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

Abstract

Provided is a fluorine-containing ether compound represented by the following formula. R1-R2-O-CH2-R3-CH2-O-R4-R5 (R3 is a perfluoropolyether chain; R2 is represented by formula (2), R4 is represented by formula (3), and R1 and R5 are each a hydrogen atom or represented by formula (4); in formula (2), a and b are integers of 0-2 and c is an integer of 2-5; in formula (3), d and e are integers of 0-2 and f is an integer of 2-5; at least one of b in formula (2) and e in formula (3) is 1 or greater; and k in formula (4) is an integer of 3-6.)

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. 2020-101575, filed on June 11, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] In order to increase the recording density in magnetic recording and reproducing devices, development of magnetic recording media suitable for high recording density is underway. Conventionally, there is a magnetic recording medium in which a recording layer is formed on a substrate, and a protective layer made of carbon or the like is formed on the recording layer. The protective layer protects the information recorded on the recording layer and improves the sliding properties of the magnetic head. The protective layer also covers the recording layer to prevent the metal contained in the recording layer from being corroded by environmental substances.

[0003] However, the durability of the magnetic recording medium cannot be sufficiently obtained by only providing a protective layer on the recording layer. Therefore, a lubricant is applied to the surface of the protective layer to form a lubricating layer with a thickness of about 0.5 to 3 nm. The lubricating layer improves the durability and protective power of the protective layer and prevents the intrusion of contaminants into the magnetic recording medium. After the lubricating layer is formed on the surface of the protective layer, a burnishing process may be carried out to remove protrusions and particles present on the surface of the magnetic recording medium and to improve the smoothness of the surface.

[0004] Lubricants used in forming a lubricating layer on a magnetic recording medium include, for example, those that contain a fluorine-based polymer having a repeating structure containing --CF2-- and having a polar group such as a hydroxyl group at the end. For example, Patent Documents 1 to 4 disclose magnetic recording media that include a lubricating layer that contains a perfluoropolyether having a hydroxyl group at its terminal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5786047 [Patent Document 2] Patent No. 4632144 [Patent Document 3] International Publication No. 2019 / 054148 [Patent Document 4] International Publication No. 2019 / 049585 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 protective layer and a thinner lubricating layer in the magnetic recording medium. However, when the thickness of the protective layer and / or the lubricating layer is thinned, the corrosion resistance of the magnetic recording medium may become insufficient. In particular, when the surface of the magnetic recording medium after the lubricating layer is formed is subjected to tape varnish, the corrosion resistance of the magnetic recording medium tends to become insufficient. For this reason, a lubricating layer that is highly effective in suppressing the corrosion of the magnetic recording medium is required.

[0007] 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 that can be used as a material for a lubricant for a magnetic recording medium, which can provide a lubricating layer having a high corrosion-inhibiting effect on the 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 excellent corrosion resistance, which has a lubricating layer containing the fluorine-containing ether compound of the present invention. [Means for solving the problem]

[0008] The present inventors have conducted extensive research in order to solve the above problems. As a result, there are ether bonds (-O-) between one or both ends of the perfluoropolyether chain and the terminal hydroxyl group (-OH), and two or more methylene groups (-(CH2) q The present inventors have found that a fluorine-containing ether compound having a linking group of a specific structure combining - (wherein q is an integer of 2 to 5), a methylene group in which one hydrogen atom is substituted with a hydroxyl group (-CH(OH)-), and a methylene group (-CH2-) can be used, and have arrived at the present invention. That is, the present invention relates to the following: The present invention includes the following first aspect.

[0009] [1] A fluorinated ether compound represented by the following formula (1): R 1 -R 2 -O-CH2-R 3 -CH2-OR 4 -R 5 (1) (In formula (1), R 3 is a perfluoropolyether chain; R 2 is expressed by the following formula (2); R 4 is expressed by the following formula (3); R 1 and R 5 is a hydrogen atom or the following formula (4).

[0010] [ka] (In formula (2), a and b are integers of 0 to 2, and c is an integer of 2 to 5; in formula (3), d and e are integers of 0 to 2, and f is an integer of 2 to 5; at least one of b in formula (2) and e in formula (3) is 1 or more; in formula (4), k is an integer of 3 to 6.)

[0011] The compound according to the first aspect of the present invention preferably includes the following features [2] to [8]. It is also preferable to combine two or more of these features. [2] The fluorine-containing ether compound according to [1], wherein the sum of a and b in the formula (2) is 1 or 2.

[0012] [3] R in the above formula (1) 1 -R 2 The fluorine-containing ether compound according to [1] or [2], wherein —O— is any one of the following formulae (2-1) to (2-8): R 1 -O(CH2)2CH(OH)CH2O- (2-1) R 1 -O(CH2)3CH(OH)CH2O- (2-2) R 1 -O(CH2)4CH(OH)CH2O- (2-3) R 1 -O(CH2)5CH(OH)CH2O- (2-4) R 1 -O(CH2)2CH(OH)CH2OCH2CH(OH)CH2O- (2-5) R 1 -O(CH2)3CH(OH)CH2OCH2CH(OH)CH2O- (2-6) R 1 -O(CH2)4CH(OH)CH2OCH2CH(OH)CH2O- (2-7) R 1 -O(CH2)5CH(OH)CH2OCH2CH(OH)CH2O- (2-8)

[0013] [4] The fluorine-containing ether compound according to any one of [1] to [3], wherein the sum of d and e in the formula (3) is 1 or 2. [5] -OR in the above formula (1) 4 -R 5 is any one of the following formulae (3-1) to (3-8): -OCH2CH(OH)(CH2)2O-R 5 (3-1) -OCH2CH(OH)(CH2)3O-R 5 (3-2) -OCH2CH(OH)(CH2)4O-R 5 (3-3) -OCH2CH(OH)(CH2)5O-R 5 (3-4) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)2O-R 5 (3-5) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)3O-R 5 (3-6) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)4O-R 5 (3-7) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)5O-R 5 (3-8) [6] R in the above formula (1) 2 and R 4 The fluorinated ether compound according to any one of [1] to [5], wherein the total number of hydroxyl groups contained therein is 1 to 4.

[0014] [7] R in the above formula (1) 3 is any one of the following formulae (5) to (7): -CF2O-(CF2CF2O) m -(CF2O) n -CF2- (5) (In formula (5), m and n each represent an average degree of polymerization and are 0 to 30; however, m or n is 0.1 or more.) -CF(CF3)-(OCF(CF3)CF2) g -OCF(CF3)- (6) (In formula (6), g represents the average degree of polymerization and is from 0.1 to 30.) -CF2CF2O-(CF2CF2CF2O) z -CF2CF2- (7) (In formula (7), z represents the average degree of polymerization and is from 0.1 to 30.)

[0015] [8] The fluorinated ether compound according to any one of [1] to [7], having a number average molecular weight in the range of 500 to 10,000. A second aspect of the present invention is the following lubricant. [9] A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to any one of [1] to [8].

[0016] A third aspect of the present invention is a magnetic recording medium as follows.

[10] A magnetic recording medium having at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate, 13. A magnetic recording medium, comprising: a lubricating layer comprising the fluorine-containing ether compound according to any one of [1] to [8].

[11] The magnetic recording medium according to

[10] , wherein the lubricating layer has an average thickness of 0.5 nm to 2.0 nm. Effect of the Invention

[0017] The fluorine-containing ether compound of the present invention is a compound represented by the above formula (1), and therefore can be used as a material for a lubricant for magnetic recording media, which can provide a lubricant layer having a high corrosion-inhibiting effect on the magnetic recording media. Since the lubricant for magnetic recording media of the present invention contains the fluorine-containing ether compound of the present invention, it is possible to form a lubricating layer that has a high corrosion-inhibiting effect on the magnetic recording medium. The magnetic recording medium of the present invention has a lubricating layer containing the fluorine-containing ether compound of the present invention, and therefore has excellent corrosion resistance.Therefore, the magnetic recording medium of the present invention has excellent reliability and durability.In addition, the magnetic recording medium of the present invention has a lubricating layer with high corrosion suppression effect, and therefore the thickness of the protective layer and / or the lubricating layer can be made thin. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of a preferred magnetic recording medium of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Preferred examples of 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. For example, the present invention is not limited to the following examples, and the number, amount, ratio, composition, type, position, material, configuration, etc. can be added, omitted, replaced, or changed within the scope of the present invention.

[0020] [Fluorine-containing ether compounds] The fluorine-containing ether compound of the present embodiment is represented by the following formula (1). R 1 -R 2 -O-CH2-R 3 -CH2-OR 4 -R 5 (1) (In formula (1), R 3 is a perfluoropolyether chain; R 2 is expressed by the following formula (2); R 4 is expressed by the following formula (3); R 1 and R 5 is a hydrogen atom or the following formula (4).

[0021] [ka] (In formula (2), a and b are integers of 0 to 2, and c is an integer of 2 to 5; in formula (3), d and e are integers of 0 to 2, and f is an integer of 2 to 5; at least one of b in formula (2) and e in formula (3) is 1 or more; in formula (4), k is an integer of 3 to 6.)

[0022] R in formula (1) 1 and R 5is a hydrogen atom or formula (4). Therefore, the fluorine-containing ether compound represented by formula (1) has a hydroxyl group at the most terminal of the chain structure. Therefore, when a lubricating layer is formed on a protective layer using a lubricant containing a fluorine-containing ether compound represented by formula (1), a suitable interaction occurs between the lubricating layer and the protective layer. Therefore, the lubricating layer has excellent adhesion to the protective layer.

