Fluorine-containing ether compounds, lubricants for magnetic recording media, and magnetic recording media

Abstract

Provided is a fluorine-containing ether compound that can form a lubricating layer with which it is possible to raise the chemical resistance of magnetic recording media even when the layer is thin and that can be used suitably as a material of a lubricant for magnetic recording media. Provided is a fluorine-containing ether compound represented by the following formula. R1-CH2-R2-CH2-OCH2-CHR3-CH2O-CH2-R4-CH2-R5 (in the formula, R2 and R4 are perfluoropolyether chains. R1 and R5 are end groups that include two or three hydroxyl groups, each of the hydroxyl groups bonding to a mutually different carbon atom, and the carbon atoms to which the hydroxyl groups are bonded bonding to each other via linking groups that include carbon atoms to which no hydroxyl groups are bonded. R3 is represented by the following formula. -(CH2)a-OH (a is an integer of 2-8.))

Description

[Technical Field]

[0001] The present invention relates to a fluorine-containing ether compound, a lubricant for magnetic recording media, and a magnetic recording media. This application claims priority based on Japanese Patent Application No. 2021-116259, filed in Japan on July 14, 2021, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] To improve the recording density of magnetic recording and playback devices, development of magnetic recording media suitable for high recording densities is underway. Conventionally, magnetic recording media have been found in which a recording layer is formed on a substrate, and a protective layer such as carbon is formed on the recording layer. The protective layer protects the information recorded on the recording layer and improves the sliding properties of the magnetic head. Furthermore, the protective layer covers the recording layer, preventing the metal contained in the recording layer from being corroded by environmental pollutants. However, simply providing a protective layer on the recording layer does not provide sufficient durability for the magnetic recording medium.

[0003] Therefore, a lubricant is applied to the surface of the protective layer to form a lubricating layer with a thickness of approximately 0.5 to 3 nm. The lubricating layer improves the durability and protective power of the protective layer and prevents contaminants from entering the magnetic recording medium. As lubricants used to form the lubricating layer of magnetic recording media, for example, those containing a compound having a polar group such as a hydroxyl group at the end of a fluorine-based polymer having a repeating structure including CF2 have been proposed (see, for example, Patent Document 1). In addition, some lubricants contain a compound in which an aliphatic hydrocarbon chain having a hydroxyl group is positioned in the center of the molecule, with perfluoropolyethers bonded to both sides (see, for example, Patent Documents 2 to 5). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] WO2009 / 066784 [Patent Document 2] US9805755 [Patent Document 3] US2020 / 0002640 [Patent Document 4] WO2021 / 019998 [Patent Document 5] WO2016 / 084781 [Overview of the project] [Problems that the invention aims to solve]

[0005] In magnetic recording and playback devices, there is a growing demand to further reduce the amount of magnetic head levitation. Therefore, there is a need to make the lubrication layer in the magnetic recording medium thinner. However, generally speaking, reducing the thickness of the lubricating layer tends to decrease the chemical resistance of the magnetic recording medium.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a fluorine-containing ether compound that can form a lubricating layer that can increase the chemical resistance of magnetic recording media even when it is thin, and that can be suitably used as a material for lubricants for magnetic recording media. Furthermore, the present invention aims to provide a lubricant for magnetic recording media containing the fluorine-containing ether compound of the present invention. Furthermore, the present invention aims to provide a magnetic recording medium having a lubricating layer containing the fluorine-containing ether compound of the present invention and possessing excellent chemical resistance. [Means for solving the problem]

[0007] The inventors of this invention have diligently conducted research to solve the above problems. As a result, a structure containing one primary hydroxyl group at the 2-position of the propanediol skeleton is arranged at the center of the chain structure, and a perfluoropolyether chain, a methylene group, and a terminal group containing two or three hydroxyl groups are bonded in this order via a methylene group (-CH2-) on both sides thereof. The inventors found that a fluorine-containing ether compound having an appropriate distance between the hydroxyl groups in the terminal group would be suitable, and thus arrived at the present invention. That is, the present invention relates to the following matters.

[0008] [1] A fluorine-containing ether compound characterized by being represented by the following formula (1). R 1 -CH2-R 2 -CH2-OCH2-CHR 3 -CH2O-CH2-R 4 -CH2-R 5 (1) (In formula (1), R 2 and R 4 are perfluoropolyether chains. R 1 and R 5 are terminal groups containing two or three hydroxyl groups, each hydroxyl group is bonded to a different carbon atom, and the carbon atoms to which the hydroxyl groups are bonded are bonded via a linking group containing a carbon atom to which no hydroxyl group is bonded. R 3 is represented by the following formula (2).) -(CH2) a -OH (2) (In formula (2), a represents an integer of 2 to 8.)

[0009] [2] The fluorine-containing ether compound according to [1], wherein a in the formula (2) is an integer of 3 to 6.

[0010] [3] The fluorine-containing ether compound according to [1] or [2], wherein R 1 and R 5 in the formula (1) are each independently any one of the following formulas (3-1) to (3-5).

[0011]

Chemical formula

[0012] [4] R in equation (1) above 2 and R 4 However, each is independently represented by the following formula (4), and is a fluorine-containing ether compound as described in any of [1] to [3]. -(CF2) v O-(CF2O) w -(CF2CF2O) x -(CF2CF2CF2O) y -(CF2CF2CF2CF2O) z -(CF2) v’ - (4) (In equation (4), w, x, y, and z represent the average degree of polymerization and are independent real numbers between 0 and 20. It is impossible for all of w, x, y, and z to be 0 at the same time. v and v' are average values ​​representing the number of -CF2- units and are independent real numbers between 1 and 3. There are no particular restrictions on the order of the repeating units in equation (4).)

