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

Abstract

This fluorine-containing ether compound is represented by formula (1). In formula (1), X represents one of formulae (2-1) to (2-5), A represents formula (3-1) or (3-2), B represents a perfluoropolyether chain, D comprises 2 to 4 polar groups and an oxygen atom that is bonded to a methylene group which is adjacent to D, and has 1 to 15 carbon atoms, and the number of carbon atoms in the shortest distance between the carbon atoms to which adjacent polar groups are bonded in D is 0 to 9.

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. 2022-210111, filed on December 27, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, the amount of information processed via the Internet has increased dramatically. Accordingly, attention has been focused on the development of recording media for storing information. Magnetic recording media, in particular, are expected to accommodate the increasing volume of information because they can store large amounts of information at low cost. Generally, a protective layer and a lubricating layer are provided on the magnetic layer (magnetic recording layer) of a magnetic recording medium to ensure the durability and reliability of the magnetic recording medium. The lubricating layer disposed on the outermost surface of the magnetic recording medium is required to have various properties such as long-term stability, chemical resistance (to prevent contamination by siloxane, etc.), wear resistance, and heat resistance.

[0003] As lubricants used in forming the lubricating layer of magnetic recording media, for example, those containing compounds having polar groups such as hydroxyl groups or amino groups at the end of a fluorine-based polymer having a repeating structure containing -CF2- have been proposed.

[0004] For example, Patent Document 1 discloses an ether composition having a skeleton in which a perfluoropolyether chain is bonded to a perfluorinated saturated hydrocarbon group having a valence of two or more, and an end group, which is an organic group having a polar group, is bonded to the end of the skeleton via a methylene group (-CH-).

[0005] Patent Documents 2 and 3 disclose fluorine-containing ether compounds having a skeleton in which three perfluoropolyether chains are bonded to a trivalent atomic group via a linking group containing a polar group, and in which a substituent that is an organic group having a polar group is bonded to the end of the skeleton via a methylene group.

[0006] Patent Document 4 discloses a fluorine-containing ether compound having a skeleton in which two perfluoropolyether chains are bonded to a divalent organic group containing an alicyclic structure and at least one polar group, and in which an end group, which is an organic group having a polar group, is bonded to the end of the skeleton via a methylene group.

[0007] Patent Document 5 describes a polymer having a skeleton in which a perfluoropolyether chain is bonded to a cyclic group via a linking group containing a polar group, and a C n F 2n+1 Lubricant compositions having a group are disclosed.

[0008] Patent Document 6 discloses a compound having a skeleton in which a perfluoropolyether chain is bonded to a benzene ring via a linking group containing a methylene group, and having a hydroxyl group at the end of the skeleton.

[0009] Patent Document 7 discloses a lubricant for magnetic disks that has a skeleton in which two perfluoropolyether chains are bonded to an aliphatic hydrocarbon chain located near the center of the molecule, and has hydroxyl groups at its ends.

[0010] Patent Documents 8 and 9 disclose fluorine-containing ether compounds having a skeleton in which three perfluoropolyether chains are connected in series via a linking group containing a hydroxyl group, and having a hydroxyl group at the end of the skeleton. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2011 / 007782 [Patent Document 2] International Publication No. 2018 / 159232 [Patent Document 3] International Publication No. 2021 / 065380 [Patent Document 4] International Publication No. 2022 / 113854 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-184339 [Patent Document 6] International Publication No. 2015 / 093237 [Patent Document 7] Patent No. 5743438 [Patent Document 8] U.S. Patent No. 10,262,685 [Patent Document 9] International Publication No. 2018 / 116742 Summary of the Invention [Problem to be solved by the invention]

[0012] In recent years, the diversification of applications for magnetic recording media has led to increasingly stringent environmental resistance requirements for magnetic recording media, which has led to demands for even greater long-term stability for lubricating layers, which have a significant impact on the reliability and durability of magnetic recording media.

[0013] Chemical resistance and spin-off resistance are known indicators of the long-term stability of a lubricating layer. Spin-off is a phenomenon in which the lubricant scatters or evaporates due to centrifugal force and heat generated by the rotation of a magnetic recording medium. Spin-off reduces the thickness of the lubricating layer, thereby degrading its chemical resistance and wear resistance. One method for suppressing spin-off is to improve the adhesion of the lubricating layer to the protective layer. Polar groups in the compounds contained in the lubricant contribute to improving the adhesion between the lubricant and the protective layer. However, if the compounds contained in the lubricant have too many polar groups, chemical contaminants are attracted to the lubricating layer formed using the lubricant, degrading the chemical resistance of the lubricating layer.

[0014] The present invention has been made in view of the above circumstances, and aims to provide a fluorine-containing ether compound that can form a lubricating layer that has excellent chemical resistance and can suppress spin-off, and that can be suitably used as a material for a lubricant for a magnetic recording medium. An 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 and is capable of forming a lubricating layer which has good chemical resistance and a high spin-off suppressing effect. An object of the present invention is to provide a magnetic recording medium having a lubricating layer containing the fluorinated ether compound of the present invention, which has good chemical resistance and a high spin-off suppressing effect. [Means for solving the problem]

[0015] The present invention includes the following aspects.

[0016] [1] A fluorine-containing ether compound represented by the following general formula (1):

[0017] [ka] (In general formula (1), X is a trivalent atomic group represented by any of the following formulas (2-1) to (2-5). A is a linking group represented by the following formula (3-1) or formula (3-2). Some or all of the three As may be the same or different from each other. B is a perfluoropolyether chain. Some or all of the three Bs may be the same or different from each other. D is a terminal group having 2 to 4 polar groups, having an ether oxygen atom bonded to a methylene group adjacent to D, having 1 to 15 carbon atoms, and having 0 to 9 carbon atoms over the shortest distance between carbon atoms to which adjacent polar groups in D are bonded. Some or all of the three Ds may be the same or different from each other.)

[0018] [ka] (In formula (2-4), a represents an integer of 0 to 5.) (In formula (2-5), b represents an integer of 0 to 5.)

[0019] [ka] (In formula (3-1), n ​​represents an integer of 0 to 6.) (In formula (3-2), m represents an integer of 1 or 2.)

[0020] [2] The fluorine-containing ether compound according to [1], wherein in the formula (2-4), a is 0, and in the formula (2-5), b is an integer of 0 to 2. [3] The fluorine-containing ether compound according to [1] or [2], wherein the polar group is at least one polar group selected from the group consisting of a hydroxyl group, an amino group, and a carboxy group. [4] The fluorine-containing ether compound according to any one of [1] to [3], wherein the polar group contains at least one hydroxyl group.

[0021] [5] The fluorine-containing ether compound according to any one of [1] to [4], wherein D in the general formula (1) is each independently a terminal group represented by any one of the following formulae (4-1) to (4-3):

[0022] [ka] (In formula (4-1), p represents an integer of 0 to 3, q ​​represents an integer of 0 to 2, and r represents an integer of 1 to 5. The total value of p and r is 1 to 5.) (In formula (4-2), s represents an integer of 0 to 2, and t represents an integer of 0 to 5.) (In formula (4-3), u represents an integer of 2 to 4. Y represents a linear alkylene group which may have an ether oxygen atom, or a single bond. When Y is the alkylene group, the total number of carbon atoms and oxygen atoms contained in Y is 1 to 5.)

[0023] [6] The fluorine-containing ether compound according to any one of [1] to [5], wherein all three Ds in the general formula (1) are the same. [7] The fluorine-containing ether compound according to any one of [1] to [6], wherein at least one of the three A's in the general formula (1) is the formula (3-1).

[0024] [8] The fluorine-containing ether compound according to any one of [1] to [7], wherein the three Bs in the general formula (1) are each independently a perfluoropolyether chain represented by the following formula (5): -(CF2) v1 -O-(CF2O) v2 -(CF2CF2O) v3 -(CF2CF2CF2O) v4 -(CF2CF2CF2CF2O) v5 -(CF2) v6 - (5) (In formula (5), v2, v3, v4, and v5 represent average degrees of polymerization and each independently represent 0 to 20. However, v2, v3, v4, and v5 cannot all be 0 at the same time. v1 and v6 represent average values ​​representing the number of CF2 and each independently represent 1 to 3. There are no particular limitations on the arrangement order of the repeating units (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) in formula (5).)

[0025] [9] The fluorine-containing ether compound according to any one of [1] to [8], wherein the three Bs in the general formula (1) are each independently any one selected from perfluoropolyether chains represented by the following formulae (5-1) to (5-4): -CF2-(OCF2CF2) h -(OCF2) i -OCF2- (5-1) (In formula (5-1), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20.) -CF2CF2-(OCF2CF2CF2) j -OCF2CF2- (5-2) (In formula (5-2), j represents the average degree of polymerization and represents 1 to 15.) -CF2CF2CF2-(OCF2CF2CF2CF2) k-OCF2CF2CF2- (5-3) (In formula (5-3), k represents the average degree of polymerization and represents 1 to 10.) -(CF2) v7 -O-(CF2CF2CF2O) v8 -(CF2CF2O) v9 -(CF2) v10 - (5-4) (In formula (5-4), v8 and v9 represent the average degree of polymerization, each independently representing 1 to 20. v7 and v10 are average values ​​representing the number of CF2, each independently representing 1 to 2.)

[0026]

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

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

[10] .

[0027]

[12] A magnetic recording medium having at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate, A magnetic recording medium, wherein the lubricating layer contains the fluorine-containing ether compound according to any one of [1] to

[10] .

[13] The magnetic recording medium according to

[12] , wherein the lubricating layer has an average film thickness of 0.5 nm to 2.0 nm. [Effects of the Invention]

[0028] The fluorine-containing ether compound of the present invention is a compound represented by the above general formula (1), and is suitable as a material for a lubricant for a magnetic recording medium. The lubricant for magnetic recording media of the present invention contains the fluorine-containing ether compound of the present invention, and therefore can form a lubricating layer that has good chemical resistance and a high spin-off suppressing effect.

[0029] The magnetic recording medium of the present invention has a lubricating layer containing the fluorine-containing ether compound of the present invention. Therefore, the magnetic recording medium of the present invention has good chemical resistance, a high spin-off suppression effect, and excellent reliability and durability. Furthermore, because the magnetic recording medium of the present invention has a lubricating layer that has good chemical resistance and can suppress spin-off, the flying height of the magnetic head can be further reduced. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of a magnetic recording medium of the present invention. [Figure 2] FIG. 1 is a diagram for explaining an environment in which continuous LUL operations are repeated. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to solve the above problems, the present inventors have conducted extensive research as described below. Conventionally, as a material for a lubricant for magnetic recording media (hereinafter sometimes abbreviated as "lubricant") to be applied to the surface of a protective layer, a fluorine-containing ether compound having a chain structure containing multiple perfluoropolyether chains and having adsorption sites with polar groups located at the ends of the chain structure and between the perfluoropolyether chains has been preferably used. The adsorption sites in the fluorine-containing ether compound bond with active sites on the protective layer, improving the adhesion of the lubricating layer to the protective layer.

[0032] However, when a thin lubricating layer is formed on a protective layer using a conventional lubricant, it is difficult to achieve a lubricating layer that has good chemical resistance and is less susceptible to spin-off, as will be shown below. That is, in order to improve the adhesion of the lubricating layer to the protective layer, the use of a fluorine-containing ether compound having multiple hydroxyl groups in the lubricant molecule can sometimes suppress spin-off. However, the proportion of polar groups in the fluorine-containing ether compound that do not interact with the active sites on the protective layer increases, which attracts environmental substances that generate pollutants to the lubricating layer and causes a decrease in the chemical resistance of the lubricating layer.

[0033] Therefore, the present inventors focused on the adsorption sites of the fluorine-containing ether compound contained in the lubricating layer that can interact with the active sites on the protective layer, and conducted extensive research as described below in order to realize a fluorine-containing ether compound that is less likely to produce adsorption sites in the lubricating layer that are not involved in the interaction with the active sites on the protective layer.

[0034] The present inventors first investigated a fluorine-containing ether compound in which three perfluoropolyether chains B are bonded to a central trivalent atomic group X via a linking group A having multiple hydroxyl groups, and an end group D having a polar group is disposed at the end of each of the three perfluoropolyether chains B. In this fluorine-containing ether compound, the trivalent atomic group X is adhered to the protective layer by three linking groups A, which are adsorption sites, disposed near the trivalent atomic group X. Furthermore, the perfluoropolyether chains B extending in three directions from the trivalent atomic group X are adhered to the protective layer by the linking groups A and the end groups D, which are adsorption sites, disposed at both ends of each perfluoropolyether chain B.

[0035] In such a fluorine-containing ether compound, the strength of the interaction of each adsorption site with the active site on the protective layer was examined so as to prevent the occurrence of adsorption sites that are not involved in the interaction with the active site on the protective layer. As a result, it was found that the fluorine-containing ether compound must have an appropriate balance between the strength of the interaction between the terminal group D and the active sites on the protective layer and the strength of the interaction between the linking group A and the active sites on the protective layer, and that the terminal group D and the linking group A must be able to interact with the active sites on the protective layer with sufficient strength.

[0036] In other words, if the interaction between terminal group D and the active sites on the protective layer and the interaction between linking group A and the active sites on the protective layer is biased toward linking group A, then terminal group D will contain an adsorbent group (polar group) that is not involved in the interaction with the active sites on the protective layer. As a result, the adsorbent group not involved in the interaction will attract chemical contaminants to the lubricating layer, reducing its chemical resistance. Furthermore, if the interaction between terminal group D and the active sites on the protective layer and / or the interaction between linking group A and the active sites on the protective layer is too weak, spin-off will occur, reducing the film thickness of the lubricating layer.

