JP2003041279A - Method for purifying lubricant and magnetic disk having membrane of lubricant obtained from the purification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification method which can reduce the number of times of solvent extraction in purifying a perfluoropolyether having a hydroxy group at the terminal. SOLUTION: In removing a low molecular weight component from a lubricant to purify it for the lubricating film 11 of a magnetic disc 1 obtained by forming, on the surface of a non-magnetic disc substrate 3, an undercoat membrane 5, a magnetic layer 7, a protective membrane 9, and a lubricating membrane 11 in the order named, a perfluoropolyether having a hydroxy group in the terminal is subjected to solvent extraction with the use of a solvent comprising a 5C completely fluorinated carbon fluoride as the major component as the good solvent and ethyl alcohol or methyl alcohol as the poor solvent. By this, the number of times of solvent extraction can be reduced in the purification of a perfluoropolyether having a hydroxy group at the terminal which becomes a lubricant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying a lubricant and a magnetic disk provided with a film of the lubricant obtained by the method, and more particularly to a method for purifying perfluoropolyether having a hydroxyl group at a terminal. And a magnetic disk provided with a perfluoropolyether film having a hydroxyl group at the end obtained by the purification method thereof.

[0002]

2. Description of the Related Art A magnetic disk, which is an information recording medium, is a nonmagnetic disk-shaped substrate on which a base film, a magnetic layer, a protective film, and a lubricating film are sequentially formed. Such a magnetic disk constitutes a magnetic disk device together with a spindle motor for rotating the magnetic disk, a magnetic head for recording information on the magnetic disk, reading the recorded information, and the like.

By the way, there is a strong demand for a large capacity of the information recording medium, so that the storage capacity of the magnetic disk is increasing. Due to the high recording density accompanying the increase in the storage capacity of the magnetic disk, the flying height of the magnetic head is reduced,
The rotation speed of the magnetic disk is increasing. Such a decrease in the flying height of the magnetic head and an increase in the speed of rotation of the magnetic disk increase the influence of air or the like on the lubricating film on the surface of the magnetic disk, and thus the thickness of the lubricating film may decrease. To be done. Since the reduction of the lubricating film on the surface of the magnetic disk affects the sliding reliability between the magnetic disk and the magnetic head, it is necessary to reduce the reduction of the thickness of the lubricating film in order to maintain the performance of the magnetic disk. There is.

Perfluoropolyether having a hydroxyl group at its terminal is used as a lubricant for forming a lubricating film of a magnetic disk. As one of the methods for reducing the decrease in the thickness of the lubricating film, it is conceivable to purify the lubricant forming the lubricating film and control the number average molecular weight of the lubricant. That is, perfluoropolyether having a hydroxyl group as a polar group has a molecular weight distribution in the range of several hundreds to about 10,000, and low molecular weight components, for example, components having a molecular weight of about 1500 or less are used for heat or magnetic disks. It is known that the air easily scatters due to the shearing force of air accompanying the rotation.
Therefore, in order to reduce the decrease in the thickness of the lubricating film,
It is considered to purify perfluoropolyether having a hydroxyl group at the terminal to become a lubricant for forming a lubricating film to remove low molecular weight components and increase the number average molecular weight of the perfluoropolyether having a hydroxyl group at the terminal. To be

Solvent extraction can be considered as one of the methods for purifying the lubricant. Solvent extraction does not require large-scale equipment as compared with a purification method such as distillation or preparative liquid chromatography, and the lubricant can be purified with relatively high accuracy. Patented the manufacturing and refining technology of lubricant by solvent extraction
677074, Japanese Patent Laid-Open No. 5-109053,
JP-A-6-215347 and JP-A-9-15767.
4, JP-A-9-291296, JP-A-10
It is proposed in Japanese Patent Publication No. -53781. In lubricant manufacturing and purification technology using solvent extraction, low molecular weight components are fractionated by utilizing the difference in solubility of each molecular weight component in a good solvent and a poor solvent. It is necessary to change the kind and ratio of the good solvent and the poor solvent used for extraction according to the molecular weight distribution.

For example, in Japanese Patent No. 2677074, a solvent extraction method of a lubricant is carried out by using esters as a good solvent and alcohols as a poor solvent. Japanese Patent Laid-Open No. 5-
109053, JP-A-5-234066,
In JP-A-6-215347 and the like, solvent extraction is performed by using esters or aliphatic cyclic ethers typified by tetrahydrofuran as good solvents and alcohols as poor solvents. Furthermore, JP-A-9-157674, JP-A-9-291296, and JP-A-10-5.
In Japanese Patent No. 3781, esterification reaction and hydrolysis are performed before and after solvent extraction.

[0007]

However, Japanese Patent No. 267
When attempting to remove the low molecular weight component contained in the lubricant composed of perfluoropolyether having a hydroxyl group at the terminal by the method proposed in Japanese Patent Publication No. 7074, solvent extraction operation must be performed three times or more. . Further, perfluoropolyether having a hydroxyl group at the terminal is a good solvent such as esters proposed in JP-A-5-109053, JP-A-5-234066 and JP-A-6-215347. Since it does not dissolve in tetrahydrofuran, it is not possible to purify perfluoropolyether having a hydroxyl group at the terminal by these methods.

