Fluorine-containing ether compound, lubricant for magnetic recording medium, and magnetic recording medium

Abstract

A fluorine-containing ether compound represented by formula (1). (1): R1-R2-CH2-R3-CH2-R4 (In the formula, R1 represents an organic group having an alicyclic structure and from 3 to 13 carbon atoms; R2 represents a group expressed by formula (2) (wherein a represents an integer from 1 to 3); R3 represents a perfluoropolyether chain; and R4 represents an end group which contains two or three polar groups that are bonded to different carbon atoms, with the carbon atoms to which the polar groups are bonded being bonded to each other via linking groups that contain carbon atoms to which polar groups are not bonded.)

Description

[Technical field]

[0001] The present invention relates to a fluorine-containing ether compound, a lubricant for a magnetic recording medium, and a magnetic recording medium. This application claims priority based on Japanese Patent Application No. 2019-169489, filed on September 18, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] In order to improve the recording density of magnetic recording and reproducing devices, development of magnetic recording media suitable for high recording density is underway. Conventionally, magnetic recording media include those in which a recording layer is formed on a substrate and a protective layer such as carbon is formed on the recording layer. The protective layer protects the information recorded on the recording layer and also improves the sliding properties of the magnetic head. However, the durability of the magnetic recording medium cannot be sufficiently obtained by simply providing a protective layer on the recording layer. For this reason, a lubricant is generally applied to the surface of the protective layer to form a lubricating layer.

[0003] Lubricants used in forming the lubricating layer of magnetic recording media include, for example, fluoropolymers with a repeating structure containing CF2. Proposed fluoropolymers are those in which compounds having polar groups such as hydroxyl groups at their terminals are linked with aromatic rings and / or saturated alicyclic structures.

[0004] Patent Document 1 discloses a composition comprising a core selected from the group consisting of triazine, benzene, diphenyl ether, polyphenyl ether, cyclic hydrocarbons or derivatives thereof, and one or more arms extending from the core. Patent Document 1 also discloses that one or more arms comprise a perfluoropolyether or a derivative of a perfluoropolyether. Patent Document 2 discloses a fluorine-containing ether compound in which three fluorine-containing ether groups having polar groups at their terminals are connected to a trivalent atom or a trivalent atomic group. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-509677 [Patent Document 2] International Publication No. 2018 / 159232 Summary of the Invention [Problem to be solved by the invention]

[0006] In magnetic recording and reproducing devices, there is a demand for an even smaller flying height of the magnetic head, which in turn requires a thinner lubricating layer in the magnetic recording medium. However, generally, when the thickness of the lubricating layer is reduced, the covering property of the lubricating layer is reduced, and the chemical resistance of the magnetic recording medium tends to be reduced.In addition, when the thickness of the lubricating layer is reduced, the adhesion between the lubricating layer covering the surface of the protective layer and the protective layer is insufficient, and the fluorine-containing ether compound in the lubricating layer is easily attached to the magnetic head, which causes pick-up.

[0007] Moreover, the magnetic recording and reproducing device is usually installed in a housing of a personal computer, etc. Therefore, the magnetic recording and reproducing device may be locally exposed to a high temperature environment, and therefore, a lubricating layer having excellent thermal stability (heat resistance) is required for the magnetic recording medium.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a fluorine-containing ether compound which has excellent chemical resistance and heat resistance even when made thin, can form a lubricating layer that suppresses pick-up, and can be suitably used as a material for a lubricant for a magnetic recording medium. Another object of the present invention is to provide a lubricant for magnetic recording media, which contains the fluorine-containing ether compound of the present invention. Another object of the present invention is to provide a magnetic recording medium having a lubricating layer containing the fluorine-containing ether compound of the present invention and having excellent reliability and durability. [Means for solving the problem]

[0009] The present inventors have conducted extensive research in order to solve the above problems. As a result, the present inventors have found that a fluorine-containing ether compound can be obtained by arranging an organic group having an alicyclic structure having 3 to 13 carbon atoms at a first end of a perfluoropolyether chain via a specific linking group and a methylene group, and by arranging a specific terminal group containing two or three polar groups at a second end via a methylene group, and thus arrived at the present invention. That is, a first aspect of the present invention is the following fluorine-containing ether compound.

[0010] [1] A fluorinated ether compound represented by the following formula (1): R 1 -R 2 -CH2-R 3 -CH2-R 4 (1) (In formula (1), R 1 is an organic group having an alicyclic structure having 3 to 13 carbon atoms; R 2 is represented by the following formula (2), where a is an integer of 1 to 3; 3 is a perfluoropolyether chain; R 4 is an end group containing two or three polar groups, each polar group being bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded being bonded to each other via a linking group containing a carbon atom to which no polar group is bonded.

[0011] [ka]

[0012] The fluorine-containing ether compound according to the first aspect of the present invention can preferably include the following characteristics, as described below. Two or more of the following characteristics may be preferably combined. [2] R 1 The fluorine-containing ether compound according to [1], wherein the alicyclic structure is a saturated alicyclic structure.

[0013] [3] R 1 The fluorine-containing ether compound according to [1] or [2], wherein the alicyclic structure is one selected from the group consisting of cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, cyclotridecane, and adamantane.

[0014] [4] R 1 and any one of carbon atoms, oxygen atoms, and nitrogen atoms contained in the R 2 The fluorine-containing ether compound according to any one of [1] to [3], wherein the carbon atom contained in

[0015] [5] R 1 The fluorine-containing ether compound according to any one of [1] to [4], wherein the alicyclic structure has a functional group selected from the group consisting of a hydroxyl group, an alkoxy group, an amido group, an amino group, a carbonyl group, a carboxy group, a nitro group, a cyano group and a sulfo group, or a substituent selected from an alkyl group having the above functional group.

[0016] [6] R 3 is represented by any one of the following formulae (3) to (5): -CF2O-(CF2CF2O) b -(CF2O) c -CF2- (3) (In formula (3), b and c represent an average degree of polymerization and each independently represents 0 to 30. However, b and c cannot simultaneously be 0.) -CF(CF3)-(OCF(CF3)CF2) d -OCF(CF3)- (4) (In formula (4), d represents the average degree of polymerization and is 0.1 to 30.) -CF2CF2O-(CF2CF2CF2O) e -CF2CF2- (5) (In formula (5), e represents the average degree of polymerization and is from 0.1 to 30.)

[0017] [7] R 4 The fluorine-containing ether compound according to any one of [1] to [6], wherein the polar group is a hydroxyl group.

[0018] [8] R 4 is a terminal group represented by any one of the following formulae (6) to (9):

[0019] [ka] (In formula (6), f represents an integer of 1 to 2, and g represents an integer of 1 to 5.) (In formula (7), h represents an integer of 2 to 5.) (In formula (8), i represents an integer of 1 to 5.) (In formula (9), j represents an integer of 1 or 2, and k represents an integer of 1 or 2.)

[0020] [9] The fluorinated ether compound according to any one of [1] to [8], having a number average molecular weight in the range of 500 to 10,000.

[10] The fluorinated ether compound according to any one of [1] to [9], wherein the compound represented by formula (1) is any one of the compounds represented by the following formulae (A) to (C) and (G) to (O):

[0021] [ka] (In formula (A), ba and ca represent average degrees of polymerization, ba represents 0 to 30, and ca represents 0 to 30. However, ba and ca cannot be 0 at the same time.) (In formula (B), bb and cb represent average degrees of polymerization, bb represents 0 to 30, and cb represents 0 to 30. However, bb and cb cannot be 0 at the same time.) (In formula (C), bc and cc represent the average degree of polymerization, bc represents 0 to 30, and cc represents 0 to 30. However, bc and cc cannot be 0 at the same time.)

[0022] [ka] (In formula (G), bg and cg represent average degrees of polymerization, bg being 0 to 30, and cg being 0 to 30. However, bg and cg cannot be 0 at the same time.) (In formula (H), bh and ch represent average degrees of polymerization, bh represents 0 to 30, and ch represents 0 to 30. However, bh and ch cannot be 0 at the same time.) (In formula (I), bi and ci represent average degrees of polymerization, bi represents 0 to 30, and ci represents 0 to 30. However, bi and ci cannot be 0 at the same time.)

[0023] [ka] (In formula (J), bj and cj represent average degrees of polymerization, bj represents 0 to 30, and cj represents 0 to 30. However, bj and cj cannot be 0 at the same time.) (In formula (K), bk and ck represent average degrees of polymerization, bk being 0 to 30, and ck being 0 to 30. However, bk and ck cannot be 0 at the same time.)

[0024] [ka] (In formula (L), bl and cl represent average degrees of polymerization, bl represents 0 to 30, and cl represents 0 to 30. However, bl and cl cannot be 0 at the same time.) (In formula (M), bm and cm represent average degrees of polymerization, bm represents 0 to 30, and cm represents 0 to 30. However, bm and cm cannot be 0 at the same time.) (In formula (N), bn represents an average degree of polymerization, and bn represents 0.1 to 30.) (In formula (O), eо represents an average degree of polymerization, and eо represents 0.1 to 30.)

[0025]

[11] The fluorinated ether compound according to any one of [1] to [9], wherein the compound represented by formula (1) is any one of the compounds represented by the following formulae (T) to (X): [ka] (In formula (T), bt and ct represent average degrees of polymerization, bt represents 0 to 30, and ct represents 0 to 30. However, bt and ct cannot be 0 at the same time.) (In formula (U), bu and cu represent average degrees of polymerization, bu represents 0 to 30, and cu represents 0 to 30. However, bu and cu cannot be 0 at the same time.) (In formula (V), bv and cv represent average degrees of polymerization, bv represents 0 to 30, and cv represents 0 to 30. However, bv and cv cannot be 0 at the same time.) (In formula (W), bw and cw represent average degrees of polymerization, bw represents 0 to 30, and cw represents 0 to 30. However, bw and cw cannot be 0 at the same time.) (In formula (X), bx and cx represent average degrees of polymerization, bx represents 0 to 30, and cx represents 0 to 30. However, bx and cx cannot be 0 at the same time.)

[12] A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to any one of [1] to

[11] .

[0026]

[13] A magnetic recording medium comprising at least a magnetic layer, a protective layer, and a lubricating layer provided in that order on a substrate, 2. A magnetic recording medium, wherein the lubricating layer contains the fluorine-containing ether compound according to any one of [1] to

[11] .

[0027]

[14] The magnetic recording medium according to

[13] , wherein the lubricating layer has an average thickness of 0.5 nm to 2 nm. Effect of the Invention

[0028] The fluorine-containing ether compound of the present invention is a compound represented by the above formula (1), and is suitable as a material for a lubricant for a magnetic recording medium. The lubricant for magnetic recording media of the present invention contains the fluorine-containing ether compound of the present invention, and therefore can form a lubricating layer that has excellent chemical resistance and heat resistance even when it is thin, and that suppresses pick-up. The magnetic recording medium of the present invention has excellent chemical resistance and heat resistance, and since it is provided with a lubricating layer that suppresses pick-up, it has excellent reliability and durability. [Brief description of the drawings]

[0029] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of a magnetic recording medium of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The fluorine-containing ether compound, the lubricant for magnetic recording media (hereinafter sometimes abbreviated as "lubricant"), and the magnetic recording media of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments.