[0023] In formula (4), k is an integer of 3 to 6, and preferably an integer of 4 to 6. Since k in formula (4) is 3 or more, R 1 and / or R 5 If is formula (4), R 1 and / or R 5 is R 2 or R 4 It is a compound in which a hydroxyl group is bonded to three or more methylene groups bonded in a straight chain to the oxygen atom of R. 1 and / or R 5 The lubricating layer containing the fluorine-containing ether compound represented by formula (4) is 1 and / or R 5 The hydrophobicity of the carbon atoms contained in the three or more methylene groups bonded in a straight chain has an appropriate hydrophobicity. As a result, the lubricating layer can prevent water from penetrating into the magnetic recording medium. On the other hand, when k in formula (4) is 1 or 2, for example, R 2 or R 4 There are insufficient methylene groups linearly bonded to the oxygen atoms of the aryl group to provide adequate hydrophobicity.

[0024] In addition, since k in formula (4) is 6 or less, R 1 and / or R 5 If is formula (4), then R 1 and / or R 5 The hydrophobicity of R is so high that it does not interfere with adhesion to the protective layer. 1 and / or R 5 A lubricating layer containing a fluorine-containing ether compound represented by formula (4) has excellent adhesion to a protective layer, can prevent the intrusion of water, and has a high corrosion-inhibiting effect on a magnetic recording medium.

[0025] R in formula (1) 2 is a divalent linking group, and is represented by formula (2). In formula (2), a is an integer of 0 to 2, b is an integer of 0 to 2, and c is an integer of 2 to 5. When a and b in formula (2) are 0, R 2 is a single bond. The sum of a and b in formula (2) (R 2 The number of hydroxyl groups contained in a) is 0 to 4. Since the sum of a and b is 4 or less, in a magnetic recording medium having a lubricating layer containing a fluorinated ether compound, it is possible to prevent the occurrence of pickup in which the fluorinated ether compound is too highly polar and adheres to a magnetic head as foreign matter (smear).

[0026] The sum of a and b in formula (2) (R 2 The number of hydroxyl groups contained in R is preferably 1 to 3, and more preferably 1 or 2. When the sum of a and b is 1 or more, R 2 When a lubricant containing a and b is used to form a lubricating layer on a protective layer, a favorable interaction occurs between the lubricating layer and the protective layer. As a result, the lubricating layer has good adhesion to the protective layer. When the sum of a and b is 3 or less, more preferably 2 or less, the hydrophilicity of the molecule is not too high, and the fluorine-containing ether compound has moderate hydrophobicity, which is more preferable.

[0027] R 1 When R is the formula (4), it is preferable that the sum of a and b in the formula (2) is 1. 1 is represented by formula (4) and the sum of a and b in formula (2) is 1, R 1 -R 2 The proportion of -O- is not too high. Therefore, there is no R 3 Thus, the compound contains a sufficient amount of perfluoropolyether chains represented by the formula (I) and thus becomes a fluorine-containing ether compound having better hydrophobicity.

[0028] In formula (2), c is an integer of 2 to 5. Since c in formula (2) is an integer of 2 to 5, when b in formula (2) is 1 or 2, R 2 is a linear combination of two or more methylene groups (-(CH2) q The lubricating layer containing a fluorine-containing ether compound in which b in formula (2) is 1 or 2 has R 2 The hydrophobicity of the carbon atoms contained in the two or more methylene groups bonded in a straight chain has an appropriate hydrophobicity. As a result, the lubricating layer can prevent water from penetrating into the magnetic recording medium. In addition, since c in formula (2) is 5 or less, when b in formula (2) is 1 or 2, R 2 The hydrophobicity of the lubricating layer is too high to impair adhesion to the protective layer. For these reasons, the lubricating layer containing the fluorine-containing ether compound in which b in formula (2) is 1 or 2 has excellent adhesion to the protective layer, can prevent water from penetrating, and has a higher corrosion inhibition effect on the magnetic recording medium. In formula (2), c is R 1 When c is a hydrogen atom, it is more preferable that c is an integer of 3 to 5, and further preferably an integer of 4 to 5. 1 When is formula (4), it is more preferable that it is an integer of 2 to 3.

[0029] When b in formula (2) is 0, the fluorine-containing ether compound has more appropriate hydrophobicity. 1 is preferably formula (4).

[0030] In formula (2), [O(CH2) c CH(OH)CH2] b is [OCH2CH(OH)CH2] a R 1 Therefore, for example, [OCH2CH(OH)CH2] a [O(CH2) c CH(OH)CH2] b R 1In comparison with the case where the fluorine-containing ether compound is disposed on the side of the magnetic recording medium, the fluorine-containing ether compound is capable of forming a lubricating layer having a higher corrosion suppression effect on the magnetic recording medium. This is presumably due to the following reasons.

[0031] For example, [OCH2CH(OH)CH2] a [O(CH2) c CH(OH)CH2] b R 1 When placed on the side, [OCH2CH(OH)CH2] a This results in a structure in which the carbon atom to which the hydroxyl group is bonded is located between the methylene groups to which the oxygen atom is bonded. This structure is highly flexible, so R 2 As a result, R in the fluorine-containing ether compound contained in the lubricating layer formed on the protective layer becomes highly flexible. 1 -R 2 As a result, the [O(CH2) c CH(OH)CH2] b It is presumed that the hydrophobic portion (two or more methylene groups bonded in a linear chain) contained in the lubricating layer becomes less likely to be arranged facing the surface opposite the protective layer, resulting in insufficient hydrophobicity of the lubricating layer and insufficient corrosion inhibition effect on the magnetic recording medium.

[0032] In contrast, [O(CH2) c CH(OH)CH2] b [OCH2CH(OH)CH2] a R 1 When placed on the side, [OCH2CH(OH)CH2] a Even with the flexibility provided by R 2 Of these, R 3 The flexibility of the perfluoropolyether chain side shown by R 1 -R 2 The effect of [O(CH2) c CH(OH)CH2] b It is presumed that the effect on the arrangement of the hydrophobic portions contained therein is small, and the hydrophobicity of the lubricating layer is sufficiently ensured.

[0033] In the fluorine-containing ether compound represented by formula (1), R 1 -R 2 -O- can be appropriately selected depending on the performance required for the lubricant containing the fluorine-containing ether compound. 1 -R 2 --O-- is preferably any one of the following formulas (2-1) to (2-8).

[0034] R 1 -O(CH2)2CH(OH)CH2O- (2-1) R 1 -O(CH2)3CH(OH)CH2O- (2-2) R 1 -O(CH2)4CH(OH)CH2O- (2-3) R 1 -O(CH2)5CH(OH)CH2O- (2-4) R 1 -O(CH2)2CH(OH)CH2OCH2CH(OH)CH2O- (2-5) R 1 -O(CH2)3CH(OH)CH2OCH2CH(OH)CH2O- (2-6) R 1 -O(CH2)4CH(OH)CH2OCH2CH(OH)CH2O- (2-7) R 1 -O(CH2)5CH(OH)CH2OCH2CH(OH)CH2O- (2-8)

[0035] When the structures of formulas (2-1) to (2-8) are substituted into formula (2), a, b, and c are as follows. Formula (2-1): a=0, b=1, c=2 Formula (2-2): a=0, b=1, c=3 Formula (2-3): a=0, b=1, c=4 Formula (2-4): a=0, b=1, c=5 Formula (2-5): a=1, b=1, c=2 Formula (2-6): a=1, b=1, c=3 Formula (2-7): a=1, b=1, c=4 Formula (2-8): a=1, b=1, c=5

[0036] R in formula (1) 4 is a divalent linking group, and is represented by formula (3). In formula (3), d is an integer of 0 to 2, e is an integer of 0 to 2, and f is an integer of 2 to 5. When d and e in formula (3) are 0, R 4 is a single bond. The sum of d and e in formula (3) (R 4 The number of hydroxyl groups contained in is 0 to 4. Since the sum of d and e is 4 or less, in a magnetic recording medium having a lubricating layer containing a fluorinated ether compound, it is possible to prevent the occurrence of pickup in which the fluorinated ether compound has too high polarity and adheres to a magnetic head as foreign matter (smear).

[0037] The sum of d and e in formula (3) (R 4 The number of hydroxyl groups contained in R is preferably 1 to 3, and more preferably 1 or 2. When the sum of d and e is 1 or more, R 4 When the lubricant containing the fluorine-containing ether compound is used to form a lubricating layer on a protective layer, a suitable interaction occurs between the lubricating layer and the protective layer. As a result, the lubricating layer has good adhesion to the protective layer. When the sum of d and e is 3 or less, more preferably 2 or less, the hydrophilicity of the molecule is not too high, and the fluorine-containing ether compound has moderate hydrophobicity, which is more preferable.

[0038] R 5 When R is the formula (4), it is preferable that the sum of d and e in the formula (3) is 1. 5 is represented by formula (4) and the sum of d and e in formula (3) is 1, -OR 4 -R 5 The proportion of R in the molecule does not become too high. 3 Thus, the compound contains a sufficient amount of perfluoropolyether chains represented by the formula (I) and thus becomes a fluorine-containing ether compound having better hydrophobicity.

