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

Abstract

This fluorine-containing ether compound is represented by the following formula. R1-CH2-R2-(CH2-R3-CH2-R2)z-CH2-R4 (x represents 1 or 2. R2 represents a perfluoropolyether chain. R3 represents a C1-50 divalent linking group having 1-6 polar groups. At least one of the x number of R3 is formula (2). R1 and R4 represent a C1-50 terminal group having 1-4 polar groups. X and Y each independently represent a C3-20 acyclic divalent saturated hydrocarbon group having 1-2 polar groups. a and b are each independently 0 or 1.)

Description

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

[0001] The present invention relates to a fluorine-containing ether compound, a coating material, a lubricant for magnetic recording media, and a magnetic recording medium. This application claims priority to Japanese Patent Application No. 2024-010872, filed on January 29, 2024, the contents of which are incorporated herein by reference.

[0002] In order to increase the recording density in magnetic recording and reproducing devices, magnetic recording media suitable for high recording densities are being developed. Conventional magnetic recording media include those in which a recording layer is formed on a substrate and a protective layer made of carbon or the like is formed on the recording layer. The protective layer protects the information recorded on the recording layer and improves the sliding properties of the magnetic head. However, simply providing a protective layer on the recording layer does not ensure sufficient durability of the magnetic recording medium. For this reason, a lubricant is generally applied to the surface of the protective layer to form a lubricating layer.

[0003] Examples of lubricants used in forming the lubricating layer of a magnetic recording medium include -CF ２ It has been proposed to use a fluorine-based polymer having a repeating structure containing -, which contains a compound having a polar group such as a hydroxyl group or an amino group at the end thereof.

[0004] For example, Patent Documents 1 and 2 disclose a glycerin structure (—O—CH ２ -CH(OH)-CH ２ -O-) at both ends ２ Disclosed is a fluorine-containing ether compound having a skeleton in which two perfluoropolyether chains are linked via a divalent linking group to which a methyl group (-) is bonded, and in which terminal groups which are organic groups having polar groups are linked to both ends of the skeleton via methylene groups.

[0005] Patent Documents 3 to 5 disclose fluorine-containing ether compounds having a skeleton in which two perfluoropolyether chains are bonded via a divalent linking group having two hydroxyl groups, and in which terminal groups which are organic groups having polar groups are bonded to both ends of the skeleton via methylene groups.

[0006] In addition, Patent Document 6 discloses a fluorine-containing ether compound having a skeleton in which two or three perfluoropolyether chains are bonded via a divalent linking group having two hydroxyl groups, and at both ends thereof, end groups which are organic groups having polar groups are bonded via a methylene group.Patent Document 7 discloses a fluorine-containing ether compound having a skeleton in which two perfluoropolyether chains are bonded via a divalent linking group having three hydroxyl groups, and at both ends thereof, end groups which are organic groups having polar groups are bonded via a methylene group.

[0007] U.S. Patent No. 10,540,997 WO 2021 / 251335 WO 2021 / 020066 Japanese Patent No. 6,804,981 Japanese Patent No. 5,743,438 U.S. Patent No. 10,262,685 WO 2021 / 019998

[0008] In recent years, in order to increase the capacity of magnetic recording media, there has been a demand for further reduction in magnetic spacing (the distance between the magnetic head and the magnetic layer of the magnetic recording medium), which has led to a demand for a smaller flying height of the magnetic head and a thinner lubricating layer in the magnetic recording medium.

[0009] However, reducing the flying height of a magnetic head generally increases the likelihood of collision between the magnetic head and the magnetic recording medium, which tends to reduce the flying stability of the magnetic head. Furthermore, if the thickness of the lubricating layer is reduced, spin-off (a phenomenon in which the lubricant scatters or evaporates due to centrifugal force and heat generated by the rotation of the magnetic recording medium) occurs, and it becomes impossible to maintain a film thickness sufficient to fulfill the function of the lubricating layer.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a fluorine-containing ether compound that can obtain excellent flying stability and form a lubricating layer that suppresses spin-off, and can be suitably used as a material for a lubricant for a magnetic recording medium. Another object of the present invention is to provide a coating material that contains the fluorine-containing ether compound of the present invention and can form a lubricating layer that obtains good flying stability and has a high spin-off suppression effect, and a lubricant for a magnetic recording medium. Another object of the present invention is to provide a magnetic recording medium that has a lubricating layer that contains the fluorine-containing ether compound of the present invention, has good flying stability, and has a high spin-off suppression effect.

[0011] The present invention includes the following aspects.

[0012] [1] A fluorinated ether compound represented by the following formula (1): R １ -CH ２ -R ２ [-CH ２ -R ３ -CH ２ -R ２ ] ｘ -CH ２ -R ４ (1) (In formula (1), x represents 1 or 2. R ２ is a perfluoropolyether chain. (x+1) R ２ may be the same in part or in whole, or may be different from each other. ３ is a divalent linking group having 1 to 50 carbon atoms and 1 to 6 polar groups. ３ At least one of R is a divalent linking group represented by the following formula (2): １ and R ４ is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms. １ and R ４ may be the same or different.)

[0013] (In formula (2), a and b each independently represent 0 or 1, and a and b cannot simultaneously represent 0. X and Y each independently represent an acyclic divalent saturated hydrocarbon group having 3 to 20 carbon atoms and having 1 or 2 polar groups. The saturated hydrocarbon group may contain an ether oxygen atom between carbon atoms, and the polar group of the saturated hydrocarbon group is bonded to a carbon atom other than the bonding terminal of the saturated hydrocarbon group.)

[0014] [2] The fluorine-containing ether compound according to [1], wherein the formula (2) is a linking group represented by any one of the following formulas (2-1) to (2-4):

[0015] (In formula (2-1), c represents an integer of 1 to 6. A １ represents a polar group.) (In formula (2-2), d represents an integer of 1 to 6. A ２ represents a polar group.) (In formula (2-3), e1 represents an integer of 1 to 6. e2 represents an integer of 1 to 6. A ３１ , A ３２ each independently represents a polar group.

[0016] [3] The fluorine-containing ether compound according to [1] or [2], wherein all of the polar groups in the formula (2) are hydroxyl groups.

[0017] [4] R in the formula (1) １ and R ４ are each independently a terminal group represented by the following formula (3):

[0018] (In formula (3), l represents an integer of 0 to 3. o represents 0 or 1. At least one of l and o is 1 or greater. When l represents 1 to 3, l m's each independently represent an integer of 1 to 6, and l n's each independently represent an integer of 1 to 6, and in one structural unit, at least one of m and n is 1. B represents an organic group having 1 to 30 carbon atoms which may contain at least one of a polar group, a halogeno group, and an ether oxygen atom, or a hydrogen atom. However, the total number of polar groups included in formula (3) is 1 to 4.)

[0019] [5] R in the formula (1) １ and R４ are each independently any one of the following formulas (3-1) to (3-5):

[0020] (In formula (3-1), p represents 0 or 1. q1, q2, q3, and q4 each independently represent an integer of 1 to 6. When p is 0, the total value of q1 and q4 is 2 to 10. When p is 1, the total value of q1, q2, q3, and q4 is 4 to 10, and at least one of q2 and q3 is 1. D represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when D is the aryl group which may have a substituent, the number of polar groups contained in D is 0 or 1.) (In formula (3-2), r represents 0 or 1. s1, s2, and s3 each independently represent an integer of 1 to 6. When r is 1, the total value of s1, s2, and s3 is 3 to 8, and at least one of s2 and s3 is 1.) (In formula (3-3), t1 and t2 each independently represent an integer of 1 to 6. E represents a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when E is the aryl group which may have a substituent, E does not contain a polar group.) (In formula (3-4), u represents an integer of 1 to 6. G represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when G is the aryl group which may have a substituent, the number of polar groups which may be included in G is 0 or 1.) (In formula (3-5), v represents 1 or 2. Each of the five Js independently represents a polar group, an alkoxy group having 1 to 8 carbon atoms, a halogeno group, or a hydrogen atom. However, when a polar group is included in the five Js, the number of polar groups among the five Js is 1.)

[0021] [6] R in the formula (1) １ and R ４ [7] The fluorine-containing ether compound according to any one of [1] to [5], wherein R in the formula (1) is the same as １ and a polar group having R ４[8] The fluorine-containing ether compound according to any one of [1] to [6], wherein the total number of polar groups contained in R in the formula (1) is 2 to 6. １ and a polar group having R ３ and a polar group having R ４ The fluorine-containing ether compound according to any one of [1] to [7], wherein all of the polar groups are hydroxyl groups.

[0022] [9] (x+1) R in the formula (1) ２ are each independently a perfluoropolyether chain represented by the following formula (4): -(CF ２ ) ｗ１ -O-(CF ２ O) ｗ２ -(CF ２ CF ２ O) ｗ３ -(CF ２ CF ２ CF ２ O) ｗ４ -(CF ２ CF ２ CF ２ CF ２ O) ｗ５ -(CF ２ ) ｗ６ - (4) (In formula (4), w2, w3, w4, and w5 represent the average degree of polymerization, and each independently represents 0 to 20. However, w2, w3, w4, and w5 cannot all be 0 at the same time. w1 and w6 are CF ２ is an average value representing the number of structural units in formula (4), each of which independently represents 1 to 3. ２ O), (CF ２ CF ２ O), (CF ２ CF ２ CF ２ O), (CF ２ CF ２ CF ２ CF ２ There are no particular restrictions on the arrangement order of O).

[0023]

[10] (x+1) R in the formula (1) ２are each independently any one selected from perfluoropolyether chains represented by the following formulas (4-1) to (4-4): ２ -(OCF ２ CF ２ ) ｈ -(OCF ２ ) ｉ -OCF ２ - (4-1) (In formula (4-1), 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 - (4-2) (In formula (4-2), 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 - (4-3) (In formula (4-3), k represents the average degree of polymerization and represents 1 to 10.) - (CF ２ ) ｗ７ -O-(CF ２ CF ２ CF ２ O) ｗ８ -(CF ２ CF ２ O) ｗ９ -(CF ２ ) ｗ１０ - (4-4) (In formula (4-4), w8 and w9 represent the average degree of polymerization, each independently representing 1 to 20. w7 and w10 represent CF ２ is an average value representing the number of

[0024]

[11] The fluorine-containing ether compound according to any one of [1] to

[10] , wherein x in the formula (1) is 1.

[12] The fluorine-containing ether compound according to any one of [1] to

[10] , wherein x in the formula (1) is 2, and two R ３ The atom contained in is R at the center of the molecule. ２ The fluorine-containing ether compound according to any one of [1] to

[10] , wherein the fluorine-containing ether compound is symmetrically arranged with respect to

[0025]

[13] The fluorine-containing ether compound represented by the formula (1) is any one of compounds represented by the following formulas (AA) to (AH), wherein Rf in the formulas (AA) to (AC) and (AE) to (AH) is ２ Ha-CF ２ CF ２ -(OCF ２ CF ２ CF ２ ) ｊ -OCF ２ CF ２ -, and Rf in formula (AD) １ Ha-CF ２ -(OCF ２ CF ２ ) ｈ -(OCF ２ ) ｉ -OCF ２ The fluorine-containing ether compound according to any one of [1] to

[11] , represented by the formula: (Two Rf in formula (AA) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AB), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AC), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AD), the average degrees of polymerization may be the same or different. １ In the formula, h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20. １The average degrees of polymerization may be the same or different. (Two Rf in formula (AE) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AF), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AG), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AH), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ The average degrees of polymerization may be the same or different.)

[14] A coated material comprising the fluorinated ether compound according to any one of [1] to

[13] .

[15] A lubricant for a magnetic recording medium, comprising the coated material according to

[14] .

[0026]

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

[13] .

[17] The magnetic recording medium according to

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

[0027] The fluorine-containing ether compound of the present invention is a compound represented by the above formula (1), and is suitable as a material for a lubricant for a magnetic recording medium. Because the coating material and the lubricant for a magnetic recording medium of the present invention contain the fluorine-containing ether compound of the present invention, they can obtain excellent flying stability and form a lubricating layer that suppresses spin-off.

[0028] 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 flying stability, a high spin-off suppression effect of the lubricating layer, and excellent reliability and durability. Furthermore, since the magnetic recording medium of the present invention has a lubricating layer that provides excellent flying stability and suppresses spin-off, the thickness of the lubricating layer can be made thinner, and the flying height of the magnetic head can be further reduced.

[0029] 1 is a schematic cross-sectional view showing an embodiment of a magnetic recording medium of the present invention.

[0030] The present inventors have conducted extensive research to solve the above problems, as described below. Conventionally, fluorine-containing ether compounds having multiple polar groups such as hydroxyl groups at the ends of a chain-like structure and at the center of the molecule (parts other than the end groups) have been preferably used as materials for lubricants for magnetic recording media (hereinafter sometimes abbreviated as "lubricants") to be applied to the surface of a protective layer. The polar groups in the fluorine-containing ether compounds bond with active sites on the protective layer, improving the adhesion of the lubricating layer to the protective layer.

[0031] However, when a thin lubricating layer is formed on a protective layer using a lubricant containing a conventional fluorine-containing ether compound, it is difficult to achieve a lubricating layer that has good flying stability and a high spin-off suppression effect, as will be shown below.

[0032] That is, if the polar group contained in the fluorine-containing ether compound contained in the lubricating layer is too much, and there is a polar group that does not interact with the active site on the protective layer, the fluorine-containing ether compound near the polar group that does not interact with the active site on the protective layer will float up and form a mass, and the smoothness of the lubricating layer will be reduced.The mass that the fluorine-containing ether compound floats up in the lubricating layer will collide with magnetic head, causing the reduction of flying stability.In particular, if there is no polar group that can interact with the protective layer in the molecular center (part other than terminal group), the molecular center of the fluorine-containing ether compound is easy to float up, and the flying stability will be reduced.

[0033] In addition, among the multiple polar groups that the fluorine-containing ether compound that is contained in lubricating layer has, if the number of polar groups that interact with the active site on protective layer is too large, the polar groups that participate in the interaction with the polar groups that are contained in other fluorine-containing ether compound molecules that exist in lubricating layer are difficult to ensure.As a result, the film that is made up of the fluorine-containing ether compound that forms lubricating layer is insufficiently dense, and with the rotation of magnetic recording medium, the fluorine-containing ether compound in the lubricating layer is easily scattered, and spin-off occurs.In particular, when there is no polar group that can participate in the interaction with the polar groups that are contained in other fluorine-containing ether compound molecules in the molecular center of the fluorine-containing ether compound, the molecular center of the fluorine-containing ether compound is separated from protective layer, and spin-off is easily caused.

[0034] In order to arrange polar group in the molecular center of fluorine-containing ether compound, the structure of fluorine-containing ether compound should be made to have a structure with a skeleton that has a plurality of perfluoropolyether chains, and between adjacent perfluoropolyether chains, a divalent linking group having polar group is arranged.However, even in the fluorine-containing ether compound with the skeleton described above, as shown below, it is difficult to ensure both the polar group that can interact with protective layer and the polar group that can participate in intermolecular interaction in the molecular center of fluorine-containing ether compound.

[0035] For example, in a fluorine-containing ether compound having a skeleton in which a divalent linking group having one or two polar groups is arranged between adjacent perfluoropolyether chains, the polar group of the divalent linking group may not be sufficiently involved in the interaction with the active site on the protective layer or the interaction with the polar group contained in other fluorine-containing ether compound molecules.This is because the sterically bulky perfluoropolyether chains arranged on both sides of the divalent linking group prevent the polar group of the divalent linking group from adsorbing to the protective layer or from approaching the polar group contained in other fluorine-containing ether compound molecules.

[0036] In addition, even if the fluorine-containing ether compound has a skeleton in which the divalent linking group having a plurality of polar groups is arranged between adjacent perfluoropolyether chains, when the divalent linking group has a rigid structure, the polar group that the divalent linking group has may not be involved in the interaction with the active site on protective layer or the interaction with the polar group contained in other fluorine-containing ether compound molecules.This is because the divalent linking group with a rigid structure cannot move freely, so when the perfluoropolyether chains arranged on both sides of the divalent linking group undergo molecular motion, they may move together with the perfluoropolyether chain, and may be separated from the polar group contained in protective layer or other fluorine-containing ether compound molecules.

[0037] In addition, even in the case of a fluorine-containing ether compound in which a flexible divalent linking group having multiple polar groups is arranged between adjacent perfluoropolyether chains, if the multiple polar groups of the divalent linking group are all located at positions sufficiently distant from each other, the multiple polar groups of the divalent linking group will each be likely to participate in the active site on the protective layer.As a result, among the multiple polar groups of the divalent linking group, the number of polar groups that can participate in the interaction with the polar groups contained in other fluorine-containing ether compound molecules present in the lubricating layer will be reduced.

[0038] Therefore, the present inventors have focused on the interaction between the polar groups of the divalent linking group and the active sites on the protective layer, the interaction with the polar groups contained in other fluorine-containing ether compounds, the distance between the polar groups of the divalent linking group, the flexibility of the divalent linking group, and the number of polar groups contained in the fluorine-containing ether compound, in a fluorine-containing ether compound having a skeleton consisting of multiple perfluoropolyether chains and divalent linking groups connecting adjacent perfluoropolyether chains, and have conducted extensive research to improve the flying stability of a lubricating layer containing this and suppress spin-off.

[0039] As a result, two or three perfluoropolyether chains and a methylene group (-CH ２and divalent linking groups connecting adjacent perfluoropolyether chains via an erythritol structure (—O—CH ), at least one of which is an erythritol structure (—O—CH ). ２ -CH(OH)-CH(OH)-CH ２ It is a structure in which a hydrocarbon group having a specific number of polar groups is linked to a methylene group (-CH ２ The present inventors have found that a fluorine-containing ether compound having a specific number of terminal groups each having a polar group is sufficient to form an ether bond (—O—) with a specific group (—), and have arrived at the present invention based on this finding.