[0031] [Fluorine-containing ether compounds] The fluorine-containing ether compound of the present embodiment is represented by the following formula (1). R 1 -R 2 -CH2-R 3 -CH2-R 4 (1) (In formula (1), R 1 R is an organic group having an alicyclic structure having 3 to 13 carbon atoms. 2 is represented by the following formula (2). In formula (2), a is an integer of 1 to 3. 3 is a perfluoropolyether chain. 4 is an end group containing two or three polar groups, each polar group being bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded being bonded to each other via a linking group containing a carbon atom to which no polar group is bonded.

[0032] [ka]

[0033] Here, we will explain why, when a lubricant containing the fluorine-containing ether compound of this embodiment is used to form a lubricant layer on the protective layer of a magnetic recording medium, even if the lubricant layer is thin, it has excellent chemical resistance and heat resistance and suppresses pick-up.

[0034] The fluorine-containing ether compound of the present embodiment is represented by the formula (1), 3 When a lubricant containing a fluorine-containing ether compound is applied onto a protective layer to form a lubricating layer, the PFPE chain coats the surface of the protective layer and imparts lubricity to the lubricating layer, thereby reducing the friction between the magnetic head and the protective layer.

[0035] As shown in equation (1), R 3 The first end of the PFPE chain represented by the formula (I) is an organic group (R 1 ) is a linking group (R 2 ) and a methylene group (-CH2-). In the fluorine-containing ether compound represented by formula (1), R 1 The alicyclic structure having 3 to 13 carbon atoms of the organic group represented by the formula (I) is stable to heat. 1 The organic group represented by the formula (1) contributes to improving the heat resistance of the lubricating layer containing the fluorine-containing ether compound of this embodiment. For this reason, by using a lubricant containing the fluorine-containing ether compound represented by the formula (1), a lubricating layer having excellent heat resistance can be obtained.

[0036] In the fluorine-containing ether compound shown in formula (1), R 1 and an organic group represented by R 3 Between the PFPE chain represented by formula (2), a linking group (R 2 ) is arranged. 2) contains 1 to 3 hydroxyl groups (-OH). As a result, the lubricating layer containing the fluorine-containing ether compound of this embodiment has excellent adhesion (tightness) to the protective layer. In addition, the linking group (R 2 ) contains an ether bond (-O-), and therefore provides appropriate flexibility to the molecular structure of the fluorinated ether compound represented by formula (1). For these reasons, the fluorinated ether compound of the present embodiment can be, for example, 1 and an organic group represented by R 3 In comparison with a fluorine-containing ether compound in which a PFPE chain is directly bonded, as represented by the formula (1), a lubricating layer containing this compound is more likely to be adsorbed to a protective film, and the adhesion between the lubricating layer and the protective layer is excellent.

[0037] In addition, as shown in equation (1), R 3 The R of the PFPE chain is represented by 2 At the opposite end (second end) is an R 4 The terminal group represented by R is arranged via a methylene group (-CH2-). 4 The terminal group represented by the formula (I) contributes to the adhesion between the protective layer to which the lubricant containing the fluorinated ether compound of the present embodiment is applied and the lubricating layer formed by applying the lubricant. 4 The two or three polar groups contained in the terminal group represented by the formula (I) suppress pick-up by bonding the fluorine-containing ether compound and the protective layer in the lubricating layer containing the fluorine-containing ether compound of this embodiment.

[0038] Also, R 4 The two or three polar groups contained in the terminal group represented by the formula (I) are bonded to different carbon atoms, and the carbon atoms to which the polar groups are bonded are bonded to each other via a linking group containing a carbon atom to which no polar group is bonded. 4 The two or three polar groups contained in it have the appropriate distance between the polar groups. As a result, R 4 The fluorine-containing ether compound having an end group represented by the formula: 4The fluorine-containing ether compound is less likely to aggregate than the fluorine-containing ether compound in which at least some of the carbon atoms bonded to the polar groups contained in the terminal group represented by the formula (1) are bonded to each other. Therefore, in the lubricating layer containing the fluorine-containing ether compound represented by the formula (1), the fluorine-containing ether compound that is not in close contact (adsorbed) with the protective layer can be prevented from aggregating and adhering to the magnetic head as foreign matter (smear), thereby suppressing pick-up. In addition, since the fluorine-containing ether compounds are less likely to aggregate with each other, the fluorine-containing ether compound in the lubricating layer is likely to be arranged in a state in which it spreads in the surface direction on the protective layer and extends uniformly. For this reason, the lubricant containing the fluorine-containing ether compound of this embodiment can cover the surface of the protective layer with a high coverage rate even if it is thin, and can form a lubricating layer with excellent chemical resistance. Therefore, the lubricant containing the fluorine-containing ether compound of this embodiment contributes to thinning the lubricating layer (reducing magnetic spacing).

[0039] From the above, it is presumed that the lubricant containing the fluorine-containing ether compound of this embodiment can cover the surface of a protective layer with a high coverage even when it is thin, has excellent chemical resistance and heat resistance, and can form a lubricating layer that suppresses pick-up.

[0040] (R 1 (an organic group represented by the formula In the fluorine-containing ether compound of the present embodiment represented by formula (1), R 1 The organic group represented by has an alicyclic structure having 3 to 13 carbon atoms. The alicyclic structure having 3 to 13 carbon atoms is preferably a saturated alicyclic structure, since it results in a fluorine-containing ether compound that can provide a lubricating layer having even better heat resistance. Examples of the saturated alicyclic structure having 3 to 13 carbon atoms include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, cyclotridecane, and adamantane. R 1As the alicyclic structure having 3 to 13 carbon atoms in the organic group represented by the formula (I), a saturated alicyclic structure having 3 to 9 carbon atoms or adamantane having good thermal stability is particularly preferred among the above, since it results in a fluorine-containing ether compound that can provide a lubricating layer having even better heat resistance.

[0041] R 1 The organic group represented by the formula (I) may have one or more alicyclic structures having 3 to 13 carbon atoms. 1 When the organic group represented by the formula (I) has a plurality of alicyclic structures having 3 to 13 carbon atoms, some or all of the plurality of alicyclic structures may be the same or different from each other. 1 The number of alicyclic structures having 3 to 13 carbon atoms in the organic group represented by the following formula (I) is preferably only one, since this makes it difficult for the fluorine-containing ether compounds to aggregate together.

[0042] R 1 The alicyclic structure having 3 to 13 carbon atoms in the organic group represented by the formula may have one or more substituents. When the alicyclic structure has two or more substituents, some or all of the two or more substituents may be the same, or may be different from each other. When the alicyclic structure having 3 to 13 carbon atoms has a substituent, the number of the substituents can be appropriately determined according to the type of the alicyclic structure having 3 to 13 carbon atoms, and is not particularly limited. When the alicyclic structure having 3 to 13 carbon atoms has a substituent, the substituent is preferably a substituent having 0 to 10 carbon atoms. If necessary, the carbon number may be 1 to 8 or 2 to 6. If the carbon number of the substituent is 0 to 10, it is preferable because a lubricating layer with good coverage can be obtained without suppressing the adsorption force of the lubricating layer to the protective layer due to the substituent having too many carbon atoms, which causes steric hindrance. The carbon number of the substituent is more preferably 0 to 5, and further preferably 0 to 2.

[0043] R 1In the case where the alicyclic structure having 3 to 13 carbon atoms of the organic group represented by the formula (I) has a substituent, specific examples of the substituent include at least one functional group selected from the group consisting of a hydroxyl group, an alkoxy group, an amide group, an amino group, a carbonyl group, a carboxy group, a nitro group, a cyano group, and a sulfo group, or a substituent selected from an alkyl group having the above-mentioned functional group. In the alkyl group having the above-mentioned functional group, the alkyl group preferably has 1 to 3 carbon atoms, and more preferably has 1 or 2 carbon atoms. Among these substituents, it is more preferable that the substituent is selected from a hydroxyl group, an alkoxy group, an amide group, an amino group, a cyano group, or an alkyl group having these.Specific examples of the substituent include -OH, -CH2OH, -CH2CH2OH, -CH2CH2CH2OH; -OCH3, -OCH2CH3, -OCH2CH2CH3; -OCH2OH, -OCH2CH2OH, -OCH2CH2CH2OH; -CONH2, -CH2CONH2, -CH2CH2CONH2; -NH2, -CH2NH2, -CH2CH2NH2, -CH2CH2CH2NH2; -CN, -CH2CN, -CH2CH2CN, and the like. Among these substituents, it is particularly preferred that the substituent is selected from hydroxyl group, amino group, amide group, or an alkyl group having these, since it is a polar group capable of hydrogen bonding. When the alicyclic structure having 3 to 13 carbon atoms has one or more substituents selected from these, the interaction between the above-mentioned substituent and the protective film arranged in contact with the lubricating layer containing the fluorine-containing ether compound increases the adsorption force of the lubricating layer to the protective layer. As a result, the lubricant containing the fluorine-containing ether compound has even better chemical resistance, which is preferable.

[0044] In the fluorine-containing ether compound represented by formula (1), R 1 and a linking group R represented by formula (2) 2 From the viewpoint of ease of synthesis, the bond with R 1 Any of the carbon atoms, oxygen atoms, and nitrogen atoms contained in R 2 Preferably, the bond is to a carbon atom contained in R 1and the oxygen or nitrogen atom contained in R 2 It is more preferable that the bond is to a carbon atom included in R 1 The oxygen atom in R 1 and an organic group represented by R 2 It is preferable that the carbon atom contained in is ether bonded (-O-). In this case, the molecular structure of the fluorine-containing ether compound represented by formula (1) has moderate flexibility. As a result, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) has better adhesion to the protective layer, which is preferable. R 1 When the alicyclic structure having 3 to 13 carbon atoms of the organic group represented by the formula: is Z, the alicyclic structure Z and R 2 The bond with the carbon atom contained in the formula (I) is specifically, 2 , ZOR 2 , Z-NH-R 2 , Z-CH2O-R 2 , Z-CH2CH2O-R 2 , Z-CH2CH2CH2O-R 2 , Z-CH2-R 2 , Z-CH2CH2-R 2 , Z-CH2CH2CH2-R 2 , Z-CH2CH2CH2CH2-R 2 , etc.

[0045] In the fluorine-containing ether compound represented by formula (1), R 1 and a linking group R represented by formula (2) 2 The carbon atom of R 1 It is preferable that the organic group represented by the formula (I) is bonded to an alicyclic structure having 3 to 13 carbon atoms through an ether bond (-O-) (i.e., the alicyclic structure Z and R 2 The bond with the carbon atom in ZOR 2 It is preferable that the lubricating layer contains the fluorine-containing ether compound represented by the formula (1) in this case as well, since it has better adhesion to the protective layer.

[0046] In the fluorine-containing ether compound of the present embodiment, R 1 The organic group represented by the formula R contains 1 to 3 hydroxyl groups (-OH). 2 Therefore, in the lubricating layer containing the fluorine-containing ether compound of this embodiment, R 2 The hydroxyl groups contained in R improve adhesion to the protective layer. 1 and the protective layer are easily brought into close proximity to each other, 1 The heat resistance improving function of the organic group represented by the formula (I) works effectively.

[0047] (R 2 )) In the fluorine-containing ether compound of the present embodiment represented by formula (1), R 2 is represented by formula (2). In formula (2), a is an integer of 1 to 3. Since a in formula (2) is 1 or more, the lubricant containing the fluorine-containing ether compound has excellent adhesion to the protective layer and can form a lubricating layer with a high coverage. In addition, since a in formula (2) is 3 or less, R 2 The number of hydroxyl groups in the 2 The polarity of the fluorine-containing ether compound does not become too high due to the presence of too many hydroxyl groups in the compound. Therefore, it is possible to prevent the lubricating layer containing the fluorine-containing ether compound from adhering to the magnetic head as a foreign matter (smear) due to the polarity of the fluorine-containing ether compound being too high, and pickup can be suppressed. 2 is expressed by formula (2), so when a is 2 or 3, R 2 In the formula (2), a is preferably 1 or 2, and more preferably 1.