Further, in solvent extraction using only poor solvents such as alcohols and ketones as in JP-A-5-234066, even if the number of solvent extraction operations can be reduced, a heterogeneous system is obtained. Therefore, the yield is low, and in order to obtain the required amount of the lubricant, the solvent extraction operation must be repeated many times. Therefore, Japanese Patent No. 26770
In the case where the conventional solvent extraction method proposed in Japanese Patent Laid-Open No. 74-234, Japanese Patent Application Laid-Open No. H5-234066, etc. is applied to the purification of perfluoropolyether having a hydroxyl group at the terminal, the solvent extraction is repeated three times or more. It is necessary to reduce the number of times of solvent extraction because it is necessary to repeat the operation, the purification work becomes complicated, and a large amount of solvent is used according to the number of times of solvent extraction.

Incidentally, JP-A-9-157674, JP-A-9-291296, and JP-A-10-53781.
Although the solvent extraction method proposed in Japanese Patent Publication etc. can also be applied to the purification of perfluoropolyether having a hydroxyl group, the purification work is not complicated because the esterification reaction and hydrolysis are performed before and after the solvent extraction. There is no change and it is not preferable.

An object of the present invention is to reduce the number of solvent extractions in the purification of perfluoropolyether having a hydroxyl group at the terminal.

[0011]

The method for purifying a lubricant according to the present invention comprises a solvent containing a fully fluorinated fluorocarbon having a main component of 5 carbon atoms as a good solvent, and ethyl alcohol as a poor solvent. Alternatively, the above problem is solved by performing solvent extraction of perfluoropolyether having a hydroxyl group at the terminal using methyl alcohol.

Further, a perfluoropolyether having a hydroxyl group at a terminal is dissolved in a good solvent containing a fully fluorinated fluorocarbon having 5 carbon atoms as a main component to form a solution, and the resulting solution is dissolved. A poor solvent consisting of ethyl alcohol or methyl alcohol is added to the liquid, and solvent extraction is performed.

According to such a method for purifying a lubricant, a good solvent containing a perfluorinated fluorocarbon having 5 as a main component capable of dissolving a perfluoropolyether having a hydroxyl group and a fluorocarbon having a hydroxyl group. High affinity with the hydroxyl group, which is the polar group of perfluoropolyether, and perfluoropolyether with a hydroxyl group, by using a poor solvent consisting of ethyl alcohol or methyl alcohol, which has poor affinity with the perfluoropolyether chain. The removal efficiency of the low molecular weight component can be improved, and the increase in the number average molecular weight of the perfluoropolyether having a hydroxyl group by one solvent extraction operation can be made higher than that by the conventional solvent extraction purification method. Therefore, the number of solvent extractions in the purification of perfluoropolyether having a hydroxyl group at the terminal can be reduced.

Further, the perfluoropolyether having a hydroxyl group at the terminal is represented by the structural formula (1) or the structural formula (2).

[0015]

[Chemical 3]

[0016]

[Chemical 4] (Where m, n, and p are positive integers). These perfluoropolyethers having a hydroxyl group at their ends are suitable as a lubricant for forming a lubricating film of a magnetic disk, and are good solvents containing perfluorinated fluorocarbons having a main component of 5 carbon atoms. And a poor solvent consisting of ethyl alcohol or methyl alcohol can be used to perform a single solvent extraction operation to sufficiently remove low-molecular weight components, and a single solvent extraction operation can control the target number average molecular weight. You can

Then, the structural formula (1) or the structural formula (2)
If the increase in the number average molecular weight of the lubricant having the structure of 1 by one solvent extraction treatment is in the range of 400 or more and 1000 or less, these lubricants are controlled to the target number average molecular weight by one solvent extraction operation. be able to.

Further, a base film, a magnetic layer, a protective film, and a lubricating film were sequentially formed on the surface of a non-magnetic disk-shaped substrate, and the lubricating film was purified by any one of the above refining methods. If it is formed of perfluoropolyether having a hydroxyl group at the terminal, a lubricating film from which low-molecular-weight components that easily scatter can be removed can be formed, so that reduction in the thickness of the lubricating film can be suppressed.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for purifying a lubricant and a magnetic disk according to the present invention will be described below with reference to FIG.
It will be described with reference to FIGS. FIG. 1 is a partial sectional view showing a schematic configuration of a magnetic disk to which the present invention is applied. FIG. 2 is a plan view showing a schematic internal configuration of a magnetic disk device including a magnetic disk to which the present invention is applied. FIG. 3 is a side view showing a schematic internal configuration of a magnetic disk device including a magnetic disk to which the present invention is applied.

In the magnetic disk 1 of this embodiment, as shown in FIG. 1, a base film 5, a magnetic layer 7, and a protective film 9 are sequentially formed on the surface of a disk-shaped substrate 3, and the protective film 9 is then formed. This is a configuration in which the lubricating film 11 is formed as the outermost layer. Substrate 3 is
It is made of a material having a relatively high surface smoothness, such as aluminum or glass. The base film 5 is, for example, C
It is made of r, Mo, W, Cu—Ti, or the like, and is formed by a sputtering method or the like. The magnetic layer 7 is, for example, Co-
It is made of Cr-Ta or the like and is formed by a sputtering method or the like. The protective film 9 is formed by depositing a carbon-based material such as amorphous carbon.

