JPH0740358B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a high recording density, which is applied to a magnetic recording device such as a magnetic tape or a magnetic disk, and is particularly excellent in running stability and durability. The present invention relates to a method for manufacturing a magnetic recording medium having abrasion resistance.

2. Description of the Related Art Conventional γ-Fe ₂ O ₃ and Co-containing γ-Fe ₂ O _{3 have been} developed for the purpose of developing magnetic recording media for magnetic disks and magnetic tapes.
Alternatively, instead of a coating type magnetic recording medium prepared by dispersing ferromagnetic powder such as CrO ₂ in an organic binder, a ferromagnetic metal thin film is directly plated on a non-magnetic substrate for the purpose of higher density at present. Development of metal thin film magnetic recording media formed by sputtering, vacuum deposition, ion plating, etc. is active.

However, the above-mentioned metal thin film magnetic recording medium causes unstable running due to friction and wear due to contact with a magnetic head or the like under high-speed relative motion when recording and reproducing a signal, and eventually wear powder or damage occurs. Do not withstand long-term use by doing. Therefore, it is strongly desired for practical use that the magnetic recording medium keeps smooth running property and wear resistance under the use environment condition.

For this reason, the ferromagnetic metal thin film is surface-treated as in the conventional USP4029541, or higher fatty acid (Japanese Patent Laid-Open No.
55-1651, USP4456661) and fluoropolymers (JP-A-59)
-167849) and other protective films have been formed to improve abrasion resistance and wear resistance.

Problems to be Solved by the Invention However, the surface treatment alone may improve the running property, but scratches easily occur on the metal thin film, and when the protective layer is directly formed, the adhesion with the ferromagnetic metal thin film is improved. Due to its weakness, phenomena such as peeling off or deterioration are eventually observed, and durability is still insufficient. Therefore,
In view of this point, the present invention, when forming the protective layer, by surface-treating the ferromagnetic metal thin film, improves the surface property of the metal thin film and the adhesiveness with the protective layer, thereby achieving a good magnetic head and the like. It is an object of the present invention to provide a magnetic recording medium excellent in running property and abrasion resistance.

Means for Solving the Problems Magnetic recording is performed by treating the surface of a ferromagnetic metal thin film provided on a non-magnetic substrate with dilute nitric acid, and further forming one or more compounds of thiols or thioglycolic acids on it. Make up the medium.

Action By treating the ferromagnetic metal thin film with dilute nitric acid, the metal components on the surface form oxides, improving its own wear resistance and adhesion with the protective layer, or by etching action to a suitable roughness. By forming the groove, the abrasion resistance is improved and the holding power of the protective layer is increased, and a magnetic recording medium excellent in running property and durability can be obtained.

Example FIG. 1 is a sectional view of a magnetic recording medium of the present invention. In the figure, 1 is a non-magnetic substrate, 2 is a ferromagnetic metal thin film, and 3 is a protective layer containing one or more compounds of thiols or thioglycolic acids.

Examples of the non-magnetic substrate 1 that can be used in the magnetic recording medium of the present invention include polymer materials such as polyamide, polyimide, polysulfone, polycarbonate, polypropylene, polyethylene, polyethylene terephthalate, poly (cellulose acetate) and polyvinyl chloride, non-magnetic metal. Material, glass,
There is a film plate made of a known material such as a ceramic material such as porcelain.

Further, as a ferromagnetic material for forming the ferromagnetic metal thin film 2,
One or more metals selected from Fe, Co, Ni or M and these
There are n, Cr, Ti, P, Y, Sm, Bi, etc., or alloys combining these oxides. Of these, ferromagnetic metal thin films composed of at least two elements selected from Co, Cr, and Ni are preferable because they have high magnetic anisotropy energy and corrosion resistance. These are vacuum deposition method, sputtering method, It can be easily formed by an ion plating method, a plating method, or the like.

