Fluorine-containing ether compound, 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)x-CH2-R4 (In the formula, x represents an integer of 1 or 2; R2 represents a perfluoropolyether chain; R3 is represented by formula (2); and R1 and R4 each represent a terminal group which has 1 to 4 polar groups and 1 to 50 carbon atoms.)

Description

[Technical Field]

[0001] The present invention relates to a fluorine-containing ether compound, a lubricant for a magnetic recording medium, and a magnetic recording medium. This application claims priority based on Japanese Patent Application No. 2022-158414, filed on September 30, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In order to increase the recording density in magnetic recording and reproducing devices, development of magnetic recording media suitable for high recording densities is underway. 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 provide sufficient durability for the magnetic recording medium. For this reason, a lubricating layer is generally formed by applying a lubricant to the surface of the protective layer.

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

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

[0005] Patent Documents 3 and 4 disclose fluorine-containing ether compounds having a skeleton containing a methylene group (-CH2-) and a group in which one hydrogen atom of the methylene group is substituted with a hydroxyl group (-CH(OH)-), in which two perfluoropolyether chains are linked via a divalent linking group having two hydroxyl groups, and in which terminal groups, which are organic groups having polar groups, are linked to both ends of the skeleton via the methylene groups.

[0006] Patent Document 5 discloses a fluorine-containing ether compound having a skeleton containing a methylene group (-CH2-) and a group in which one hydrogen atom of the methylene group is substituted with a hydroxyl group (-CH(OH)-), in which two or three perfluoropolyether chains are linked via a divalent linking group having two hydroxyl groups, and in which terminal groups that are organic groups having polar groups are linked to both ends of the skeleton via the methylene groups.

[0007] Patent Documents 6 and 7 disclose fluorine-containing ether compounds having a skeleton in which two perfluoropolyether chains are linked via a divalent linking group containing a benzene ring or an alicyclic structure, and in which terminal groups that are organic groups having polar groups are linked to both ends of the skeleton via methylene groups (-CH-). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 10,540,997 [Patent Document 2] International Publication No. 2021 / 251335 [Patent Document 3] International Publication No. 2021 / 020066 [Patent Document 4] Patent No. 6804981 [Patent Document 5] U.S. Patent No. 10,262,685 [Patent Document 6] International Publication No. 2021 / 065380 [Patent Document 7] International Publication No. 2022 / 113854 Summary of the Invention [Problem to be solved by the invention]

[0009] 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 thinner lubricating layers in magnetic recording media. However, reducing the thickness of the lubricating layer generally reduces the chemical resistance of the magnetic recording medium. Furthermore, if the lubricating layer is thinned, spin-off occurs, making it impossible to maintain a sufficient film thickness to fulfill its lubricating function. Spin-off is a phenomenon in which the lubricant scatters or evaporates due to centrifugal force and heat generated by the rotation of the magnetic recording medium.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a fluorine-containing ether compound that has excellent chemical resistance, can 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 lubricant for magnetic recording media which contains the fluorine-containing ether compound of the present invention and is capable of forming a lubricating layer which has good chemical resistance and a high spin-off suppressing effect. Another object of the present invention is to provide a magnetic recording medium having a lubricating layer which contains the fluorine-containing ether compound of the present invention, has good chemical resistance, and is highly effective in suppressing spin-off. [Means for solving the problem]

[0011] The present invention includes the following aspects. A first aspect of the present invention provides the following fluorine-containing ether compound:

[0012] [1] A fluorine-containing ether compound represented by the following formula (1): R 1 -CH2-R 2[-CH2-R 3 -CH2-R 2 ] x -CH2-R 4 (1) (In formula (1), x represents an integer of 1 to 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; R 3 is a divalent linking group represented by the following formula (2); when x is 2, two R 3 may be the same or different; R 1 and R 4 is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms; R 1 and R 4 may be the same or different.)

[0013] [ka] (In formula (2), Y represents a non-cyclic divalent saturated hydrocarbon group having 2 to 8 carbon atoms, which may have an ether oxygen atom between the carbon atoms.)

[0014] The fluorine-containing ether compound of the first aspect of the present invention preferably has the characteristics described in the following [2] to

[10] . It is also preferable to arbitrarily combine two or more of the characteristics described in the following [2] to

[10] . [2] The fluorine-containing ether compound according to [1], wherein the formula (2) is a linking group represented by the following formula (2-1) or (2-2):

[0015] [ka] (In formula (2-1), a represents an integer of 2 to 8; a number of R a and R b each independently represents a hydrogen atom or a methyl group; a R bThe total number of carbon atoms contained in the formula (2-1) is 2 to 8; the oxygen atom at the left end of the formula (2-1) is R 1 The oxygen atom at the right end is bonded to the methylene group on the side of the 4 It bonds to the methylene group on the side.) (In formula (2-2), b represents an integer of 2 to 4; b R c each independently represents -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, or -CH2CH(CH3)-; b R c The total number of carbon atoms contained in formula (2-2) is 4 to 8; the oxygen atom at the left end of formula (2-2) is R 1 The oxygen atom at the right end is bonded to the methylene group on the side of the 4 It bonds to the methylene group on the side.) [3] R in the formula (1) 1 and R 4 are each independently a terminal group represented by the following formula (3):

[0016] [ka] (In formula (3), l represents an integer of 1 to 3. l m's each independently represent an integer of 1 to 6; l n's each independently represent an integer of 1 to 6; in one repeating unit, at least one of m and n is 1; A represents an alkyl group which may have a polar group, an organic group containing a carbon-carbon unsaturated bond which may have a polar group, or a hydrogen atom.) [4] R in the formula (1) 1 and R 4 are each independently a terminal group represented by the following formula (3-1) or (3-2):

[0017] [ka] (In formula (3-1), p represents an integer of 0 to 3, q ​​represents an integer of 0 to 2, and r represents an integer of 1 to 5; the total value of p and r is 1 to 5; and B represents a polar group.) (In formula (3-2), s represents an integer of 0 to 2, and t represents an integer of 1 to 5.)

[0018] [5] R in the formula (1) 1 and R 4 The fluorine-containing ether compound according to any one of [1] to [4], wherein [6] R in the formula (1) 1 and the polar group R 4 The fluorine-containing ether compound according to any one of [1] to [5], wherein the total number of polar groups contained in the above is 2 to 6. [7] R in the formula (1) 1 and the polar group R 4 The fluorine-containing ether compound according to any one of [1] to [6], wherein all of the polar groups contained in the fluorine-containing ether compound are hydroxyl groups.

[0019] [8] (x+1) R in the formula (1) 2 are each independently a perfluoropolyether chain represented by the following formula (4): -(CF2) w1 -O-(CF2O) w2 -(CF2CF2O) w3 -(CF2CF2CF2O) w4 -(CF2CF2CF2CF2O) w5 -(CF2) w6 - (4) (In formula (4), w2, w3, w4, and w5 represent the average degree of polymerization and each independently represent 0 to 20; provided that w2, w3, w4, and w5 cannot all be 0 at the same time; w1 and w6 represent the average value representing the number of CF2 and each independently represent 1 to 3; there are no particular limitations on the arrangement order of the repeating units (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) in formula (4).)

[0020] [9] (x+1) R in the formula (1) 2 are each independently any one selected from perfluoropolyether chains represented by the following formulae (4-1) to (4-4): -CF2-(OCF2CF2) h -(OCF2) i -OCF2- (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.) -CF2CF2-(OCF2CF2CF2) j -OCF2CF2- (4-2) (In formula (4-2), j represents the average degree of polymerization and represents 1 to 15.) -CF2CF2CF2-(OCF2CF2CF2CF2) k -OCF2CF2CF2- (4-3) (In formula (4-3), k represents the average degree of polymerization and represents 1 to 10.) -(CF2) w7 -O-(CF2CF2CF2O) w8 -(CF2CF2O) w9 -(CF2) 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 the average number of CF2, each independently representing 1 to 2.)

[0021]

[10] The fluorinated ether compound according to any one of [1] to [9], which has a number average molecular weight in the range of 500 to 10,000. A second aspect of the present invention provides the following lubricant for a magnetic recording medium.

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

[10] .

[0022] A third aspect of the present invention provides the following magnetic recording medium.

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

[10] . The magnetic recording medium according to the third aspect of the present invention preferably has the characteristics described in

[13] below.

[13] The magnetic recording medium according to

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

[0023] The fluorine-containing ether compound of the present invention is a compound represented by the above formula (1), and is suitable as a material for a lubricant for a magnetic recording medium. The lubricant for magnetic recording media of the present invention contains the fluorine-containing ether compound of the present invention, and therefore can form a lubricating layer that has good chemical resistance and a high spin-off suppressing effect.

[0024] The magnetic recording medium of the present invention has a lubricating layer containing the fluorine-containing ether compound of the present invention. Therefore, the magnetic recording medium of the present invention has good chemical resistance, a high spin-off suppression effect, and excellent reliability and durability. Furthermore, because the magnetic recording medium of the present invention has a lubricating layer that has good chemical resistance and can suppress spin-off, the thickness of the lubricating layer can be made thinner, thereby further reducing magnetic spacing. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of a magnetic recording medium of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to solve the above problems, the present inventors have conducted extensive research as described below. Conventionally, fluorine-containing ether compounds having polar groups such as hydroxyl groups at the terminals and center of a chain structure have been preferably used as materials for lubricants for magnetic recording media (hereinafter sometimes abbreviated as "lubricants") that are 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.

[0027] However, when a thin lubricating layer is formed on a protective layer using a lubricant containing a conventional fluorine-containing ether compound, it has been difficult to achieve a lubricating layer that has good chemical resistance and a high spin-off suppression effect, as will be shown below.

[0028] For example, in a fluorine-containing ether compound in which a divalent linking group having only one hydroxyl group is arranged between multiple perfluoropolyether chains, the hydroxyl groups of the divalent linking group may be prevented from adsorbing to the protective layer by the sterically bulky perfluoropolyether chains arranged on both sides, and may not be able to participate in the interaction with the active sites on the protective layer.

[0029] Furthermore, a fluorine-containing ether compound in which a divalent linking group having a rigid structure is arranged between multiple perfluoropolyether chains may not be able to participate in the interaction with the active site on the protective layer, even if the divalent linking group has multiple hydroxyl groups. This is because the divalent linking group having a rigid structure cannot move freely, and therefore, when the perfluoropolyether chains arranged on both sides of the divalent linking group undergo molecular motion, it may move in conjunction with the perfluoropolyether chain and move away from the protective layer.

[0030] Furthermore, in a fluorine-containing ether compound in which a divalent linking group having multiple hydroxyl groups and in which the hydroxyl groups are located close to each other is arranged between multiple perfluoropolyether chains, the hydroxyl groups contained in the divalent linking group tend to interact with each other within the molecule, even if the compound has a highly flexible structure in which two glycerin structures are directly bonded (-O-CH2-CH(OH)-CH2-O-CH2-CH(OH)-CH2-O-).As a result, the hydroxyl groups of the divalent linking group are less likely to be involved in interactions with polar groups contained in other fluorine-containing ether compound molecules present in the lubricating layer.

[0031] In this way, in the fluorine-containing ether compound contained in the lubricant, <1> Active sites on the protective layer or <2> If there is a polar group that is not involved in the interaction with the polar group contained in other fluorine-containing ether compound molecules present in the lubricating layer, contaminants are likely to be taken in near this polar group.In addition, the adhesion with the protective layer is insufficient, and the lubricant is likely to scatter or evaporate due to the centrifugal force and heat generated by the rotation of the magnetic recording medium.Therefore, it is necessary to consider whether the polar group in the fluorine-containing ether compound contained in the lubricant is the above-mentioned <1> or <2> If the lubricating layer is not easily involved in the interaction with the metal, the chemical resistance and spin-off suppression effect of the lubricating layer will be poor.

[0032] Therefore, the present inventors have investigated the relationship between the polar group in the molecule of the fluorine-containing ether compound contained in the lubricating layer and the above-mentioned <1> and <2> We conducted extensive research, focusing on the interaction between As a result, they found that a fluorine-containing ether compound having a divalent linking group linking multiple perfluoropolyether chains via a methylene group (-CH2-) has a structure represented by formula (2) containing two glycerin structures and an acyclic saturated hydrocarbon group of appropriate length disposed between them, and has terminal groups having polar groups at both ends of the molecule.

[0033] The divalent linking group represented by formula (2) in such a fluorine-containing ether compound has a highly flexible structure in which two glycerin structures have hydroxyl groups, and the acyclic saturated hydrocarbon group contained in the divalent linking group ensures that the distance between the two glycerin structures is appropriate. Moreover, the acyclic saturated hydrocarbon group has higher fluidity than, for example, a cyclic organic group, and has very little effect of hindering the movement of the two glycerin structures. Therefore, the hydroxyl groups contained in the divalent linking group represented by formula (2) can move freely and independently, and interaction within the same fluorine-containing ether compound molecule is suppressed, resulting in the above-mentioned <1> and <2> It is presumed that the hydroxyl group contained in the divalent linking group represented by formula (2) and the above <1> The interaction between the hydroxyl group contained in the divalent linking group represented by formula (2) and the above contributes to improving the adhesion between the lubricating layer and the protective layer. <2> The interaction with the fluorine-containing ether compound is an intermolecular interaction with other fluorine-containing ether compounds, and contributes to the formation of a dense film that is difficult to separate from the protective layer. Therefore, the lubricating layer containing the above fluorine-containing ether compound is dense and difficult to separate, has high adhesion to the protective layer, and is unlikely to cause spin-off. In addition, <1> and <2> The hydroxyl groups that are not involved in the interaction with the polymer are less likely to take up pollutants, resulting in good chemical resistance.

[0034] Furthermore, in the above-mentioned fluorine-containing ether compound, the perfluoropolyether chain is arranged between the terminal group having a polar group and the divalent linking group represented by formula (2). Therefore, the perfluoropolyether chain makes it difficult for the polar group in the terminal group and the hydroxyl group in the divalent linking group to interact intramolecularly, and the terminal group and the linking group can each independently interact with the protective layer. That is, two or three perfluoropolyether chains have terminal groups or linking groups at both ends that interact with the protective layer. Therefore, the perfluoropolyether chain is prevented from floating up and becoming bulky. Therefore, the thickness of the lubricating layer containing the above-mentioned fluorine-containing ether compound can be further reduced. In other words, the lubricating layer containing the above-mentioned fluorine-containing ether compound can maintain its function as a lubricating layer even when its thickness is reduced.

[0035] Furthermore, the present inventors have confirmed that by using a lubricant containing the above-mentioned fluorine-containing ether compound, a lubricating layer having good chemical resistance and a high spin-off suppressing effect can be formed, and have arrived at the present invention.