[0040] In such a fluorine-containing ether compound, at least one of the divalent linking groups linking adjacent perfluoropolyether chains has a structure in which an erythritol structure is linked to a hydrocarbon group having a specific number of polar groups, and therefore, as shown below, both polar groups capable of interacting with the protective layer and polar groups capable of participating in intermolecular interactions are sufficiently secured in the central part of the molecule of the fluorine-containing ether compound.

[0041] Erythritol structure (—O—CH ２ -CH(OH)-CH(OH)-CH ２ The internal 1,2-diol structure (—CH ２ -CH(OH)-CH(OH)-CH ２ -), carbon atoms bonded to hydroxyl groups are bonded to each other. Therefore, the hydroxyl groups are close to each other, and steric and electrostatic repulsion between the hydroxyl groups is likely to occur. Furthermore, in the erythritol structure, a carbon atom bonded to a hydroxyl group is further bonded to a carbon atom bonded to another hydroxyl group, and therefore free rotation is likely to be suppressed. For these reasons, the two hydroxyl groups contained in the erythritol structure are in an opposite conformation with respect to the carbon chain in the erythritol structure. Therefore, the dipole moments generated by the two hydroxyl groups contained in the erythritol structure cancel each other out, and the surface free energy of the entire fluorine-containing ether compound molecule is reduced.

[0042] Furthermore, the distance between the active sites on the protective layer is sufficiently larger than the distance between the hydroxyl groups contained in the erythritol structure. Moreover, as described above, the two hydroxyl groups contained in the erythritol structure are in opposite conformations with respect to the carbon chain in the erythritol structure. For these reasons, the two hydroxyl groups contained in the erythritol structure are not simultaneously in a direction approaching the protective layer, and only one of the two hydroxyl groups can interact with the active site on the protective layer. Therefore, the other of the two hydroxyl groups can participate in the intermolecular interaction between the fluorine-containing ether compounds.

[0043] In the past, the structures of fluorine-containing ether compounds used in lubricants have been designed so that as many polar groups as possible contained in the compound are arranged in a way that facilitates interaction with the active sites on the protective layer, in order to improve adhesion to the protective layer. For this reason, structures such as the erythritol structure, in which carbon atoms to which hydroxyl groups are bonded are bonded, resulting in adjacent hydroxyl groups being oriented in opposite directions on the protective layer, have tended to be avoided.

[0044] Furthermore, conventionally, studies have been made to arrange adjacent polar groups at a sufficient distance so that all polar groups contained in a fluorinated ether compound are likely to participate in an interaction with the active site on the protective layer. For example, when all of the multiple polar groups contained in a fluorinated ether compound are arranged at a sufficient distance from each other, all of the polar groups are likely to participate in an interaction with the protective layer, and the interaction between the polar groups of the fluorinated ether compounds is not sufficiently obtained.

[0045] However, the present inventors deliberately made some of the polar groups in the fluorinated ether compound hydroxyl groups of an erythritol structure, thereby securing polar groups that can participate in intermolecular interactions between fluorinated ether compounds. Based on this, they thought that the number of polar groups that can interact with active sites on the protective layer could be adjusted as needed, and so they made at least one of the divalent linking groups have a structure in which an erythritol structure is linked to a hydrocarbon group having a specific number of polar groups.

[0046] In the above-mentioned fluorine-containing ether compound, at least one of the divalent linking groups has a methylene group (—CH ２ The divalent linking group forms an ether bond (—O—) with an erythritol structure and a hydrocarbon group having a specific number of carbon atoms and a specific number of polar groups, and is a structure in which the erythritol structure is linked to the hydrocarbon group having a specific number of carbon atoms and a specific number of polar groups. Therefore, at least one of the divalent linking groups is made moderately rigid due to the bulkiness of the erythritol structure and the hydrocarbon group having the polar group, and intramolecular interactions of the polar groups are suppressed. Moreover, this divalent linking group is given moderate flexibility by the ether bonds formed on both sides of the divalent linking group, and therefore the movement of the polar groups is not easily hindered. Therefore, the polar groups in the divalent linking group are likely to be involved in interactions with active sites on the protective layer and in intermolecular interactions.

[0047] Furthermore, the bulkiness of the erythritol structure restricts its movement, thereby imparting appropriate rigidity to the fluorinated ether compound molecule and suppressing intramolecular interactions between polar groups, making the polar groups more likely to participate in intermolecular interactions between fluorinated ether compounds. Furthermore, the oxygen atoms located at both ends of the erythritol structure easily rotate freely, allowing the internal 1,2-diol structure contained in the erythritol structure to move independently. As a result, the hydroxyl groups of the erythritol structure are less likely to be hindered from participating in intermolecular interactions.

[0048] In contrast, for example, if the mobility of the fluorinated ether compound is too high, the polar groups contained in the fluorinated ether compound tend to form intramolecular interactions, and therefore the polar groups are less likely to participate in intermolecular interactions.

[0049] Thus, in the center of the molecule of the above-mentioned fluorine-containing ether compound, the polar group that can interact with protective layer and the polar group that can participate in the interaction between molecules are sufficiently ensured.Therefore, the lubricating layer that contains the above-mentioned fluorine-containing ether compound can be prevented from the center of the molecule being lifted up and forming a mass due to the interaction between the polar group that exists in the center of the molecule of the fluorine-containing ether compound and protective layer.As a result, the lubricating layer that is flat and is hard to collide with magnetic head, and can obtain good flying stability.

[0050] Furthermore, the lubricating layer containing the above-mentioned fluorine-containing ether compound is dense because the polar group present in the center of the molecule of the fluorine-containing ether compound allows sufficient intermolecular interaction between the fluorine-containing ether compounds. Therefore, the lubricating layer containing the above-mentioned fluorine-containing ether compound is less likely to scatter due to the rotation of the magnetic recording medium, and has excellent spin-off resistance.

[0051] Furthermore, in such a fluorine-containing ether compound, the divalent linking groups connecting adjacent perfluoropolyether chains and the number of polar groups arranged at both ends of the molecule are appropriate, so that the compound is less likely to aggregate and a sufficient number of polar groups capable of interacting with the protective layer can be secured, thereby obtaining a lubricating layer with excellent adhesion to the protective layer, high flying stability, and high spin-off suppression effect.

[0052] Furthermore, the present inventors have confirmed that by using a lubricant containing the above-mentioned fluorine-containing ether compound, it is possible to form a lubricating layer that can obtain good flying stability and suppress spin-off even when the thickness is thin, and have arrived at the present invention.

[0053] The fluorine-containing ether compound, coating material, lubricant for magnetic recording media, and magnetic recording media of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments. In this specification, the term "polar group" does not include halogeno groups (-F, -Cl, -Br, etc.) or ether bonds (-O-).

[0054] [Fluorine-containing ether compound] The fluorine-containing ether compound of the present embodiment is represented by the following formula (1): １ -CH２ -R ２ [-CH ２ -R ３ -CH ２ -R ２ ] ｘ -CH ２ -R ４ (1) (In formula (1), x represents 1 or 2. R ２ is a perfluoropolyether chain. (x+1) R ２ may be the same in part or in whole, or may be different from each other. ３ is a divalent linking group having 1 to 50 carbon atoms and 1 to 6 polar groups. ３ At least one of R is a divalent linking group represented by the following formula (2): １ and R ４ is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms. １ and R ４ may be the same or different.)

[0055] (In formula (2), a and b each independently represent 0 or 1, and a and b cannot simultaneously represent 0. X and Y each independently represent an acyclic divalent saturated hydrocarbon group having 3 to 20 carbon atoms and having 1 or 2 polar groups. The saturated hydrocarbon group may contain an ether oxygen atom between carbon atoms, and the polar group of the saturated hydrocarbon group is bonded to a carbon atom other than the bonding terminal of the saturated hydrocarbon group.)

[0056] The fluorine-containing ether compound of the present embodiment is, as represented by formula (1), ３ and a divalent linking group represented by R ２ and a perfluoropolyether chain (hereinafter sometimes referred to as a PFPE chain) represented by the following formula (1) are connected via a methylene group to form a skeleton. １ and the other end of the skeleton is connected via a methylene group to an end group represented by R ４ The terminal group shown in is attached.

[0057] In the fluorine-containing ether compound represented by formula (1), x is 1 or 2. In the fluorine-containing ether compound represented by formula (1), x is 1 or 2, so that R ２ The number of PFPE chains (x+1) represented by the formula (1) is 2 or 3. Therefore, the fluorine-containing ether compound represented by the formula (1) is different from a compound having one PFPE chain, in that the number of adjacent R ２ A divalent linking group R ３ In addition, the fluorine-containing ether compound represented by formula (1) is ３ At least one of the PFPE chains is a divalent linking group represented by formula (2). As a result, the fluorine-containing ether compound represented by formula (1) has polar groups sufficiently arranged in the central part of the molecule, and can form a lubricating layer having excellent adhesion to a protective layer, as compared with, for example, a compound having one PFPE chain.

[0058] In addition, the fluorine-containing ether compound represented by formula (1) is not too large in molecule compared with the compound having 4 or more PFPE chains, and can move freely.Therefore, compared with the compound having 4 or more PFPE chains, the fluorine-containing ether compound represented by formula (1) is more likely to wet and spread on the protective layer, and can form a thin and uniform lubricating layer.In order to form a more uniform lubricating layer, x is preferably 1.

[0059] (R ３ In the fluorine-containing ether compound represented by formula (1), R ３ is a divalent linking group having 1 to 50 carbon atoms and having 1 to 6 polar groups.

[0060] x R in formula (1) ３ One of the R ３ Since the number of polar groups contained in is one or more, when a lubricating layer is formed on a protective layer using a lubricant containing a fluorine-containing ether compound represented by formula (1), a favorable interaction occurs between the lubricating layer and the protective layer. As a result, a lubricating layer that has excellent adhesion to the protective layer and further has favorable intermolecular interaction between the polar groups can be formed, thereby suppressing spin-off can be formed. ３The number of polar groups contained in the compound (I) may be 2 or more, or 3 or more, so that the resulting fluorine-containing ether compound has excellent adhesion to the protective layer.

[0061] x R ３ One of the R ３ Since the number of polar groups contained in x R is 6 or less, in a lubricating layer containing a fluorine-containing ether compound represented by formula (1), it is possible to prevent the polarity of the fluorine-containing ether compound from being too high, causing the fluorine-containing ether compound to aggregate and form clumps, which would result in the loss of smoothness of the lubricating layer. ３ One of the R ３ The number of polar groups contained in R is preferably 4 or less. ３ When the number of polar groups contained in the compound is 4 or less, a particularly smooth lubricating layer is easily obtained, and the resulting fluorine-containing ether compound is capable of forming a lubricating layer that provides good flying stability.

[0062] x R in formula (1) ３ At least one of the groups is a divalent linking group represented by formula (2). That is, when x is 1, R ３ is expressed by formula (2), and when x is 2, one or both of R ３ is expressed by equation (2).

[0063] In formula (1), x is 2 and two R ３ are each a divalent linking group represented by formula (2), two R ３ may be the same or different. ３ When the two R ３ "The two R ３ The atoms contained in are R located at the center of the molecule. ２ This means that the elements are arranged symmetrically with respect to each other.

[0064] The number of polar groups contained in the divalent linking group represented by formula (2) is 3 or more. Therefore, when x in formula (1) is 1, R ３The number of polar groups contained in is 3 or more.Therefore, when a lubricating layer is formed on a protective layer using a lubricant containing a fluorine-containing ether compound in which x in formula (1) is 1, a favorable interaction occurs between the lubricating layer and the protective layer.Therefore, the fluorine-containing ether compound has excellent adhesion to the protective layer, and further, the intermolecular interaction between the polar groups is favorably formed, and the lubricating layer can be formed to suppress spin-off.

[0065] In formula (1), x is 2 and one of R ３ does not correspond to formula (2), two R ３ The total number of polar groups in one of the R ３ is a divalent linking group represented by formula (2) containing three or more polar groups, so the other R ３ Even if the compound does not fall under the formula (2) and has only one polar group, the interaction between the polar group and the protective layer can be effectively obtained.

[0066] In formula (1), x is 2 and both R ３ is formula (2), two R ３ The number of polar groups contained in may be the same or different, but is preferably the same, because the coating state of the fluorine-containing ether compound on the protective layer becomes more uniform, and a lubricating layer with better adhesion can be formed.

[0067] In formula (1), x is 2 and both R ３ is formula (2), two R ３ The total number of polar groups contained in the two R ３ The polar group of the fluorine-containing ether compound effectively interacts with the protective layer. As a result, the fluorine-containing ether compound can form a lubricating layer that has high adhesion to the protective layer. Therefore, a lubricating layer with better spin-off resistance can be obtained.

[0068] In formula (1), when x is 2, two R ３The total number of polar groups in the lubricating layer containing the fluorine-containing ether compound in which x in formula (1) is 2 can be prevented from being too high in polarity, causing the fluorine-containing ether compound to aggregate and form lumps, resulting in loss of smoothness of the lubricating layer. ３ In addition, in the formula (1), x is 2 and one of R ３ does not correspond to formula (2), it is more preferable that the total number of polar groups contained in the divalent linking group represented by formula (2) and the number of polar groups contained in the divalent linking group not corresponding to formula (2) is 6 or less.

[0069] R ３ The polar groups contained in each of the formula (I) and (II) are independently a hydroxyl group (-OH), a carboxyl group (-COOH), a formyl group (-(C=O)H), a carbonyl group (-(C=O)R ７ ;R ７ is an organic group, a sulfo group (-SO ３ H), a cyano group (—CN), and a group having an amide bond (—NR ８ COR ９ or -CONR １０ R １１ ;R ８ , R ９ , R １０ and R １１ are each independently a hydrogen atom or an organic group; an amino group (—NR １２ R １３ ;R １２ and R １３ are each independently a hydrogen atom or an organic group.) The group having an amide bond is preferably a group bonded at a carbon atom constituting the amide bond as shown in the above formula (for example, a carboxamide group (-C(=O)NH ２ )) and a group bonding at a nitrogen atom constituting an amide bond (for example, an acetamide group (—NHC(═O)CH ３ In the group having an amide bond, the R ８ and R ９ may be bonded to each other to form a ring,１０ and R １１ may be bonded to each other to form a ring. ８ , R ９ , R １０ and R １１ are preferably each independently selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, and a butyl group.

[0070] R ３ Preferably, the lubricating layer contains at least one polar group selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond. This is because the hydroxyl group, the cyano group, and the group having an amide bond are chemically stable, and a lubricating layer containing a fluorine-containing ether compound having these polar groups will not deteriorate over the long term. In addition, the hydroxyl group, the cyano group, and the group having an amide bond are not too acidic and are unlikely to corrode the substrate.

[0071] x R in formula (1) ３ Each of the R preferably contains at least one hydroxyl group as a polar group. This is because the state of coating of the fluorine-containing ether compound on the protective layer becomes more uniform. In this embodiment, x R ３ It is preferable that all of the polar groups contained in R are hydroxyl groups. ３ When all of the polar groups of are hydroxyl groups, the fluorine-containing ether compound can be more uniformly coated on the protective layer.

[0072] x R in formula (1) ３ One of the R ３ The number of carbon atoms contained in one R is 1 to 50. ３ Since the number of carbon atoms contained in is 1 or more, R ３ This allows the polarity of the divalent linking group represented by the formula (I) to be kept low. This prevents the fluorine-containing ether compound from aggregating and forming clumps, making it possible to form a lubricating layer that provides good flying stability. ３ The number of carbon atoms contained in is preferably 2 or more, and more preferably 3 or more.

[0073] Also, x R ３The number of carbon atoms contained in the divalent linking group represented by formula (2), which is at least one of the above, is 7 or more. Therefore, the polarity of the divalent linking group represented by formula (2) can be maintained low, and the fluorine-containing ether compound can be prevented from aggregating and forming clumps, resulting in a lubricating layer with good flying stability.

[0074] One R ３ Since the number of carbon atoms contained in is 50 or less, R ３ The divalent linking group represented by the formula (I) has a flexible structure, which improves the adhesion between the lubricating layer containing the fluorine-containing ether compound and the protective layer, thereby providing a lubricating layer that can suppress spin-off. ３ The number of carbon atoms contained in the alkyl group is preferably 30 or less, and more preferably 16 or less.

[0075] (a divalent linking group represented by formula (2)) x R ３ The divalent linking group represented by formula (2) is at least one of R ２ A methylene group (-CH ２ The divalent linking group represented by formula (2) has an oxygen atom (ether oxygen atom) bonded to a polar group (-O-). The oxygen atom located at the end of the divalent linking group represented by formula (2) forms an ether bond (-O-) with the atoms bonded to both sides of it. This ether bond imparts appropriate flexibility to the fluorine-containing ether compound represented by formula (1) and increases the affinity between the polar group of the divalent linking group represented by formula (2) and the protective layer. As a result, the fluorine-containing ether compound represented by formula (1) can form a lubricating layer that has excellent adhesion to the protective layer.

[0076] The linking group represented by formula (2) has an erythritol structure (—O—CH ２ -CH(OH)-CH(OH)-CH ２ -O-). Therefore, the fluorine-containing ether compound represented by formula (1) has, at the center of the molecule, a hydroxyl group capable of interacting with the protective layer and a hydroxyl group capable of participating in intermolecular interactions. Therefore, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) has good flying stability and suppresses spin-off.

[0077] In formula (2), a and b are each independently 0 or 1, and a and b are not both 0. In formula (2), X and Y are each independently an acyclic, divalent, saturated hydrocarbon group having 3 to 20 carbon atoms and 1 or 2 polar groups.

