range and improve the sustainability, and have completed the present invention, in which a ferromagnetic metal thin film is formed on a non-magnetic support, The magnetic metal thin film is coated with a lubricant layer containing a perfluoroalkylcarboxylic acid ester and a sulfur-based extreme pressure agent.

The perfluoroalkylcarboxylic acid ester used in the present invention has the general formula C _n F _{2n + 1} COOR (wherein n represents an integer of 6 to 10 and R represents a carbon-hydrogen group having 9 to 25 carbon atoms). ), Which can be easily synthesized by reacting a perfluoroalkylcarboxylic acid with a corresponding alcohol.

In the above perfluoroalkylcarboxylic acid ester, the carbon number n of the perfluoroalkylcarboxylic acid moiety is
It is preferably in the range of 6-10. This carbon number n is 6
If it is less than the above range, the lubrication effect is insufficient, and conversely, if the carbon number exceeds 10, solidification occurs in the low temperature range, and therefore the lubrication effect under low temperature conditions deteriorates. The same applies to the number of carbon atoms of the hydrocarbon group of the ester portion, and in the above general formula, the number of carbon atoms of the hydrocarbon group R is preferably 1 to 25, more preferably 9 to 25. . If the number of carbon atoms in the hydrocarbon group R is less than 9, the lubricating effect will be insufficient, and if it exceeds 25, the lubricating effect at low temperatures will be lost. The hydrocarbon group R may be a long chain alkyl group, a branched alkyl group or an alkylene chain having a double bond.

On the other hand, the extreme pressure agent used in the present invention reacts with a metal surface due to frictional heat accompanied when a metal contact is partially generated in the boundary lubrication region, and forms a reaction product film to cause friction / friction. It has a function of preventing wear.

Examples of the sulfur-based extreme pressure agent used in the present invention include sulfur macadam whale oil, sulfurized dipentene and other mineral oils having unsaturated bonds, fats and oils, sulfurized fats and oils produced by adding sulfur to a fatty acid, and disulfide. Benzyl, diphenyl disulfide,
Disulfides such as di-t-butyl disulfide, di-sec-butyl disulfide, di-n-butyl disulfide, di-t-octyl disulfide, diethyl disulfide, dibenzyl sulfide, diphenyl sulfide, divinyl sulfide. , Dimethyl sulfide, diethyl sulfide, di-t-butyl sulfide, di-sec-butyl sulfide, di-n-butyl sulfide, etc., monosulfides, dimethyl trisulfide, di-t-butyl trisulfide, polysulfide di- Polysulfides such as t-nonyl and olefin polysulfide, general formula (In the formula, R represents a hydrocarbon group.), Thiocarbonates and elemental sulfur.

The compounding ratio of the above-mentioned perfluoroalkylcarboxylic acid ester and the sulfur-based extreme pressure agent is 30:70 to 70:30 by weight.
Is preferred. In addition to the above-mentioned perfluoroalkylcarboxylic acid ester and sulfur-based extreme pressure agent, a conventionally known lubricant may be used in combination.

As a method for adhering a lubricant layer containing these perfluoroalkylcarboxylic acid ester and a sulfur-based extreme pressure agent to a ferromagnetic metal thin film, a solution obtained by dissolving the above lubricant in a solvent is used as a ferromagnetic metal thin film. It may be applied or sprayed on the surface, or conversely, the ferromagnetic metal thin film may be dipped in this solution and dried.

Here, the coating amount is preferably from ^{0.5mg / m 2 ~100mg / m 2} , and more preferably ^{1mg / m 2 ~20mg / m 2} .
If this coating amount is too small, the effects of lowering the friction coefficient and improving wear resistance and durability will not be apparent, while if it is too large, sticking phenomenon will occur with the ferromagnetic metal thin film of the sliding member. On the contrary, the running performance becomes worse.

The magnetic recording medium to which the present invention is applied is one in which a ferromagnetic metal thin film is provided as a magnetic layer on a non-magnetic support. Here, as the material of the non-magnetic support, polyesters such as polyethylene terephthalate, Polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide and polyamideimide,
Examples include light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass. The form of this non-magnetic support may be any of film, sheet, disk, card, drum and the like.