[0036] Preferred examples of the fluorine-containing ether compound, lubricant for magnetic recording media, and magnetic recording media of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments. The present invention allows addition, omission, substitution, and modification of the number, amount, position, ratio, material, configuration, type, order, etc., within the scope of the present invention.

[0037] [Fluorine-containing ether compounds] The fluorine-containing ether compound of the present embodiment is represented by the following formula (1). R 1 -CH2-R 2 [-CH2-R 3 -CH2-R 2 ] x -CH2-R 4 (1) (In formula (1), x represents an integer of 1 to 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; R 3 is a divalent linking group represented by the following formula (2); when x is 2, two R 3 may be the same or different; R 1 and R 4 is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms; R 1 and R 4 may be the same or different.)

[0038] [ka] (In formula (2), Y represents a non-cyclic divalent saturated hydrocarbon group having 2 to 8 carbon atoms, which may have an ether oxygen atom between the carbon atoms.)

[0039] 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 The PFPE chain has a skeleton in which the PFPE chain is connected to the R 1 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.

[0040] In the fluorine-containing ether compound represented by formula (1), x represents an integer of 1 to 2. In the fluorine-containing ether compound represented by formula (1), x represents an integer of 1 to 2, and therefore, R 2 The number of PFPE chains (x+1) represented by R is 2 or 3. 2 Unlike the compound with one PFPE chain, 2 R in between 3 A divalent linking group having a hydroxyl group represented by the formula: 2 In comparison with a compound having one PFPE chain, the compound has excellent adhesion to the protective layer and provides a lubricating layer that is less susceptible to spin-off. 2 Compared to compounds with four or more PFPE chains, the molecules are not too large and can move freely. Therefore, they easily spread on the protective layer, making it easier to obtain a thin, uniformly thick lubricating layer. In addition, since x is an integer between 1 and 2, R 2 R placed between 3 The number of -R in Eq. (1) is 1 or 2. 2 [-CH2-R 3 -CH2-R 2 ] xThe number of hydroxyl groups in - is likely to be appropriate, and a lubricating layer with good adhesion to the protective layer is likely to be obtained. In addition, the fluorine-containing ether compound represented by formula (1) is less likely to produce polar groups that are not involved in interactions with active sites on the protective layer or polar groups contained in other fluorine-containing ether compounds present in the lubricating layer, compared to when x is 3 or more, and <1> and <2> Hydroxyl groups that are not involved in interactions with the surface of the lubricant are less likely to take in contaminants, and a lubricating layer with good chemical resistance can be formed.

[0041] (R 3 a divalent linking group represented by In the fluorine-containing ether compound represented by formula (1), x R 3 is a divalent linking group represented by formula (2). The divalent linking group represented by formula (2) has oxygen atoms at both ends of a chain structure, and is connected to R 3 The oxygen atom contained in the chain structure of the divalent linking group represented by formula (2) forms an ether bond, imparting appropriate flexibility to the fluorine-containing ether compound represented by formula (1), and increasing the affinity between the hydroxyl group of the divalent linking group represented by formula (2) and the protective layer.

[0042] The divalent linking group represented by formula (2) contains a glycerin structure (-O-CH2-CH(OH)-CH2-O-) at both ends. Because the glycerin structure is flexible, the structure represented by formula (2), in which these two glycerin structures are linked by an acyclic saturated hydrocarbon group (described below), is extremely flexible. Therefore, even when the perfluoropolyether chains arranged on both sides undergo molecular motion, the two hydroxyl groups in the divalent linking group represented by formula (2) can move freely and independently, making it easier to maintain interactions between the hydroxyl groups in the divalent linking group and both the active sites on the protective layer and the polar groups contained in other fluorinated ether compounds present in the lubricating layer. This reduces the number of hydroxyl groups in the divalent linking group that are not involved in the interaction and that may capture contaminants. Therefore, a lubricating layer containing the above-mentioned fluorinated ether compound has excellent chemical resistance. In addition, since the hydroxyl groups in the two glycerin structures are likely to be involved in interactions with the protective layer or intermolecular interactions with other fluorinated ether compounds, the lubricating layer containing the above-mentioned fluorinated ether compound becomes dense, and the occurrence of spin-off is suppressed.

[0043] The divalent linking group represented by formula (2) has two hydroxyl groups. Because the divalent linking group represented by formula (2) has two hydroxyl groups, the lubricating layer containing the fluorine-containing ether compound has good adhesion (adhesion) to the protective layer. That is, even if one hydroxyl group in formula (2) is prevented from adsorbing to the protective layer due to the bulkiness of the adjacent perfluoropolyether chains, the other hydroxyl group can be adsorbed onto the protective layer. Moreover, since the number of hydroxyl groups in the divalent linking group is two, in a magnetic recording medium having a lubricating layer containing a fluorine-containing ether compound, the polarity of the fluorine-containing ether compound increases, causing the molecules to aggregate, thereby reducing adhesion to the protective layer and preventing spin-off.

[0044] In the divalent linking group represented by formula (2), Y is an acyclic divalent saturated hydrocarbon group having 2 to 8 carbon atoms. Since Y contains two or more carbon atoms, the distance between the hydroxyl groups in the two glycerin structures bonded to both sides of Y is maintained at an appropriate level. Therefore, the two hydroxyl groups in the divalent linking group represented by formula (2) can move independently. Furthermore, since Y contains eight or fewer carbon atoms, the bulkiness of Y reduces the effect of hindering the movement of the two glycerin structures bonded to both sides of Y. The number of carbon atoms contained in Y is preferably 3 to 6. When Y contains three or more carbon atoms, the distance between the two hydroxyl groups contained in the divalent linking group represented by formula (2) becomes more appropriate. As a result, the hydroxyl groups in the divalent linking group are more likely to interact with the active sites on the protective layer and the polar groups contained in other fluorinated ether compounds present in the lubricating layer. Furthermore, when Y contains three or more carbon atoms, the saturated hydrocarbon group reduces the affinity with contaminants, thereby suppressing the uptake of contaminants by the lubricating layer, resulting in improved chemical resistance.

[0045] Y in the divalent linking group represented by formula (2) is a saturated hydrocarbon group. Therefore, for example, compared to when Y has an unsaturated bond, it has higher flexibility and is less likely to interfere with the movement of the two glycerin structures bonded to both sides of Y. Furthermore, Y in the divalent linking group represented by formula (2) is acyclic. Therefore, for example, compared to when Y has a cyclic structure, it has higher fluidity and is less likely to interfere with the movement of the two glycerin structures bonded to both sides of Y.

[0046] Y in the divalent linking group represented by formula (2) may contain an ether oxygen atom (-O-) between carbon atoms. When Y contains an ether oxygen atom between carbon atoms, the flexibility is further improved. Y may be linear or branched.

[0047] x R 3 are preferably each independently a divalent linking group represented by the following formula (2-1) or (2-2). [ka] (In formula (2-1), a represents an integer of 2 to 8; a number of R a and R b each independently represents a hydrogen atom or a methyl group; a R b The total number of carbon atoms contained in the formula (2-1) is 2 to 8; the oxygen atom at the left end of the formula (2-1) is R 1 The oxygen atom at the right end is bonded to the methylene group on the side of the 4 It bonds to the methylene group on the side.) (In formula (2-2), b represents an integer of 2 to 4; b R c each independently represents -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, or -CH2CH(CH3)-; b R c The total number of carbon atoms contained in formula (2-2) is 4 to 8; the oxygen atom at the left end of formula (2-2) is R 1 The oxygen atom at the right end is bonded to the methylene group on the side of the 4 It bonds to the methylene group on the side.)

[0048] The divalent linking group represented by formula (2-1) is a divalent linking group represented by formula (2) in which -OYO- is -O-(-CR a R b -) a -O-. a represents an integer of 2 to 8. a number of R a and R b each independently represents a hydrogen atom or a methyl group. In the divalent linking group represented by formula (2-1), two glycerin structures are linked by a saturated hydrocarbon group containing no ether oxygen atoms and having a total of 2 to 8 carbon atoms. a (-CR a R b -) does not contain an ether oxygen atom and a R a and R b are each independently a hydrogen atom or a methyl group, the divalent linking group represented by formula (2-1) has low affinity with pollutants. a R bWhen the number of carbon atoms contained in (-) is 3 or more, the fluorine-containing ether compound has a much lower affinity with contaminants and can form a lubricating layer that is less likely to take in contaminants.

[0049] Since a in formula (2-1) is 2 or more, there are at least 8 atoms, not including ether oxygen atoms, between the hydroxyl groups contained in the glycerin structures at both ends. Therefore, the distance between the hydroxyl groups contained in the glycerin structures at both ends is appropriate. This prevents the hydroxyl groups contained in the glycerin structures at both ends from aggregating together within the molecule, allowing them to move independently. In addition, when a in formula (2-1) is 8 or less and there are a number of (-CR a R b Since the total number of carbon atoms contained in the glycerin structure (-) is 8 or less, the rigidity of the saturated hydrocarbon group does not have much of an effect on hindering the movement of the glycerin structures at both ends.

[0050] In the divalent linking group represented by formula (2-1), the saturated hydrocarbon group containing no ether oxygen atom reduces the polarity around the glycerin structures at both ends, reducing the affinity with pollutants. 3 A lubricating layer containing a fluorine-containing ether compound in which is a divalent linking group represented by formula (2-1) is preferred because it has better chemical resistance.

[0051] The divalent linking group represented by formula (2-2) is a divalent linking group represented by formula (2), wherein -OYO- is -O-(R c -O) b b represents an integer of 2 to 4. b R c each independently represents -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, or -CH2CH(CH3)-. In the divalent linking group represented by formula (2-2), two glycerin structures are linked by a saturated hydrocarbon group containing an ether oxygen atom and having a total of 4 to 8 carbon atoms.

[0052] Since b in formula (2-2) is 2 or more, there are at least 11 atoms, including an ether oxygen atom, between the hydroxyl groups contained in the glycerin structures at both ends. Therefore, the distance between the hydroxyl groups contained in the glycerin structures at both ends is appropriate. This prevents the hydroxyl groups contained in the glycerin structures at both ends from aggregating together within the molecule, allowing them to move independently. In addition, when b in formula (2-2) is 4 or less, there is an ether oxygen atom between the two glycerin structures, and there are b R c Since the total number of carbon atoms contained in the glycerin structure is eight or less, the rigidity of the saturated hydrocarbon group does not have much of an effect of hindering the movement of the glycerin structure at both ends.

[0053] In the divalent linking group represented by formula (2-2), the saturated hydrocarbon group located between the two glycerin structures is an ether oxygen atom and R c This structure has a regular arrangement with a repeating structure consisting of R, which improves the intermolecular interaction of fluorine-containing ether compounds. 3 A lubricating layer containing a fluorine-containing ether compound in which is a divalent linking group represented by formula (2-2) becomes denser and spin-off is further suppressed, which is preferable.

[0054] In formula (1), when x is 2, two R 3 may be the same or different. Two R 3 When the two R's are the same, the fluorine-containing ether compound is more uniformly coated on the protective layer, and a lubricating layer with better adhesion can be formed. 3 "The two R 3 The atoms contained in are R located in the center of the chain structure of the molecule. 2 This means that the elements are arranged symmetrically with respect to each other.

[0055] (R 1 and R 4 (end group indicated by In the fluorine-containing ether compound represented by formula (1), R 1 and R 4 is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms. In this embodiment, R 1 and R 4 are the above-mentioned terminal groups, a lubricating layer containing a fluorine-containing ether compound represented by formula (1) has good chemical resistance and a high spin-off suppressing effect.

[0056] More specifically, 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. As a result, the lubricating layer has excellent adhesion to the protective layer and a high spin-off suppression effect. In addition, R 1 and R 4 The number of polar groups contained in each is four or less, so R 1 and R 4 The polar groups contained in R are unlikely to be uninvolved in interactions with the active sites on the protective layer or with polar groups contained in other fluorine-containing ether compounds present in the lubricating layer, and a lubricating layer having high chemical resistance and spin-off suppression effects can be obtained. 1 and R 4 Since the number of polar groups contained in each of R is 4 or less, it is possible to prevent the polarity of the fluorine-containing ether compound in the lubricating layer containing 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. 1 and R 4 The number of polar groups contained in each of R is preferably 3 or less, and most preferably 2, so that the resulting fluorine-containing ether compound can provide a lubricating layer with better chemical resistance and spin-off suppression effect. 1 and R 4 When the number of polar groups contained in each of R 1 and R 4 This effectively prevents the aggregation of polar groups in the terminal groups represented by R 1 and R 4The polar groups contained in the fluorine-containing ether compound are more unlikely to be free from interaction with the active sites on the protective layer or with polar groups contained in other fluorine-containing ether compounds present in the lubricating layer. As a result, the fluorine-containing ether compound can prevent contaminants from being incorporated into the magnetic recording medium and can form a lubricating layer with higher chemical resistance and spin-off suppression effects.

[0057] R 1 and R 4 may be the same or different. 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 4 and 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.

[0058] R in Equation (1) 1 and the polar group R 4 The total number of polar groups contained in R is preferably 2 to 6, more preferably 3 to 6, and even more preferably 4 to 6. When the total number of polar groups is 2 or more, R in the fluorine-containing ether compound 1 and R 4 The interaction between the polar groups and the protective layer is stronger. This results in a fluorine-containing ether compound that can form a lubricating layer that has high adhesion to the protective layer. As a result, the lubricating layer formed from the fluorine-containing ether compound has excellent chemical resistance. When the total number of the above polar groups is 6 or less, the polarity of the fluorine-containing ether compound does not become too high, and the affinity with contaminants can be kept low. Therefore, the fluorine-containing ether compound can form a lubricating layer with better chemical resistance.

[0059] R 1 and R 4and each have 1 to 50 carbon atoms, preferably 3 to 20, and more preferably 4 to 15. If the number of carbon atoms is 1 or more, the affinity with contaminants is reduced, resulting in a lubricating layer with good chemical resistance. If the number of carbon atoms is 50 or less, the terminal group portion has a flexible structure, improving the adhesion of the fluorine-containing ether compound, resulting in a lubricating layer that can suppress spin-off.

[0060] R 1 and R 4 R can be appropriately selected depending on the performance required of the lubricant containing the fluorine-containing ether compound. 1 and R 4 The 1 to 4 polar groups each have may be the same in part or all, or may be different from each other. R 1 and R 4 The polar groups contained in the hydroxyl group (-OH), amino group (-NH2), carboxyl group (-COOH), formyl group (-(C=O)H), carbonyl group (-CO-), sulfo group (-SO3H), cyano group (-CN), and groups with an amide bond (-NR 7 COR 8 or -CONR 9 R 10 ;R 7 , R 8 , R 9 and R 10 are each independently a hydrogen atom or an organic group.) The group having an amide bond includes, as shown in the above formula, both a group bonded at a carbon atom constituting the amide bond (for example, a carboxamide group (-C(=O)NH2)) and a group bonded at a nitrogen atom constituting the amide bond (for example, an acetamide group (-NHC(=O)CH3)). In the group having an amide bond, the R 7 and R 8 may be bonded to each other to form a ring, and the R 9 and R 10 may be bonded to each other to form a ring. 7 , R 8 , R 9and R 10 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.