[0013] [5] R in equation (1) above 2 and R 4 However, each is independently represented by one of the following formulas (5) to (9), and is a fluorine-containing ether compound as described in any of [1] to [4]. -CF2O-(CF2O) w5 -(CF2CF2O) x5 -CF2- (5) (In equation (5), w5 and x5 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) -CF2O-(CF2CF2O) x6 -CF2- (6) (In equation (6), x6 represents the average degree of polymerization and is a real number between 1 and 20.) -CF2CF2O-(CF2CF2CF2O) y7 -CF2CF2- (7) (In equation (7), y7 represents the average degree of polymerization and is a real number between 1 and 20.) -(CF2) v8 O-(CF2CF2O) x8 -(CF2CF2CF2O) y8 -(CF2) v8’ - (8) (In equation (8), x8 and y8 represent the average degree of polymerization and are independent real numbers between 1 and 20. v8 and v8' are average values ​​representing the number of -CF2- and are independent real numbers between 1 and 2.) -CF2CF2CF2O-(CF2CF2CF2CF2O) z9 -CF2CF2CF2- (9) (In equation (9), z9 represents the average degree of polymerization and is a real number between 1 and 20.)

[0014] [6] In equation (1) above, R 1 and R 5 A fluorine-containing ether compound described in any of [1] to [5], which is the same as [1]. [7] In equation (1) above, R 2 and R 4 A fluorine-containing ether compound described in any of [1] to [6], which is the same as [1]. [8] A fluorine-containing ether compound according to any of [1] to [7], wherein the number average molecular weight is in the range of 500 to 10000.

[0015] A lubricant for magnetic recording media, characterized by containing a fluorine-containing ether compound as described in any of [9] [1] to [8].

[0016]

[10] 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 characterized in that the lubricating layer contains a fluorine-containing ether compound as described in any of [1] to [8].

[11] The magnetic recording medium according to

[10] , wherein the average thickness of the lubricating layer is 0.5 nm to 2.0 nm. [Effects of the Invention]

[0017] Since the fluorine-containing ether compound of the present invention is a compound represented by the above formula (1), it can form a lubricating layer that can increase the chemical resistance of magnetic recording media even when it is thin, and is therefore suitable as a material for lubricants for magnetic recording media. Because the lubricant for magnetic recording media of the present invention contains the fluorine-containing ether compound of the present invention, it is possible to form a lubricating layer that can increase the chemical resistance of the magnetic recording media even when it is thin. The magnetic recording medium of the present invention is provided with a lubricating layer containing the fluorine-containing ether compound of the present invention, and therefore exhibits excellent chemical resistance, excellent reliability, and durability. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the magnetic recording medium of the present invention. [Modes for carrying out the invention]

[0019] The fluorine-containing ether compound, lubricant for magnetic recording media (hereinafter sometimes abbreviated as "lubricant"), and magnetic recording media of the present invention will be described in detail below. However, the present invention is not limited to the embodiments shown below.

[0020] [Fluorine-containing ether compounds] The fluorine-containing ether compound of this embodiment is represented by the following formula (1). R 1 -CH2-R 2 -CH2-OCH2-CHR 3 -CH2O-CH2-R 4 -CH2-R 5 (1) (In formula (1), R 2 and R 4 This is a perfluoropolyether chain. 1 and R 5R is a terminal group that contains two or three hydroxyl groups, each hydroxyl group being bonded to a different carbon atom, and the carbon atoms to which the hydroxyl groups are bonded are connected via a linking group that includes a carbon atom not to which a hydroxyl group is bonded. 3 This is expressed by the following formula (2). -(CH2) a -OH (2) (In equation (2), a represents an integer between 2 and 8.)

[0021] "R 1 and R 5 " In the fluorine-containing ether compound represented by formula (1), R 1 and R 5 R is a terminal group containing two or three hydroxyl groups. 1 and R 5 The two or three hydroxyl groups in the terminal group shown are each bonded to a different carbon atom. 1 and R 5 In the terminal group shown, the carbon atoms to which the hydroxyl group is bonded are connected via a linking group that includes carbon atoms not to which the hydroxyl group is bonded.

[0022] The fluorine-containing ether compound represented by formula (1) is R 1 and R 5 Since it has terminal groups represented by (1), it has an appropriate surface energy. In addition, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) has R 1 and R 5 The hydroxyl groups contained in the compound ensure adhesion to the protective layer. Therefore, a lubricating layer containing a fluorine-containing ether compound represented by formula (1) can improve the chemical resistance of magnetic recording media even when it is thin.

[0023] In contrast, for example, R 1 and R 5When some or all of the two or three hydroxyl groups contained in each terminal group represented by are bonded to the same carbon atom, or when the carbon atoms to which the hydroxyl groups are bonded are directly bonded to each other, the number of hydroxyl groups that do not interact with the protective layer increases due to steric constraints of the molecular structure. Hydroxyl groups that do not participate in the interaction with the protective layer increase the intermolecular forces between fluorine-containing ether compounds, promoting aggregation of the fluorine-containing ether compounds. Aggregation of fluorine-containing ether compounds is undesirable because it makes it difficult to reduce the thickness of the lubricating layer formed using the fluorine-containing ether compound. Furthermore, hydroxyl groups that do not participate in the interaction with the protective layer are undesirable because they participate in interactions with impurities such as siloxanes, promoting chemical contamination of the lubricating layer containing the fluorine-containing ether compound.