The ferromagnetic metal thin film that is the magnetic layer is formed as a continuous film by a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method, and a sputtering method.

In the above vacuum evaporation method, a ferromagnetic metal material is evaporated by resistance heating, high frequency heating, electron beam heating, etc. under vacuum of 10 ^-4 to 10 ^-8 Torr, and an evaporated metal (ferromagnetic metal material) is deposited on a disk substrate. In order to obtain a high coercive force, an oblique evaporation method in which the ferromagnetic metal material is obliquely evaporated on the substrate is generally adopted. Alternatively, the above vapor deposition is also included in order to obtain a higher coercive force.

The ion plating method is also a type of vacuum deposition method, and DC glow discharge or RF glow discharge is caused in an inert gas atmosphere of 10 ^-4 to 10 ^-3 Torr to evaporate the ferromagnetic metal material during discharge. It is to let.

The above-mentioned sputtering method is a method of causing a glow discharge in an atmosphere containing 10 ⁻³ to 10 ⁻¹ Torr of argon gas as a main component, and knocking out atoms on the target surface with the generated argon gas ions. DC 2
There are a polar and tripolar sputtering method, a high frequency sputtering method, a magnetron sputtering method using magnetron discharge, and the like. When this sputtering method is used, a base film of Cr, W, V or the like may be formed.

In any of the above methods, a base metal film such as Bi, Sb, Pb, Sn, Ga, In, Cd, Ge, Si, and Tl is formed on the substrate in advance, and the substrate surface is formed. By forming the film in the vertical direction, a magnetic layer having no magnetic anisotropy orientation and excellent in-plane isotropy can be formed, which is suitable for a magnetic disk, for example.

When forming a metal magnetic thin film by such a vacuum thin film forming technique, Fe, Co,
In addition to Ni and other metals, Co-Ni alloys, Co-Pt alloys, Co-Ni-Pt
Alloy, Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Co-
Examples thereof include B alloys, Co-Ni-Fe-B alloys, Co-Cr alloys, and those containing metals such as Cr and Al. Particularly, when a Co-Cr alloy is used, a perpendicular magnetization film is formed.

The thickness of the magnetic layer formed by such a method is 0.04
It is about 1 μm.

[Action]

The lubricant layer containing the perfluoroalkylcarboxylic acid ester and the sulfur-based extreme pressure agent adheres to the ferromagnetic metal thin film to exert a good lubricating effect and reduce the friction coefficient. In particular, perfluoroalkylcarboxylic acid ester exerts a good lubricating effect even at a low temperature, and the combined use of an extreme pressure agent improves the adhesion to the ferromagnetic metal thin film and maintains the lubricity.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Synthesis Example 1. Nonadecafluorodecanoic acid isostearyl ester An ester reaction was carried out by isostearyl alcohol and nonadecafluorodecanoic acid in toluene using p-toluenesulfonic acid as a catalyst, that is, after heating under reflux for 1 hour, 3
Water was removed from the solvent over a period of time, and toluene was further removed under reduced pressure using an evaporator, followed by vacuum distillation for purification. (Note that isostearyl alcohol was synthesized by converting commercially available isostearic acid to n-butyl ester and then reducing it with lithium aluminum hydride.) The boiling point bp of the obtained fraction was 140 to 145 ° C / 0.2 mmHg. It was

In addition, the product was confirmed by infrared spectroscopy (IR), nuclear magnetic resonance analysis (NMR), and mass spectrometry (MASS).
As a result, absorption characteristic of CF bond from 1210 to 1380 cm ^-1 ,
This structure was determined by the absorption of ester at 1780 cm ^-1 and the absorption of CH stretching vibration at 2910 cm ^-1 and the molecular ion peak M ⁺ at 765 in the mass spectrum by the chemical ion method.

