JPH02216616A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having a lubricating layer of a uniform thickness with good adhesion to a base layer and excellent lubricating performance by constituting the lubricating layer of specific perfluoropolyether on a magnetic layer. CONSTITUTION:The surface of the medium is coated with perfluoropolyether lubricant to form the lubricating layer. The lubricating layer comprises specific perfluoropolyether: the main chain thereof is expressed by formula I, at least one end of the chain has a polar group linked by an aromatic ring, the weight average mol.wt. ranges from 2,000 to 3,500, and the proportion of a low boiling point component with weight average mol.wt. <=500 ranges 3.5 to 10wt.%. This perfluoropolyether is treated by heating at a range from 100 to 200 deg.C for one to five hours and filtered with reduced pressure to be used. In formula I, l, m and n represent integers. Thereby, the obtd. medium has good adhesion with the base layer, uniform thickness and excellent lubricating performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to magnetic recording media, and more particularly to improving the lubrication performance of the surface of magnetic recording media.

[Conventional technology]

In magnetic recording media (hereinafter 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 running of the magnetic head. It is known to form a lubricating layer coated with perfluoropolyether as a lubricant. 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 order to increase this adhesion, perfluoropolyethers with various polar groups at the molecular ends have been proposed, but the one that is expected to have the strongest adhesion is one with aromatic as a polar group. It is a perfluoropolyether with a hydrophilic group via a group ring. Perfluoropolyethers with this aromatic ring introduced at the end of the molecule improve the orientation of the molecule, so
A uniform film with strong adhesion can be formed, and the film has a lower coefficient of friction than conventional perfluoropolyether, resulting in a durable lubricating layer with excellent lubrication performance.

[Problem to be solved by the invention]

However, the above-mentioned perfluoropolyether having a parent group via an aromatic ring at the end of the molecule has the disadvantage that the yield during synthesis is low and the quality varies depending on the synthesis loft. For this reason, media with such a structure and a lubricating layer coated with perfluoropolyether have variations in the thickness and abrasion resistance of the lubricating layer depending on the manufacturing loft, and as a result, the magnetic head can There was also a drawback that variations occurred in the phenomenon of adsorption to. This phenomenon of adsorption of the magnetic head is a type of adhesion using lubricant as an intermediary, and is particularly likely to occur in a high humidity atmosphere.

In a fixed magnetic disk device that uses the C8S method, if the magnetic head is attracted to the surface of the medium, stick-slip occurs when the medium contacts and slides when it starts rotating, causing head cracking in a short period of time. The problem arises that

This invention was made in view of the above points, and
Good adhesion with the underlying layer on the outermost surface of the media.

It is an object of the present invention to provide a medium having a lubricating layer with uniform thickness, excellent lubrication performance, resistance to magnetic head attraction, and good durability.

[Failure to solve the problem]

According to the present invention, the above object is to provide a medium having a lubricating layer made of perfluoropolyether on a magnetic layer, in which the lubricating layer has a main chain portion having the following formula (N),
It has a polar group on at least one end via an aromatic ring, the weight average molecular weight is in the range of 2000 to 3500, and the content of low boiling components with a weight average molecular weight of 500 or less is 3.5% to 10% by weight. Perfluoropolyether having a weight% or less of This is achieved by coating a fluoropolyether.

10C2F4O+7+CF2O±1←C3FgO-h
-(I) [in formula (I), f! , m, and n each represent an integer. [Function] "Perfluoropolyether J whose main chain partial general formula is the above formula (]) and which has a polar group at least one terminal via an aromatic ring (hereinafter simply referred to as perfluoropolyether (A) ) can form a film with strong adhesion to the underlying layer, but on the other hand, the quality varies due to poor yield during synthesis, and the characteristics of the obtained film vary depending on the synthesis loft. It is also a stable perfluoropolyether.

The present inventors have found that the broadening of the molecular weight distribution of perfluoropolyether (A), particularly the presence of low-boiling components with a weight average molecular weight of 15,009 or less, is closely related to this instability. Perfluoropolyether (Δ), which has a high content of low-boiling components, is unstable and thermally weak, causing the structure of the polar group to collapse, resulting in a decrease in adhesion to the underlying layer during film formation.

Such low-boiling components are detected by gel chromatography/UV detection method. When perfluoropolyether (A), which has a high content of low-boiling components, is directly applied to the surface of a medium to form a lubricating layer, it may dry after application or be heated by the ambient temperature during use of the medium, causing a large amount of moisture to form on the surface of the medium. Loss on heating occurs, and impurities accompanying the collapse of the structure of the polar group occur, weakening the adhesion of perfluoropolyether (A), and as a result, the thickness of the lubricating layer becomes uneven and the lubricating performance deteriorates. I will do it. Furthermore, since the polar group whose structure has been destroyed by heating is hydrophilic, water is likely to be drawn into this region in a high humidity atmosphere, making it easier for the magnetic head to be attracted to the polar group.