For the lubricating film 11 formed on the outermost layer, a lubricant made of perfluoropolyether having a hydroxyl group at the terminal represented by the structural formula (1) or the structural formula (2) is used. The magnetic disk 1 having the film formed thereon is formed by a dipping method in which the magnetic disk 1 is dipped in the lubricant, pulled up, and then dried.

[0022]

[Chemical 5]

[0023]

[Chemical 6] (Where m, n and p are positive integers) The number average molecular weight of the perfluoropolyether having a hydroxyl group at the terminal represented by the structural formula (1) or structural formula (2) is 20.
It is about 0 to 4000, and contains a low molecular weight component that is easily scattered when used as a lubricating film of a magnetic disk, that is, a component having a molecular weight of 1500 or less. Therefore, as the lubricant for forming the lubricating film 11, a lubricant obtained by removing low molecular weight components to increase the number average molecular weight in the range of 400 or more and 1000 or less, that is, the number average molecular weight is 2400 to 2400.
The one controlled to about 5000 is used.

As a purification method for removing the low-molecular component of perfluoropolyether having a hydroxyl group at the terminal represented by the structural formula (1) or structural formula (2), a purification method by solvent extraction is used. At this time, since the compound represented by the structural formula (1) or the structural formula (2) has a hydroxyl group (—OH) as a polar group, the poor solvent has poor affinity with the perfluoropolyether chain. Moreover, it is necessary to select a solvent having a high affinity with the hydroxyl group. Therefore, in the method for purifying a lubricant by the solvent extraction method of the present invention, a perfluorinated solvent having a carbon number of 5 as a main component, which is a fluorine-containing solvent capable of dissolving perfluoropolyether having a hydroxyl group at a terminal as a good solvent A solvent extraction operation is performed by using a solvent containing a fluorocarbon as a poor solvent from alcohols using ethyl alcohol or methyl alcohol. Further, by changing the mixing ratio of the good solvent and the poor solvent, the amount of the low molecular weight component dissolved in the poor solvent is controlled, and the number average molecular weight of the perfluoropolyether having a hydroxyl group at the terminal as a lubricant is aimed. The number average molecular weight can be controlled.

In the lubricant refining method of the present embodiment as described above, the lubricant represented by the structural formula (1) or the structural formula (2) is sufficiently low-molecular benign by a single solvent extraction operation. Since the amount can be removed, the lubricant can be used as a target number average molecular weight in one solvent extraction operation, that is, the number average molecular weight of 2400 to 50.
It can be controlled to about 00. Therefore, the number of solvent extractions in the purification of perfluoropolyether having a hydroxyl group at the terminal can be reduced.

As shown in FIGS. 2 and 3, the magnetic disk device 13 having the magnetic disk 1 having the lubricant film 11 formed of the lubricant refined by the lubricant refining method of the present invention is a magnetic disk. From a spindle motor 15 for rotating the magnetic disk 1, a magnetic head 17 for recording information on the magnetic disk 1 and reading information from the magnetic disk 1, and an arm 19 having the magnetic head 17 attached to an end thereof. A magnetic head slider 21, an actuator 23 for pivoting the arm 19 by pivotally supporting the end of the arm 19 on the side opposite to the side where the magnetic head 17 is attached, rotation of the spindle motor 15, and magnetic head 17
And a control circuit 25 for controlling the operation of the actuator 23, a casing 27 accommodating these devices, and the like.

The magnetic head 17 includes an actuator 21.
When the arm 19 is moved by the drive, the magnetic head 1 moves on the recording surface of the magnetic disk 1 with a predetermined flying height. At this time, even if the flying height of the magnetic head 17 decreases due to the high recording density of the magnetic disk 17 and the magnetic head 17 contacts the magnetic disk 1, the lubrication having a sufficient thickness formed on the surface of the magnetic disk 17 is performed. With the film 11, the magnetic head 17
The magnetic disk 1 slides smoothly, and the contact between the magnetic head 17 and the magnetic disk 1 prevents problems in the operation of the magnetic head 17 and the rotating operation of the magnetic disk 1. Therefore, if the lubricating film is scattered and the thickness of the lubricating film is reduced, the sliding reliability between the magnetic head and the magnetic disk may be deteriorated, and a malfunction may occur in the operation of the magnetic head or the rotating operation of the magnetic disk.

On the other hand, the magnetic disk 1 of this embodiment
In the lubricating film 11 of No. 3, a solvent containing a perfluorinated fluorocarbon having a main component of 5 as a fluorine-containing solvent was used as a good solvent, and ethyl alcohol or methyl alcohol was used as a poor solvent. Purified by solvent extraction operation,
It is formed of the lubricant represented by the structural formula (1) or the structural formula (2) from which the low-molecular-weight component that easily scatters is removed.
Therefore, it is difficult to reduce the thickness of the lubricating film 11, the sliding reliability of the magnetic disk 1 can be improved, and the magnetic disk device 13 provided with the magnetic disk 1 can operate the magnetic head and rotate the magnetic disk. It is possible to improve reliability with less trouble.