[0037] Therefore, the present inventors have conducted extensive research into the trivalent atomic group X, and the structures of the terminal group D and linking group A in the above-mentioned fluorine-containing ether compound. As a result, they found that a fluorine-containing ether compound having a skeleton in which three perfluoropolyether chains B are bonded to a trivalent atomic group X represented by the above formulas (2-1) to (2-5) via a divalent linking group A represented by the above formula (3-1) or (3-2), and a specific terminal group D is bonded to the end of each perfluoropolyether chain B via a methylene group, is sufficient. The terminal group D has 2 to 4 polar groups, an ether oxygen atom bonded to the methylene group adjacent to D, has 1 to 15 carbon atoms, and the shortest distance between carbon atoms bonding adjacent polar groups in D is 0 to 9 carbon atoms.

[0038] In a lubricating layer containing such a fluorine-containing ether compound, the terminal group D and linking group A in the fluorine-containing ether compound can interact with the active sites on the protective layer with sufficient strength, and the strength of the interaction between the terminal group D and the active sites on the protective layer and the strength of the interaction between the linking group A and the active sites on the protective layer are properly balanced, so that adsorption sites not involved in the interaction with the active sites on the protective layer are unlikely to occur. As a result, a lubricating layer with excellent adhesion to the protective layer and little spin-off can be formed. In addition, since this fluorine-containing ether compound has few polar groups not involved in the interaction with the active sites on the protective layer, it can suppress the attraction of chemical contaminants to the lubricating layer, and form a lubricating layer with excellent chemical resistance. Furthermore, this fluorine-containing ether compound has three perfluoropolyether chains B, and the number of carbon atoms in the terminal group D is not too large. Therefore, a lubricating layer containing this compound has low surface free energy, is less likely to develop spots with high surface free energy locally, and is less likely to be contaminated by chemical contaminants.

[0039] Furthermore, the present inventors have confirmed that by using a lubricant containing the above-mentioned fluorine-containing ether compound, a lubricating layer having good chemical resistance and a high spin-off suppression effect can be formed, and have arrived at the present invention.

[0040] The fluorine-containing ether compound, the lubricant for a magnetic recording medium, and the magnetic recording medium of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0041] [Fluorine-containing ether compounds] The fluorine-containing ether compound of the present embodiment is represented by the following general formula (1).

[0042] [ka] (In general formula (1), X is a trivalent atomic group represented by any of the following formulas (2-1) to (2-5). A is a linking group represented by the following formula (3-1) or formula (3-2). Some or all of the three As may be the same or different from each other. B is a perfluoropolyether chain. Some or all of the three Bs may be the same or different from each other. D is a terminal group having 2 to 4 polar groups, having an ether oxygen atom bonded to a methylene group adjacent to D, having 1 to 15 carbon atoms, and having 0 to 9 carbon atoms over the shortest distance between carbon atoms to which adjacent polar groups in D are bonded. Some or all of the three Ds may be the same or different from each other.)

[0043] [ka] (In formula (2-4), a represents an integer of 0 to 5.) (In formula (2-5), b represents an integer of 0 to 5.)

[0044] [ka] (In formula (3-1), n ​​represents an integer of 0 to 6.) (In formula (3-2), m represents an integer of 1 or 2.)

[0045] (Trivalent atomic group represented by X) X is a trivalent atomic group represented by any one of the above formulas (2-1) to (2-5). Therefore, the three perfluoropolyether chains B bonded to the trivalent atomic group X via the divalent linking group A are arranged so as to extend in three directions from the trivalent atomic group X. As a result, a lubricating layer having excellent adhesion to the protective layer can be formed.

[0046] When the trivalent atomic group X is any of formulas (2-1) to (2-3), the three linking sites to the divalent linking group A in formulas (2-1) to (2-3) are spaced apart by the same number of carbon atoms. When the trivalent atomic group X is any of formulas (2-4), the central tertiary or quaternary carbon atom in formula (2-4) and the two carbon atoms adjacent thereto are the three linking sites to the divalent linking group A. When the trivalent atomic group X is any of formulas (2-5), the three carbon atoms adjacent to the central tertiary or quaternary carbon atom in formula (2-5) are the three linking sites to the divalent linking group A. Therefore, the three perfluoropolyether chains B bonded to the trivalent atomic groups represented by formulas (2-1) to (2-5) via the divalent linking group A can be spread at approximately equal intervals in three directions relative to the trivalent atomic group X, which is believed to provide better coverage for the protective layer.

[0047] The trivalent atomic groups X represented by formulas (2-1) to (2-5) all have an appropriate steric bulkiness. Specifically, the trivalent atomic groups represented by formulas (2-1) to (2-3) have a bulky ring structure at the center. The trivalent atomic groups represented by formulas (2-4) to (2-5) are bulky because they have a tertiary or quaternary carbon atom at the center. For this reason, the trivalent atomic group X appropriately suppresses the interaction between the hydroxyl group of the linking group A and the active site on the protective layer.

[0048] Here, for example, if a divalent or trivalent atomic group that has little steric hindrance to the linking group A is arranged instead of the trivalent atomic group X represented by formulas (2-1) to (2-5), the interaction between the linking group A and the active sites on the protective layer becomes too strong. As a result, the balance between the strength of the interaction between the linking group A and the active sites on the protective layer and the strength of the interaction between the terminal group D and the active sites on the protective layer is disrupted, and the chemical resistance of the lubricating layer containing the fluorine-containing ether compound is reduced.

[0049] Furthermore, for example, when a divalent atomic group that is highly sterically hindered by the linking group A is arranged instead of the trivalent atomic group X represented by formulas (2-1) to (2-5), the divalent atomic group can suppress the interaction between the hydroxyl group of the linking group A and the active site on the protective layer, but only two perfluoropolyether chains B are bonded to the divalent atomic group. Therefore, compared to a lubricating layer containing a fluorine-containing ether compound represented by formula (1) in which three perfluoropolyether chains B are arranged extending in three directions, the coverage with the protective layer is insufficient, and sufficient chemical resistance cannot be obtained.

[0050] In formula (2-4), a represents an integer of 0 to 5. Since a is 5 or less, -(CH2) a The substituent represented by -H is not too bulky, and the trivalent atomic group represented by formula (2-4) has a structure with appropriate steric bulkiness. From the viewpoint of easy availability of raw materials, a is preferably an integer of 0 to 1, and more preferably 0.

[0051] In formula (2-5), b represents an integer of 0 to 5. Since b is 5 or less, -(CH2) b The substituent represented by -H is not too bulky, and the trivalent atomic group represented by formula (2-5) has a structure with appropriate steric bulkiness. From the viewpoint of easy availability of raw materials, b is preferably an integer of 0 to 3, and more preferably an integer of 0 to 2.

[0052] (Linking group represented by A) A is a divalent linking group represented by formula (3-1) or (3-2). The linking group A can interact with the active sites on the protective layer with sufficient strength due to the synergistic effect of the functions [A-1] to [A-3] shown below. Furthermore, the strength of the interaction of the linking group A with the active sites on the protective layer is properly balanced with the strength of the interaction between the terminal group D and the active sites on the protective layer due to the synergistic effect of the functions [A-4] and [A-5] shown below. In other words, the interaction between the linking group A and the active sites on the protective layer can be prevented from becoming too strong compared with the interaction between the terminal group D and the active sites on the protective layer. As a result, a shortage of active sites on the protective layer that can interact with the terminal group D can be prevented, preventing the generation of polar groups that are not involved in the interaction with the active sites on the protective layer. This prevents polar groups that are not involved in the interaction with the active sites on the protective layer from attracting chemical contaminants to the lubricating layer and deteriorating the chemical resistance of the lubricating layer.

[0053] [A-1] The linking group A has two or three hydroxyl groups. Specifically, the divalent linking group represented by formula (3-1) has two hydroxyl groups. The divalent linking group represented by formula (3-2) has two or three hydroxyl groups. Since the linking group A has two or more hydroxyl groups, even if some of the hydroxyl groups of the linking group A are prevented from adsorbing to the protective layer due to the bulkiness of the adjacent trivalent atomic group X and the perfluoropolyether chain B, the remaining hydroxyl groups can be adsorbed onto the protective layer. Therefore, the lubricating layer containing the above fluorine-containing ether compound has good adhesion and suppresses spin-off.

[0054] Here, for example, when a divalent linking group having only one hydroxyl group is arranged instead of the linking group A, the adsorption of the hydroxyl group of the divalent linking group to the protective layer may be inhibited by the trivalent atomic group X and the perfluoropolyether chain B, and the hydroxyl group may not be involved in the interaction with the active site on the protective layer.

[0055] [A-2] Linking group A has an ether oxygen atom bonded to a methylene group bonded to perfluoropolyether chain B. Therefore, linking group A has appropriate flexibility and can move freely independently without interlocking with perfluoropolyether chain B. As a result, linking group A is less likely to separate from the protective layer due to the movement of linking group A in conjunction with the molecular movement of perfluoropolyether chain B, and the hydroxyl group of linking group A is more likely to be involved in interaction with the active site on the protective layer.

[0056] [A-3] The linking group A has a chain structure of 6 or more atoms. Specifically, the divalent linking group represented by formula (3-1) has a chain structure with 6 to 12 atoms. The divalent linking group represented by formula (3-2) has a chain structure with 9 atoms when m is 1 and 13 atoms when m is 2. Therefore, in the fluorine-containing ether compound represented by general formula (1), the linking group A ensures a sufficient distance between the adjacent trivalent atomic group X and the perfluoropolyether chain B. Moreover, the linking group A has appropriate flexibility because ether oxygen atoms are located at both ends of the chain structure. For these reasons, the bulkiness of the trivalent atomic group X and the perfluoropolyether chain B does not have an excessive effect on the adsorptive power of the hydroxyl group of the linking group A to the protective layer. Therefore, the hydroxyl group of the linking group A can interact with the active site on the protective layer with sufficient strength. That is, the adhesive force of the hydroxyl group of the linking group A to the protective layer can be maintained at an appropriate strength.

[0057] [A-4] The linking group A is arranged between the trivalent atomic group X and the perfluoropolyether chain B. Therefore, the interaction of the hydroxyl group of the linking group A with the active sites on the protective layer is buffered by the trivalent atomic group X and the perfluoropolyether chain B, which have sterically bulky skeletons and are arranged on both sides of the linking group A, and the interaction of the hydroxyl group of the linking group A with the active sites on the protective layer is moderately suppressed.

[0058] [A-5] The linking group A has three or less hydroxyl groups, which prevents the interaction between the linking group A and the active sites on the protective layer from becoming too strong. The number of hydroxyl groups in the linking group A is preferably two, which provides a more appropriate balance between the strength of the interaction between the linking group A and the active sites of the terminal group D on the protective layer.

[0059] In the divalent linking group represented by formula (3-1), there are 0 to 6 carbon atoms between the carbon atoms to which the two hydroxyl groups in formula (3-1) are bonded, so the distance between the two hydroxyl groups is appropriate. Because the number of carbon atoms between the two carbon atoms to which the hydroxyl groups are bonded is 6 or less, the distance between the hydroxyl groups is not too great, and a synergistic effect is obtained in which the two hydroxyl groups mutually support the interaction with the protective layer. Therefore, a lubricating layer having sufficient adhesion to the protective layer and suppressing spin-off can be formed. Because the synergistic effect in which the two hydroxyl groups in formula (3-1) mutually support the interaction between the hydroxyl groups and the protective layer is more pronounced, n in formula (3-1) is preferably 0 to 4, more preferably 0 to 2.

[0060] The divalent linking group represented by formula (3-2) contains a structure in which two or three glycerin structures (-O-CH2-CH(OH)-CH2-) are linked together. Because glycerin structures are flexible, the structure represented by formula (3-2) in which two or three of these are linked together is extremely flexible, allowing the hydroxyl groups to move flexibly. Therefore, even when the perfluoropolyether chain B arranged on the terminal side of the linking group A undergoes molecular movement, the two or three hydroxyl groups in the divalent linking group represented by formula (3-2) can move independently and freely, making it easy to maintain the interaction between the hydroxyl groups in the divalent linking group and the protective layer.

[0061] In formula (3-2), m represents an integer of 1 to 2. When m is 1, the number of hydroxyl groups in the divalent linking group represented by formula (3-2) is 2. Therefore, when all three linking groups A in general formula (1) are represented by formula (3-2) and m is 1, the total number of hydroxyl groups disposed in the linking group A of the fluorine-containing ether compound represented by general formula (1) is 6. When m is 2, the number of hydroxyl groups in the divalent linking group represented by formula (3-2) is 3. Therefore, when all three linking groups A in general formula (1) are represented by formula (3-2) and m is 2, the total number of hydroxyl groups disposed in the linking group A of the fluorine-containing ether compound represented by general formula (1) is 9. Therefore, when m is 1 or 2, the number of interaction points with the protective layer is appropriate, a lubricating layer with sufficient adhesion can be formed, and deterioration of spin-off can be suppressed.

[0062] The three linking groups A in general formula (1) may be partially or entirely the same, or may be different from each other. Therefore, the number of hydroxyl groups possessed by the three linking groups A may be the same, or may be different from each other. It is preferable that the number of hydroxyl groups possessed by the three linking groups A is all the same, since this makes the coating state of the fluorine-containing ether compound on the protective layer more uniform and allows the formation of a lubricating layer with better adhesion. Furthermore, if the structures of the three linking groups A are all the same, it is more preferable because the synthesis of the fluorine-containing ether compound is easy.

[0063] At least one of the three linking groups A in general formula (1) is preferably formula (3-1). The linking group A represented by formula (3-1) does not have an ether oxygen atom between adjacent hydroxyl groups, and therefore has superior rigidity compared to the linking group represented by formula (3-2) which has an ether oxygen atom between adjacent hydroxyl groups. Therefore, when perfluoropolyether chains B are arranged via the linking group A represented by formula (3-1), each perfluoropolyether chain B is likely to be arranged extending in three directions on the protective layer relative to the trivalent atomic group X. As a result, even if the lubricating layer is thin, excellent adhesion and coverage to the protective layer can be obtained.

