JPH0520673A - Magnetic recording medium and method for refining liquid lubricant used for the same - Google Patents

Abstract

PURPOSE:To develop a proper method of refining perfluoropolyeter and to obtain, a medium excellent in lubricating performance with using the perfluoropolyether so that the perfluoropolyether can be refined till it becomes soluble in an alternate fluorocarbon and that no Flon(CFC) 113 is used during application of a lubricant CONSTITUTION:Perfluoropolyether as a liquid lubricant is refined by chromatographic separation into mol.wt. by the interaction the perfluoropolyether and polystyrene GPC packing material ta remove low mol.wt. components and impurities which are unstable components for the product. It is preferable to refine the lubricant till it has MW between >=2800 and <=4500, and <=1.6 MW/Mn. It is more preferable to refine the lubricant to obtain MW between >=2800 and <=4500 and <=1.6 MW/Mn because the lubricant becomes soluble in an alternate chloro fluorocarbon.

Description

Detailed Description of the Invention

The present invention relates to a method for purifying perfluoropolyether as a liquid lubricant and a magnetic recording medium having a lubricating layer coated with perfluoropolyether purified by the method.

[0002]

2. Description of the Related Art In a magnetic recording medium (hereinafter also simply referred to as "medium"), it is necessary to reduce the friction coefficient of its surface and enhance the lubricating performance so as to stabilize the contact running of a magnetic head. In addition, a lubricating layer in which perfluoropolyether is applied as a liquid lubricating layer is formed on the surface of the protective layer of the medium. This lubricating layer needs to be formed on the surface of the medium with a uniform film thickness and with good durability and stability, and the adhesiveness with the protective layer as the underlayer is important. In order to improve this adhesion, perfluoropolyethers having various polar groups at their molecular terminals have been proposed. Among them, the one expected to have the strongest adhesion is the aromatic group as a polar group. It is a perfluoropolyether having a hydrophilic group via a group ring.

The perfluoropolyether in which the aromatic ring is introduced into the terminal of the molecule improves the orientation of the molecule, so that a uniform film having strong adhesion can be formed and the effect of reducing the friction coefficient can be obtained. A large and durable lubricating layer with excellent lubricating performance can be obtained.

[0004]

However, the above-mentioned perfluoropolyether having an aromatic ring at the molecular end is
There are drawbacks that the quality is unstable, the heat resistance is relatively low, it may change over time depending on the lot, and the quality may vary greatly. Therefore, in a medium having a lubricating layer coated with perfluoropolyether having such a structure, the film thickness uniformity and wear resistance of the lubricating layer vary depending on the synthetic lot of perfluoropolyether. The phenomenon that the magnetic head is attracted to the surface of the medium also varies.

Further, conventionally, chlorofluorocarbon, especially chlorofluorocarbon 113, has been used as a solvent for the perfluoropolyether coating liquid when forming the lubricating layer. However, in recent years, the ozone layer depletion of the stratosphere by CFC 113 has become a serious problem, and the use of CFC 113 is being regulated. However, H other than Freon 113
Alternative CFCs such as CFC, HFC, and FC have a problem in solubility of perfluoropolyether, and low molecular weight components,
There is a drawback that perfluoropolyether containing a large amount of impurity components is not completely dissolved.

The present invention has been made in view of the above points, and has found a refining method for improving the heat resistance of perfluoropolyether as a liquid lubricant and reducing the variation in quality. Using perfluoropolyether with aromatic ring at the end of the molecule, which has the required uniform quality, has good adhesion to the protective layer, thermal stability, uniform film thickness, and excellent lubrication performance. Providing a medium with layers is a problem to be solved. Also,
Further, by the purification method, the perfluoropolyether having an aromatic ring at the molecular end is purified to the extent that it completely dissolves in the CFC substitute, and CFC 11 is used as a solvent for the coating liquid.
The problem to be solved is to make it possible not to use 3.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the molecular weight of perfluoropolyether is changed by the interaction between perfluoropolyether which is a liquid lubricant and polystyrene-based GPC filler. Chromatographic separation is performed, and purification is performed by a method of removing low molecular weight components and impurity components, which are unstable components.