[0024] In the fluorine-containing ether compound represented by formula (1), R 1 The hydroxyl group contained in and R 5 The total number of hydroxyl groups contained in is 4 to 6. Since the above total number is 4 or more, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) has high adhesion to the protective layer. Furthermore, since the above total number is 6 or less, in a magnetic recording medium having a lubricating layer containing the fluorine-containing ether compound represented by formula (1), it is possible to prevent the occurrence of pickups where the lubricating layer adheres to the magnetic head as foreign matter (smear) due to the high polarity of the fluorine-containing ether compound.

[0025] R 1 The number of hydroxyl groups contained and R 5 It is preferable that the number of hydroxyl groups contained in is the same as R. 1 and R 5 Each contains two hydroxyl groups, or R 1 and R 5 Preferably, each of these compounds contains three hydroxyl groups. In this case, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) adheres to the protective layer in a well-balanced manner. Therefore, a lubricating layer with high coverage is easily obtained.

[0026] R 1and R 5 The terminal groups represented by are preferably, in particular, independently one of the following formulas (3-1) to (3-5).

[0027] [ka] (In equation (3-1), i is an integer between 0 and 1, and j is an integer between 1 and 4.) (In equation (3-2), k is an integer between 1 and 2, and l is an integer between 1 and 3.) (In equation (3-3), m is an integer between 1 and 3.) (In equation (3-4), n is an integer between 1 and 2.)

[0028] In the fluorine-containing ether compound represented by formula (1), R 1 and R 5 However, if each terminal group is independently represented by one of the above formulas (3-1) to (3-5), a synergistic effect due to the presence of (a) to (c) below results in a more appropriate surface energy. As a result, by forming a lubricating layer on the protective layer using a lubricant containing this, a suitable interaction occurs between the lubricating layer and the protective layer. From this, R 1 and R 5 However, a lubricating layer containing a fluorine-containing ether compound, each independently represented by one of the above formulas (3-1) to (3-5), imparts superior chemical resistance to a magnetic recording medium equipped with it.

[0029] (a)R 1 and R 5 Each contains two or three hydroxyl groups. (b) A linear linking group with an appropriate number of atoms is positioned between the carbon atom to which the terminal hydroxyl group located at the very end is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded. (c)R 1 and / or R 5If there are three hydroxyl groups in the compound, then at the terminal group with three hydroxyl groups, a linear linking group with an appropriate number of atoms is positioned between the carbon atom to which the hydroxyl group located on the perfluoropolyether chain side is bonded and the carbon atom to which the adjacent hydroxyl group is bonded.

[0030] In formula (3-1), i is an integer between 0 and 1, and j is an integer between 1 and 4. The terminal group represented by formula (3-1) does not contain an oxygen atom between the carbon atom to which the terminal hydroxyl group located at the very end is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded. Therefore, the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-1) has a sufficiently low surface energy, and a magnetic recording medium equipped with a lubricating layer containing this compound provides excellent chemical resistance.

[0031] In the terminal group represented by formula (3-1), i is 0 or 1, so it has two or three hydroxyl groups. Therefore, the fluorine-containing ether compound represented by formula (1) has a sufficiently large number of hydroxyl groups involved in interaction with the protective layer, and can form a lubricating layer that exhibits excellent adhesion to the protective layer. Furthermore, the number of hydroxyl groups in the terminal group represented by formula (3-1) is three or less. Therefore, compared to, for example, the case where the number of hydroxyl groups in the terminal group is more than three, the surface energy of the fluorine-containing ether compound represented by formula (1) is lower, and the surface energy of the fluorine-containing ether compound is appropriate.

[0032] In the terminal group represented by formula (3-1), since j is an integer of 1 or greater, there is a linking group consisting of one or more methylene groups 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. Therefore, the intramolecular interaction between the terminal hydroxyl group and the hydroxyl group adjacent to the terminal hydroxyl group is small, and intramolecular aggregation is unlikely to occur. As a result, it becomes a fluorine-containing ether compound that exhibits excellent adhesion to the protective layer and can form a lubricating layer that shows excellent pickup suppression effect.

[0033] In the terminal group represented by formula (3-1), j is an integer less than or equal to 4. This ensures that the number of carbon atoms in formula (3-1) is within an appropriate range relative to the number of hydroxyl groups in formula (3-1). Therefore, the terminal group represented by formula (3-1) has polarity suitable for interaction with the protective layer. Thus, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-1) exhibits more favorable interaction with the protective layer.

[0034] In equation (3-2), k is an integer between 1 and 2, and l is an integer between 1 and 3. In the terminal group represented by formula (3-2), since k is 1 or 2, there are two or three hydroxyl groups. Therefore, the fluorine-containing ether compound represented by formula (1) has a sufficiently large number of hydroxyl groups involved in interaction with the protective layer, and can form a lubricating layer that exhibits excellent adhesion to the protective layer. Furthermore, the number of hydroxyl groups in the terminal group represented by formula (3-2) is three or less. Therefore, compared to, for example, the case where the number of hydroxyl groups in the terminal group is more than three, the surface energy of the fluorine-containing ether compound represented by formula (1) is lower, and the surface energy of the fluorine-containing ether compound is appropriate.

[0035] The terminal group represented by formula (3-2) contains an oxygen atom in the linking group positioned between the carbon atom to which the terminal hydroxyl group is bonded and the carbon atom to which the adjacent hydroxyl group is bonded. However, since l is an integer of 1 or more in the terminal group represented by formula (3-2), it has a linear linking group in which one or more methylene groups are bonded between the carbon atom to which the terminal hydroxyl group is bonded and the oxygen atom adjacent to the terminal hydroxyl group (ether bond). Therefore, the molecular mobility is appropriate, the intramolecular interaction between the terminal hydroxyl group and the adjacent hydroxyl group is small, and intramolecular aggregation is unlikely to occur. As a result, the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-2) exhibits excellent adhesion to the protective layer and can form a lubricating layer that exhibits an excellent pickup suppression effect.