[0048] (R 3 (perfluoropolyether chain represented by In the fluorine-containing ether compound represented by formula (1), R 3is a perfluoropolyether chain (PFPE chain). In the fluorine-containing ether compound represented by formula (1), it is preferable that only one PFPE chain is contained in the molecule. When only one PFPE chain is contained in the molecule, R 1 and R 4 does not contain a PFPE chain. If there is one PFPE chain in the molecule, the fluorine-containing ether compounds are less likely to aggregate with each other. Therefore, in the lubricating layer containing the fluorine-containing ether compound, the fluorine-containing ether compound is likely to be arranged in a uniformly extending state by spreading in the surface direction on the protective layer, which is preferable.

[0049] R 3 is not particularly limited and can be appropriately selected depending on the performance required of the lubricant containing the fluorine-containing ether compound. R 3 is preferably any one of the following formulas (3) to (5). 3 When the formula is any one of formulas (3) to (5), the synthesis of the fluorine-containing ether compound is easy, which is preferable.

[0050] Also, R 3 When R is any one of formulas (3) to (5), the ratio of the number of oxygen atoms (the number of ether bonds (-O-)) to the number of carbon atoms in the perfluoropolyether chain is appropriate. This results in a fluorine-containing ether compound with appropriate hardness. Therefore, the fluorine-containing ether compound applied onto the protective layer is less likely to aggregate on the protective layer, and a thinner lubricating layer can be formed with a sufficient coverage. In addition, R 3 When is any one of the formulas (3) to (5), the fluorine-containing ether compound provides a lubricating layer having good chemical resistance.

[0051] -CF2O-(CF2CF2O) b -(CF2O) c -CF2- (3) (In formula (3), b and c represent an average degree of polymerization and each independently represents 0 to 30. However, b and c cannot simultaneously be 0.)

[0052] In formula (3), the arrangement order of the repeating units (CF2-CF2-O) and (CF2-O) is not particularly limited. In formula (3), the number b of (CF2-CF2-O) and the number c of (CF2-O) may be the same or different. However, b and c cannot be 0 at the same time. Formula (3) may include any of a random copolymer, a block copolymer, and an alternating copolymer composed of monomer units (CF2-CF2-O) and (CF2-O).

[0053] R in formula (1) 3 When R is represented by formula (3), b, which indicates the average degree of polymerization, is 0 to 30, preferably 1 to 20, and more preferably 1 to 15. b may be 1 to 10 or 1 to 5. 3 When the formula (3) is represented, c indicating the average degree of polymerization is 0 to 30, preferably 0 to 20, and more preferably 0 to 15. c may be 1 to 10 or 1 to 5. When c is 0, b is preferably 1 to 17.

[0054] -CF(CF3)-(OCF(CF3)CF2) d -OCF(CF3)- (4) (In formula (4), d represents the average degree of polymerization and is 0.1 to 30.) In formula (4), when d, which indicates the average degree of polymerization, is 0.1 to 30, the number average molecular weight of the fluorinated ether compound of this embodiment tends to be in the preferred range. d is preferably 1 to 30, more preferably 2 to 20, and further preferably 3 to 10.

[0055] -CF2CF2O-(CF2CF2CF2O) e -CF2CF2- (5) (In formula (5), e represents the average degree of polymerization and is from 0.1 to 30.) In formula (5), when e, which indicates the average degree of polymerization, is 0.1 to 30, the number average molecular weight of the fluorinated ether compound of this embodiment tends to be in the preferred range. e is preferably 1 to 20, more preferably 2 to 15, and further preferably 2 to 8.

[0056] (R 4 (Terminal group represented by In the fluorine-containing ether compound represented by formula (1), R 4 is a terminal group containing two or three polar groups, each of which is bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded are bonded via a linking group containing a carbon atom to which no polar group is bonded. 4 It is preferable that the end group represented by the following formula (I) does not contain a perfluoropolyether chain (PFPE chain). R 4 Since the number of polar groups contained in R is two or three, the lubricant containing the fluorine-containing ether compound has excellent adhesion to the protective layer and can form a lubricating layer with a high coverage. 4 The number of polar groups contained in R is preferably two. 4 If the number of polar groups contained in R is too large, the polarity of the fluorine-containing ether compound becomes too high, and the lubricating layer containing the fluorine-containing ether compound is likely to adhere to the magnetic head as a foreign matter (smear), resulting in pickup. 4 Since the number of polar groups contained in the compound is 2 or 3, the occurrence of pick-up due to the fluorine-containing ether compound having too high a polarity can be suppressed.

[0057] R 4 Examples of the two or three polar groups in the terminal group represented by the formula (I) include a hydroxyl group (-OH), an amino group (-NH2), a carboxyl group (-COOH), and a mercapto group (-SH). Note that an ether bond (-O-) is represented by the formula (I). 4 Among the above polar groups, the polar group is preferably a hydroxyl group. 4The two or three polar groups contained in the terminal group represented by the formula (I) may be different from each other or may all be the same, and it is preferable that all of them are hydroxyl groups.

[0058] Hydroxyl groups have a strong interaction with the protective layer of the magnetic recording medium, especially with the protective layer made of a carbon-based material. 4 When some or all of the two or three polar groups in the terminal group represented by the formula (I) are hydroxyl groups, the lubricating layer containing the fluorine-containing ether compound has even stronger adhesive power to the protective film, which is preferable.

[0059] R 4 It is preferable that the terminal group represented by R contains an ether bond. 4 In the terminal group represented by the formula (I), two or three polar groups are bonded to different carbon atoms, and the carbon atoms to which the polar groups are bonded are preferably bonded via a linking group containing an oxygen atom (a linking group containing -O- (ether bond)). The linking group containing an ether bond is represented by the formula (I). 4 When the carbon atoms bonded to the polar groups are bonded to each other via a linking group containing an ether bond, for example, the two polar groups contained in the terminal group are bonded to different carbon atoms, and compared with a fluorine-containing ether compound in which the carbon atoms bonded to the polar groups are bonded to each other, the lubricating layer containing this is more likely to be adsorbed to the protective film, and the adhesion between the lubricating layer and the protective layer is excellent.

[0060] R in formula (1) 4 The terminal group represented by the following formula (1) can be appropriately selected depending on the performance required for the lubricant containing the fluorine-containing ether compound. R in formula (1) 4 is preferably a terminal group represented by any one of the following formulas (6) to (9). 4 contributes to high adhesion and coverage between the protective layer to which the lubricant containing the fluorinated ether compound of this embodiment is applied and the lubricating layer formed by applying the lubricant.

[0061] [ka] (In formula (6), f represents an integer of 1 to 2, and g represents an integer of 1 to 5.) (In formula (7), h represents an integer of 2 to 5.) (In formula (8), i represents an integer of 1 to 5.) (In formula (9), j represents an integer of 1 or 2, and k represents an integer of 1 or 2.)

[0062] In formula (6), f represents an integer of 1 to 2, and is preferably 2 from the viewpoint of adhesion to the protective layer. In formula (6), g represents an integer of 1 to 5. When g is an integer of 1 to 5, the distance between hydroxyl groups in the terminal group represented by formula (6) becomes appropriate, resulting in a fluorine-containing ether compound that is excellent in adhesion to a protective layer and can form a lubricating layer with a high coverage. From the viewpoint of adhesion to a protective layer, g is preferably 1 or 2, and most preferably 1.

[0063] In formula (7), h represents an integer of 2 to 5. In this case, R 3 The distance between the side hydroxyl group and the terminal hydroxyl group is appropriate, resulting in a fluorine-containing ether compound that is excellent in adhesion to a protective layer and can form a lubricating layer with a high coverage. From the viewpoint of adhesion to a protective layer, h is preferably 2 or 3, and most preferably 2.

[0064] In formula (8), i represents an integer from 1 to 5. In this case, R 3 The distance between the side hydroxyl group and the terminal hydroxyl group becomes appropriate, and the fluorine-containing ether compound can form a lubricating layer having excellent adhesion to a protective layer and high coverage. From the viewpoint of adhesion to a protective layer, i is preferably 1 or 2, and most preferably 1.

[0065] In formula (9), j represents an integer of 1 to 2, and is preferably 2 from the viewpoint of adhesion to the protective layer. In formula (9), k represents an integer of 1 to 2. In this case, R 3The distance between the side hydroxyl group and the terminal hydroxyl group is appropriate, resulting in a fluorine-containing ether compound that has excellent adhesion to a protective layer and can form a lubricating layer with a high coverage. From the viewpoint of adhesion to a protective layer, k is preferably 1.

[0066] In the fluorine-containing ether compound of the present embodiment, R 2 1 to 3 hydroxyl groups in R 4 Two or three polar groups arranged at an appropriate distance within the range of 3 The lubricating layer containing the fluorine-containing ether compound of this embodiment has excellent adhesion (tightness) with the protective layer, and can cover the surface of the protective layer with a high coverage. Therefore, the lubricating layer containing the fluorine-containing ether compound of this embodiment has good chemical resistance, can be further thinned, and can contribute to the reduction of magnetic spacing in magnetic recording media.

[0067] Specifically, the fluorine-containing ether compound represented by formula (1) is preferably any one of the compounds represented by the following formulae (A) to (O) and (T) to (X). The repeat numbers represented by ba through bm and ca through cm in formulas (A) through (M), bn in formula (N), eо in formula (O), and bt through bx and ct through cx in formulas (T) through (X) are all values ​​indicating the average degree of polymerization, and are not necessarily integers.

[0068] [ka] (In formula (A), ba and ca represent average degrees of polymerization, ba represents 0 to 30, and ca represents 0 to 30. However, ba and ca cannot be 0 at the same time.) (In formula (B), bb and cb represent average degrees of polymerization, bb represents 0 to 30, and cb represents 0 to 30. However, bb and cb cannot be 0 at the same time.) (In formula (C), bc and cc represent the average degree of polymerization, bc represents 0 to 30, and cc represents 0 to 30. However, bc and cc cannot be 0 at the same time.)

[0069] [ka] (In formula (D), bd and cd represent average degrees of polymerization, bd represents 0 to 30, and cd represents 0 to 30. However, bd and cd cannot be 0 at the same time.) (In formula (E), be and ce represent average degrees of polymerization, be represents 0 to 30, and ce represents 0 to 30. However, be and ce cannot be 0 at the same time.) (In formula (F), bf and cf represent average degrees of polymerization, bf represents 0 to 30, and cf represents 0 to 30. However, bf and cf cannot be 0 at the same time.)

[0070] [ka] (In formula (G), bg and cg represent average degrees of polymerization, bg being 0 to 30, and cg being 0 to 30. However, bg and cg cannot be 0 at the same time.) (In formula (H), bh and ch represent average degrees of polymerization, bh represents 0 to 30, and ch represents 0 to 30. However, bh and ch cannot be 0 at the same time.) (In formula (I), bi and ci represent average degrees of polymerization, bi represents 0 to 30, and ci represents 0 to 30. However, bi and ci cannot be 0 at the same time.)