[0061] R 1 and R 4 The polar groups contained in each of the above are preferably at least one selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond. This is because the groups having a hydroxyl group, a cyano group, and an amide bond are chemically stable, and the lubricating layer containing the fluorine-containing ether compound having these polar groups will not deteriorate over the long term. In addition, the groups having a hydroxyl group, a cyano group, and an amide bond are not too acidic, and therefore have little effect on corroding the substrate.

[0062] R 1 and R 4 More preferably, R each contains at least one hydroxyl group as a polar group. 1 and R 4 Since the lubricating layer contains a hydroxyl group, 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, resulting in a lubricating layer that has excellent adhesion to the protective layer and a high spin-off suppression effect. R 1 and R 4 It is more preferable that all of the polar groups in R are hydroxyl groups. 1 and R 4 When all of the polar groups of the fluorine-containing ether compound are hydroxyl groups, the state of coating of the fluorine-containing ether compound on the protective layer can be made more uniform.

[0063] In the fluorine-containing ether compound represented by formula (1), R 1 and R 4 are preferably each independently a terminal group represented by the following formula (3):

[0064] [ka] (In formula (3), l represents an integer of 1 to 3; l m's each independently represent an integer of 1 to 6; l n's each independently represent an integer of 1 to 6; in one repeating unit, at least one of m and n is 1; A represents an alkyl group which may have a polar group, an organic group containing a carbon-carbon unsaturated bond which may have a polar group, or a hydrogen atom.)

[0065] R 1 and R 4 is a terminal group represented by formula (3), R 2 It has an oxygen atom bonded to a methylene group (-CH2-) that is bonded to R 1 and R 4 is R 1 and R 4 Each of these has an oxygen atom at the end that bonds to the adjacent CH2. 1 and R 4 The oxygen atom located at the end of R forms an ether bond (-O-) with the atoms bonded on both sides of it. This ether bond provides the fluorine-containing ether compound represented by formula (1) with appropriate flexibility, and 1 and R 4 This increases the affinity between the polar group in the terminal group represented by formula (1) 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.

[0066] In formula (3), l is an integer of 1 to 3, preferably an integer of 1 to 2, and most preferably 1. When l in formula (3) is 3 or less, it is possible to prevent the number of hydroxyl groups in the terminal groups represented by formula (3) from becoming too large, thereby preventing an increase in affinity with contaminants, and a lubricating layer with good chemical resistance can be obtained. When l in formula (3) is 2 or 3, 2 or 3 repeating units (-(CH2) m -CH(OH)-(CH2) 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.

[0067] 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. One repeating unit (-(CH2) m -CH(OH)-(CH2) n In the formula (II), at least one of m and n is 1. This is because the mobility of the hydroxyl group in the repeating unit is not reduced by the excessive number of carbon atoms in the alkylene group between the carbon atom to which the hydroxyl group is bonded and the ether oxygen atom.

[0068] In formula (3), A represents an alkyl group which may have a polar group, an organic group containing a carbon-carbon unsaturated bond which may have a polar group, or a hydrogen atom. When A in formula (3) is an alkyl group having no polar group, examples of A include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. When A in formula (3) is an alkyl group having a polar group, the polar group may be R 1 and R 4 The polar groups mentioned above as preferred examples of the polar group contained in the above can be used. Among these polar groups, at least one selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond is more preferred. Hydroxyl groups, cyano groups, and groups having an amide bond are preferred because they are chemically stable and the lubricating layer containing a fluorine-containing ether compound having these polar groups will not deteriorate over the long term. In addition, groups having a hydroxyl group, a cyano group, and an amide bond are not too acidic and will hardly corrode the substrate.

[0069] When A in formula (3) is an alkyl group having a polar group, examples of A 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-cyanobutyl group, a 2-acetamidoethyl group, a 3-acetamidopropyl group, a 4-acetamidobutyl group, a 2-carboxamidoethyl group, a 3-carboxamidopropyl group, and a 4-carboxamidobutyl group. Among the above, 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, and a 3-carboxamidopropyl group is preferred, and any one of a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, and a 2-acetamidoethyl group is more preferred.

[0070] When A in formula (3) is an organic group containing a carbon-carbon unsaturated bond, A may be an organic group containing at least one selected from the group consisting of aromatic hydrocarbons, unsaturated heterocycles, alkenyl groups, and alkynyl groups. The functional groups (active sites) present in large numbers on the protective layer include locally charged sites and sites with widely distributed charges. R represented by formula (2) 3 The hydroxyl group contained in formula (3) and formula (4) exhibits adsorption ability by interacting with the locally charged sites on the protective layer through hydrogen bonds with the hydrogen atoms. On the other hand, when the organic group represented by A in formula (3) is an organic group containing an aromatic hydrocarbon, an unsaturated heterocycle, an alkenyl group, or an alkynyl group, these have a delocalized charge and exhibit adsorption ability by interacting with the sites on the protective layer where the charge distribution is widespread. Therefore, R represented by formula (2) 3The hydroxyl group contained in formula (3) and the organic group containing a carbon-carbon unsaturated bond represented by A contained in formula (3) are adsorbed to different sites on the protective layer. 3 The hydroxyl group contained in formula (3) and the organic group containing a carbon-carbon unsaturated bond represented by A contained in formula (3) can independently interact with the functional group (active site) on the protective layer. As a result, R 1 and / or R 4 When is a terminal group represented by formula (3) and A in formula (3) is an organic group containing a carbon-carbon unsaturated bond, the lubricating layer containing the fluorine-containing ether compound will have excellent adhesion to the protective layer.

[0071] When A in formula (3) is an organic group containing a carbon-carbon unsaturated bond and having no polar group, A is, for example, a phenyl group, a methoxyphenyl group, a fluorinated phenyl group, a naphthyl group, a phenethyl group, a methoxyphenethyl group, a fluorinated phenethyl group, a benzyl group, a methoxybenzyl group, a naphthylmethyl group, a methoxynaphthyl 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 pyrrolyl group, a pyrazol ... Examples thereof include a lysyl group, a pyrimidinyl group, a pyridazinyl group, a pyrazinyl group, an indolinyl group, a benzofuranyl group, a benzothienyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a benzopyrazolyl group, a benzisoxazolyl group, a benzisothiazolyl group, a quinolyl group, an isoquinolyl group, a quinazolinyl group, a quinoxalinyl group, a phthalazinyl group, a cinnolinyl 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, and a hexynyl group. Among the above, A is preferably any one of a phenyl group, a methoxyphenyl group, a naphthyl group, a phenethyl group, a methoxyphenethyl group, a fluorinated phenethyl group, a thienylethyl group, an allyl group, a butenyl group, and a propargyl group, and more preferably any one of a phenyl group, a methoxyphenyl group, an allyl group, and a butenyl group. When A is any one of a phenyl group, a methoxyphenyl group, an allyl group, and a butenyl group, the interaction with the site on the protective layer where the charge distribution is widespread can be strengthened, and the adhesion to the protective layer can be improved.

[0072] When A in formula (3) is an organic group containing a carbon-carbon unsaturated bond having a polar group, the polar group can be R 1 and R 4 The polar groups listed as preferred examples of the polar group contained in can be used. Among these polar groups, at least one selected from the group consisting of a cyano group and a group having an amide bond is more preferred. A cyano group and a group having an amide bond are preferred because they are chemically stable and do not deteriorate over the long term when the lubricating layer contains a fluorine-containing ether compound having these polar groups. In addition, a cyano group and a group having an amide bond are not too acidic and have almost no corrosive effect on the substrate.

[0073] When A in formula (3) is an organic group containing a carbon-carbon unsaturated bond having a polar group, examples of A include a cyanophenyl group, a carboxamidophenyl group, an acetamidophenyl group, a cyanonaphthyl group, a carboxamido naphthyl group, an acetamido naphthyl group, a cyanophenethyl group, a carboxamidophenethyl group, an acetamidophenethyl group, a cyanobenzyl group, a carboxamidobenzyl group, and an acetamidobenzyl group.

[0074] Among the above, any one of a cyanophenyl group, a carboxamidophenyl group, an acetamidophenyl group, a cyanonaphthyl group, a carboxamido naphthyl group, an acetamido naphthyl group, a cyanobenzyl group, a carboxamidobenzyl group, and an acetamidobenzyl group is preferable, and any one of a cyanophenyl group, a carboxamidophenyl group, and an acetamidophenyl group is more preferable.

[0075] When A in formula (3) is a hydrogen atom, A forms a hydroxyl group with the oxygen atom in formula (3). When A is a hydrogen atom, the repeating unit (-(CH2) m -CH(OH)-(CH2) n In the repeating unit (—O—), n is preferably 2 or greater. When n is 2 or greater in the repeating unit to which A is bonded, the distance between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group becomes more appropriate, and the adhesion to the protective layer can be improved.

[0076] In the fluorine-containing ether compound represented by formula (1), R 1 and R 4 are each independently a terminal group represented by formula (3-1) or (3-2).

[0077] [ka] (In formula (3-1), p represents an integer of 0 to 3, q ​​represents an integer of 0 to 2, and r represents an integer of 1 to 5; the total value of p and r is 1 to 5; and B represents a polar group.) (In formula (3-2), s represents an integer of 0 to 2, and t represents an integer of 1 to 5.)

[0078] Each polar group contained in the terminal group represented by formula (3-1) and formula (3-2) is bonded to a different carbon atom. In formula (3-1) and formula (3-2), the carbon atoms bonded to the polar groups are bonded to each other via a linking group containing a carbon atom not bonded to a polar group. Therefore, R 1 and / or R 4is a terminal group represented by formula (3-1) or formula (3-2), the linking group containing a carbon atom not bonded to a polar group allows both the terminal polar group and the hydroxyl group adjacent to the terminal polar group to be oriented in such a way that they can adhere to the protective layer, and therefore it is presumed that a lubricating layer containing a fluorine-containing ether compound represented by formula (1) can suppress spin-off.

[0079] In the terminal group represented by formula (3-1), the linking group between the carbon atom to which the terminal polar group B is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal polar group B is bonded contains an oxygen atom forming an ether bond. In formula (3-1), p represents an integer of 0 to 3, r represents an integer of 1 to 5, and the sum of p and r is 1 to 5. Therefore, the linking group has a linear structure consisting of 3 to 7 atoms, including carbon atoms to which the polar group B and the hydroxyl group are not bonded.

[0080] In the terminal group represented by formula (3-1), the linking group contains an oxygen atom forming an ether bond and has a linear structure consisting of three or more atoms, including polar group B and a carbon atom not bonded to a hydroxyl group, so the distance between polar group B and the hydroxyl group adjacent to polar group B is appropriate. This prevents the polar group B from interacting with the hydroxyl group adjacent to polar group B within the molecule, allowing both polar group B and the hydroxyl group adjacent to polar group B to adhere to the protective layer. Furthermore, because the linking group has a linear structure consisting of three or more atoms, even if it contains an oxygen atom forming an ether bond, the molecular mobility is appropriate, intramolecular aggregation is unlikely to occur, and excellent adhesion to the protective layer is achieved.

[0081] In the terminal group represented by formula (3-1), the linking group contains an oxygen atom forming an ether bond and has a linear structure consisting of 7 atoms or less, including a carbon atom not bonded to the polar group B and a hydroxyl group, so the linking group is not too bulky and does not have much of an effect of interfering with the movement of the polar group.For these reasons, a lubricating layer containing a fluorine-containing ether compound having an terminal group represented by formula (3-1), in which the linking group is a linear structure consisting of 3 to 7 atoms, including a carbon atom not bonded to the polar group B and a hydroxyl group, has excellent adhesion to the protective layer, exhibits high chemical resistance, and has a high spin-off suppression effect.

[0082] In formula (3-1), the sum of p and r is 1 to 5, preferably 1 to 3. In formula (3-1), the carbon atom contained in the linking group disposed between the carbon atoms bonded to the polar groups prevents the intramolecular interaction between adjacent polar groups from occurring prior to the interaction between the polar groups and the protective layer, thereby improving the adhesion between the polar groups in formula (3-1) and the protective layer. On the other hand, if the number of carbon atoms contained in the linking group is too large, the flexibility of the terminal group represented by formula (3-1) decreases, making it difficult to uniformly coat the protective layer. In the terminal group represented by formula (3-1), the sum of p and r is 5 or less, so the alkylene chain in the main chain portion of formula (3-1) is not too long. Therefore, the long rigid alkylene chain reduces the flexibility of the terminal portion, weakening the interaction with the protective layer and preventing the terminal portion from lifting up. p is preferably 0 or 1, more preferably 0. r is preferably 1 or 2, more preferably 1.

[0083] In formula (3-1), B represents a polar group. B can be R 1 and R 4The polar groups mentioned above as preferred examples of the polar group contained in can be used. Among these polar groups, it is more preferable that B is 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 groups having a hydroxyl group, a cyano group, and an amide bond are chemically stable, and the lubricating layer containing the fluorine-containing ether compound having these polar groups will not deteriorate over the long term. In addition, the groups having a hydroxyl group, a cyano group, and an amide bond are not too acidic, and will hardly corrode the substrate.

[0084] In formula (3-1), q represents an integer of 0 to 2. The number of polar groups in formula (3-1) is q+2. 1 and R 4 The number of polar groups contained in each of the formulas is preferably 3 or less, and most preferably 2. Therefore, q in formula (3-1) is preferably 0 or 1, and more preferably 0.

[0085] In the terminal group represented by formula (3-2), the linking group between the carbon atom to which the terminal hydroxyl group is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded does not contain an oxygen atom. This reduces intramolecular interaction and reduces intramolecular aggregation, resulting in excellent adhesion to the protective layer. In formula (3-2), t represents an integer of 1 to 5. Therefore, the linking group has a linear structure consisting of 1 to 5 atoms, including a carbon atom to which no hydroxyl group is bonded. Because the linking group contained in formula (3-2) has a linear structure consisting of one or more atoms, including a carbon atom to which no hydroxyl group is bonded, the distance between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group is appropriate. This prevents intramolecular interaction between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group, reducing intramolecular aggregation.

[0086] Similarly to formula (3-1), if the number of carbon atoms contained in the linking group disposed between the carbon atoms bonded to the polar groups in formula (3-2) is too large, the flexibility of the terminal group represented by formula (3-2) decreases, making it difficult to uniformly coat the entire surface of the protective layer. In the terminal group represented by formula (3-2), t is 5 or less, so the alkylene chain in the main chain portion of formula (3-2) is not too long. Therefore, a long, rigid alkylene chain reduces the flexibility of the terminal portion, preventing a decrease in the interaction between the terminal hydroxyl group and the protective layer. t is preferably 1 or 2, and more preferably 1.