[0039] In formula (3), f is an integer of 2 to 5. Since f in formula (3) is an integer of 2 to 5, when e in formula (3) is 1 or 2, R 4 is a linear combination of two or more methylene groups (-(CH2) q The lubricating layer containing a fluorine-containing ether compound in which e in formula (3) is 1 or 2 has R 4 The hydrophobicity of the carbon atoms contained in the two or more methylene groups bonded in a straight chain has an appropriate hydrophobicity. As a result, the lubricating layer can prevent water from penetrating into the magnetic recording medium. In addition, since f in formula (3) is 5 or less, when e in formula (3) is 1 or 2, R 4 The hydrophobicity of the lubricating layer is too high to impair adhesion to the protective layer. For these reasons, a lubricating layer containing a fluorine-containing ether compound in which e in formula (3) is 1 or 2 has excellent adhesion to the protective layer, can prevent water from penetrating, and has a higher corrosion inhibition effect on the magnetic recording medium. In formula (3), f is R 5 When f is a hydrogen atom, it is more preferable that f is an integer of 3 to 5, and further preferably 4 to 5. 5 When is formula (4), it is more preferable that it is an integer of 2 to 3.

[0040] When e in formula (3) is 0, the fluorine-containing ether compound has more appropriate hydrophobicity, so that R 5 is preferably formula (4).

[0041] In formula (3), [CHCH(OH)(CH) f O] e is [CHCH(OH)CHO] d R 5 Therefore, for example, [CH2CH(OH)CH2O] d [CH2CH(OH)(CH2) f O] e R 5In comparison with the case where the fluorine-containing ether compound is disposed on the side of the magnetic recording medium, the fluorine-containing ether compound is capable of forming a lubricating layer having a higher corrosion suppression effect on the magnetic recording medium. This is presumably due to the following reasons.

[0042] For example, [CHCH(OH)CHO] d [CH2CH(OH)(CH2) f O] e R 5 When the carbon atom is located on the side of the oxygen atom, a structure is formed in which the carbon atom to which the hydroxyl group is bonded is located between the methylene groups to which the oxygen atom is bonded. This structure is highly flexible, so it is suitable for use in the R 4 As a result, R in the fluorine-containing ether compound contained in the lubricating layer formed on the protective layer becomes highly flexible. 4 -R 5 As a result, the [CH2CH(OH)(CH2) f O] e It is presumed that the hydrophobic portion (two or more methylene groups bonded in a linear chain) contained in the lubricating layer becomes less likely to be arranged facing the surface opposite the protective layer, resulting in insufficient hydrophobicity of the lubricating layer and insufficient corrosion inhibition effect on the magnetic recording medium.

[0043] In contrast, [CH2CH(OH)(CH2) f O] e [CH2CH(OH)CH2O] d R 5 When placed on the side, [CH2CH(OH)CH2O] d Even with the flexibility provided by R 4 -R 5 The effect on the flexibility of the lubricant layer is small. Therefore, the [CH2CH(OH)(CH2) f O] e It is presumed that the effect on the arrangement of the hydrophobic portions contained therein is small, and the hydrophobicity of the lubricating layer is sufficiently ensured.

[0044] In the fluorine-containing ether compound represented by formula (1), -OR 4 -R 5can be appropriately selected depending on the performance required for the lubricant containing the fluorine-containing ether compound. 4 -R 5 is preferably any one of the following formulas (3-1) to (3-8).

[0045] -OCH2CH(OH)(CH2)2O-R 5 (3-1) -OCH2CH(OH)(CH2)3O-R 5 (3-2) -OCH2CH(OH)(CH2)4O-R 5 (3-3) -OCH2CH(OH)(CH2)5O-R 5 (3-4) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)2O-R 5 (3-5) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)3O-R 5 (3-6) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)4O-R 5 (3-7) -OCH2CH(OH)CH2OCH2CH(OH)(CH2)5O-R 5 (3-8)

[0046] When the structures of formulas (3-1) to (3-8) are substituted into formula (3), d, e, and f are as follows. Formula (3-1): d=0, e=1, f=2 Equation (3-2): d=0, e=1, f=3 Equation (3-3): d=0, e=1, f=4 Equation (3-4): d=0, e=1, f=5 Equation (3-5): d=1, e=1, f=2 Equation (3-6): d=1, e=1, f=3 Equation (3-7): d=1, e=1, f=4 Equation (3-8): d=1, e=1, f=5

[0047] In the fluorine-containing ether compound represented by formula (1), R2 and R 4 Each of them contains 0 to 4 hydroxyl groups. At least one of b in formula (2) and e in formula (3) is 1 or more, so that R 2 The hydroxyl group contained in R 4 The total number of hydroxyl groups contained in R is 1 to 8. The fluorine-containing ether compound represented by formula (1) is 2 and R 4 Since the total number of hydroxyl groups contained in R is 1 or more, when a lubricant containing this is used to form a lubricating layer on a protective layer, a lubricating layer with excellent adhesion to the protective layer is obtained. 2 and R 4 Since the total number of hydroxyl groups contained in is 8 or less, it is possible to prevent the polarity of the fluorine-containing ether compound from becoming too high, and thus prevent the occurrence of pickup in which the fluorine-containing ether compound adheres to the magnetic head as foreign matter (smear). 2 and R 4 The total number of hydroxyl groups contained therein is preferably 1 to 4, and more preferably 2 to 3.

[0048] In the fluorine-containing ether compound represented by formula (1), R 1 -R 2 -O- and -OR 4 -R 5 may be the same or different. R 1 -R 2 -O- and -OR 4 -R 5 When R is the same, the fluorine-containing ether compound is likely to wet and spread evenly on the protective layer, and a lubricating layer having a uniform thickness is likely to be obtained. As a result, the lubricating layer containing this fluorine-containing ether compound is likely to have a good coverage rate, which is preferable. 1 -R 2 -O- and -OR 4 -R 5 If the same, R 1 -R 2 -O- and -OR 4 -R 5 In comparison with the case where the dimensions are different, the manufacturing process can be simplified and the manufacturing process can be performed efficiently.

[0049] In the fluorine-containing ether compound represented by the above formula (1), R 3 is a perfluoropolyether chain (PFPE chain). 3 When the lubricant containing the fluorine-containing ether compound of this embodiment is applied onto the protective layer to form a lubricating layer, the PFPE chain shown in the formula (I) coats the surface of the protective layer. It also imparts lubricity to the lubricating layer, thereby reducing the friction between the magnetic head and the protective layer. Furthermore, the PFPE chain imparts water resistance to the lubricating layer containing the fluorine-containing ether compound of this embodiment due to its low surface energy, thereby improving the corrosion resistance of the magnetic recording medium provided with the lubricating layer.

[0050] R 3 is a PFPE chain and can be appropriately selected depending on the performance required for the lubricant containing the fluorine-containing ether compound. Examples of the PFPE chain include perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer, perfluoroisopropylene oxide polymer, and copolymers thereof.

[0051] Specifically, R in formula (1) 3 is preferably any one of the following formulas (5) to (7). The sequence of the repeating units (CF2CF2O) and (CF2O) in formula (5) is not particularly limited. Formula (5) may include any of a random copolymer, a block copolymer, and an alternating copolymer composed of monomer units (CF2-CF2-O) and (CF2-O).

[0052] -CF2O-(CF2CF2O) m -(CF2O) n -CF2- (5) (In formula (5), m and n each represent an average degree of polymerization and are 0 to 30; however, m or n is 0.1 or more.) -CF(CF3)-(OCF(CF3)CF2) g -OCF(CF3)- (6) (In formula (6), g represents the average degree of polymerization and is from 0.1 to 30.) -CF2CF2O-(CF2CF2CF2O) z -CF2CF2- (7) (In formula (7), z represents the average degree of polymerization and is from 0.1 to 30.)

[0053] In formula (5), m and n each represent an average degree of polymerization and are 0 to 30 (provided that m or n is 0.1 or more), in formula (6), g represents an average degree of polymerization and is 0.1 to 30, and in formula (7), z represents an average degree of polymerization and is 0.1 to 30. When m, n, g, and z are 0.1 or more, the fluorine-containing ether compound has good wear resistance and can provide a lubricating layer that can further suppress corrosion of the magnetic recording medium. When m, n, g, and z are each 30 or less, the viscosity of the fluorine-containing ether compound is not too high, and the lubricant containing the fluorine-containing ether compound is easy to apply, which is preferable. Each of m, n, g, and z each represents an average degree of polymerization and are preferably 2 to 20, more preferably 3 to 8, in order to provide a fluorine-containing ether compound that is easy to wet and spread on the protective layer and easily provides a lubricating layer having a uniform thickness. Each of m, n, g, and z may be 0.1 to 25, 0.5 to 18, 1 to 15, 5 to 10, 3 to 10, or 3 to 6, as necessary.

[0054] R in formula (1) 3 When R is any one of the formulas (5) to (7), the synthesis of the fluorine-containing ether compound is easy, which is preferable. 3 is formula (5) or formula (7), it is more preferable since the raw materials are easily available. Also, R 3 When is any one of formulas (5) to (7), 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. Therefore, the fluorine-containing ether compound has an appropriate hardness. Therefore, the fluorine-containing ether compound applied on the protective layer is unlikely to aggregate on the protective layer, and a thinner lubricating layer can be formed with a sufficient coverage.

[0055] In particular, R in formula (1) 3is formula (7) having a repeating unit containing three -CF2- groups bonded in a linear chain, the lubricating layer containing the fluorine-containing ether compound can more effectively suppress corrosion of the magnetic recording medium due to the excellent hydrophobicity caused by the PFPE chain.