[0029]

EXAMPLE An example of a lubricant refined by a lubricant refining method according to the present invention and a magnetic disk having a lubricant film formed using this lubricant will be described with reference to FIGS.
Will be described with reference to. FIG. 4 is a graph showing changes in the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of the poor solvent, ethyl alcohol. FIG. 5: is a figure which shows the change of the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of methyl alcohol which is a poor solvent. FIG. 6 is a graph showing changes in the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of the poor solvent, ethyl alcohol. FIG. 7: is a figure which shows the change of the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of methyl alcohol which is a poor solvent. FIG. 8 is a diagram showing changes in the film thickness of the lubricating film with respect to the operating time of the magnetic disk device. FIG. 9 is a diagram showing changes in the film thickness of the lubricating film with respect to the operating time of the magnetic disk device. (Example 1) Z-DOL (manufactured by Ausimont) having a number average molecular weight of 2000 represented by the following structural formula (1) was used as a perfluoropolyether having a hydroxyl group at the terminal, and ethyl alcohol was used as a poor solvent. PF-505 which is a solvent containing perfluorinated fluorocarbon as a good solvent
2 (manufactured by 3M) was used to control the number average molecular weight of the lubricant having the structure of Structural Formula (1) by changing the mixing ratio of the poor solvent, ethyl alcohol.

[0030]

[Chemical 7] (Where m and n are positive integers) First, Z-D which is a lubricant having the structure of structural formula (1)
30 g of OL was weighed in an Erlenmeyer flask, and 60 g of PF-5052 as a good solvent was added thereto to dissolve Z-DOL. Next, 540 g of ethyl alcohol, which is a poor solvent, was added dropwise to this solution over 1 hour, and the solution was vigorously stirred so that the solution did not separate into two layers. After the dropping was completed, the solution was further stirred for 2 hours, and the solution was transferred to a separating funnel.
It was left for 24 hours. After standing for 24 hours, the lower layer of the solution which was completely separated into two layers, that is, only the component used as the lubricant was extracted. After extraction, the solvent was completely removed by an evaporator.

The number average molecular weight of Z-DOL before and after solvent extraction was analyzed by nuclear magnetic resonance analysis (hereinafter abbreviated as NMR). Such a solvent extraction operation was performed while changing the mixing ratio of the good solvent and the poor solvent. At this time, 30 parts by weight of Z
-The total amount of the good solvent and the poor solvent was set to 600 parts by weight with respect to DOL. (Comparative Example 1) PF-50 used in Example 1 as a good solvent
A solvent extraction operation and an analysis of the number average molecular weight were performed in the same manner as in Example 1 except that ethyl acetate was used instead of 52. (Comparative Example 2) After the solvent extraction operation was performed in the same manner as in Comparative Example 1, the same solvent extraction operation as in Comparative Example 1 was repeated twice, and the number average molecular weight was analyzed. (Comparative Example 3) Z-DOL having a number average molecular weight of 2000 used in Example 1 was subjected to a solvent extraction operation using only a poor solvent, ethyl alcohol, that is, 100% ethyl alcohol. That is, 30 g of Z-DOL was weighed in an Erlenmeyer flask, and 600 g of ethyl alcohol was added dropwise over 1 hour. After the addition was completed, the solution was stirred for 2 hours, then the solution was transferred to a separating funnel and left for 24 hours. After standing for 24 hours, only the component used as the lower layer lubricant was extracted. After extraction,
The solvent was completely removed with an evaporator. The number average molecular weight of Z-DOL before and after solvent extraction was NM as in Example 1.
Analyzed by R. (Comparative Example 4) After the same solvent extraction operation as in Comparative Example 3 was performed, the same solvent extraction operation as in Comparative Example 3 was repeated twice.

The results of Example 1 in which PF-5052 was used as a good solvent and ethyl alcohol was used as a poor solvent to extract the lubricant having the structure of the structural formula (1), and ethyl acetate was used as a good solvent Comparative Example 1 in which solvent extraction was performed using ethyl alcohol as the solvent, Comparative Example 2 in which the solvent extraction operation in Comparative Example 1 was performed three times, Comparative Example 3 in which solvent extraction was performed using only ethyl alcohol, and Solvent extraction operation in Comparative Example 3 was performed 3 FIG. 4 shows the results of Comparative Example 4 performed repeatedly. In Example 1 to which the present invention was applied, as shown in FIG. 4, the number average molecular weight of Z-DOL was increased in the range of 400 or more and 1000 or less by one solvent extraction operation, and the low molecular weight component was sufficiently contained. It was confirmed that it was removed. That is, in Example 1, 1
It was possible to control Z-DOL to a target number average molecular weight of about 2400 to 3000 by a single solvent extraction operation.