[0087] Furthermore, since the linking group does not contain an oxygen atom forming an ether bond and has a linear structure consisting of five or fewer atoms including a carbon atom not bonded to a hydroxyl group, the linking group is less likely to become too bulky and hinder the movement of the hydroxyl group. For these reasons, a lubricating layer containing a fluorine-containing ether compound in which the linking group has a linear structure consisting of 1 to 5 atoms including a carbon atom that does not contain an oxygen atom forming an ether bond and does not have a hydroxyl group bonded thereto exhibits excellent adhesion to the protective layer, excellent chemical resistance, and a high spin-off suppression effect.

[0088] In formula (3-2), s represents an integer of 0 to 2. The number of polar groups in formula (3-2) is s+2. 1 and R 4 The number of polar groups contained in each of the formulas is preferably 3 or less, and most preferably 2. Therefore, s in formula (3-2) is preferably 0 or 1, and more preferably 0.

[0089] When x in formula (1) is 2, the fluorine-containing ether compound contains R 3 There are two R 3 Each of these has two hydroxyl groups, so when x is 2, the ratio of R to the total number of polar groups in the fluorine-containing ether compound is 1 and R 4The ratio of polar groups in the protective layer is reduced. Since the number of active sites in the protective layer is limited, R 1 and R 4 When the proportion of polar groups in the 1 and R 4 Therefore, when x is 2, R 1 and R 4 R is preferably a structure represented by formula (3-1) or formula (3-2) which has a relatively strong interaction with the protective layer. 1 and R 4 are respectively represented by formula (3-1) or formula (3-2), for example, R 1 and / or R 4 In this case, compared to when the carbon atoms to which the hydroxyl groups are bonded are directly connected, the hydroxyl groups in the molecule are less likely to aggregate and more likely to interact with the protective layer. 1 and R 4 When each of these is formula (3-1) or formula (3-2), even if x is 2, the terminal portion of the fluorinated ether compound is unlikely to lift up, and the adhesion to the protective layer is unlikely to decrease.

[0090] (R 2 (PFPE chain shown as In the fluorine-containing ether compound represented by formula (1), R 2 is a perfluoropolyether chain. 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 R not only covers the surface of the protective layer but also 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.

[0091] (x+1) R 2 The (x+1) R may be partially or entirely the same, or may be different from each other. 2It is preferable that all of the (x+1) R are the same. This is because the coating state of the fluorine-containing ether compound on the protective layer becomes more uniform, 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 repeating unit structure but different average degrees of polymerization.

[0092] 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.

[0093] (x+1) R in Equation (1) 2 are each preferably independently a PFPE chain represented by the following formula (4) derived from a polymer or copolymer of perfluoroalkylene oxide. -(CF2) w1 -O-(CF2O) w2 -(CF2CF2O) w3 -(CF2CF2CF2O) w4 -(CF2CF2CF2CF2O) w5 -(CF2) w6 - (4) (In formula (4), w2, w3, w4, and w5 represent the average degree of polymerization and each independently represent 0 to 20; provided that w2, w3, w4, and w5 cannot all be 0 at the same time; w1 and w6 represent the average value representing the number of CF2 and each independently represent 1 to 3; there are no particular limitations on the arrangement order of the repeating units (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) in formula (4).)

[0094] 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 are average values ​​indicating the number of CF2, and each independently represents 1 to 3. w1 and w6 are determined depending on the structure of the repeating unit arranged at the end of the chain structure in the PFPE chain represented by formula (4), etc. In formula (4), (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) are repeating units. There are no particular limitations on the arrangement order of the repeating units in formula (4). There are also no particular limitations on the number of types of repeating units in formula (4).

[0095] (x+1) R in Equation (1) 2 are preferably each independently any one selected from the PFPE chains represented by the following formulas (4-1) to (4-4). (x+1) R 2 are each one selected from the PFPE chains represented by formulas (4-1) to (4-4), a fluorine-containing ether compound can be obtained that provides a lubricating layer with good lubricity. 2 When each of the (x+1) R 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. This results in a fluorine-containing ether compound with appropriate hardness. Therefore, the fluorine-containing ether compound applied to the protective layer is less likely to aggregate on the protective layer, and a thinner lubricating layer can be formed with a sufficient coverage. 2 However, a lubricating layer formed by a fluorine-containing ether compound that is any one selected from the PFPE chains represented by formulas (4-1) to (4-4) becomes denser and can further suppress spin-off.

[0096] -CF2-(OCF2CF2) h -(OCF2) i -OCF2- (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.) -CF2CF2-(OCF2CF2CF2) j -OCF2CF2- (4-2) (In formula (4-2), j represents the average degree of polymerization and represents 1 to 15.) -CF2CF2CF2-(OCF2CF2CF2CF2) k -OCF2CF2CF2- (4-3) (In formula (4-3), k represents the average degree of polymerization and represents 1 to 10.) -(CF2) w7 -O-(CF2CF2CF2O) w8 -(CF2CF2O) w9 -(CF2) 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 the average number of CF2, each independently representing 1 to 2.)

[0097] In formula (4-1), the arrangement order of the repeating units (OCF2CF2) and (OCF2) is not particularly limited. In formula (4-1), the number h of (OCF2CF2) and the number i of (OCF2) may be the same or different. The PFPE chain represented by formula (4-1) may be a polymer of (OCF2CF2). In addition, the PFPE chain represented by formula (4-1) may be any of a random copolymer, a block copolymer, and an alternating copolymer composed of (OCF2CF2) and (OCF2).

[0098] 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, and therefore the fluorine-containing ether compound provides 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, and therefore the viscosity of the fluorine-containing ether compound does not become too high, and lubricants containing the fluorine-containing ether compound are easily applied, which is preferable. h, i, j, and k, which indicate the average degree of polymerization, are preferably 1 to 10, more preferably 1.5 to 8, and even more preferably 2 to 7, and therefore the fluorine-containing ether compound easily wets and spreads on the protective layer, and a lubricating layer with a uniform thickness is easily obtained.

[0099] In formula (4-4), the arrangement order of the repeating units (CFCFCFO) and (CFCFO) is not particularly limited. In formula (4-4), the number w8 of (CFCFCFO) and the number w9 of (CFCFO), which indicate the average degree of polymerization, may be the same or different. Formula (4-4) may include any of a random copolymer, a block copolymer, and an alternating copolymer composed of the monomer units (CFCFCFO) and (CFCFO).

[0100] 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. In formula (4-4), w7 and w10 are average values ​​indicating the number of CF2, and each independently represents 1 to 2. w7 and w10 are determined depending on the structure of the repeating unit located at the end of the chain structure in the PFPE chain represented by formula (4-4), etc.

[0101] In the fluorine-containing ether compound represented by formula (1), when x is 1, two R 2 is the same, and R 1 and R 4 This is because the resulting 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 is the same, and R 1 Side R 2 and R 4 Side R 2 is the same, and R 1 and R 4 This is because the resulting fluorine-containing ether compound can be produced easily and efficiently.

[0102] Specifically, the fluorine-containing ether compound represented by formula (1) is preferably any one of the compounds represented by the following formulae (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG). When the compound represented by formula (1) is any of the compounds represented by the following formulae (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG), the raw materials are easily available, and even if the thickness is thin, it is possible to form a lubricating layer that has better chemical resistance and is highly effective in suppressing spin-off of magnetic recording media.

[0103] In the compounds represented by the following formulae (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG), Rf1, Rf2, and Rf3, which represent PFPE chains, respectively have the following structures. That is, in the compounds represented by the following formulae (AA) to (AJ), (BC) to (BR), (CA) to (CF), and (DB) to (DG), Rf1 is a PFPE chain represented by the above formula (4-1). In the compounds represented by the following formulae (BA) and (DA), Rf2 is a PFPE chain represented by the above formula (4-2). In the compound represented by the following formula (BB), Rf3 is a PFPE chain represented by the above formula (4-3). In addition, h and i in Rf1, j in Rf2, and k in Rf3, which represent the PFPE chain in formulas (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG), are values ​​that indicate the average degree of polymerization, and therefore are not necessarily integers.

[0104] [ka]

[0105] In the compounds represented by the following formulae (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG), R 3 is a linking group represented by the above formula (2-1) or (2-2). In the compounds represented by the following formulas (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG), R 1 and R 4 is a terminal group represented by the above formula (3), (3-1) or (3-2).

[0106] In the compounds represented by the following formulas (AA) to (AG), x in formula (1) is 1. 3 is the linking group represented by the above formula (2-1). 1 and R 4 is the terminal group represented by the above formula (3-1). 2 is the PFPE chain represented by the above formula (4-1). In the compounds represented by the following formulas (AH) to (AJ), x in formula (1) is 1. 3 is the linking group represented by the above formula (2-2). 1 and R 4 is the terminal group represented by the above formula (3-1). 2 is the PFPE chain represented by the above formula (4-1).

[0107] In the compounds represented by the following formulas (BA) and (BB), x in formula (1) is 1. 3 is the linking group represented by the above formula (2-1). 1 and R 4 is the terminal group represented by the above formula (3-1). Formula (BA) is R 2 is the above formula (4-2), and formula (BB) is R 2 is the PFPE chain represented by the above formula (4-3). In the compounds represented by the following formulas (BC) to (BR), x in formula (1) is 1. 3is a linking group represented by the above formula (2-1). Formulas (BC), (BE), (BF), (BH) to (BJ), (BL), (BQ), and (BR) are R 1 and R 4 The above formula (3-1), formulas (BD), (BG), and (BK) are R 1 and R 4 is the above formula (3-2), and formulas (BM) to (BP) are R 1 and R 4 is a terminal group represented by formula (3) that does not fall under the above formulas (3-1) and (3-2). 2 is the PFPE chain represented by the above formula (4-1).

[0108] In the compounds represented by the following formulas (CA) to (CE), x in formula (1) is 2. 3 is the linking group represented by the above formula (2-1). 1 and R 4 is the terminal group represented by the above formula (3-1). 2 is the PFPE chain represented by the above formula (4-1). In the compound represented by the following formula (CF), x in formula (1) is 2. 3 is the linking group represented by the above formula (2-2). 1 and R 4 is the terminal group represented by the above formula (3-1). 2 is the PFPE chain represented by the above formula (4-1).

[0109] In the compound represented by the following formula (DA), x in formula (1) is 2. 3 is the linking group represented by the above formula (2-1). 1 and R 4 is the terminal group represented by the above formula (3-1). 2 is the PFPE chain represented by the above formula (4-2). In the compounds represented by the following formulas (DB) to (DG), x in formula (1) is 2. 3 is a linking group represented by the above formula (2-1). Formulas (DB), (DD) to (DF) are R 1 and R 4 is the above formula (3-1), and formula (DC) is R1 and R 4 is the above formula (3-2), and formula (DG) is R 1 and R 4 is a terminal group represented by formula (3) that does not fall under the above formulas (3-1) and (3-2). 2 is the PFPE chain represented by the above formula (4-1).

[0110] [ka] (In the two Rf1s in formula (AA), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AB), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AC), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AD), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0111] [ka] (In the two Rf1s in formula (AE), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AF), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AG), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AH), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0112] [ka] (In the two Rf1s in formula (AI), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (AJ), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0113] [ka] (In the two Rf2 in formula (BA), j represents the average degree of polymerization and represents 1 to 15; j in the two Rf2 may be the same or different.) (In the two Rf3s in formula (BB), k represents the average degree of polymerization and represents 1 to 10; k in the two Rf3s may be the same or different.) (In the two Rf1s in formula (BC), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BD), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0114] [ka] (In the two Rf1s in formula (BE), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BF), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BG), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BH), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0115] [ka] (In the two Rf1s in formula (BI), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BJ), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BK), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BL), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0116] [ka] (In the two Rf1s in formula (BM), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BN), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BO), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BP), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different; and Me represents a methyl group.)

[0117] [ka] (In the two Rf1s in formula (BQ), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.) (In the two Rf1s in formula (BR), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; h and i in the two Rf1s may be the same or different.)

[0118] [ka] (In the three Rf1s in formula (CA), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or different from each other.) (In the three Rf1s in formula (CB), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.) (In the three Rf1s in formula (CC), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.)

[0119] [ka] (In the three Rf1s in formula (CD), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or different from each other.) (In the three Rf1s in formula (CE), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.) (In the three Rf1s in formula (CF), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.)

[0120] [ka] (In the three Rf2 in formula (DA), j represents the average degree of polymerization and represents 1 to 15; some or all of the j in the three Rf2 may be the same or may be different from each other.) (In the three Rf1s in formula (DB), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.) (In the three Rf1s in formula (DC), h and i represent the average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.)

[0121] [ka] (In the three Rf1s in formula (DD), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.) (In the three Rf1s in formula (DE), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.) (In the three Rf1s in formula (DF), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or different from each other.) (In the three Rf1s in formula (DG), h and i represent an average degree of polymerization, h represents 1 to 20, and i represents 0 to 20; some or all of h and i in the three Rf1s may be the same or may be different from each other.)

[0122] 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.

[0123] The number average molecular weight (Mn) of fluorine-containing ether compounds was measured using AVANCEIII400 manufactured by Bruker Biospin. 1 H-NMR measurement and 19 These are values ​​measured by F-NMR. Specifically, 19 The number of repeating units of the PFPE chain is calculated from the integrated value measured by F-NMR to determine the number average molecular weight. For NMR (nuclear magnetic resonance) measurements, the sample is diluted in a hexafluorobenzene / d-acetone (4 / 1 v / v) solvent and measured. 19 The reference for F-NMR chemical shifts is the hexafluorobenzene peak at -164.7 ppm. 1 The reference for H-NMR chemical shifts is the acetone peak at 2.2 ppm.

[0124] The fluorine-containing ether compound of this embodiment is preferably subjected to molecular weight fractionation by an appropriate method to make the molecular weight dispersity (ratio of weight average molecular weight (Mw) / number average molecular weight (Mn)) 1.3 or less. In this embodiment, the method for molecular weight fractionation is not particularly limited, but for example, molecular weight fractionation by silica gel column chromatography, gel permeation chromatography (GPC), or the like, molecular weight fractionation by supercritical extraction, or the like can be used.

[0125] "Manufacturing method" The method for producing the fluorinated ether compound of the present embodiment is not particularly limited, and the compound can be produced by a conventionally known production method. The fluorinated ether compound of the present embodiment can be produced, for example, by the production method shown below.

[0126] [First manufacturing method (x is 1)] (R 1 and R 4 and are the same, and the two R 2 are the same) R in Equation (1) 2 A fluorine-based compound is prepared in which a hydroxymethyl group (-CH2OH) is placed at each end of the perfluoropolyether chain corresponding to the above.