[0064] (End group represented by D) In the fluorine-containing ether compound represented by general formula (1), D is a terminal group having 2 to 4 polar groups, an ether oxygen atom bonded to a methylene group adjacent to D, and having 1 to 15 carbon atoms, wherein the shortest distance between carbon atoms to which adjacent polar groups in D are bonded is 0 to 9 carbon atoms. The terminal group D can interact with the active sites on the protective layer with sufficient strength due to the synergistic effect of the functions of [D-1] to [D-3] shown below. Moreover, the strength of the interaction of the terminal group D with the active sites on the protective layer is properly balanced with the strength of the interaction between the linking group A and the active sites on the protective layer due to the function of [D-4] shown below.

[0065] [D-1] The terminal group D has two or more polar groups, so when a lubricating layer is formed on a protective layer using a lubricant containing a fluorine-containing ether compound, a favorable interaction occurs between the lubricating layer and the protective layer. As a result, the lubricating layer has excellent adhesion to the protective layer and a high spin-off suppression effect.

[0066] [D-2] Terminal group D has an ether oxygen atom at the end bonded to the methylene group adjacent to terminal group D. The ether oxygen atom at the end of terminal group D forms an ether bond (-O-) with the adjacent methylene group. This ether bond imparts appropriate flexibility to the fluorine-containing ether compound represented by general formula (1) and increases the affinity between the polar group of terminal group D and the protective layer. For this reason, the fluorine-containing ether compound represented by general formula (1) is less likely to produce polar groups that are not involved in the interaction with the active sites on the protective layer, and can form a lubricating layer that can uniformly coat the entire surface of the protective layer and has excellent adhesion to the protective layer.

[0067] [D-3] In the terminal group D, the number of carbon atoms in the shortest distance between carbon atoms bonding adjacent polar groups in the terminal group D is 9 or less, and the distance between adjacent polar groups is not too far. Therefore, the terminal group D has sufficient flexibility, and when each polar group contained in the terminal group D interacts with an active site on the protective layer, a synergistic effect is obtained, supporting the interaction of adjacent polar groups with the active site on the protective layer. As a result, the polar group contained in the terminal group D is less likely to detach from the protective layer and become a polar group not involved in the interaction with the active site on the protective layer. Therefore, the fluorine-containing ether compound represented by general formula (1) can form a lubricating layer with excellent adhesion to the protective layer and a high spin-off suppression effect. The number of carbon atoms in the shortest distance between carbon atoms bonding adjacent polar groups is preferably 0 to 6, more preferably 0 to 4.

[0068] [D-4] Since the terminal group D has four or less polar groups, in a lubricating layer containing a fluorine-containing ether compound, the strength of the interaction between the linking group A and the terminal group D and the active sites on the protective layer is properly balanced, and polar groups that do not interact with the active sites on the protective layer are less likely to be generated. This reduces the attraction of chemical contaminants to the lubricating layer, and prevents a decrease in the chemical resistance of the lubricating layer. The number of polar groups contained in the terminal group D is preferably 2 to 3, and most preferably 2, because polar groups that do not interact with the active sites on the protective layer are less likely to be generated, resulting in a fluorine-containing ether compound with a good balance of spin-off resistance and chemical resistance. When each of the three terminal groups D contains two polar groups, a magnetic recording medium having a lubricating layer containing a fluorine-containing ether compound has a better balance between the interaction between the linking group A and the active sites on the protective layer and the interaction between the terminal group D and the active sites on the protective layer.

[0069] Furthermore, the number of carbon atoms contained in the terminal group D is 15 or less. If there is a portion in the lubricating layer containing a fluorine-containing ether compound where the number of carbon atoms relative to the number of fluorine atoms is high, spots with high surface free energy may occur locally, and the lubricating layer may be contaminated by chemical contaminants. In contrast, the lubricating layer containing the fluorine-containing ether compound represented by general formula (1) has 15 or less carbon atoms contained in the terminal group D, so has low surface free energy and is less susceptible to contamination by chemical contaminants. It is preferable that the number of carbon atoms contained in the terminal group D is 10 or less.

[0070] The three terminal groups D in general formula (1) may be partially or entirely the same, or may be different from each other. Therefore, the number of polar groups possessed by the three terminal groups D may be the same, or may be different from each other. The number of polar groups possessed by the three terminal groups D is preferably the same, since this makes the coating state of the fluorine-containing ether compound on the protective layer more uniform and allows the formation of a lubricating layer with better adhesion. Furthermore, if the structures of the three terminal groups D are all the same, it is more preferable because the synthesis of the fluorine-containing ether compound is easy.

[0071] The total number of polar groups possessed by the three terminal groups D in general formula (1) is 6 to 12, preferably 6 to 9, more preferably 6 to 7, and most preferably 6. Since the total number of polar groups is 6 or more, the interaction between the polar groups possessed by the terminal groups D in the fluorinated ether compound and the protective layer is strong. This causes the terminal groups D of the fluorinated ether compound to separate from the protective layer, suppressing spin-off, which reduces the thickness of the lubricating layer. Therefore, the fluorinated ether compound provides a lubricating layer with a high spin-off suppression effect. When the total number of polar groups is 9 or less, polar groups not involved in the bond between the lubricating layer and the active sites on the protective layer are less likely to be generated. This further suppresses the attraction of chemical contaminants to the lubricating layer by polar groups not involved in the bond between the lubricating layer and the active sites on the protective layer. This allows the formation of a lubricating layer with superior chemical resistance, which is preferable.

[0072] The polar group possessed by the terminal group D is preferably a polar group selected from the group consisting of a hydroxyl group (-OH), an amino group (-NH2), a carboxy group (-COOH), a carbonyl group (-CO-), and a sulfo group (-SO3H). The two to four polar groups possessed by each terminal group D may be partially or entirely the same, or may be different from one another. Among the above, the polar group possessed by the terminal group D is preferably at least one polar group selected from the group consisting of a hydroxyl group, an amino group, and a carboxy group. When the protective layer to which the lubricant is applied is formed of nitrogen-containing carbon, the hydroxyl group, the amino group, and the carboxy group can form a hydrogen bond with the nitrogen atom, thereby increasing the affinity with the protective layer.

[0073] It is more preferable that the terminal group D contains at least one hydroxyl group as a polar group. If at least one of the two to four polar groups contained in the terminal group D is a hydroxyl group, when the protective layer to which the lubricant is applied is formed of nitrogen-containing carbon, the adhesion between the protective layer and the lubricating layer containing the fluorine-containing ether compound is further improved. It is even more preferable that the polar groups contained in the terminal group D are all hydroxyl groups, as this will enable the formation of a lubricating layer with even better adhesion to the protective layer.

[0074] In the fluorine-containing ether compound represented by general formula (1), the terminal groups D are preferably each independently a terminal group represented by any one of formulas (4-1) to (4-3).

[0075] [ka] (In formula (4-1), p represents an integer of 0 to 3, q ​​represents an integer of 0 to 2, and r represents an integer of 1 to 5. The total value of p and r is 1 to 5.) (In formula (4-2), s represents an integer of 0 to 2, and t represents an integer of 0 to 5.) (In formula (4-3), u represents an integer of 2 to 4. Y represents a linear alkylene group which may have an ether oxygen atom, or a single bond. When Y is the alkylene group, the total number of carbon atoms and oxygen atoms contained in Y is 1 to 5.)

[0076] In the terminal group represented by formula (4-1), the linking group between the carbon atom to which the terminal hydroxyl group is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded contains an ether oxygen atom. In formula (4-1), p represents an integer of 0 to 3, r represents an integer of 1 to 5, and the sum of p and r is 1 to 5. Therefore, the linking group has a linear structure consisting of 3 to 7 atoms, including a carbon atom to which no hydroxyl group is bonded.

[0077] In the terminal group represented by formula (4-1), the linking group contains an ether oxygen atom and has a linear structure consisting of three or more atoms, including a carbon atom not bonded to a hydroxyl group, so the distance between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group is appropriate. This prevents the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group from interacting with each other within the molecule, allowing both the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group to adhere to the protective layer. Furthermore, because the linking group has a linear structure consisting of three or more atoms, molecular mobility is appropriate and intramolecular aggregation is unlikely to occur.

[0078] Since the linking group contains an ether oxygen atom and has a linear structure consisting of 7 or less atoms including a carbon atom not bonded to a hydroxyl group, the linking group is not too hydrophobic to impair adhesion to the protective layer. For these reasons, a lubricating layer containing a fluorine-containing ether compound having a terminal group represented by formula (4-1) has excellent adhesion to the protective layer, excellent chemical resistance, and a high spin-off suppression effect.

[0079] In formula (4-1), the sum of p and r is 1 to 5, preferably 1 to 3. In the terminal group D, the carbon atom contained in the linking group arranged between the carbon atoms bonded to the hydroxyl groups prevents the intramolecular interaction between adjacent hydroxyl groups from taking precedence over the interaction between the hydroxyl groups and the protective layer, improving the adhesion between the hydroxyl groups in the terminal group D and the protective layer. On the other hand, if the number of carbon atoms contained in the linking group is too large, the flexibility of the terminal group D decreases, making it difficult to uniformly coat the protective layer. In the terminal group represented by formula (4-1), the sum of p and r is 5 or less, so the alkylene chain in the main chain of the terminal group D is not too long. Therefore, the long rigid alkylene chain reduces the flexibility of the terminal portion, weakening the interaction with the protective layer and preventing the terminal portion from lifting. Furthermore, because the alkylene chain in the main chain of the terminal group D is not too long, spots with high surface free energy, consisting of a large number of carbon atoms relative to the number of fluorine atoms, are less likely to occur in the lubricating layer containing a fluorine-containing ether compound. Therefore, it is possible to form a lubricating layer that is less susceptible to contamination by chemical contaminants. p is preferably 0 or 1, and more preferably 0. r is preferably 1 or 2, and more preferably 1.

[0080] In formula (4-1), q represents an integer of 0 to 2. The number of hydroxyl groups in formula (4-1) is q+2, and as described above, the number of hydroxyl groups contained in each of D is preferably 2 to 3, and most preferably 2. Therefore, q in formula (4-1) is preferably 0 or 1, and more preferably 0. When q in formula (4-1) is 0 and the sum of p and r is 2 or more, p is preferably 1 or more. This is because an ether oxygen atom is positioned close to the primary hydroxyl group in formula (4-1), improving the flexibility of movement of the primary hydroxyl group and strengthening the interaction between the primary hydroxyl group and the protective layer.

[0081] In the terminal group D represented by formula (4-2), the linking group between the carbon atom to which the terminal hydroxyl group is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded does not contain an ether oxygen atom. In formula (4-2), t represents an integer of 0 to 5. Therefore, the linking group is either a single bond (the carbon atom to which the terminal hydroxyl group is bonded is directly bonded to the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded) or has a linear structure consisting of 1 to 5 atoms, including a carbon atom to which no hydroxyl group is bonded. This ensures an appropriate distance between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group, which supports the interaction of each hydroxyl group with the protective layer and results in excellent adhesion to the protective layer.

[0082] In the terminal group D represented by formula (4-2), t is 5 or less, so the alkylene chain of the main chain portion of D is not too long. Therefore, the long, rigid alkylene chain reduces the flexibility of the terminal portion, weakening the interaction with the protective layer and preventing the terminal portion from lifting, resulting in a uniform protective layer coating. Furthermore, because t is 5 or less, spots with high surface free energy consisting of portions with a high ratio of carbon atoms to fluorine atoms are unlikely to occur in the lubricating layer containing the fluorine-containing ether compound. This results in a low surface free energy of the lubricating layer, preventing contamination by chemical contaminants. t is preferably 0 to 4, more preferably 0 to 2, and even more preferably 0 to 1.

[0083] In the terminal group D represented by formula (4-2), the linking group is a single bond or has a linear structure consisting of 1 to 5 atoms including a carbon atom that does not contain an ether oxygen atom and has no hydroxyl group bonded thereto, so that the linking group is not so hydrophobic as to impair adhesion to the protective layer. For these reasons, a lubricating layer containing a fluorine-containing ether compound having a terminal group represented by formula (4-2) has excellent adhesion to the protective layer, excellent chemical resistance, and a high spin-off suppression effect.

[0084] In formula (4-2), s represents an integer of 0 to 2. The number of polar groups in formula (4-2) is s+2, and as described above, the number of polar groups contained in each of the terminal groups D is preferably 2 to 3, and most preferably 2. Therefore, s in formula (4-2) is preferably 0 or 1, and more preferably 0.

[0085] The terminal group D represented by formula (4-3) has no secondary hydroxyl groups but two terminal primary hydroxyl groups. When the hydroxyl groups contained in the terminal group D are primary hydroxyl groups, the hydroxyl groups are more likely to interact with the active sites on the protective layer than when they are secondary hydroxyl groups. The terminal group represented by formula (4-3) has no secondary hydroxyl groups but only two primary hydroxyl groups that are likely to interact with the active sites on the protective layer. Therefore, when the terminal group D is a terminal group represented by formula (4-3), the resulting fluorine-containing ether compound can form a lubricating layer that has good adhesion to the protective layer.

[0086] In the terminal group represented by formula (4-3), the linking group between the carbon atoms to which two primary hydroxyl groups are bonded contains a carbon atom to which no hydroxyl group is bonded and an ether oxygen atom. In formula (4-3), u represents an integer of 2 to 4. Y represents a linear alkylene group which may have an ether oxygen atom, or a single bond. When Y is the alkylene group, the total number of carbon atoms and oxygen atoms contained in Y is 1 to 5. Therefore, the linking group has a structure consisting of 3 to 10 atoms, including a carbon atom to which no hydroxyl group is bonded and an ether oxygen atom.