[0078] The polar groups contained in X and Y in formula (2) include the above-mentioned R ３ Examples of the polar group contained in X and Y include those exemplified above. The polar group contained in X and Y is more preferably a polar group selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond. This is because the hydroxyl group, the cyano group, and the group having an amide bond are chemically stable, and the lubricating layer containing the fluorine-containing ether compound having these polar groups does not deteriorate over the long term. In addition, the group having a hydroxyl group, a cyano group, and an amide bond is not too acidic, and therefore does not corrode the substrate.

[0079] It is preferable that all of the polar groups contained in X and Y in formula (2) are hydroxyl groups. That is, it is preferable that all of the polar groups contained in formula (2) are hydroxyl groups. In this case, the coating state of the lubricating layer containing the fluorine-containing ether compound on the protective layer becomes more uniform, and the flying stability becomes even better.

[0080] X and Y each independently have 1 to 2 polar groups. Therefore, the total number of polar groups possessed by a Xs and b Ys is 1 to 4. Since the total number of polar groups is 1 or more, when a lubricating layer is formed on a protective layer using a lubricant containing a fluorine-containing ether compound, the polar group possessed by X or Y in formula (2) can be involved in interaction with the protective layer and / or intermolecular interaction. Therefore, the resulting fluorine-containing ether compound can form a lubricating layer with good flying stability and a high spin-off suppression effect.

[0081] In addition, since the total number of polar groups possessed by a X's and b Y's is 4 or less, the polarity of the fluorine-containing ether compound can be prevented from becoming too high and agglomerating to form lumps, resulting in a fluorine-containing ether compound capable of forming a lubricating layer with high flying stability. The total number of polar groups possessed by a X's and b Y's is preferably 2 or less, so that the fluorine-containing ether compound can form a lubricating layer with even better flying stability.

[0082] The polar group of the divalent saturated hydrocarbon group forming X and Y is bonded to a carbon atom other than the bond terminal of the divalent saturated hydrocarbon group. Therefore, the number of carbon atoms in X and Y is independently 3 or more. Since the number of carbon atoms in X and Y is 3 or more, X and Y are appropriately rigid, suppressing intramolecular interactions of the polar groups contained in formula (2). Furthermore, since the number of carbon atoms in X and Y is independently 20 or less, X and Y are prevented from becoming too bulky, hindering the movement of the polar groups in formula (2), and inhibiting the interaction of the polar groups contained in formula (2) with the protective layer. The number of carbon atoms in X and Y is preferably 3 to 10, and more preferably 3 to 6.

[0083] Since X and Y in formula (2) are acyclic divalent saturated hydrocarbon groups, the linking group represented by formula (2) is too bulky compared to when X and Y have a cyclic structure, which can prevent the movement of the polar group in formula (2) from being hindered and the interaction with the protective layer from being inhibited. X and Y may be linear divalent saturated hydrocarbon groups or may be branched. It is more preferable that X and Y are linear divalent saturated hydrocarbon groups because they can move more flexibly.

[0084] The divalent saturated hydrocarbon group forming X and Y may contain an ether oxygen atom between the carbon atoms. Such X and / or Y may be, for example, a group having two -CH ２ -CH(OH)-CH ２ Between the -, a methylene group (-CH ２ A structure in which an oxygen atom (ether oxygen atom) bonded to a hydroxyl group (-CH ２ -CH(OH)-CH ２-O-CH ２ -CH(OH)-CH ２ -) etc.

[0085] Formula (2) is preferably a linking group represented by any one of the following formulas (2-1) to (2-4): In formulas (2-1) to (2-4), the oxygen atom at the left terminal is R １ The oxygen atom at the right end is bonded to the methylene group at the side of the ４ It bonds to the methylene group on the side.

[0086] (In formula (2-1), c represents an integer of 1 to 6. A １ represents a polar group.) (In formula (2-2), d represents an integer of 1 to 6. A ２ represents a polar group.) (In formula (2-3), e1 represents an integer of 1 to 6. e2 represents an integer of 1 to 6. A ３１ , A ３２ each independently represents a polar group.

[0087] A in formula (2-1) １ , A in formula (2-2) ２ , A in formula (2-3) ３１ , A ３２ The polar groups represented by the formula (2) can be those described as the polar groups contained in X and Y, and each independently represents a hydroxyl group or an acetamide group (—NHC(═O)CH ３ ) is preferred.

[0088] The divalent linking group represented by formula (2-1) is a group in which a in formula (2) is 1, b is 0, and X in formula (2) is a polar group A １ In formula (2-1), c represents an integer of 1 to 6.

[0089] The divalent linking group represented by formula (2-1) has, in addition to the hydroxyl group of the erythritol structure, a terminal ether oxygen atom in the erythritol structure and R １ A polar group A bonded to a linear saturated hydrocarbon group sandwiched between an ether oxygen atom bonded to a methylene group on the side １ This polar group A １is particularly likely to be involved in interaction with the protective layer because it can move flexibly. As a result, when the divalent linking group represented by formula (2) is a divalent linking group represented by formula (2-1), the central portion of the fluorine-containing ether compound is less likely to lift off from the protective layer, resulting in a lubricating layer with better lifting stability.

[0090] The divalent linking group represented by formula (2-2) is a group in which a in formula (2) is 0, b is 1, and Y in formula (2) is a polar group A ２ In formula (2-2), d represents an integer of 1 to 6.

[0091] The divalent linking group represented by formula (2-2) has, in addition to the hydroxyl group of the erythritol structure, a terminal ether oxygen atom in the erythritol structure and R ４ A polar group A bonded to a linear saturated hydrocarbon group sandwiched between an ether oxygen atom bonded to a methylene group on the side ２ This polar group A ２ is particularly likely to be involved in interaction with the protective layer because it can move flexibly. As a result, when the divalent linking group represented by formula (2) is a divalent linking group represented by formula (2-2), the central portion of the fluorine-containing ether compound is less likely to lift off from the protective layer, resulting in a lubricating layer with better lifting stability.

[0092] Since c in the linking group represented by formula (2-1) and d in the linking group represented by formula (2-2) are 1 or more, the polarity of the divalent linking group can be maintained low. Therefore, the fluorine-containing ether compound can be prevented from agglomerating and forming lumps, resulting in a lubricating layer with better flying stability. Furthermore, since c and d are 6 or less, the divalent linking groups represented by formula (2-1) and formula (2-2) have a flexible structure, the adhesion between the lubricating layer containing this and the protective layer is improved, and a lubricating layer that can effectively suppress spin-off can be obtained. c and d are each independently preferably 1 to 4, more preferably 1 to 2.

[0093] The divalent linking group represented by formula (2-3) is a group represented by formula (2) in which a is 1, b is 1, and X in formula (2) is a polar group A ３１Y in formula (2) is a linear saturated hydrocarbon group having one polar group A ３２ In formula (2-3), e1 represents an integer of 1 to 6, and e2 represents an integer of 1 to 6.

[0094] The divalent linking group represented by formula (2-3) has, in addition to the hydroxyl group of the erythritol structure, a terminal ether oxygen atom in the erythritol structure and R １ A polar group A bonded to a linear saturated hydrocarbon group sandwiched between an ether oxygen atom bonded to a methylene group on the side ３１ and a terminal ether oxygen atom in the erythritol structure, and R ４ A polar group A bonded to a linear saturated hydrocarbon group sandwiched between an ether oxygen atom bonded to a methylene group on the side ３２ This polar group A ３１ , A ３２ is capable of flexible movement, and therefore is likely to be involved not only in interaction with the protective layer but also in intermolecular interactions. As a result, when the divalent linking group represented by formula (2) is a divalent linking group represented by formula (2-3), the intermolecular interactions between the fluorine-containing ether compounds become stronger, resulting in a lubricating layer with even better spin-off resistance.

[0095] In the linking group represented by formula (2-3), e1 and e2 are 1 or more, so the polarity of the divalent linking group can be maintained low. Therefore, the fluorine-containing ether compound can be prevented from agglomerating and forming a lubricating layer with better flying stability. In addition, since e1 and e2 are 6 or less, the divalent linking group represented by formula (2-3) has a flexible structure, and the adhesion between the lubricating layer containing this and the protective layer is improved, so that a lubricating layer that can effectively suppress spin-off can be obtained. e1 and e2 are each independently preferably 1 to 4, more preferably 1 to 2.

[0096] In the linking group represented by formula (2-3), e1 and e2 may be the same or different. When e1 and e2 are the same, the state of coverage of the fluorinated ether compound on the protective layer becomes more uniform, which is preferable.

[0097] The divalent linking group represented by formula (2-4) is one in which a in formula (2) is 1, b is 0, and X in formula (2) is a linear saturated hydrocarbon group having two hydroxyl groups (or, a in formula (2) is 0, b is 1, and Y in formula (2) is a linear saturated hydrocarbon group having two hydroxyl groups).

[0098] The divalent linking group represented by formula (2-4) is a structure in which two erythritol structures are linked by sharing their oxygen atoms. The two internal 1,2-diol structures (—CH ２ -CH(OH)-CH(OH)-CH ２ The hydroxyl group in the formula (2-4) is unlikely to form intramolecular interactions. For this reason, the fluorine-containing ether compound containing the divalent linking group represented by formula (2-4) is prevented from aggregating and forming clumps, and can form a lubricating layer with good flying stability.

[0099] Examples of the divalent linking group represented by formula (2) include divalent linking groups represented by the following formulas. Examples of the linking group represented by formula (2-1) include formulas (2-1A) to (2-1D). Examples of the linking group represented by formula (2-2) include formulas (2-2A) to (2-2D). Examples of the linking group represented by formula (2-3) include formulas (2-3A) to (2-3F). The divalent linking group represented by formula (2) is not limited to these divalent linking groups.

[0100] The dotted lines in the following formulas (2-1A) to (2-1D), (2-2A) to (2-2D), and (2-3A) to (2-3F) represent the R ３ In these formulas, the oxygen atom at the left end is a bond bonded to the methylene group adjacent to R in formula (1). １ The oxygen atom at the right end is bonded to the methylene group at the side of the ４ It bonds to the methylene group on the side.

[0101]

[0102] (Divalent linking group not corresponding to formula (2)) In formula (1), x is 2 and two R ３When only one of the groups is a divalent linking group represented by formula (2) and the other is a divalent linking group not corresponding to formula (2), the divalent linking group not corresponding to formula (2) is a methylene group (-CH ２ Preferably, the divalent linking group has 3 to 16 carbon atoms, 1 to 3 hydroxyl groups, and forms an ether bond (—O—) with the alkyl group (—). Furthermore, the divalent linking group that does not fall under the formula (2) preferably has a linear saturated hydrocarbon group having 3 to 16 carbon atoms that may contain an ether oxygen atom between the carbon atoms, and a hydroxyl group bonded to a carbon atom other than the terminal of the saturated hydrocarbon group.

[0103] In particular, the divalent linking group not corresponding to formula (2) has a glycerin structure (—O—CH ２ -CH(OH)-CH ２ the hydroxyl group of a structure in which a glycerin structure is increased by a methylene group; the hydroxyl group of an erythritol structure (—O—CH ２ -CH(OH)-CH(OH)-CH ２ It is preferable that the divalent linking group contains a hydroxyl group selected from the group consisting of a hydroxyl group of the formula (1) (—O—) and a hydroxyl group of a structure in which two hydroxyl groups of an erythritol structure are connected by a methylene group. The reason for this is that the hydroxyl group of a divalent linking group that does not fall under formula (2) is likely to be involved in interactions with active sites on the protective layer and in intermolecular interactions.

[0104] Specific examples of divalent linking groups that do not fall under formula (2) include any of the divalent linking groups represented by the following formulae (XA) to (XL). The divalent linking groups that do not fall under formula (2) are not limited to these divalent linking groups. The divalent linking groups that do not fall under formula (2) are preferably any of the divalent linking groups represented by the following formulae (XA) to (XL) because they are easy to produce. The dotted lines in the following formulae (XA) to (XL) represent the positions of R in formula (1). ３ In these formulas, the oxygen atom at the left end is a bond bonded to the methylene group adjacent to R in formula (1). １ The oxygen atom at the right end is bonded to the methylene group at the side of the ４ It bonds to the methylene group on the side.

[0105]

[0106] (R １ and R ４ In the fluorine-containing ether compound represented by formula (1), R １ and R ４ are terminal groups having 1 to 4 polar groups and 1 to 50 carbon atoms. １ and R ４ are the above-mentioned terminal groups, a lubricating layer containing a fluorine-containing ether compound represented by formula (1) can obtain good flying stability and has a high spin-off suppressing effect. １ and R ４ can be appropriately selected depending on the performance required of the lubricant containing the fluorine-containing ether compound. １ and R ４ may be the same or may be different from each other.

[0107] R １ and R ４ Since the number of polar groups contained in each of R is one or more, 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. Therefore, the lubricating layer has excellent adhesion to the protective layer. １ and R ４ Since the number of polar groups contained in each of R is four or less, it is possible to prevent the fluorine-containing ether compound from aggregating into clumps in the lubricating layer containing the fluorine-containing ether compound due to excessively high polarity of the fluorine-containing ether compound. １ and R ４ The number of polar groups contained in each of the above is preferably 2 to 4, and more preferably 2 to 3, in order to obtain a fluorine-containing ether compound that provides a lubricating layer with better flying stability and spin-off suppression effect.

[0108] R １ The number of polar groups in R ４ The number of polar groups in R may be the same or different. １ The number of polar groups in R ４and the number of polar groups therein are preferably the same, since this results in a more uniform coating state of the fluorine-containing ether compound on the protective layer and allows the formation of a lubricating layer with better adhesion.

[0109] R in formula (1) １ The polar group contained in R ４ The total number of polar groups contained in R is preferably 2 to 6, more preferably 3 to 6, and most preferably 4 to 6. When the total number of polar groups is 2 or more, R １ and R ４ The interaction between the polar groups contained in the protective layer and the protective layer is effectively obtained. As a result, the fluorine-containing ether compound has high adhesion to the protective layer and can form a lubricating layer with strong intermolecular interaction. Furthermore, when the total number of the polar groups is 6 or less, the polarity of the fluorine-containing ether compound is too high, and aggregation to form lumps can be prevented.

[0110] R １ and R ４ The 1 to 4 polar groups each have may be the same in part or in whole, or may be different from each other. １ and R ４ The polar group contained in the above-mentioned R ３ Examples of the polar group contained in R include those exemplified above. １ and R ４ The polar group contained in R in formula (1) is preferably a polar group selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond. １ and R ４ Each of R preferably contains at least one hydroxyl group, １ and a polar group having R ４ It is more preferable that all of the polar groups contained in the hydroxyl group are hydroxyl groups.

[0111] In addition, the fluorine-containing ether compound is more uniformly coated on the protective layer, so that R １ and a polar group having R ３ and a polar group having R ４ It is more preferable that all of the polar groups contained in the compound are hydroxyl groups.

[0112] R １ and R ４ The number of carbon atoms in the terminal group represented by R is 1 to 50, preferably 3 to 20, and more preferably 4 to 15. １ and R ４ Since the number of carbon atoms in the terminal group represented by R is 1 or more, the polarity of the terminal group can be kept low. Therefore, it is possible to prevent the fluorine-containing ether compound from having too high a polarity and agglomerating to form a mass. １ and R ４ Since the number of carbon atoms in the terminal group represented by the formula (I) is 50 or less, the terminal group has a flexible structure, and the adhesion between the lubricating layer containing the fluorine-containing ether compound and the protective layer is improved.

[0113] In the fluorine-containing ether compound represented by formula (1), R １ and R ４ are each independently an end group represented by the following formula (3), since this improves the adhesion between the lubricating layer containing the fluorine-containing ether compound and the protective layer.

[0114] (In formula (3), l represents an integer of 0 to 3. o represents 0 or 1. At least one of l and o is 1 or greater. When l represents 1 to 3, l m's each independently represent an integer of 1 to 6, and l n's each independently represent an integer of 1 to 6, and in one structural unit, at least one of m and n is 1. B represents an organic group having 1 to 30 carbon atoms which may contain at least one of a polar group, a halogeno group, and an ether oxygen atom, or a hydrogen atom. However, the total number of polar groups included in formula (3) is 1 to 4.)

[0115] R １ and R ４ is a terminal group represented by formula (3), R １ and R ４ is R ２ A methylene group (-CH ２ -), i.e., R １ and R ４ is R １ and R ４ -CH adjacent to each２ It has an oxygen atom at the end that bonds to -. １ and R ４ The oxygen atom located at the end of R forms an ether bond (—O—) with the atoms bonded to both sides of it. This ether bond imparts appropriate flexibility to the fluorine-containing ether compound represented by formula (1), and １ and R ４ This increases the affinity between the protective layer and the polar group in the terminal group represented by formula (1). As a result, the fluorine-containing ether compound represented by formula (1) can form a lubricating layer that has excellent adhesion to the protective layer.

[0116] At least one of l and o in formula (3) is 1 or more. When o in formula (3) is 0, l is an integer of 1 to 3, preferably an integer of 1 to 2. When o in formula (3) is 0 and l is 3 or less, the polarity of the terminal group represented by formula (3) is too high, so that the fluorinated ether compound can be prevented from aggregating and forming clumps. When o in formula (3) is 1, l is an integer of 0 to 2, preferably an integer of 0 to 1. When o in formula (3) is 1 and l is 2 or less, the polarity of the terminal group represented by formula (3) is too high, so that the fluorinated ether compound can be prevented from aggregating and forming clumps.

[0117] In formula (3), l m's each independently represent an integer of 1 to 6, and l n's each independently represent an integer of 1 to 6. When l in formula (3) is 2 or 3, two or three structural units (-(CH ２ ) ｍ -CH(OH)-(CH ２ ) ｎ The combinations of m and n in —O—) may be different from one another, or some or all of them may be the same.