[0127] Next, the hydroxyl group of the hydroxymethyl group located at one end of the fluorine-based compound and the R 1 The group corresponding to (=R 4 (first reaction) with an epoxy compound having a group corresponding to R 2 At one end of the perfluoropolyether chain corresponding to 1 The group corresponding to (=R 4 An intermediate compound 1-1 having a group corresponding to

[0128] R in Equation (1) 1 The group corresponding to (=R 4 Examples of epoxy compounds having a group corresponding to the following formula (5-1) include compounds represented by the following formulas (5-1) to (5-16). THP in the following formulas (5-1) to (5-13) represents a tetrahydropyranyl group. Me in the following formula (5-14) represents a methyl group.

[0129] [ka]

[0130] R in Equation (1) 1 The group corresponding to (=R4 The epoxy compound having a group corresponding to R in formula (1) can be produced by the following method. 1 or R 4 The compound represented by formula (5-2) can be produced by a method in which a diol having a structure corresponding to a portion of the terminal group represented by formula (5-3) is prepared, one hydroxyl group is protected by a known method, and then the diol is reacted with a halogen compound such as a bromine compound or a chlorine compound having an epoxy group. For example, when producing a compound represented by formula (5-2), one hydroxyl group of a glycol having the corresponding structure is protected with dihydropyran (DHP) and then reacted with epibromohydrin, as shown in formula (6-1) below. THP in formula (6-1) below represents a tetrahydropyranyl group.

[0131] [ka]

[0132] The epoxy compound may be produced by the following method: 2-(2-bromoethoxy)tetrahydro-2H-pyran and R 1 or R 4 The compound represented by formula (5-4) can be produced by reacting 2-(2-bromoethoxy)tetrahydro-2H-pyran with 3-buten-1-ol, followed by oxidation with m-chloroperbenzoic acid, as shown in formula (6-2) below. THP in formula (6-2) below represents a tetrahydropyranyl group.

[0133] [ka]

[0134] The epoxy compound may be produced by the following method:1 or 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 or R 4 The compound represented by formula (5-1) is subjected to an addition reaction with an alcohol having an alkenyl group corresponding to a portion of the terminal group represented by formula (5-2). The resulting compound is then oxidized with m-chloroperbenzoic acid (mCPBA). The hydroxyl group generated by the addition reaction may be protected by a known method before the compound obtained by the addition reaction is oxidized with m-chloroperbenzoic acid (mCPBA). For example, the compound represented by formula (5-5) can be produced by adding an epoxy compound represented by formula (5-1) to allyl alcohol, protecting the resulting compound with dihydropyran (DHP), and then oxidizing the resulting compound with m-chloroperbenzoic acid (mCPBA), as shown in formula (6-3) below. THP in formula (6-3) below represents a tetrahydropyranyl group.

[0135] [ka]

[0136] Thereafter, the hydroxyl group of the hydroxymethyl group located at one end of the intermediate compound 1-1 produced in the first reaction described above is reacted with the R 3 is reacted with a compound having two corresponding epoxy groups (second reaction). R in Equation (1) 3 As a compound having two epoxy groups corresponding to the above, for example, compounds represented by the following formulas (7-1) to (7-10) can be used.

[0137] [ka]

[0138] R in Equation (1) 3A compound having two epoxy groups corresponding to R can be prepared using the method shown below. 3 For example, the compound represented by formula (7-1) can be produced by reacting 1,3-propanediol with twice the molar amount of epibromohydrin, as shown in the following formula (8-1):

[0139] [ka]

[0140] R in Equation (1) 3 The compound having two epoxy groups corresponding to the above may be produced by a method of oxidizing a compound having two alkenyl groups with m-chloroperbenzoic acid (mCPBA), or a commercially available product may be used. 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 are the same, and the two R 2 can be prepared.

[0141] [Second manufacturing method (when x is 1)] (R 1 and R 4 and differ, and / or two R 2 are different) First, R 1 Side R 2 The hydroxyl group at one end of the perfluoropolyether chain of the fluorine-based compound, which has a hydroxymethyl group at each end, corresponds to R 1 An epoxy compound having a group corresponding to the formula (I) is reacted with the compound to obtain intermediate compound 1a (first reaction). Next, R 4 Side R 2 The hydroxyl group at one end of the perfluoropolyether chain of the fluorine-based compound, which has a hydroxymethyl group at each end, corresponds to R4 An epoxy compound having a group corresponding to the formula (II) is reacted to obtain intermediate compound 1b (second reaction).

[0142] Next, the hydroxyl group at one end of the intermediate compound 1a is reacted with the R 3 After reacting with a compound having an epoxy group and an alkenyl group corresponding to the above, the double bond of the resulting compound is oxidized to obtain intermediate compound 1-2 (third reaction). R in Equation (1) 3 As the compound having an epoxy group and an alkenyl group corresponding to the above, for example, compounds represented by the formulae (9-1) to (9-10) described below can be used.

[0143] Next, the hydroxyl group at one end of the intermediate compound 1b is reacted with the epoxy group of the intermediate compound 1-2 obtained in the third reaction (fourth 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 differ, and / or two R 2 can be prepared.

[0144] [Third manufacturing method (when x is 2)] (R 1 and R 4 are the same, and the two R 3 is the same, and R 1 Side R 2 and R 4 Side R 2 are the same) First, in the same manner as in the first manufacturing method, R 1 Side and R 4 Side R 2 At one end of the perfluoropolyether chain corresponding to 1 The group corresponding to (=R 4 An intermediate compound 1-1 having a group corresponding to (first reaction) is obtained.

[0145] Next, R in the center of the molecule in formula (1) 2A fluorine-based compound having a hydroxymethyl group (-CHOH) at each end of a perfluoropolyether chain corresponding to formula (1) is prepared. Then, the hydroxyl groups of the hydroxymethyl groups at both ends of the fluorine-based compound are reacted with the R 3 is reacted with a compound having an epoxy group and an alkenyl group corresponding to the above to obtain intermediate compound 2-1 (second reaction).

[0146] R in Equation (1) 3 As the compound having an epoxy group and an alkenyl group corresponding to the above, for example, compounds represented by the following formulas (9-1) to (9-10) can be used.

[0147] [ka]

[0148] R in Equation (1) 3 The compound having an epoxy group and an alkenyl group corresponding to R 3 The compound represented by formula (9-1) can be produced by reacting a diol having a structure corresponding to Y in formula (2) with allyl bromide and epibromohydrin in this order. For example, the compound represented by formula (9-1) can be produced by reacting 1,3-propanediol with allyl bromide and epibromohydrin in this order, as shown in formula (10-1) below.

[0149] [ka]

[0150] R in Equation (1) 3 The compound having an epoxy group and an alkenyl group corresponding to the above may be produced by reacting a compound having two alkenyl groups with m-chloroperbenzoic acid (mCPBA) to oxidize one of the alkenyl groups, or a commercially available product may be used.

[0151] Next, the intermediate compound 2-1 produced in the second reaction is oxidized by the action of m-chloroperbenzoic acid (mCPBA) (third reaction). This results in the formation of the R 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 following: The third reaction may be carried out after the hydroxyl group of the intermediate compound 2-1 is appropriately protected by a known method.

[0152] Thereafter, the hydroxyl group of the hydroxymethyl group located at one end of the intermediate compound 1-1 is reacted with the epoxy groups located at both ends of the intermediate compound 3-1 (fourth reaction).

[0153] 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 is the same, and R 1 Side R 2 and R 4 Side R 2 can be prepared.

[0154] [4th manufacturing method (when x is 2)] (R 1 Side R 3 and R 4 Side R 3 and are the same, and R 1 and R 4 and / or R 1 Side R 2 and R 4 Side R 2 are different) In the first reaction of the third production method, intermediate compound 1a and intermediate compound 1b are obtained instead of intermediate compound 1-1. Then, intermediate compound 3-1 is obtained in the same manner as in the second and third reactions of the third production method. 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.

[0155] 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 are the same, and R 1 and R 4 and / or R 1 Side R 2 and R 4 Side R 2 can be prepared.

[0156] [5th ​​manufacturing method (x is 2)] (R 1 Side R 3 and R 4 Side R 3 Unlike R 1 and R 4 and are the same, and R 1 Side R 2 and R 4 Side R 2 are the same) In the second reaction of the third production method, R 3 Instead of a compound having an epoxy group and an alkenyl group, R 1 Side R 3 and a compound having an epoxy group and an alkenyl group corresponding to R in formula (1). 4 Side R 3 The fluorine-based compound is reacted with a compound having an epoxy group and an alkenyl group corresponding to the compound shown in formula (1) to obtain intermediate compound 2-2. The third and fourth reactions are then 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.

[0157] 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 are the same, and R 1Side R 2 and R 4 Side R 2 can be prepared. 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 may be the same as or different from.

[0158] [Lubricants for magnetic recording media] The lubricant for a magnetic recording medium of this embodiment contains a fluorine-containing ether compound represented by the above formula (1). The lubricant of the present embodiment can be used by mixing, as needed, known materials used as lubricant materials, as long as the properties resulting from the inclusion of the fluorinated ether compound represented by the above formula (1) are not impaired.

[0159] 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), and the like. 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.

[0160] 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 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more.

[0161] The lubricant of this embodiment contains the fluorine-containing ether compound represented by the above formula (1), and therefore can form a lubricating layer that has excellent chemical resistance and a high spin-off suppressing effect.

[0162] [Magnetic recording media] The magnetic recording medium of this embodiment has at least a magnetic layer, a protective layer, and a lubricating layer provided in this order on a substrate. In the magnetic recording medium of this embodiment, one or more underlayers may be provided between the substrate and the magnetic layer, as needed, and at least one of an adhesive layer and a soft magnetic layer may also be provided between the underlayer and the substrate.

[0163] FIG. 1 is a schematic cross-sectional view showing one embodiment of the magnetic recording medium of the present invention. The magnetic recording medium 10 of this embodiment has a structure in which an adhesive layer 12, a soft magnetic layer 13, a first underlayer 14, a second underlayer 15, a magnetic layer 16, a protective layer 17, and a lubricating layer 18 are sequentially provided on a substrate 11.

[0164] "substrate" The substrate 11 may be, for example, a non-magnetic substrate in which a film made of NiP or a NiP alloy is formed on a base made of a metal or alloy material such as Al or an Al alloy. The substrate 11 may be a non-magnetic substrate made of a non-metallic material such as glass, ceramics, silicon, silicon carbide, carbon, or resin, or may be a non-magnetic substrate having a NiP or NiP alloy film formed on a base made of any of these non-metallic materials.

[0165] "Adhesion layer" The adhesive layer 12 prevents the progress of corrosion of the substrate 11, which occurs when the substrate 11 and the soft magnetic layer 13 provided on the adhesive layer 12 are disposed in contact with each other. The material of the adhesive layer 12 can be appropriately selected from, for example, Cr, a Cr alloy, Ti, a Ti alloy, CrTi, NiAl, an AlRu alloy, etc. The adhesive layer 12 can be formed by, for example, a sputtering method.

[0166] "Soft magnetic layer" The soft magnetic layer 13 preferably has a structure in which a first soft magnetic film, an intermediate layer made of a Ru film, and a second soft magnetic film are laminated in this order. That is, the soft magnetic layer 13 preferably has a structure in which the intermediate layer made of a Ru film is sandwiched between two soft magnetic films, and the soft magnetic films above and below the intermediate layer are antiferro-coupling (AFC).

[0167] The first and second soft magnetic films may be made of a material such as a CoZrTa alloy or a CoFe alloy. It is preferable to add Zr, Ta, or Nb to the CoFe alloy used in the first and second soft magnetic films. This promotes the amorphization of the first and second soft magnetic films. As a result, it is possible to improve the orientation of the first underlayer (seed layer) and reduce the flying height of the magnetic head. The soft magnetic layer 13 can be formed by, for example, a sputtering method.

[0168] "First base layer" The first underlayer 14 is a layer that controls the orientation and crystal size of the second underlayer 15 and magnetic layer 16 that are provided thereon. The first underlayer 14 may be, for example, a Cr layer, a Ta layer, a Ru layer, or a CrMo alloy layer, a CoW alloy layer, a CrW alloy layer, a CrV alloy layer, or a CrTi alloy layer. The first underlayer 14 can be formed by, for example, a sputtering method.

[0169] "Second base layer" The second underlayer 15 is a layer that controls the orientation of the magnetic layer 16. The second underlayer 15 is preferably a layer made of Ru or a Ru alloy. The second underlayer 15 may be a single layer or multiple layers. When the second underlayer 15 is multiple layers, all the layers may be made of the same material, or at least one layer may be made of a different material. The second underlayer 15 can be formed by, for example, a sputtering method.

[0170] "Magnetic layer" The magnetic layer 16 is a magnetic film whose easy axis of magnetization is oriented perpendicular or parallel to the substrate surface. The magnetic layer 16 contains Co and Pt. To improve the SNR characteristics, the magnetic layer 16 may contain oxides, Cr, B, Cu, Ta, Zr, or the like. Examples of oxides contained in the magnetic layer 16 include SiO2, SiO, Cr2O3, CoO, Ta2O3, and TiO2.

[0171] The magnetic layer 16 may be composed of a single layer, or may be composed of multiple magnetic layers made of materials with different compositions. For example, when the magnetic layer 16 is composed of three layers, namely, a first magnetic layer, a second magnetic layer, and a third magnetic layer stacked in this order from the bottom, the first magnetic layer preferably has a granular structure made of a material containing Co, Cr, and Pt and further containing an oxide. The oxide contained in the first magnetic layer is preferably an oxide of Cr, Si, Ta, Al, Ti, Mg, Co, or the like. Among these, TiO2, Cr2O3, SiO2, and the like are particularly suitable. Furthermore, the first magnetic layer is preferably made of a composite oxide containing two or more types of oxides. Among these, Cr2O3-SiO2, Cr2O3-TiO2, SiO2-TiO2, and the like are particularly suitable.

[0172] The first magnetic layer may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re in addition to Co, Cr, Pt, and oxides. The second magnetic layer can be made of the same material as the first magnetic layer, and preferably has a granular structure.

[0173] The third magnetic layer preferably has a non-granular structure made of a material containing Co, Cr, and Pt and not containing oxides, and may contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn in addition to Co, Cr, and Pt.

[0174] When magnetic layer 16 is formed of multiple magnetic layers, it is preferable to provide a non-magnetic layer between adjacent magnetic layers. When magnetic layer 16 is formed of three layers, namely, a first magnetic layer, a second magnetic layer, and a third magnetic layer, it is preferable to provide a non-magnetic layer between the first magnetic layer and the second magnetic layer and between the second magnetic layer and the third magnetic layer.