[0087] In the terminal group represented by formula (4-3), the linking group contains an ether oxygen atom and has a structure consisting of three or more atoms, including a carbon atom not bonded to a hydroxyl group, so the distance between the two primary hydroxyl groups is appropriate. This allows each hydroxyl group to support interaction with the protective layer. Therefore, the resulting fluorine-containing ether compound can form a lubricating layer with good adhesion to the protective layer.

[0088] In the terminal group represented by formula (4-3), the linking group contains an ether oxygen atom and has a structure consisting of 10 or less atoms, including carbon atoms that are not bonded to a hydroxyl group. Therefore, the linking group is not too hydrophobic, which does not impair adhesion to the protective layer. Furthermore, in a lubricating layer containing a fluorine-containing ether compound, spots with high surface free energy, consisting of a portion with a high ratio of carbon atoms to fluorine atoms, are unlikely to occur, resulting in a low surface free energy of the lubricating layer. Therefore, a lubricating layer containing a fluorine-containing ether compound having a terminal group represented by formula (4-3) has excellent adhesion to the protective layer, excellent chemical resistance, and a high spin-off suppression effect.

[0089] Since u in formula (4-3) is 2 or more, -O-(CH2) u The distance between the primary hydroxyl group contained in -OH (hereinafter sometimes referred to as the "side chain portion") and the bulky moiety, such as the PFPE chain represented by B bonded to the terminal group D via a methylene group, and the tertiary carbon atom to which the side chain portion of formula (4-3) is bonded, is sufficiently large. Therefore, the primary hydroxyl group contained in the side chain portion of formula (4-3) can easily move freely. Furthermore, since u is 4 or less, the flexibility of the side chain portion of formula (4-3) is maintained. Furthermore, in a lubricating layer containing the fluorine-containing ether compound, spots with high surface free energy consisting of a portion with a high number of carbon atoms relative to the number of fluorine atoms are unlikely to occur, resulting in a low surface free energy state of the lubricating layer. Therefore, the fluorine-containing ether compound can form a lubricating layer that has excellent adhesion to a protective layer, excellent chemical resistance, and a high spin-off suppression effect. u is preferably 2 or 3, and more preferably 2.

[0090] In formula (4-3), the primary hydroxyl group in -Y-CH2-OH is bonded to the carbon atom to which the side chain portion of formula (4-3) is bonded via -Y-CH2-. This allows the primary hydroxyl group in -Y-CH2-OH to move freely and easily participate in interactions with the active sites on the protective layer.

[0091] Since the primary hydroxyl group contained in -Y-CH2-OH in formula (4-3) is more likely to be involved in the interaction with the active site on the protective layer, it is preferable that Y in formula (4-3) is a straight-chain alkylene group that may have an ether oxygen atom, rather than a single bond. In this case, the distance between the primary hydroxyl group contained in -Y-CH2-OH and bulky moieties such as the PFPE chain represented by B bonded to the terminal group D via a methylene group and the tertiary carbon atom to which the side chain portion of formula (4-3) is bonded becomes longer, and the primary hydroxyl group contained in -Y-CH2-OH can move more freely.

[0092] In formula (4-3), when Y is a linear alkylene group that may have an ether oxygen atom, the total number of carbon atoms and oxygen atoms contained in Y is 1 to 5. In the terminal group represented by formula (4-3), the total number of carbon atoms and oxygen atoms contained in Y is 5 or less, so the alkylene chain of the main chain portion in formula (4-3) is not too long. Therefore, the long rigid alkylene chain reduces the flexibility of the terminal portion, weakening the interaction with the protective layer and preventing the terminal portion from lifting up. Furthermore, in the lubricating layer containing the fluorine-containing ether compound, spots with high surface free energy consisting of portions with a high number of carbon atoms relative to the number of fluorine atoms are less likely to occur, resulting in a low surface free energy of the lubricating layer. The total number of carbon atoms and oxygen atoms contained in Y is preferably 1 to 4, more preferably 1 to 3. The number of carbon atoms contained in Y is preferably 1 to 3, more preferably 1 to 2.

[0093] When Y in formula (4-3) is a linear alkylene group which may have an ether oxygen atom, specific examples of Y include -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2OCH2-, -CH2OCH2CH2-, -CH2OCH2CH2CH2-, -CH2CH2OCH2-, and the like.

[0094] (PFPE chain shown as B) In the fluorine-containing ether compound represented by general formula (1), B is a perfluoropolyether chain. When a lubricant containing the fluorine-containing ether compound of this embodiment is applied to a protective layer to form a lubricating layer, the PFPE chain represented by B coats the surface of the protective layer and imparts lubricity to the lubricating layer, thereby reducing the frictional force between the magnetic head and the protective layer. The PFPE chain represented by B is appropriately selected depending on the performance required of the lubricant containing the fluorine-containing ether compound.

[0095] The three B's may be partly or entirely the same, or may be different from one another. It is preferable that all three B's are the same. This is because the fluorine-containing ether compound is more uniformly coated on the protective layer, resulting in a lubricating layer with better adhesion. Two or more of the three B's being the same means that two or more of the three B's have the same repeating unit structure of the PFPE chain. The same B's also include those with the same repeating unit structure but different average degrees of polymerization.

[0096] The PFPE chain represented by B may be a polymer or copolymer of perfluoroalkylene oxide. Examples of perfluoroalkylene oxide include perfluoromethylene oxide, perfluoroethylene oxide, perfluoro-n-propylene oxide, perfluoroisopropylene oxide, and perfluorobutylene oxide.

[0097] It is preferred that the three B's in the general formula (1) are each independently a PFPE chain represented by the following formula (5) derived from a polymer or copolymer of perfluoroalkylene oxide. -(CF2) v1 -O-(CF2O) v2 -(CF2CF2O) v3 -(CF2CF2CF2O) v4 -(CF2CF2CF2CF2O) v5 -(CF2) v6 - (5) (In formula (5), v2, v3, v4, and v5 represent average degrees of polymerization and each independently represent 0 to 20. However, v2, v3, v4, and v5 cannot all be 0 at the same time. v1 and v6 represent average values ​​representing the number of CF2 and each independently represent 1 to 3. There are no particular limitations on the arrangement order of the repeating units (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) in formula (5).)

[0098] In formula (5), v2, v3, v4, and v5 represent average degrees of polymerization, each independently representing 0 to 20, preferably 0 to 15, and more preferably 0 to 10. In formula (5), v1 and v6 are average values ​​indicating the number of CF2, and each independently represents 1 to 3. v1 and v6 are determined depending on the structure of the repeating unit located at the end of the chain structure in the PFPE chain represented by formula (5), etc. In formula (5), (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) are repeating units. There are no particular limitations on the arrangement order of the repeating units in formula (5). There are also no particular limitations on the number of types of repeating units in formula (5).

[0099] The three B's in general formula (1) are preferably each independently any one selected from the PFPE chains represented by the following formulae (5-1) to (5-4). When the three B's are each any one selected from the PFPE chains represented by the formulae (5-1) to (5-4), a fluorinated ether compound can be obtained that provides a lubricating layer with good lubricity. Furthermore, when the three B's are each any one selected from the PFPE chains represented by the formulae (5-1) to (5-4), the ratio of the number of oxygen atoms (the number of ether bonds (-O-)) to the number of carbon atoms in the PFPE chain is appropriate. This results in a fluorinated ether compound with appropriate hardness. Therefore, the fluorinated ether compound applied to the protective layer is less likely to aggregate on the protective layer, allowing for the formation of a thinner lubricating layer with sufficient coverage. Furthermore, the fluorinated ether compound has appropriate flexibility, allowing for the formation of a lubricating layer with better chemical resistance.

[0100] -CF2-(OCF2CF2) h -(OCF2) i -OCF2- (5-1) (In formula (5-1), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20.) -CF2CF2-(OCF2CF2CF2) j -OCF2CF2- (5-2) (In formula (5-2), j represents the average degree of polymerization and represents 1 to 15.) -CF2CF2CF2-(OCF2CF2CF2CF2) k -OCF2CF2CF2- (5-3) (In formula (5-3), k represents the average degree of polymerization and represents 1 to 10.) -(CF2) v7 -O-(CF2CF2CF2O) v8 -(CF2CF2O) v9 -(CF2) v10 - (5-4) (In formula (5-4), v8 and v9 represent the average degree of polymerization, each independently representing 1 to 20. v7 and v10 are average values ​​representing the number of CF2, each independently representing 1 to 2.)

[0101] In formula (5-1), the arrangement order of the repeating units (OCF2CF2) and (OCF2) is not particularly limited. In formula (5-1), the number h of (OCF2CF2) and the number i of (OCF2) may be the same or different. The PFPE chain represented by formula (5-1) may be a polymer of (OCF2CF2). In addition, the PFPE chain represented by formula (5-1) may be any of a random copolymer, a block copolymer, and an alternating copolymer composed of (OCF2CF2) and (OCF2).

[0102] In formulas (5-1) to (5-3), h, which indicates the average degree of polymerization, is 1 to 20, i, which is 0 to 20, j, which is 1 to 15, and k, which is 1 to 10, and therefore the fluorine-containing ether compound provides a lubricating layer with good lubricity. Furthermore, in formulas (5-1) to (5-3), h and i, which indicate the average degree of polymerization, are 20 or less, j is 15 or less, and k is 10 or less, and therefore the viscosity of the fluorine-containing ether compound does not become too high, and lubricants containing the fluorine-containing ether compound are easily applied, which is preferable. h, i, j, and k, which indicate the average degree of polymerization, are preferably 1 to 10, more preferably 1.5 to 8, and even more preferably 2 to 7, and therefore the fluorine-containing ether compound easily wets and spreads on the protective layer, and a lubricating layer with a uniform thickness is easily obtained.

[0103] Furthermore, in formula (5-1), it is particularly preferable that h, which indicates the average degree of polymerization, is 4 to 5, and i is 4 to 5. When h and i are 4 or more, the spin-off resistance is further improved. Furthermore, when h and i are 5 or less, the lubricating layer using this improves its coverage with the protective layer, and the chemical resistance is further improved. In addition, in formula (5-1), when i, which indicates the average degree of polymerization, is 0, a lubricating layer with good chemical resistance and spin-off resistance is preferably obtained when h, which indicates the average degree of polymerization, is 6 to 8. In formula (5-2), when j, which indicates the average degree of polymerization, is 3.5 to 5.0, a lubricating layer with good chemical resistance and spin-off resistance is preferably obtained.

[0104] In formula (5-4), there is no particular restriction on the arrangement order of the repeating units (CFCFCFO) and (CFCFO). In formula (5-4), the number v8 of (CFCFCFO) and the number v9 of (CFCFO) may be the same or different. Formula (5-4) may include any of a random copolymer, a block copolymer, and an alternating copolymer composed of the monomer units (CFCFCFO) and (CFCFO).

[0105] In formula (5-4), v8 and v9, which represent the average degree of polymerization, are each independently 1 to 20, preferably 1 to 15, and more preferably 1 to 10. In formula (5-4), v7 and v10 are average values ​​indicating the number of CF2, and each independently represents 1 to 2. v7 and v10 are determined depending on the structure of the repeating unit located at the end of the chain structure in the PFPE chain represented by formula (5-4), etc.

[0106] In the fluorine-containing ether compound represented by general formula (1), it is preferred that three As, three Bs, and three Ds in general formula (1) are the same. That is, it is preferred that three -A-CH2-B-CH2-Ds in general formula (1) are the same. This is because the fluorine-containing ether compound can be produced easily and efficiently.

[0107] Specifically, the fluorine-containing ether compound represented by general formula (1) is preferably any of the compounds represented by the following formulae (AA) to (AU) and (BA) to (BD): When the compound represented by general formula (1) is any of the compounds represented by the following formulae (AA) to (AU) and (BA) to (BD), the raw materials are easily available, and even if the thickness is thin, a lubricating layer can be formed which has better chemical resistance and is highly effective in suppressing spin-off of magnetic recording media.

[0108] In the compounds represented by the following formulae (AA) to (AH), (AJ) to (AU), and (BA) to (BD), the three -A-CH2-B-CH2-D in the general formula (1) are the same. In the compounds represented by the following formulae (AA) to (AU), and (BA) to (BD), Rf1, Rf2, and Rf3, which represent PFPE chains, each have the following structure. That is, in the compounds represented by the following formulae (AA) to (AQ), (AT), (AU), and (BA) to (BD), Rf1 is a PFPE chain represented by the above formula (5-1). In the compound represented by the following formula (AR), Rf2 is a PFPE chain represented by the above formula (5-2). In the compound represented by the following formula (AS), Rf3 is a PFPE chain represented by the above formula (5-3). In addition, h and i in Rf1, j in Rf2, and k in Rf3, which represent the PFPE chain in formulas (AA) to (AU) and (BA) to (BD), are values ​​indicating the average degree of polymerization, and therefore are not necessarily integers.

[0109] [ka]

[0110] In the compounds represented by the following formulae (AA) to (AU) and (BA) to (BD), X is a linking group represented by the above formulae (2-1) to (2-5). In the compounds represented by the following formulae (AA) to (AU) and (BA) to (BD), A is a linking group represented by the above formula (3-1) or (3-2). In the compounds represented by the following formulae (AA) to (AU) and (BA) to (BD), D is a terminal group represented by any one of the above formulae (4-1) to (4-3).