The medium according to the present invention has a weight average molecular weight in the range of 2,000 to 3,500, and a content of low-boiling components with a weight average molecular weight of 500 or less in the range of 3.5% to 10% by weight. Perfluoropolyether (Δ
), and then add it to 10% depending on the content of low-boiling components.
Heat treatment is performed at a temperature in the range of 0°C or higher and 200°C or lower for a period of 1 hour or more and 5 hours or less, and the treated liquid is filtered under reduced pressure. Perfluoropolyether purified by removing impurities (
This is a medium having a lubricating layer formed using 8).

The lubricating layer formed in this way has a significantly reduced heating loss, and since no impurities are generated due to the collapse of the structure of the perfluoropolyether (8), it has strong adhesion with the underlying layer and has a uniform film thickness. media with such a lubricant layer have good lubricating performance, excellent wear resistance, and good durability. Become a highly reliable medium.

In addition, when the weight average molecular weight of perfluoropolyether (A) is less than 2,000, the friction coefficient of the lubricating layer becomes large, and when it exceeds 3,500, the magnetic head is likely to be attracted to it. It is necessary that

〔Example〕

Example 1 A perfluoropolyether (with a weight average molecular weight IM of 2000 and a low-boiling component content of 3.5% by weight with a weight average molecular repulsion of 500 or less by gel chromatography/UV detection)
A) was heat-treated at 200° C. for 1 hour, and the treated solution was filtered under reduced pressure to remove impurities. Dissolve the thus purified perfluoropolyether (Δ) in trifluorotrichloroethane as a solvent! The solution was applied by dip coating to the surface of the amorphous carbon protective layer formed on the surface of the magnetic layer on the support, and dried to form a lubricating layer to prepare a medium.

Example 2 A perfluoropolyether with a weight average molecular weight IM of 2300 and a low-boiling component content of 4.5% by weight with a weight average molecular weight of 500 or less as determined by gel chromatography and UV detection (
A medium was produced in the same manner as in Example 1, except that A) was heat-treated at a temperature of 200° C. for 1 hour to obtain a treatment liquid.

Example 3 A perfluoropolyether with a weight average molecular weight IM of 3500 and a low-boiling component content of 5.5% by weight with a weight average molecular weight of 500 or less determined by gel chromatography and UV detection (
A medium was produced in the same manner as in Example 1, except that A) was heat-treated at a temperature of 150° C. for 1 hour to obtain a treatment liquid.

Example 4 A medium was produced in the same manner as in Example 3, except that the heat treatment temperature of perfluoropolyether (Δ) was changed to 200°C.

Example 5 Perfluoropolyether (A) having a weight average molecular weight Mw of 2800 and a low boiling component content of 7.7% by weight with an M weight average molecular weight of 500 or less as determined by gel chromatography/UV detection at a temperature of 150°C. A medium was produced in the same manner as in Example 1, except that the treatment solution was obtained by processing for 1 hour.

Example 6 A medium was produced in the same manner as in Example 5, except that the heat treatment temperature of perfluoropolyether (A) was changed to 200°C.

Example 7 A medium was produced in the same manner as in Example 5, except that the heat treatment of perfluoropolyether (A>) was changed to heat treatment at a temperature of 200° C. for 3 hours.

Example 8 Weight average molecular weight M is 3200, weight average molecule determined by gel chromatography/UV detection! ! Perfluoropolyether containing 10% by weight of low-boiling components of 500 or less (
A medium was prepared in the same manner as in Example 1, except that A) was heat-treated at 200° C. for 1 hour to obtain a treatment liquid.

Example 9 A medium was produced in the same manner as in Example 8, except that the heat treatment of perfluoropolyether (A) was changed to heat treatment at a temperature of 200° C. for 3 hours.

Example IO A medium was produced in the same manner as in Example 8, except that the heat treatment of perfluoropolyether (A) was changed to a heat treatment at a temperature of 200° C. for 5 hours.

Comparative Example 1 The perfluoropolyether (A) used in Example 1 was
A medium was produced in the same manner as in Example 1, except that it was used as it was without S treatment.

Comparative Example 2 A medium was produced in the same manner as in Example 2, except that the perfluoropolyether (A) used in Example 2 was used as it was without any purification treatment.

Comparative Example 3 A medium was produced in the same manner as in Example 3, except that the perfluoropolyether (A) used in Example 3 was used as it was without any purification treatment.

Comparative Example 4 A medium was produced in the same manner as in Example 5, except that the perfluoropolyether (Δ) used in Example 5 was used as it was without any purification treatment.

Comparative Example 5 A medium was produced in the same manner as in Example 8, except that the perfluoropolyether (A) used in Example 8 was used as it was without any purification treatment.

The content of low-boiling components having a weight average molecular weight of 9 or less and a weight average molecular weight of 500 or less of the perfluoropolyethers used in the above Examples and Comparative Examples and the heat treatment conditions of each Example are summarized in Table 1.