[0036] In the terminal group represented by formula (3-2), l is an integer less than or equal to 3. As a result, the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-2) has a sufficiently low surface energy. Consequently, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) can further improve the chemical resistance of the magnetic recording medium.

[0037] The terminal group represented by formula (3-3) contains an oxygen atom in the linking group positioned between the carbon atom to which the terminal hydroxyl group is bonded and the carbon atom to which the adjacent hydroxyl group is bonded. However, since m is an integer of 1 or more in the terminal group represented by formula (3-3), it has a linear linking group in which one or more methylene groups are linked between the carbon atom to which the terminal hydroxyl group is bonded and the oxygen atom adjacent to the terminal hydroxyl group (ether bond), similar to the terminal group represented by formula (3-2). Furthermore, the terminal group represented by formula (3-3) has a linear linking group in which two methylene groups are linked between the oxygen atom adjacent to the terminal hydroxyl group (ether bond) and the carbon atom to which the hydroxyl group located on the perfluoropolyether chain is bonded. As a result, the molecular mobility is appropriate, intramolecular interactions between the terminal hydroxyl group and the adjacent hydroxyl group are small, and intramolecular aggregation is unlikely to occur.

[0038] In the terminal group represented by formula (3-3), m is an integer less than or equal to 3, similar to l in the terminal group represented by formula (3-2). Therefore, the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-3) has a sufficiently low surface energy, similar to the case with the terminal group represented by formula (3-2).

[0039] In formula (3-4), n is an integer between 1 and 2. Since n is 1 or 2 in the terminal group represented by formula (3-4), the intramolecular interaction between the hydroxyl group located on the perfluoropolyether chain side and the hydroxyl group adjacent to it is smaller compared to, for example, the case where n is 0, and intramolecular aggregation is less likely to occur. As a result, it becomes a fluorine-containing ether compound that exhibits excellent adhesion to the protective layer and a good pickup suppression effect. Also, since n is 1 or 2 in the terminal group represented by formula (3-4), the surface energy of the fluorine-containing ether compound represented by formula (1) is lower compared to, for example, the case where n is 3. Furthermore, since the terminal group represented by formula (3-4) contains three hydroxyl groups, the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-4) can form a lubricating layer that exhibits excellent adhesion to the protective layer. From these points, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) having the terminal group represented by formula (3-4) can further improve the chemical resistance of the magnetic recording medium.

[0040] The terminal groups represented by formula (3-5) do not contain an oxygen atom between the carbon atom to which the terminal hydroxyl group located at the very end is bonded and the carbon atom to which the hydroxyl group adjacent to the terminal hydroxyl group is bonded. Therefore, the fluorine-containing ether compound represented by formula (1) having the terminal groups represented by formula (3-5) has a sufficiently low surface energy. Furthermore, because the terminal groups represented by formula (3-5) contain three hydroxyl groups, they exhibit excellent adhesion to the protective layer and can form a lubricating layer that exhibits excellent pickup suppression effect. For these reasons, a lubricating layer containing the fluorine-containing ether compound represented by formula (1) having the terminal groups represented by formula (3-5) can further enhance the chemical resistance of the magnetic recording medium.

[0041] In the fluorine-containing ether compound represented by formula (1), R 1 and R 5 It is preferable that they are the same. 1 and R 5If they are the same, it becomes a fluorine-containing ether compound that easily spreads uniformly on the protective layer and easily forms a lubricating layer having a uniform film thickness. As a result, the lubricating layer containing this fluorine-containing ether compound tends to have a good coverage rate, and can further enhance the chemical resistance of the magnetic recording medium. Also, R 1 and R 5 are the same, and in some cases, the fluorine-containing ether compound can be efficiently produced with fewer manufacturing steps as compared with the case where R 1 and R 5 are different.

[0042] "R 3 " In the fluorine-containing ether compound represented by formula (1), R 3 is a substituent containing one primary hydroxyl group and is represented by the following formula (2). -(CH2) a -OH (2) (In formula (2), a represents an integer of 2 to 8.) In the substituent represented by formula (2), a is an integer of 2 to 8, preferably an integer of 3 to 6, and more preferably an integer of 4 to 5.

[0043] Since a in the substituent represented by formula (2) is 2 or more, the distance between the hydroxyl group contained in R 3 and the perfluoropolyether chain (R 2 , R 4 ) becomes appropriate. Therefore, the bond due to the electrostatic interaction between the hydroxyl group of R 3 contained in this and the protective layer is hardly inhibited by the adjacent perfluoropolyether chains (R 2 , R 4 ). Therefore, good adhesion between the lubricating layer and the protective layer is obtained by the electrostatic interaction between the hydroxyl group of R 3 contained in the lubricating layer and the protective layer. As a result, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) has a high coverage rate and can enhance the chemical resistance of the magnetic recording medium. It is preferable that a in the substituent represented by formula (2) is 3 or more, and more preferably 4 or more.

[0044] In a lubricating layer containing a fluorine-containing ether compound represented by formula (1), the perfluoropolyether chain (R) contained in the fluorine-containing ether compound 2 , R 4 ) has no electrostatic interaction with the protective layer. R in the lubricating layer 2 , R 4 This forms a film at a distance of 3 Å or more from the protective layer. On the other hand, hydroxyl groups contained in fluorine-containing ether compounds can have electrostatic interactions with the protective layer. However, for hydroxyl groups in the lubricating layer to have electrostatic interactions with the protective layer, the distance between the hydroxyl groups and the protective layer needs to be reduced to about 2 Å.