[0175] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 can suitably be made of, for example, Ru, a Ru alloy, a CoCr alloy, or a CoCrX1 alloy (X1 represents one or more elements selected from Pt, Ta, Zr, Re, Ru, Cu, Nb, Ni, Mn, Ge, Si, O, N, W, Mo, Ti, V, and B).

[0176] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 preferably uses an alloy material containing an oxide, metal nitride, or metal carbide. Specifically, oxides that can be used include, for example, SiO2, Al2O3, Ta2O5, Cr2O3, MgO, Y2O3, and TiO2. Metal nitrides that can be used include, for example, AlN, Si3N4, TaN, and CrN. Metal carbides that can be used include, for example, TaC, BC, and SiC. The non-magnetic layer can be formed by, for example, a sputtering method.

[0177] To achieve higher recording density, the magnetic layer 16 is preferably a magnetic layer for perpendicular magnetic recording, in which the axis of easy magnetization is oriented perpendicular to the substrate surface, but may also be a magnetic layer for longitudinal magnetic recording. The magnetic layer 16 may be formed by any conventionally known method such as vapor deposition, ion beam sputtering, magnetron sputtering, etc. The magnetic layer 16 is usually formed by sputtering.

[0178] "Protective layer" The protective layer 17 protects the magnetic layer 16. The protective layer 17 may be composed of one layer or multiple layers. A carbon-based protective layer is preferably used as the protective layer 17, and an amorphous carbon protective layer is particularly preferred. If the protective layer 17 is a carbon-based protective layer, the interaction with the polar groups (particularly hydroxyl groups) contained in the fluorine-containing ether compound in the lubricating layer 18 is further enhanced, which is preferable.

[0179] The adhesion between the carbon-based protective layer and the lubricating layer 18 can be controlled by using hydrogenated carbon and / or nitrogenated carbon for the carbon-based protective layer and adjusting the hydrogen and / or nitrogen content in the carbon-based protective layer. The hydrogen content in the carbon-based protective layer is preferably 3 atomic % to 20 atomic % when measured by hydrogen forward scattering (HFS). The nitrogen content in the carbon-based protective layer is preferably 4 atomic % to 15 atomic % when measured by X-ray photoelectron spectroscopy (XPS).

[0180] The hydrogen and / or nitrogen contained in the carbon-based protective layer does not need to be uniformly contained throughout the carbon-based protective layer. The carbon-based protective layer is preferably a compositionally graded layer, for example, in which nitrogen is contained on the lubricating layer 18 side of protective layer 17 and hydrogen is contained on the magnetic layer 16 side of protective layer 17. In this case, the adhesion between the magnetic layer 16 and lubricating layer 18 and the carbon-based protective layer is further improved.

[0181] 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.

[0182] The protective layer 17 can be formed by sputtering using a target material containing carbon, chemical vapor deposition (CVD) using a hydrocarbon raw material such as ethylene or toluene, or ion beam deposition (IBD). When a carbon-based protective layer is formed as protective layer 17, it can be deposited by, for example, DC magnetron sputtering. In particular, when a carbon-based protective layer is formed as protective layer 17, it is preferable to deposit an amorphous carbon protective layer by plasma CVD. The amorphous carbon protective layer deposited by plasma CVD has a uniform surface with little roughness.

[0183] "Lubricant layer" The lubricating layer 18 prevents contamination of the magnetic recording medium 10. The lubricating layer 18 also reduces the frictional force of the magnetic head of the magnetic recording / reproducing device that slides on the magnetic recording medium 10, thereby improving the durability of the magnetic recording medium 10. 1, the lubricating layer 18 is formed on and in contact with the protective layer 17. The lubricating layer 18 is formed by applying the magnetic recording medium lubricant of the above-described embodiment onto the protective layer 17. Therefore, the lubricating layer 18 contains the above-described fluorine-containing ether compound.

[0184] 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.

[0185] The average thickness of the lubricating layer 18 is preferably 0.5 nm (5 Å) to 2.0 nm (20 Å), and more preferably 0.5 nm (5 Å) to 1.2 nm (12 Å). When the average thickness of the lubricating layer 18 is 0.5 nm or more, the lubricating layer 18 is formed with a uniform thickness without forming an island or mesh-like structure. Therefore, the surface of the protective layer 17 can be covered with the lubricating layer 18 at a high coverage rate. Furthermore, by setting the average thickness of the lubricating layer 18 to 2.0 nm or less, the lubricating layer 18 can be made sufficiently thin, and the flying height of the magnetic head can be made sufficiently small.

[0186] "Method for forming lubricating layer" A method for forming the lubricating layer 18 includes, for example, preparing a magnetic recording medium in the middle of manufacturing in which all layers up to the protective layer 17 are formed on the substrate 11, applying a solution for forming a lubricating layer onto the protective layer 17, and drying the solution.

[0187] The lubricant layer forming solution can be obtained by dispersing and dissolving the lubricant for a magnetic recording medium according to the above embodiment in a solvent as needed, and adjusting the viscosity and concentration to suit the coating method. Examples of the solvent used in the lubricating layer-forming solution include fluorine-based solvents such as Vertrel (registered trademark) XF (trade name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.).

[0188] The method for applying the lubricating layer-forming solution is not particularly limited, but examples thereof include spin coating, spraying, paper coating, and dipping. When using the dipping method, for example, the following method can be used. First, the substrate 11 on which each layer up to the protective layer 17 has been formed is immersed in a lubricant layer-forming solution placed in an immersion tank of a dip coating device. Next, the substrate 11 is lifted from the immersion tank at a predetermined speed. In this way, the lubricant layer-forming solution is applied to the surface of the substrate 11 above the protective layer 17. By using the dipping method, the lubricating layer forming solution can be applied uniformly to the surface of the protective layer 17, and the lubricating layer 18 can be formed on the protective layer 17 with a uniform thickness.

[0189] In this embodiment, it is preferable to perform a heat treatment on the substrate 11 on which the lubricating layer 18 is formed. By performing the heat treatment, the adhesion between the lubricating layer 18 and the protective layer 17 is improved, and the adhesive force between the lubricating layer 18 and the protective layer 17 is also improved. The heat treatment temperature is preferably 100°C to 180°C, and more preferably 100°C to 160°C. When the heat treatment temperature is 100°C or higher, the effect of improving the adhesion between the lubricating layer 18 and the protective layer 17 can be sufficiently obtained. Furthermore, by setting the heat treatment temperature to 180°C or lower, thermal decomposition of the lubricating layer 18 due to the heat treatment can be prevented. The heat treatment time can be adjusted appropriately depending on the heat treatment temperature, and is preferably 10 minutes to 120 minutes.

[0190] In this embodiment, in order to further improve the adhesive strength 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.

[0191] The magnetic recording medium 10 of this embodiment includes at least a magnetic layer 16, a protective layer 17, and a lubricating layer 18, which are sequentially formed on a substrate 11. In the magnetic recording medium 10 of this embodiment, a lubricating layer 18 containing the above-described 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 chemical resistance and a high spin-off suppression effect. Therefore, the magnetic recording medium 10 of this embodiment has excellent reliability, particularly in suppressing silicon contamination, and durability. This contributes to reducing magnetic spacing and ensures stable operation over 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 installed in a magnetic disk device using the LUL (Load Unload) method. [Example]

[0192] 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. [Example 1] The compound represented by the above formula (AA) was obtained by the method shown below. (First reaction) Place HOCH2CF2O (CF2CF2O) in a 100 mL recovery flask under a nitrogen gas atmosphere. h (CF2O) i 20 g of a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CH2OH (where h, representing the average degree of polymerization, is 4.5, and i, representing the average degree of polymerization, is 4.5), 4.12 g of a compound represented by the above formula (5-1), and 20 mL of t-butanol were charged and stirred at room temperature until homogeneous to form a mixture. 1.12 g of potassium tert-butoxide was added to this mixture, and the mixture was reacted by stirring at 70°C for 16 hours.

[0193] The compound represented by formula (5-1) was synthesized by protecting the hydroxyl group of ethylene glycol monoallyl ether with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0194] The reaction product obtained after the reaction was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 9.74 g of the compound represented by the following formula (11) as intermediate compound 1-1.

[0195] [ka] (Rf1 in formula (11) is a PFPE chain represented by the above formula (4-1); in Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5; THP represents a tetrahydropyranyl group.)

[0196] (Second reaction) Next, under a nitrogen gas atmosphere, 9.61 g of the compound represented by formula (11), which is the intermediate compound 1-1 obtained above, 0.75 g of the compound represented by formula (7-1), and 20 mL of t-butanol were placed in a 100 mL recovery flask and stirred at room temperature until a homogeneous mixture was obtained. To this mixture, 0.45 g of potassium tert-butoxide was added, and the mixture was stirred at 70 °C for 16 hours to react. The compound represented by formula (7-1) was synthesized by reacting one molecule of 1,3-propanediol with two molecules of epibromohydrin.

[0197] After the reaction, the resulting reaction mixture was returned to room temperature, and 50 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 4 hours. The reaction mixture was then transferred in small portions to a separatory funnel containing 100 mL of saturated aqueous sodium bicarbonate and extracted twice with 200 mL of ethyl acetate. The organic layer was washed sequentially with 100 mL of brine, 100 mL of saturated aqueous sodium bicarbonate, and 100 mL of brine, and then dehydrated using anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 3.38 g of compound (AA). Rf1 in formula (AA) represents the PFPE chain represented by formula (4-1) above. For the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5.

[0198] The obtained compound (AA) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0199] [Example 2] The compound represented by the above formula (AB) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (7-2) was used instead of the compound represented by formula (7-1), to obtain 3.43 g of compound (AB) (Rf1 in formula (AB) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0200] The compound represented by formula (7-2) was synthesized by reacting one molecule of ethylene glycol with two molecules of epibromohydrin.

[0201] The obtained compound (AB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0202] [Example 3] The compound represented by the above formula (AC) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (7-3) was used instead of the compound represented by formula (7-1), to obtain 3.43 g of compound (AC) (Rf1 in formula (AC) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0203] The compound represented by formula (7-3) used was a commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0204] The obtained compound (AC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0205] [Example 4] The compound represented by the above formula (AD) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that the compound represented by formula (7-4) was used instead of the compound represented by formula (7-1), to obtain 3.61 g of compound (AD) (Rf1 in formula (AD) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0206] The compound represented by formula (7-4) was synthesized by reacting one molecule of 1,6-hexanediol with two molecules of epibromohydrin.

[0207] The obtained compound (AD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(8H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0208] [Example 5] The compound represented by the above formula (AE) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (7-5) was used instead of the compound represented by formula (7-1), to obtain 3.68 g of compound (AE) (Rf1 in formula (AE) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0209] The compound represented by formula (7-5) was synthesized by reacting one molecule of 1,8-octanediol with two molecules of epibromohydrin.

[0210] The obtained compound (AE) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(12H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0211] [Example 6] The compound represented by the above formula (AF) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (7-6) was used instead of the compound represented by formula (7-1), to obtain 3.52 g of compound (AF) (Rf1 in formula (AF) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0212] The compound represented by formula (7-6) used was a commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0213] The obtained compound (AF) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=0.90(6H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0214] [Example 7] The compound represented by the above formula (AG) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (7-7) was used instead of the compound represented by formula (7-1), to obtain 3.21 g of compound (AG) (Rf1 in formula (AG) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0215] The compound represented by formula (7-7) was synthesized by reacting one molecule of 2,3-butanediol with two molecules of epibromohydrin.

[0216] The obtained compound (AG) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.15-1.20(6H), 3.40-3.85(36H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0217] [Example 8] The compound represented by the above formula (AH) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that the compound represented by formula (7-8) was used instead of the compound represented by formula (7-1), to obtain 3.35 g of compound (AH) (Rf1 in formula (AH) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0218] The compound represented by formula (7-8) was synthesized by reacting one molecule of dipropylene glycol with two molecules of epibromohydrin.

[0219] The obtained compound (AH) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(42H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0220] [Example 9] The compound represented by the above formula (AI) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that the compound represented by formula (7-9) was used instead of the compound represented by formula (7-1), to obtain 3.63 g of compound (AI) (Rf1 in formula (AI) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0221] The compound represented by formula (7-9) was synthesized by reacting one molecule of diethylene glycol with two molecules of epibromohydrin.

[0222] The obtained compound (AI) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=, 3.40-3.85(42H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0223] [Example 10] The compound represented by the above formula (AJ) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that a compound represented by formula (7-10) was used instead of the compound represented by formula (7-1) in Example 1, to obtain 3.81 g of compound (AJ) (Rf1 in formula (AJ) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0224] The compound represented by formula (7-10) was synthesized by reacting one molecule of tetraethylene glycol with two molecules of epibromohydrin.

[0225] The obtained compound (AJ) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=3.40-3.85(50H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0226] [Example 11] The compound represented by the above formula (BA) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH, HOCH2CF2CF2O(CF2CF2CF2O) j The same procedures as in Example 1 were performed, except that a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CF2CH2OH (where j, representing the average degree of polymerization, is 4.5) was used, and 3.49 g of compound (BA) (Rf2 in formula (BA) is a PFPE chain represented by the above formula (4-2). In the two Rf2s, j, representing the average degree of polymerization, is 4.5) was obtained.

[0227] The resulting compound (BA) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-84.0~-83.0(36F), -86.4(8F), -124.3(8F), -130.0~-129.0(18F)

[0228] [Example 12] The compound represented by the above formula (BB) was obtained by the method shown below. HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH, HOCH2CF2CF2CF2O(CF2CF2CF2CF2O) k The same procedures as in Example 1 were performed, except that a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CF2CF2CH2OH (where k, indicating the average degree of polymerization, is 3.0) was used, and 3.23 g of compound (BB) (Rf3 in formula (BB) is a PFPE chain represented by the above formula (4-3). In the two Rf3s, k, indicating the average degree of polymerization, is 3.0) was obtained.

[0229] The obtained compound (BB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-84.0~-83.0(32F), -122.5(8F), -126.0(24F), -129.0~-128.0(8F)

[0230] [Example 13] The compound represented by the above formula (BC) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (5-2) was used instead of the compound represented by formula (5-1), to obtain 3.45 g of compound (BC) (Rf1 in formula (BC) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0231] The compound represented by formula (5-2) was synthesized by protecting one hydroxyl group of 1,3-propanediol with dihydropyran, followed by the reaction with epibromohydrin.

[0232] The resulting compound (BC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(6H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0233] [Example 14] The compound represented by the above formula (BD) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (5-3) was used instead of the compound represented by formula (5-1), to obtain 3.12 g of compound (BD) (Rf1 in formula (BD) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0234] The compound represented by formula (5-3) was synthesized by protecting 3-buten-1-ol with dihydropyran and then oxidizing it with m-chloroperbenzoic acid.

