JPH02141923A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To lower the coefft. of dynamic friction and to enhance a traveling property and durability by specifying the value of the polarity term component of the surface free energy of a lubricating agent layer at the time of providing the lubricating agent layer on the thin magnetic film of the magnetic recording medium of a thin film type. CONSTITUTION:The lubricating agent layer 1 having >=2.0erg/cm and <=6.0erg/ cm value of the polarity term component gammas<p> of the surface free energy gamma is provided on the thin magnetic film 2 formed on a nonmagnetic base 3. This layer makes contribution to a drastic decrease of the coefft. of dynamic friction and exhibits an excellent effect in improving the traveling property and durability. On the other hand, the lubricating agent layer having the value of gammas<p> below 2.0erg/cm has the too small interaction between the polar group and the thin magnetic film and leads to an increase in the coefft. of dynamic friction. On the other hand, the lubricating agent layer having the value of gammas<p> in excess of 6erg/cm has the too large surface energy and exerts adverse influence upon the durability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a magnetic thin film formed on a non-magnetic support.
This invention relates to thin film magnetic recording media.

[Summary of the invention]

The present invention provides a thin-film magnetic recording medium in which a magnetic thin film is formed on a non-magnetic support, in which a polar term component, which is one of the components of surface free energy, is present on the surface of the magnetic thin film. O
erg/cff1 or more6. By providing a lubricant layer having a value of Oerg/c+11 or less, it is intended to lower the dynamic friction coefficient of the magnetic recording medium and improve running performance and durability.

[Conventional technology]

Conventionally, magnetic recording media are coated-type magnetic recording media that are created by coating a polymer binder solution containing magnetic powder and additives dispersed on a non-magnetic support, aligning it in a magnetic field, and then drying it. It is widely used in practical applications.

As the magnetic powder, γ-Fete, which belongs to the ferrimagnetic system, is used.
,, , These iron oxides containing iron oxides such as Fe=On and Co, or BaO 6FezOi, as well as metal powders mainly composed of Fe and Co belonging to the ferromagnetic system, and CrO□ are representative examples. It can be used as a material.

These materials are prepared and used in the form of submicron-sized needles, plates, and granules. Examples of the additives include abrasives such as Cr2O, SiO□, various lubricants, and stabilizers, and examples of the polymer binder include vinyl chloride-vinyl acetate copolymer resin, polyurethane resin, Polyester resin etc. are commonly used.

In order to meet the demand for high-density magnetic recording that has been increasing in recent years, so-called thin-film magnetic recording media, in which the magnetic material itself is directly deposited on a non-magnetic support using a thin-film mold, has been developed. The media is getting attention. That is, as the magnetic material, ferromagnetic materials such as Co--Ni alloy, Fe, 0. ,C.

Contains Fe50. It is a magnetic recording medium in which a ferrimagnetic material such as ferrimagnetic material is formed on a non-magnetic support such as a polyester film, polyimide film, or aluminum substrate by vacuum thin film forming technology such as vacuum evaporation, ion blasting, or sputtering or plating method. .

This thin-film magnetic recording medium can be manufactured by selecting manufacturing conditions.
Not only can the coercive force (Hc) and squareness ratio (Rs) be increased, but since the magnetic thin film does not contain polymer binders or additives, the saturation magnetic flux density (Bad) is large, and therefore the thickness of the magnetic thin film can be increased. It is possible to make it extremely thin. Furthermore, compared to coating-type magnetic recording media, the surface of the magnetic thin film is extremely smooth and has excellent adhesion to the track surface of the magnetic head.

Because of these characteristics, thin-film magnetic recording media have low recording demagnetization caused by demagnetizing fields, low spacing loss with the track surface of the magnetic head, excellent electromagnetic conversion characteristics in the short wavelength region, and are suitable for high-density magnetic recording. It has sufficient performance to meet the demands.

However, in thin-film magnetic recording media, it is difficult to incorporate lubricants or abrasives into the magnetic thin film, and because the surface properties of the magnetic thin film are extremely good, the coefficient of dynamic friction is large, causing the magnetic head to track It is easy to cause adhesion to surfaces such as drum surfaces, so-called stick-slip and sticking problems during actual running cannot be ignored, and there is a tendency for reliability such as durability and running performance to be lacking.

Conventionally, in thin-film magnetic recording media, a lubricant layer is formed by applying an organic solvent solution of a fluorine compound lubricant to the surface of the magnetic thin film and then drying this in a dry chamber. Attempts have been made to reduce the coefficient of dynamic friction and improve durability and running performance.

[Problem to be solved by the invention]

However, the thin-film magnetic recording medium according to the above-mentioned technology does not necessarily exhibit satisfactory durability and runnability. Naturally, there are differences in the improvement effects depending on the type of lubricant, and therefore, in search of even slightly superior materials, a wide variety of lubricants with different molecular structures have been synthesized and subjected to practical tests.

In this practical test, sample magnetic tapes, magnetic disks, and other thin-film magnetic recording media are mounted on actual VTRs and disk drives to evaluate running performance and durability, but it takes time to prepare the samples. In addition, actual driving tests required many different types of equipment and a constant temperature room, making it inappropriate to quickly test and screen a large number of lubricants. In addition, the evaluation results do not necessarily have good reproducibility, and a single measurement lacks reliability.
It was necessary to spend a huge amount of time repeating the same actual driving test several times and making judgments based on the average value. As a practical matter, even with such evaluation techniques, it is currently not possible to obtain a thin-film magnetic recording medium that satisfies running properties and durability in actual running on VTRs and disk drives.

On the other hand, the present inventors have conducted various studies on the dynamic friction coefficient, runnability, and durability of thin-film magnetic recording media, and have come to the following conclusion.

In other words, the friction phenomenon between a thin-film magnetic recording medium with a very thin lubricant layer on a magnetic thin film and the track surface or drum surface of a magnetic head is considered to belong to the boundary friction region due to boundary lubrication. It will be done.

Therefore, it is important to understand the surface chemical properties of the lubricant layer surface, especially the value of the surface free energy γ3 of the lubricant layer surface.
It was found that this is an important factor in boundary friction due to boundary lubrication.

In other words, the object of the present invention is to measure and evaluate the value of surface free energy and provide a lubricant layer on the magnetic thin film with this value set within a certain range, thereby reducing the coefficient of dynamic friction and improving running performance and durability. An object of the present invention is to provide a thin-film magnetic recording medium with excellent properties.

[Means to solve the problem]

In order to solve the above-mentioned problems, the magnetic recording medium of the present invention has a polar apex-basal molecule, p, which is one of the constituent components of the surface free energy γ, and has a value of 2. Oerg/cl1 or more 6.0er
A lubricant layer having a thickness of 7 cm or less is provided on a magnetic thin film of a thin film type magnetic recording medium.

As the lubricant layer used in the present invention, for example,
A lubricant made of a series of perfluoroalkylcarboxylic acid amine salts as described in No. 2-163595 is used, and a solution of these lubricants dissolved in an organic solvent is applied to the surface of the magnetic thin film or immersed in the solution.

The amount of lubricant applied to the surface of the magnetic thin film depends on the molecular weight of the lubricant, but is 1 to several mg per square meter of the surface of the magnetic thin film, and is equivalent to the lubricant forming a monomolecular adsorption film. Just apply the appropriate amount.

[Effect]

When considering the structure of the lubricant that forms the lubricant layer, the major factors that reduce the coefficient of friction due to boundary lubrication are:
It is a polar group that adsorbs to the surface of a magnetic thin film, and it is the polar apex molecule p of the surface free energy γ that is involved in the polarity of this polar group. In other words, the value of p for this authoritative apex molecule is 2. Oerg/cd or higher6. Oerg/c4
A lubricant layer within the following range exhibits optimal interaction with the magnetic thin film surface.

This contributes to a significant reduction in the coefficient of dynamic friction and brings about excellent effects in improving running performance and durability.

On the other hand, the value of rs' is 2. In a lubricant layer with less than Oerg/c-, the interaction between the polar group and the magnetic thin film is too small, resulting in a large dynamic friction coefficient, and on the other hand, the values of γ and P are 6erg/cff.
If the lubricant layer exceeds l, the surface energy becomes too large, which adversely affects durability.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

Implementation ■Sat FIG. 1 shows a cross section of a magnetic recording medium according to the present invention.

In FIG. 1, a magnetic thin film 2 is formed by continuously depositing, for example, a Co8ON i 20 alloy to a thickness of 1000 mm on a Jt support 3 made of a polyethylene terephthalate (PET) film with a thickness of 14 μm, for example, by an oblique deposition method. Formed.

As a lubricant, a compound represented by the following chemical formula (1), which is one of the series of perfluoroalkyl salts described in Japanese Patent Application No. 163595/1982, is used as a lubricant. and ethanol in an I:1 mixed solvent, and this solution was coated on the magnetic thin film 2 in an amount of 2. The lubricant layer 1 was applied using a gravure transfer method so that the amount of the magnetic recording medium was 1 mg/+a.
The pancake was cut into a pancake with a width of m, and then cut into a predetermined length and loaded into an 8 mm VTR cassette to obtain a sample tape 1 for measurement.

Next, a method for determining the polar apex molecule sp of the surface free energy T from the sample tape 1 according to this embodiment will be described. As a surface free energy analysis method, a method using the contact angle with the working liquid has been proposed (F, M, F
osvkes, Ind, Eng, Chem, +
56 (12), 40 (1964)'). According to this report, surface tension or surface free energy γ3
is constructed in an additive manner by dispersion terms γ, d and polar terms γ, p.

γS=γs4+γs (A) Sunkyuta T3
bt is a term based on Roaton dispersion force, and polar terms γ and p are terms based on bipolar force or Coulomb electrostatic force.

This T! ' and Ts' are as reported by Kaelble et al.
It can be determined by the following formula. (J, Adhes
ion, 2°66 (1970)).

Here, -a is the adhesion work, which is obtained by measuring the contact angle θ of the working liquid from the equation Wa=rt(1+cosθ)(E). Actually, water and methylene iodide are dropped on the surface of the lubricant layer 1 on the magnetic thin film 2, and the contact angle is measured.
The polar terms T and p were calculated using the following formula.

In place of the lubricant (1) used in Example 1, the following molecular formula (2) to
Sample tapes 2 to 4 according to this example were prepared in exactly the same manner as in Example 17 except that the compound shown in (4) was selected.

C*F+wCOO-HJ"C+5H1y
(2) CJ+ 5cOo-HsN"Cz4H4s
(3) C*F+*C0O-HsN”C
+zlha (4) The sample tapes 2 to 4 were prepared by the method described in Example 1 to determine the polarity term T of the surface free energy T.

I asked for

In place of the compound (1) used in Example 1, compounds represented by the following chemical formulas (5) and (6) from a series of perfluoropolyethers described in Japanese Patent Application No. 133926/1982 were used. Sample tapes 5 and 6 according to this example were prepared in the same manner as in Example 1 except for the following.

C+ yHsscoocHz-Posblin-Z-D
OL-CHzOOCC+? H3S (5)F(CP
tCPtCPtO), -ChCFzCHg00CC+J
3s (6) (n is a natural number) Fomblin-Z-DOL is Montefuo
It is made by stm.

The sample tapes 5 and 6 were prepared using the method described in Example 1 to obtain polar apex-bottom molecules with a surface free energy of γ3! I asked for #.

[In place of the lubricant (1) described in Example 1, perfluorocarboxylic acid 00 represented by the following chemical formula 〇D~03)
, perfluorocarboxylic acid alkyl ester 021, and alkylcarboxylic acid fluoroalkyl ester 0 were selected as lubricants, and in the same manner as in Example 1 except that sample tapes 11 to 13 according to comparative examples were prepared.

C? FtsCOOH00 (, rF 1scOOcsHr r Q
7JCsH+ tcOOcHzcJ+s 0
3) All of these 00~ planes are compounds that are generally available as reagents. For sample tapes 11 to 13 according to the comparative examples, the polar term Ts' of the surface free energy T was determined by the method described in Example 1.

For each sample tape prepared as described above, 25
The dynamic friction coefficient μ was measured under measurement environmental conditions of ℃ 60 RH. This is shown in the following table and in Figure 2 together with the value of the polar apex-basal molecule s' of the surface free energy T3 obtained earlier.The measurement of the kinetic friction coefficient μ was carried out using each sample tape attached to a guide pin made of stainless steel 5US304. The lubricant layer sides of the two were brought into contact with each other, and a constant load was applied and the vehicle was run at a constant speed of 5+ww/sec.

As is clear from the table above and FIG. 2, the sample tapes 1 to 6 according to the examples in which the value of the polar apex-basin molecule p of the surface free energy T is in the range of 2≦rs'≦6 have a coefficient of kinetic friction. In all cases, μ was less than 0.3, indicating stable running. On the other hand, Sample Tapes 11-13 according to Comparative Examples in which the value of the polar apex-bottom molecule sI' was less than 2 or more than 6 all had a dynamic friction coefficient μ of 0.3 or more, and running was unstable. In addition, we confirmed the durability through actual running tests using a home-use 8mm VTR, and found that for sample tapes 1 to 6, the still durability up to -3 dB was over 180 minutes, and the shuttle durability up to the same <-3 dB drop. The durability (shuttle time: 2 minutes/time) exceeded 250 O5 deviations, and the durability was sufficiently satisfactory for practical use. On the other hand, Sample Tapes 11 to 13 according to Comparative Examples had unsatisfactory characteristics in both still durability and shuttle durability compared to Sample Tapes 1 to 6 according to Examples.

When the surface of the magnetic thin film was observed under a microscope after these actual running tests, no flaws or damage were observed in the sample tape of the example, whereas some flaws or damage were observed in the sample tape of the comparative example. .

As described above, the magnetic recording medium according to the present invention, which has a lubricant layer having a polar element of surface free energy γ, and a value of p in the range of 2≦rs'≦6, has a dynamic friction coefficient μ of 0. 3
It is small in size and runs stably, and has shown sufficient durability in actual running tests using home VTRs. That is,
It can be seen that the dynamic friction coefficient, running performance, and durability can be determined simply by measuring the value of rs'.

In this example, Co-
Although the Ni alloy diagonally evaporated tape has been shown as an example, other thin film media such as perpendicular recording discs obtained by sputtering a Co-Cr alloy onto an aluminum alloy or glass substrate support can also be used. The value of Ts' is 2≦Ts'
By providing a lubricant layer selected within the range of ≦6, remarkable improvements in running performance and durability were observed.

〔Effect of the invention〕

When providing a lubricant layer on the magnetic thin film surface of a thin film type magnetic recording medium, by selecting the value of the polar type component p of the surface free energy γ of the lubricant layer in the range of 2≦γ and p≦6. , it is possible to obtain the effect of improving running stability and durability in actual running due to a reduction in the coefficient of dynamic friction μ. In other words, by simply measuring the γ and e values of the lubricant layer in a simple direction, it is possible to judge whether the running properties and durability of a thin film magnetic recording medium are good or bad. This will greatly contribute to the development and production of thin-film magnetic recording media with excellent reliability.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a magnetic recording medium according to the present invention, and FIG. 2 is a correlation diagram between the polar term component of surface free energy and the coefficient of dynamic friction. 1-----111...-Lubricant layer 2--------
---...-Magnetic thin film 3- Non-magnetic support The present invention + CJ's a cross section of a certain body Whistle 1 Figure 2

Claims (1)

[Claims] A magnetic thin film of a magnetic recording medium formed by forming a magnetic thin film on a non-magnetic support has a value of a polar component, which is one of the components of surface free energy, of 2.0 erg/cm^2 or more6.
．． A magnetic recording medium characterized by providing a lubricant layer of 0erg/cm^2 or less.