In the present invention, by treating the ferromagnetic metal thin film 2 with dilute nitric acid, the metal components on the surface are oxidized, the wear resistance of itself and the adhesion to the protective layer are improved, and a magnetic recording medium excellent in running property is obtained. . For example, when the ferromagnetic metal thin film is a Co-Cr vapor deposition film, when the dilute nitric acid solution concentration is 0.001 to 0.1 N (N) and this is immersed for a suitable time, Cr is oxidized and CrO _x
Is increased by 2 to 3 times, or the surface roughness of the medium is roughened from several tens of Å to 100 to 200 Å by the etching action to improve the abrasion resistance and the holding power of the protective layer. This treatment method is fully effective when the dilute nitric acid solution concentration is 0.01 N and the immersion time is 10 minutes or less. It is recognized in the following examples that the solution temperature has the most suitable modifying effect on the lubricity at around room temperature.

Further, the surface portion of these ferromagnetic metal thin films 2 is improved from the viewpoint of adhesion to the protective layer even if it is oxidized from the beginning within a range that does not affect practical characteristics due to introduction of oxygen during thin film formation. , A more preferable phenomenon.

In the present invention, the compound of thiols or thioglycolic acid used in the protective layer 3 is a linear structure hydrocarbon group or fluorocarbon group having a straight chain or a side chain on the side opposite to the polar group of the aromatic ring. And a thiol group or a thioglycolic acid group, which are represented by the following formula (A) or (B).

(However, R is a hydrocarbon group having 12 to 24 carbon atoms or a fluorohydrocarbon group having 8 to 16 carbon atoms).

From the chemical structure of these compounds, hydrocarbon groups or fluorohydrocarbon groups play a role of good lubricity,
The thiol group or thioglycolic acid group is strongly bonded to the ferromagnetic metal thin film, so peeling due to shearing of the magnetic head etc. is small, and the intervening aromatic ring has a solid structure, which also has excellent wear resistance. it is conceivable that. Therefore, when these compounds are formed as the protective layer 3, excellent running properties and wear resistance are obtained. The carbon number of these compounds is 11 if they are hydrocarbon groups.
In the following, deterioration of lubricity due to low molecular weight and easy decomposition due to heat generated by sliding with a magnetic head etc., and if it is 25 or more, not only addition of difficulty in synthesis and solubility but also running property I can't expect much in terms. Therefore, the carbon number is preferably 12 to 24, and the carbon number of the fluorohydrocarbon group is preferably 8 to 16 from the same viewpoint. The formation of the protective layer 3 can be easily achieved by a wet method by diluting an appropriate amount of these compounds with a solvent, roll coating, spin coating, Langmuir-Blodgett method, or a dry method such as vapor deposition. It is also possible to use the compounds alone or in combination.

On the other hand, it is preferable that the film thickness is a thin film, but if it is too thin, pinholes are likely to occur in the film formation and the metal thin film itself affects the film, so that sufficient lubricity cannot be obtained. If the thickness is thick, the output of the signal may be reduced due to the superposing loss, so 400 Å or less is preferable. Therefore, the protective layer 3 is formed of the thiol compound or thioglycolic acid compound of the present invention by the above method.

Example 1 A sample was prepared by forming Co—Cr (weight ratio of Co: Cr = 8: 2) with a film thickness of 1300Å (analyzed by AES) on a 12 μm-thick polyimide film by a vacuum continuous vapor deposition method (Sample No.). .1).

This was further treated as a test piece of 40 × 70 mm under the following conditions and then evaluated.

The reciprocating friction coefficient was evaluated, and the friction element has a steel ball (S
UJ2), load P = 10 gf, running speed V = 1.0 mm / sec, and the coefficient of dynamic friction (μk) was measured, and comparison was made at the beginning of running and 10 passes. The results are shown in Table 1.

