| 摘要 |
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. |