[0111] [ka] (In the three Rf1s in formula (AA), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AB), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AC), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AD), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0112] [ka] (In the three Rf1s in formula (AE), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AF), h and i represent an average degree of polymerization, where h represents 1 to 20 and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AG), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AH), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0113] [ka] (In the three Rf1s in formula (AI), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AJ), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AK), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AL), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0114] [ka] (In the three Rf1s in formula (AM), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AN), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AO), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AP), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0115] [ka] (In the three Rf1s in formula (AQ), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf2s in formula (AR), j represents the average degree of polymerization and represents 1 to 15. The j's in the three Rf2s may be different from one another, or some or all of them may be the same.) (In the three Rf3s in formula (AS), k represents the average degree of polymerization and represents 1 to 10. The k's in the three Rf3s may be different from one another, or some or all of them may be the same.) (In the three Rf1s in formula (AT), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (AU), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0116] [ka] (In the three Rf1s in formula (BA), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (BB), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (BC), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.) (In the three Rf1s in formula (BD), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. The h and i in the three Rf1s may be different from each other, or some or all of them may be the same.)

[0117] The fluorine-containing ether compound of this embodiment preferably has a number-average molecular weight (Mn) in the range of 500 to 10,000, more preferably in the range of 1,000 to 5,000, even more preferably in the range of 2,000 to 4,800, and particularly preferably in the range of 3,000 to 4,600. When the number-average molecular weight is 500 or more, a lubricating layer formed from a lubricant containing the fluorine-containing ether compound of this embodiment will have excellent heat resistance. The number-average molecular weight of the fluorine-containing ether compound is more preferably 1,000 or more. Furthermore, when the number-average molecular weight is 10,000 or less, the viscosity of the fluorine-containing ether compound becomes appropriate, and by applying a lubricant containing this, a thin lubricating layer can be easily formed. The number-average molecular weight of the fluorine-containing ether compound is preferably 5,000 or less, since this results in a manageable viscosity when applied to a lubricant.

[0118] The number average molecular weight (Mn) of fluorine-containing ether compounds was measured using AVANCEIII400 manufactured by Bruker Biospin. 1 H-NMR and 19 These are values ​​measured by F-NMR. Specifically, 19 The number of repeating units of the PFPE chain is calculated from the integrated value measured by F-NMR to determine the number average molecular weight. For NMR (nuclear magnetic resonance) measurements, the sample is diluted in a hexafluorobenzene / d-acetone (4 / 1 v / v) solvent and measured. 19 The reference for F-NMR chemical shifts is the hexafluorobenzene peak at -164.7 ppm. 1The reference for H-NMR chemical shifts is the acetone peak at 2.2 ppm.

[0119] The fluorine-containing ether compound of this embodiment is preferably subjected to molecular weight fractionation by an appropriate method to make the molecular weight dispersity (ratio of weight average molecular weight (Mw) / number average molecular weight (Mn)) 1.3 or less. In this embodiment, the method for molecular weight fractionation is not particularly limited, but for example, molecular weight fractionation by silica gel column chromatography, gel permeation chromatography (GPC), or the like, molecular weight fractionation by supercritical extraction, or the like can be used.

[0120] [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.

[0121] [First manufacturing method] (When D is a terminal group represented by formula (4-1) or (4-2)) A fluorine-based compound is prepared in which a hydroxymethyl group (-CH2OH) is arranged at each end of a perfluoropolyether chain corresponding to B in general formula (1).

[0122] Next, the hydroxyl group of the hydroxymethyl group located at one end of the fluorine-based compound is reacted with an epoxy compound having a group corresponding to D in general formula (1) (first reaction). This gives intermediate compound 1-1, which has a group corresponding to D at one end of the perfluoropolyether chain corresponding to B.

[0123] As the epoxy compound having a group corresponding to D in general formula (1), for example, compounds represented by the following formulae (6-1) to (6-11) can be used. THP in the following formulae (6-1) to (6-11) represents a tetrahydropyranyl group. The compounds represented by the following formulae (6-1) to (6-11) can be produced by known methods.

[0124] [ka]

[0125] An epoxy compound having a group corresponding to D in general formula (1) can be produced, for example, by the method shown below. That is, as shown in the following formula (7-1), it can be produced by a method in which an alcohol having a structure (R in formula (7-1)) corresponding to a portion of the terminal group represented by D in general formula (1) is reacted with a halogen compound such as a bromine compound or a chlorine compound having an epoxy group (in formula (7-1), the halogen compound is a bromine compound). Before reacting the alcohol with the halogen compound having an epoxy group, the hydroxyl group contained in R of the alcohol represented by R-OH may be protected by a known method. The number of methylene groups contained in the halogen compound having an epoxy group (a1 in formula (7-1)) is 1 to 4 and can be appropriately determined depending on the structure of the terminal group of the compound to be synthesized.

[0126] [ka] (In formula (7-1), R represents a structure corresponding to a part of the terminal group represented by D in general formula (1). a1 represents an integer of 1 to 4.)

[0127] The epoxy compound may be produced by the following method. Specifically, as shown in the following formula (7-2), an alcohol having a structure (R in formula (7-2)) corresponding to a portion of the terminal group represented by D in general formula (1) is reacted with a halogen compound such as a bromine compound or a chlorine compound having an alkenyl group (formula (7-2) is when the halogen compound is a bromine compound). The resulting compound is then oxidized with m-chloroperbenzoic acid (mCPBA). Before reacting the alcohol with the halogen compound having an alkenyl group, the hydroxyl group contained in R of the alcohol represented by R—OH may be protected by a known method. The number of methylene groups contained in the halogen compound having an alkenyl group (a2 in formula (7-2)) is 1 to 4 and can be determined appropriately depending on the structure of the terminal group of the compound to be synthesized.

[0128] [ka] (In formula (7-2), R represents a structure corresponding to a part of the terminal group represented by D in general formula (1). a2 represents an integer of 1 to 4.)

[0129] The epoxy compound may be produced by the following method. Specifically, as shown in formula (7-3) below, an alcohol having a structure (R in formula (7-3)) corresponding to a portion of the terminal group represented by D in general formula (1) is subjected to an addition reaction with a compound having an alkenyl group and an epoxy group. The compound obtained by the addition reaction is then oxidized by the action of m-chloroperbenzoic acid (mCPBA). Before the compound obtained by the addition reaction is oxidized by the action of m-chloroperbenzoic acid (mCPBA), the hydroxyl group generated by the addition reaction may be protected by a known method. The number of methylene groups (a3 in formula (7-3)) contained in the compound having an alkenyl group and an epoxy group is 1 to 4 and can be determined appropriately depending on the structure of the terminal group of the compound to be synthesized.

[0130] [ka] (In formula (7-3), R represents a structure corresponding to a part of the terminal group represented by D in general formula (1). a3 represents an integer of 1 to 4.)

[0131] Thereafter, the terminal hydroxyl group of the intermediate compound 1-1 produced in the first reaction described above is subjected to an addition reaction with a compound having two epoxy groups corresponding to A in general formula (1), thereby obtaining intermediate compound 1-2 (second reaction). As the compound having two epoxy groups corresponding to A in general formula (1), for example, compounds represented by the following formulae (8-1) to (8-5) can be used, in which THP represents a tetrahydropyranyl group.

[0132] [ka]

[0133] A compound having two epoxy groups corresponding to A in general formula (1) can be produced by the following method. For example, a compound represented by formula (8-4) can be produced by reacting m-chloroperbenzoic acid (mCPBA) with the alkenyl group of a compound (allyl glycidyl ether) having an alkenyl group and an epoxy group, thereby oxidizing the alkenyl group, as shown in the following formula (9-1).

[0134] [ka]

[0135] The compound represented by formula (8-5) can be produced by the method shown in formula (9-2) below. A halogen compound such as a bromine compound or chlorine compound having an epoxy group (formula (9-2) is when the halogen compound is a bromine compound) is reacted with an alcohol having an alkenyl group (allyl alcohol). The secondary hydroxyl group of the compound produced after the reaction is then protected with dihydropyran, and the alkenyl group is oxidized by the action of m-chloroperbenzoic acid (mCPBA). THP in formula (9-2) represents a tetrahydropyranyl group.

[0136] [ka]

[0137] As the compound having two epoxy groups corresponding to A in general formula (1), a commercially available product may be used.

[0138] A protecting group such as a tetrahydropyranyl group is introduced into the secondary hydroxyl group of the intermediate compound 1-2 having an epoxy group and a secondary hydroxyl group, which is produced in the second reaction described above, and then the compound is reacted with a triol corresponding to X in general formula (1) (third reaction).

[0139] Examples of triols that can be used for X in general formula (1) include 1,3,5-cyclohexanetriol, 1,3,5-benzenetriol, 1,3,5-cyclohexanetrimethanol, glycerin, 2-methyl-1,2,3-propanetriol, trimethylolmethane, trimethylolethane, and trimethylolpropane.

[0140] After the above steps, a deprotection reaction is carried out using a known method to obtain a compound represented by general formula (1) in which three perfluoropolyether chains B are bonded to the trivalent atomic group X represented by formulas (2-1) to (2-5) via the linking group A represented by formula (3-1) or (3-2), and the terminal group D is a terminal group represented by formula (4-1) or (4-2).

[0141] [Second manufacturing method] (When D is a terminal group represented by formula (4-3)) In the first production method, the intermediate compound 1-1 produced in the first reaction has a terminal hydroxyl group at one end of the perfluoropolyether chain and a secondary hydroxyl group at the other end. After introducing a protecting group such as a tert-butyldimethylsilyl group to this terminal hydroxyl group, the secondary hydroxyl group is protected with a -(CH2) group of the terminal group represented by formula (4-3). uA halogen compound in which the hydroxyl group at —OH is protected is reacted, and then the protecting group of the terminal hydroxyl group is deprotected using a known method to obtain intermediate compound 2-1 (first reaction).

[0142] The terminal group -(CH2) represented by formula (4-3) u Examples of halogen compounds in which the hydroxyl group in —OH is protected include compounds represented by the following formulae (10-1) to (10-3): THP in formulae (10-1) to (10-3) represents a tetrahydropyranyl group.

[0143] [ka]

[0144] The obtained intermediate compound 2-1 is subjected to an addition reaction with a compound having two epoxy groups corresponding to A in general formula (1) by a method similar to the second reaction in the first production method (second reaction). The obtained compound is subjected to an addition reaction with a triol corresponding to X in general formula (1) by a method similar to the third reaction in the first production method (third reaction).

[0145] After the above steps, a deprotection reaction is carried out using a known method to obtain a compound represented by general formula (1) in which three perfluoropolyether chains B are bonded to the trivalent atomic group X represented by formulas (2-1) to (2-5) via the linking group A represented by formula (3-1) or (3-2), and the terminal group D is the terminal group represented by formula (4-3).

[0146] [Third manufacturing method] (When at least one of the three -A-CH2-B-CH2-Ds bonded to X in general formula (1) is different) Two or three intermediate compounds corresponding to -A-CH2-B-CH2-D are synthesized by the same method as the first reaction and the second reaction of the first or second production method. Then, the triol corresponding to X in general formula (1) is reacted sequentially with the two or three intermediate compounds corresponding to -A-CH2-B-CH2-D. After the above steps, a deprotection reaction can be carried out using a known method to produce a compound in which at least one of the three -A-CH2-B-CH2-Ds bonded to X in general formula (1) is different.

[0147] [Lubricants for magnetic recording media] The lubricant for a magnetic recording medium of this embodiment contains a fluorine-containing ether compound represented by the above general formula (1). The lubricant of the present embodiment can be used by mixing, as needed, known materials used as lubricant materials, as long as the properties resulting from the inclusion of the fluorinated ether compound represented by the general formula (1) are not impaired.

[0148] 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.

[0149] When the lubricant of the present embodiment contains a material other than the fluorinated ether compound represented by the general formula (1), the content of the fluorinated ether compound represented by the general formula (1) in the lubricant of the present embodiment is preferably 50 mass% or more, more preferably 70 mass% or more.

[0150] The lubricant of this embodiment contains the fluorine-containing ether compound represented by the general formula (1) above, and therefore can form a lubricating layer that has excellent chemical resistance and a high spin-off suppressing effect.

[0151] [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, as needed, and at least one of an adhesive layer and a soft magnetic layer may also be provided between the underlayer and the substrate.

[0152] FIG. 1 is a schematic cross-sectional view showing one embodiment of the 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.

[0153] "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. 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 may be a non-magnetic substrate having a NiP or NiP alloy film formed on a base made of any of these non-metallic materials.

[0154] "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.

[0155] "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 antiferro-coupling (AFC).

[0156] 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 Zr, Ta, or Nb to the CoFe alloy used in the first and second soft magnetic films. This promotes the amorphization of the first and second soft magnetic films. As a result, it is possible to improve the orientation of the first underlayer (seed layer) and reduce the flying height of the magnetic head. The soft magnetic layer 13 can be formed by, for example, a sputtering method.

[0157] "First base layer" The first underlayer 14 is a layer that controls the orientation and crystal size of the second underlayer 15 and magnetic layer 16 that are provided thereon. The first underlayer 14 may be, for example, 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, or a CrTi alloy layer. The first underlayer 14 can be formed by, for example, a sputtering method.

[0158] "Second base layer" The second underlayer 15 is a layer that controls the 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 single layer or multiple layers. When the second underlayer 15 is multiple layers, all the layers may be made of the same material, or at least one layer may be made of a different material. The second underlayer 15 can be formed by, for example, a sputtering method.

[0159] "Magnetic layer" The magnetic layer 16 is a magnetic film whose easy axis of magnetization is oriented perpendicular or parallel to the substrate surface. The magnetic layer 16 contains Co and Pt. To improve the SNR characteristics, the magnetic layer 16 may contain oxides, Cr, B, Cu, Ta, Zr, or the like. Examples of oxides contained in the magnetic layer 16 include SiO2, SiO, Cr2O3, CoO, Ta2O3, and TiO2.