[0118] One structural unit (-(CH ２ ) ｍ -CH(OH)-(CH ２ ) ｎIn the formula (I), at least one of m and n is 1. This is because the mobility of the hydroxyl group in the structural unit is not reduced due to the alkylene group having too many carbon atoms between the carbon atom to which the hydroxyl group is bonded and the ether oxygen atom.

[0119] In formula (3), B is a hydrogen atom or an organic group having 1 to 30 carbon atoms which may contain at least one of a polar group, a halogeno group, and an ether oxygen atom. When B is an organic group having 1 to 30 carbon atoms, the number of carbon atoms in B is 1 or more, so that the terminal group represented by formula (3) is appropriately rigid, thereby suppressing intramolecular interactions. Furthermore, since B has 30 or less carbon atoms, the terminal group represented by formula (3) is prevented from becoming too bulky, hindering the movement of the polar group and inhibiting interaction with the protective layer. When B is an organic group having 1 to 30 carbon atoms, the number of carbon atoms in B is preferably 1 to 15, and more preferably 2 to 10.

[0120] In formula (3), when B is an organic group having 1 to 30 carbon atoms, B may contain a polar group. In this case, the adhesion of the fluorine-containing ether compound represented by formula (1) to the protective layer is improved, and it is easy to form a lubricating layer that can provide a sufficient coating state even if the thickness is reduced. When B contains a polar group, the number of polar groups is preferably one. In this case, it is possible to further prevent the polarity of the fluorine-containing ether compound represented by formula (1) from becoming too high and agglomerating to form clumps.

[0121] When B in formula (3) contains a polar group, the polar group may be any of the above-mentioned R ３ The polar group contained in B in formula (3) is more preferably a polar group selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond.

[0122] In formula (3), when B is an organic group having 1 to 30 carbon atoms, B may have a halogeno group. In this case, the surface free energy of B in formula (3) is lowered compared to when the organic group does not have a halogeno group. As a result, a fluorine-containing ether compound is obtained that can form a lubricating layer with excellent lubricity and smoothness. When B in formula (3) contains a halogeno group, the halogeno group is preferably a fluoro group or a chloro group, and more preferably a fluoro group. This is because it has a significant effect of lowering the surface free energy of B.

[0123] In formula (3), when B is an organic group having 1 to 30 carbon atoms, B may contain an ether oxygen atom. When B contains an ether oxygen atom, the ether oxygen atom contained in B imparts appropriate flexibility to the fluorinated ether compound represented by formula (1) and increases the affinity between the polar group and the protective layer. When B contains an ether oxygen atom, the number of ether oxygen atoms contained in B is preferably 1 or 2. In this case, the fluorinated ether compound represented by formula (1) can be prevented from becoming too flexible and causing intramolecular interactions.

[0124] In formula (3), when B is an organic group having 1 to 30 carbon atoms, B is preferably an acyclic organic group. When B is acyclic, compared to when B has a cyclic structure, it is possible to prevent the bulkiness of B from being too large, which would hinder the movement of the polar group and inhibit the interaction with the protective layer. The acyclic organic group may be linear or branched. When B is a linear organic group, the mobility of the polar group is increased, and a favorable interaction with the protective layer is obtained, which is more preferable.

[0125] In the formula (3), when B is a hydrogen atom, it bonds with an adjacent oxygen atom to form a terminal hydroxyl group. In this case, a hydroxyl group located at the end of the molecule is preferred because it exhibits good interaction with the protective layer.

[0126] When B in formula (3) is an organic group having a polar group, examples of B include a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 4-hydroxybutyl group, a 5-hydroxypentyl group, a 6-hydroxyhexyl group, a 2-aminoethyl group, a 3-aminopropyl group, a 2-carboxyethyl group, a 3-carboxypropyl group, a 2-carbonylethyl group, a 3-carbonylpropyl group, a 2-acetylethyl group, a 3-acetylpropyl group, a 2-sulfoethyl group, a 3-sulfopropyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, a 4-cyano Examples of the alkyl group include a butyl group, a 2-acetamidoethyl group, a 3-acetamidopropyl group, a 4-acetamidobutyl group, a 2-carboxamidoethyl group, a 3-carboxamidopropyl group, a 4-carboxamidobutyl group, a cyanophenyl group, a carboxamidophenyl group, an acetamidophenyl group, a cyanonaphthyl group, a carboxamidonaphthyl group, an acetamidonaphthyl group, a cyanophenethyl group, a carboxamidophenethyl group, an acetamidophenethyl group, a cyanobenzyl group, a carboxamidobenzyl group, and an acetamidobenzyl group.

[0127] Among the above organic groups having a polar group, B is preferably any one of a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 4-hydroxybutyl group, a 5-hydroxypentyl group, a 6-hydroxyhexyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, a 2-acetamidoethyl group, a 2-carboxamidoethyl group, a 3-carboxamidopropyl group, a cyanophenyl group, a carboxamidophenyl group, an acetamidophenyl group, a cyanobenzyl group, a carboxamidobenzyl group, and an acetamidobenzyl group, and more preferably any one of a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, a 2-acetamidoethyl group, a cyanophenyl group, a carboxamidophenyl group, and an acetamidophenyl group.

[0128] When B in formula (3) is an organic group having no polar group, examples of B include a methyl group, an ethyl group, a propyl group, a butyl group, a vinyl group, an allyl group, a butenyl group, a propynyl group, a propargyl group, a butynyl group, a methylbutynyl group, a pentynyl group, a methylpentynyl group, a hexynyl group, a phenyl group, a naphthyl group, a benzyl group, a phenethyl group, a naphthylmethyl group, a pyrrolyl group, a pyrazolyl group, a methylpyrazolylmethyl group, an imidazolyl group, a furyl group, a furfuryl group, an oxazolyl group, an isoxazolyl group, a thienyl group, a thienylethyl group, a thiazolyl group, a methylthiazolylethyl group, an isothiazolyl group, a pyridyl group, a pyrimidinyl group, a pyridazolyl group, a nyl group, pyrazinyl group, indolinyl group, benzofuranyl group, benzothienyl group, benzimidazolyl group, benzoxazolyl group, benzothiazolyl group, benzopyrazolyl group, benzisoxazolyl group, benzisothiazolyl group, quinolyl group, isoquinolyl group, quinazolinyl group, quinoxalinyl group, phthalazinyl group, cinnolinyl group, trifluoroethyl group, pentafluoropropyl group, heptafluorobutyl group, phenyl fluoride group, benzyl fluoride group, phenethyl fluoride group, methoxyethyl group, phenoxyethyl group, methoxyphenyl group, methoxynaphthyl group, methoxybenzyl group, and methoxyphenethyl group.

[0129] Among the above organic groups not having a polar group, B is preferably any one of a methyl group, an ethyl group, an allyl group, a butenyl group, a propargyl group, a phenyl group, a naphthyl group, a benzyl group, a phenethyl group, a thienylethyl group, a trifluoroethyl group, a pentafluoropropyl group, a fluorinated phenyl group, a methoxyethyl group, and a methoxyphenyl group, and more preferably any one of a methyl group, an allyl group, a butenyl group, a phenyl group, a benzyl group, a trifluoroethyl group, a pentafluoropropyl group, and a methoxyphenyl group.

[0130] R １ and R ４ are each independently a terminal group represented by any one of formulas (3-1) to (3-5).

[0131] (In formula (3-1), p represents 0 or 1. q1, q2, q3, and q4 each independently represent an integer of 1 to 6. When p is 0, the total value of q1 and q4 is 2 to 10. When p is 1, the total value of q1, q2, q3, and q4 is 4 to 10, and at least one of q2 and q3 is 1. D represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when D is the aryl group which may have a substituent, the number of polar groups contained in D is 0 or 1.) (In formula (3-2), r represents 0 or 1. s1, s2, and s3 each independently represent an integer of 1 to 6. When r is 1, the total value of s1, s2, and s3 is 3 to 8, and at least one of s2 and s3 is 1.) (In formula (3-3), t1 and t2 each independently represent an integer of 1 to 6. E represents a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when E is the aryl group which may have a substituent, E does not contain a polar group.) (In formula (3-4), u represents an integer of 1 to 6. G represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when G is the aryl group which may have a substituent, the number of polar groups which may be included in G is 0 or 1.) (In formula (3-5), v represents 1 or 2. Each of the five Js independently represents a polar group, an alkoxy group having 1 to 8 carbon atoms, a halogeno group, or a hydrogen atom. However, when a polar group is included in the five Js, the number of polar groups among the five Js is 1.)

[0132] The terminal group represented by formula (3-1) is a glycerin structure (—O—CH ２ -CH(OH)-CH ２ -O-), or a structure in which a glycerin structure is increased in carbon atoms by a methylene group, or a structure in which two glycerin structures are linked together by sharing their respective oxygen atoms, or a structure in which glycerin structures are increased in carbon atoms by a methylene group are linked together by sharing their respective oxygen atoms, to which D is bonded via at least one methylene group.

[0133] The terminal group represented by formula (3-2) is a glycerin structure (—O—CH２ -CH(OH)-CH ２ -O-), or a structure in which a glycerin structure is increased in carbon atoms by a methylene group, or a structure in which two glycerin structures are linked together by sharing their respective oxygen atoms, or a structure in which two glycerin structures are increased in carbon atoms by a methylene group are linked together by sharing their respective oxygen atoms, and the structure has a hydroxyl group at the end.

[0134] The glycerin structure and / or the structure obtained by increasing the carbon content of the glycerin structure, which are contained in the terminal groups represented by formula (3-1) and formula (3-2), have appropriate rigidity. Therefore, the terminal groups represented by formula (3-1) and formula (3-2) can be prevented from forming intramolecular interactions. Furthermore, the ether bond contained in the glycerin structure and the structure obtained by increasing the carbon content of the glycerin structure imparts appropriate mobility to the terminal groups represented by formula (3-1) and formula (3-2). Therefore, the hydroxyl group contained in the terminal group represented by formula (3-1) and formula (3-2) is likely to be involved in the interaction with the protective layer. As a result, a fluorine-containing ether compound is obtained that can form a lubricating layer that exhibits favorable interaction with the protective layer.

[0135] In formula (3-1), D represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. When D is a polar group, D is the same as R ３ Among the above polar groups, a polar group selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond is more preferred, and a hydroxyl group is most preferred.

[0136] When D is an aryl group which may have a substituent, the number of polar groups contained in D is 0 or 1. When D is an aryl group which may have a substituent, an aryl group which may have a substituent included in the organic group which can be used for B in the above-mentioned formula (3) can be used.

[0137] In the terminal group represented by formula (3-1), p represents 0 or 1. When p is 0, the total value of q1 and q4 is 2 or more, and when p is 1, the total value of q1, q2, q3, and q4 is 4 or more. Therefore, the terminal group represented by formula (3-1) does not have too few carbon atoms in the main chain. Therefore, it is possible to prevent the polarity from being too high and the fluorine-containing ether compound from aggregating.

[0138] In the terminal group represented by formula (3-1), when p is 0, the total value of q1 and q4 is 10 or less, and when p is 1, the total value of q1, q2, q3, and q4 is 10 or less, and at least one of q2 and q3 is 1. Therefore, the terminal group represented by formula (3-1) does not have an excessively long alkylene chain in the main chain. 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.

[0139] q1, q2, q3, and q4 each independently represent an integer of 1 to 6. q1, q2, q3, and q4 each independently preferably represent an integer of 1 to 3, and more preferably represent an integer of 1 or 2. It is preferable that at least one of q1, q2, q3, and q4 is 2 or greater.

[0140] In the terminal group represented by formula (3-2), r represents 0 or 1. When r is 0, s1 is 1 or more, and when r is 1, the total value of s1, s2, and s3 is 3 or more. Therefore, the terminal group represented by formula (3-2) does not have too few carbon atoms in the main chain. Therefore, it is possible to prevent the polarity from being too high and the fluorine-containing ether compound from aggregating.

[0141] In the terminal group represented by formula (3-2), when r is 0, s1 is 6 or less, and when r is 1, the total value of s1, s2, and s3 is 8 or less, and at least one of s2 and s3 is 1. Therefore, the terminal group represented by formula (3-2) does not have an excessively long alkylene chain in the main chain. 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.

[0142] s1, s2, and s3 each independently represent an integer of 1 to 6. s1, s2, and s3 each independently preferably represent an integer of 1 to 3, and more preferably represent an integer of 1 or 2. At least one of s1, s2, and s3 is preferably 2 or greater.

[0143] The terminal group represented by formula (3-3) has a glycerin structure (—O—CH ２ -CH(OH)-CH ２ -O-) or a structure in which a glycerin structure is increased by a methylene group, and an erythritol structure (-O-CH ２ -CH(OH)-CH(OH)-CH ２ -O-) are linked by sharing their respective oxygen atoms, and E is bonded to the end of the linkage via at least one methylene group. The glycerin structure, the structure in which the glycerin structure is increased in carbon atoms by a methylene group, and the erythritol structure all have appropriate rigidity. Therefore, the hydroxyl group contained in the terminal group represented by formula (3-3) is inhibited from forming intramolecular interactions. In addition, since the ether bond possessed by the terminal group represented by formula (3-3) is flexible, the hydroxyl group in formula (3-3) is likely to be involved in interactions with the protective layer. As a result, a fluorine-containing ether compound having a terminal group represented by formula (3-3) can form a lubricating layer that exhibits favorable interactions with the protective layer.

[0144] E in formula (3-3) represents a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when E is the aryl group which may have a substituent, E does not contain a polar group. Since E in formula (3-3) does not contain a polar group, it is possible to prevent the polarity of the terminal group represented by formula (3-3) from being too high, and the fluorine-containing ether compound from aggregating into clumps.

[0145] In the terminal group represented by formula (3-3), t1 and t2 each independently represent an integer of 1 to 6. Because t1 and t2 are 1 or greater, the number of carbon atoms in the terminal group represented by formula (3-3) is not too small. This prevents the fluorine-containing ether compound from aggregating due to excessively high polarity. Furthermore, in the terminal group represented by formula (3-3), t1 and t2 are 6 or less. Therefore, the long rigid alkylene chain of the terminal group represented by formula (3-3) reduces the flexibility of the terminal portion, weakening the interaction with the protective layer and preventing the terminal portion from lifting up. t1 and t2 each independently preferably represent 1 to 3, more preferably 1 to 2.

[0146] The terminal group represented by formula (3-4) has an erythritol structure (—O—CH ２ -CH(OH)-CH(OH)-CH ２ —O—), and G is bonded to its terminal via at least one methylene group. Since the erythritol structure has a moderate rigidity, the hydroxyl group contained in the terminal group represented by formula (3-4) is inhibited from forming intramolecular interactions. Furthermore, since the ether bond of the terminal group represented by formula (3-4) is flexible, the hydroxyl group in formula (3-4) is likely to be involved in interactions with the protective layer. As a result, a fluorine-containing ether compound having a terminal group represented by formula (3-4) can form a lubricating layer that exhibits favorable interactions with the protective layer.

[0147] G in formula (3-4) represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when G is the aryl group which may have the substituent, the number of polar groups which may be contained in G is 0 or 1. Since the number of polar groups contained in G in formula (3-4) is 0 or 1, it is possible to prevent the polarity of the terminal group represented by formula (3-4) from being too high, and the fluorine-containing ether compound from aggregating into clumps.

[0148] In the terminal group represented by formula (3-4), u represents an integer of 1 to 6. Since u is 1 or more, the number of carbon atoms in formula (3-4) is not too small. Therefore, it is possible to prevent the fluorine-containing ether compound from aggregating due to excessively high polarity. Furthermore, since u is 6 or less, the flexibility of the terminal portion is reduced due to the long rigid alkylene chain, and the interaction between the hydroxyl group contained in the terminal group represented by formula (3-4) and the protective layer is weakened, preventing the terminal portion from lifting up. Furthermore, in the terminal group represented by formula (3-4), u is preferably 1 to 3, and more preferably 1 to 2.

[0149] In formula (3-5), v represents 1 or 2. Therefore, the terminal group represented by formula (3-5) is one glycerin structure (—O—CH ２ -CH(OH)-CH ２ -O-), or has an aryl group at the end of a structure in which two glycerin structures are linked by sharing their respective oxygen atoms. The glycerin structure has appropriate rigidity, and therefore can suppress the polar group in the terminal group represented by formula (3-5) from forming an intramolecular interaction. In addition, the ether bond in the glycerin structure imparts appropriate mobility to the terminal group represented by formula (3-5). Therefore, the polar group contained in the terminal group represented by formula (3-5) is likely to be involved in an interaction with the protective layer. As a result, a fluorine-containing ether compound having a terminal group represented by formula (3-5) can form a lubricating layer that exhibits favorable interaction with the protective layer.

[0150] In the terminal group represented by formula (3-5), five Js each independently represent a polar group, an alkoxy group having 1 to 8 carbon atoms, a halogeno group, or a hydrogen atom. When a polar group is included in the five Js, the number of polar groups among the five Js is 1. When a polar group is included in the five Js in formula (3-5), the position of the polar group may be any position of the five Js.

[0151] In the terminal group represented by formula (3-5), when the five Js contain polar groups, the benzene ring to which the polar groups are bonded is rigid and therefore difficult to rotate freely. Therefore, the hydroxyl group contained in the glycerin structure in formula (3-5) and the polar group contained in J can be prevented from forming an intramolecular interaction. Therefore, the fluorine-containing ether compound having the terminal group represented by formula (3-5) is prevented from aggregating into clumps.