[0056] Specifically, the fluorine-containing ether compound represented by formula (1) is preferably any of the compounds represented by the following formulae (1A) to (1P), (2A) to (2P), and (3A) to (3P). Note that the repeat numbers za to zp in formulae (1A) to (1P), the repeat numbers ya to yp in formulae (2A) to (2P), and the repeat numbers ma to mp and na to np in formulae (3A) to (3P) are values ​​indicating the average degree of polymerization, and are not necessarily integers.

[0057] The compound represented by formula (1A) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (7), and R 4 is the formula (3), d=0, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (1B) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=3. 3 is Equation (7), and R 4 is the formula (3), d=0, e=1, f=3, and R 5 is a hydrogen atom. The compound represented by formula (1C) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (7), and R 4 is the formula (3), d=0, e=1, f=4, and R 5 is a hydrogen atom.

[0058] The compound represented by formula (1D) is R 1 is a hydrogen atom, and R2 is the formula (2), where a=0, b=1, and c=5. R 3 is Equation (7), and R 4 is the formula (3), d=0, e=1, f=5, and R 5 is a hydrogen atom. The compound represented by formula (1E) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (7), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (1F) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (7), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0059] The compound represented by formula (1G) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=5. R 3 is Equation (7), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (1H) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (7), and R 4 is the formula (3), d=1, e=1, f=4, and R 5 is a hydrogen atom. The compound represented by formula (1I) is R 1 is a hydrogen atom, and R 2 is the formula (2) where a=1, b=1, and c=2. R3 is Equation (7), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0060] The compound represented by formula (1J) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is Equation (7), and R 4 is the formula (3), where d=0, e=1, and f=4. R 5 is a hydrogen atom. The compound represented by formula (1K) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is Equation (7), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (1L) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (7), and R 4 is the formula (3), where d=0, e=1, and f=2. R 5 is equation (4) where k=3.

[0061] The compound represented by formula (1M) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (7), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (1N) is R 1 is equation (4) where k=3. R 2is the formula (2), where a=0, b=1, and c=3. 3 is Equation (7), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (1P) is R 1 is equation (4) where k=6. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (7), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom.

[0062] The compound represented by formula (2A) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is the formula (5) where n=0. R 4 is the formula (3), where d=0, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (2B) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=3. 3 is the formula (5) where n=0. R 4 is the formula (3), d=0, e=1, f=3, and R 5 is a hydrogen atom. The compound represented by formula (2C) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is the formula (5) where n=0. R 4 is the formula (3), d=0, e=1, f=4, and R 5 is a hydrogen atom.

[0063] The compound represented by formula (2D) is R 1 is a hydrogen atom, and R2 is the formula (2), where a=0, b=1, and c=5. R 3 is the formula (5) where n=0. R 4 is the formula (3), d=0, e=1, f=5, and R 5 is a hydrogen atom. The compound represented by formula (2E) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is the formula (5) where n=0. R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (2F) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is the formula (5) where n=0. R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0064] The compound represented by formula (2G) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=5. R 3 is the formula (5) where n=0. R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (2H) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is the formula (5) where n=0. R 4 is the formula (3), d=1, e=1, f=4, and R 5 is a hydrogen atom. The compound represented by formula (2I) is R 1 is a hydrogen atom, and R 2is the formula (2) where a=1, b=1, and c=2. R 3 is the formula (5) where n=0. R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0065] The compound represented by formula (2J) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is the formula (5) where n=0. R 4 is the formula (3), where d=0, e=1, and f=4. R 5 is a hydrogen atom. The compound represented by formula (2K) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is the formula (5) where n=0. R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (2L) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is the formula (5) where n=0. R 4 is the formula (3), where d=0, e=1, and f=2. R 5 In equation (4), k=3.

[0066] The compound represented by formula (2M) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is the formula (5) where n=0. R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (2N) is R1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=3. 3 is the formula (5) where n=0. R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (2P) is R 1 is equation (4) where k=6. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is the formula (5) where n=0. R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom.

[0067] The compound represented by formula (3A) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (5), and R 4 is the formula (3), d=0, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (3B) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=3. 3 is Equation (5), and R 4 is the formula (3), d=0, e=1, f=3, and R 5 is a hydrogen atom. The compound represented by formula (3C) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (5), and R 4 is the formula (3), d=0, e=1, f=4, and R 5 is a hydrogen atom.

[0068] The compound represented by formula (3D) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=5. R 3 is Equation (5), and R 4 is the formula (3), d=0, e=1, f=5, and R 5 is a hydrogen atom. The compound represented by formula (3E) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (5), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (3F) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (5), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0069] The compound represented by formula (3G) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=5. R 3 is Equation (5), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom. The compound represented by formula (3H) is R 1 is a hydrogen atom, and R 2 is the formula (2), where a=0, b=1, and c=4. 3 is Equation (5), and R 4 is the formula (3), d=1, e=1, f=4, and R 5 is a hydrogen atom. The compound represented by formula (3I) is R 1 is a hydrogen atom, and R 2is the formula (2) where a=1, b=1, and c=2. R 3 is Equation (5), and R 4 is the formula (3), d=1, e=1, f=2, and R 5 is a hydrogen atom.

[0070] The compound represented by formula (3J) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is Equation (5), and R 4 is the formula (3), where d=0, e=1, and f=4. R 5 is a hydrogen atom. The compound represented by formula (3K) is R 1 is equation (4) where k=3. R 2 is the formula (2) where a=1 and b=0. R 3 is Equation (5), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (3L) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (5), and R 4 is the formula (3), where d=0, e=1, and f=2. R 5 is equation (4) where k=3.

[0071] The compound represented by formula (3M) is R 1 is equation (4) where k=3. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (5), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (3N) is R 1 is equation (4) where k=3. R2 is the formula (2), where a=0, b=1, and c=3. 3 is Equation (5), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom. The compound represented by formula (3P) is R 1 is equation (4) where k=6. R 2 is the formula (2), where a=0, b=1, and c=2. 3 is Equation (5), and R 4 is the formula (3), where d=1, e=1, and f=2. R 5 is a hydrogen atom.

[0072] [ka] (In formula (1A), za represents the average degree of polymerization and is 0.1 to 30.) (In formula (1B), zb represents the average degree of polymerization and is 0.1 to 30.) (In formula (1C), zc represents the average degree of polymerization and is 0.1 to 30.) (In formula (1D), zd represents the average degree of polymerization and is 0.1 to 30.) (In formula (1E), ze represents the average degree of polymerization and is 0.1 to 30.) (In formula (1F), zf represents an average degree of polymerization and is 0.1 to 30.) (In formula (1G), zg represents the average degree of polymerization and is 0.1 to 30.)

[0073] [ka] (In formula (1H), zh represents the average degree of polymerization and is 0.1 to 30.) (In formula (1I), zi represents the average degree of polymerization and is 0.1 to 30.) (In formula (1J), zj represents the average degree of polymerization and is 0.1 to 30.) (In formula (1K), zk represents the average degree of polymerization and is 0.1 to 30.) (In formula (1L), zl represents the average degree of polymerization and is 0.1 to 30.) (zm in formula (1M) represents the average degree of polymerization and is 0.1 to 30.) (In formula (1N), zn represents the average degree of polymerization and is 0.1 to 30.) (In formula (1P), zp represents the average degree of polymerization and is 0.1 to 30.)

[0074] [ka] (In formula (2A), ya represents an average degree of polymerization and is 0.1 to 30.) (In formula (2B), yb represents an average degree of polymerization and is 0.1 to 30.) (In formula (2C), yc represents the average degree of polymerization and is 0.1 to 30.) (In formula (2D), yd represents the average degree of polymerization and is 0.1 to 30.) (In formula (2E), ye represents the average degree of polymerization and is 0.1 to 30.) (In formula (2F), yf represents an average degree of polymerization and is 0.1 to 30.) (In formula (2G), yg represents the average degree of polymerization and is 0.1 to 30.)

[0075] [ka] (In formula (2H), yh represents an average degree of polymerization and is 0.1 to 30.) (In formula (2I), yi represents the average degree of polymerization and is 0.1 to 30.) (In formula (2J), yj represents the average degree of polymerization and is 0.1 to 30.) (In formula (2K), yk represents the average degree of polymerization and is 0.1 to 30.) (In formula (2L), yl represents an average degree of polymerization and is 0.1 to 30.) (In formula (2M), ym represents the average degree of polymerization and is 0.1 to 30.) (In formula (2N), yn represents the average degree of polymerization and is 0.1 to 30.) (In formula (2P), yp represents the average degree of polymerization and is 0.1 to 30.)

[0076] [ka] (In formula (3A), ma and na represent average degrees of polymerization, each ranging from 0.1 to 30.) (In formula (3B), mb and nb represent average degrees of polymerization, each ranging from 0.1 to 30.) (In formula (3C), mc and nc represent average degrees of polymerization, each ranging from 0.1 to 30.) (In formula (3D), md and nd represent average degrees of polymerization, each ranging from 0.1 to 30.) (In formula (3E), me and ne represent the average degree of polymerization and are 0.1 to 30.) (In formula (3F), mf and nf represent average degrees of polymerization and are 0.1 to 30.) (mg and ng in formula (3G) represent the average degree of polymerization and are 0.1 to 30.)