[0045] Therefore, R in the lubricating layer 3 The hydroxyl group contained in and R 2 , R 4 If the distance is too close, a film will form at a position more than 3 Å away from the protective layer. 2 , R 4 R 3 The hydroxyl groups contained in the material become less likely to approach the protective layer. In other words, R in the lubricating layer 3 The hydroxyl groups contained in are inhibited from having electrostatic interactions with the protective layer. As a result, R in the lubricating layer 3 The electrostatic interaction between the hydroxyl groups contained in the lubricant and the protective layer becomes difficult to achieve, resulting in insufficient adhesion between the lubricant layer and the protective layer, and thus reducing the chemical resistance of the magnetic recording medium equipped with the lubricant layer.

[0046] Specifically, for example, in the following two cases, R in the lubricating layer 3 The hydroxyl group contained in and R 2 , R 4 The distance between us is too close. (i) R in fluorine-containing ether compounds represented by formula (1) 3 If is -OH (in other words, if a in equation (2) is 0); (ii) R in fluorine-containing ether compounds represented by formula (1) 3 When is -CH2OH (in other words, when a in equation (2) is 1). Therefore, R in the lubrication layer 3The hydroxyl groups contained in the material are prevented from having electrostatic interactions with the protective layer. As a result, R in the lubricating layer 3 The hydroxyl groups contained in it do not readily exhibit their function as adsorption units for the protective layer.

[0047] Furthermore, since the number of a in the substituent represented by formula (2) is 2 or more, R 3 The hydroxyl groups contained in have a sufficiently high degree of freedom within the molecule. Therefore, the lubricating layer containing the fluorine-containing ether compound represented by formula (1) is R 3 The hydroxyl groups contained in the material readily interact with the protective layer, resulting in good adhesion to the protective layer. In contrast, for example, R 3 When R is -OH or -CH2OH, compared to when it is a substituent represented by formula (2), 3 The hydroxyl group contained in has a low degree of freedom within the molecule. Therefore, R 3 The interaction between the hydroxyl groups contained in the material and the protective layer is difficult to achieve, resulting in insufficient adhesion to the protective layer.

[0048] Furthermore, since a in the substituent represented by formula (2) is 8 or less, the fluorine-containing ether compound applied to the protective layer is less likely to be bulky, and a thin lubricating layer can be formed with sufficient coverage. Also, since a in the substituent represented by formula (2) is 8 or less, the overall surface energy of the fluorine-containing ether compound molecule is sufficiently low, resulting in a fluorine-containing ether compound that can form a lubricating layer that can increase the chemical resistance of the magnetic recording medium. Preferably, a in the substituent represented by formula (2) is 6 or less, and more preferably 5 or less.

[0049] In contrast, if the value of 'a' in the substituent represented by formula (2) is greater than 8, a thin lubricating layer may not be obtained when the methylene chain in formula (2) of the fluorine-containing ether compound coated on the protective layer interacts perpendicularly to the protective layer. Furthermore, the longer the methylene chain in formula (2), the higher the overall surface energy of the fluorine-containing ether compound molecule, making it easier for chemical substances to adhere to the lubricating layer containing it. If the value of 'a' in the substituent represented by formula (2) is greater than 8, the overall surface energy of the fluorine-containing ether compound molecule is high, and therefore sufficient chemical resistance cannot be obtained.

[0050] From these, R 3 A lubricating layer containing a fluorine-containing ether compound, in which the substituent is represented by formula (2) above, exhibits excellent adhesion to the protective layer and can enhance the chemical resistance of the magnetic recording medium even when it is thin.

[0051] In the fluorine-containing ether compound represented by formula (1), R 3 R 2 A linking group that attaches to R 4 A linking group is bonded to the hydrogen atom. Therefore, R in a lubricating layer containing a fluorine-containing ether compound represented by formula (1) 3 R 2 or R 4 It can approach the protective layer without being sterically hindered by atoms or groups of atoms other than the fluorine compound. As a result, the fluorine-containing ether compound represented by formula (1) exhibits excellent adhesion to the protective layer and can form a lubricating layer that enhances the chemical resistance of the magnetic recording medium. In contrast, for example, R in a fluorine-containing ether compound represented by formula (1) 3 When a hydrogen atom is bonded to a carbon atom, R 3 R in the lubricating layer is subjected to steric hindrance by other atoms or groups of atoms. 3 It is difficult for the material to approach the protective layer, and adhesion to the protective layer tends to be insufficient.

[0052] In the fluorine-containing ether compound represented by formula (1), two perfluoropolyether chains (R 2 , R 4 The number of hydroxyl groups located between them is R 3 It contains only one hydroxyl group. Therefore, the fluorine-containing ether compound represented by formula (1) has fewer hydroxyl groups that do not participate in interaction with the active site on the protective layer compared to, for example, a fluorine-containing ether compound in which two or more hydroxyl groups are arranged between two perfluoropolyether chains. Thus, the fluorine-containing ether compound represented by formula (1) has good adhesion to the protective layer and can form a lubricating layer in which substances that cause chemical contamination are less likely to adhere.