On the other hand, when ethyl acetate is used as the good solvent, as shown in the results of Comparative Examples 1 and 3, Z-DOL should be controlled to a desired number average molecular weight in one solvent extraction operation. However, as shown in the results of Comparative Examples 2 and 4, Z-DOL could not be increased to the target number average molecular weight unless the solvent extraction operation was repeated 3 times. (Example 2) The solvent extraction operation and the number average molecular weight analysis were carried out in the same manner as in Example 1 except that methyl alcohol was used in place of the ethyl alcohol used in Example 1 as the poor solvent. (Comparative Example 5) PF-50 used in Example 2 as a good solvent
The solvent extraction operation and the number average molecular weight analysis were performed in the same manner as in Example 2 except that ethyl acetate was used instead of 52. (Comparative Example 6) After the solvent extraction operation was performed in the same manner as in Comparative Example 5, the same solvent extraction operation as in Comparative Example 5 was repeated twice, and the number average molecular weight was analyzed. (Comparative Example 7) A solvent extraction operation was performed with 100% methyl alcohol in the same manner as in Comparative Example 3 except that methyl alcohol was used instead of the ethyl alcohol used in Comparative Example 3, and the number average molecular weight was analyzed. (Comparative Example 8) After performing the solvent extraction operation in the same manner as in Comparative Example 7, the same solvent extraction operation as in Comparative Example 5 was repeated twice to analyze the number average molecular weight.

The results of Example 2 in which PF-5052 was used as a good solvent and methyl alcohol was used as a poor solvent to extract the lubricant having the structure of the structural formula (1), and ethyl acetate was used as a good solvent were the poor solvent. Comparative Example 5 in which the solvent extraction was performed using methyl alcohol, Comparative Example 6 in which the solvent extraction operation of Comparative Example 5 was performed three times, Comparative Example 7 in which the solvent extraction was performed only with methyl alcohol, and the solvent extraction operation of Comparative Example 7 were performed. The results of Comparative Example 8 performed three times are shown in FIG. Also in Example 2 to which the present invention is applied, as shown in FIG. 5, the number average molecular weight of Z-DOL is increased in the range of 400 or more and 1000 or less by one solvent extraction operation, and the low molecular weight components are sufficiently removed. Was confirmed. That is, also in Example 2, the number average molecular weight 2 for Z-DOL was 2 in one solvent extraction operation.
It could be controlled to about 400 to 3000.

On the other hand, when ethyl acetate is used as the good solvent, Z-DOL should be controlled to a desired number average molecular weight in one solvent extraction operation as shown by the results of Comparative Examples 5 and 7. However, as shown in the results of Comparative Examples 6 and 8, Z-DOL could not be increased to the desired number average molecular weight unless the solvent extraction operation was repeated 3 times. (Example 3) Instead of Z-DOL which is a lubricant having the structure of structural formula (1) used in Example 1 as a perfluoropolyether having a hydroxyl group at the terminal, a structural formula (2) shown below was used. Z-DOL TX200, a lubricant represented
The solvent extraction operation and the number average molecular weight analysis were performed in the same manner as in Example 1 except that 0 (number average molecular weight 2200, manufactured by Ausimont) was used.

[0036]

[Chemical 8] (Where m, n and p are positive integers) (Comparative Example 9) PF-5 used in Example 3 as a good solvent.
The solvent extraction operation and the number average molecular weight analysis were performed in the same manner as in Example 3 except that ethyl acetate was used instead of 052.
(Comparative example 10).

After carrying out the solvent extraction operation in the same manner as in Comparative Example 9, the solvent extraction operation in the same manner as in Comparative Example 9 was repeated twice, and the number average molecular weight was analyzed. (Comparative Example 11) Instead of Z-DOL which is the lubricant having the structure of Structural Formula (1) used in Comparative Example 3 as a perfluoropolyether having a hydroxyl group at the terminal, it is represented by Structural Formula (2). Solvent extraction operation and number average molecular weight analysis were performed in the same manner as in Comparative Example 3 except that Z-DOL TX2000, which was a lubricant, was used. That is, ethyl alcohol 100
%, The solvent extraction operation was performed, and the number average molecular weight was analyzed. (Comparative Example 12) After performing a solvent extraction operation in the same manner as in Comparative Example 11, the same solvent extraction operation as in Comparative Example 11 was repeated twice to analyze the number average molecular weight.

The results of Example 3 in which PF-5052 was used as a good solvent and ethyl alcohol was used as a poor solvent to extract the lubricant having the structure of the structural formula (2), and ethyl acetate was used as a good solvent were the poor solvent. As Comparative Example 9 in which solvent extraction was performed using ethyl alcohol, Comparative Example 10 in which the solvent extraction operation of Comparative Example 9 was performed three times, Comparative Example 11 in which solvent extraction was performed using only ethyl alcohol, and Solvent extraction operation in Comparative Example 11 was 3 FIG. 6 shows the results of Comparative Example 12 performed repeatedly. Also in Example 3 to which the present invention is applied, as shown in FIG. 6, the number average molecular weight of Z-DOL TX2000 increases in the range of 400 or more and 1000 or less by one solvent extraction operation, and low molecular weight components are sufficiently removed. It was confirmed that it was done. That is,
In Example 3 as well, it was possible to control Z-DOL to a target number average molecular weight of about 260 to 3200 by a single solvent extraction operation.