[0077] [ka] (In formula (3H), mh and nh each represent an average degree of polymerization and are 0.1 to 30.) (In formula (3I), mi and ni represent average degrees of polymerization and are 0.1 to 30.) (In formula (3J), mj and nj represent average degrees of polymerization and are 0.1 to 30.) (In formula (3K), mk and nk represent average degrees of polymerization and are 0.1 to 30.) (In formula (3L), ml and nl represent the average degree of polymerization and are 0.1 to 30.) (In formula (3M), mm and nm represent the average degree of polymerization, and are 0.1 to 30.) (In formula (3N), mn and nn represent the average degree of polymerization and are 0.1 to 30.) (In formula (3P), mp and np represent the average degree of polymerization and are 0.1 to 30.)

[0078] It is preferable that the compound represented by formula (1) is any of the compounds represented by the above formulas (1A) to (1P), (2A) to (2P), and (3A) to (3P), because the raw materials are easily available and a lubricating layer that can suppress corrosion of the magnetic recording medium can be formed even if the lubricating layer is thin.

[0079] The fluorine-containing ether compound of this embodiment can be selected arbitrarily, but the number average molecular weight (Mn) is preferably within the range of 500 to 10,000. 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. The number average molecular weight of the fluorine-containing ether compound is more preferably 1,000 or more. In addition, when the number average molecular weight is 10,000 or less, the viscosity of the fluorine-containing ether compound becomes appropriate, and a thin lubricating layer can be easily formed by applying a lubricant containing this. The number average molecular weight of the fluorine-containing ether compound is preferably 3,000 or less, since the viscosity becomes easy to handle when applied to a lubricant. The number average molecular weight may be in the range of, for example, 500 to 3000, 600 to 2500, 700 to 2000, 800 to 1600, 900 to 1500, 1000 to 1400, or 1100 to 1300.

[0080] 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.

[0081] "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.

[0082] First, R in Equation (1) 3 A fluorine-based compound is prepared in which a hydroxymethyl group (-CH2OH) is arranged at each end of a perfluoropolyether chain corresponding to the above. Next, the hydroxyl group of the hydroxymethyl group located at one end of the fluorine-based compound is converted to R 1 -R 2 The hydroxyl group of the hydroxymethyl group located at the other end is then replaced with a group consisting of -OR 4 -R 5 (second reaction)

[0083] The first and second reactions can be carried out by a conventional method. 1 , R 2 , R 4 , R 5 The reaction time can be appropriately determined depending on the type of R. In addition, either the first reaction or the second reaction may be carried out first. 1 and R 5 is the same, and R 2 and R 4 In the case where the first and second reactions are the same, the first and second reactions may be carried out simultaneously. By the above method, the compound represented by formula (1) can be obtained.

[0084] In this embodiment, R 2 is expressed as formula (2), R 4 In order to produce a fluorine-containing ether compound represented by formula (3), it is preferable to use an epoxy compound. This epoxy compound may be a commercially available product. In addition, the epoxy compound may be used in the range of R 1 or R 5The epoxy compound may be synthesized by reacting an alcohol having a structure corresponding to the terminal group represented by the following formula with any one selected from epichlorohydrin, epibromohydrin, and 2-bromoethyloxirane. The epoxy compound may also be synthesized by oxidizing an unsaturated bond.

[0085] The fluorine-containing ether compound of the present embodiment is a compound represented by formula (1), R 2 is expressed by equation (2), and R 4 is expressed by equation (3), and R 1 and R 5 is a hydrogen atom or formula (4). Furthermore, a and b in formula (2) are integers of 0 to 2, d and e in formula (3) are integers of 0 to 2, and at least one of b in formula (2) and e in formula (3) is 1 or more. Therefore, the fluorine-containing ether compound represented by formula (1) is 2 and / or R 4 and at the most terminals of both of the chain structures, a total of three or more hydroxyl groups are contained. Therefore, the lubricating layer containing the fluorine-containing ether compound of this embodiment has good adhesion to the protective layer.

[0086] The fluorine-containing ether compound represented by formula (1) is R 3 It has a perfluoropolyether chain (PFPE chain) represented by the formula: R 3 In the lubricating layer containing the fluorine-containing ether compound, R coats the surface of the protective layer and imparts water resistance to the lubricating layer due to its low surface energy. Moreover, in the fluorine-containing ether compound represented by formula (1), c in formula (2) is an integer of 2 to 5, f in formula (3) is an integer of 2 to 5, and at least one of b in formula (2) and e in formula (3) is 1 or more. Therefore, in the fluorine-containing ether compound represented by formula (1), R 2 and / or R 4 However, it has a hydrophobic portion consisting of two or more methylene groups bonded in a straight chain. For these reasons, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) has good water resistance, is difficult for water to pass through, and can prevent water from penetrating into the magnetic recording medium.

[0087] The fluorine-containing ether compound represented by formula (1) has both a hydrophilic portion (three or more hydroxyl groups) and a hydrophobic portion (PFPE chain and two or more methylene groups bonded in a linear chain) in the molecule. It is presumed that, in a lubricant containing the fluorine-containing ether compound represented by formula (1), the hydrophilic portion in the fluorine-containing ether compound interacts with the protective layer, and the hydrophobic portion is arranged facing the surface opposite to the protective layer. As a result, it is presumed that a lubricant layer that has good adhesion to the protective layer, can prevent water from penetrating into the magnetic recording medium, and can suppress corrosion of the magnetic recording medium can be obtained.

[0088] Furthermore, in the fluorine-containing ether compound represented by formula (1), R 1 and / or R 5 is represented by formula (4), k in formula (4) is an integer of 3 to 6, so that the hydroxyl groups at the most terminals of one or both of the chain structures are bonded to three or more methylene groups bonded in a linear fashion. 1 and / or R 5 It is presumed that a lubricating layer containing a fluorine-containing ether compound represented by formula (4) can prevent water from penetrating into the magnetic recording medium due to the hydrophobicity of three or more methylene groups bonded in a linear chain, and can more effectively suppress corrosion of the magnetic recording medium.

[0089] [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.

[0090] 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.

[0091] When the lubricant of the present 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 the present 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. However, it is not limited to only these examples.

[0092] The lubricant of this embodiment contains a fluorine-containing ether compound represented by formula (1), and therefore has good adhesion to the protective layer, can prevent water from penetrating into the magnetic recording medium, and can form a lubricating layer that can suppress corrosion of the magnetic recording medium. The lubricating layer made of the lubricant of this embodiment has a high corrosion suppression effect on the magnetic recording medium, and therefore can be made thin.

[0093] [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. An adhesive layer and / or a soft magnetic layer may also be provided between the underlayer and the substrate.

[0094] 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.

[0095] "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.

[0096] "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.

[0097] "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).

[0098] The first and second soft magnetic films may be made of a material such as a CoZrTa alloy or 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 enables the flying height of the magnetic head to be reduced. The soft magnetic layer 13 can be formed by, for example, a sputtering method.

[0099] "First base layer" The first underlayer 14 is a layer that controls the orientation and crystal size of the second underlayer 15 and the magnetic layer 16 that are 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.

[0100] "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.

[0101] "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 a layer containing Co and Pt, and may be a layer containing an oxide, Cr, B, Cu, Ta, Zr, etc. to further improve the SNR characteristics. The oxides contained in the magnetic layer 16 include SiO2, SiO, Cr2O3, CoO, Ta2O3, TiO2, and the like.

[0102] 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.

[0103] The first magnetic layer may contain, in addition to Co, Cr, Pt, and oxides, one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re. The second magnetic layer may be made of the same material as the first magnetic layer, and preferably has a granular structure.

[0104] 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 may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn.

[0105] 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.

[0106] 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).

[0107] 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.

[0108] 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.

[0109] "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.

[0110] 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).

[0111] 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.

[0112] The thickness of the protective layer 17 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.

[0113] 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, or an IBD (ion beam deposition) method. 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.

[0114] "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.

[0115] 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.

[0116] The average thickness of the lubricating layer 18 is preferably 0.5 nm (5 Å) to 2.0 nm (20 Å), and more preferably 0.5 nm (5 Å) to 1.0 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. In addition, by setting the average thickness of the lubricating layer 18 to 2.0 nm or less, the lubricating layer 18 can be made sufficiently thin, and the flying height of the magnetic head can be sufficiently reduced.

[0117] 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, generating contaminants. The generated contaminants (aggregated components) will adhere (transfer) to the magnetic head as smear during magnetic recording and reproduction, damaging the magnetic head or degrading the magnetic recording and reproduction characteristics of the magnetic recording and reproduction device.

[0118] 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.

[0119] "Method of forming lubricating layer" A method for forming the lubricating layer 18 includes, for example, preparing a magnetic recording medium in the middle of manufacture in which all layers up to the protective layer 17 are formed on the substrate 11, applying a solution for forming a lubricating layer onto the protective layer 17, and drying the same.

[0120] The lubricant layer forming solution can be obtained 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).

[0121] 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.

[0122] In this embodiment, it is preferable to perform a burnishing (precision polishing) step after forming the lubricating layer 18 on the surface of the substrate 11. By performing the burnishing step, protruding defects and particles present on the surface of the substrate 11 on which the lubricating layer 18 has been formed can be removed, and a magnetic recording medium 10 with a smooth surface can be obtained. A smooth surface of the magnetic recording medium 10 is preferable because it reduces spacing loss with the magnetic head and improves signal characteristics.

[0123] The burnishing process may be, for example, a process of scanning a burnishing tape over the surface of the substrate 11 on which the lubricating layer 18 is formed. The burnishing tape may be, for example, a resin film carrying abrasive grains. The grain size of the abrasive grains may be, for example, #6000 to #20000.

[0124] 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 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.