[0160] 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, namely, a first magnetic layer, a second magnetic layer, and a third magnetic layer stacked in this 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. The oxide contained in the first magnetic layer is preferably an oxide of Cr, Si, Ta, Al, Ti, Mg, Co, or the like. Among these, TiO2, Cr2O3, SiO2, and the like are particularly suitable. Furthermore, the first magnetic layer is preferably made of a composite oxide containing two or more types of oxides. Among these, Cr2O3-SiO2, Cr2O3-TiO2, SiO2-TiO2, and the like are particularly suitable.

[0161] The first magnetic layer may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re in addition to Co, Cr, Pt, and oxides. The second magnetic layer can be made of the same material as the first magnetic layer, and preferably has a granular structure.

[0162] The third magnetic layer preferably has a non-granular structure made of a material containing Co, Cr, and Pt and not containing oxides, and may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn in addition to Co, Cr, and Pt.

[0163] When magnetic layer 16 is formed of multiple magnetic layers, it is preferable to provide a non-magnetic layer between adjacent magnetic layers. When magnetic layer 16 is formed of three layers, namely, a first magnetic layer, a second magnetic layer, and a third magnetic layer, it is preferable to provide a non-magnetic layer between the first magnetic layer and the second magnetic layer and between the second magnetic layer and the third magnetic layer.

[0164] The non-magnetic layer provided between adjacent magnetic layers of 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).

[0165] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 preferably uses an alloy material containing an oxide, metal nitride, or metal carbide. Specifically, oxides that can be used include, for example, SiO2, Al2O3, Ta2O5, Cr2O3, MgO, Y2O3, and TiO2. Metal nitrides that can be used include, for example, AlN, Si3N4, TaN, and CrN. Metal carbides that can be used include, for example, TaC, BC, and SiC. The non-magnetic layer can be formed by, for example, a sputtering method.

[0166] 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 longitudinal magnetic recording. The magnetic layer 16 may be formed by any conventionally known method such as vapor deposition, ion beam sputtering, magnetron sputtering, etc. The magnetic layer 16 is usually formed by sputtering.

[0167] "Protective layer" The protective layer 17 protects the magnetic layer 16. The protective layer 17 may be composed of one layer or multiple layers. A carbon-based protective layer is preferably used as the protective layer 17, and an amorphous carbon protective layer is particularly preferred. If the protective layer 17 is a carbon-based protective layer, the interaction with the polar groups (particularly hydroxyl groups) contained in the fluorine-containing ether compound in the lubricating layer 18 is further enhanced, which is preferable.

[0168] The adhesion between the carbon-based protective layer and the lubricating layer 18 can be controlled by using hydrogenated carbon and / or nitrogenated carbon for the carbon-based protective layer and adjusting the hydrogen and / or nitrogen content in the carbon-based protective layer. The hydrogen content in the carbon-based protective layer is preferably 3 atomic % to 20 atomic % when measured by hydrogen forward scattering (HFS). The nitrogen content in the carbon-based protective layer is preferably 4 atomic % to 15 atomic % when measured by X-ray photoelectron spectroscopy (XPS).

[0169] 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, for example, in which nitrogen is contained on the lubricating layer 18 side of protective layer 17 and hydrogen is contained on the magnetic layer 16 side of protective layer 17. In this case, the adhesion between the magnetic layer 16 and lubricating layer 18 and the carbon-based protective layer is further improved.

[0170] The thickness of the protective layer 17 is preferably 1 nm to 7 nm. When the thickness of the protective layer 17 is 1 nm or more, sufficient performance as the protective layer 17 can be obtained. When 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.

[0171] The protective layer 17 can be formed by sputtering using a target material containing carbon, chemical vapor deposition (CVD) using a hydrocarbon raw material such as ethylene or toluene, or ion beam deposition (IBD). When a carbon-based protective layer is formed as protective layer 17, it can be deposited by, for example, DC magnetron sputtering. In particular, when a carbon-based protective layer is formed as protective layer 17, it is preferable to deposit an amorphous carbon protective layer by plasma CVD. The amorphous carbon protective layer deposited by plasma CVD has a uniform surface with little roughness.

[0172] "Lubricating layer" The lubricating layer 18 prevents contamination of the magnetic recording medium 10. The lubricating layer 18 also reduces the frictional force of the magnetic head of the magnetic recording / 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 is formed by applying the magnetic recording medium lubricant of the above-described embodiment onto the protective layer 17. Therefore, the lubricating layer 18 contains the above-described fluorine-containing ether compound.

[0173] When the protective layer 17 disposed below the lubricating layer 18 is a carbon-based protective layer, the lubricating layer 18 bonds with the protective layer 17 with particularly high bonding strength. As a result, even if the thickness of the lubricating layer 18 is thin, it becomes easier to obtain a magnetic recording medium 10 in which the surface of the protective layer 17 is covered with a high coverage, and contamination of the surface of the magnetic recording medium 10 can be effectively prevented.

[0174] 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 1.2 nm (12 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 forming an island or mesh-like structure. Therefore, the surface of the protective layer 17 can be covered with the lubricating layer 18 at a high coverage rate. Furthermore, 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 made sufficiently small.

[0175] "Method for forming lubricating layer" A method for forming the lubricating layer 18 includes, for example, preparing a magnetic recording medium in the middle of manufacturing in which the layers up to the protective layer 17 are formed on the substrate 11, applying a solution for forming the lubricating layer onto the protective layer 17, and drying the solution.

[0176] The lubricant layer forming solution can be obtained by dispersing and dissolving the lubricant for a magnetic recording medium according to the above embodiment in a solvent as needed, and adjusting the viscosity and concentration to suit the coating method. Examples of solvents used in the lubricating layer-forming solution include fluorine-based solvents such as Vertrel (registered trademark) XF (trade name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.) and / or Asahiklin (registered trademark) AE-3000 (trade name, manufactured by AGC Corporation).

[0177] The method for applying the lubricating layer-forming solution 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 a lubricant layer-forming solution placed in an immersion tank of a dip coating device. 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 lubricating layer forming solution can be applied uniformly to the surface of the protective layer 17, and the lubricating layer 18 can be formed on the protective layer 17 with a uniform thickness.

[0178] 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 also improved. The heat treatment temperature is preferably 100°C to 180°C, and more preferably 100°C to 160°C. When 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 due to the heat treatment can be prevented. The heat treatment time can be adjusted appropriately depending on the heat treatment temperature, and is preferably 10 minutes to 120 minutes.

[0179] In this embodiment, in order to further improve the adhesion of the lubricating layer 18 to the protective layer 17, the lubricating layer 18 may be irradiated with ultraviolet (UV) rays before or after the heat treatment.

[0180] The magnetic recording medium 10 of this embodiment has at least a magnetic layer 16, a protective layer 17, and a lubricating layer 18 sequentially formed on a substrate 11. In the magnetic recording medium 10 of this embodiment, a lubricating layer 18 containing the above-mentioned fluorine-containing ether compound is formed on and in contact with the protective layer 17. This lubricating layer 18 has good chemical resistance and is highly effective in suppressing spin-off. Therefore, the magnetic recording medium 10 of this embodiment has excellent reliability and durability. As a result, the magnetic recording medium 10 of this embodiment can achieve a low magnetic head flying height (e.g., 10 nm or less) and operates stably for a long period of time, even in harsh environments associated with diverse applications. Therefore, the magnetic recording medium 10 of this embodiment is particularly suitable as a magnetic disk to be installed in a magnetic disk device using the LUL (Load Unload) method. [Example]

[0181] 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.

[0182] [Example 1] The compound (AA-1) represented by the above formula (AA) was obtained by the method shown below. (First reaction) Place HOCH2CF2O (CF2CF2O) in a 100 mL recovery flask under a nitrogen gas atmosphere. h(CF2O) i 20 g of a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CH2OH (where h, representing the average degree of polymerization, is 4.5, and i, representing the average degree of polymerization, is 4.5), 4.05 g of a compound represented by the above formula (6-1), and 20 mL of t-butanol were charged and stirred at room temperature until homogeneous to form a mixture. 1.12 g of potassium tert-butoxide was added to this mixture, and the mixture was reacted by stirring at 70°C for 16 hours.

[0183] The compound represented by formula (6-1) was synthesized by protecting the hydroxyl group of ethylene glycol monoallyl ether with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0184] The reaction product obtained after the reaction was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 9.6 g of the compound represented by the following formula (11) as intermediate compound 1-1.

[0185] [ka] (Rf1 in formula (11) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group.)

[0186] (Second reaction) Next, 9.0 g of the compound represented by formula (11), which is intermediate compound 1-1 obtained above, 0.64 g of 1,2,3,4-diepoxybutane represented by formula (8-1) above, and 20 mL of t-butanol were charged into a 100 mL recovery flask under a nitrogen gas atmosphere, and the mixture was stirred at room temperature until homogeneous. 0.40 g of potassium tert-butoxide was added to the mixture, and the mixture was reacted by stirring at 70°C for 16 hours.

[0187] The reaction product obtained after the reaction was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 7.1 g of the compound represented by the following formula (12) as intermediate compound 1-2.

[0188] [ka] (Rf1 in formula (12) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group.)

[0189] (Third reaction) Next, the compound represented by formula (12), intermediate compound 1-2 obtained above, was protected with dihydropyran to obtain the compound represented by formula (13). Then, 7.0 g of the compound represented by formula (13) was added to a 100 mL recovery flask under a nitrogen gas atmosphere, and 0.23 g of 1,3,5-cyclohexanetriol and 20 mL of t-butanol were added. The mixture was stirred at room temperature until homogeneous, forming a mixture. 0.40 g of potassium tert-butoxide was added to the mixture, and the mixture was allowed to react with stirring at 70°C for 48 hours.

[0190] [ka] (Rf1 in formula (13) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group.)

[0191] After the reaction, the resulting reaction mixture was returned to room temperature, and 50 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 4 hours. The reaction mixture was then transferred in small portions to a separatory funnel containing 100 mL of saturated aqueous sodium bicarbonate and extracted twice with 200 mL of ethyl acetate. The organic layer was washed sequentially with 100 mL of brine, 100 mL of saturated aqueous sodium bicarbonate, and 100 mL of brine, and then dehydrated using anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 3.2 g of compound (AA-1). Rf1 in formula (AA) is the PFPE chain represented by formula (5-1) above. For the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5.

[0192] The obtained compound (AA-1) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0193] [Example 2] The compound (AA-2) represented by the above formula (AA) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH (where h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5), HOCH2CF2O(CF2CF2O) h (CF2O) iThe same operations as in Example 1 were performed except that a compound (number average molecular weight 815, molecular weight distribution 1.1) represented by CF2CH2OH (in the formula, h, which indicates the average degree of polymerization, is 3.5, and i, which indicates the average degree of polymerization, is 3.5) was used, thereby obtaining 4.5 g of compound (AA-2) (Rf1 in formula (AA) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 3.5, and i, which indicates the average degree of polymerization, is 3.5).

[0194] The obtained compound (AA-2) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(21F), -78.5(6F), -80.5(6F), -91.0~-88.5(42F)

[0195] [Example 3] The compound (AA-3) represented by the above formula (AA) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH (where h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5), HOCH2CF2O(CF2CF2O) h (CF2O) i The same operations as in Example 1 were performed except that a compound (number average molecular weight 1180, molecular weight distribution 1.1) represented by CF2CH2OH (in the formula, h, which indicates the average degree of polymerization, is 5.5, and i, which indicates the average degree of polymerization, is 5.5) was used, thereby obtaining 3.5 g of compound (AA-3) (Rf1 in formula (AA) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 5.5, and i, which indicates the average degree of polymerization, is 5.5).

[0196] The obtained compound (AA-3) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(33F), -78.5(6F), -80.5(6F), -91.0~-88.5(66F)

[0197] [Example 4] The compound represented by the above formula (AB) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (6-2) was used instead of the compound represented by formula (6-1), to obtain 4.4 g of compound (AB) (Rf1 in formula (AB) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0198] The compound represented by formula (6-2) was synthesized by protecting one hydroxyl group of 1,3-propanediol with dihydropyran, followed by reaction with epibromohydrin.

[0199] The obtained compound (AB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(6H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F) [Example 5] The compound represented by the above formula (AC) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (6-3) was used instead of the compound represented by formula (6-1), to obtain 4.2 g of compound (AC) (Rf1 in formula (AC) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0200] The compound represented by formula (6-3) was synthesized by protecting the hydroxyl group of glycidol with dihydropyran.

[0201] The obtained compound (AC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(36H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0202] [Example 6] The compound represented by the above formula (AD) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (6-4) was used instead of the compound represented by formula (6-1), to obtain 4.3 g of compound (AD) (Rf1 in formula (AD) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0203] The compound represented by formula (6-4) was synthesized by protecting the hydroxyl group of 3-buten-1-ol with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0204] The obtained compound (AD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(6H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(36H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0205] [Example 7] The compound (AE) represented by the above formula (AE) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (6-5) was used instead of the compound represented by formula (6-1), to obtain 4.3 g of compound (AE) (Rf1 in formula (AE) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0206] The compound represented by formula (6-5) was synthesized by reacting the hydroxyl group of 3-buten-1-ol with 2-(2-bromoethoxy)tetrahydro-2H-pyran, followed by oxidation with m-chloroperbenzoic acid.

[0207] The obtained compound (AE) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(6H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0208] [Example 8] The compound represented by the above formula (AF) was obtained by the method shown below. The same operation as in Example 1 was performed except that the compound represented by formula (6-6) was used instead of the compound represented by formula (6-1), to obtain 3.7 g of compound (AF) (Rf1 in formula (AF) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0209] The compound of formula (6-6) was synthesized by subjecting the compound of formula (6-1) to an addition reaction with allyl alcohol, protecting the hydroxyl group of the resulting compound with dihydropyran, and then oxidizing it with m-chloroperbenzoic acid.