[0235] The obtained compound (BD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(6H), 3.40-3.85(30H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0236] [Example 15] The compound represented by the above formula (BE) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (5-4) was used instead of the compound represented by formula (5-1) in Example 1, to obtain 3.34 g of compound (BE) (Rf1 in formula (BE) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0237] The compound represented by formula (5-4) was synthesized by reacting 3-buten-1-ol with 2-(2-bromoethoxy)tetrahydro-2H-pyran, followed by oxidation with m-chloroperbenzoic acid.

[0238] The resulting compound (BE) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(6H), 3.40-3.85(38H), 3.85-4.10(8H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0239] [Example 16] The compound represented by the above formula (BF) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-5) was used instead of the compound represented by formula (5-1), to obtain 3.71 g of compound (BF) (Rf1 in formula (BF) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0240] The compound of formula (5-5) was synthesized by subjecting the compound of formula (5-1) to an addition reaction with allyl alcohol, protecting the resulting product with dihydropyran, and then oxidizing it with m-chloroperbenzoic acid.

[0241] The resulting compound (BF) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(50H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0242] [Example 17] The compound represented by the above formula (BG) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (5-6) was used instead of the compound represented by formula (5-1), to obtain 3.52 g of compound (BG) (Rf1 in formula (BG) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0243] The compound of formula (5-6) was synthesized by the addition reaction of the compound of formula (5-3) with allyl alcohol, followed by protection with dihydropyran and oxidation with m-chloroperbenzoic acid.

[0244] The obtained compound (BG) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(6H), 3.40-3.85(42H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0245] [Example 18] The compound represented by the above formula (BH) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-7) was used instead of the compound represented by formula (5-1), to obtain 3.63 g of compound (BH) (Rf1 in formula (BH) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0246] The compound of formula (5-7) was synthesized by the addition reaction of the compound of formula (5-1) with 3-buten-1-ol, followed by protection with dihydropyran and oxidation with m-chloroperbenzoic acid.

[0247] The resulting compound (BH) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(6H), 3.40-3.85(50H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0248] [Example 19] The compound represented by the above formula (BI) was obtained by the method shown below. (First reaction) In the same manner as in the first reaction of Example 1, a compound represented by formula (11) was obtained as intermediate compound 1a.

[0249] (Second reaction) The same procedure as in the first reaction of Example 1 was carried out, except that the compound represented by formula (5-5) was used instead of the compound represented by formula (5-1), to obtain a compound represented by formula (12) as intermediate compound 1b.

[0250] [ka] (Rf1 in formula (12) is a PFPE chain represented by the above formula (4-1); in Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5; THP represents a tetrahydropyranyl group.)

[0251] (Third reaction) Next, under a nitrogen gas atmosphere, 9.66 g of the compound represented by formula (11), which is the intermediate compound 1a obtained above, 0.69 g of the compound represented by formula (9-1) above, and 20 mL of t-butanol were charged into 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 stirred at 70 °C for 16 hours to react. The compound represented by formula (9-1) was synthesized by reacting 1,3-propanediol with allyl bromide and epibromohydrin in that order.

[0252] The reaction mixture obtained above was cooled to 25°C, transferred to a separatory funnel containing 100 mL of water, and extracted three times with 100 mL of ethyl acetate. The organic layer was washed with water and dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was oxidized with m-chloroperbenzoic acid and then purified by silica gel column chromatography to obtain 7.58 g of the compound represented by the following formula (13) as intermediate compound 1-2.

[0253] [ka] (Rf1 in formula (13) is a PFPE chain represented by the above formula (4-1); in Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5; THP represents a tetrahydropyranyl group.)

[0254] (Fourth reaction) Next, 7.35 g of the compound represented by formula (12), which is intermediate compound 1b obtained above, 7.58 g of the compound represented by formula (13), which is intermediate compound 1-2 obtained above, and 20 mL of t-butanol were charged into a 100 mL recovery flask under a nitrogen gas atmosphere, and the mixture was stirred at room temperature until it became homogeneous. 0.45 g of potassium tert-butoxide was added to the mixture, and the mixture was reacted by stirring at 70°C for 16 hours.

[0255] After the reaction, the resulting reaction mixture was returned to room temperature, and 50 g of a 10% hydrogen chloride-methanol solution (hydrogen chloride-methanol reagent (5-10%), manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 4 hours. The reaction mixture was then transferred in small portions to a separatory funnel containing 100 mL of saturated aqueous sodium bicarbonate and extracted twice with 200 mL of ethyl acetate. The organic layer was washed sequentially with 100 mL of brine, 100 mL of saturated aqueous sodium bicarbonate, and 100 mL of brine, and then dehydrated over anhydrous sodium sulfate. After filtering off the desiccant, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 4.54 g of compound (BI). (Rf1 in formula (BI) represents the PFPE chain represented by formula (4-1) above. In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5.)

[0256] The obtained compound (BI) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(44H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0257] [Example 20] The compound represented by the above formula (BJ) was obtained by the method shown below. The same operations as in Example 1 were performed, except that the compound represented by formula (5-8) was used instead of the compound represented by formula (5-1), to obtain 3.67 g of compound (BJ) (Rf1 in formula (BJ) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0258] The compound represented by formula (5-8) was synthesized by protecting one hydroxyl group of 1,6-hexanediol with dihydropyran, followed by the reaction with epibromohydrin.

[0259] The obtained compound (BJ) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(18H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0260] [Example 21] The compound represented by the above formula (BK) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-9) was used instead of the compound represented by formula (5-1), to obtain 3.48 g of compound (BK) (Rf1 in formula (BK) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0261] The compound represented by formula (5-9) was synthesized by protecting 7-octen-1-ol with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0262] The obtained compound (BK) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(18H), 3.40-3.85(30H), 3.85-4.10(8H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0263] [Example 22] The compound represented by the above formula (BL) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that the compound represented by formula (5-10) was used instead of the compound represented by formula (5-1), to obtain 3.02 g of compound (BL) (Rf1 in formula (BL) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0264] The compound represented by formula (5-10) was synthesized by protecting 2-bromoethanol with dihydropyran, reacting it with 5-hexen-1-ol, and then oxidizing it with m-chloroperbenzoic acid.

[0265] The obtained compound (BL) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(14H), 3.40-3.85(38H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0266] [Example 23] The compound represented by the above formula (BM) was obtained by the method shown below. The same operations as in Example 1 were performed except that the compound represented by formula (5-11) was used instead of the compound represented by formula (5-1), to obtain 3.14 g of compound (BM) (Rf1 in formula (BM) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0267] The compound represented by formula (5-11) was synthesized by protecting the allylic alcohol with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0268] The resulting compound (BM) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(30H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0269] [Example 24] The compound represented by the above formula (BN) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-12) was used instead of the compound represented by formula (5-1), to obtain 3.28 g of compound (BN) (Rf1 in formula (BN) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0270] The compound represented by formula (5-12) was synthesized by protecting the two hydroxyl groups of 1-allyloxy-2,3-propanediol with dihydropyran, followed by oxidation with m-chloroperbenzoic acid.

[0271] The resulting compound (BN) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(42H), 3.85-4.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0272] [Example 25] The compound represented by the above formula (BO) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-13) was used instead of the compound represented by formula (5-1), to obtain 3.31 g of compound (BO) (Rf1 in formula (BO) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0273] The compound represented by formula (5-13) was synthesized by adding allyl alcohol to allyl glycidyl ether, protecting the resulting hydroxyl groups with dihydropyran, and then oxidizing one of the allyl groups with m-chloroperbenzoic acid.

[0274] The resulting compound (BO) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(44H), 3.85-4.10(8H), 5.40-6.10(6H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0275] [Example 26] The compound represented by the above formula (BP) was obtained by the method shown below. The same operation as in Example 1 was performed, except that the compound represented by formula (5-14) was used instead of the compound represented by formula (5-1), to obtain 3.52 g of compound (BP) (Rf1 in formula (BP) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0276] The compound represented by formula (5-14) was synthesized by reacting p-methoxyphenol with epibromohydrin.

[0277] The resulting compound (BP) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 3.40-3.85(34H), 3.85-4.10(8H), 6.30-7.10(8H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0278] [Example 27] The compound represented by the above formula (BQ) was obtained by the method shown below. The same operation as in Example 1 was performed, except that a compound represented by formula (5-15) was used instead of the compound represented by formula (5-1) in Example 1, to obtain 3.36 g of compound (BQ) (Rf1 in formula (BQ) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0279] The compound represented by formula (5-15) was synthesized by reacting N-(2-hydroxyethyl)acetamide with epibromohydrin.

[0280] The obtained compound (BQ) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 1.90(6H), 3.40-3.85(36H), 3.85-4.10(8H), 6.30-6.50(2H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0281] [Example 28] The compound represented by the above formula (BR) was obtained by the method shown below. The same operation as in Example 1 was performed, except that a compound represented by formula (5-16) was used instead of the compound represented by formula (5-1) in Example 1, to obtain 3.57 g of compound (BR) (Rf1 in formula (BR) is a PFPE chain represented by the above formula (4-1). In the two Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0282] The compound represented by formula (5-16) was synthesized by reacting 2-cyanoethanol with epibromohydrin.

[0283] The resulting compound (BR) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(2H), 2.00-2.10(4H), 3.40-3.85(32H), 3.85-4.10(8H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(18F), -78.5(4F), -80.5(4F), -91.0~-88.5(36F)

[0284] [Example 29] The compound represented by the above formula (CA) was obtained by the method shown below. The same procedure as in Example 1 was performed, except that a compound represented by the following formula (14) was used instead of the compound represented by formula (7-1), to obtain 4.03 g of compound (CA) (Rf1 in formula (CA) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0285] [ka] (Rf1 in formula (14) is a PFPE chain represented by the above formula (4-1); in Rf1, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0286] The compound represented by formula (14) is HOCH2CF2O(CF2CF2O) h (CF2O) i The compound (number average molecular weight: 1000, molecular weight distribution: 1.1) represented by CF2CH2OH (where h, representing the average degree of polymerization, is 4.5, and i, representing the average degree of polymerization, is 4.5) was reacted with the compound represented by formula (9-1), followed by oxidation with m-chloroperbenzoic acid to synthesize the compound.

[0287] The obtained compound (CA) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(54H), 3.85-4.10(12H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0288] [Example 30] The compound represented by the above formula (CB) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (9-2) was used instead of the compound represented by formula (9-1), to obtain 4.11 g of compound (CB) (Rf1 in formula (CB) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0289] The compound represented by formula (9-2) was synthesized by reacting ethylene glycol with allyl bromide and epibromohydrin in this order.

[0290] The resulting compound (CB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=3.40-3.85(54H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0291] [Example 31] The compound represented by the above formula (CC) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (9-5) was used instead of the compound represented by formula (9-1), to obtain 4.32 g of compound (CC) (Rf1 in formula (CC) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0292] The compound represented by formula (9-5) was synthesized by reacting 1,8-octanediol with allyl bromide and epibromohydrin in that order.

[0293] The resulting compound (CC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.20-1.85(24H), 3.40-3.85(54H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0294] [Example 32] The compound represented by the above formula (CD) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (9-6) was used instead of the compound represented by formula (9-1), to obtain 4.21 g of compound (CD) (Rf1 in formula (CD) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0295] The compound represented by formula (9-6) was synthesized by reacting 2,2-dimethyl-1,3-propanediol with allyl bromide and epibromohydrin in that order.

[0296] The resulting compound (CD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=0.90(12H), 3.40-3.85(54H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0297] [Example 33] The compound represented by the above formula (CE) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (9-7) was used instead of the compound represented by formula (9-1), to obtain 3.96 g of compound (CE) (Rf1 in formula (CE) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0298] The compound represented by formula (9-7) was synthesized by reacting 2,3-butanediol with allyl bromide and epibromohydrin in that order.

[0299] The obtained compound (CE) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.15-1.20(12H), 3.40-3.85(50H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0300] [Example 34] The compound represented by the above formula (CF) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (9-9) was used instead of the compound represented by formula (9-1), to obtain 4.35 g of compound (CF) (Rf1 in formula (CF) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0301] The compound represented by formula (9-9) was synthesized by reacting diethylene glycol with allyl bromide and epibromohydrin in this order.

[0302] The resulting compound (CF) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=3.40-3.85(62H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0303] [Example 35] The compound represented by the above formula (DA) was obtained by the method shown below. In the synthesis of the compound represented by formula (11) and the compound represented by formula (14), HOCH2CF2O(CF2CF2O) h (CF2O) i Instead of the compound represented by CF2CH2OH, HOCH2CF2CF2O(CF2CF2CF2O) j The same procedures as in Example 29 were performed except that a compound (number average molecular weight 1000, molecular weight distribution 1.1) represented by CF2CF2CH2OH (where j, indicating the average degree of polymerization, is 4.5) was used, and 4.25 g of compound (DA) (Rf2 in formula (DA) is a PFPE chain represented by the above formula (4-2). In the three Rf2s, j, indicating the average degree of polymerization, is 4.5) was obtained.

[0304] The obtained compound (DA) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(54H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-84.0~-83.0(54F), -86.4(12F), -124.3(12F), -130.0~-129.0(27F)

[0305] [Example 36] The compound represented by the above formula (DB) was obtained by the method shown below. The same procedure as in Example 29 was performed, except that the compound represented by formula (5-5) was used instead of the compound represented by formula (5-1), to obtain 4.41 g of compound (DB) (Rf1 in formula (DB) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0306] The obtained compound (DB) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(66H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0307] [Example 37] The compound represented by the above formula (DC) was obtained by the method shown below. The same procedure as in Example 29 was performed, except that the compound represented by formula (5-3) was used instead of the compound represented by formula (5-1), to obtain 3.81 g of compound (DC) (Rf1 in formula (DC) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0308] The obtained compound (DC) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(8H), 3.40-3.85(46H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0309] [Example 38] The compound represented by the above formula (DD) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (5-4) was used instead of the compound represented by formula (5-1), to obtain 4.07 g of compound (DD) (Rf1 in formula (DD) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0310] The obtained compound (DD) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(8H), 3.40-3.85(54H), 3.85-4.10(12H) 19F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0311] [Example 39] The compound represented by the above formula (DE) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (5-15) was used instead of the compound represented by formula (5-1), to obtain 4.18 g of compound (DE) (Rf1 in formula (DE) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0312] The resulting compound (DE) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 1.90(6H), 3.40-3.85(52H), 3.85-4.10(12H), 6.30-6.50(2H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0313] [Example 40] The compound represented by the above formula (DF) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (5-16) was used instead of the compound represented by formula (5-1), to obtain 4.32 g of compound (DF) (Rf1 in formula (DF) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which represents the average degree of polymerization, is 4.5, and i, which represents the average degree of polymerization, is 4.5).