Synthesis Example 2. Pentadecafluorodecanoic acid isostearyl ester By the same method as in Synthesis Example 1 above, isostearyl alcohol and pentadecafluorooctanoic acid in toluene,
The reaction was performed using p-toluenesulfonic acid as a catalyst.

bp 120 to 134 ° C (0.2 mmHg) IR 1200 to 1400 cm ^-1 1780 cm ^-1 2920 cm ^-1 M ⁺ 665 Synthesis example 3. Pentadecafluorooctanoic acid isononyl ester (CH ₃ ) ₃ C (CH ₂ ) CH (CH ₃ ) CH ₂ CH ₂ OCO (CF ₂ ) ₆ CF _{3 In} the same manner as in Synthesis Example 1 above, isononyl alcohol and pentadecalfluorooctanoic acid were added to toluene in p
-Reacted with toluene sulfonic acid as catalyst.

bp 94 ° C (0.2mmHg) IR 1210 to 1390cm ^-1 1785cm ^-1 2850 to 2960cm ^-1 M ⁺ 539 Synthesis example 4. Pentadecafluorooctanoic acid linoleyl ester CH ₃ (CH ₂ ) ₃ (CH ₂ CH = CH) ₂ (CH ₂ ) ₈ OCO (CF ₂ ) ₆ CF ₃ By the same method as in Synthesis Example 1 above, linoleyl alcohol and pentadecafluorooctanoic acid were added to p-
The reaction was carried out using toluenesulfonic acid as a catalyst.

bp 135~139 ℃ (0.2mmHg) was deposited with Co by ^{IR 1210~1380cm -1 1780cm -1 2850~3020cm -1 M} + 663 Example 14μm oblique deposition thick polyethylene terephthalate film, a film thickness of 1000Å strong A magnetic metal thin film was formed.

Next, on the surface of the ferromagnetic metal thin film, a perfluoroalkylcarboxylic acid ester (synthesized in the above synthesis example) shown in Table 1 and a sulfur-based extreme pressure agent (weight ratio 1: 1) were used as a solvent (acetone: A solution diluted with ethyl ether = 1: 1) was applied so that the application amount was 10 mg / m ^2, and cut into 1/2 inch width to prepare a sample tape.

With respect to each of the prepared sample tapes, the dynamic friction coefficient and the shuttle durability under the conditions of a temperature of 25 ° C., a relative humidity (RH) of 50%, and −5 ° C. were measured. This dynamic friction coefficient is
This is a test using a guide pin made of stainless steel (SUS304) with a constant tension and a speed of 5 mm / sec. Further, the shuttle durability was evaluated by the number of shuttles until the output decreased by -3 dB after the shuttle traveled for 2 minutes each time. For still durability, the decay time of the output up to −3 dB in the paused state was evaluated. In addition, as a comparative example, a blank tape on which no lubricant was applied was also measured. The results are shown in Table 2.

As is clear from this table, in each of the examples of the present invention, the coefficient of dynamic friction was small under each condition of room temperature and low temperature, the running was extremely stable, and the tape surface was not damaged even after running 100 times back and forth. I couldn't see it at all. Also, the durability was extremely good, and the output did not decrease by -3 dB even after 150 shuttles. On the other hand, in the tape of the comparative example having no lubricant layer, the coefficient of friction increased as the number of times of reciprocation was increased, the operation was unstable, the tape was worn, and the durability was poor.

〔The invention's effect〕

As is clear from the above description, in the present invention, since the perfluoroalkylcarboxylic acid ester and the sulfur-based extreme pressure agent are used as the lubricant of the ferromagnetic metal thin film type magnetic recording medium, under any temperature condition. In addition, the dynamic friction coefficient can be reduced, and a magnetic recording medium having excellent running stability and abrasion resistance can be obtained.

In particular, since the freezing point temperature of perfluoroalkylcarboxylic acid ester is low, the effect is great when used at low temperatures.

Furthermore, the combined use of the sulfur-based extreme pressure agent increases the adhesion to the ferromagnetic metal thin film, the lubrication effect is maintained for a long time, and the reaction product film is formed by the frictional heat associated with the metal contact, resulting in a severe condition. It can be used well even under the conditions of use.

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Claims (2)

[Claims] 1. A ferromagnetic metal thin film is formed on a non-magnetic support, and a lubricant layer containing a perfluoroalkylcarboxylic acid ester and a sulfur-based extreme pressure agent is deposited on the ferromagnetic metal thin film. And a magnetic recording medium. 2. A perfluoroalkylcarboxylic acid ester having the general formula C _n F _{2n + 1} COOR (wherein n represents an integer of 6 to 10 and R represents a carbon-hydrogen group having 9 to 25 carbon atoms). )
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a compound represented by: