JPH0334121A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the medium having a good adhesive property on a protective film and has good friction and wear characteristics by using a lubricant, the main chain part of which consists of perfluoropolyether and which is limited in viscosity, content of a low boiling component and content of a middle boiling component. CONSTITUTION:A layer coated with the lubricant of the a fluorocarbon system is provided on the protective film provided on a magnetic layer. The main chain part of the lubricating layer consists of the perfluoropolyether which has the polar group via an arom. ring at the terminal. The viscosity is in a 72.0 to 85.0 cSt range and the measurement by gas chromatography is executed. The lubricant contg. the low boiling component of <=250 weight average mol. wt. at <=1.2 X 10<5> cps and the middle boiling component of the weight average mol. wt. ranging 250 or over and <=500 at <=1.5 X 10<6> cps is applied on the protective film in this case.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium provided with a lubricant layer coated with a lubricant.

[Conventional technology]

For magnetic recording media (hereinafter also simply referred to as media), it is necessary to reduce the friction coefficient of the surface and improve the lubrication performance to stabilize the contact operation with the magnetic head. A lubricant is applied to form a lubricant layer. This lubricating layer needs to be stably formed with a uniform thickness and good durability on the surface of the medium, and adhesion with the underlying layer is important.

In magnetic recording media, a protective film is usually provided on the magnetic layer made of a thin ferromagnetic metal film, and a lubricant is applied onto this protective film, but the protective film itself is stable, and Since the protective film made of amorphous carbon is extremely stable, it is difficult to apply lubricant uniformly and with good adhesion on top of it, so various efforts have been made to strengthen the bond with the lubricant and form a good lubricant layer. is being done.

Regarding lubricants, attempts have been made to increase the bonding strength with the protective film of the underlying layer by adding various polar groups to the molecular terminals of fluorocarbon-based lubricants. Among these, lubricants whose main chain is made of perfluoropolyether and which have a polar group at the end via an aromatic ring have excellent bonding strength with protective films, especially those made of amorphous carbon. In a medium equipped with a lubricant layer coated with a suitable lubricant, it is possible to suppress phenomena such as an increase in the coefficient of friction and wear caused by contact operation with a magnetic head.

[Problem to be solved by the invention]

However, the aforementioned lubricant in which the main 11 parts are perfluoropolyether and has a polar group at the end via an aromatic ring has the disadvantage that the quality varies widely due to low manufacturing yields and other reasons. .

For this reason, a medium having a lubricating layer coated with such a lubricant has the disadvantage that there are variations in friction and wear characteristics, and there is also variation in the phenomenon in which the magnetic head is attracted to the surface of the medium.

The problem to be solved by this invention is to eliminate the above-mentioned drawbacks and stably provide a medium having a lubricating layer with good adhesion and excellent lubrication performance on a protective film without variation. .

[Means to solve the problem]

According to the present invention, the above problem can be solved in a medium having a lubricant layer formed by further coating a fluorocarbon lubricant on a protective film provided on a magnetic layer. Made of fluoropolyether, has a polar group at the end via an aromatic ring, and has a viscosity of 72.0 cSt or more8
5.0 cSt or less, and the weight average molecular weight is 250 as measured by gas chromatography.
Low 1 below! lBa content is 1.2 x 10'cp
s or less, and the weight average molecular weight is in the range of more than 250 and less than 500, and the content of medium and high components is 1.5 X lO'cps
This problem can be solved by applying the following lubricant.

[Effect]

Perfluoropolyether, which has a polar group at the end via an aromatic ring, physically adsorbs to the surface of the protective film, which is the base layer, based on π-electron bonds, and can form a film with strong bonding strength with the base layer. In particular, by increasing the electronegativity of the terminal, the bonding force can be strengthened. However, on the other hand, the problem arises that the bond at the terminal end is easily broken due to external stress such as heat, making the structure unstable. The lower the molecular weight, the more susceptible it is to thermal stress, and the bond at the end is more likely to break.
The stability of the lubricant is affected by the amount of lubricant, resulting in variations in quality and variations in the adhesion between the protective film and the lubricant layer. A lubricant containing few low molecular weight components can form a stable film with strong bonding strength.

Additionally, the higher the viscosity of the lubricant (the higher the weight average molecular weight), the better the frictional properties of the resulting lubricant layer.
If the viscosity is too large, it will easily absorb moisture in a high-humidity atmosphere, leading to a decrease in bonding strength and causing phenomena such as magnetic head adsorption or lubricant migration.Magnetic head adsorption is It also depends on the thickness of the lubricating layer; the thicker the layer, the more easily it will be absorbed.

In order to ensure good lubrication performance and avoid adsorption of the magnetic head, it is necessary to control the thickness of the lubricant layer within an appropriate range depending on the performance of the lubricant. In the case of a lubricant with a high viscosity, the magnetic head is likely to be attracted to it as described above, so in order to prevent the adhesion, it is necessary to reduce the upper limit of the film thickness according to the viscosity, and the allowable range of the film thickness of the lubricant layer is narrower,
Another problem arises in that it becomes difficult to form a lubricating layer.

As a result of considering these points, we found that the main chain is made of perfluoropolyether, has a polar group at the end via an aromatic ring, and its viscosity, low-boiling component content, and medium-to-high component content are as described above. By using a limited number of lubricants, the protective film has a lubricating layer with good adhesion, good friction and wear characteristics, and is less likely to attract the magnetic head. The medium will be stably obtained.