By this purification method, the weight average molecular weight M _w is in the range of 2,800 or more and 4,500 or less, and the molecular weight distribution spread M _w / M _N is 1.6 or less. And more preferably the weight average molecular weight M _w
Is in the range of 3,200 or more and 4,500 or less, and the main chain component general formula purified so that the broadening of the molecular weight distribution M _w / M _N is 1.3 or less is the following formula (I), A medium having a lubricating layer formed by coating a perfluoropolyether having an aromatic ring at one end on a protective layer.

[0009]

[Chemical 2]

[In the formula (I), l and m each represent an integer. ]

[0011]

"Perfluoropolyether having a main chain component of the general formula (I) and having an aromatic ring at least at one end" (hereinafter, also simply referred to as "perfluoropolyether (A)") is an underlayer. Although it is possible to form a film having a strong adhesive force with the surface of the protective layer, on the other hand, it is also a perfluoropolyether in which the characteristics of the film obtained are also unstable due to the unstable quality.

The present inventors have found that the molecular weight distribution of the perfluoropolyether (A) is wide, especially the weight average molecular weight 1,
It was noted that the presence of low molecular weight components below 000 is closely related to this instability.

The presence of the low molecular weight component and the impurity component is directly linked to the instability of the perfluoropolyether (A). The higher the content of these components, the weaker the thermal behavior,
As a result, the structure of the polar group is destroyed, and the adhesion between the perfluoropolyether (A) and the protective layer is weakened. When a lubricating layer is formed by coating the surface of the protective layer with perfluoropolyether (A) having a large amount of low molecular weight components and impurities, it is heated on the medium surface by drying after coating or by the ambient temperature when the medium is used. A large heating loss occurs, and further, impurities accompanying the collapse of the polar group structure occur,
The adhesion between the perfluoropolyether (A) and the protective layer becomes weak, and as a result, the film thickness of the lubricating layer becomes non-uniform, and the lubricating performance and wear resistance decrease. Further, since the polar group whose structure has been destroyed by heating is hydrophilic to some extent, water is likely to be caught in this portion in a high humidity atmosphere, and adsorption of the magnetic head is likely to occur.

As described above, in the perfluoropolyether (A) which is a liquid lubricant used in the lubricating layer of the medium, it is important to reduce its low molecular weight component and impurity component as much as possible. As a result of pursuing the method, the present inventors have found that perfluoropolyether and polystyrene GP
We have found a purification method that can arbitrarily remove the low molecular weight component by a large-scale preparative purification method in which the chromatographic separation due to the interaction of the C filler is scaled up.

By coating the protective layer with the perfluoropolyether (A) purified by this method, the perfluoropolyether (A) is firmly adhered to the protective layer, and the thickness reduction due to heating is significantly reduced. Since the impurities due to the collapse of the end structure of perfluoropolyether (A) are not generated, the uniformity of the film thickness is improved, the wear resistance is excellent, and the adsorption of the magnetic head is less likely to occur. It is possible to obtain a medium that can be formed and has excellent lubrication performance.

Purification of the perfluoropolyether (A) is carried out so that the weight average molecular weight M _w is in the range of 2,800 or more and 4,500 or less and the molecular weight distribution spread M _w / M _N is 1.6 or less. It is desirable to be seen. Further, the weight average molecular weight M _w is in the range of 3,200 or more and 4,500 or less,
If purified so that the spread of the molecular weight distribution M _w / M _N becomes 1.3 or less, the solubility will be improved and it will also be completely dissolved in the alternative CFC. Therefore, it is necessary to use CFC 113 as the coating liquid. Is preferred, which is preferable.