Table 1: The content of low-boiling components was determined by gel chromatography/UV detection method.
The weight average molecular weight contents of different types of perfluoropolyales (A) are shown in FIG. In Figure 1, the horizontal axis shows the weight average molecular weight at the peak N (L) in UV detection, and the vertical axis shows the content (wt%).Table 2 shows the weight average molecular weight corresponding to each peak Nα. show.

Table 2 Also, Figure 2 shows the weight average molecular weight of 280 used in Example 5.
0, low-boiling component content with a weight average molecular weight of 500 or less 7.
Regarding 7% by weight perfluoropolyether (A),
FIG. 3 is a diagram showing the results of examining changes in low-boiling component content due to purification treatment (heat treatment and vacuum filtration) using gel chromatography/Uv detection method. In Fig. 2, the solid line is the one without purification treatment, the - dotted line is the one with purification treatment of heating at 150°C for 1 hour followed by vacuum filtration, and the dotted line is at 200°C.
, the results are shown for those subjected to a purification treatment of heating for 1 hour and then filtering under reduced pressure. It is clear from FIG. 2 that the content of low-boiling components is reduced by the purification treatment, and that the content of low-boiling components is further reduced by increasing the heat treatment temperature.

Next, for each medium of Examples and Comparative Examples,
The heating loss and film thickness variation rate of the lubricating layer when heat treated for 1 hour at a temperature of 33°C.

The adsorption critical film thickness at which the magnetic head would not be adsorbed to the surface of the lubricant layer when left in an atmosphere with a relative humidity of 80% for 24 hours was investigated. The results are shown in Table 3.

Table 3 As can be seen by comparing the Examples and Comparative Examples in Table 3, perfluoropolyether (A) can form a lubricating layer with better properties by purifying it by vacuum filtration after heat treatment. It becomes like this. In other words, the heating loss of the lubricating layer is reduced, the film thickness variation rate is reduced, and a uniform film thickness is maintained, so that the adhesion with the underlying layer and abrasion resistance do not deteriorate, and the adsorption criticality is maintained. The film thickness does not become thinner.

In addition, impurities that occur due to the collapse of the structure of perfluoropolyether (A) are removed, leaving only those with a good structure. The film thickness becomes thicker.

Therefore, it is possible to obtain a lubricating layer that has excellent adhesion and abrasion resistance, and is less likely to attract magnetic heads.

From the results of Examples 1 to 10, the effect of this purification is more noticeable as the perfluoropolyether (Δ) has a higher content of low-boiling components, and does not appear much when the content of low-boiling components is about 3.5%, Furthermore, it can be seen that the higher the heating temperature and the longer the heating time in the heat treatment during purification, the more pronounced the effect appears. Furthermore, from the results of Examples 8 and 9゜1O and Comparative Example 5, when the content of low-boiling components is increased to about 10% by weight, 200℃
It can be seen that even if the heat treatment is performed at a temperature of 5 hours, a sufficient effect is still not obtained. From these points, it can be seen that it is desirable to use perfluoropolyether (A) having a low-boiling component content in the range of 3.5% by weight or more and 10% by weight or less.

〔Effect of the invention〕

According to this invention, the general formula of the main chain portion is the above formula (I), has a polar group at least one end via an aromatic ring, and has a weight average molecular weight within the range of 2000 to 3500. , a perfluoropolyether having a weight average molecular weight of 500 or less and a low-boiling component content of 3.5% by weight or more and 10% by weight or less is heated at a temperature of 100°C or more and 200°C or less for 1 hour or less. A lubricating layer on the surface of the medium is formed using perfluoropolyether as a filtrate obtained by heat treatment for a time within a range of 100 hr or less and filtration under reduced pressure. The lubricating layer formed from perfluoropolyether purified in this way has good adhesion to the underlying layer, has a uniform film thickness, has excellent lubrication performance, has high wear resistance, and is difficult to attract magnetic heads. , it is a layer with good durability, has excellent lubrication performance and abrasion resistance, and the magnetic head is easily attracted to the magnetic head.A medium with good durability and high reliability can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the results of examining the low-boiling component content of five types of perfluoropolyethers used in Examples of this invention by gel chromatography and UV detection, and Figure 2 is a diagram showing the results of Example 5. Gel chromatography and UV peak No. of the perfluoropolyether used in the study were conducted to examine changes in the content of low-boiling components due to purification treatment. Figure 1 Peak No. Second

Claims (1)

[Scope of Claims] 1) In a magnetic recording medium having a lubricating layer made of perfluoropolyether on a magnetic layer, the lubricating layer has a general formula of the main chain portion of the following formula (I), and at least one of the lubricating layers has a general formula of the following formula (I). It has a polar group at the end via an aromatic ring, has a weight average molecular weight in the range of 2000 to 3500, and has a low boiling point content of 3.5% by weight to 10% by weight with a weight average molecular weight of 500 or less. Perfluoropolyether as a filtrate obtained by heat-treating a perfluoropolyether falling within the range of 100°C to 200°C for a period of 1 hour to 5 hours and filtering it under reduced pressure. A magnetic recording medium characterized in that it is formed by coating. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) [In formula (I), l, m, and n each represent an integer. ]