[0071] [ka] (In formula (J), bj and cj represent average degrees of polymerization, bj represents 0 to 30, and cj represents 0 to 30. However, bj and cj cannot be 0 at the same time.) (In formula (K), bk and ck represent average degrees of polymerization, bk being 0 to 30, and ck being 0 to 30. However, bk and ck cannot be 0 at the same time.)

[0072] [ka] (In formula (L), bl and cl represent average degrees of polymerization, bl represents 0 to 30, and cl represents 0 to 30. However, bl and cl cannot be 0 at the same time.) (In formula (M), bm and cm represent average degrees of polymerization, bm represents 0 to 30, and cm represents 0 to 30. However, bm and cm cannot be 0 at the same time.) (In formula (N), bn represents an average degree of polymerization, and bn represents 0.1 to 30.) (In formula (O), eо represents an average degree of polymerization, and eо represents 0.1 to 30.)

[0073] [ka] (In formula (T), bt and ct represent average degrees of polymerization, bt represents 0 to 30, and ct represents 0 to 30. However, bt and ct cannot be 0 at the same time.) (In formula (U), bu and cu represent average degrees of polymerization, bu represents 0 to 30, and cu represents 0 to 30. However, bu and cu cannot be 0 at the same time.) (In formula (V), bv and cv represent average degrees of polymerization, bv represents 0 to 30, and cv represents 0 to 30. However, bv and cv cannot be 0 at the same time.) (In formula (W), bw and cw represent average degrees of polymerization, bw represents 0 to 30, and cw represents 0 to 30. However, bw and cw cannot be 0 at the same time.) (In formula (X), bx and cx represent average degrees of polymerization, bx represents 0 to 30, and cx represents 0 to 30. However, bx and cx cannot be 0 at the same time.)

[0074] The compounds represented by the formulas (A) to (O) and (T) to (X) are all R 2 is expressed by equation (2), and R 2 In the formulae (A) to (N) and (T) to (X), R 3 is formula (3), and the compound represented by formula (O) is R 3 is equation (5). In addition, the compounds represented by the formulas (A) to (L) and (T) to (X) are all R 4 is represented by formula (9), and in formula (9), j is 2 and k is 1. The compounds represented by formulas (M) to (O) are represented by R 4 is equation (6), where f is 2 and g is 1.

[0075] The compound represented by formula (A) is R 1 The alicyclic structure of is cyclopropane. The compound represented by formula (B) is R 1 The alicyclic structure is cyclobutane. The compound represented by formula (C) is R 1 The alicyclic structure of is cyclopentane. The compound represented by formula (D) is R 1 The alicyclic structure is cyclononane. The compound represented by formula (E) is R 1 The alicyclic structure of is cyclotridecane. The compound represented by formula (F) is R 1 The alicyclic structure is adamantane. The compounds represented by the formulae (G) to (O) and (T) are 1 The alicyclic structure of is cyclopentane. The compounds represented by the formulae (U) to (X) are 1 The alicyclic structure of is cyclohexane. In the above formula, ba to bm and bt to bx may be 0, 1 to 20, 1 to 10, or 1 to 5. ca to cm and ct to cx may be 0, 1 to 20, 1 to 10, or 1 to 5. bn and eo may be 1 to 20, 1 to 10, or 1 to 5.

[0076] It is preferable that the compound represented by formula (1) is any of the compounds represented by the above formulas (A) to (O) and (T) to (X), since the raw materials are easily available, and a lubricating layer can be formed that has better heat resistance and chemical resistance even if it is thin, and that further suppresses pick-up.

[0077] The number average molecular weight (Mn) of the fluorine-containing ether compound of this embodiment is preferably in the range of 500 to 10,000, more preferably in the range of 700 to 7,000, and particularly preferably in the range of 1,000 to 3,000. When the number average molecular weight is 500 or more, the lubricant containing the fluorine-containing ether compound of this embodiment is less likely to evaporate, and the lubricant can be prevented from evaporating and transferring to the magnetic head. When the number average molecular weight is 10,000 or less, the viscosity of the fluorine-containing ether compound is appropriate, and a thin lubricating layer can be easily formed by applying a lubricant containing the compound. When the number average molecular weight is 3,000 or less, the viscosity becomes easy to handle when applied to a lubricant, so it is more preferable.

[0078] The number average molecular weight (Mn) of fluorine-containing ether compounds was measured using AVANCEIII400 manufactured by Bruker Biospin. 1 H-NMR and 19 This is a value measured by F-NMR. In the NMR (nuclear magnetic resonance) measurement, the sample was diluted in a single or mixed solvent such as hexafluorobenzene, d-acetone, or d-tetrahydrofuran and used for the measurement. 19 The standard for F-NMR chemical shifts is the hexafluorobenzene peak at -164.7 ppm. 1 The reference for H-NMR chemical shifts was set to the acetone peak at 2.2 ppm.

[0079] "Manufacturing method" The method for producing the fluorinated ether compound of the present embodiment is not particularly limited, and the compound can be produced by a conventionally known production method. The fluorinated ether compound of the present embodiment can be produced, for example, by the production method shown below. First, -CH2-R in formula (1) 3 The compound corresponding to -CH2- is HO-CH2-R 3 Next, this compound is added with R in formula (1). 1 -R 2- is subjected to an addition reaction with an epoxide to give an alicyclic structure corresponding to the above. This produces a compound represented by the following formula (1-1).

[0080] R 1 -R 2 -CH2-R 3 -CH2-OH (1-1) (In formula (1-1), R 1 , R 2 , R 3 are R in formula (1), 1 , R 2 , R 3 is the same as

[0081] R in formula (1) used as a raw material for the compound represented by formula (1-1) 1 -R 2 An epoxide that gives an alicyclic structure corresponding to - is, for example, R 1 It can be produced by subjecting epibromohydrin to an addition reaction with an alcohol having an alicyclic structure corresponding to the following formula: Specifically, for example, R in formula (1) 1 When the alicyclic structure corresponding to the formula is cyclopentane, the cyclopentanol and epibromohydrin are subjected to an addition reaction to obtain the compound represented by the formula (1) R 1 -R 2 -Epoxides which give the corresponding alicyclic structures can be prepared.

[0082] Next, the compound represented by formula (1-1) is reacted with an epoxide containing one or more polar groups to convert the terminal hydroxyl group (-OH) of the compound represented by formula (1-1) into R 4 A fluorine-containing ether compound represented by formula (1) is produced. Epoxides containing one or more polar groups can be prepared, for example, by the addition reaction of ethylene glycol with epibromohydrin.

[0083] The produced fluorine-containing ether compound represented by formula (1) is preferably purified, for example, by a method using column chromatography. By the above method, the fluorine-containing ether compound represented by formula (1) can be obtained.

[0084] The fluorine-containing ether compound of the present embodiment is a compound represented by the above formula (1). Therefore, when a lubricating layer is formed on a protective layer using a lubricant containing this compound, R 3 The surface of the protective layer is covered with the PFPE chain represented by the formula (I) and the frictional force between the magnetic head and the protective layer is reduced. In addition, the lubricating layer formed using the lubricant containing the fluorine-containing ether compound of this embodiment has a structure represented by the formula (I). 1 Since the alicyclic structure of the organic group represented by the formula (I) is stable to heat, the compound has excellent heat resistance.

[0085] In addition, the lubricating layer containing the fluorine-containing ether compound of this embodiment is formed by mixing the R 2 and R 4 The polymer is adhered to the protective layer by bonds between the protective layer and two or three polar groups contained in the terminal group represented by the formula:

[0086] Moreover, in the fluorine-containing ether compound of the present embodiment, R 4 The two or three polar groups contained in the terminal group represented by are bonded to different carbon atoms, and the carbon atoms to which the polar groups are bonded are bonded to each other via a linking group.Therefore, the lubricating layer containing the fluorine-containing ether compound of this embodiment has good flexibility.Therefore, the lubricating layer containing the fluorine-containing ether compound of this embodiment is easily adsorbed to the protective film, and has excellent adhesion to the protective layer. As described above, the fluorine-containing ether compound of this embodiment provides a lubricating layer that is firmly bonded to the protective layer, has excellent heat resistance and chemical resistance, and is suppressed from picking up.

[0087] [Lubricants for magnetic recording media] The lubricant for a magnetic recording medium of this embodiment contains a fluorine-containing ether compound represented by formula (1). The lubricant of the present embodiment can be used by mixing, as necessary, known materials used as lubricant materials, so long as the properties resulting from the inclusion of the fluorinated ether compound represented by formula (1) are not impaired.

[0088] Specific examples of known materials include FOMBLIN (registered trademark) ZDIAC, FOMBLIN ZDEAL, FOMBLIN AM-2001 (all manufactured by Solvay Solexis), Moresco A20H (manufactured by Moresco), etc. The known material to be mixed with the lubricant of the present embodiment preferably has a number average molecular weight of 1,000 to 10,000.

[0089] When the lubricant of this embodiment contains other materials than the fluorine-containing ether compound represented by formula (1), the content of the fluorine-containing ether compound represented by formula (1) in the lubricant of this embodiment is preferably 50% by mass or more, more preferably 70% by mass or more. The content of the fluorine-containing ether compound represented by formula (1) may be 80% by mass or more, or 90% by mass or more. The upper limit can be selected arbitrarily, and may be, for example, 99% by mass or less, 95% by mass or less, or 90% by mass or less.

[0090] The lubricant of the present embodiment contains the fluorine-containing ether compound represented by formula (1), so that even if the thickness is thin, the surface of the protective layer can be covered with a high coverage rate, and a lubricant layer with excellent adhesion to the protective layer can be formed. Therefore, according to the lubricant of the present embodiment, even if the thickness is thin, a lubricant layer having excellent chemical resistance and heat resistance and suppressing pick-up can be obtained.

[0091] [Magnetic recording media] The magnetic recording medium of this embodiment has at least a magnetic layer, a protective layer, and a lubricating layer provided in this order on a substrate. In the magnetic recording medium of this embodiment, one or more underlayers may be provided between the substrate and the magnetic layer, if necessary. Also, an adhesive layer and / or a soft magnetic layer may be provided between the underlayer and the substrate.

[0092] FIG. 1 is a schematic cross-sectional view showing one embodiment of a magnetic recording medium of the present invention. The magnetic recording medium 10 of this embodiment has a structure in which an adhesive layer 12, a soft magnetic layer 13, a first underlayer 14, a second underlayer 15, a magnetic layer 16, a protective layer 17, and a lubricating layer 18 are sequentially provided on a substrate 11.

[0093] "substrate" The substrate 11 may be, for example, a non-magnetic substrate in which a film made of NiP or a NiP alloy is formed on a base made of a metal or alloy material such as Al or an Al alloy. Furthermore, the substrate 11 may be a non-magnetic substrate made of a non-metallic material such as glass, ceramics, silicon, silicon carbide, carbon, or resin, or a non-magnetic substrate having a NiP or NiP alloy film formed on a base made of these non-metallic materials.

[0094] "Adhesion layer" The adhesive layer 12 prevents the progress of corrosion of the substrate 11, which occurs when the substrate 11 and the soft magnetic layer 13 provided on the adhesive layer 12 are disposed in contact with each other. The material of the adhesive layer 12 can be appropriately selected from, for example, Cr, a Cr alloy, Ti, a Ti alloy, CrTi, NiAl, an AlRu alloy, etc. The adhesive layer 12 can be formed by, for example, a sputtering method.