[0017]

EXAMPLE As a method for purifying perfluoropolyether by large-scale preparative chromatography separation, for example, there is a method according to the following steps. (A) Dilute perfluoropolyether two times with Freon 113 or several alternative Freons. Examples of the alternative CFCs include HCFC (AK225 manufactured by Asahi Glass Co., Ltd., HCFC141b manufactured by Central Glass Co., Ltd.), HFC (5FP manufactured by Daikin Industries, Ltd.), FC (Fluorinert FC-77 manufactured by 3M Company, Fomblin Solvent ZS manufactured by Japan Enmont Co., Ltd.). -100) is used. (B) Pump up this solution to remove polystyrene G
Pass through a PC filler (for example, Showa Denko GPC803). (C) CFC 113 or alternative CFC is flowed in the filler as a mobile phase. (D) Due to the interaction between the perfluoropolyether and the pore size of the filler, the perfluoropolyether molecules are eluted in order from the largest one. (E) The eluted perfluoropolyether is arbitrarily separated according to its molecular weight. (F) Concentrate the Freon 113 or the alternative Freon as a solvent.

Thus, the perfluoropolyether was added to Gel Permeation Chromatogr.
Chromatographic separation by aphy (GPC), fractionation at an arbitrary point according to molecular weight, and removal of low molecular weight components and impurity components that are chromatographically separated after the fractionation point to a level corresponding to the fractionation point. A purified quality perfluoropolyether is obtained.

FIG. 1 is a diagram showing an example of a weight average molecular weight distribution when perfluoropolyether is chromatographically separated by molecular weight due to interaction with a polystyrene-based GPC filler. The horizontal axis shows the weight average molecular weight and the vertical axis shows the average molecular weight. Indicates the content (arbitrary scale). ~ Indicates an example of a preparative point during purification.

Perfluoropolyether (A) having a weight average molecular weight M _W of 2,500 and a molecular weight spread M _W / M _N of 1.70 is fractionated at the fractionation points shown in FIG. 1 by the above-mentioned purification method. To obtain a purified product 1. The purified product 1 was eluted by the preparative point in the large-scale preparative chromatographic separation.
In the same manner, purified products 2, 3, 4, and 5 were obtained by collecting at each of the collecting points ,.

With respect to these purified products, the yield at the time of purification,
Table 1 shows the removal rates of low molecular weight components and impurity components, the weight average molecular weight M _{W of} each purified product, the spread of molecular weight M _W / M _N , and the solubility of CFC substitutes together with those of the unpurified product before purification. Shown together.

[0022]

[Table 1]

As can be seen from Table 1, the higher the degree of purification and the better the solubility, the higher the degree of purification that is obtained by performing the purification by the above-mentioned large-scale preparative chromatographic separation and preparatively collecting at the preparative point of the chromatographic separation. The yield will be low.

The molecular weight distribution of each of the unpurified product and the purified products 4, 3, 1 of perfluoropolyether (A) was examined by GPC. The results are shown in FIGS. As shown in FIG. 2, the unpurified product contains a large amount of low-molecular weight components having a weight-average molecular weight of 2,200 or less. However, by performing purification, as shown in FIGS. The content is reduced. Moreover, as the separation point for purification by chromatographic separation is changed to the earlier stage, the content of this low molecular weight component becomes smaller as shown in FIGS. You can see that it will increase.

Each of these purified products 1 to 5 is a fluorocarbon 1
13 or each of the coating liquids dissolved in CFC substitutes is applied to the surface of the protective layer formed on the magnetic recording layer on the non-magnetic substrate by a dip coating method or a spin coating method to form a lubricating layer, and the temperature is 100 ° C. After heating for 1 hour in Examples 1 to 5
The medium of was produced. In addition, unrefined CFC 113
A medium of Comparative Example 1 was prepared in the same manner using the coating solution dissolved in.

For each medium thus obtained,
Heating film thickness reduction rate of the lubricating layer when heat-treated at a temperature of 120 ° C for 1 hour, and when the medium is left in an atmosphere of a temperature of 33 ° C and a relative humidity of 80% for 24 hours, the magnetic head is attracted to the surface of the lubricating layer. Not adsorbing limit film thickness that shows the limit lubricating layer film thickness, and good CSS (ContactStart)
The CSS resistance evaluated by the number of repetitions of Stop) was examined. The results are shown in Table 2.