[0314] The obtained compound (DF) 1H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 2.00-2.10(4H), 3.40-3.85(48H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0315] [Example 41] The compound represented by the above formula (DG) was obtained by the method shown below. The same operation as in Example 29 was performed except that the compound represented by formula (5-11) was used instead of the compound represented by formula (5-1), to obtain 3.86 g of compound (DG) (Rf1 in formula (DG) is a PFPE chain represented by the above formula (4-1). In the three Rf1s, h, which indicates the average degree of polymerization, is 4.5, and i, which indicates the average degree of polymerization, is 4.5).

[0316] The resulting compound (DG) 1 H-NMR measurement and 19 F-NMR measurements were carried out and the structure was identified based on the following results. 1 H-NMR (acetone-D6): δ[ppm]=1.65-1.85(4H), 3.40-3.85(46H), 3.85-4.10(12H) 19 F-NMR (acetone-D6): δ[ppm]=-55.5~-51.5(27F), -78.5(6F), -80.5(6F), -91.0~-88.5(54F)

[0317] The compounds (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG) of Examples 1 to 41 thus obtained are respectively substituted into the formula (1), and the value of x, R 1 , R 2 , R 3 , R4 The structures of the compounds are shown in Table 1. All compounds except for compound (BI) are R 1 and R 4 The structure is the same.

[0318] [Table 1]

[0319] [Table 2]

[0320] [Comparative Example 1] The compound represented by the following formula (ZA) was synthesized by the method described in Patent Document 1.

[0321] [ka] (Rf1 in formula (ZA) is a PFPE chain represented by the above formula (4-1); in the two Rf1s, h representing the average degree of polymerization is 7.0, and i representing the average degree of polymerization is 0.)

[0322] Comparative Example 2 The compound represented by the following formula (ZB) was synthesized by the method described in Patent Document 2.

[0323] [ka] (Rf1 in formula (ZB) is a PFPE chain represented by the above formula (4-1); in the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0324] Comparative Example 3 The compound represented by the following formula (ZC) was synthesized by the method described in Patent Document 3.

[0325] [ka] (Rf1 in formula (ZC) is a PFPE chain represented by the above formula (4-1); in the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0326] Comparative Example 4 The compound represented by the following formula (ZD) was synthesized by the method described in Patent Document 4.

[0327] [ka] (Rf2 in formula (ZD) is a PFPE chain represented by the above formula (4-2); in the two Rf2s, j representing the average degree of polymerization is 4.5.)

[0328] Comparative Example 5 The compound represented by the following formula (ZE) was synthesized by the method described in Patent Document 5.

[0329] [ka] (Rf1 in formula (ZE) is a PFPE chain represented by the above formula (4-1); in the three Rf1s, h representing the average degree of polymerization is 7.0, and i representing the average degree of polymerization is 0.)

[0330] Comparative Example 6 The compound represented by the following formula (ZF) was synthesized by the method described in Patent Document 6.

[0331] [ka] (Rf1 in formula (ZF) is a PFPE chain represented by the above formula (4-1); in the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0332] Comparative Example 7 The compound represented by the following formula (ZG) was synthesized by the method described in Patent Document 7.

[0333] [ka] (Rf1 in formula (ZG) is a PFPE chain represented by the above formula (4-1); in the two Rf1s, h representing the average degree of polymerization is 4.5, and i representing the average degree of polymerization is 4.5.)

[0334] The number average molecular weights (Mn) of the compounds thus obtained in Examples 1 to 41 and Comparative Examples 1 to 7 were measured by the above-mentioned method. The results are shown in Tables 3 and 4.

[0335] Next, solutions for forming lubricating layers were prepared by the method described below using the compounds obtained in Examples 1 to 41 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 41 and Comparative Examples 1 to 7.

[0336] "Lubricant layer forming solution" The compounds obtained in Examples 1 to 41 and Comparative Examples 1 to 7 were each dissolved in a fluorine-based solvent, Vertrel (registered trademark) XF (trade name, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.), and diluted with Vertrel XF so that the film thickness when applied to the protective layer would be 9.0 Å to 9.5 Å, to prepare a solution for forming a lubricating layer.

[0337] "Magnetic recording media" A magnetic recording medium was prepared by sequentially depositing an adhesive layer, a soft magnetic layer, a first underlayer, a second underlayer, a magnetic layer, and a protective layer on a substrate having a diameter of 65 mm. The protective layer was made of carbon. On the protective layer of a magnetic recording medium on which each layer up to the protective layer had been formed, the lubricating layer-forming solutions of Examples 1 to 41 and Comparative Examples 1 to 7 were applied by dipping under the conditions of an immersion speed of 10 mm / sec, an immersion time of 30 seconds, and a pull-up speed of 1.2 mm / sec. The magnetic recording medium coated with the lubricating layer-forming solution was then placed in a thermostatic chamber, and a heat treatment was performed at 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.

[0338] (film thickness measurement) The thickness of the lubricating layer of each of the magnetic recording media thus obtained in Examples 1 to 41 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 Tables 3 and 4.

[0339] Next, the magnetic recording media of Examples 1 to 41 and Comparative Examples 1 to 7 were subjected to the following chemical resistance test and spin-off characteristic test.

[0340] [Chemical resistance test] The degree of contamination of magnetic recording media by environmental substances that generate contaminants in high-temperature environments was evaluated using the method described below. Si ions were used as the environmental substances. The degree of contamination of magnetic recording media by contaminants generated by the environmental substances was evaluated by measuring the amount of Si adsorption as the amount of contaminant.

[0341] Specifically, the magnetic recording media to be evaluated were stored for 240 hours in a high-temperature environment of 85°C and 0% humidity in the presence of siloxane-based silicon rubber. The amount of silicon adsorption present on the surface of the magnetic recording media was then analyzed and measured using secondary ion mass spectrometry (SIMS), and the degree of contamination by silicon ions was evaluated as the amount of silicon adsorption. The degree of contamination was evaluated based on the following criteria, with the amount of silicon adsorption in Comparative Example 5 set at 1.00. The results are shown in Tables 3 and 4.

[0342] "Chemical Resistance Evaluation Criteria" A+: Si adsorption amount is less than 0.60 A: Si adsorption amount is 0.60 or more and less than 0.70 B: Si adsorption amount is 0.70 or more and less than 0.90 C:Si adsorption amount is 0.90 or more and less than 1.10 D: Si adsorption amount is 1.10 or more

[0343] [Spin-off characteristic test] The magnetic recording medium was mounted on a spin stand and rotated at 10,000 rpm for 72 hours at 80°C. Before and after this operation, the thickness of the lubricating layer was measured using FT-IR at a position 20 mm radius from the center of the magnetic recording medium, and the reduction rate of the lubricating layer thickness before and after the test was calculated. The calculated reduction rate of the film thickness was used to evaluate the spin-off characteristics according to the following evaluation criteria.

[0344] "Evaluation criteria for spin-off characteristics" A+: Film thickness reduction rate less than 2% A: Film thickness reduction rate: 2% or more, less than 3% B: Film thickness reduction rate 3% or more, less than 5% C: Film thickness reduction rate 5% or more, less than 10% D: Film thickness reduction rate of 10% or more

[0345] [comprehensive evaluation] Based on the results of the chemical resistance test and spin-off property test, a comprehensive evaluation was made based on the following criteria. "comprehensive evaluation" A: Both the chemical resistance test and spin-off property test were evaluated as A+ or A. B: Either the chemical resistance test evaluation or the spin-off property test evaluation is B, and the other is A+, A, or B C: Either the chemical resistance test rating or the spin-off property test rating is C, and the other is A+, A, B, or C. D: At least one of the chemical resistance test evaluation and spin-off property test evaluation is D

[0346] [Table 3]

[0347] [Table 4]

[0348] As shown in Tables 3 and 4, R 3 is a divalent linking group represented by formula (2-1) or formula (2-2), and the magnetic recording media of Examples 1 to 41, which used fluorine-containing ether compounds (AA) to (AJ), (BA) to (BR), (CA) to (CF), and (DA) to (DG) satisfying formula (1), were evaluated as A+, A, or B in all evaluation items of the chemical resistance test and spin-off property test. This confirmed that the lubricating layers of the magnetic recording media of Examples 1 to 41 had good chemical resistance and a high spin-off suppression effect.

[0349] R 1 and R 4 is a terminal group represented by formula (3-1), p is 0, q is 0, and r is 1, and R 2 The compounds (AA) to (AJ) and (CA) to (CF) in which R is a perfluoropolyether chain represented by formula (4-1) were used were compared with Examples 1 to 10 and 29 to 34. 3 Among the compounds in which Y in formula (2) is a linking group represented by (2-1), Examples 1, 3 to 7, 29, and 31 to 33, which used compounds (AA), (AC) to (AG), (CA), and (CC) to (CE) in which Y in formula (2) contains 3 or more carbon atoms, were evaluated as A+ in the chemical resistance test, showing good results.

[0350] R 3 In Examples 8 to 10 and 34, which used compounds (AH) to (AJ) and compound (CF) in which is a linking group represented by formula (2-2), the spin-off property test was evaluated as A+, which showed good results.

[0351] In contrast, in Comparative Examples 1 to 7, which used compounds (ZA) to (ZG), the evaluation results for all evaluation items in the chemical resistance test and spin-off property test were C or D, and the overall evaluation results were C or D for all of them.

[0352] More specifically, in the compound (ZA) used in Comparative Example 1 and the compound (ZB) used in Comparative Example 2, the linking group between the perfluoropolyether chains contains only one hydroxyl group. Therefore, sufficient interaction between the linking group and the protective layer is not achieved, causing the central part of the fluorinated ether compound to float, making it easier for contaminants to become trapped, which is thought to be why the chemical resistance test result was D. Furthermore, in compounds (ZA) and (ZB), bulky perfluoropolyether chains are arranged on both sides of the glycerin structure. This prevents the free movement of the hydroxyl groups in the glycerin structure, making it difficult for the hydroxyl groups to participate in interactions with the active sites on the protective layer or polar groups in other fluorinated ether compounds present in the lubricating layer, which is thought to be why the spin-off property test result was D. Furthermore, compound (ZF) used in Comparative Example 6 and compound (ZG) used in Comparative Example 7 have two or three hydroxyl groups in the linking group between the perfluoropolyether chains. However, in compounds (ZF) and (ZG), the two glycerin structures are bonded via a unit containing a rigid ring structure, which restricts the movement of the hydroxyl groups. This is thought to be why sufficient interaction between the linking group and the protective layer is not achieved, causing the central part of the fluorinated ether compound to float up, making it easier for contaminants to become trapped, resulting in a result of C or D in the chemical resistance test.

[0353] 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 are bonded only via a rigid alkylene chain. This prevents the free movement of the hydroxyl groups contained in the linking group, making it difficult for the hydroxyl groups to participate in interactions with active sites on the protective layer or polar groups in other fluorinated ether compounds present in the lubricating layer, which is thought to be why the spin-off property test was evaluated as D. In addition, in the compound (ZE) used in Comparative Example 5, the perfluoropolyether chains are bonded to each other by a linking group having two hydroxyl groups. However, because the distance between the two hydroxyl groups of the linking group is short, the two hydroxyl groups of the linking group tend to interact with each other within the molecule. For this reason, the two hydroxyl groups of the linking group are less likely to be involved in interactions with polar groups contained in other fluorine-containing ether compound molecules present in the lubricating layer, which is thought to be why the compound received a C rating in the chemical resistance test and spin-off property test. [Industrial Applicability]

[0354] By using a lubricant for magnetic recording media containing the fluorine-containing ether compound of the present invention, it is possible to form a lubricating layer that has good chemical resistance and a high spin-off suppressing effect even if it is thin. [Explanation of symbols]

[0355] 10...magnetic recording medium, 11...substrate, 12...adhesion layer, 13...soft magnetic layer, 14...first underlayer, 15...second underlayer, 16...magnetic layer, 17...protective layer, 18...lubricating layer.

Claims

1. A fluorine-containing ether compound represented by the following formula (1) and having a number average molecular weight in the range of 500 to 10,000: 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 an integer of 1 to 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; R ３ is a divalent linking group represented by the following formula (2-1) or (2-2); when x is 2, two R ３ may be the same or different; R １ and R ４ is a terminal group having 1 to 4 polar groups and 1 to 50 carbon atoms; R １ and R ４ may be the same or different; the polar group possessed by R 1 and R 4 is at least one selected from the group consisting of a hydroxyl group, a cyano group, and a group having an amide bond. 【Chemistry 1】 (In formula (2-1), a represents an integer of 2 to 8; a R a and R b each independently represent a hydrogen atom or a methyl group; the total number of carbon atoms contained in a (-CR a R b -) is 2 to 8; the oxygen atom at the left end of formula (2-1) is bonded to the methylene group on the R 1 side in formula (1), and the oxygen atom at the right end is bonded to the methylene group on the R 4 side in formula (1).) (In formula (2-2), b represents an integer of 2 to 4; b R c s each independently represent —CH 2 CH 2 —, —CH 2 CH 2 CH 2 —, —CH(CH 3 )CH 2 —, or —CH 2 CH(CH 3 )—; the total number of carbon atoms contained in the b R c s is 4 to 8; the oxygen atom at the left terminal of formula (2-2) is bonded to the methylene group on the R 1 side in formula (1), and the oxygen atom at the right terminal is bonded to the methylene group on the R 4 side in formula (1).)

2. R in the formula (1) １ and R ４ and each independently represent a terminal group represented by the following formula (3): 【Chemistry 2】 (In formula (3), l represents an integer of 1 to 3; l m's each independently represent an integer of 1 to 6; l n's each independently represent an integer of 1 to 6; in one repeating unit, at least one of m and n is 1; A represents an alkyl group which may have a polar group, an organic group containing a carbon-carbon unsaturated bond which may have a polar group, or a hydrogen atom.)

3. R in the formula (1) １ and R ４ are each independently a terminal group represented by the following formula (3-1) or (3-2): 【Transformation 3】 (In formula (3-1), p represents an integer of 0 to 3, q ​​represents an integer of 0 to 2, and r represents an integer of 1 to 5; the total value of p and r is 1 to 5; and B represents a polar group.) (In formula (3-2), s represents an integer of 0 to 2, and t represents an integer of 1 to 5.)

4. R in the formula (1) １ and R ４ The fluorine-containing ether compound according to claim 1 or 2, wherein

5. 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.

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

7. (x+1) R in the formula (1) ２ and each independently represent 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 average degrees of polymerization, each independently representing 0 to 20; provided that w2, w3, w4, and w5 cannot all be 0 at the same time; w1 and w6 are each independently a value of CF ２ is an average value representing the number of repeating 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).

8. (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): -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 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

9. A lubricant for magnetic recording media, comprising the fluorine-containing ether compound according to claim 1 or 2.

10. A magnetic recording medium having at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate, 3. A magnetic recording medium, wherein the lubricating layer comprises the fluorine-containing ether compound according to claim 1.

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

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