[0210] The obtained compound (AF) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(15H), 2.50(3H), 3.35~3.85(63H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0211] [Example 9] The compound represented by the above formula (AG) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (6-7) was used instead of the compound represented by formula (6-1), to obtain 3.8 g of compound (AG) (Rf1 in formula (AG) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0212] The compound of formula (6-7) was synthesized by the addition reaction of the compound of formula (6-4) with allyl alcohol, protecting the hydroxyl group of the resulting compound with dihydropyran, and then oxidizing it with m-chloroperbenzoic acid.

[0213] The obtained compound (AG) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(6H), 1.95~2.10(15H), 2.50(3H), 3.35~3.85(51H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0214] [Example 10] The compound represented by the above formula (AH) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (6-8) was used instead of the compound represented by formula (6-1), to obtain 3.7 g of compound (AH) (Rf1 in formula (AH) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0215] The compound of formula (6-8) was synthesized by adding the compound of formula (6-1) with 3-buten-1-ol, protecting the hydroxyl group of the resulting compound with dihydropyran, and then oxidizing it with m-chloroperbenzoic acid.

[0216] The obtained compound (AH) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(6H), 1.95~2.10(15H), 2.50(3H), 3.35~3.85(63H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0217] [Example 11] The compound represented by the above formula (AI) was obtained by the method shown below. An addition reaction was carried out in the same manner as in Example 1, except that the amount of the compound represented by formula (13) used in the third reaction in Example 1 was reduced to ⅔ and reacted with 1,3,5-cyclohexanetriol.

[0218] The reaction product obtained after the reaction was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 4.6 g of the compound represented by the following formula (14) as an intermediate compound.

[0219] [ka] (In the two Rf1s in formula (14), h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5. THP represents a tetrahydropyranyl group.)

[0220] Then, 4.0 g of the compound represented by formula (14) was added to a 100 mL recovery flask under a nitrogen gas atmosphere, and 2.0 g of the compound represented by formula (15), which is the intermediate compound of Example 8, and 20 mL of t-butanol were added and stirred at room temperature until a homogeneous mixture was obtained. 0.4 g of potassium tert-butoxide was added to this mixture, and the mixture was reacted by stirring at 70°C for 24 hours.

[0221] [ka] (In Rf1 in formula (15), h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5. THP represents a tetrahydropyranyl group.)

[0222] After the reaction, the resulting reaction mixture was returned to room temperature, and 50 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 4 hours. The reaction mixture was then transferred in small portions to a separatory funnel containing 100 mL of saturated aqueous sodium bicarbonate and extracted twice with 200 mL of ethyl acetate. The organic layer was washed sequentially with 100 mL of brine, 100 mL of saturated aqueous sodium bicarbonate, and 100 mL of brine, and then dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 2.5 g of compound (AI). (Rf1 in formula (AI) is the PFPE chain represented by formula (5-1) above. For the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5.)

[0223] The obtained compound (AI) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(13H), 2.50(3H), 3.35~3.85(53H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0224] [Example 12] The compound represented by the above formula (AJ) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (6-9) was used instead of the compound represented by formula (6-1), to obtain 4.6 g of compound (AJ) (Rf1 in formula (AJ) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0225] The compound represented by formula (6-9) was synthesized by protecting one hydroxyl group of 1,6-hexanediol with dihydropyran, followed by reaction with epibromohydrin.

[0226] The obtained compound (AJ) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(24H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0227] [Example 13] The compound represented by the above formula (AK) was obtained by the method shown below. The same operation as in Example 1 was performed except that the compound represented by formula (6-10) was used instead of the compound represented by formula (6-1), to obtain 4.2 g of compound (AK) (Rf1 in formula (AK) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0228] The compound represented by formula (6-10) was synthesized by protecting the hydroxyl group of 7-octen-1-ol with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0229] The obtained compound (AK) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(30H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(36H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0230] [Example 14] The compound represented by the above formula (AL) was obtained by the method shown below. The same operation as in Example 1 was performed except that the compound represented by formula (6-11) was used instead of the compound represented by formula (6-1), to obtain 4.3 g of compound (AL) (Rf1 in formula (AL) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0231] The compound represented by formula (6-11) was synthesized by reacting the hydroxyl group of 5-hexen-1-ol with 2-(2-bromoethoxy)tetrahydro-2H-pyran, followed by oxidation with m-chloroperbenzoic acid.

[0232] The obtained compound (AL) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(18H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0233] [Example 15] The compound represented by the above formula (AM) was obtained by the method shown below. The same operation as in Example 1 was performed except that 1,2,7,8-diepoxyoctane represented by formula (8-2) was used instead of the compound represented by formula (8-1), to obtain 4.8 g of compound (AM) (Rf1 in formula (AM) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5).

[0234] The obtained compound (AM) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(24H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0235] [Example 16] The compound represented by the above formula (AN) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (8-3) was used instead of the compound represented by formula (8-1), to obtain 4.8 g of compound (AN) (Rf1 in formula (AN) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0236] The compound represented by formula (8-3) was synthesized by oxidizing 1,9-decadiene with m-chloroperbenzoic acid.

[0237] The obtained compound (AN) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.65~1.85(36H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0238] [Example 17] The compound represented by the above formula (AO) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (8-4) was used instead of the compound represented by formula (8-1), to obtain 5.0 g of compound (AO) (Rf1 in formula (AO) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0239] The compound represented by formula (8-4) was synthesized by oxidizing allyl glycidyl ether with m-chloroperbenzoic acid.

[0240] The resulting compound (AO) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(60H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0241] [Example 18] The compound represented by the above formula (AP) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (6-6) was used instead of the compound represented by formula (6-1), and the compound represented by formula (8-4) was used instead of the compound represented by formula (8-1), to obtain 3.8 g of compound (AP) (Rf1 in formula (AP) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0242] The obtained compound (AP) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(15H), 2.50(3H), 3.35~3.85(75H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0243] [Example 19] The compound represented by the above formula (AQ) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (8-5) was used instead of the compound represented by formula (8-1), to obtain 3.5 g of compound (AQ) (Rf1 in formula (AQ) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0244] The compound represented by formula (8-5) was synthesized by reacting one molecule of epibromohydrin with two molecules of allyl alcohol, protecting the secondary hydroxyl group of the compound produced after the reaction with dihydropyran, and then oxidizing it with m-chloroperbenzoic acid.

[0245] The obtained compound (AQ) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(15H), 2.50(3H), 3.35~3.85(75H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0246] [Example 20] The compound (AA-4) represented by the above formula (AA) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH (where h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5), HOCH2CF2O(CF2CF2O) h (CF2O) i The same operations as in Example 1 were performed except that a compound (number average molecular weight 990, molecular weight distribution 1.1) represented by CF2CH2OH (in the formula, h, which indicates the average degree of polymerization, is 7.0, and i, which indicates the average degree of polymerization, is 0) was used, thereby obtaining 4.6 g of compound (AA-4) (Rf1 in formula (AA) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 7.0, and i, which indicates the average degree of polymerization, is 0).

[0247] The obtained compound (AA-4) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-78.5(6F), -81.0(6F), -91.0~-88.5(84F)

[0248] [Example 21] The compound represented by the above formula (AR) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH, HOCH2CF2CF2O(CF2CF2CF2O) jThe same procedures as in Example 1 were carried out except that a compound (number average molecular weight 1020, molecular weight distribution 1.1) represented by CF2CF2CH2OH (where j, representing the average degree of polymerization, is 4.5) was used, and 4.7 g of compound (AR) (Rf2 in formula (AR) is a PFPE chain represented by the above formula (5-2). In the three Rf2s, j, representing the average degree of polymerization, is 4.5) was obtained.

[0249] The obtained compound (AR) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-84.0~-83.0(54F), -86.4(12F), -124.3(12F), -130.0~-129.0(27F)

[0250] [Example 22] The compound represented by the above formula (AS) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH, HOCH2CF2CF2CF2O(CF2CF2CF2CF2O) k The same operations as in Example 1 were performed, except that a compound (number average molecular weight 995, molecular weight distribution 1.1) represented by CF2CF2CF2CH2OH (where k, indicating the average degree of polymerization, is 3.0) was used, and 4.1 g of compound (AS) (Rf3 in formula (AS) is a PFPE chain represented by the above formula (5-3). In the three Rf3s, k, indicating the average degree of polymerization, is 3.0) was obtained.

[0251] The obtained compound (AS) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-84.0~-83.0(48F), -122.5(12F), -126.0(36F), -129.0~-128.0(12F)

[0252] [Example 23] The compound represented by the above formula (AT) was obtained by the method shown below.

[0253] (First reaction) The primary hydroxyl group of the compound represented by the above formula (11) described in Example 1 was protected with tert-butyldimethylchlorosilane to obtain a compound represented by the formula (16).

[0254] [ka] (Rf1 in formula (16) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group, and TBS represents a tert-butyldimethylsilyl group.)

[0255] Next, 7.0 g of the intermediate compound represented by formula (16) obtained above, 0.96 g of 2-(2-bromoethoxy)tetrahydro-2H-pyran represented by formula (10-1) above, and 20 mL of t-butanol were placed in a 100 mL recovery flask under a nitrogen gas atmosphere and stirred at room temperature until a homogeneous mixture was obtained. 0.50 g of potassium tert-butoxide was added to this mixture, and the mixture was allowed to react with stirring at 70°C for 8 hours.

[0256] The reaction product obtained after the reaction was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 5.5 g of the compound represented by the following formula (17) as an intermediate compound.

[0257] [ka] (Rf1 in formula (17) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group, and TBS represents a tert-butyldimethylsilyl group.)

[0258] The tert-butyldimethylsilyl group of the compound represented by formula (17), which is the intermediate compound obtained above, was deprotected using tetrabutylammonium fluoride to obtain a compound represented by formula (18) below.

[0259] [ka] (Rf1 in formula (18) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group.)

[0260] (Second and third reactions) The same operations as in the second and third reactions of Example 1 were performed, except that the compound represented by formula (18) was used instead of the compound represented by formula (11), to obtain 4.0 g of compound (AT) (Rf1 in formula (AT) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0261] The obtained compound (AT) 1 H-NMR measurement and19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(60H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0262] [Example 24] The compound represented by the above formula (AU) was obtained by the method shown below. By the method described in Example 5, a compound represented by formula (19), which is an intermediate compound of the first reaction, was obtained.

[0263] [ka] (Rf1 in formula (19) is a PFPE chain represented by the above formula (5-1). In Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5. THP represents a tetrahydropyranyl group.)

[0264] The same procedure as in Example 23 was performed except that the compound represented by formula (19) was used instead of the compound represented by formula (11), to obtain 4.3 g of compound (AU) (Rf1 in formula (AU) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0265] The obtained compound (AU) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(48H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0266] [Example 25] The compound represented by the above formula (BA) was obtained by the method shown below. The same operation as in Example 1 was performed except that 1,3,5-benzenetriol was used instead of 1,3,5-cyclohexanetriol, to obtain 2.9 g of compound (BA) (Rf1 in formula (BA) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0267] The resulting compound (BA) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.95~2.10(12H), 3.35~3.85(45H), 3.85~4.10(12H), 6.60~6.80(3H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0268] [Example 26] The compound represented by the above formula (BB) was obtained by the method shown below. The same operation as in Example 1 was performed except that 1,3,5-cyclohexanetrimethanol was used instead of 1,3,5-cyclohexanetriol, to obtain 5.1 g of compound (BB) (Rf1 in formula (BB) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0269] The obtained compound (BB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.19(3H), 1.95~2.10(12H), 2.50(3H), 3.35~3.85(54H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0270] [Example 27] The compound represented by the above formula (BC) was obtained by the method shown below. The same operation as in Example 1 was performed except that glycerin was used instead of 1,3,5-cyclohexanetriol, to obtain 4.4 g of compound (BC) (Rf1 in formula (BC) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0271] The resulting compound (BC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.95~2.10(12H), 3.35~3.85(50H), 3.85~4.10(12H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0272] [Example 28] The compound represented by the above formula (BD) was obtained by the method shown below. The same operation as in Example 1 was performed except that trimethylolpropane was used instead of 1,3,5-cyclohexanetriol, to obtain 4.3 g of compound (BD) (Rf1 in formula (BD) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0273] The obtained compound (BD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.10(3H), 1.65~1.85(2H), 1.95~2.10(12H), 3.35~3.85(51H), 3.85~4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0274] The structures of X, A, B, and D when the compounds (AA) to (AU) and (BA) to (BD) of Examples 1 to 28 thus obtained are respectively substituted into general formula (1) are shown in Table 1. Note that, except for compound (AI), all compounds have the same structure for the three As, three Bs, and three Ds in general formula (1). The three Ds of compound (AI) are represented in Table 1 as D1, D2, and D3, respectively.

[0275] [Table 1]

[0276] [Comparative Example 1] The compound represented by the following formula (ZA) was synthesized by the method described in Patent Document 1.

[0277] [ka] (In formula (ZA), d, which indicates the average degree of polymerization, is 7.0.)

[0278] Comparative Example 2 The compound represented by the following formula (ZB) was synthesized by the method described in Patent Document 2.

[0279] [ka] (Rf1 in formula (ZB) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0280] Comparative Example 3 The compound represented by the following formula (ZC) was synthesized by the method described in Patent Document 2.

[0281] [ka] (Rf1 in formula (ZC) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0282] Comparative Example 4 The compound represented by the following formula (ZD) was synthesized by the method described in Patent Document 3.

[0283] [ka] (Rf1 in formula (ZD) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0284] Comparative Example 5 The compound represented by the following formula (ZE) was synthesized by the method described in Patent Document 4.

[0285] [ka] (Rf1 in formula (ZE) is a PFPE chain represented by the above formula (5-1). In the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0286] Comparative Example 6 The compound represented by the following formula (ZF) was synthesized by the method described in Patent Document 5.

[0287] [ka]

[0288] Comparative Example 7 The compound represented by the following formula (ZG) was synthesized by the method described in Patent Document 6.