[0152] In the terminal group represented by formula (3-5), when five Js contain polar groups, J is ３ Among the above polar groups, J is more preferably a polar group selected from the group consisting of a cyano group and a group having an amide bond, and is preferably a cyano group, an acetamide group (—NHC(═O)CH ３ ) or a carboxamide group (—C(═O)NH ２ ) is more preferably a polar group selected from the group consisting of. When the polar group is a polar group selected from the group consisting of a cyano group, an acetamide group, or a carboxamide group, the resulting fluorine-containing ether compound can form a lubricating layer with stronger interaction with the protective layer. In addition, since the acidity of a cyano group, an acetamide group, or a carboxamide group is not too high, a fluorine-containing ether compound having these groups hardly corrodes the substrate.

[0153] When the five J in formula (3-5) contain polar groups, some or all of the four J other than the polar groups may be the same, or may be different from each other. When the five J contain polar groups, it is preferable that all of the four J other than the polar groups are the same.

[0154] In the terminal group represented by formula (3-5), when no polar group is included in the five J's, the surface free energy of the fluorine-containing ether compound is lower than when one of the five J's is a polar group. Therefore, a lubricating layer containing a fluorine-containing ether compound having an terminal group represented by formula (3-5) will have excellent smoothness and lubricity.

[0155] In the terminal group represented by formula (3-5), when the five Js do not include a polar group, some or all of the five Js may be the same or different from each other. When the five Js are not polar groups, it is preferable that each of them independently represents a methoxy group, a fluoro group, or a hydrogen atom.

[0156] R １ and R ４ When is a terminal group that does not fall under the formula (3), it is also preferably represented by the following formula (3-6) or (3-7).

[0157] (In formula (3-6), g1 represents an integer of 1 to 6. g1 R ａ and R ｂ each independently represents a hydrogen atom or a methyl group.) (In formula (3-7), g2 represents an integer of 1 to 6.)

[0158] The terminal group represented by formula (3-6) has g1 -CR between two glycerin structures. ａ R ｂ - g 1 -CR ａ R ｂ - is -CH ２ -, -CH(CH ３ ) -, -C(CH ３ ) ２ - may be either.

[0159] In the terminal group represented by formula (3-6), when the organic group between the two glycerin structures has a linear structure, in other words, R ａ and R ｂ When is a hydrogen atom, the terminal group is not too bulky compared to when the organic group has a branch. Therefore, the movement of the hydroxyl groups of the two glycerin structures is hindered, and the interaction with the protective layer is prevented from being inhibited. As a result, the fluorine-containing ether compound can form a lubricating layer that exhibits favorable interaction with the protective layer.

[0160] In the terminal group represented by formula (3-6), when the organic group between the two glycerin structures is a branched structure, in other words, -CR ａ R ｂ - is -CH (CH ３)- and / or -C(CH ３ ) ２ When the glycerin structure contains -, the organic group becomes suitably rigid compared to when the organic group has a linear structure, and therefore, the intramolecular interaction between the hydroxyl groups of the two glycerin structures can be effectively suppressed, and the fluorinated ether compound represented by formula (1) can be prevented from aggregating into clumps.

[0161] In formula (3-6), g1 represents an integer of 1 to 6. Because g1 is 1 or more, the terminal group represented by formula (3-6) has appropriate rigidity. Furthermore, because g1 is 6 or less, the terminal group represented by formula (3-6) does not become too bulky, and it is possible to prevent the movement of the hydroxyl group in formula (3-6) from being hindered, thereby preventing the interaction with the protective layer from being inhibited. g1 is preferably 1 to 4, and more preferably 1 to 2.

[0162] The terminal group represented by formula (3-7) is a group in which the organic group between the two glycerin structures is -CH ２ -(CF ２ ) ｇ２ -CH ２ -. g2 represents an integer of 1 to 6. The terminal group represented by formula (3-7) contains a linear perfluoroalkylene chain having 1 to 6 carbon atoms, which reduces affinity with chemical substances in the environment. As a result, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) has excellent smoothness and lubricity.

[0163] Since g2 in formula (3-7) is 1 or more, the terminal group represented by formula (3-7) becomes appropriately rigid, and intramolecular interactions can be suppressed. Furthermore, since g2 is 6 or less, the terminal group represented by formula (3-7) does not become too bulky, and the movement of the hydroxyl group is prevented from being hindered, and the interaction with the protective layer is prevented from being inhibited. In formula (3-7), g2 is preferably 1 to 4, and more preferably 2 to 4.

[0164] When x in formula (1) is 2, the fluorine-containing ether compound contains R ３ Since formula (2) has 3 to 6 polar groups, x is 2 and at least one of R ３is represented by formula (2), the polarity of the fluorine-containing ether compound tends to be high. １ , R ４ Preferably, at least one of R contains at least one carbon atom that is not bonded to either a polar group or an ether oxygen atom. １ , R ４ The carbon atoms that are not bonded to either the polar group or the ether oxygen atom in the formula (1) are restricted in their movement, and therefore impart an appropriate rigidity to the fluorinated ether compound molecule, thereby suppressing intramolecular interactions between the polar groups contained in formula (1), and making it possible to prevent the fluorinated ether compound from aggregating.

[0165] Also, x is 2 and at least one of R ３ is represented by formula (2), the ratio of R １ and R ４ Since the number of active sites in the protective layer is limited, the ratio of the number of polar groups in R １ and R ４ When the ratio of polar groups in the １ and R ４ Therefore, when x in formula (1) is 2, R １ , R ４ It is also preferable that at least one of the above is an end group in which carbon atoms bonded to polar groups are bonded to each other via a linking group containing a carbon atom not bonded to a polar group. In an end group in which carbon atoms bonded to polar groups are bonded to each other via a linking group containing a carbon atom not bonded to a polar group, the interaction within the molecule is suppressed, and therefore the interaction with the protective layer is relatively strong. For this reason, R １ , R ４ is a terminal group in which carbon atoms bonded to polar groups are bonded to each other via a linking group containing a carbon atom not bonded to a polar group, R １ , R ４ This can prevent the end portions from lifting up due to insufficient interaction between the adhesive layer and the protective layer.

[0166] When x in formula (1) is 2, R１ , R ４ It is more preferable that at least one of is an end group selected from the group consisting of a terminal group in which at least one of q1, q2, q3, and q4 in the formula (3-1) is 2 or more, a terminal group in which at least one of s1, s2, and s3 in the formula (3-2) is 2 or more, a terminal group represented by the formula (3-6), and a terminal group represented by the formula (3-7), because this can more effectively suppress aggregation of the fluorinated ether compound.

[0167] R １ and R ４ Examples of the linking group include, but are not limited to, the terminal groups represented by the following formulae. Examples of the linking group represented by formula (3-1) include the following formulae (3-1A) to (3-1M). Examples of the linking group represented by formula (3-2) include the following formulae (3-2A) to (3-2I). Examples of the linking group represented by formula (3-3) include the following formulae (3-3A) to (3-3D). Examples of the linking group represented by formula (3-4) include the following formulae (3-4A) to (3-4D). Examples of the linking group represented by formula (3-5) include the following formulae (3-5A) to (3-5E). Examples of the linking group represented by formula (3-6) include the following formulae (3-6A) to (3-6D). Examples of the linking group represented by formula (3-7) include the following formulae (3-7A) to (3-7B).

[0168] The dotted lines in the following formulas (3-1A) to (3-1M), (3-2A) to (3-2I), (3-3A) to (3-3D), (3-4A) to (3-4D), (3-5A) to (3-5E), (3-6A) to (3-6D), and (3-7A) to (3-7B) represent the R １ or R ４ is a bond bonded to the methylene group adjacent to

[0169]

[0170]

[0171]

[0172] (R ２In the fluorine-containing ether compound represented by formula (1), R ２ is a perfluoropolyether chain. A perfluoropolyether chain refers to a polyether chain in which all hydrogen atoms on carbon atoms are substituted with fluorine atoms. ２ When a lubricating layer is formed by applying a lubricant containing the fluorine-containing ether compound of this embodiment onto a protective layer, the PFPE chain represented by the formula (R) 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. ２ The PFPE chain represented by the formula (I) is appropriately selected depending on the performance required of the lubricant containing the fluorine-containing ether compound.

[0173] (x+1) R ２ may be the same in part or in whole, or may be different from each other. ２ It is preferable that all (x+1) R 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. ２ Two or more of the R ２ are the same, (x+1) R ２ Among them, R ２ It means that two or more of the same R are included. ２ The term also includes those having the same structure of structural units but different average degrees of polymerization.

[0174] R ２ Examples of the PFPE chain represented by the formula (1) include those made of 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.

[0175] (x+1) R in formula (1) ２are each independently preferably a PFPE chain represented by the following formula (4) derived from a polymer or copolymer of perfluoroalkylene oxide: -(CF ２ ) ｗ１ -O-(CF ２ O) ｗ２ -(CF ２ CF ２ O) ｗ３ -(CF ２ CF ２ CF ２ O) ｗ４ -(CF ２ CF ２ CF ２ CF ２ O) ｗ５ -(CF ２ ) ｗ６ - (4) (In formula (4), w2, w3, w4, and w5 represent the average degree of polymerization, and each independently represents 0 to 20. However, w2, w3, w4, and w5 cannot all be 0 at the same time. w1 and w6 are CF ２ is an average value representing the number of structural units in formula (4), each of which independently represents 1 to 3. ２ O), (CF ２ CF ２ O), (CF ２ CF ２ CF ２ O), (CF ２ CF ２ CF ２ CF ２ There are no particular restrictions on the arrangement order of O).

[0176] In formula (4), w2, w3, w4, and w5 represent average degrees of polymerization, each independently representing 0 to 20, preferably 0 to 15, and more preferably 0 to 10. In formula (4), w1 and w6 represent CF ２ The values ​​of w1 and w6 are determined depending on the structure of the structural unit located at the end of the chain structure in the PFPE chain represented by formula (4). ２ O), (CF ２ CF ２ O), (CF ２ CF ２ CF２ O), (CF ２ CF ２ CF ２ CF ２ O) is a structural unit. There is no particular limitation on the order of the structural units in formula (4). There is also no particular limitation on the number of types of structural units in formula (4).

[0177] (x+1) R in formula (1) ２ are each independently any one selected from the PFPE chains represented by the following formulas (4-1) to (4-4): ２ is any one selected from the PFPE chains represented by formulas (4-1) to (4-4), the resulting fluorine-containing ether compound provides a lubricating layer with good lubricity. ２ is any one selected from the PFPE chains represented by formulas (4-1) to (4-4), 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. Therefore, the fluorine-containing ether compound has an appropriate hardness. Therefore, the fluorine-containing ether compound applied on the protective layer is less likely to aggregate on the protective layer, and a thinner lubricating layer can be formed with a sufficient coverage. In addition, (x+1) R ２ However, a lubricating layer containing a fluorine-containing ether compound which is any one selected from the PFPE chains represented by formulas (4-1) to (4-4) is more dense and can further suppress spin-off, and is therefore preferred.

[0178] -CF ２ -(OCF ２ CF ２ ) ｈ -(OCF ２ ) ｉ -OCF ２ - (4-1) (In formula (4-1), 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 CF２ - (4-2) (In formula (4-2), 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 - (4-3) (In formula (4-3), k represents the average degree of polymerization and represents 1 to 10.) - (CF ２ ) ｗ７ -O-(CF ２ CF ２ CF ２ O) ｗ８ -(CF ２ CF ２ O) ｗ９ -(CF ２ ) ｗ１０ - (4-4) (In formula (4-4), w8 and w9 represent the average degree of polymerization, each independently representing 1 to 20. w7 and w10 represent CF ２ is an average value representing the number of

[0179] In formula (4-1), the structural unit (OCF ２ CF ２ ) and (OCF ２ In formula (4-1), there is no particular limitation on the arrangement order of (OCF ２ CF ２ ) and the number h (OCF ２ The number i of (OCF ２ CF ２ The PFPE chain represented by formula (4-1) may be a polymer of (OCF ２ CF ２ ) and (OCF ２ ) may be any of a random copolymer, a block copolymer, and an alternating copolymer.

[0180] In formulas (4-1) to (4-3), 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, so that the fluorine-containing ether compound can provide a lubricating layer with good lubricity. Furthermore, in formulas (4-1) to (4-3), 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, so that the viscosity of the fluorine-containing ether compound does not become too high, and a lubricant containing the fluorine-containing ether compound is 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, so that the fluorine-containing ether compound can easily wet and spread on the protective layer and provide a lubricating layer with a uniform thickness.

[0181] In formula (4-4), the structural unit (CF ２ CF ２ CF ２ O) and (CF ２ CF ２ In formula (4-4), the order of the groups (CF) representing the average degree of polymerization is not particularly limited. ２ CF ２ CF ２ O) number w8 and (CF ２ CF ２ The number w9 of monomer units (CF ２ CF ２ CF ２ O) and (CF ２ CF ２ O) may be a random copolymer, a block copolymer, or an alternating copolymer.

[0182] In formula (4-4), w8 and w9, which represent the average degree of polymerization, are each independently 1 to 20, preferably 1 to 15, and more preferably 1 to 10. w7 and w10 in formula (4-4) are each independently 1 to 20, more preferably 1 to 15, and even more preferably 1 to 10. ２ and each independently represents 1 to 2. w7 and w10 are determined depending on the structure of the structural unit located at the end of the chain structure in the PFPE chain represented by formula (4-4).

[0183] In the fluorine-containing ether compound represented by formula (1), when x is 1, two R ２ are the same, and R １ and R ４ and are preferably the same. This is because the fluorine-containing ether compound can be produced easily and efficiently. In the fluorine-containing ether compound represented by formula (1), when x is 2, two R ３ are the same, and R １ Side R ２ and R ４ Side R ２ and R １ and R ４ This is because the resulting fluorine-containing ether compound can be produced easily and efficiently.

[0184] Specifically, the fluorine-containing ether compound represented by formula (1) is preferably any of the compounds represented by the following formulae (AA) to (AH) and (BA) to (BC): When the compound represented by formula (1) is any of the compounds represented by the following formulae (AA) to (AH) and (BA) to (BC), the raw materials are easily available, and even if the thickness is thin, a lubricating layer can be formed which has even better flying stability and a high spin-off suppression effect.

[0185] In the compounds represented by the following formulae (AA) to (AH) and (BA) to (BC), Rf representing a PFPE chain １ , Rf ２ , Rf ３ are the following structures. That is, in the compound represented by the following formula (AD), Rf １ is a PFPE chain represented by the above formula (4-1). In the compounds represented by the following formulae (AA) to (AC), (AE) to (AH), (BB), and (BC), Rf ２ is a PFPE chain represented by the above formula (4-2). In the compound represented by the following formula (BA), Rf ３ is a PFPE chain represented by the above formula (4-3). １ h and i, Rf ２ j and Rf in ３Since k in the above formula is a value indicating the average degree of polymerization, it is not necessarily an integer.

[0186]

[0187] In the compounds represented by the following formulas (AA) to (AH) and (BA), x in formula (1) is 1, and in the compounds represented by (BB) and (BC), x in formula (1) is 2. The compounds represented by the following formulas (AA) to (AH) and (BA) are ３ is a linking group represented by any one of the above formulas (2-1) to (2-4), and R １ and R ４ is the terminal group represented by the above formula (3-1) or (3-2).

[0188] Formulas (AA) to (AC), (AE) to (AH), (BB), and (BC) are R ２ is a PFPE chain represented by the above formula (4-2), and formula (AD) is R ２ is a PFPE chain represented by the above formula (4-1), and formula (BA) is R ２ is the PFPE chain represented by the above formula (4-3). The compound represented by the following formula (BB) is １ Side R ３ is a linking group represented by formula (2-2), and R ４ Side R ３ is a linking group represented by formula (2-1), and R １ and R ４ is the terminal group represented by the above formula (3-1). The compound represented by the following formula (BC) is １ Side R ３ is a linking group represented by formula (2-2), and R ４ Side R ３ is a linking group represented by formula (XA), and R １ and R ４ is the terminal group represented by the above formula (3-1).

[0189] The compounds represented by the following formulae (AA) to (AH) and (BA) to (BC) are all R １ and R ４ are the same, and (x+1) R ２ In addition, the compound represented by the following formula (BB) has two R ３The atoms contained in R are located at the center of the molecule. ２ are arranged symmetrically with respect to the two R ３ is the same.

[0190] (Two Rf in formula (AA) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AB), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AC), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AD), the average degrees of polymerization may be the same or different. 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 The average degrees of polymerization may be the same or different.

[0191] (Two Rf in formula (AE) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AF), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AG), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AH), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ The average degrees of polymerization may be the same or different.

[0192] (Two Rf in formula (BA) ３ In the formula, k represents the average degree of polymerization and represents 1 to 10. ３ In the formula (BB), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (BC), the average degrees of polymerization may be the same for some or all of the three Rf ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the above, the average degrees of polymerization may be the same for some or all of the polymers, or may be different from each other.

[0193] The fluorine-containing ether compound of this embodiment preferably has a number average molecular weight (Mn) in the range of 500 to 10,000, particularly preferably in the range of 1,000 to 5,000. When the number average molecular weight is 500 or more, a lubricating layer made of 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, so that the viscosity becomes easy to handle when applied to a lubricant.

[0194] The number average molecular weight (Mn) of the fluorine-containing ether compound was measured by AVANCEIII400 manufactured by Bruker Biospin. １ H-NMR and １９ This is a value measured by F-NMR. １９ The number average molecular weight is determined by calculating the number of structural units in the PFPE chain from the integrated value measured by F-NMR. For NMR (nuclear magnetic resonance) measurements, the sample is diluted in a hexafluorobenzene / d-acetone (4 / 1 v / v) solvent. １９The reference for F-NMR chemical shifts is the hexafluorobenzene peak at −164.7 ppm. １ The reference for H-NMR chemical shifts is the acetone peak at 2.2 ppm.