[0125] The magnetic recording medium 10 of this embodiment is a substrate 11 on which at least a magnetic layer 16, a protective layer 17, and a lubricating layer 18 are sequentially provided. In the magnetic recording medium 10 of this embodiment, a lubricating layer 18 containing the above-mentioned fluorine-containing ether compound is formed in contact with the protective layer 17. This lubricating layer 18 is highly effective in suppressing corrosion of the magnetic recording medium 10. Therefore, the magnetic recording medium 10 of this embodiment has few contaminants present on the surface, has excellent corrosion resistance, and is reliable and durable. In addition, since the magnetic recording medium 10 of this embodiment has a lubricating layer 18 with a high corrosion suppression effect, the thickness of the protective layer 17 and / or the lubricating layer 18 can be made thin. 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 pick-up. EXAMPLES

[0126] 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.

[0127] Example 1 Under a nitrogen gas atmosphere, HOCH2CF2CF2O (CF2CF2CF2O) was added to a 100 mL eggplant flask. z 10.3 g of a compound (number average molecular weight 1025, molecular weight distribution 1.1) represented by CF2CF2CH2OH (z in the formula is 4.5), 3.44 g of a compound represented by the following formula (12), and 10 mL of t-butanol were charged and stirred at room temperature until homogenized. 0.34 g of potassium tert-butoxide was further added to this homogenous liquid, and the mixture was reacted at 70°C for 30 hours with stirring to obtain a reaction product. The compound represented by formula (12) was obtained by protecting the hydroxyl group of 3-buten-1ol with a tetrahydropyranyl (THP) group and then oxidizing the double bond.

[0128] [ka]

[0129] The resulting reaction product was allowed to cool to 25°C, and 20 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 2 hours. The reaction solution was transferred little by little to a separatory funnel containing 70 mL of 8% sodium bicarbonate water, and extracted twice with 150 mL of ethyl acetate. The organic layer was washed with water and dehydrated using anhydrous sodium sulfate (desiccant). After filtering off the drying agent, the filtrate was concentrated and the residue was purified by silica gel column chromatography to obtain 7.65 g of compound (1A) (in formula (1A), za, which indicates the average degree of polymerization, is 4.5).

[0130] The obtained compound (1A) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1A); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(18H)

[0131] Example 2 The same operation as in Example 1 was carried out except that 3.73 g of a compound represented by the following formula (13) was used instead of the compound represented by formula (12), to obtain 7.83 g of compound (1B) (in formula (1B), zb indicating the average degree of polymerization is 4.5). Compound (13) was obtained by protecting the hydroxyl group of 4-penten-1ol with a THP group and then oxidizing the double bond.

[0132] [ka]

[0133] The obtained compound (1B) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1B); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(18H)

[0134] Example 3 The same operation as in Example 1 was carried out except that 3.73 g of a compound represented by the following formula (14) was used instead of the compound represented by formula (12), thereby obtaining 8.01 g of compound (1C) (in formula (1C), zc indicating the average degree of polymerization is 4.5). Compound (14) was obtained by protecting the hydroxyl group of 5-hexen-1ol with a THP group and then oxidizing the double bond.

[0135] [ka]

[0136] The obtained compound (1C) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1C); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(12H), 3.4-4.2(18H)

[0137] Example 4 The same operation as in Example 1 was carried out except that 3.73 g of a compound represented by the following formula (15) was used instead of the compound represented by formula (12), thereby obtaining 8.19 g of compound (1D) (in formula (1D), zd indicating the average degree of polymerization is 4.5). Compound (15) was obtained by protecting the hydroxyl group of 6-hepten-1ol with a THP group and then oxidizing the double bond.

[0138] [ka]

[0139] The obtained compound (1D) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1D); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(16H), 3.4-4.2(18H)

[0140] Example 5 Under a nitrogen gas atmosphere, HOCH2CF2CF2O (CF2CF2CF2O) was added to a 100 mL eggplant flask. z 20.0 g of a compound (number average molecular weight 1025, molecular weight distribution 1.1) represented by CF2CF2CH2OH (z in the formula is 4.5), 2.07 g of a compound represented by the above formula (12), and 20 mL of t-butanol were charged and stirred at room temperature until homogenous. 0.67 g of potassium tert-butoxide was further added to this homogenous liquid, and the mixture was reacted at 70°C for 30 hours with stirring to obtain a reaction product.

[0141] The reaction product was cooled to 25°C, transferred to a separatory funnel containing 50 mL of water, and extracted twice with 150 mL of ethyl acetate. The organic layer was washed with water and dehydrated with anhydrous sodium sulfate (desiccant). After the drying agent was filtered off, the filtrate was concentrated and the residue was purified by silica gel column chromatography to obtain 9.38 g of the compound represented by the formula (16).

[0142] [ka] (In formula (16), z, which indicates the average degree of polymerization, is 4.5.)

[0143] In a nitrogen gas atmosphere, 9.30 g of the compound represented by the above formula (16), 1.99 g of the compound represented by the following formula (17), and 25 mL of t-butanol were charged into a 100 mL recovery flask and stirred at room temperature until the mixture became homogeneous. 0.14 g of potassium tert-butoxide was added to this homogeneous liquid and reacted at 70°C for 16 hours with stirring. The compound represented by formula (17) was obtained by reacting 1,2,4-butanetriol with benzaldehyde to form an acetal compound, which was then reacted with epibromohydrin.

[0144] [ka]

[0145] The resulting reaction product was allowed to cool to 25°C, and 20 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 2 hours. The reaction solution was transferred little by little to a separatory funnel containing 70 mL of 8% sodium bicarbonate water, and extracted twice with 150 mL of ethyl acetate. The organic layer was washed with water and dehydrated using anhydrous sodium sulfate (desiccant). After filtering off the drying agent, the filtrate was concentrated and the residue was purified by silica gel column chromatography to obtain 6.45 g of compound (1E) (in formula (1E), ze indicating the average degree of polymerization is 4.5).

[0146] The obtained compound (1E) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1E); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(24H)

[0147] Example 6 The same operation as in Example 5 was carried out, except that 2.40 g of the compound represented by the above formula (14) was used instead of the compound represented by the formula (12), and 9.60 g of the compound represented by the following formula (18) was obtained as an intermediate, to obtain 6.58 g of formula (1F) (in formula (1F), zf indicating the average degree of polymerization is 4.5).

[0148] [ka] (In formula (18), z, which indicates the average degree of polymerization, is 4.5.)

[0149] The obtained compound (1F) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1F); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(24H)

[0150] Example 7 The same operation as in Example 5 was carried out, except that 2.57 g of the compound represented by the above formula (15) was used instead of the compound represented by the formula (12), and 9.70 g of the compound represented by the following formula (19) was obtained as an intermediate, to obtain 6.50 g of formula (1G) (in formula (1G), zg indicating the average degree of polymerization is 4.5).

[0151] [ka] (In formula (19), z, which indicates the average degree of polymerization, is 4.5.)

[0152] The obtained compound (1G) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1G); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(10H), 3.4-4.2(24H)

[0153] Example 8 Instead of the compound represented by formula (12), 2.40 g of the compound represented by formula (14) was used, and the compound represented by formula (18) was synthesized as an intermediate. Then, the same operation as in Example 5 was carried out, except that instead of the compound represented by formula (17), 2.84 g of the compound represented by formula (20) was used, to obtain 6.69 g of formula (1H) (in formula (1H), zh, which indicates the average degree of polymerization, is 4.5). The compound represented by formula (20) was obtained by reacting the compound represented by formula (14) with allyl alcohol, protecting the hydroxyl group of the resulting compound with a THP group, and further oxidizing the double bond.

[0154] [ka]

[0155] The obtained compound (1H) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1H); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(14H), 3.4-4.2(24H)

[0156] Example 9 The same procedure as in Example 1 was carried out except that 5.00 g of the compound represented by formula (17) was used instead of the compound represented by formula (12), to obtain 8.55 g of compound (1I) (in formula (1I), zi indicating the average degree of polymerization is 4.5). The obtained compound (1I) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1I); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(30H)

[0157] Example 10 Instead of the compound represented by formula (12), 2.40 g of the compound represented by formula (14) was used, and the compound represented by formula (18) was synthesized as an intermediate. Then, the same operation as in Example 5 was carried out, except that 1.68 g of the compound represented by the following formula (21) was used instead of the compound represented by formula (17), to obtain 6.26 g of formula (1J) (in formula (1J), zj, which indicates the average degree of polymerization, is 4.5). The compound represented by formula (21) was obtained by protecting one hydroxyl group of propanediol with a THP group and reacting the other hydroxyl group with epibromohydrin.

[0158] [ka]

[0159] The obtained compound (1J) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1J); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(22H)

[0160] Example 11 The same operation as in Example 5 was carried out except that 2.60 g of the compound represented by the above formula (21) was used instead of the compound represented by the formula (12) to obtain 9.73 g of the compound represented by the formula (22) as an intermediate, thereby obtaining 6.26 g of formula (1K) (in formula (1K), zk indicating the average degree of polymerization is 4.5).

[0161] [ka] (In formula (22), z, which indicates the average degree of polymerization, is 4.5.)

[0162] The obtained compound (1K) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1K); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(28H)

[0163] Example 12 The same operation as in Example 1 was performed except that 4.61 g of a compound represented by the following formula (23) was used instead of the compound represented by formula (12), thereby obtaining 8.40 g of compound (1L) (in formula (1L), zl indicating the average degree of polymerization is 4.5). The compound represented by formula (23) was obtained by oxidizing the double bond of a compound obtained by reacting 3-buten-1ol with 2-(3-chloropropoxy)tetrahydro-2H-pyran.