[0289] [ka] (Rf2 in formula (ZG) is a PFPE chain represented by the above formula (5-2). In the three Rf2s, j, which indicates the average degree of polymerization, is 4.5.)

[0290] [Comparative Example 8] The compound represented by the following formula (ZH) was synthesized by the method described in Patent Document 7.

[0291] [ka] (Rf1 in formula (ZH) is a PFPE chain represented by the above formula (5-1). In the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0292] Comparative Example 9 The compound represented by the following formula (ZI) was synthesized by the method described in Patent Document 8.

[0293] [ka] (Rf1 in formula (ZI) is a PFPE chain represented by the above formula (5-1). In the three Rf1s, h representing the average degree of polymerization is 7.0, and i representing the average degree of polymerization is 0.) [Comparative Example 10] The compound represented by the following formula (ZJ) was synthesized by the method described in Patent Document 9.

[0294] [ka] (Rf1 in formula (ZJ) is a PFPE chain represented by the above formula (5-1). In the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0295] The number average molecular weights (Mn) of the compounds thus obtained in Examples 1 to 28 and Comparative Examples 1 to 10 were measured by the above-mentioned method. The results are shown in Tables 2 and 3.

[0296] Next, solutions for forming lubricating layers were prepared by the method described below using the compounds obtained in Examples 1 to 28 and Comparative Examples 1 to 10. Then, using the obtained solutions for forming lubricating layers, lubricating layers for magnetic recording media were formed by the method described below, thereby obtaining the magnetic recording media of Examples 1 to 28 and Comparative Examples 1 to 10.

[0297] "Lubricant layer forming solution" The compounds obtained in Examples 1 to 28 and Comparative Examples 1 to 10 were each dissolved in a fluorine-based solvent, Vertrel (registered trademark) XF (trade name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.), and diluted with Vertrel XF so that the film thickness when applied to the protective layer would be 9.0 Å to 9.5 Å, to prepare a solution for forming a lubricating layer.

[0298] "Magnetic recording media" A magnetic recording medium was prepared by sequentially depositing an adhesive layer, a soft magnetic layer, a first underlayer, a second underlayer, a magnetic layer, and a protective layer on a substrate having a diameter of 65 mm. The protective layer was made of carbon. On the protective layer of a magnetic recording medium on which each layer up to the protective layer had been formed, the lubricating layer-forming solutions of Examples 1 to 28 and Comparative Examples 1 to 10 were applied by dipping under the conditions of an immersion speed of 10 mm / sec, an immersion time of 30 seconds, and a pull-up speed of 1.2 mm / sec. The magnetic recording medium coated with the lubricating layer-forming solution was then placed in a thermostatic chamber, and a heat treatment was performed at 140°C for 10 minutes to remove the solvent in the lubricating layer-forming solution and improve the adhesion between the protective layer and the lubricating layer, thereby forming a lubricating layer on the protective layer and obtaining a magnetic recording medium.

[0299] (film thickness measurement) The thickness of the lubricating layer of each of the magnetic recording media thus obtained in Examples 1 to 28 and Comparative Examples 1 to 10 was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name: Nicolet iS50, manufactured by Thermo Fisher Scientific). The results are shown in Tables 2 and 3.

[0300] Next, the magnetic recording media of Examples 1 to 28 and Comparative Examples 1 to 10 were subjected to the following chemical resistance test and spin-off resistance test.

[0301] [Chemical resistance test] The following chemical resistance tests were carried out and the chemical resistance was evaluated based on the following evaluation criteria. The results are shown in Tables 2 and 3.

[0302] A load / unload (LUL) hard disk drive was prepared and equipped with a magnetic recording medium with a lubricant layer. A perpendicular magnetic recording head was used as the hard disk drive head. A commercially available silicone rubber gel chip (1 cm x 1 cm x 0.5 cm) was placed inside the hard disk drive, and continuous LUL operation was repeated under the following conditions until the spindle motor drive current exceeded the threshold. As shown in Figure 2, the continuous LUL operation was performed in a dry environment (relative humidity below 10%), with a 5-hour cycle of 25°C → 60°C → 25°C (1 hour for each ramp-up and ramp-down). The endurance time was defined as the time from the start of continuous LUL operation until the spindle motor drive current exceeded the threshold. When the endurance time exceeded 150 hours, the perpendicular magnetic recording head used in the test was observed using a scanning electron microscope (SEM), and the contamination area on the head was evaluated using SEM images.

[0303] When the compounds in the lubricating layer are uniformly distributed on the protective layer without gaps, the cyclic siloxane vaporized from the silicone rubber gel chips is prevented from adhering to the magnetic recording medium. This reduces the load on the spindle motor of the hard disk drive, extending its service life. On the other hand, when the compounds in the lubricating layer aggregate, gaps are formed in the lubricating layer, allowing the vaporized cyclic siloxane to adhere to the magnetic recording medium. This results in a load on the spindle motor of the hard disk drive, shortening its service life.

[0304] "Chemical Resistance Test Evaluation Criteria" A+: Durability is 150 hours or more and the head contamination area is 50 μm 2 below A: Durability is 150 hours or more and the head contamination area is 50 μm 2 Ultra, 100μm 2 below B: Durability is 150 hours or more and the head contamination area is 100 μm 2 super C: Durability is 100 hours or more but less than 150 hours D: Durability is less than 100 hours

[0305] [Spin-off resistance test] The magnetic recording medium was mounted on a spin stand and rotated at 10,000 rpm for 72 hours in an environment with a relative humidity of 60% and a temperature of 80°C. Before and after this operation, the thickness of the lubricating layer was measured using FT-IR at a position 20 mm radius from the center of the magnetic recording medium, and the thickness reduction rate of the lubricating layer was calculated 24, 48, and 72 hours after the start of the test. If the thickness reduction rate of the magnetic recording medium exceeded 9% before 72 hours, the evaluation was stopped midway. The spin-off resistance was evaluated using the evaluation time and the calculated thickness reduction rate according to the following evaluation criteria.

[0306] "Evaluation criteria for spin-off resistance testing" A+: Film thickness reduction rate after 72 hours is 2% or less A: Film thickness reduction rate after 72 hours: over 2% and under 3% B: Film thickness reduction rate after 72 hours: over 3% and under 9% C: Film thickness reduction rate after 72 hours is over 9% D: Film thickness reduction rate after 48 hours: over 9%

[0307] [comprehensive evaluation] Based on the results of the chemical resistance test and spin-off resistance test, a comprehensive evaluation was made based on the following criteria. "comprehensive evaluation" A: Both the chemical resistance test and spin-off resistance test were evaluated as A+ or A. B: Either the chemical resistance test rating or the spin-off resistance test rating is B, and the other is A+, A, or B. C: Either the chemical resistance test rating or the spin-off resistance test rating is C, and the other is A+, A, B, or C. D: At least one of the chemical resistance test evaluation and spin-off resistance test evaluation is D

[0308] [Table 2]

[0309] [Table 3]

[0310] As shown in Table 2, the evaluation results of the chemical resistance test and the spin-off resistance test were both good in Examples 1 to 28. In contrast, as shown in Table 3, the results of Comparative Examples 1 to 10 were poor in either or both of the chemical resistance test and the spin-off resistance test.

[0311] Example 2 is a compound in which the molecular weight of the perfluoropolyether chain B is lower than that of Example 1. Therefore, Example 2 showed improved coating properties and better chemical resistance. On the other hand, Example 2 showed good results, although the spin-off resistance tended to decrease. Example 3 is a compound in which the molecular weight of the perfluoropolyether chain B is higher than that of Example 1. Therefore, Example 3 showed good results, although the chemical resistance tended to decrease, and better spin-off resistance.

[0312] Examples 8 to 10 and 18 have a structure in which all three terminal groups D have three hydroxyl groups. It is believed that these compounds exhibited superior chemical resistance and spin-off resistance due to a stronger interaction with the protective layer.

[0313] Examples 12 and 13 showed good chemical resistance, but tended to be weaker than Example 1. This is thought to be because Examples 12 and 13 have a structure in which the lubricating layer containing a fluorine-containing ether compound has a portion with a high carbon atom to fluorine atom ratio. Examples 12 and 14 differ in the position of the ether bond introduced between the two hydroxyl groups of D. More specifically, in Example 14, the ether bond is introduced closer to the primary hydroxyl group than in Example 12. This is thought to impart flexibility to the movement of the primary hydroxyl group in Example 14, resulting in a stronger interaction with the protective layer. This is thought to be why Example 14 exhibited better chemical resistance than Example 12.

[0314] Comparative Example 1 is a compound having no polar group between the trivalent atomic group and the perfluoropolyether chain, and the terminal group is represented by formula (4-2). Comparative Example 1 showed poor chemical resistance and spin-off resistance. This is thought to be because only the terminal group interacts with the protective layer through the polar group, resulting in insufficient adhesion. Comparative Example 2 is a compound in which the trivalent atomic group has a structure represented by formula (2-1), but the linking group and the terminal group each contain one hydroxyl group, and therefore the chemical substance resistance was good, but the spin-off resistance was poor. Comparative Example 3 is a compound having a trivalent atomic group represented by formula (2-1) and a terminal group represented by formula (4-2), but containing one hydroxyl group in the linking group. Therefore, compared to Comparative Example 2, the chemical substance resistance was reduced and the spin-off resistance was improved, but both were inferior results.

[0315] Comparative Example 4 is a compound in which the trivalent atomic group is represented by formula (2-2) and the terminal group has a structure represented by formula (4-1), but the linking group contains one hydroxyl group, resulting in good spin-off resistance but poor chemical resistance. Comparative Example 5 is a compound having a central cyclic structure and an end group represented by formula (4-1), but with two perfluoropolyether chains bonded to the central cyclic structure via linking groups, and one hydroxyl group contained in the linking groups, resulting in poor chemical resistance and spin-off resistance. Comparative Example 6 is a compound in which the trivalent atomic group has a structure represented by formula (2-2), but the linking group contains one hydroxyl group and the terminal group does not have a polar group, resulting in poor chemical resistance and spin-off resistance.

[0316] Comparative Example 7 is a compound in which the trivalent atomic group has a structure represented by formula (2-2), but the linking group does not have a polar group and the terminal group is a hydroxyl group, resulting in poor chemical resistance and spin-off resistance. Comparative Example 8 is a compound in which two perfluoropolyether chains are linked via a linking group represented by formula (3-1) and the terminal group is represented by formula (4-2), and therefore the chemical resistance and spin-off resistance were poor. Comparative Example 9 is a compound in which three perfluoropolyether chains are linked via a linking group represented by formula (3-2) and the terminal group is represented by formula (4-2), and therefore the chemical resistance and spin-off resistance were poor. Comparative Example 10 is a compound in which three perfluoropolyether chains are linked via a linking group having one hydroxyl group and the terminal group is represented by formula (4-1), and therefore the chemical resistance and spin-off resistance were poor.

[0317] From the above, it was found that by forming a lubricating layer containing the compounds of Examples 1 to 28 on the protective layer of a magnetic recording medium, a lubricating layer with good chemical resistance and high spin-off suppression effect can be obtained, even if the thickness is thin, at 9.0 Å to 9.5 Å. [Industrial Applicability]

[0318] 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 has good chemical resistance and a high spin-off suppressing effect. [Explanation of symbols]

[0319] 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, 18...lubricating layer.

Claims

1. A compound represented by any one of the following formulas (AA) to (AU) and (BA) to (BD): A fluorine-containing ether compound, characterized in that in the compounds represented by the formulae (AA) to (AQ), (AT), (AU), and (BA) to (BD), Rf 1 is a PFPE chain represented by the following formula (5-1); in the compound represented by the formula (AR), Rf 2 is a PFPE chain represented by the formula (5-2); and in the compound represented by the formula (AS), Rf 3 is a PFPE chain represented by the formula (5-3). -CF 2 - (OCF 2 CF 2 ) h - (OCF 2 ) i -OCF 2 - (5-1) (In formula (5-1), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20.) -CF 2 CF 2 - (OCF 2 CF 2 CF 2 ) j -OCF 2 CF 2 - (5-2) (In formula (5-2), j represents the average degree of polymerization and represents 1 to 15.) -CF 2 CF 2 CF 2 - (OCF 2 CF 2 CF 2 CF 2 ) k -OCF 2 CF 2 CF 2 - (5-3) (In formula (5-3), k represents the average degree of polymerization and represents 1 to 10.) 【Chemistry 1】 (The three Rf in formula (AA) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AB) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AC) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AD) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) 【Chemistry 2】 (The three Rf in formula (AE) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AF) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AG) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AH) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) 【Transformation 3】 (The three Rf in formula (AI) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AJ) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AK) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AL) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) 【Chemistry 4】 (The three Rf in formula (AM) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AN) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AO) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AP) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) 【Transformation 5】 (The three Rf in formula (AQ) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AR) ２ In the formula, j represents the average degree of polymerization, and represents 1 to 15. ２ The j's in may be different from one another, or some or all of them may be the same.) (The three Rf in formula (AS) ３ In the formula, k represents the average degree of polymerization and represents 1 to 10. ３ The k's in may be different from one another, or some or all of them may be the same.) (The three Rf in formula (AT) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (AU) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) 【Transformation 6】 (The three Rf in formula (BA) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (BB) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (BC) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.) (The three Rf in formula (BD) １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １ In the formula, h and i may be different from each other, or some or all of them may be the same.)

2. 2. The fluorine-containing ether compound according to claim 1, which has a number average molecular weight in the range of 500 to 10,000.

3. A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to claim 1.

4. A magnetic recording medium having at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate, 2. A magnetic recording medium, wherein the lubricating layer comprises the fluorine-containing ether compound according to claim 1.

5. 5. The magnetic recording medium according to claim 4, wherein the lubricating layer has an average film thickness of 0.5 nm to 2.0 nm.

Images