On the other hand, when ethyl acetate was used as the good solvent, as shown in the results of Comparative Examples 9 and 11, Z-DOL should be controlled to a desired number average molecular weight in one solvent extraction operation. However, as shown in the results of Comparative Examples 10 and 12, the solvent extraction operation was repeated three times to obtain Z-.
It was not possible to increase DOL TX2000 to the desired number average molecular weight. Therefore, structural formula (2)
When ethyl acetate is used as a good solvent when controlling the number average molecular weight of the lubricant having the structure of 1, the solvent extraction operation must be repeated four times or more in order to obtain the desired number average molecular weight of the lubricant. . Example 4 The solvent extraction operation and the number average molecular weight analysis were performed in the same manner as in Example 3 except that methyl alcohol was used as the poor solvent instead of ethyl alcohol used in Example 3. (Comparative Example 13) PF-5 used in Example 4 as a good solvent
The solvent extraction operation and the number average molecular weight analysis were carried out in the same manner as in Example 4 except that ethyl acetate was used instead of 052. (Comparative Example 14) A solvent extraction operation was performed in the same manner as in Comparative Example 13, and then the same solvent extraction operation as in Comparative Example 13 was repeated twice to analyze the number average molecular weight. (Comparative Example 15) A solvent extraction operation was performed with 100% methyl alcohol in the same manner as in Comparative Example 11 except that methyl alcohol was used instead of the ethyl alcohol used in Comparative Example 11, and the number average molecular weight was analyzed. (Comparative example 16).

After carrying out the solvent extraction operation in the same manner as in Comparative Example 15, the solvent extraction operation in the same manner as in Comparative Example 15 was repeated twice, and the number average molecular weight was analyzed.

The results of Example 4 in which PF-5052 was used as a good solvent and ethyl alcohol was used as a poor solvent to extract the lubricant having the structure of the structural formula (2) by solvent, and ethyl acetate was used as a good solvent were the poor solvent. Comparative Example 13 in which solvent extraction was performed using ethyl alcohol as Comparative Example 14, Comparative Example 14 in which the solvent extraction operation of Comparative Example 13 was performed three times, Comparative Example 15 in which solvent extraction was performed using methyl alcohol alone, and the solvent extraction operation of Comparative Example 15 were performed in 3 FIG. 7 shows the results of Comparative Example 16 performed repeatedly. Also in Example 4 to which the present invention is applied, as shown in FIG. 7, the number average molecular weight of Z-DOL TX2000 increases in the range of 400 or more and 1000 or less by one solvent extraction operation, and low molecular weight components are sufficiently removed. It was confirmed that it was done. That is, also in Example 4, it was possible to control Z-DOL to a target number average molecular weight of about 260 to 3200 by a single solvent extraction operation.

On the other hand, when ethyl acetate is used as the good solvent, as shown by the results of Comparative Examples 13 and 15, Z-DOL should be controlled to a desired number average molecular weight in one solvent extraction operation. And Comparative Examples 14 and 16
As shown in the result of Z, even if the solvent extraction operation is repeated three times, Z
-DOL TX2000 could not be increased to the desired number average molecular weight. Therefore, in the case of controlling the number average molecular weight of the lubricant having the structure of the structural formula (2), if ethyl acetate is used as the good solvent, the solvent extraction operation is performed in order to make the lubricant have the target number average molecular weight. Four
Must be repeated more than once. (Embodiment 5) A base film 5, a magnetic layer 7, and a protective film 9 are formed on the surface of a glass substrate 1 having a diameter of 63.5 mm, that is, 2.5 inches.
A magnetic disk 1 having the configuration of the present embodiment in which the above was sequentially formed was prepared. A lubricant film 11 was formed on the protective film 9 of the magnetic disk 1 by using the lubricant having the structure of the structural formula (1) obtained in Examples 1 and 2 described above.

Structural formula (1) for forming the lubricating film 11
As the lubricant having the structure of, a solvent extracted with an ethyl alcohol ratio of 95%, a solvent extracted with an ethyl alcohol ratio of 18%, a solvent extracted with a methyl alcohol ratio of 95%, and A solvent extracted with a methyl alcohol ratio of 18% was used. The number average molecular weight of the lubricant having the structure of structural formula (1) obtained by solvent extraction with an ethyl alcohol ratio of 95% is increased by about 920 from that before solvent extraction. The number average molecular weight of the lubricant having the structure of structural formula (1) solvent-extracted at a ratio of ethyl alcohol of 18% is about 550 higher than that before the solvent extraction. The number average molecular weight of the lubricant having the structure of structural formula (1) solvent-extracted at a methyl alcohol ratio of 95% is about 900 higher than that before extraction. The number average molecular weight of the lubricant having the structure of structural formula (1) extracted with a solvent at a methyl alcohol ratio of 18% is increased by about 520 from that before the extraction.