[0027]

[Table 2]

From Tables 1 and 2, perfluoropolyether
Ether (A) by the above-mentioned method for large-scale preparative chromatography separation.
, Weight average molecular weight M_WIs over 2,800 and over 4,500
Molecular weight spread M in the lower range_W/ M_NIs less than 1.6
Performed by refining so that
The superiority of the example media is clear. In addition, M after purification _W
Is large M_W/ M_NThe smaller the value, the better the media
You can see that The medium of Comparative Example 1 has a CSS resistance of 3
Over 10,000 times, the adsorption limit film thickness is relatively thick, but the heating film thickness is reduced.
It is considered that there is a high possibility that a big problem will occur.

Further, as shown in Table 1, there has hitherto been no alternative CFC capable of completely dissolving the unpurified perfluoropolyether (A), but by the above-mentioned method, M _W of 3,200 or more 4 , Purified to a M _W / M _N ratio of 1.3 or less within a range of 500 or less is completely soluble in many CFC alternatives. Therefore, if the thus-purified perfluoropolyether (A) is used, it is not necessary to use CFC 113 as a solvent when forming the lubricating layer, and the obtained effect is very large.

[0030]

According to the present invention, the interaction between the liquid lubricant perfluoropolyether and the polystyrene-based GPC filler causes the perfluoropolyether to be chromatographically separated according to its molecular weight, resulting in a low quality unstable component. By refining by removing the molecular weight component and the impurity component, it is possible to obtain perfluoropolyether having improved heat resistance and less variation in quality.

By such a purification method, a perfluoropolyether having a main chain moiety general formula (I) and an aromatic ring at least at one end has a weight average molecular weight M _W of 2 , 800 or more and 4,500 or less so that the molecular weight spreads M _W / M _{N to} be 1.6 or less, and the resulting perfluoropolyether is applied to the protective layer to form a lubricating layer. By doing so, it is possible to obtain a magnetic recording medium having a lubricating layer that has good adhesion to the protective layer, is thermally stable, has a uniform film thickness, is less likely to be attracted by the magnetic head, and has excellent lubricating performance. Become.

Furthermore, by the above-mentioned purification method, the weight average molecular weight M
_The perfluoropolyether purified to have a molecular weight spread M _W / M _N of 1.3 or less in the range of _W of 3,200 or more and 4,500 or less becomes soluble in many alternative CFCs and the lubricating layer It is possible to obtain the effect that it is not necessary to use the Freon 113 for coating.

[Brief description of drawings]

FIG. 1 Perfluoropolyether is polystyrene type G
Diagram showing an example of weight average molecular weight distribution when chromatographically separated by molecular weight due to interaction with PC filler

FIG. 2 is a diagram obtained by examining the weight average molecular weight distribution of an unpurified product by GPC.

FIG. 3 is a diagram obtained by examining the weight average molecular weight distribution of purified product 4 by GPC.

FIG. 4 is a diagram obtained by examining the weight average molecular weight distribution of purified product 3 by GPC.

FIG. 5 is a diagram obtained by examining the weight average molecular weight distribution of purified product 1 by GPC.

Claims (3)

[Claims] 1. A perfluoropolyether that is a liquid lubricant and a polystyrene-based GPC filler are subjected to an interaction to perform chromatographic separation of the perfluoropolyether by molecular weight to remove low molecular weight components and impurity components that are quality unstable components. A method for purifying a liquid lubricant, comprising: 2. Purified by the above-mentioned purification method such that the weight average molecular weight M _W is in the range of 2,800 or more and 4,500 or less and the broadening of the molecular weight distribution M _W / M _N is 1.6 or less. A magnetic recording medium characterized in that the main chain portion has a general formula (I) below and has a lubricating layer formed by coating a perfluoropolyether having an aromatic ring on at least one end. [Chemical 1] [In the formula (I), l and m each represent an integer. ] 3. A weight average molecular weight M _w of 3,200 or more 4,
Within the range of 500 or less, the broadening of the molecular weight distribution M _W /
The magnetic recording medium according to claim 1, wherein a perfluoropolyether purified so that M _N is 1.3 or less is used.