〔Example〕

A protective film made of amorphous carbon is formed on a magnetic layer made of a cobalt-nickel alloy provided on a support, and lubricant A or lubricant E of the quality shown in Table 1 is applied thereon to form a lubricant layer. , and five types of media A to E were prepared. All lubricants have a main chain composed of perfluoropolyether and have a polar group at the end via an aromatic ring. In Table 1, low-boiling component content and middle component content are low-boiling component content with a weight average molecular weight of 250 or less. 6 Middle component content with a weight average molecular weight of more than 250 and 500 or less. Each was measured by A gas chromatography analysis chart for lubricant B is illustrated in FIG. 4, and a gas chromatography analysis chart for lubricant C is illustrated in FIG. 5, respectively. Further, the viscosity is a value at a temperature of 20°C.

Table 1 Regarding medium B and medium C, in combination with a magnetic head, CS S (Contact 5tart 5t
Illustrated the relationship between the number of C8S cycles and the coefficient of kinetic friction by repeating OP). The results for medium B are shown in Figure 1.
The results for medium C are shown in FIG. The quality of lubricant B and lubricant C is almost the same except for the content of low-boiling components, but as seen in Figures 1 and 2, the coefficient of kinetic friction of medium B slightly increases even after repeating C8S. However, by repeating C8S, the coefficient of dynamic friction of medium C increases significantly. There is a large difference in friction and wear characteristics between media B and media C.
It is clear that the low-boiling components of a lubricant greatly influence the friction and wear characteristics of the medium.

When we investigated the relationship between the low-boiling component content of the lubricant and the kinetic friction coefficient of the medium after 30,000 cycles of C3S, we obtained the relationship shown in Figure 3. It has been found that by using this material, a medium with excellent friction and wear characteristics can be obtained.

Furthermore, the quality of the dynamic friction coefficient and the static friction coefficient of the lubricants A to lubricant E was examined using medium A to medium E, and the overall quality of the lubrication performance was determined. The results are shown in Table 1.

Lubricant A has a high content of low-boiling components and a high content of middle components, a high viscosity (weight average molecule Jl), and a large dynamic friction coefficient 3 and static friction coefficient, resulting in poor lubricating performance. As mentioned above, since the lubricant C has a high content of low-boiling components, the coefficient of dynamic friction is large and the lubricating performance is poor. Lubricant E has a small content of low-boiling components and a small content of middle components, and the coefficient of dynamic friction is small and good. However, the viscosity is too high and the coefficient of static friction is large, causing magnetic head adsorption or lubricant Migration is likely to occur, resulting in defects.

The lubricant has a low content of low-boiling components and a low content of middle components, has a relatively low viscosity, and exhibits good lubricating performance. Lubricant B has a lower content of both low-boiling components and middle components, has a lower viscosity, and has excellent lubricating performance. but,
It is known that the coefficient of dynamic friction increases as the viscosity further decreases. From the above points, the viscosity of the lubricant is 72cS
It can be seen that the range of t or more and 85 cSt or less is suitable, the low-boiling component content is preferably 1.2 x lo'cps or less, and the middle component content is preferably 1.5 x IO'cps or less.

Furthermore, Figure 6 shows the results of investigating the relationship between the thickness of the lubricant layer and the coefficient of dynamic friction and coefficient of static friction for lubricants B and E.
Each is shown in FIG. Lubricant B has a small coefficient of dynamic friction and a coefficient of static friction, and exhibits good lubrication performance, with a wide allowable range for the film thickness of the lubricant layer, but lubricant E has a narrow allowable range for the film thickness, and the lubricant layer has an appropriate film thickness. From this point of view, it is desirable that the viscosity of the lubricant does not exceed 85 cSt.

〔Effect of the invention〕

According to this invention, the main chain portion is made of perfluoropolyether and has a polar group at its terminal via an aromatic ring,
Also, its viscosity and low-boiling component content.

By using a lubricant with a limited content of medium-boiling components, it has good adhesion to the protective film and good friction and wear characteristics.
In addition, it is possible to stably obtain a magnetic recording medium having an a-slip layer with excellent lubrication performance and which is less likely to attract a magnetic head.

In addition, in limiting the quality of this lubricant, we decided to limit the content of low-boiling components and medium-boiling components by gas chromatography measurements, and by viscosity instead of weight average molecular weight. This method also has the effect of being practical because it allows selecting a good lubricant with good reproducibility using a simple method.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the number of C8S and the coefficient of dynamic friction of medium B using a/ll agent B according to the present invention, and Fig. 2 is a diagram showing the relationship between the C8S number and the coefficient of dynamic friction of medium B using lubricant C with a high content of low-boiling components. C8S
A diagram showing the relationship between the number of times and the coefficient of kinetic friction, Figure 3 shows the low-boiling component content of the lubricant and the C3S3 of the medium in which the lubricant is used.
A diagram showing the relationship with the coefficient of kinetic friction after 10,000 cycles, Figures 4 and 5 are diagrams showing gas chromatography analysis charts of lubricant B and lubricant C, respectively, and Figures 6 and 7 are diagrams showing the relationship between lubricant B and lubricant C. Lubricant layer thickness and dynamic friction coefficient for medium B and medium E using agent B and lubricant E. Stillness II! FIG. 4 is a diagram showing the relationship with the friction coefficient. Fig.

Claims (1)

[Claims] 1) In a magnetic recording medium equipped with a lubricating layer in which a fluorocarbon-based lubricant is further coated on a protective film provided on the magnetic layer, the lubricating layer has a main chain made of perfluoropolyether and a terminal portion made of perfluoropolyether. It has a polar group via an aromatic ring, has a viscosity in the range of 72.0 cSt or more and 85.0 cSt or less, and has a weight average molecular weight of 250 or less as measured by gas chromatography, and has a low-boiling component content of 1
．． 2×10^5cps or less and weight average molecular weight is 25
Medium-boiling component content in the range of more than 0 and less than 500 is 1.5×
A magnetic recording medium characterized in that it is formed by applying a lubricant of 10^8 cps or less.