[0095] "Soft magnetic layer" The soft magnetic layer 13 preferably has a structure in which a first soft magnetic film, an intermediate layer made of a Ru film, and a second soft magnetic film are laminated in this order. That is, the soft magnetic layer 13 preferably has a structure in which the intermediate layer made of a Ru film is sandwiched between two soft magnetic films, and the soft magnetic films above and below the intermediate layer are anti-ferro-coupling (AFC).

[0096] Examples of materials for the first soft magnetic film and the second soft magnetic film include a CoZrTa alloy and a CoFe alloy. It is preferable to add any one of Zr, Ta, and Nb to the CoFe alloy used in the first and second soft magnetic films, which promotes the amorphization of the first and second soft magnetic films, improves the orientation of the first underlayer (seed layer), and reduces the flying height of the magnetic head. The soft magnetic layer 13 can be formed by, for example, a sputtering method.

[0097] "First base layer" The first underlayer 14 is a layer for controlling the orientation and crystal size of the second underlayer 15 and the magnetic layer 16 provided thereon. Examples of the first underlayer 14 include a Cr layer, a Ta layer, a Ru layer, or a CrMo alloy layer, a CoW alloy layer, a CrW alloy layer, a CrV alloy layer, and a CrTi alloy layer. The first underlayer 14 can be formed by, for example, a sputtering method.

[0098] "Second base layer" The second underlayer 15 is a layer that controls good orientation of the magnetic layer 16. The second underlayer 15 is preferably a layer made of Ru or a Ru alloy. The second underlayer 15 may be a layer consisting of one layer, or may be composed of multiple layers. When the second underlayer 15 is composed of multiple layers, all the layers may be composed of the same material, or at least one layer may be composed of a different material. The second underlayer 15 can be formed by, for example, a sputtering method.

[0099] "Magnetic layer" The magnetic layer 16 is a magnetic film with an easy axis of magnetization oriented perpendicular or parallel to the substrate surface. The magnetic layer 16 is, for example, a layer containing Co and Pt, and may be a layer containing an oxide, Cr, B, Cu, Ta, Zr, or the like to further improve the SNR characteristics. Examples of oxides contained in the magnetic layer 16 include SiO2, SiO, Cr2O3, CoO, Ta2O3, and TiO2.

[0100] The magnetic layer 16 may be composed of a single layer, or may be composed of multiple magnetic layers made of materials with different compositions. For example, when the magnetic layer 16 is composed of three layers, a first magnetic layer, a second magnetic layer, and a third magnetic layer, stacked in order from the bottom, the first magnetic layer preferably has a granular structure made of a material containing Co, Cr, and Pt and further containing an oxide. As the oxide contained in the first magnetic layer, for example, oxides such as Cr, Si, Ta, Al, Ti, Mg, and Co are preferably used. Among them, TiO2, Cr2O3, SiO2, and the like can be particularly preferably used. In addition, the first magnetic layer is preferably made of a composite oxide to which two or more kinds of oxides are added. Among them, Cr2O3-SiO2, Cr2O3-TiO2, SiO2-TiO2, and the like can be particularly preferably used.

[0101] The first magnetic layer may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re, in addition to Co, Cr, Pt, and oxides. The second magnetic layer may be made of the same material as the first magnetic layer. The second magnetic layer preferably has a granular structure.

[0102] The third magnetic layer preferably has a non-granular structure made of a material that contains Co, Cr, and Pt and does not contain oxides. In addition to Co, Cr, and Pt, the third magnetic layer preferably contains one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn.

[0103] When the magnetic layer 16 is formed of multiple magnetic layers, it is preferable to provide a nonmagnetic layer between adjacent magnetic layers. When the magnetic layer 16 is formed of three layers, a first magnetic layer, a second magnetic layer, and a third magnetic layer, it is preferable to provide a nonmagnetic layer between the first magnetic layer and the second magnetic layer and between the second magnetic layer and the third magnetic layer.

[0104] The non-magnetic layer provided between adjacent magnetic layers in the magnetic layer 16 can suitably be made of, for example, Ru, a Ru alloy, a CoCr alloy, or a CoCrX1 alloy (X1 represents one or more elements selected from Pt, Ta, Zr, Re, Ru, Cu, Nb, Ni, Mn, Ge, Si, O, N, W, Mo, Ti, V, and B).

[0105] For the non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16, it is preferable to use an alloy material containing an oxide, a metal nitride, or a metal carbide. Specifically, for example, SiO2, Al2O3, Ta2O5, Cr2O3, MgO, Y2O3, TiO2, etc. can be used as the oxide. For example, AlN, Si3N4, TaN, CrN, etc. can be used as the metal nitride. For example, TaC, BC, SiC, etc. can be used as the metal carbide. The nonmagnetic layer can be formed by, for example, a sputtering method.

[0106] In order to achieve higher recording density, the magnetic layer 16 is preferably a magnetic layer for perpendicular magnetic recording in which the axis of easy magnetization is oriented perpendicular to the substrate surface, but may also be a magnetic layer for in-plane magnetic recording. The magnetic layer 16 may be formed by any known method such as vapor deposition, ion beam sputtering, magnetron sputtering, etc. The magnetic layer 16 is usually formed by sputtering.

[0107] "Protective layer" The protective layer 17 protects the magnetic layer 16. The protective layer 17 may be made of a single layer or multiple layers. Examples of materials for the protective layer 17 include carbon, carbon containing nitrogen, and silicon carbide. A carbon-based protective layer, particularly an amorphous carbon protective layer, can be preferably used as the protective layer 17. When the protective layer 17 is a carbon-based protective layer, the interaction with the hydroxyl group contained in the fluorine-containing ether compound in the lubricating layer 18 is further enhanced, which is preferable.

[0108] The adhesion between the carbon-based protective layer and the lubricating layer 18 can be controlled by making the carbon-based protective layer from hydrogenated carbon and / or nitrogenated carbon and adjusting the hydrogen content and / or nitrogen content in the carbon-based protective layer. The hydrogen content in the carbon-based protective layer is preferably 3 to 20 atomic % when measured by hydrogen forward scattering (HFS). The nitrogen content in the carbon-based protective layer is preferably 4 to 15 atomic % when measured by X-ray photoelectron spectroscopy (XPS).

[0109] The hydrogen and / or nitrogen contained in the carbon-based protective layer does not need to be uniformly contained throughout the carbon-based protective layer. The carbon-based protective layer is preferably a compositionally graded layer in which, for example, nitrogen is contained on the lubricating layer 18 side of the protective layer 17, and hydrogen is contained on the magnetic layer 16 side of the protective layer 17. In this case, the adhesion between the magnetic layer 16 and the lubricating layer 18 and the carbon-based protective layer is further improved.

[0110] The thickness of the protective layer 17 can be selected arbitrarily, but is preferably 1 nm to 7 nm. If the thickness of the protective layer 17 is 1 nm or more, sufficient performance as the protective layer 17 can be obtained. If the thickness of the protective layer 17 is 7 nm or less, it is preferable from the viewpoint of making the protective layer 17 thinner.

[0111] The protective layer 17 can be formed by a sputtering method using a target material containing carbon, a CVD (chemical vapor deposition) method using a hydrocarbon raw material such as ethylene or toluene, an IBD (ion beam deposition) method, or the like. When a carbon-based protective layer is formed as the protective layer 17, it can be deposited by, for example, a DC magnetron sputtering method. In particular, when a carbon-based protective layer is formed as the protective layer 17, it is preferable to deposit an amorphous carbon protective layer by a plasma CVD method. The amorphous carbon protective layer deposited by the plasma CVD method has a uniform surface with small roughness.

[0112] "Lubricating layer" The lubricating layer 18 prevents contamination of the magnetic recording medium 10. In addition, the lubricating layer 18 reduces the frictional force of the magnetic head of the magnetic recording and reproducing device that slides on the magnetic recording medium 10, thereby improving the durability of the magnetic recording medium 10. 1, the lubricating layer 18 is formed on and in contact with the protective layer 17. The lubricating layer 18 contains the above-mentioned fluorine-containing ether compound.

[0113] When the protective layer 17 disposed below the lubricating layer 18 is a carbon-based protective layer, the lubricating layer 18 is bonded with a high bonding strength to the protective layer 17. As a result, even if the thickness of the lubricating layer 18 is thin, it is easy to obtain a magnetic recording medium 10 in which the surface of the protective layer 17 is covered with a high coverage rate, and contamination of the surface of the magnetic recording medium 10 can be effectively prevented.

[0114] The average thickness of the lubricating layer 18 can be selected arbitrarily, but is preferably 0.5 nm (5 Å) to 2 nm (20 Å), and more preferably 0.5 nm (5 Å) to 1 nm (10 Å). When the average thickness of the lubricating layer 18 is 0.5 nm or more, the lubricating layer 18 is formed with a uniform thickness without being island-shaped or mesh-shaped. Therefore, the surface of the protective layer 17 can be covered with the lubricating layer 18 with a high coverage rate. In addition, by setting the average thickness of the lubricating layer 18 to 2 nm or less, the lubricating layer 18 can be made sufficiently thin, and the flying height of the magnetic head can be sufficiently reduced.

[0115] If the surface of the protective layer 17 is not covered with the lubricating layer 18 at a sufficiently high coverage rate, environmental substances adsorbed to the surface of the magnetic recording medium 10 will pass through the gaps in the lubricating layer 18 and penetrate underneath the lubricating layer 18. The environmental substances that penetrate underneath the lubricating layer 18 will be adsorbed and bonded to the protective layer 17 to generate contaminants. Then, during magnetic recording and reproduction, these contaminants (aggregated components) will adhere (transfer) to the magnetic head as smear, damaging the magnetic head or degrading the magnetic recording and reproduction characteristics of the magnetic recording and reproduction device.

[0116] Examples of environmental substances that generate pollutants include siloxane compounds (cyclic siloxanes, linear siloxanes), ionic impurities, hydrocarbons with relatively high molecular weights such as octacosane, and plasticizers such as dioctyl phthalate. Examples of metal ions contained in ionic impurities include sodium ions and potassium ions. Examples of inorganic ions contained in ionic impurities include chloride ions, bromide ions, nitrate ions, sulfate ions, and ammonium ions. Examples of organic ions contained in ionic impurities include oxalate ions and formate ions.

[0117] "Method of forming lubricating layer" The method for forming the lubricating layer 18 can be selected arbitrarily, but one example is a method in which a magnetic recording medium in the middle of manufacture is prepared in which each layer up to the protective layer 17 is formed on the substrate 11, and a solution for forming a lubricating layer is applied onto the protective layer 17 and dried.

[0118] The lubricant layer forming solution can be obtained, for example, by dispersing and dissolving the lubricant for magnetic recording media of the above-mentioned embodiment in a solvent as necessary, and adjusting the viscosity and concentration to be suitable for the coating method. Examples of the solvent used in the lubricant layer forming solution include fluorine-based solvents such as Vertrel (registered trademark) XF (product name, manufactured by Mitsui DuPont Fluorochemicals).

[0119] The method for applying the solution for forming the lubricating layer is not particularly limited, but examples thereof include spin coating, spraying, paper coating, and dipping. When using the dipping method, for example, the following method can be used. First, the substrate 11 on which each layer up to the protective layer 17 has been formed is immersed in the lubricant layer forming solution placed in the immersion tank of a dip coater. Next, the substrate 11 is lifted from the immersion tank at a predetermined speed. In this way, the lubricant layer forming solution is applied to the surface of the substrate 11 above the protective layer 17. By using the dipping method, the lubricant layer forming solution can be applied uniformly onto the surface of the protective layer 17, and the lubricant layer 18 can be formed on the protective layer 17 with a uniform thickness.