[0164] [ka]

[0165] The obtained compound (1L) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1L); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(26H)

[0166] Example 13 The same operation as in Example 5 was carried out, except that 2.76 g of the compound represented by the above formula (23) was used instead of the compound represented by the formula (12), and 9.82 g of the compound represented by the following formula (24) was obtained as an intermediate, to obtain 6.71 g of formula (1M) (in formula (1M), zm indicating the average degree of polymerization is 4.5).

[0167] [ka] (In formula (24), z, which indicates the average degree of polymerization, is 4.5.)

[0168] The obtained compound (1M) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1M); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(6H), 3.4-4.2(28H)

[0169] Example 14 The same operation as in Example 5 was performed except that 2.93 g of a compound represented by the following formula (25) was used instead of the compound represented by formula (12), and 9.99 g of a compound represented by the following formula (26) was obtained as an intermediate, thereby obtaining 6.62 g of formula (1N) (in formula (1N), zn indicating the average degree of polymerization is 4.5). The compound represented by formula (25) was obtained by oxidizing the double bond of the compound obtained by reacting 4-penten-1ol with 2-(3-chloropropoxy)tetrahydro-2H-pyran.

[0170] [ka]

[0171] [ka] (In formula (26), z, which indicates the average degree of polymerization, is 4.5.)

[0172] The obtained compound (1N) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1N); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(28H)

[0173] Example 15 The same operation as in Example 5 was carried out, except that 3.27 g of a compound represented by the following formula (27) was used instead of the compound represented by formula (12), and 10.10 g of a compound represented by the following formula (28) was obtained as an intermediate, to obtain 6.80 g of formula (1P) (in formula (1P), zp indicating the average degree of polymerization is 4.5). The compound represented by formula (27) was obtained by protecting one hydroxyl group of hexanediol with a THP group and reacting the other hydroxyl group with 2-bromoethyloxirane.

[0174] [ka]

[0175] [ka] (In formula (28), z, which indicates the average degree of polymerization, is 4.5.)

[0176] The obtained compound (1P) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (1P); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(12H), 3.4-4.2(28H)

[0177] (Examples 16 to 30) HOCH2CF2CF2O(CF2CF2CF2O) zInstead of the compound represented by CF2CF2CH2OH (where z is 4.5) (number average molecular weight 1025, molecular weight distribution 1.1), HOCH2CF2O(CF2CF2O) m Formulas (2A) to (2P) were obtained by carrying out the same operations as in Examples 1 to 15, except that a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CH2OH (where m is 7.0) was used.

[0178] The obtained compound (2A) (in the formula (2A), ya, which indicates the average degree of polymerization, is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2A); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(18H) The obtained compound (2B) (in the formula (2B), yb indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2B); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(18H) The obtained compound (2C) (in the formula (2C), yc indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2C); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(12H), 3.4-4.2(18H)

[0179] The obtained compound (2D) (in the formula (2D), yd indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2D); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(16H), 3.4-4.2(18H) The obtained compound (2E) (in the formula (2E), ye indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2E); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(24H) The obtained compound (2F) (in the formula (2F), yf indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2F); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(24H)

[0180] The obtained compound (2G) (in the formula (2G), yg indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2G); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(10H), 3.4-4.2(24H) The obtained compound (2H) (in the formula (2H), yh indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2H); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(14H), 3.4-4.2(24H) The obtained compound (2I) (in formula (2I), yi indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2I); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(30H)

[0181] The obtained compound (2J) (in the formula (2J), yj indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2J); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(22H) The obtained compound (2K) (in the formula (2K), yk indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2K); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(28H) The obtained compound (2L) (in formula (2L), yl indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2L); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(26H)

[0182] The obtained compound (2M) (in the formula (2M), ym indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2M); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(6H), 3.4-4.2(28H) The obtained compound (2N) (in formula (2N), yn indicating the average degree of polymerization is 7.0) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (2N); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(28H) The obtained compound (2P) (in formula (2P), yp indicating the average degree of polymerization is 7.0) 1H-NMR measurement was performed, and the structure was identified from the following results. Compound (2P); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(12H), 3.4-4.2(28H)

[0183] (Examples 31 to 45) HOCH2CF2CF2O(CF2CF2CF2O) z Instead of the compound represented by CF2CF2CH2OH (where z is 4.5) (number average molecular weight 1025, molecular weight distribution 1.1), HOCH2CF2O(CF2CF2O) m (CF2O) n Formulas (3A) to (3P) were obtained by carrying out the same operations as in Examples 1 to 15, except that a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CH2OH (where m is 4.5 and n is 4.5) was used.

[0184] The obtained compound (3A) (in the formula (3A), ma and na, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3A); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(18H) The obtained compound (3B) (in the formula (3B), mb and nb, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3B); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(18H) The obtained compound (3C) (in the formula (3C), mc and nc, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3C); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(12H), 3.4-4.2(18H)

[0185] The obtained compound (3D) (in the formula (3D), md and nd, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3D); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(16H), 3.4-4.2(18H) The obtained compound (3E) (in the formula (3E), me and ne, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3E); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(24H) The obtained compound (3F) (in the formula (3F), mf and nf, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3F); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(24H)

[0186] The obtained compound (3G) (in the formula (3G), mg and ng, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3G); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(10H), 3.4-4.2(24H) The obtained compound (3H) (in the formula (3H), mh and nh each indicating the average degree of polymerization is 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3H); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(14H), 3.4-4.2(24H) The obtained compound (3I) (in the formula (3I), mi and ni, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3I); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(4H), 3.4-4.2(30H)

[0187] The obtained compound (3J) (in the formula (3J), mj and nj, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3J); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(22H) The obtained compound (3K) (in the formula (3K), mk and nk, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3K); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(4H), 3.4-4.2(28H) The obtained compound (3L) (in formula (3L), ml and nl indicating the average degree of polymerization are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3L); 1 H-NMR(CD3COCD3); δ[ppm]1.3-1.7(8H), 3.4-4.2(26H)

[0188] The obtained compound (3M) (in the formula (3M), mm and nm indicating the average degree of polymerization are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3M); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(6H), 3.4-4.2(28H) The obtained compound (3N) (in the formula (3N), mn and nn, which indicate the average degree of polymerization, are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3N); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(8H), 3.4-4.2(28H) The obtained compound (3P) (in the formula (3P), mp and np indicating the average degree of polymerization are 4.5) 1 H-NMR measurement was performed, and the structure was identified from the following results. Compound (3P); 1 H-NMR(CD3COCD3); δ[ppm]1.5-1.8(12H), 3.4-4.2(28H)

[0189] "Comparative Example 1" The compound represented by the following formula (S) was synthesized by the method described in Patent Document 1. HO-CH2CH(OH)CH2O-CH2-CF2CF2O(C3F6O) zs CF2CF2-CH2-OCH2CH(OH)CH2-OH (S) (In formula (S), zs, which indicates the average degree of polymerization, is 4.5.)

[0190] "Comparative Example 2" The compound represented by the following formula (T) was synthesized by the method described in Patent Document 2. HOCH2CH2O-CH2CH(OH)CH2O-CH2-CF2O(CF2CF2O) mt (CF2O) nt CF2-CH2-OCH2CH(OH)CH2-OCH2CH2OH (T) (In formula (T), mt, which indicates the average degree of polymerization, is 4.5, and nt, which indicates the average degree of polymerization, is 4.5.)

[0191] "Comparative Example 3" The compound represented by the following formula (U) was synthesized by the method described in Patent Document 3.

[0192] [ka] (In formula (U), mu indicating the average degree of polymerization is 4.5, and nu indicating the average degree of polymerization is 4.5.)

[0193] "Comparative Example 4" The compound represented by the following formula (V) was synthesized by the method described in Patent Document 3.

[0194] [ka] (In formula (V), mv indicating the average degree of polymerization is 4.5, and nv indicating the average degree of polymerization is 4.5.)

[0195] "Comparative Example 5" The compound represented by the following formula (W) was synthesized by the method described in Patent Document 4.

[0196] [ka] (In formula (W), mw indicating the average degree of polymerization is 4.5, and nw indicating the average degree of polymerization is 4.5.)

[0197] "Comparative Example 6" The compound represented by the following formula (X) was synthesized by the method described in Patent Document 4.

[0198] [ka] (In formula (X), mx indicating the average degree of polymerization is 4.5, and nx indicating the average degree of polymerization is 4.5.)

[0199] The compounds of Examples 1 to 45 and Comparative Examples 1 to 6 thus obtained are represented by the formula (1) 1 and R 5 The structure of R 2 (a, b, c in formula (2)), R 3 The structure of R 4The structures of (d, e, and f in formula (3)) are shown in Tables 1 to 4.

[0200] [Table 1]

[0201] [Table 2]

[0202] [Table 3]

[0203] [Table 4]

[0204] The number average molecular weights (Mn) of the compounds in Examples 1 to 45 and Comparative Examples 1 to 6 are as follows: 1 H-NMR and 19 The average molecular weights were determined by F-NMR measurement. The results are shown in Tables 1 to 4. It is estimated that the average molecular weights of the synthesized compounds vary by about 1 to 5 due to the molecular weight distribution of the fluoropolyether used as the raw material of the compounds, differences in the operations used to synthesize the compounds, and the like.