[0053] Furthermore, in the fluorine-containing ether compound represented by formula (1), R 1 and -CHR 3 - and -CHR 3 -and R 5 Between them, each is a perfluoropolyether chain (R 2 , R 4 ) is positioned there. Therefore, R 3 The hydroxyl group contained in and R 1 and R 5 The distance between the terminal group represented by and the hydroxyl group is appropriate. Therefore, R 3 The hydroxyl groups contained in R 1 and R 5 The hydroxyl groups of the terminal groups represented by are less likely to have their binding to the active site on the protective layer inhibited by adjacent hydroxyl groups.

[0054] Therefore, in the fluorine-containing ether compound represented by formula (1), R 3 The hydroxyl group that R 1 and R 5 The hydroxyl groups of the terminal groups represented by are all likely to be involved in bonding with active sites on the protective layer. In other words, the hydroxyl groups of the fluorine-containing ether compound in this embodiment are unlikely to be hydroxyl groups that do not participate in bonding with active sites on the protective layer. As a result, the lubricating layer containing the fluorine-containing ether compound in this embodiment has a high coverage rate, and the chemical resistance of the magnetic recording medium can be increased.

[0055] Furthermore, in the above fluorine-containing ether compounds, R 3 The hydroxyl group that R 1 and R 5 Because the distance between the terminal group represented by and the hydroxyl group is appropriate, R 3 The hydroxyl group that R 1 and R 5 It is less likely to aggregate with the hydroxyl group of the terminal group represented by . Moreover, each perfluoropolyether chain (R 2 , R 4 Both ends of ) are R 3 The hydroxyl group that R 1 The hydroxyl group of the terminal group represented by, or R 5 The hydroxyl groups of the terminal groups represented by the symbol adhere to the protective layer. As a result, the fluorine-containing ether compound applied to the protective layer does not tend to be bulky. Therefore, the fluorine-containing ether compound of this embodiment spreads easily on the protective layer, making it easy to obtain a lubricating layer with a uniform coating. Consequently, the lubricating layer containing the fluorine-containing ether compound of this embodiment can improve the chemical resistance of the magnetic recording medium.

[0056] "R 2 and R 4 " In the fluorine-containing ether compound represented by formula (1), R 2 , R 4 This is a perfluoropolyether chain (hereinafter sometimes referred to as a "PFPE chain"). 2 , R 4 The PFPE chain shown in this embodiment, when a lubricant containing the fluorine-containing ether compound of this embodiment is applied to the protective layer to form a lubricating layer, covers the surface of the protective layer and imparts lubricity to the lubricating layer, thereby reducing the frictional force between the magnetic head and the protective layer. 2 and R 4 These are selected appropriately according to the performance requirements of the lubricant containing the fluorine-containing ether compound.

[0057] R 2 and R 4This may be, for example, a structure represented by formula (4) derived from a polymer or copolymer of perfluoroalkylene oxides. -(CF2) v O(CF2O) w (CF2CF2O) x (CF2CF2CF2O) y (CF2CF2CF2CF2O) z (CF2) v’ - (4) (In equation (4), w, x, y, and z represent the average degree of polymerization and are independent real numbers between 0 and 20. It is impossible for all of w, x, y, and z to be 0 at the same time. v and v' are average values ​​representing the number of -CF2- units and are independent real numbers between 1 and 3. There are no particular restrictions on the order of the repeating units in equation (4).)

[0058] In formula (4), w, x, y, and z represent the average degree of polymerization and are each independently real numbers from 0 to 20, preferably from 0 to 16, and more preferably from 0 to 6. In formula (4), v and v' are average values ​​representing the number of -CF2- and are each independently real numbers from 1 to 3. v and v' are determined according to the structure of the repeating units located at the ends of the chain structure in the polymer represented by formula (4). In equation (4), (CF2O), (CF2CF2O), (CF2CF2CF2O), and (CF2CF2CF2CF2O) are repeating units. There are no particular restrictions on the order in which the repeating units are arranged in equation (4). There are also no particular restrictions on the number of different types of repeating units in equation (4).

[0059] R in equation (1) 2 , R 4 It is more preferable that each of these independently be one of the following equations (5) to (9). There are no particular restrictions on the sequence of the repeating units (CF2CF2O) and (CF2O) in formula (5). Formula (5) may include any of the monomer units (CF2CF2O) and (CF2O), such as a random copolymer, a block copolymer, or an alternating copolymer. There are no particular restrictions on the order of the repeating units (CF2CF2O) and (CF2CF2CF2O) in formula (8). Formula (8) may include any of the monomer units (CF2CF2O) and (CF2CF2CF2O), such as a random copolymer, a block copolymer, or an alternating copolymer. In formula (8), v8 and v8' are average values ​​indicating the number of -CF2- molecules, and are independently real numbers between 1 and 2. v8 and v8' are determined in the polymer represented by formula (8) according to the structure of the repeating units located at the ends of the chain structure.

[0060] -CF2O-(CF2O) w5 -(CF2CF2O) x5 -CF2- (5) (In equation (5), w5 and x5 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) -CF2O-(CF2CF2O) x6 -CF2- (6) (In equation (6), x6 represents the average degree of polymerization and is a real number between 1 and 20.) -CF2CF2O-(CF2CF2CF2O) y7 -CF2CF2- (7) (In equation (7), y7 represents the average degree of polymerization and is a real number between 1 and 20.) -(CF2) v8 O-(CF2CF2O) x8 -(CF2CF2CF2O) y8 -(CF2) v8’ - (8) (In equation (8), x8 and y8 represent the average degree of polymerization and are independent real numbers between 1 and 20. v8 and v8' are average values ​​representing the number of -CF2- and are independent real numbers between 1 and 2.) -CF2CF2CF2O-(CF2CF2CF2CF2O) z9 -CF2CF2CF2- (9) (In equation (9), z9 represents the average degree of polymerization and is a real number between 1 and 20.)