The lubricating film 11 was formed by a dipping method using a solution prepared by dissolving a lubricant at a predetermined concentration in a fluorine-based solvent HFE-7100 (manufactured by 3M). A magnetic disk device 13 including the magnetic disk 1 having such a lubricating film 11 was formed. Using this magnetic disk device 13, the number of rotations of the magnetic disk 1 is set to 4500 rpm,
In the environment of 2 ° C., the magnetic head slider 21 was randomly seeked on the surface of the magnetic disk 1 within a radius of 16 mm to 28 mm, and the change in the film thickness of the lubricating film 11 with respect to the operating time of the magnetic disk device 13 was measured. The film thickness is a Fourier transform infrared spectrophotometer (hereinafter abbreviated as FT-IR).
It was measured by. The initial film thickness of the lubricating film 11 is
It was 2.0 nm. (Comparative Example 17) A lubricant having an unpurified structure represented by the structural formula (1), that is, an untreated lubricant was used in Example 5.
A film thickness of 2.0 is formed on the protective film 9 of the magnetic disk 1 by the same method as described above.
A lubricating film having a thickness of 10 nm was formed, and the change in the film thickness of the lubricating film 11 with respect to the operating time of the magnetic disk device 13 was measured.

PF-5052 was used as a solvent, and ethyl alcohol or methyl alcohol was used as a poor solvent to carry out solvent extraction to form a lubricating film 11 with a lubricant having a structure of structural formula (1) in which the number average molecular weight was controlled. FIG. 8 shows the results of Example 5 and the results of Comparative Example 17 in which a lubricating film having a structure of untreated structural formula (1) was used to form a lubricating film. In Example 5 to which the present invention is applied, in which the lubricant film is formed with a solvent-extracted lubricant with a ratio of ethyl alcohol or methyl alcohol of 95%, as shown in FIG. The film thickness of the lubricating film when the time is 1000 hours is about 1.6 nm, and the film thickness is kept sufficient even when the operating time of the magnetic disk device 13 is 1000 hours.

On the other hand, even when the lubricant film is formed by the solvent-extracted lubricant with the ratio of ethyl alcohol or methyl alcohol being 18%, the film thickness of the lubricant film when the operating time of the magnetic disk device 13 is 1000 hours Is about 1.2n
m, the operating time of the magnetic disk device 13 is 1000
A sufficient film thickness is maintained even for time. On the other hand, in Comparative Example 17 in which the lubricant film was formed with the untreated lubricant, the film thickness of the lubricant film was reduced to about 0.7 nm when the magnetic disk device 13 was operated for 1000 hours. As described above, the lubricant film formed of the lubricant having the structure of the structural formula (1) in which the number average molecular weight is controlled by the method for controlling the number average molecular weight of the present invention is less likely to scatter, and thus the reduction in the film thickness is reduced. it can. (Example 6) Example 5 was repeated except that the lubricant film 11 was formed on the protective film 9 of the magnetic disk 1 using the lubricant having the structure of the structural formula (2) obtained in Examples 3 and 4 described above. Similarly to the above, the magnetic disk 1 was prepared, and the change in the film thickness of the lubricating film 11 with respect to the operating time of the magnetic disk device 13 was measured by FT-IR.

As the lubricant having the structure of the structural formula (2) for forming the lubricating film 11, a solvent extracted with an ethyl alcohol ratio of 95%, or a solvent extracted with an ethyl alcohol ratio of 18%. And solvent-extracted at a ratio of methyl alcohol of 95%, and solvent-extracted at a ratio of methyl alcohol of 18%. The lubricant having the structure represented by the structural formula (2) obtained by solvent extraction with the ratio of ethyl alcohol being 95% has the number average molecular weight increased by about 850 from that before the solvent extraction. The lubricant having the structure of structural formula (2) obtained by solvent extraction with an ethyl alcohol ratio of 18% has a number average molecular weight of about 450 compared with that before solvent extraction.
It has increased. The number average molecular weight of the lubricant having the structure of structural formula (1) solvent-extracted at a methyl alcohol ratio of 95% is increased by about 830 from that before extraction. A lubricant having a structure of structural formula (1) solvent-extracted with a methyl alcohol ratio of 18% has a number average molecular weight of about 42 compared with that before extraction.
It is increasing by 0. (Comparative Example 18) A lubricant having a structure of structural formula (2) in which the number average molecular weight is not controlled by a solvent extraction method is used, and the film thickness is formed on the protective film 9 of the magnetic disk 1 in the same manner as in Example 6. A 2.0 nm lubricating film is formed on the magnetic disk device 1
The change in the film thickness of the lubricating film 11 with respect to the operating time of 3 was measured.

PF-5052 was used as a solvent, and ethyl alcohol or methyl alcohol was used as a poor solvent to carry out solvent extraction to form a lubricant film 11 with a lubricant having a structure of the formula (2) in which the number average molecular weight was controlled. FIG. 9 shows the result of Example 6 and the result of Comparative Example 18 in which a lubricant film was formed with a lubricant having a structure of untreated structural formula (2), that is, a lubricant whose number average molecular weight is not controlled. In Example 5 to which the present invention is applied, in which the lubricant film is formed by the solvent-extracted lubricant with the ratio of ethyl alcohol or methyl alcohol being 95%, as shown in FIG. The film thickness of the lubricating film when the time is 1000 hours is about 1.8 nm, and a sufficient film pressure is maintained even when the operation time of the magnetic disk device 13 is 1000 hours.