[0195] 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, and 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.

[0196] "Production Method" The production method of the fluorinated ether compound of this embodiment is not particularly limited, and the compound can be produced using a conventionally known production method. The fluorinated ether compound of this embodiment can be produced, for example, using the production method shown below.

[0197] [First production method (when x is 1)] (R １ and R ４ are the same, and the two R ２ is the same) <First Reaction> R in formula (1) ２ At both ends of the perfluoropolyether chain corresponding to ２ A fluorine-based compound in which a hydroxyl group (OH) is arranged is prepared.

[0198] Next, the hydroxyl group of the hydroxymethyl group located at one end of the fluorine-based compound and the R １ A group corresponding to (=R ４ The epoxy compound having the group corresponding to R ２ At one end of the perfluoropolyether chain corresponding to １ A group corresponding to (=R ４ An intermediate compound 1 having a group corresponding to

[0199] R in formula (1) １ A group corresponding to (=R ４Examples of the epoxy compound having a group corresponding to the following formula (5-1A) to (5-1M), (5-2A) to (5-2I), (5-3A) to (5-3D), (5-4A) to (5-4D), (5-5A) to (5-5E), (5-6A) to (5-6D), (5-7A), and (5-7B) can be used.

[0200] In the following formulas (5-1A) to (5-1F), (5-1H), (5-1J) to (5-1M), (5-2A) to (5-2I), (5-3A) to (5-3D), (5-4A) to (5-4D), (5-5D), (5-5E), (5-6A) to (5-6D), (5-7A), and (5-7B), THP represents a tetrahydropyranyl group.

[0201]

[0202]

[0203]

[0204] R in formula (1) １ A group corresponding to (=R ４ The epoxy compound having a group corresponding to R in formula (1) can be produced, for example, by the method shown below. １ A terminal group represented by (=R ４ The diol can be produced by a method in which a diol having a structure corresponding to a part of the terminal group represented by the formula (I) is prepared, one of the hydroxyl groups is protected by a known method, and then the diol is reacted with a halogen compound such as a bromine compound having an epoxy group or a chlorine compound having an epoxy group.

[0205] Specifically, for example, the compound represented by formula (5-1B) can be produced by the method shown in formula (6-1) below. That is, one of the hydroxyl groups of 1,3-propanediol is protected with dihydropyran (DHP) and then reacted with epibromohydrin. THP in formula (6-1) below represents a tetrahydropyranyl group.

[0206]

[0207] R １ A group corresponding to (=R４ The epoxy compound having the group corresponding to R in formula (1) may be produced, for example, by the method shown below. １ A terminal group represented by (=R ４ The compound is reacted with the hydroxyl group of an alcohol having an alkenyl group corresponding to part of the terminal group represented by the formula (1), and then the resulting compound is oxidized with m-chloroperbenzoic acid (mCPBA).

[0208] Specifically, for example, the compound represented by formula (5-1C) can be produced by the method shown in formula (6-2) below. That is, the compound can be produced by reacting 2-(2-bromoethoxy)tetrahydro-2H-pyran with 3-buten-1-ol, and then oxidizing the resulting compound with m-chloroperbenzoic acid (mCPBA). In formula (6-2), THP represents a tetrahydropyranyl group, and mCPBA represents m-chloroperbenzoic acid.

[0209]

[0210] R １ A group corresponding to (=R ４ The epoxy compound having a group corresponding to R in formula (1) may be produced, for example, by the following method. １ A terminal group represented by (=R ４ An epoxy compound having a structure corresponding to a part of the terminal group represented by the formula (1) and having a hydroxyl group protected by a protecting group at one end is produced by a known method. １ A terminal group represented by (=R ４ The compound obtained by the addition reaction is then subjected to an addition reaction with an alcohol having an alkenyl group corresponding to part of the terminal group represented by the formula (III). The compound obtained is then reacted with m-chloroperbenzoic acid (mCPBA) to oxidize the compound. Before the compound obtained by the addition reaction is reacted with m-chloroperbenzoic acid (mCPBA) to oxidize the compound, the hydroxyl group generated by the addition reaction may be protected by a known method.

[0211] Specifically, for example, the compound represented by formula (5-1D) can be produced by the method shown in formula (6-3) below. １ A terminal group represented by (=R ４ An epoxy compound represented by formula (5-1A) having a structure corresponding to a part of the terminal group represented by formula (5-1A) is produced. Next, the epoxy compound represented by formula (5-1A) is subjected to an addition reaction with allyl alcohol. Thereafter, the hydroxyl group generated by the addition reaction is protected with dihydropyran (DHP) and oxidized by the action of m-chloroperbenzoic acid (mCPBA). In the following formula (6-3), THP represents a tetrahydropyranyl group, DHP represents dihydropyran, and mCPBA represents m-chloroperbenzoic acid.

[0212]

[0213] <Second Reaction> The hydroxyl group of the hydroxymethyl group located at one end of the intermediate compound 1 produced in the first reaction described above and R ３ The R used in the second reaction is reacted with a compound having a group corresponding to ３ Examples of compounds having a group corresponding to R include compounds having two epoxy groups, compounds having one epoxy group and one leaving group, and compounds having two leaving groups. ３ Examples of the leaving group contained in the compound having a group corresponding to the above include a chloro group, a bromo group, an iodo group, a p-toluenesulfonyloxy group, and a methanesulfonyloxy group.

[0214] R in formula (1) ３ Examples of compounds having a group corresponding to the formula (a compound having two epoxy groups, a compound having one epoxy group and one leaving group, or a compound having two leaving groups) include compounds represented by the following formulas (7-1A) to (7-1D), (7-3A) to (7-3D), (7-3F), and (7-4). THP in the following formulas (7-1A) to (7-1D), (7-3B) to (7-3D), (7-3F), and (7-4) represents a tetrahydropyranyl group.

[0215]

[0216] R ３ The compound having two epoxy groups used as the compound having a group corresponding to R can be produced, for example, by the method shown below. ３ and a hydroxyl group of a diol having a group corresponding to a part of a linking group represented by R ３ In this case, the halogen compound is reacted with the diol in an amount twice as large as the amount of the diol by mole.

[0217] Specifically, for example, the compound represented by formula (7-3A) can be produced by reacting a diol compound represented by formula (8A) with epibromohydrin in a molar amount twice that of the diol compound represented by formula (8-1) below.

[0218]

[0219] R ３ The compound having two epoxy groups used as the compound having a group corresponding to R may be produced, for example, by the method shown below. ３ and a diepoxy compound having a group corresponding to a part of the linking group represented by R ３ The diepoxy compound is reacted with the hydroxyl group of an alcohol having an alkenyl group corresponding to a portion of the linking group represented by the formula (I). At this time, the diepoxy compound is reacted with an alcohol having an alkenyl group in an amount twice the molar amount of the diepoxy compound. Thereafter, the hydroxyl group generated by this reaction may be appropriately protected. Subsequently, the resulting compound can be produced by a method of oxidizing it with m-chloroperbenzoic acid (mCPBA).

[0220] Specifically, for example, the compound represented by formula (7-3B) can be produced by the method shown in formula (8-2) below. That is, 1,3-butadiene diepoxide is reacted with twice the molar amount of 3-buten-1-ol. The hydroxyl group of the resulting compound is protected with dihydropyran (DHP), and then oxidized by the action of m-chloroperbenzoic acid (mCPBA). In formula (8-2) below, THP represents a tetrahydropyranyl group, DHP represents dihydropyran, and mCPBA represents m-chloroperbenzoic acid.

[0221]

[0222] After the second reaction, a deprotection reaction is carried out using a known method to obtain a compound represented by the formula (1) in which x is 1 and R １ and R ４ are the same, and the two R ２ can be prepared.

[0223] [Second manufacturing method (when x is 1)] (R １ and R ４ and / or two R ２ (When different) <First reaction> R １ Side R ２ A fluorine-based compound having a hydroxymethyl group at each end of a perfluoropolyether chain corresponding to R is prepared. １ with an epoxy compound having a group corresponding to the formula: to obtain intermediate compound 1a.

[0224] <Second reaction> Also, R ４ Side R ２ A fluorine-based compound having a hydroxymethyl group at each end of a perfluoropolyether chain corresponding to R is prepared. ４ An epoxy compound having a group corresponding to the formula: is reacted to give intermediate compound 1b.

[0225] <Third Reaction> Next, the hydroxyl group at one end of the intermediate compound 1a is reacted with the R ３The R used in the third reaction of the second production method is reacted with a compound having a group corresponding to ３ Examples of compounds having a group corresponding to R include compounds having an epoxy group and an alkenyl group, or compounds having a leaving group and an alkenyl group. ３ Examples of the leaving group contained in the compound having a group corresponding to the formula (I) include a chloro group, a bromo group, an iodo group, a p-toluenesulfonyloxy group, a methanesulfonyloxy group, etc. Then, the double bond of the resulting compound is oxidized to obtain intermediate compound 1-2.

[0226] R used in the third reaction of the second production method ３ Examples of compounds having a group corresponding to the formula (a compound having an epoxy group and an alkenyl group, or a compound having a leaving group and an alkenyl group) that can be used include compounds represented by the following formulas (9-1A) to (9-1D), (9-3A) to (9-3D), and (9-4). THP in the following formulas (9-1A) to (9-1D), (9-3B) to (9-3D), and (9-4) represents a tetrahydropyranyl group.

[0227]

[0228] R used in the third reaction of the second production method ３ The compound having an epoxy group and an alkenyl group, which is a compound having a group corresponding to R ３ and one hydroxyl group of a diol having a group corresponding to a part of a linking group represented by R ３ The compound obtained after the reaction is reacted with a halogen compound having an alkenyl group corresponding to a part of the linking group represented by R ３ The compound can be produced by reacting a halogen compound having an epoxy group corresponding to a part of the linking group represented by the formula:

[0229] Specifically, for example, the compound represented by formula (9-3A) can be produced by reacting a diol compound represented by formula (8A) with allyl bromide and epibromohydrin in this order, as shown in the following formula (10-1).

[0230]

[0231] R used in the third reaction of the second production method ３ The compound having an epoxy group and an alkenyl group, which is a compound having a group corresponding to R ３ and a diepoxy compound having a group corresponding to a part of the linking group represented by R ３ The diepoxy compound is reacted with the hydroxyl group of an alcohol having an alkenyl group corresponding to a portion of the linking group represented by the formula (I). At this time, the diepoxy compound is reacted with an alcohol having an alkenyl group in an amount twice the molar amount of the diepoxy compound. Thereafter, the hydroxyl group generated by this reaction may be appropriately protected. Next, the resulting compound is reacted with m-chloroperbenzoic acid (mCPBA) to oxidize one of the alkenyl groups, thereby producing the compound.

[0232] For example, the compound represented by formula (9-3B) can be produced by the method shown in formula (10-2) below. 1,3-Butadiene diepoxide is reacted with twice the molar amount of 3-buten-1-ol. The hydroxyl group generated by this reaction is then protected with dihydropyran (DHP), and one of the alkenyl groups is oxidized by the action of m-chloroperbenzoic acid. In formula (10-2) below, THP represents a tetrahydropyranyl group, DHP represents dihydropyran, and mCPBA represents m-chloroperbenzoic acid.

[0233]

[0234] <Fourth Reaction> Next, the hydroxyl group at one end of intermediate compound 1b is reacted with the epoxy group of intermediate compound 1-2 obtained in the third reaction. After the above steps, a deprotection reaction is carried out using a known method to obtain a compound represented by the formula (1) where x is 1 and R １ and R ４ and / or two R ２ can be prepared.

[0235] [Third Production Method (when x is 2)] (R １ and R ４are the same, and the two R ３ are the same, and R １ Side R ２ and R ４ Side R ２ is the same) <First Reaction> In the same manner as in the first production method, １ side (=R ４ side) R ２ At one end of the perfluoropolyether chain corresponding to １ A group corresponding to (=R ４ The intermediate compound 1 is obtained having a group corresponding to

[0236] <Second Reaction> Next, R at the center of the molecule in formula (1) ２ At both ends of the perfluoropolyether chain corresponding to ２ Next, a fluorine-based compound having hydroxyl groups of hydroxymethyl groups arranged at both ends of the fluorine-based compound and R ３ to give intermediate compound 2-1.

[0237] R used in the second reaction of the third production method ３ As a compound having a group corresponding to the formula (I), R ３ Examples of compounds having a group corresponding to the formula (a compound having an epoxy group and an alkenyl group, or a compound having a leaving group and an alkenyl group) include those exemplified above.

[0238] <Third Reaction> Next, the intermediate compound 2-1 produced in the second reaction is reacted with m-chloroperbenzoic acid (mCPBA) to oxidize the alkenyl group. As a result, the R at the center of the molecule in formula (1) ２ At both ends of the perfluoropolyether chain corresponding to the two R ３ This gives an intermediate compound 3-1 having an epoxy group corresponding to the formula: The third reaction may be carried out after the hydroxyl group of the intermediate compound 2-1 is appropriately protected by a known method.

[0239] <Fourth Reaction> Then, the hydroxyl group of the hydroxymethyl group located at one end of the intermediate compound 1 is reacted with the epoxy groups located at both ends of the intermediate compound 3-1. After the above steps, a deprotection reaction is carried out to obtain a compound represented by the formula (1) where x is 2 and R １ and R ４ are the same, and the two R ３ are the same, and R １ Side R ２ and R ４ Side R ２ can be prepared.

[0240] [Fourth Production Method (when x is 2)] (R １ Side R ３ and R ４ Side R ３ and R １ and R ４ and / or R １ Side R ２ and R ４ Side R ２ In the first reaction of the third production method, instead of the intermediate compound 1, the intermediate compound 1a and the intermediate compound 1b in the second production method are obtained.

[0241] Next, intermediate compound 3-1 is obtained by the same procedures as in the second and third reactions of production method 3. Then, intermediate compound 1a and intermediate compound 1b are sequentially reacted with the epoxy groups located at both ends of intermediate compound 3-1, respectively.

[0242] After the above steps, a deprotection reaction is carried out to obtain a compound represented by the formula (1) where x is 2 and R １ Side R ３ and R ４ Side R ３ and R １ and R ４ and / or R １ Side R ２ and R ４ Side R ２ can be prepared.

[0243] [Fifth Production Method (when x is 2)] (R １ Side R３ and R ４ Side R ３ Unlike R １ and R ４ and R １ Side R ２ and R ４ Side R ２ The R used in the second reaction of the third production method is the same ３ Instead of a compound having a group corresponding to R in formula (1), １ Side R ３ (a compound having an epoxy group and an alkenyl group, or a compound having a leaving group and an alkenyl group) and a compound having a group corresponding to R ４ Side R ３ The fluorine-based compound is reacted with a compound having a group corresponding to the formula (a compound having an epoxy group and an alkenyl group, or a compound having a leaving group and an alkenyl group) to sequentially obtain intermediate compound 2-2.

[0244] Then, the third and fourth reactions are carried out in the same manner as in the third production method, except that intermediate compound 2-2 is used instead of intermediate compound 2-1. After the above steps, a deprotection reaction is carried out to obtain a compound represented by the formula (1) where x is 2 and R １ Side R ３ and R ４ Side R ３ Unlike R １ and R ４ and R １ Side R ２ and R ４ Side R ２ can be prepared.

[0245] In the third to fifth production methods for producing a compound in which x is 2, R ２ The perfluoropolyether chain corresponding to the other R ２ It is also possible to manufacture the same as other R ２ It is also possible to manufacture something different from the above.

[0246] [Lubricant for magnetic recording media] The lubricant for magnetic recording media (coating material) of this embodiment contains a fluorine-containing ether compound represented by the above formula (1). The lubricant of this embodiment can be used by mixing, as needed, with known materials used as lubricant materials, as long as the properties resulting from the inclusion of the fluorine-containing ether compound represented by the above formula (1) are not impaired.

[0247] 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 this embodiment preferably has a number average molecular weight of 1,000 to 10,000.

[0248] When the lubricant of the present embodiment contains a material other than the fluorinated ether compound represented by the above formula (1), the content of the fluorinated ether compound represented by the above formula (1) in the lubricant of the present embodiment is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0249] The lubricant of this embodiment contains the fluorine-containing ether compound represented by the above formula (1), and therefore can obtain excellent flying stability and form a lubricating layer with a high spin-off suppression effect. In this embodiment, the case where the coating material of the present invention is used as a lubricant for a magnetic recording medium has been described as an example, but the use of the coating material of the present invention is not limited to a lubricant for a magnetic recording medium.

[0250] [Magnetic Recording Medium] The magnetic recording medium (e.g., hard disk) of this embodiment has at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate. In the magnetic recording medium of this embodiment, one or more underlayers can be provided between the substrate and the magnetic layer as needed. In addition, at least one of an adhesive layer and a soft magnetic layer can be provided between the underlayer and the substrate.

[0251] 1 is a schematic cross-sectional view showing one embodiment of a magnetic recording medium of the present invention. The magnetic recording medium 10 of this embodiment has a structure in which an adhesive layer 12, a soft magnetic layer 13, a first underlayer 14, a second underlayer 15, a magnetic layer 16, a protective layer 17, and a lubricating layer 18 are sequentially provided on a substrate 11.

[0252] "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. Alternatively, the substrate 11 may be a non-magnetic substrate made of a non-metallic material such as glass, ceramics, silicon, silicon carbide, carbon, or resin, or a non-magnetic substrate in which a film of NiP or a NiP alloy is formed on a base made of such a non-metallic material.

[0253] "Adhesion Layer" The adhesion 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 adhesion layer 12 are disposed in contact with each other. The material of the adhesion layer 12 can be appropriately selected from, for example, Cr, Cr alloy, Ti, Ti alloy, CrTi, NiAl, AlRu alloy, etc. The adhesion layer 12 can be formed by, for example, a sputtering method.