[0061] In equation (5), w5 and x5, which represent the average degree of polymerization, are independently real numbers between 1 and 20. In equation (6), x6, which represents the average degree of polymerization, is a real number between 1 and 20. In equation (7), y7, which represents the average degree of polymerization, is a real number between 1 and 20. In equation (8), x8 and y8, which represent the average degree of polymerization, are independently real numbers between 1 and 20. In equation (9), z9, which represents the average degree of polymerization, is a real number between 1 and 20.

[0062] When w5, x5, x6, y7, x8, y8, and z9 are 1 or greater, a fluorine-containing ether compound is obtained that yields a lubricating layer with good lubricity. When w5, x5, x6, y7, x8, and y8 are each 20 or less, the viscosity of the fluorine-containing ether compound does not become too high, making it easier to apply the lubricant containing it. Furthermore, when z9 is 10 or less, the viscosity of the fluorine-containing ether compound does not become too high, making it even easier to apply the lubricant containing it, which is preferable.

[0063] Furthermore, since it is a fluorine-containing ether compound that spreads easily on the protective layer and yields a lubricating layer with a uniform film thickness, w5 and x5 in formula (5) are preferably 1 to 16, and more preferably 2 to 8. For similar reasons, x6 in formula (6) is preferably 1 to 16, and more preferably 2 to 8; y7 in formula (7) is preferably 1 to 10, and more preferably 1 to 5; x8 and y8 in formula (8) are preferably 1 to 10, and more preferably 1 to 5; and z9 in formula (9) is more preferably 1 to 6, and even more preferably 1 to 3.

[0064] R in equation (1) 2 , R 4 However, if it is any of formulas (5) to (9), the synthesis of the fluorine-containing ether compound is easy and therefore preferable. 2 , R 4 However, if it is any of formulas (5) to (7), it is more preferable because the raw materials are easily available. Also, R 2 , R 4However, if the formula is any of equations (6) to (8), the ratio of oxygen atoms (ether bond (-O-)) to carbon atoms in the perfluoropolyether chain is appropriate. As a result, a fluorine-containing ether compound with appropriate hardness is formed. Therefore, the fluorine-containing ether compound applied to the protective layer is less likely to aggregate on the protective layer, and an even thinner lubricating layer can be formed with sufficient coverage.

[0065] In the fluorine-containing ether compound represented by formula (1), R 2 , R 4 The PFPE chains indicated by are preferably the same. Note that "the PFPE chains are the same" includes cases where the structure of the PFPE chains (type and number of repeating units) is the same, but the average degree of polymerization is different. 2 , R 4 When the PFPE chains shown are the same, differences in the mobility of the PFPE chains do not cause strain in the molecule, and the molecular asymmetry does not increase. Therefore, it is presumed that the material can adhere uniformly to the protective layer, thereby increasing the coverage rate of the protective layer.

[0066] Furthermore, R 2 and R 4 The same, R 1 and R 5 The fluorine-containing ether compounds that are the same are -OCH2-CHR 3 Because it has a symmetrical structure centered on -CH2O-, it is more preferable as it is easy to wet and spread uniformly on the protective layer, and a lubricating layer with a uniform film thickness can be easily obtained. 2 and R 4 The same, R 1 and R 5 Fluorine-containing ether compounds, which are the same as those mentioned above, can be easily and efficiently manufactured with fewer manufacturing steps.

[0067] The fluorine-containing ether compound represented by formula (1) is preferably one of the compounds represented by the following formulas (A) to (J) and (O). Note that xa1, xa2, xb1, xb2, zc1, zc2, yd1, yd2, ye1, ye2, yf1, yf2, yg1, yg2, xh1, xh2, wh1, wh2, xi1, xi2, yi1, yi2, xj1, xj2, wj1, wj2, xo1, xo2 in equations (A) to (J) and (O) are values ​​that represent the average degree of polymerization. Therefore, these values ​​are not necessarily integers.

[0068] The compounds represented by the following formulas (A) to (J) and (O) are all R 1 and R 5 They are the same. Also, the compounds represented by the following formulas (A) to (J) and (O) are all R 2 and R 4 They are the same. R in the compound represented by the following formula (A) 3 This is expressed by equation (2), where a is 2. 1 and R 5 This is expressed by equation (3-1), where i is 1 and j is 1. 2 and R 4 This is expressed by equation (6). R in the compound represented by the following formula (B) 3 This is expressed by equation (2), where a is 2. 1 and R 5 This is expressed by equation (3-2), where k is 1 and l is 3. 2 and R 4 This is expressed by equation (6).

[0069] R in the compound represented by the following formula (C) 3 This is expressed by equation (2), where a is 3. 1 and R 5 This is expressed by equation (3-4), where n is 1. 2 and R 4 This is expressed by equation (9). R in the compound represented by the following formula (D) 3 This is expressed by equation (2), where a is 3. 1 and R 5This is expressed by equation (3-2), where k is 2 and l is 3. 2 and R 4 This is expressed by equation (7).

[0070] R in the compound represented by the following formula (E) 3 This is expressed by equation (2), where a is 4. 1 and R 5 This is expressed by equation (3-2), where k is 1 and l is 2. 2 and R 4 This is expressed by equation (7). R in the compound represented by the following formula (F) 3 This is expressed by equation (2), where a is 4. 1 and R 5 This is expressed by equation (3-2), where k is 2 and l is 1. 2 and R 4 This is expressed by equation (7).