According to this, the unprocessed sample No. 1 has μk from the beginning.
The damage on the Co-Cr surface was clearly generated even about 5 passes during the course of the run, and the fluctuation of μk began to occur. It was On the other hand, in Sample Nos. 2 and 3, the initial runnability was slightly improved to μk of 0.25,0.23, but scratches occurred as the running continued and μk was 0.47,0.38 at 10 Pass.
It wasn't good to rise to.

However, in sample No. 4, μk was small from the beginning,
Even after passing, it was 0.22, showing almost no change, and no significant scratches were observed on the surface observation.

Therefore, the recording medium obtained by treating the ferromagnetic metal thin film with diluted nitric acid is
It was found that the magnetic recording medium has improved runnability and excellent abrasion resistance as compared with other treatment methods.

Example 2 A sample having a film thickness of 1500 Å was prepared on the polyethylene terephthalate film having a film thickness of 30 μm with the same metal composition as in Example 1. Then, this was further treated with a test piece having the same size as in Example 1 at the following dilute nitric acid concentration (N), immersion time (min) and immersion temperature (° C), and the same measurement as in Example 1 was performed after 20 passes. .mu.k and surface observation were compared.

From the above, it can be seen that the runnability and wearability of these are all improved as compared with the untreated sample No. 1. The treatment conditions are preferably a concentration of 0.001 to 0.1 N, an immersion time of 10 to 60 min, and an immersion temperature of about 25 ° C. Further, in the case of 0.01 N, 10 min, 25 ° C., abrasion resistance is improved by 15 to 20 times as compared with untreated, and this condition is most preferable. At this time, the surface analysis of the medium shows that
ESCA and AES analyzes showed that CrOx was segregated on the surface, and when it was observed with a surface roughness meter, it was etched to 100 to 200Å. From this, it is considered that the recording medium has improved runnability as CrOx wear resistance and the contact area decrease.

From this, it is clear that the recording medium treated under the above conditions is effective in the abrasion resistance and the abrasion resistance.

Example 3 Next, sample No. 1 was tested with a test piece having a diameter of 100 mm for 0.01 N for 5 min.
After dilute nitric acid treatment (at 25 ° C.), chloroform solution containing 0.1 wt% each of p-tridecylthiophenol and p-tridecylphenylthioglycolic acid was added to about 1
50 Å thickness (ellipsometry) spin coating (1000
Sample (sample No.12, 13) applied twice at rpm, 20 sec.
And a sample (sample for which these were applied directly to sample No. 1
Nos. 14 and 15) were prepared and evaluated in the same manner as in Example 1.
Tested up to 200Pass. This is shown in Table 3.

Note that p-tridecylthiophenol is obtained by sulfonating tridecylbenzene with sulfuric acid, acylating with thionyl chloride in tetrahydrofuran, and further reacting with a zinc catalyst (in sulfuric acid acidity) to obtain p-tridecylthioglycolic acid. Is synthesized by further treating p-tridecylthiophenol with monochloroacetic acid in the presence of alkali. Therefore, the thiols and thioglycolic acids described in the following examples all use compounds synthesized by these methods.

According to this, each of Sample Nos. 12 to 15 has excellent characteristics such that the μk value is as small as 0.2 or less at the initial stage, and running scratches are hardly observed even on the surface observation. However, for samples with a direct protective layer such as sample Nos. 14 and 15, as the running continued, the coating film eventually peeled off and scratches were formed on the metal thin film, and μk increased after 200 Pass. The running performance is unstable. In contrast, diluted nitric acid treated sample No. 12,
It was found that No. 13 is an excellent recording medium with good running performance and continuity. This means that by cleaning the metal thin film with a dilute nitric acid treatment, unnecessary organic contaminants are removed, or by modifying the metal component, the wettability of the coating film is improved and the retention in the etching part is improved. It is considered to be a thing. Therefore, it can be seen that when a compound of thiols or thioglycolic acids is further formed as a protective layer after the surface treatment, a magnetic recording medium excellent in abrasion resistance and abrasion resistance can be obtained.