[0254] "Soft Magnetic Layer" The soft magnetic layer 13 preferably has a structure in which a first soft magnetic film, an intermediate layer made of a Ru film, and a second soft magnetic film are laminated in this order. That is, the soft magnetic layer 13 preferably has a structure in which the intermediate layer made of a Ru film is sandwiched between two soft magnetic films, and the soft magnetic films above and below the intermediate layer are anti-ferro-coupling (AFC).

[0255] Examples of materials for the first and second soft magnetic films include CoZrTa alloys and CoFe alloys. It is preferable to add Zr, Ta, or Nb to the CoFe alloy used for 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, for example, by sputtering.

[0256] "First Underlayer" 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. Examples of the first underlayer 14 include a Cr layer, a Ta layer, a Ru layer, or a CrMo alloy layer, a CoW alloy layer, a CrW alloy layer, a CrV alloy layer, and a CrTi alloy layer. The first underlayer 14 can be formed by, for example, a sputtering method.

[0257] "Second Underlayer" The second underlayer 15 is a layer that controls the orientation of the magnetic layer 16 so that it is favorable. The second underlayer 15 is preferably a layer made of Ru or a Ru alloy. The second underlayer 15 may be a layer consisting of a single layer, or may be made of multiple layers. When the second underlayer 15 consists of multiple layers, all of 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, for example, by a sputtering method.

[0258] "Magnetic Layer" The magnetic layer 16 is made of a magnetic film whose axis of easy magnetization is oriented perpendicular or horizontal to the substrate surface. The magnetic layer 16 is a layer containing Co and Pt. To improve the SNR characteristics, the magnetic layer 16 may be a layer containing oxides, Cr, B, Cu, Ta, Zr, etc. Examples of oxides contained in the magnetic layer 16 include SiO ２ , SiO, Cr ２ O ３ , CoO, Ta ２ O ３ , TiO ２ etc.

[0259] The magnetic layer 16 may be composed of a single layer, or may be composed of multiple magnetic layers made of materials with different compositions. For example, when the magnetic layer 16 is composed of three layers, a first magnetic layer, a second magnetic layer, and a third magnetic layer stacked in 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. As the oxide contained in the first magnetic layer, it is preferable to use an oxide of, for example, Cr, Si, Ta, Al, Ti, Mg, Co, or the like. Among them, TiO is particularly preferable. ２, Cr ２ O ３ , SiO ２ The first magnetic layer is preferably made of a composite oxide containing two or more kinds of oxides. ２ O ３ -SiO ２ , Cr ２ O ３ -TiO ２ , SiO ２ -TiO ２ The first magnetic layer may contain, in addition to Co, Cr, Pt, and oxides, one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re.

[0260] The second magnetic layer can be made of the same material as the first magnetic layer. The second magnetic layer preferably has a granular structure. The third magnetic layer preferably has a non-granular structure made of a material containing Co, Cr, and Pt and not containing oxides. In addition to Co, Cr, and Pt, the third magnetic layer can contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn.

[0261] When the magnetic layer 16 is formed of multiple magnetic layers, it is preferable to provide a non-magnetic layer between adjacent magnetic layers. When the 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.

[0262] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 can be suitably 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).

[0263] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 is preferably made of an alloy material containing an oxide, a metal nitride, or a metal carbide. Specifically, the oxide may be, for example, SiO２ , Al ２ O ３ , Ta ２ O ５ , Cr ２ O ３ , MgO, Y ２ O ３ , TiO ２ Examples of metal nitrides that can be used include AlN and Si. ３ N ４ , TaN, CrN, etc. can be used as the metal carbide. TaC, BC, SiC, etc. can be used as the metal carbide. The non-magnetic layer can be formed by, for example, sputtering.

[0264] 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. The magnetic layer 16 may also be a magnetic layer for in-plane magnetic recording. The magnetic layer 16 may be formed by any conventionally known method, such as vapor deposition, ion beam sputtering, or magnetron sputtering. The magnetic layer 16 is usually formed by sputtering.

[0265] "Protective Layer" The protective layer 17 protects the magnetic layer 16. The protective layer 17 may be composed of a single 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.

[0266] 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 contents in the carbon-based protective layer. The hydrogen content in the carbon-based protective layer is preferably 3 atomic % to 20 atomic % as measured by hydrogen forward scattering (HFS). The nitrogen content in the carbon-based protective layer is preferably 4 atomic % to 15 atomic % as measured by X-ray photoelectron spectroscopy (XPS).

[0267] 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 the protective layer 17 and hydrogen is contained on the magnetic layer 16 side of the protective layer 17. In this case, the adhesion between the magnetic layer 16 and the lubricating layer 18 and the carbon-based protective layer is further improved.

[0268] 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.

[0269] 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, ion beam deposition (IBD), or the like. When a carbon-based protective layer is formed as the protective layer 17, it can be formed by DC magnetron sputtering, for example. In particular, when a carbon-based protective layer is formed as the protective layer 17, it is preferable to form an amorphous carbon protective layer by plasma CVD. An amorphous carbon protective layer formed by plasma CVD has a uniform surface with little roughness.

[0270] "Lubricant Layer" The lubricant layer 18 prevents contamination of the magnetic recording medium 10. The lubricant layer 18 also reduces the frictional force of the magnetic head of the magnetic recording and reproducing device sliding on the magnetic recording medium 10, thereby improving the durability of the magnetic recording medium 10. As shown in FIG. 1 , the lubricant layer 18 is formed on and in contact with the protective layer 17. The lubricant layer 18 is formed by applying the magnetic recording medium lubricant of the above-mentioned embodiment onto the protective layer 17. Therefore, the lubricant layer 18 contains the above-mentioned fluorine-containing ether compound.

[0271] 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.

[0272] 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 with a high coverage. 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 sufficiently reduced.

[0273] "Method for forming lubricating layer" As a method for forming the lubricating layer 18, for example, a method is given in which a magnetic recording medium in the middle of manufacture in which each layer up to the protective layer 17 is formed on the substrate 11, and a solution for forming a lubricating layer is applied to the protective layer 17 and dried.

[0274] The lubricant layer-forming solution can be obtained by dissolving and dispersing the magnetic recording medium lubricant of the above embodiment in a solvent as needed, and adjusting the viscosity and concentration to suit the coating method. Examples of the solvent used in the lubricant layer-forming solution include fluorine-based solvents such as Vertrel (registered trademark) XF (trade name, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.).

[0275] The method for applying the lubricant layer-forming solution is not particularly limited, and examples thereof include spin coating, spraying, paper coating, and dipping. When using the dipping method, the following method can be used, for example. First, the substrate 11 on which each layer up to the protective layer 17 has been formed is immersed in the lubricant layer-forming solution placed in the immersion tank of a dip coating device. Next, the substrate 11 is pulled out of the immersion tank at a predetermined speed. In this way, the lubricant layer-forming solution is applied to the surface of the protective layer 17 of the substrate 11. By using the dipping method, the lubricant layer-forming solution can be applied uniformly to the surface of the protective layer 17, and the lubricant layer 18 can be formed on the protective layer 17 with a uniform film thickness.

[0276] In this embodiment, it is preferable to subject the substrate 11 on which the lubricating layer 18 is formed to a heat treatment. By subjecting the substrate 11 to a heat treatment, the adhesion between the lubricating layer 18 and the protective layer 17 is improved, and the adhesive strength 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. A heat treatment temperature of 100°C or higher sufficiently improves the adhesion between the lubricating layer 18 and the protective layer 17. 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.

[0277] 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.

[0278] 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. Even with a thin film thickness, this lubricating layer 18 has good levitation stability and a high spin-off suppression effect. 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 contribute to reducing magnetic spacing, allowing the magnetic head levitation height to be reduced (e.g., 10 nm or less), and operates stably for long periods 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 mounted in a magnetic disk device using the LUL (Load Unload) method.

[0279] 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.

[0280] [Example 1] The compound represented by the above formula (AA) was obtained by the following method. (First Reaction) HOCH ２ CF２ CF ２ O (CF ２ CF ２ CF ２ O) ｊ CF ２ CF ２ CH ２ 20 g of a compound (number average molecular weight = 950, molecular weight distribution < 1.1) represented by formula (5-1A), 4.35 g of a compound represented by formula (5-1A), and 20 mL of t-butanol were charged and stirred at room temperature until homogenous to obtain a mixture. 1.15 g of potassium tert-butoxide was added to this mixture, and the mixture was reacted with stirring at 70°C for 16 hours.

[0281] The compound represented by formula (5-1A) was synthesized by protecting the hydroxyl group of ethylene glycol monoallyl ether with dihydropyran, and then oxidizing the vinyl group with m-chloroperbenzoic acid.

[0282] 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. The desiccant was removed by filtration, and the filtrate was concentrated. The residue was purified by silica gel column chromatography to obtain 11.25 g of a compound represented by the following formula (11) as intermediate compound 1.

[0283] (Rf in formula (11) ２ is the PFPE chain represented by the above formula (4-2). ２ In the formula, j, which indicates the average degree of polymerization, is 4.0. THP represents a tetrahydropyranyl group.

[0284] (Second Reaction) In a nitrogen gas atmosphere, 5.61 g of the compound represented by formula (11), which is intermediate compound 1 obtained above, 0.48 g of the compound represented by formula (7-1A), and 10 mL of t-butanol were placed in a 100 mL recovery flask and stirred at room temperature until a homogeneous mixture was obtained. 0.45 g of potassium tert-butoxide was added to this mixture, and the mixture was allowed to react with stirring at 70°C for 16 hours.

[0285] The compound represented by formula (7-1A) was produced by the following method. The primary hydroxyl groups of 3-butene-1,2-diol were protected using t-butyldimethylsilyl chloride, and the secondary hydroxyl groups were protected using dihydropyran. Thereafter, the protecting groups of the primary hydroxyl groups were deprotected using tetrabutylammonium fluoride, and the resulting primary hydroxyl groups were reacted with epibromohydrin. The compound obtained after the reaction was oxidized using m-chloroperbenzoic acid to synthesize the compound represented by formula (7-1A).

[0286] After the reaction, the reaction solution obtained 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, followed by stirring at room temperature for 4 hours. Thereafter, the reaction solution was transferred little by little 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 with 100 mL of brine, 100 mL of saturated aqueous sodium bicarbonate, and 100 mL of brine in that order, and dehydrated with anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated. The residue was purified by silica gel column chromatography to obtain compound (AA) (Rf ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0.

[0287] The obtained compound (AA) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 3.40-3.85 (36H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0288] [Example 2] A compound represented by the above formula (AB) was obtained by the method shown below. The same procedure as in Example 1 was carried out, except that a compound represented by formula (5-2A) was used instead of a compound represented by formula (5-1A), to obtain compound (AB) (Rf ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0.

[0289] The compound represented by formula (5-2A) was synthesized by oxidizing the vinyl group of 2-allyloxytetrahydropyran with m-chloroperbenzoic acid.

[0290] The obtained compound (AB) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 3.40-3.85 (28H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0291] [Example 3] A compound represented by the above formula (AC) was obtained by the method shown below. Compound (AC) (Rf in formula (AC)) was obtained by the same procedure as in Example 1, except that a compound represented by formula (5-2E) was used instead of a compound represented by formula (5-1A). ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0.

[0292] The compound represented by formula (5-2E) was synthesized by reacting 3-buten-1-ol with the compound represented by formula (5-2A), protecting the resulting hydroxyl group with dihydropyran, and then oxidizing the vinyl group with m-chloroperbenzoic acid.

[0293] The obtained compound (AC)１ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 1.65-1.85 (4H), 3.40-3.85 (40H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0294] [Example 4] The compound represented by the above formula (AD) was obtained by the following method. The compound represented by formula (5-2A) was used instead of the compound represented by formula (5-1A), and HOCH ２ CF ２ CF ２ O (CF ２ CF ２ CF ２ O) ｊ CF ２ CF ２ CH ２ Instead of the compound represented by OH, ２ CF ２ O (CF ２ CF ２ O) ｈ CF ２ CH ２ The same procedure as in Example 1 was carried out to obtain compound (AD) (Rf １ is a PFPE chain represented by the above formula (4-1). １ In the above formula, h, which indicates the average degree of polymerization, is 5.0, and i is 0.

[0295] The obtained compound (AD) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６): δ [ppm] = 3.40-3.85 (28H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -80.5 (8F), -91.0 to -88.5 (40F)

[0296] [Example 5] A compound represented by the above formula (AE) was obtained by the method shown below. The same procedure as in Example 1 was carried out, except that a compound represented by formula (5-2A) was used instead of a compound represented by formula (5-1A), and a compound represented by formula (7-3A) was used instead of a compound represented by formula (7-1A), to obtain compound (AE) (Rf ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0. The compound represented by formula (7-3A) was synthesized by the method shown in formula (8-1) above.

[0297] The obtained compound (AE) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 3.40-3.85 (34H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0298] [Example 6] A compound represented by the above formula (AF) was obtained by the method shown below. Compound (AF) (Rf in formula (AF)) was obtained by the same procedure as in Example 1, except that a compound represented by formula (7-3B) was used instead of a compound represented by formula (7-1A). ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0. The compound represented by formula (7-3B) was synthesized by the method shown in formula (8-2) above.

[0299] The obtained compound (AF) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 1.65-1.85 (4H), 3.40-3.85 (34H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0300] [Example 7] A compound represented by the above formula (AG) was obtained by the method shown below. The same procedure as in Example 1 was carried out, except that a compound represented by formula (5-2A) was used instead of a compound represented by formula (5-1A), and a compound represented by formula (7-3B) was used instead of a compound represented by formula (7-1A), to obtain compound (AG) (Rf ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0.

[0301] The obtained compound (AG) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 1.65-1.85 (4H), 3.40-3.85 (26H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0302] [Example 8] A compound represented by the above formula (AH) was obtained by the method shown below. The same procedure as in Example 1 was carried out, except that a compound represented by formula (5-2A) was used instead of a compound represented by formula (5-1A), and a compound represented by formula (7-4) was used instead of a compound represented by formula (7-1A), to obtain compound (AH) (where Rf ２ is a PFPE chain represented by the above formula (4-2). ２ In this formula, j, which indicates the average degree of polymerization, is 4.0.

[0303] The compound represented by formula (7-4) was synthesized by the method shown in formula (8-3) below. The first reaction of formula (8-3) was carried out by the method described in a non-patent document (Org. Let. 2012, Vol. 14, p. 4802). In formula (8-3), PhI(OAc) ２ represents iodobenzene diacetate, DHP represents dihydropyran, mCPBA represents m-chloroperbenzoic acid, and THP represents a tetrahydropyranyl group.

[0304]

[0305] The obtained compound (AH) １ H-NMR and １９ F-NMR measurement was carried out, and the structure was identified from the following results. １ H-NMR (acetone-D ６ ): δ [ppm] = 3.40-3.85 (22H), 3.85-4.10 (8H) １９ F-NMR (acetone-D ６ ): δ [ppm] = -84.0 to -83.0 (32F), -86.4 (8F), -124.3 (8F), -130.0 to -129.0 (16F)

[0306] The compounds (AA) to (AH) of Examples 1 to 8 thus obtained were applied to the formula (1), and the value of x, R １ , R ２ , R ３ , R ４ The structure is shown in Table 1.

[0307]

[0308] Comparative Example 1 A compound represented by the following formula (ZA) was synthesized by the method described in Patent Document 1.

[0309] (Rf in formula (ZA) １ is a PFPE chain represented by the above formula (4-1). １ In the formula, h representing the average degree of polymerization is 7.0, and i representing the average degree of polymerization is 0.

[0310] Comparative Example 2 A compound represented by the following formula (ZB) was synthesized by the method described in Patent Document 2.

[0311] (Rf in formula (ZB) １ is a PFPE chain represented by the above formula (4-1). １ In the formula, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.

[0312] Comparative Example 3 A compound represented by the following formula (ZC) was synthesized by the method described in Patent Document 3.

[0313] (Rf in formula (ZC) １ is a PFPE chain represented by the above formula (4-1). １ In the formula, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.

[0314] Comparative Example 4 A compound represented by the following formula (ZD) was synthesized by the method described in Patent Document 4.

[0315] (Rf in formula (ZD) ２ is a PFPE chain represented by the above formula (4-2). ２ In this case, j, which indicates the average degree of polymerization, is 4.5.

[0316] Comparative Example 5 A compound represented by the following formula (ZE) was synthesized by the method described in Patent Document 5.

[0317] (Rf in formula (ZE) １ is a PFPE chain represented by the above formula (4-1). １In the formula, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.

[0318] Comparative Example 6 A compound represented by the following formula (ZF) was synthesized by the method described in Patent Document 6.

[0319] (Rf in formula (ZF) １ is a PFPE chain represented by the above formula (4-1). １ In the formula, h representing the average degree of polymerization is 7.0, and i representing the average degree of polymerization is 0.

[0320] Comparative Example 7 A compound represented by the following formula (ZG) was synthesized by the method described in Patent Document 7.

[0321] (Rf in formula (ZG) ２ is a PFPE chain represented by the above formula (4-2). ２ In this case, j, which indicates the average degree of polymerization, is 4.5.

[0322] The number average molecular weights (Mn) of the compounds thus obtained in Examples 1 to 8 and Comparative Examples 1 to 7 were measured by the above-mentioned method. The results are shown in Table 2.

[0323] Next, solutions for forming lubricating layers were prepared by the method described below using the compounds obtained in Examples 1 to 8 and Comparative Examples 1 to 7. 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 8 and Comparative Examples 1 to 7.