On the other hand, even if the lubricant film is formed by the solvent-extracted lubricant with the ratio of ethyl alcohol or methyl alcohol being 18%, the film thickness of the lubricant film when the operating time of the magnetic disk device 13 is 1000 hours of operation time. Is about 1.5n
m, the operating time of the magnetic disk device 13 is 1000
It keeps a sufficient membrane pressure even for time. On the other hand, in Comparative Example 17 in which the lubricant film was formed with the untreated lubricant, the thickness of the lubricant film decreased to about 1.0 nm when the magnetic disk device 13 was operated for 1000 hours. As described above, the lubricating film formed of the lubricant having the structure of the structural formula (2) in which the number average molecular weight is controlled by the method of controlling the number average molecular weight of the present invention is less likely to scatter, and thus the reduction in the film thickness is reduced. it can.

As described above, according to the method for purifying a lubricant of the present invention, the number of times of solvent extraction in the purification of perfluoropolyether having a hydroxyl group at the terminal can be reduced. Further, since the number of times of solvent extraction can be reduced, the solvent extraction work can be simplified and the amount of solvent used can be reduced. In addition, in the magnetic disk having the lubricating film formed by the lubricant refined by the refining method of the present invention, the reduction of the film pressure of the lubricating film can be suppressed. Furthermore, since the reduction of the film pressure of the lubricating film can be reduced, the sliding reliability between the magnetic disk and the magnetic head can be improved.

Further, in the present embodiment, the lubricant having the structure of the structural formula (1) and the lubricant having the structure of the structural formula (2) are exemplified as the lubricant, but the present invention is not limited to these. Not only the lubricant but also various lubricants made of perfluoropolyether having a hydroxyl group at the terminal can be applied. However,
When applying the conventional purification method by solvent extraction, the lubricant having the structure of structural formula (2) requires at least four or more solvent extraction operations in order to control the number average molecular weight to a desired value. On the other hand, if the purification method of the present invention is used,
It is possible to control the target number average molecular weight with a single solvent extraction operation,
The refining method of the present invention has a great effect of reducing the solvent extraction operation particularly for the lubricant having the structure of structural formula (2).

[0052]

According to the present invention, it is possible to reduce the number of solvent extractions in the purification of perfluoropolyether having a hydroxyl group at the terminal.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a schematic configuration of an embodiment of a magnetic disk to which the present invention is applied.

FIG. 2 is a plan view showing a schematic internal configuration of an embodiment of a magnetic disk device including a magnetic disk to which the present invention is applied.

FIG. 3 is a side view showing a schematic internal configuration of an embodiment of a magnetic disk device including a magnetic disk to which the present invention is applied.

FIG. 4 is a diagram showing changes in the number average molecular weight of a lubricant after solvent extraction with respect to the ratio of ethyl alcohol which is a poor solvent.

FIG. 5 is a diagram showing changes in the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of methyl alcohol which is a poor solvent.

FIG. 6 is a diagram showing changes in the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of ethyl alcohol which is a poor solvent.

FIG. 7 is a diagram showing changes in the number average molecular weight of the lubricant after solvent extraction with respect to the ratio of methyl alcohol which is a poor solvent.

FIG. 8 is a diagram showing a change in film thickness of a lubricating film with respect to operating time of a magnetic disk device.

FIG. 9 is a diagram showing changes in the film thickness of the lubricating film with respect to the operating time of the magnetic disk device.

[Explanation of symbols]

1 magnetic disk 3 substrates 5 Base film 7 Magnetic layer 9 Protective film 11 Lubrication film

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI theme code (reference) C10N 40:18 C10N 40:18 70:00 70:00 (72) Inventor Hiroyuki Matsumoto 2880 Kunifuzu, Odawara-shi, Kanagawa Address, Hitachi Ltd. Storage Division (72) Inventor Hiroji Tani 2880, Kozu, Odawara-shi, Kanagawa F-Term, Hitachi Ltd. Storage Division (reference) 4H104 CD04A EA03A JA01 PA16 5D006 AA01 DA03 FA06

Claims (5)

[Claims] 1. A perfluoropolyether having a hydroxyl group at the end using a solvent containing a fully fluorinated fluorocarbon having a carbon number of 5 as a main component as a good solvent and ethyl alcohol or methyl alcohol as a poor solvent. A method for purifying a lubricant, which comprises performing solvent extraction. 2. A perfluoropolyether having a hydroxyl group at a terminal is dissolved in a good solvent containing a fully fluorinated fluorocarbon having 5 carbon atoms as a main component to produce a solution, and the produced solution is dissolved. A method for purifying a lubricant, wherein a poor solvent consisting of ethyl alcohol or methyl alcohol is added to the liquid and solvent extraction is performed. 3. The perfluoropolyether having a hydroxyl group at the terminal is represented by structural formula (1) or structural formula (2): [Chemical 2] (Where m, n, and p are positive integers), The method for purifying a lubricant according to claim 1 or 2, wherein 4. The lubricant according to claim 3, wherein an increase in the number average molecular weight of the perfluoropolyether having a hydroxyl group at the terminal by a single solvent extraction treatment is in the range of 400 or more and 1000 or less. Purification method. 5. A base film, a magnetic layer, a protective film, and a lubricating film are sequentially formed on the surface of a non-magnetic disk-shaped substrate, and the lubricating film is any one of claims 1 to 4. A magnetic disk formed of perfluoropolyether having a hydroxyl group at the end purified by the purification method described in 1.