Example 4 A sample in which 950Å Co-Cr was formed on a polyimide film having a thickness of 12 μm was prepared (Sample No. 16), and the sample was directly applied to the sample and treated with dilute nitric acid under the same conditions as in Example 3. Samples each having a thickness of 130Å formed with p-stearyl thiophenol by roll coating were prepared and cut into 8 mm wide tapes (Sample Nos. 17 and 18).

With a cylinder with a diameter of 60 mm and a ferrite head with a width of 100 μm and 6R fixed, a tension of 100 gf was applied to one end of the tape and the change over time in the output was examined with a pen recorder at a frequency of 7.3 MHz and a peripheral speed of 5.5 m / sec. The reduced time and the surface observation at that time were compared. This is shown in Table 4.

Sample No. 18 thus treated with dilute nitric acid was about 10 times more than when the protective layer was not formed at all by the still tester, and about 2 times as much as when only the protective layer was not formed.
It has double the long-term reliability and can realize a practical magnetic recording medium.

Example 5 A sample obtained by vapor-depositing a ferromagnetic metal thin film having a composition shown in Table 5 on a polyamide having a thickness of 20 μm was treated as a test piece having a diameter of 60 mm in the same manner as in Example 4, and carbonization of thiols or thioglycolic acids was performed. A protective layer was laminated with a compound in which a hydrogen group or a fluorohydrocarbon group was changed. Then, these surface conditions were measured by contact angle with water (2.5 μl, after 30 sec) and pin-
A disc type friction coefficient meter was used to compare μk after 1 hour and surface observation. At this time, a sample in which a ferromagnetic metal thin film was deposited in an oxygen atmosphere of 0.1 Torr was also added. This is 100-150Å from the surface
The recording medium has a layer containing more oxygen than the metal component at the depth of, and is indicated by Ox in Table 5. The thickness of the protective layer is measured by ellipsometry, and the head is 6R SUJ2, V =
The test was conducted at a radius of 13 mm at 3 m / sec.

From the above, sample Nos. 19 to 30 all have contact angles of 8
The surface energy state was as high as 0 to 97 degrees and low, indicating that the μk was 0.14 to 0.26 and the running property was good. The surface observation revealed that they were almost intact, and even if there were scratches, only traces were produced.

Therefore, after dilute nitric acid treatment, 400 Å of thiol or thioglycolic acid compounds having a hydrocarbon group having 12 to 24 carbon atoms or a fluorohydrocarbon group having 8 to 16 carbon atoms are used.
It is understood that by laminating the layers below, a magnetic recording medium having excellent lubricity and wear resistance can be obtained.

EFFECTS OF THE INVENTION The magnetic recording medium according to the present invention has a durability improved in running property by forming a protective layer of a thiol compound or a thioglycolic acid compound after the surface of a ferromagnetic metal thin film is treated with dilute nitric acid. A good magnetic recording medium can be obtained.

[Brief description of drawings]

The figure is a cross-sectional view of a magnetic recording medium in an example of the present invention. 1 ... Non-magnetic substrate, 2 ... Ferromagnetic metal thin film, 3 ... Protective layer.

Claims (4)

[Claims] 1. A surface of a ferromagnetic metal thin film provided on a non-magnetic substrate is treated with dilute nitric acid, and the upper surface thereof is subjected to the following formula (A).
Alternatively, a method for producing a magnetic recording medium, which comprises forming a protective layer containing at least one compound of thiols or thioglycolic acid shown in (B). (However, R is a hydrocarbon group having 12 to 24 carbon atoms or a fluorohydrocarbon group having 8 to 16 carbon atoms). 2. The method for producing a magnetic recording medium according to claim 1, wherein the concentration of the dilute nitric acid solution is 0.001 to 0.1 N. 3. The method for producing a magnetic recording medium according to claim 1, wherein the protective layer is formed to have a film thickness of 400 Å or less. 4. The method for producing a magnetic recording medium according to claim 1, wherein the surface composition of the ferromagnetic metal thin film is oxidized.