[0120] In this embodiment, it is preferable to perform a heat treatment on the substrate 11 on which the lubricating layer 18 is formed. By performing the heat treatment, the adhesion between the lubricating layer 18 and the protective layer 17 is improved, and the adhesive force between the lubricating layer 18 and the protective layer 17 is improved. The heat treatment temperature can be selected arbitrarily, but is preferably 100 to 180° C. If the heat treatment temperature is 100° C. or higher, the effect of improving the adhesion between the lubricating layer 18 and the protective layer 17 can be sufficiently obtained. Furthermore, by setting the heat treatment temperature to 180° C. or lower, thermal decomposition of the lubricating layer 18 can be prevented. The heat treatment time is preferably 10 to 120 minutes.

[0121] In this embodiment, in order to further improve the adhesion of the lubricating layer 18 to the protective layer 17, the lubricating layer 18 of the substrate 11 may be irradiated with ultraviolet (UV) rays before or after the heat treatment.

[0122] The magnetic recording medium 10 of this embodiment is a medium in which at least a magnetic layer 16, a protective layer 17, and a lubricating layer 18 are sequentially provided on a substrate 11. In the magnetic recording medium 10 of this embodiment, a lubricating layer 18 containing the above-mentioned fluorine-containing ether compound is formed on the protective layer 17. Even though the lubricating layer 18 is thin, it covers the surface of the protective layer 17 with a high coverage rate. Therefore, in the magnetic recording medium 10 of this embodiment, environmental substances that generate contaminants such as ionic impurities are prevented from penetrating through the gaps in the lubricating layer 18. Therefore, the magnetic recording medium 10 of this embodiment has a small amount of contaminants present on its surface. In addition, the lubricating layer 18 in the magnetic recording medium 10 of this embodiment is less likely to generate foreign matter (smear), and can suppress pickup. In addition, the lubricating layer 18 in the magnetic recording medium 10 of this embodiment has excellent chemical resistance and heat resistance. Therefore, the magnetic recording medium 10 of this embodiment has excellent reliability and durability. EXAMPLES

[0123] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0124] [Example 1] A compound represented by the above formula (A) (in formula (A), ba indicating the average degree of polymerization is 4.5, and ca indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,2-cyclopropanediol was reacted with epibromohydrin to synthesize a compound represented by the following formula (10). In addition, a product of the reaction between 3-allyloxy-1,2-propanediol-2-methoxymethyl ether and 2-(bromopropoxy)tetrahydro-2H-pyran was oxidized to synthesize a compound represented by the following formula (11).

[0125] [ka]

[0126] In a 200 mL eggplant flask, add HOCH2CF2O (CF2CF2O) s (CF2O) t Fluoropolyether (number average molecular weight 1000, molecular weight distribution 1.1) (40.0 g) represented by CF2CH2OH (where s, which indicates the average degree of polymerization, is 4.5, and t, which indicates the average degree of polymerization, is 4.5), the compound represented by the above formula (10) (6.10 g), and t-BuOH (tertiary butyl alcohol) (40.0 mL) were charged and stirred at room temperature until homogenized. Furthermore, t-BuOK (potassium tertiary butoxide) (1.35 g) was added to the above-mentioned eggplant flask, heated to 70°C, and reacted by stirring for 18 hours.

[0127] The reaction product was then cooled to 25°C, water was added, and further, Bertrel (registered trademark) XF (hereinafter sometimes referred to as "Bertrel XF") manufactured by Mitsui DuPont Fluorochemicals was added as a solvent to extract the organic layer, which was then washed with water. Anhydrous sodium sulfate was added to the organic layer to dehydrate it, and the drying agent was filtered off, and the filtrate was concentrated. The residue was purified by silica gel column chromatography to obtain a compound (17.5 g) represented by the following formula (12).

[0128] [ka] (In formula (12), s, which indicates the average degree of polymerization, is 4.5, and t, which indicates the average degree of polymerization, is 4.5.)

[0129] In a nitrogen gas atmosphere, the compound represented by the above formula (12) (17.5 g), the compound represented by the above formula (11) (2.67 g), and t-BuOH (tertiary butyl alcohol) (65.0 mL) were charged into a 200 mL eggplant flask and stirred at room temperature until homogenized. Further, t-BuOK (potassium tertiary butoxide) (0.235 g) was added to the eggplant flask, heated to 70°C, and reacted with stirring for 16 hours.

[0130] The reaction product was then cooled to 25°C, and water (3.3mL) and 5-10% hydrochloric acid / methanol (trade name: X0041, hydrogen chloride-methanol reagent (5-10%), manufactured by Tokyo Chemical Industry Co., Ltd.) (21.5mL) were added, followed by stirring at room temperature for 3 hours. 5% aqueous sodium bicarbonate solution (100mL) was added to the resulting residue, which was then extracted with ethyl acetate, and the organic layer was washed with water. Anhydrous magnesium sulfate was then added to the organic layer for dehydration, and the drying agent was filtered off, after which the filtrate was concentrated. The residue was purified by silica gel column chromatography to obtain 11.1g of compound (A).

[0131] The obtained compound (A) 1 H-NMR and 19 F-NMR measurement was performed, and the structure was identified based on the following results. 1H-NMR (acetone-d6): δ[ppm]=1.2~2.0(4H), 3.20~4.20(30H) 19 F-NMR (acetone-d6): δ[ppm]=-51.99~-55.72(9F), -78.48(2F), -80.66(2F), -89.16~-91.14(18F)

[0132] [Example 2] A compound represented by the above formula (B) (in formula (B), bb indicating the average degree of polymerization is 4.5, and cb indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,2-cyclobutane dimethanol was reacted with epibromohydrin to synthesize a compound represented by the following formula (13).

[0133] [ka]

[0134] The same procedure as in Example 1 was carried out, except that 6.10 g of the compound represented by formula (13) was used instead of the compound represented by formula (10) used in Example 1, to obtain 10.5 g of compound (B).

[0135] The obtained compound (B) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(6H), 3.20~4.20(34H)

[0136] [Example 3] A compound represented by the above formula (C) (in formula (C), bc indicating the average degree of polymerization is 4.5, and cc indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,2-cyclopentanediol, epibromohydrin, and 2-(bromoethoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (14).

[0137] [ka]

[0138] The same procedure as in Example 1 was carried out, except that 6.10 g of the compound represented by formula (14) was used instead of the compound represented by formula (10) used in Example 1, to obtain 11.9 g of compound (C).

[0139] The obtained compound (C) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 3.20~4.20(34H)

[0140] [Example 4] A compound represented by the above formula (D) (in formula (D), bd indicating the average degree of polymerization is 4.5, and cd indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,5-cyclononanediol and epibromohydrin were reacted to synthesize a compound represented by the following formula (15).

[0141] [ka]

[0142] The same procedure as in Example 1 was carried out, except that 6.10 g of the compound represented by formula (15) was used instead of the compound represented by formula (10) used in Example 1, to obtain 11.9 g of compound (D).

[0143] The obtained compound (D) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(16H), 3.20~4.20(30H)

[0144] [Example 5] A compound represented by the above formula (E) (in formula (E), be indicating the average degree of polymerization is 4.5, and ce indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,6-cyclotridecanediol and epibromohydrin were reacted to synthesize a compound represented by the following formula (16).

[0145] [ka]

[0146] The same procedure as in Example 1 was carried out except that 6.78 g of the compound represented by formula (16) was used instead of the compound represented by formula (10) used in Example 1, to obtain 12.4 g of compound (E).

[0147] The obtained compound (E) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(24H), 3.20~4.20(30H)

[0148] [Example 6] A compound represented by the above formula (F) (in formula (F), bf indicating the average degree of polymerization is 4.5, and cf indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,3,5-adamantanetriol was reacted with epibromohydrin to synthesize a compound represented by the following formula (17).

[0149] [ka]

[0150] The same procedure as in Example 1 was carried out, except that 3.81 g of the compound represented by formula (17) was used instead of the compound represented by formula (10) used in Example 1, to obtain 12.3 g of compound (F).

[0151] The obtained compound (F) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(13H), 3.20~4.20(33H)

[0152] [Example 7] A compound represented by the above formula (G) (in formula (G), bg indicating the average degree of polymerization is 4.5, and cg indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 7-cyclopenta-1-heptene was oxidized to synthesize a compound represented by the following formula (18).

[0153] [ka]

[0154] The same procedure as in Example 1 was carried out except that 9.99 g of the compound represented by formula (18) was used instead of the compound represented by formula (10) used in Example 1, to obtain 12.5 g of compound (G).

[0155] The obtained compound (G) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(21H), 3.20~4.20(25H)

[0156] [Example 8] A compound represented by the above formula (H) (in formula (H), bh indicating the average degree of polymerization is 4.5, and ch indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 3-amino-cyclopent-1-ol was reacted with epibromohydrin to synthesize a compound represented by the following formula (19).

[0157] [ka]

[0158] The same procedure as in Example 1 was carried out except that 2.89 g of the compound represented by formula (19) was used instead of the compound represented by formula (10) used in Example 1, to obtain 11.3 g of compound (H).

[0159] The obtained compound (H) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 3.20~4.20(31H)

[0160] [Example 9] The compound represented by the above formula (I) (in formula (I), bi indicating the average degree of polymerization is 4.5, and ci indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1-methoxy-cyclopent-3-ol was reacted with epibromohydrin to synthesize a compound represented by the following formula (20).

[0161] [ka]

[0162] The same procedure as in Example 1 was carried out except that 4.64 g of the compound represented by formula (20) was used instead of the compound represented by formula (10) used in Example 1, to obtain 12.1 g of compound (I).

[0163] The obtained compound (I) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 3.20~4.20(32H)

[0164] [Example 10] A compound represented by the above formula (J) (in formula (J), bj indicating the average degree of polymerization is 4.5, and cj indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1-amido-cyclopent-3-ol was reacted with epibromohydrin to synthesize a compound represented by the following formula (21).

[0165] [ka]

[0166] The same procedure as in Example 1 was carried out, except that 2.64 g of the compound represented by formula (21) was used instead of the compound represented by formula (10) used in Example 1, to obtain 10.9 g of compound (J).

[0167] The obtained compound (J) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 2.6(1H), 3.20~4.20(30H)

[0168] [Example 11] A compound represented by the above formula (K) (in formula (K), bk indicating the average degree of polymerization is 4.5, and ck indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1-methylamino-cyclopent-3-ol was reacted with epibromohydrin to synthesize a compound represented by the following formula (22).

[0169] [ka]

[0170] The same procedure as in Example 1 was carried out except that 2.64 g of the compound represented by formula (22) was used instead of the compound represented by formula (10) used in Example 1, thereby obtaining 10.9 g of compound (K).

[0171] The obtained compound (K) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(9H), 3.20~4.20(32H)

[0172] [Example 12] A compound represented by the above formula (L) (in formula (L), bl indicating the average degree of polymerization is 4.5, and cl indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1-cyano-cyclopent-3-ol was reacted with epibromohydrin to synthesize a compound represented by the following formula (23).

[0173] [ka]

[0174] The same procedure as in Example 1 was carried out except that 2.64 g of the compound represented by formula (23) was used instead of the compound represented by formula (10) used in Example 1, to obtain 10.9 g of compound (L).

