TECHNICAL FIELD

Cross Reference To Related Applications

This application is a National Stage of International Application No. PCT/JP2019/022850 filed on Jun. 10, 2019, claiming priority based on Japanese Patent Application No. 2018-111894 filed in Japan on Jun. 12, 2018, the contents of which are incorporated herein by reference.

The present invention relates to a fullerene compound, a lubricant for a magnetic recording medium, and a magnetic recording medium.

BACKGROUND OF THE INVENTION

Recently, as a method for improving the recording capacity of a magnetic recording medium, HAMR (Heat Assisted Magnetic Recording) has been developed. This HAMR system is a next-generation recording technology that records and reproduces magnetic fields while applying thermal offset by way of local heating with near-field light. By using this technology, even a weak signal is not affected by surrounding thermal noise, and reliability can be maintained. However, since the HAMR system is heated by near-field light, further heat resistance and repeated durability are required for the lubricant. Specifically, heat resistance of 250° C. or more is required. Further, even under such an environment, in order to realize high reliability of the magnetic recording medium device, it is important to design a lubricant film capable of maintaining excellent lubricating property even if the magnetic recording medium device slides repeatedly.

In response to this demand, there are patents proposing the use of materials with excellent heat resistance and the use of ionic liquids.

For example, Patent Document 1 discloses a compound of a perfluoropolyether having a carboxyl group at the terminal, and a diamine. Excellent lubricating property and durability are disclosed.

Patent Document 2 discloses a lubricant containing an ionic liquid formed from a sulfonic acid or a carboxylic acid having a perfluoropolyether skeleton, and an amine basing a perfluoroalkyl chain bonded to a nitrogen atom via an unsubstituted alkylene group having 2 to 5 carbon atoms. Excellent heat resistance and lubricating property (low coefficient, of friction) are disclosed.

Patent Document 3 discloses a lubricant containing a fullerene derivative having a fullerene skeleton and a perfluoropolyether chain. An excellent coaling property is disclosed.

However, these prior arts do not provide sufficient heat resistance and lubricating property in the next-generation recording technology such as the HAMR system.

Patent Document

Patent Document 1: Japanese Unexamined Patent Application Publication No. H5-93059

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2016-9509

Patent Document 3: Japanese Unexamined Patent Application Publication No. 2015-135710

SUMMARY OP THE INVENTION

Problem to Be Solved by the Invention

It is an object of the present invention to provide a fullerene compound which can be suitably used as a material of a lubricant for a magnetic recording medium which can realize sufficient heat resistance and lubricating property even in a next-generation recording technology such as the HAMR system. It is another object of the present invention to provide a magnetic recording medium having a lubricant for a magnetic recording medium containing die fullerene compound of die present invention.

Means to Solve the Problem

As a result of intensive investigation, the present inventors found that an ionic liquid compound formed from a Bronsted acid and a Bronsted base, one of which contains a group having a fullerene is a promising compound.

In other words, the present invention relates to the following:

[1] A fullerene compound, which is an ionic liquid represented by general formula (1), wherein the ionic liquid is formed from a Bronsted acid (Hn1X) and a Bronsted base ([R2R3)N—]m1—R1);

one of the Bronsted acid and the Bronsted base comprises a group having a fullerene; and

the other one of the Bronsted acid and the Bronzed base comprises a perfluoroalkyl chain.



wherein at least one of R1, R2and R3is a hydrocarbon group having 1 to 20 carbon atoms;

at least one of X, R1, R2and R3has a fullerene skeleton, and at least one of X, R1, R2and R3has a perfluoroalkyl chain;

R2and R3may be bonded to each other to form a nitrogen-containing heterocycle; and

n1, n2, m1, and m2are integers of 1 to 6, and n1×n2=m1×m2.

[2] The fullerene compound according to [1], wherein the Bronsted acid, in a molecule, comprises

a fullerene skeleton, and

a sulfonic acid group or a carboxylic acid group; and

the Bronsted base comprises a perfluoropolyether chain.

[3] The fullerene compound according to [1], wherein the Bronsted acid, in a molecule, comprises

a perfluoropolyether chain, and

a sulfonic acid group or a carboxylic acid group; and

the Bronsted base comprises a fullerene skeleton.

[4] The fullerene compound according to [1] or [2], wherein the Bronsted acid is a compound represented by formula (6), (7), or (8);

the Bronsted base is a compound represented by formula (10) or (11),
Cn(OH)x-y(OSO3H)y(6)

wherein Cnrepresents a fullerene which is a base structure of polyhydroxylated fullerene hydrogen sulfate ester;

x is a number in the range of 10 to 30:

y is a number in the range of 5 to 10; and

Cnis at least one kind selected from C60, C70, C76, C78, C80, C82, and C84.


NH2(CH2CH2O)pCH2CF2—(OCF2CF2)m(OCF2)n—OCF2CH2(OCH2CH2)qNH2(10)

wherein p and q are 1 to 3; m is 1 to 30; and n is 0 to 30.
CF3CF2CF2CF2—(OCF2CF2)2—OCF2CH2OCH2CH2NH2(11)

[5] The fullerene compound according to [1] or [3], wherein the Bronsted acid is a compound represented by any one of the following formulae (12) to (15); and

the Bronsted base is a compound represented by formula (16),
HO3S(CH2)3OCH2CF2—(OCF2CF2)m(OCF2)n—OCF2CH2O(CH2)3SO3H   (12)

wherein m is 1 to 30 and n is 0 to 30.
CF3CF2CF2CF2—(OCF2CF2)2—OCF2CH2O(CH2)3SO3H   (13)
HOOCCF2—(OCF2CF2)m(OCF2)n—OCF2COOH   (14)

wherein m is 1 to 30 and n is 0 to 30,
CF3CF2CF2CF2—(OCF2CF2)2—OCF2COOH   (15)



[6] The fullerene compound according to any one of [1] to [5], wherein the thermal decomposition temperature of the ionic liquid is 300° C. or higher.

[7] The fullerene compound according to any one of [1] to [6], wherein the number average molecular weight is in the range of 500 to 20,000.

[8] A lubricant for a magnetic recording medium comprising the fullerene compound according to any one of [1] to [7].

[9] A magnetic recording medium in which at least a magnetic layer, a protective layer, and a lubricant layer are sequentially provided on a substrate, wherein the lubricant layer contains the fullerene compound according to any one of [1] to [7].

[10] The magnetic recording medium according to [9], wherein the lubricant layer has an average film thickness of 0.5 nm to 2.5 nm.

Effect of the Invention

According to the present invention, thermal stability such as evaporation or thermal decomposition of the lubricant can be improved, and excellent lubrication characteristics can be maintained over a long period of time. By using this lubricant as a magnetic recording medium, it is possible to provide a magnetic recording medium having high reliability, particularly a magnetic recording medium having high reliability even in the HAMR system.