[0205] Next, a lubricant layer-forming solution was prepared by the method described below using the compounds obtained in Examples 1 to 45 and Comparative Examples 1 to 6. 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 45 and Comparative Examples 1 to 6.

[0206] "Lubricant layer forming solution" The compounds obtained in Examples 1 to 45 and Comparative Examples 1 to 6 were each dissolved in a fluorine-based solvent, Vertrel (registered trademark) XF (product name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.), and diluted with Vertrel so that the film thickness when applied onto the protective layer would be approximately 9 Å, to prepare a solution for forming a lubricating layer.

[0207] "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 and had a thickness of 2.7 nm. 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 45 and Comparative Examples 1 to 6 were applied by dipping, respectively, 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.

[0208] Thereafter, a burnishing process was carried out in which a burnishing tape carrying abrasive grains of grain size #6000 was scanned over the surface of the magnetic recording medium on which the lubricating layer had been formed. The magnetic recording medium after the burnishing process was placed in a thermostatic chamber at 120° C. and subjected to a heat treatment in which it was heated for 10 minutes. By the above steps, magnetic recording media (with burnish) of Examples 1 to 45 and Comparative Examples 1 to 6 were obtained.

[0209] Moreover, magnetic recording media (without burnish) of Examples 1 to 45 and Comparative Examples 1 to 6 were obtained in the same manner as the magnetic recording media with burnish, except that the burnishing step was not carried out.

[0210] (film thickness measurement) The thickness of the lubricating layer of each of the magnetic recording media (without varnish) thus obtained in Examples 1 to 45 and Comparative Examples 1 to 6 was measured using an FT-IR (product name: Nicolet iS50, manufactured by Thermo Fisher Scientific Co., Ltd.) The results are shown in Tables 5 to 8.

[0211] [Table 5]

[0212] [Table 6]

[0213] [Table 7]

[0214] [Table 8]

[0215] Next, the following corrosion resistance test was carried out on the magnetic recording media of Examples 1 to 45 and Comparative Examples 1 to 6, both with and without varnish. (Corrosion resistance test) The magnetic recording medium was exposed to conditions of 85°C and 90% relative humidity for 48 hours. After that, the number of corroded areas on the magnetic recording medium was counted using an optical surface analyzer and evaluated based on the following evaluation criteria. The results are shown in Tables 5 to 8.

[0216] "Evaluation Criteria" A: 500 or less B: 501 or more, 1000 or less C: 1001 or more, 1500 or less D: 1501 or more, 2000 or less E: 2001 and above

[0217] As shown in Tables 5 to 7, the magnetic recording media of Examples 1 to 45 having a lubricating layer containing a compound represented by formula (1), whether with or without varnish, had good corrosion resistance, with the results of the corrosion resistance test being A or B. It is presumed that this was achieved by the compound represented by formula (1) contained in the lubricating layer of the magnetic recording media of Examples 1 to 45 having both a hydrophilic portion (four to six hydroxyl groups) and a hydrophobic portion (a PFPE chain and two or more methylene groups bonded in a linear chain) in the molecule.

[0218] In particular, R in formula (1) 3When the compound was of formula (7) having a repeating unit containing three -CF2- groups bonded in a linear chain (e.g., Examples 1, 10, and 15), the results of the corrosion resistance test when varnished were better than when the compound was of formula (5) having a repeating unit containing two -CF2- groups bonded in a linear chain (e.g., Examples 16, 25, 30, 31, 40, and 45).

[0219] Furthermore, when c in formula (2) was 4 (e.g., Examples 6, 21, and 36), the results of the corrosion resistance test with varnish were better than when c in formula (2) was 2 (e.g., Examples 5, 20, and 35). Furthermore, when f in formula (3) was 4 (e.g., Example 10), the results of the corrosion resistance test with varnish were better than when f in formula (2) was 2 (e.g., Example 11).

[0220] Furthermore, when a in formula (2) was 0 and b was 1, and d in formula (3) was 0 and e was 1 (e.g., Examples 1, 16, and 31), the results of the corrosion resistance test were better with and / or without varnish than when a and b in formula (2) were 1, and d and e in formula (3) were 1 (e.g., Examples 9, 24, and 39). In addition, R in formula (1) 1 is represented by formula (4) and k is 6 (e.g., Example 15), R in formula (1) 1 The results of the corrosion resistance test in the case of using varnish were better than those in the case of using hydrogen atoms (eg, Example 5).

[0221] In contrast, Comparative Example 1 in which b in formula (2) and e in formula (3) are both 0, and Comparative Example 2 in which b in formula (2) and e in formula (3) are both 0 and R 1 and R 5 is represented by formula (4) and k is 2; 1 and R 5 is represented by formula (4) and k is 2; 1As shown in Table 8, the magnetic recording media of Comparative Examples 4 to 6, in which is not a hydrogen atom or formula (4), showed a result of C in the corrosion resistance test when no varnish was used, and a result of D or E when varnish was used, and thus had inferior corrosion resistance compared to the magnetic recording media of Examples 1 to 45. [Industrial Applicability]

[0222] By using a lubricant for magnetic recording media containing the fluorine-containing ether compound of the present invention, it is possible to form a lubricating layer that is thin but has excellent corrosion resistance. [Explanation of symbols]

[0223] 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 -O-CH ２ -R ３ -CH ２ -O-R ４ -R ５ (1) (In formula (1), R ３ is a perfluoropolyether chain; R ２ is represented by the following formula (2); R ４ is represented by the following formula (3); R １ and R ５ is a hydrogen atom or the following formula (4): 【Chemistry 1】 (In formula (2), a and b are integers of 0 to 2, and c is an integer of 2 to 5; in formula (3), d and e are integers of 0 to 2, and f is an integer of 2 to 5; at least one of b in formula (2) and e in formula (3) is 1 or more; in formula (4), k is an integer of 3 to 6.)

2. The fluorine-containing ether compound according to claim 1, wherein the sum of a and b in the formula (2) is 1 or 2.

3. R in the formula (1) １ -R ２ The fluorine-containing ether compound according to claim 1 or 2, wherein —O— is any one of the following formulas (2-1) to (2-8): R １ -O(CH ２ ) ２ CH(OH)CH ２ O- (2-1) R １ -O(CH ２ ) ３ CH(OH)CH ２ O- (2-2) R １ -O(CH ２ ) ４ CH(OH)CH ２ O- (2-3) R １ -O(CH ２ ) ５ CH(OH)CH ２ O- (2-4) R １ -O(CH ２ ) ２ CH(OH)CH ２ OCH ２ CH(OH)CH ２ O- (2-5) R １ -O(CH ２ ) ３ CH(OH)CH ２ OCH ２ CH(OH)CH ２ O- (2-6) R １ -O(CH ２ ) ４ CH(OH)CH ２ OCH ２ CH(OH)CH ２ O- (2-7) R １ -O(CH ２ ) ５ CH(OH)CH ２ OCH ２ CH(OH)CH ２ O- (2-8)

4. The fluorine-containing ether compound according to any one of claims 1 to 3, wherein the sum of d and e in said formula (3) is 1 or 2.

5. In the formula (1), -O-R ４ -R ５ The fluorine-containing ether compound according to any one of claims 1 to 4, wherein the fluorine-containing ether compound is represented by any one of the following formulas (3-1) to (3-8): -OCH ２ CH(OH)(CH) ２ ) ２ O-R ５ (3-1) -OCH ２ CH(OH)(CH) ２ ) ３ O-R ５ (3-2) -OCH ２ CH(OH)(CH) ２ ) ４ O-R ５ (3-3) -OCH ２ CH(OH)(CH) ２ ) ５ O-R ５ (3-4) -OCH ２ CH(OH)CH ２ OCH ２ CH(OH)(CH) ２ ) ２ O-R ５ (3-5) -OCH ２ CH(OH)CH ２ OCH ２ CH(OH)(CH) ２ ) ３ O-R ５ (3-6) -OCH ２ CH(OH)CH ２ OCH ２ CH(OH)(CH) ２ ) ４ O-R ５ (3-7) -OCH ２ CH(OH)CH ２ OCH ２ CH(OH)(CH) ２ ) ５ O-R ５ (3-8)

6. R in the formula (1) ２ and R ４ The fluorine-containing ether compound according to any one of claims 1 to 5, wherein the total number of hydroxyl groups contained in

7. R in the formula (1) ３ The fluorine-containing ether compound according to any one of claims 1 to 6, wherein is represented by the following formulas (5) to (7): -CF ２ O-(CF ２ CF ２ O) ｍ -(CF ２ O) ｎ -CF ２ - (5) (In formula (5), m and n each represent an average degree of polymerization and are 0 to 30; however, m or n is 0.1 or more.) -CF(CF ３ )-(OCF(CF ３ )CF ２ ) ｇ -OCF(CF ３ )- (6) (In formula (6), g represents the average degree of polymerization and is 0.1 to 30.) -CF ２ CF ２ O-(CF ２ CF ２ CF ２ O) ｚ -CF ２ CF ２ - (7) (In formula (7), z represents the average degree of polymerization and is 0.1 to 30.)

8. The fluorine-containing ether compound according to any one of claims 1 to 7, having a number average molecular weight in the range of 500 to 10,000.

9. A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to any one of claims 1 to 8.

10. A magnetic recording medium having at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate, 9. A magnetic recording medium, comprising the lubricating layer comprising the fluorine-containing ether compound according to claim 1.

11. 11. The magnetic recording medium according to claim 10, wherein the average thickness of the lubricating layer is from 0.5 nm to 2.0 nm.

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