[0175] The obtained compound (L) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 2.5(1H), 3.20~4.20(28H)

[0176] [Example 13] A compound represented by the above formula (M) (in formula (M), bm indicating the average degree of polymerization is 4.5, and cm indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, the compound represented by the following formula (24) was synthesized by oxidizing the product obtained by reacting 3-allyloxy-1,2-propanediol-2-methoxymethyl ether with 2-(bromoethoxy)tetrahydro-2H-pyran.

[0177] [ka]

[0178] The same procedure as in Example 3 was carried out except that 2.64 g of the compound represented by formula (24) was used instead of the compound represented by formula (11) used in Example 3, to obtain 10.9 g of compound (M).

[0179] The obtained compound (M) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(6H), 3.20~4.20(38H)

[0180] [Example 14] A compound represented by the above formula (N) (wherein bn, which indicates the average degree of polymerization, is 6.5) was obtained by the method described below. HOCH2CF2O(CF2CF2O) used in Example 13 s (CF2O) t CF2CH2OH (wherein s, which indicates the average degree of polymerization, is 4.5, and t, which indicates the average degree of polymerization, is 4.5), instead of fluoropolyether represented by HOCH2CF2O(CF2CF2O) u The same procedure as in Example 13 was carried out except that 40.0 g of fluoropolyether represented by CF2CH2OH (wherein u, which indicates the average degree of polymerization, is 6.5) was used, to obtain 10.9 g of compound (N).

[0181] The obtained compound (N) 1 H-NMR and 19 F-NMR measurement was performed, and the structure was identified based on the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(6H), 3.20~4.20(38H) 19F-NMR (acetone-d6): δ[ppm]=-77.85~-79.00(4F), -88.50~-91.22(26F)

[0182] [Example 15] The compound represented by the above formula (O) (wherein e0, which indicates the average degree of polymerization, is 4.5) was obtained by the method described below. HOCH2CF2O(CF2CF2O) used in Example 13 s (CF2O) t CF2CH2OH (wherein s, which indicates the average degree of polymerization, is 4.5, and t, which indicates the average degree of polymerization, is 4.5), instead of fluoropolyether represented by HOCH2CF2CF2O (CF2CF2CF2O) v The same procedure as in Example 13 was carried out except that 40.0 g of fluoropolyether represented by CF2CF2CH2OH (wherein v, which indicates the average degree of polymerization, is 4.5) was used, to obtain 10.7 g of compound (O).

[0183] The obtained compound (O) 1 H-NMR and 19 F-NMR measurement was performed, and the structure was identified based on the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(6H), 3.20~4.20(38H) 19 F-NMR (acetone-d6): δ[ppm]=-82.66~-84.00(20F), -85.16~-86.91(4F), -123.16~-124.91(4F), -128.47~-130.20(4F)

[0184] [Example 16] A compound represented by the above formula (T) (in formula (T), bt indicating the average degree of polymerization is 4.5, and ct indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,2-cyclopentanediol, epibromohydrin, and 2-(bromopropoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (28).

[0185] [ka]

[0186] The same procedure as in Example 1 was carried out except that 5.90 g of the compound represented by formula (28) was used instead of the compound represented by formula (10) used in Example 1, to obtain 11.9 g of compound (T).

[0187] The obtained compound (T) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(10H), 3.20~4.20(34H)

[0188] [Example 17] A compound represented by the above formula (U) (in formula (U), bu indicating the average degree of polymerization is 4.5, and cu indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,3,5-cyclohexanetriol, t-butyldimethylchlorosilane, epibromohydrin, and 2-(bromoethoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (29).

[0189] [ka] (In formula (29), TBS represents a t-butyldimethylsilyl group.)

[0190] The same procedure as in Example 1 was carried out, except that 7.20 g of the compound represented by formula (29) was used instead of the compound represented by formula (10) used in Example 1, to obtain 10.8 g of compound (U).

[0191] The obtained compound (U) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 3.20~4.20(36H)

[0192] [Example 18] A compound represented by the above formula (V) (in formula (V), bv indicating the average degree of polymerization is 4.5, and cv indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,3,5-cyclohexanetriol, t-butyldimethylchlorosilane, epibromohydrin, and 2-(bromopropoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (30).

[0193] [ka] (In formula (30), TBS represents a t-butyldimethylsilyl group.)

[0194] The same procedure as in Example 1 was carried out except that 7.50 g of the compound represented by formula (30) was used instead of the compound represented by formula (10) used in Example 1, to obtain 10.4 g of compound (V).

[0195] The obtained compound (V) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(10H), 3.20~4.20(36H)

[0196] [Example 19] A compound represented by the above formula (W) (in formula (W), bw indicating the average degree of polymerization is 4.5, and cw indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,3,5-cyclohexanetriol, epibromohydrin, and 2-(bromoethoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (31).

[0197] [ka]

[0198] The same procedure as in Example 1 was carried out except that 6.50 g of a compound represented by formula (31) was used instead of the compound represented by formula (10) used in Example 1, to obtain 9.5 g of compound (W).

[0199] The obtained compound (W) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(8H), 3.20~4.20(40H)

[0200] [Example 20] A compound represented by the above formula (X) (in formula (X), bx indicating the average degree of polymerization is 4.5, and cx indicating the average degree of polymerization is 4.5) was obtained by the method shown below. First, 1,3,5-cyclohexanetriol, epibromohydrin, and 2-(bromopropoxy)tetrahydro-2H-pyran were reacted to synthesize a compound represented by the following formula (32).

[0201] [ka]

[0202] The same procedure as in Example 1 was carried out except that 5.50 g of the compound represented by formula (32) was used instead of the compound represented by formula (10) used in Example 1, to obtain 8.4 g of compound (X).

[0203] The obtained compound (X) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(12H), 3.20~4.20(40H)

[0204] [Comparative Example 1] The compound represented by the following formula (P) was obtained by the method described below.

[0205] [ka] (In formula (P), bp indicating the average degree of polymerization is 4.5, and cp indicating the average degree of polymerization is 4.5.)

[0206] First, allyl alcohol and epibromohydrin were reacted to synthesize a compound represented by the following formula (25).

[0207] [ka]

[0208] The same procedure as in Example 13 was carried out except that 2.64 g of the compound represented by formula (25) was used instead of the compound represented by formula (14) used in Example 13, to obtain 10.9 g of compound (P).

[0209] The obtained compound (P) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=3.20~4.20(29H), 5.00~6.00(3H)

[0210] [Comparative Example 2] The compound represented by the following formula (Q) was obtained by the method described below.

[0211] [ka] (In formula (Q), bq, which indicates the average degree of polymerization, is 4.5, and cq, which indicates the average degree of polymerization, is 4.5.)

[0212] First, phenol and epibromohydrin were reacted to synthesize a compound represented by the following formula (26).

[0213] [ka]

[0214] The same procedure as in Example 13 was carried out except that 2.64 g of the compound represented by formula (26) was used instead of the compound represented by formula (14) used in Example 13, to obtain 10.9 g of compound (Q).

[0215] The obtained compound (Q) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=3.20~4.20(27H), 6.6~7.4(5H)

[0216] [Comparative Example 3] The compound represented by the following formula (R) was obtained by the method described below.

[0217] [ka] (In formula (R), br indicating the average degree of polymerization is 4.5, and cr indicating the average degree of polymerization is 4.5.)

[0218] First, 1-butanol and epibromohydrin were reacted to synthesize a compound represented by the following formula (27).

[0219] [ka]

[0220] The same procedure as in Example 13 was carried out except that 2.64 g of the compound represented by formula (27) was used instead of the compound represented by formula (14) used in Example 13, to obtain 10.9 g of compound (R).

[0221] The obtained compound (R) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR (acetone-d6): δ[ppm]=1.2~2.0(7H), 3.20~4.20(29H)

[0222] [Comparative Example 4] The compound represented by the following formula (S) was obtained by the method described below.

[0223] [ka] (In formula (S), bs indicating the average degree of polymerization is 4.5, and cs indicating the average degree of polymerization is 4.5.)

[0224] The same procedure as in Example 13 was carried out except that 2.64 g of the compound represented by formula (24) was used instead of the compound represented by formula (14) used in Example 13, to obtain 10.9 g of compound (S).

[0225] The obtained compound (S) 1 H-NMR measurement was performed, and the structure was identified from the following results. 1 H-NMR(acetone-d6):δ[ppm]=3.20~4.20(38H)

[0226] The number average molecular weights of the compounds of Examples 1 to 20 and Comparative Examples 1 to 4 thus obtained were determined by the method described above. 1 H-NMR and 19 The average molecular weight of the synthesized compound was determined by F-NMR measurement. The results are shown in Table 1. It is estimated that the average molecular weight of the synthesized compound varies by about 1 to 5 due to the molecular weight distribution of the fluoropolyether used as the raw material of the compound, the difference in the operation when synthesizing the compound, and the like.

[0227] [Table 1]

[0228] (Heat resistance test) The compounds of Examples 1 to 20 and Comparative Examples 1 to 4 were subjected to heat resistance tests and evaluated by the method described below. The weight loss of each compound with respect to the temperature increase was measured using TG-DTA (manufacturer: Seiko Instruments, model number: EXSTAR6000), and the temperature at which the weight loss reached 5% was defined as the thermal decomposition temperature. The measurement conditions were a temperature increase rate of 10°C / min and an air flow rate of 200mL / min. The results are shown in Table 1.

[0229] "Heat resistance evaluation" ○(Good): Thermal decomposition temperature is 250℃ or higher △(OK): Thermal decomposition temperature is 100℃ or higher and less than 250℃ × (Not acceptable): Thermal decomposition temperature is less than 100℃

[0230] Next, a lubricant layer-forming solution was prepared by the method described below using the compounds obtained in Examples 1 to 20 and Comparative Examples 1 to 4. Then, the lubricant layer of the magnetic recording medium was formed by the method described below using the obtained lubricant layer-forming solution, thereby obtaining the magnetic recording media of Examples 1 to 20 and Comparative Examples 1 to 4.

[0231] "Lubricant layer forming solution" The compounds obtained in Examples 1 to 20 and Comparative Examples 1 to 4 were each dissolved in a fluorine-based solvent, Vertrel (registered trademark) XF (product name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.), and further diluted with Vertrel XF so that the film thickness when applied onto the protective layer would be 9 Å to 10 Å, to prepare a solution for forming a lubricating layer.

[0232] "Magnetic recording media" A magnetic recording medium was prepared by sequentially providing an adhesive layer, a soft magnetic layer, a first underlayer, a second underlayer, a magnetic layer, and a protective layer on a substrate having a diameter of 65 mm. The protective layer was made of carbon. On the protective layer of the magnetic recording medium on which each layer up to the protective layer had been formed, the lubricant layer forming solutions of Examples 1 to 20 and Comparative Examples 1 to 4 were applied by dipping under the conditions of an immersion speed of 10 mm / sec, an immersion time of 30 sec, and a pull-up speed of 1.2 mm / sec. The magnetic recording medium coated with the lubricant layer-forming solution was then placed in a thermostatic chamber at 120°C and heated for 10 minutes to remove the solvent in the lubricant layer-forming solution, thereby forming a lubricant layer on the protective layer and obtaining the magnetic recording medium.

[0233] (film thickness measurement) The thickness of the lubricating layer of each of the magnetic recording media thus obtained in Examples 1 to 20 and Comparative Examples 1 to 4 was measured using an FT-IR (product name: Nicolet iS50, manufactured by Thermo Fisher Scientific Co., Ltd.) The results are shown in Table 1.

[0234] In addition, the following chemical resistance tests and pick-up suppression tests were conducted on the magnetic recording media of Examples 1 to 20 and Comparative Examples 1 to 4. The results are shown in Table 1.