[0324] "Lubricant Layer-Forming Solution" The compounds obtained in Examples 1 to 8 and Comparative Examples 1 to 7 were each dissolved in a fluorine-based solvent, Vertrel (registered trademark) XF (trade name, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.), and diluted with Vertrel XF so that the film thickness when applied to the protective layer would be 8.0 Å (0.8 nm) to 8.5 Å (0.85 nm), to prepare a lubricant layer-forming solution.

[0325] "Magnetic Recording Medium" A magnetic recording medium was prepared by sequentially providing an adhesive layer, a soft magnetic layer, a first underlayer, a second underlayer, a magnetic layer, and a protective layer on a substrate with a diameter of 65 mm. The protective layer was made of carbon. The lubricant layer-forming solutions of Examples 1 to 8 and Comparative Examples 1 to 7 were applied by dipping onto the protective layer of the magnetic recording medium, on which each layer up to the protective layer had been formed. The dipping was performed under the following conditions: an immersion speed of 10 mm / sec, an immersion time of 30 seconds, and a pull-up speed of 1.2 mm / sec.

[0326] 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 120°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.

[0327] (Film Thickness Measurement) The film thickness of the lubricating layer of the magnetic recording media thus obtained in Examples 1 to 8 and Comparative Examples 1 to 7 was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name: Nicolet iS50, manufactured by Thermo Fisher Scientific). The results are shown in Table 2.

[0328] Next, the following flying stability test and spin-off characteristic test were carried out on the magnetic recording media of Examples 1 to 8 and Comparative Examples 1 to 7. The results are shown in Table 2.

[0329] [Flying Stability Test] The following glide test and credence measurement were carried out, and the flying stability was evaluated based on the following evaluation criteria. The results are shown in Table 2.

[0330] "Glide Test" The glide test checks whether there are any protrusions on the surface of the magnetic recording medium. That is, when recording / reproducing data on the magnetic recording medium using a magnetic head, if there are any protrusions on the surface of the magnetic recording medium that are higher than the flying height (the distance between the magnetic recording medium and the magnetic head), the magnetic head may collide with the protrusions, causing damage to the magnetic head or defects in the magnetic recording medium. In the glide test, 50 magnetic recording media are checked for the presence or absence of any protrusions on the surface that are higher than the flying height.

[0331] Specifically, the distance between the inspection magnetic head and the magnetic recording medium was set to 0.25 microinches, and the inspection magnetic head was moved over the magnetic recording medium. If the inspection magnetic head output a signal due to a collision with a protrusion on the surface of the magnetic recording medium, the magnetic recording medium was judged to be defective, and the rest were judged to be pass. Then, the number of magnetic recording media judged to be pass out of the 50 magnetic recording media was used for evaluation.

[0332] "Credence Measurement" When the above-mentioned glide test is performed, noise temporarily increases, and even at the same location on the magnetic recording medium, signals resulting from collisions with surface protrusions may or may not be detected during multiple measurements. This phenomenon is called creedence. Creedence is not detected as a protrusion in the glide test and is not used to determine whether the glide test passed or failed. However, a temporary increase in noise during the glide test generally indicates unevenness in the lubricant layer or the presence of relatively soft foreign matter. For this reason, the glide test was performed on the magnetic recording medium, and the average greedence value was calculated by dividing the total number of detected creedences by the number of magnetic recording media (50) subjected to the glide test. This value was used as an index of the smoothness and cleanliness of the lubricant layer.

[0333] "Evaluation criteria" A+: Number of sheets that passed the glide test was 45 or more and the average credence was less than 0.5 A: Number of sheets that passed the glide test was 45 or more and the average credence was 0.5 or more and less than 1.0 B: Number of sheets that passed the glide test was 45 or more and the average credence was 1.0 or more and less than 5.0 C: Number of sheets that passed the glide test was 45 or more and the average credence was 5.0 or more D: Number of sheets that passed the glide test was less than 45

[0334] [Spin-off property test] A magnetic recording medium was mounted on a spin stand and rotated at a rotation speed of 10,000 rpm in an environment of 80°C for 72 hours. Before and after this operation, the film thickness of the lubricating layer at a position 20 mm radius from the center of the magnetic recording medium was measured using FT-IR, and the film thickness reduction rate of the lubricating layer before and after the test was calculated. The spin-off property was evaluated using the calculated film thickness reduction rate according to the evaluation criteria shown below.

[0335] "Evaluation criteria for spin-off characteristics" A+: Film thickness reduction rate less than 2% A: Film thickness reduction rate 2% or more but less than 3% B: Film thickness reduction rate 3% or more but less than 5% C: Film thickness reduction rate 5% or more but less than 10% D: Film thickness reduction rate 10% or more

[0336] [Overall Evaluation] An overall evaluation was performed based on the results of the flying stability test and the spin-off characteristic test, according to the following criteria: "Overall Evaluation" A: Both the flying stability test evaluation and the spin-off characteristic test evaluation were A+ or A B: One of the flying stability test evaluation and the spin-off characteristic test evaluation was B, and the other was A+, A, or B C: One of the flying stability test evaluation and the spin-off characteristic test evaluation was C, and the other was A+, A, B, or C D: At least one of the flying stability test evaluation and the spin-off characteristic test evaluation was D

[0337]

[0338] As shown in Tables 1 and 2, the perfluoropolyether chain (R ２ ) R placed between ３ is a divalent linking group represented by any one of formulas (2-1) to (2-4), and the magnetic recording media of Examples 1 to 8 using fluorine-containing ether compounds (AA) to (AH) satisfying formula (1) were all evaluated as A+, A, or B in the flying stability test and spin-off characteristic test, and the overall evaluation was A or B. From this, it was confirmed that the lubricating layers of the magnetic recording media of Examples 1 to 8 were able to obtain good flying stability and had a high spin-off suppression effect.

[0339] In particular, the magnetic recording media of Examples 5 to 7 had good results in the spin-off characteristics test, with a rating of A+. This is due to the R ３ is the formula (2-3), which is a divalent linking group having four hydroxyl groups, and therefore, it is presumed that an interaction between the hydroxyl groups and the protective layer is effectively obtained in the center of the molecule, and a lubricating layer with high adhesion to the protective layer is formed.

[0340] The magnetic recording medium of Example 8 also showed a good result of A+ in the flying stability test. This is due to the R ３ is represented by formula (2-4), and the internal 1,2-diol structure (—CH ２ -CH(OH)-CH(OH)-CH ２ It is presumed that this is because, since the hydroxyl group is a divalent linking group having two hydroxyl groups (-), it is difficult for the hydroxyl groups to form intramolecular interactions at the center of the molecule, and therefore it is possible to secure a sufficient number of hydroxyl groups that can participate in intermolecular interactions and interactions with the protective layer.

[0341] In contrast, as shown in Tables 1 and 2, the magnetic recording media of Comparative Examples 1 to 7, which used compounds (ZA) to (ZG), were all rated C or D in the flying stability test and spin-off characteristic test, and the overall rating was C or D.

[0342] More specifically, the compound (ZA) used in Comparative Example 1 and the compound (ZB) used in Comparative Example 2 have only one hydroxyl group contained in the linking group between perfluoropolyether chains.Therefore, it is difficult for the compound (ZA) and the compound (ZB) to secure a polar group that can participate in intermolecular interaction in the center of the molecule.As a result, in Comparative Example 1 and Comparative Example 2, the fluorine-containing ether compound in the lubricating layer is easily scattered, and it is thought that the result of the spin-off property test is D.

[0343] In the compound (ZC) used in Comparative Example 3 and the compound (ZD) used in Comparative Example 4, the two hydroxyl groups contained in the linking group between perfluoropolyether chains are bonded only through rigid alkylene chains.Therefore, in the compound (ZC) and the compound (ZD), the free movement of the hydroxyl group contained in the linking group is hindered, and the hydroxyl group is less likely to be involved in the interaction with the active site on the protective layer.In addition, in the compound (ZC) and the compound (ZD), only two hydroxyl groups are contained in the linking group.As a result, in Comparative Example 3 and Comparative Example 4, the molecular center of the fluorine-containing ether compound is likely to float and form a mass, and it is considered that the evaluation of the floating stability test is D.

[0344] The compound (ZE) used in Comparative Example 5 has a linking group containing an erythritol structure between the perfluoropolyether chains. However, the compound (ZE) does not have any polar groups in the linking group other than the two hydroxyl groups in the erythritol structure. Therefore, the compound (ZE) does not have a sufficient number of polar groups in the center of the molecule that can interact with the protective layer and that can participate in intermolecular interactions. As a result, it is believed that Comparative Example 5 showed inferior results in the flying stability test and spin-off characteristic test compared to Examples 1 to 8, which used compounds (AA) to (AH).

[0345] In the compound (ZF) used in Comparative Example 6, the distance between the two hydroxyl groups contained in each of the two linking groups arranged between the perfluoropolyether chains is sufficiently large.Therefore, the hydroxyl groups contained in the two linking groups can each move very flexibly, and are easily involved in the interaction with the active site on the protective layer.In addition, in the compound (ZF), each linking group contains only two hydroxyl groups.For these reasons, in the compound (ZF), it is difficult to secure a sufficient number of polar groups that can participate in intermolecular interaction in the center of the molecule of the fluorine-containing ether compound.As a result, in Comparative Example 6, the fluorine-containing ether compound in the lubricating layer is easily scattered, and it is thought that the result of the spin-off property test is D.

[0346] In the compound (ZG) used in Comparative Example 7, the distance between the three hydroxyl groups contained in the linking group arranged between the perfluoropolyether chains is sufficiently large.In addition, one of the three hydroxyl groups is a primary hydroxyl group that can move relatively freely.Therefore, the hydroxyl groups contained in the linking group can move very flexibly, and are easily involved in the interaction with the active site on the protective layer.For these reasons, in the compound (ZG), it is difficult to secure a sufficient number of polar groups that can participate in intermolecular interaction at the center of the molecule of the fluorine-containing ether compound.As a result, in Comparative Example 7, the fluorine-containing ether compound in the lubricating layer is easily scattered, and the result of the spin-off property test is considered to be D.

[0347] 10: magnetic recording medium 11: substrate 12: adhesive layer 13: soft magnetic layer 14: first underlayer 15: second underlayer 16: magnetic layer 17: protective layer 18: lubricating layer

Claims

1. A fluorine-containing ether compound represented by the following formula (1): １ -CH ２ -R ２ [-CH ２ -R ３ -CH ２ -R ２ ] ｘ -CH ２ -R ４ (1) (In formula (1), x represents 1 or 2. R ２ is a perfluoropolyether chain. (x+1) R ２ may be the same in part or in whole, or may be different from each other. ３ is a divalent linking group having 1 to 50 carbon atoms and 1 to 6 polar groups. ３ At least one of R is a divalent linking group represented by the following formula (2): １ and R ４ is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms. １ and R ４ may be the same or different.) (In formula (2), a and b each independently represent 0 or 1, and a and b cannot simultaneously represent 0. X and Y each independently represent an acyclic divalent saturated hydrocarbon group having 3 to 20 carbon atoms and having 1 or 2 polar groups. The saturated hydrocarbon group may contain an ether oxygen atom between carbon atoms, and the polar group of the saturated hydrocarbon group is bonded to a carbon atom other than the bonding terminal of the saturated hydrocarbon group.) 2. The fluorine-containing ether compound according to claim 1, wherein the formula (2) is a linking group represented by any one of the following formulas (2-1) to (2-4): (In formula (2-1), c represents an integer of 1 to 6. A １ represents a polar group.) (In formula (2-2), d represents an integer of 1 to 6. A ２ represents a polar group.) (In formula (2-3), e1 represents an integer of 1 to 6. e2 represents an integer of 1 to 6. A ３１ , A ３２ each independently represents a polar group.) 3. The fluorine-containing ether compound according to claim 1 or 2, wherein all of the polar groups in said formula (2) are hydroxyl groups.

4. R in the formula (1) １ and R ４ The fluorine-containing ether compound according to claim 1 or 2, wherein each of the groups independently represents a terminal group represented by the following formula (3): (In formula (3), l represents an integer of 0 to 3. o represents 0 or 1. At least one of l and o is 1 or greater. When l represents 1 to 3, l m's each independently represent an integer of 1 to 6, and l n's each independently represent an integer of 1 to 6, and in one structural unit, at least one of m and n is 1. B represents an organic group having 1 to 30 carbon atoms which may contain at least one of a polar group, a halogeno group, and an ether oxygen atom, or a hydrogen atom. However, the total number of polar groups included in formula (3) is 1 to 4.) 5. R in the formula (1) １ and R ４ each independently represent any one of the following formulas (3-1) to (3-5): (In formula (3-1), p represents 0 or 1. q1, q2, q3, and q4 each independently represent an integer of 1 to 6. When p is 0, the total value of q1 and q4 is 2 to 10. When p is 1, the total value of q1, q2, q3, and q4 is 4 to 10, and at least one of q2 and q3 is 1. D represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when D is the aryl group which may have a substituent, the number of polar groups contained in D is 0 or 1.) (In formula (3-2), r represents 0 or 1. s1, s2, and s3 each independently represent an integer of 1 to 6. When r is 1, the total value of s1, s2, and s3 is 3 to 8, and at least one of s2 and s3 is 1.) (In formula (3-3), t1 and t2 each independently represent an integer of 1 to 6. E represents a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when E is the aryl group which may have a substituent, E does not contain a polar group.) (In formula (3-4), u represents an integer of 1 to 6. G represents a polar group, a hydrogen atom, a vinyl group, an ethynyl group, a perfluoroalkyl group, or an aryl group which may have a substituent. However, when G is the aryl group which may have a substituent, the number of polar groups which may be included in G is 0 or 1.) (In formula (3-5), v represents 1 or 2. Each of the five Js independently represents a polar group, an alkoxy group having 1 to 8 carbon atoms, a halogeno group, or a hydrogen atom. However, when a polar group is included in the five Js, the number of polar groups among the five Js is 1.) 6. R in the formula (1) １ and R ４ The fluorine-containing ether compound according to claim 1 or 2, wherein 7. R in the formula (1) １ and a polar group having R ４ 3. The fluorine-containing ether compound according to claim 1, wherein the total number of polar groups contained in the compound is 2 to 6.

8. R in the formula (1) １ and a polar group having R ３ and a polar group having R ４ 3. The fluorine-containing ether compound according to claim 1, wherein all of the polar groups of the formula (I) are hydroxyl groups.

9. (x+1) R in the formula (1) ２ are each independently a perfluoropolyether chain represented by the following formula (4): -(CF ２ ) ｗ１ -O-(CF ２ O) ｗ２ -(CF ２ CF ２ O) ｗ３ -(CF ２ CF ２ CF ２ O) ｗ４ -(CF ２ CF ２ CF ２ CF ２ O) ｗ５ -(CF ２ ) ｗ６ - (4) (In formula (4), w2, w3, w4, and w5 represent the average degree of polymerization, and each independently represents 0 to 20. However, w2, w3, w4, and w5 cannot all be 0 at the same time. w1 and w6 are CF ２ is an average value representing the number of structural units in formula (4), each of which independently represents 1 to 3. ２ O), (CF ２ CF ２ O), (CF ２ CF ２ CF ２ O), (CF ２ CF ２ CF ２ CF ２ There are no particular restrictions on the arrangement order of O).

10. (x+1) R in the formula (1) ２ are each independently any one selected from perfluoropolyether chains represented by the following formulas (4-1) to (4-4): ２ -(OCF ２ CF ２ ) ｈ -(OCF ２ ) ｉ -OCF ２ - (4-1) (In formula (4-1), 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 - (4-2) (In formula (4-2), 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 - (4-3) (In formula (4-3), k represents the average degree of polymerization and represents 1 to 10.) - (CF ２ ) ｗ７ -O-(CF ２ CF ２ CF ２ O) ｗ８ -(CF ２ CF ２ O) ｗ９ -(CF ２ ) ｗ１０ - (4-4) (In formula (4-4), w8 and w9 represent the average degree of polymerization, each independently representing 1 to 20. w7 and w10 represent CF ２ is an average value representing the number of 11. The fluorine-containing ether compound according to claim 1 or 2, wherein x in formula (1) is 1.

12. In the formula (1), x is 2 and two R ３ The atom contained in is R at the center of the molecule. ２ The fluorine-containing ether compound according to claim 1 or 2, wherein the fluorine-containing ether compound is symmetrically arranged with respect to 13. The fluorine-containing ether compound represented by the formula (1) is any one of the compounds represented by the following formulas (AA) to (AH), wherein Rf in formulas (AA) to (AC) and (AE) to (AH) is ２ Ha-CF ２ CF ２ -(OCF ２ CF ２ CF ２ ) ｊ -OCF ２ CF ２ -, and Rf in formula (AD) １ Ha-CF ２ -(OCF ２ CF ２ ) ｈ -(OCF ２ ) ｉ -OCF ２ 2. The fluorine-containing ether compound according to claim 1, wherein (Two Rf in formula (AA) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AB), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AC), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AD), the average degrees of polymerization may be the same or different. 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 The average degrees of polymerization may be the same or different. (Two Rf in formula (AE) ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AF), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AG), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ In the formula (AH), the average degrees of polymerization may be the same or different. ２ In the formula, j represents the average degree of polymerization, which is 1 to 15. ２ The average degrees of polymerization may be the same or different.

14. A coated article comprising the fluorine-containing ether compound according to claim 1 or 2.

15. A lubricant for magnetic recording media, comprising the coating material according to claim 14.

16. A magnetic recording medium comprising a substrate and at least a magnetic layer, a protective layer, and a lubricating layer provided thereon, wherein the lubricating layer contains the fluorine-containing ether compound according to claim 1 or 2.

17. The magnetic recording medium according to claim 16, wherein the average film thickness of the lubricating layer is 0.5 nm to 2.0 nm.

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