[0235] (Chemical Resistance Test) The following evaluation method was used to investigate the contamination of magnetic recording media by environmental substances that generate contaminants in a high-temperature environment. In the evaluation method described below, Si ions were used as the environmental substances, and the amount of Si adsorption was measured as the amount of contaminants that contaminate the magnetic recording media and are generated by the environmental substances.

[0236] Specifically, the magnetic recording medium to be evaluated was kept in the presence of siloxane-based Si rubber for 240 hours in a high-temperature environment of 85°C and 0% humidity. The amount of Si adsorption on the surface of the magnetic recording medium was then analyzed and measured using secondary ion mass spectrometry (SIMS), and the degree of contamination by Si ions was evaluated as the amount of Si adsorption. The amount of Si adsorption was evaluated using a numerical value when the result of Comparative Example 1 was set to 1.00. The results are shown in Table 1. The smaller the numerical value, the better the chemical resistance.

[0237] (Pickup suppression test) The magnetic recording medium and the magnetic head were mounted on a spin stand, and the magnetic head was floated at a fixed point for 10 minutes while rotating the magnetic recording medium under reduced pressure (approximately 250 torr) at room temperature. After that, the surface of the magnetic head facing the magnetic recording medium (the surface of the lubricant layer) was analyzed using an ESCA (Electron Spectroscopy for Chemical Analysis) analyzer. Then, the amount of lubricant attached to the magnetic head was evaluated according to the following criteria based on the intensity (signal intensity (au)) of the peak derived from fluorine measured by ESCA.

[0238] "Pickup suppression test evaluation" ◎ (Excellent): The ESCA signal strength is very small, less than 500 (very little lubricant adhered to the head) Good: ESCA signal strength is small, between 501 and 1000 (low amount of lubricant on the head) × (Not acceptable): ESCA signal strength is 1001 or more (a large amount of lubricant is attached to the head)

[0239] Moreover, a comprehensive evaluation was performed on the compounds and magnetic recording media of Examples 1 to 20 and Comparative Examples 1 to 4 based on the following criteria. The results are shown in Table 1. (comprehensive evaluation) ◯ (Good): Heat resistance is rated ◯, the amount of Si adsorption is 0.60 or less, and the pick-up suppression test is rated ⊚ (Excellent) or ◯ (Good). × (Fail): Does not meet the criteria for a good overall rating.

[0240] As shown in Table 1, in Examples 1 to 20, the results of the heat resistance test, the chemical substance resistance test (amount of Si adsorption), and the pick-up suppression test were all good, and the overall evaluation was ◯ (good). In contrast, in Comparative Examples 1 to 4, the results of the heat resistance test, chemical resistance test (Si adsorption amount), and pick-up suppression test taken together were inferior to those of Examples 1 to 20, and the overall evaluation was × (unacceptable).

[0241] More specifically, R in formula (1) 1 In Comparative Example 1, in which a compound (P) having a chain structure including a double bond was used instead of the organic group represented by the formula (I), the heat resistance test was evaluated as ×, and the chemical resistance test showed poor results. In addition, R in formula (1) 1 In Comparative Example 2, in which a compound (Q) having a benzene ring was used instead of the organic group represented by the following formula, the pick-up suppression test was evaluated as × (fail). In addition, R in formula (1) 1 In Comparative Example 3, in which a compound (R) having a linear alkyl group was used instead of the organic group represented by the following formula, the results of the chemical resistance test were poor. In addition, R in formula (1) 1 In Comparative Example 4, in which a compound (S) having a linear alkyl group substituted with a terminal hydroxyl group was used instead of the organic group represented by the following formula, the results of the chemical resistance test were poor.

[0242] From the above results, it was found that by forming a lubricating layer containing the compounds of Examples 1 to 20 on the protective layer of a magnetic recording medium, even if the thickness is as thin as 9 Å to 10 Å, pick-up is unlikely to occur and a lubricating layer with excellent chemical resistance and heat resistance can be obtained. [Industrial Applicability]

[0243] The present invention provides a fluorine-containing ether compound capable of forming a lubricating layer that has excellent chemical resistance and heat resistance even when made thin and that suppresses pick-up. By using a lubricant for magnetic recording media containing the fluorinated ether compound of the present invention, it is possible to form a lubricating layer which, even if thin, has excellent heat resistance and chemical resistance and suppresses pick-up. [Explanation of symbols]

[0244] 10 magnetic recording medium, 11 substrate, 12 adhesion layer, 13 soft magnetic layer, 14 first underlayer, 15 second underlayer, 16 magnetic layer, 17 protective layer, and 18 lubricating layer.

Claims

1. A fluorine-containing ether compound represented by the following formula (1): R １ -R ２ -CH ２ -R ３ -CH ２ -R ４ (1) (In formula (1), R １ is one kind selected from the group consisting of cyclopropane, cyclobutane, cyclopentane, and cyclohexane, and is an organic group having an alicyclic structure which may have one or more substituents, the substituents being selected from the group consisting of -OH, -CH 2 OH, -CH 2 CH 2 OH, -CH 2 CH 2 CH 2 OH; -OCH 3 , -OCH 2 CH 3 , -OCH 2 CH 2 CH 3 ; -OCH 2 OH, -OCH 2 CH 2 OH, -OCH 2 CH 2 CH 2 OH; -CONH 2 , -CH 2 NH 2 , -CH 2 CH 2 NH 2 , -CH 2 CH 2 CH 2 NH 2 ; and -CN, and when the alicyclic structure is Z, the bond between the alicyclic structure Z and a carbon atom contained in R 2 is Z-R 2 , Z-O-R 2 , Z-NH-R 2 , Z-CH 2 O-R 2 , Z-CH 2 CH 2 O-R 2 , Z-CH 2 CH 2 CH 2 O-R 2 , Z-CH 2 -R 2 , Z-CH 2 CH 2 -R 2 , Z-CH 2 CH 2 CH 2 -R 2 , Z-CH 2 CH 2 CH 2 CH 2 -R 2 ; ２ is represented by the following formula (2), where a is an integer of 1 to 3; R ３ is a perfluoropolyether chain; R ４ is an end group represented by any one of the following formulas (6) to (9). 【Chemistry 1】 【Chemistry 2】 (In formula (6), f represents an integer of 1 to 2, and g represents an integer of 1 to 5.) (In formula (7), h represents an integer of 2 to 5.) (In formula (8), i represents an integer of 1 to 5.) (In formula (9), j represents an integer of 1 or 2, and k represents an integer of 1 or 2.)

2. The R ３ The fluorine-containing ether compound according to claim 1, wherein the compound is represented by any one of the following formulas (3) to (5): -CF ２ O-(CF ２ CF ２ O) ｂ -(CF ２ O) ｃ -CF ２ - (3) (In formula (3), b and c represent the average degree of polymerization and each independently represents 0 to 30. However, b and c cannot be 0 at the same time.) -CF(CF ３ )-(OCF(CF ３ )CF ２ ) ｄ -OCF(CF ３ )- (4) (In formula (4), d represents the average degree of polymerization and is 0.1 to 30.) -CF ２ CF ２ O-(CF ２ CF ２ CF ２ O) ｅ -CF ２ CF ２ - (5) (In formula (5), e represents the average degree of polymerization and is 0.1 to 30.)

3. A fluorine-containing ether compound according to claim 1 or claim 2, wherein the substituents are selected from the group consisting of -OH, -CH 2 OH, -OCH 3, -OCH 2 CH 2 OH, -OCH 2 CH 2 CH 2 OH, -CONH 2, -CH 2 NH 2 and -CN, and when the alicyclic structure is Z, the bond between the alicyclic structure Z and the carbon atom contained in R 2 is one type selected from Z-O-R 2, Z-NH-R 2, Z-CH 2 O-R 2 and Z-CH 2 CH 2 CH 2 CH 2 -R 2.

4. The fluorine-containing ether compound according to any one of claims 1 to 3, having a number average molecular weight in the range of 500 to 10,000.

5. The fluorine-containing ether compound according to any one of claims 1 to 4, wherein the compound represented by formula (1) is any one of compounds represented by the following formulas (A) to (C) and (G) to (O): 【Chemistry 3】 (In formula (A), ba and ca represent average degrees of polymerization, ba represents 0 to 30, and ca represents 0 to 30. However, ba and ca cannot be 0 at the same time.) (In formula (B), bb and cb represent average degrees of polymerization, bb represents 0 to 30, and cb represents 0 to 30. However, bb and cb cannot be 0 at the same time.) (In formula (C), bc and cc represent average degrees of polymerization, bc being 0 to 30, and cc being 0 to 30. However, bc and cc cannot be 0 at the same time.) 【Chemistry 4】 (In formula (G), bg and cg represent average degrees of polymerization, bg being 0 to 30, and cg being 0 to 30. However, bg and cg cannot be 0 at the same time.) (In formula (H), bh and ch represent the average degree of polymerization, bh represents 0 to 30, and ch represents 0 to 30. However, bh and ch cannot be 0 at the same time.) (In formula (I), bi and ci represent average degrees of polymerization, bi represents 0 to 30, and ci represents 0 to 30. However, bi and ci cannot be 0 at the same time.) 【Chemistry 5】 (In formula (J), bj and cj represent average degrees of polymerization, bj represents 0 to 30, and cj represents 0 to 30. However, bj and cj cannot be 0 at the same time.) (In formula (K), bk and ck represent average degrees of polymerization, bk being 0 to 30, and ck being 0 to 30. However, bk and ck are not 0 at the same time.) 【Chemistry 6】 (In formula (L), bl and cl represent average degrees of polymerization, bl being 0 to 30, and cl being 0 to 30. However, bl and cl cannot be 0 at the same time.) (In formula (M), bm and cm represent average degrees of polymerization, bm being 0 to 30, and cm being 0 to 30. However, bm and cm cannot be 0 at the same time.) (In formula (N), bn represents an average degree of polymerization, and bn represents 0.1 to 30.) (In formula (O), eo represents an average degree of polymerization, and eo represents 0.1 to 30.)

6. The fluorine-containing ether compound according to any one of claims 1 to 4, wherein the compound represented by formula (1) is any one of compounds represented by the following formulas (T) to (X): 【Chemistry 7】 (In formula (T), bt and ct represent average degrees of polymerization, bt represents 0 to 30, and ct represents 0 to 30. However, bt and ct cannot be 0 at the same time.) (In formula (U), bu and cu represent average degrees of polymerization, bu represents 0 to 30, and cu represents 0 to 30. However, bu and cu cannot be 0 at the same time.) (In formula (V), bv and cv represent average degrees of polymerization, bv being 0 to 30, and cv being 0 to 30. However, bv and cv cannot be 0 at the same time.) (In formula (W), bw and cw represent average degrees of polymerization, bw being 0 to 30, and cw being 0 to 30. However, bw and cw cannot be 0 at the same time.) (In formula (X), bx and cx represent average degrees of polymerization, bx represents 0 to 30, and cx represents 0 to 30. However, bx and cx cannot be 0 at the same time.)

7. A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to any one of claims 1 to 6.

8. A magnetic recording medium comprising at least a magnetic layer, a protective layer, and a lubricating layer provided in this order on a substrate, 7. A magnetic recording medium, comprising the lubricating layer comprising the fluorine-containing ether compound according to claim 1.

9. 9. The magnetic recording medium according to claim 8, wherein the average thickness of the lubricating layer is from 0.5 nm to 2 nm.

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