[0071] R in the compound represented by the following formula (G) 3 This is expressed by equation (2), where a is 5. 1 and R 5 This is expressed by equation (3-2), where k is 1 and l is 1. 2 and R 4 This is expressed by equation (7). R in the compound represented by the following formula (H) 3 This is expressed by equation (2), where a is 6. 1 and R 5 This is expressed by equation (3-1), where i is 1 and j is 4. 2 and R 4 This is expressed by equation (5).

[0072] R in the compound represented by the following formula (I) 3 This is expressed by equation (2), where a is 6. 1 and R 5This is expressed by equation (3-3), where m is 1. 2 and R 4 This is expressed by equation (5). R in the compound represented by the following formula (J) 3 This is expressed by equation (2), where a is 8. 1 and R 5 This is expressed by equation (3-3), where m is 2. 2 and R 4 This is expressed by equation (5).

[0073] R in the compound represented by the following formula (O) 3 This is expressed by equation (2), where a is 2. 1 and R 5 This is expressed by equation (3-5). R 2 and R 4 This is expressed by equation (6).

[0074] [ka] (In equation (A), xa1 and xa2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) (In equation (B), xb1 and xb2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.)

[0075] [ka] (In equation (C), zc1 and zc2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) (In equation (D), yd1 and yd2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.)

[0076] [ka] (In equation (E), ye1 and ye2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) (In equation (F), yf1 and yf2 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.)

[0077] [ka] (In equation (G), yg1 and yg2 represent the average degree of polymerization, each independently representing a real number between 1 and 20.) (In equation (H), xh1, xh2, wh1, and wh2 represent the average degree of polymerization, each independently representing a real number between 1 and 20.)

[0078] [ka] (In equation (I), xi1, xi2, wi1, and wi2 represent the average degree of polymerization, each independently representing a real number between 1 and 20.) (In equation (J), xj1, xj2, wj1, and wj2 represent the average degree of polymerization, each independently representing a real number between 1 and 20.)

[0079] [ka] (In equation (O), xo1 and xo2 represent the average degree of polymerization, each independently representing a real number between 1 and 20.)

[0080] It is preferable that the compound represented by formula (1) is one of the compounds represented by formulas (A) to (J) or (O) above, as the raw materials are readily available and a lubricating layer can be formed that provides high chemical resistance to magnetic recording media even with a thin thickness.

[0081] The fluorine-containing ether compound in this embodiment preferably has a number-average molecular weight (Mn) in the range of 500 to 10000, more preferably in the range of 500 to 5000, and particularly preferably in the range of 1000 to 3000. When the number-average molecular weight is 500 or more, the lubricant containing the fluorine-containing ether compound in this embodiment is less likely to evaporate, preventing the lubricant from evaporating and transferring to the magnetic head. When the number-average molecular weight is 10000 or less, the viscosity of the fluorine-containing ether compound becomes appropriate, and a thin lubricating layer can be easily formed by applying a lubricant containing it. When the number-average molecular weight is 5000 or less, the viscosity becomes easy to handle when applied to a lubricant, which is therefore more preferable.

[0082] The number-average molecular weight (Mn) of fluorine-containing ether compounds was determined using a Bruker BioSpin AVANCE III 400. 1 H-NMR and 19 These values ​​were measured by 1F-NMR. In the NMR (nuclear magnetic resonance) measurements, the sample was diluted in one or a mixture of solvents such as hexafluorobenzene, d-acetone, and d-tetrahydrofuran for use in the measurement. 19 The reference point for the F-NMR chemical shift was set to the hexafluorobenzene peak at -164.7 ppm. 1 The 1H-NMR chemical shift reference was set to a peak of 2.2 ppm for acetone.

[0083] "Manufacturing method" The method for producing the fluorine-containing ether compound of this embodiment is not particularly limited and can be produced using conventionally known production methods. The fluorine-containing ether compound of this embodiment can be produced, for example, using the production method shown below.

[0084] (1st manufacturing method) R 1 and R 5 and are the same, R 2 , R 4 When producing a compound in which the two PFPE chains shown are the same, the following production method can be used. First, in equation (1), R 2 (=R 4 A fluorine-based compound is prepared in which a hydroxymethyl group (-CH2OH) is positioned at both ends of the perfluoropolyether chain corresponding to ). Next, the hydroxyl group of the hydroxymethyl group positioned at one end of the fluorine-based compound and the R in formula (1) are taken together. 1 (=R 5 The epoxy compound having a group consisting of ) is reacted (first reaction). By carrying out the first reaction, R 2 (=R 4 At one end of the perfluoropolyether chain corresponding to ), R 1 (=R 5 An intermediate compound 1 having a group corresponding to ) is obtained.

[0085] R 1 (=R 5 An epoxy compound having a group consisting of ) may be reacted with the above-mentioned fluorine-based compound after protecting the hydroxyl group with an appropriate protecting group. When producing the fluorine-containing ether compound of this embodiment, the epoxy compound used in the first reaction can be synthesized by the following method. For example, the R of the fluorine-containing ether compound to be produced 1 (or R 5 It can be synthesized by reacting an alcohol having a structure corresponding to a group consisting of ) with a compound having an epoxy group. As the epoxy group-containing compound, any of epichlorohydrin, epibromohydrin, 2-bromoethyloxirane, or allyl glycidyl ether can be used. The epoxy compound may be synthesized by a method of oxidizing the unsaturated bond, or it may be purchased and used as a commercially available product.

[0086] Subsequently, the hydroxyl group of the hydroxymethyl group located at one end of intermediate compound 1 obtained in the first reaction is subjected to a nucleophilic substitution reaction with the two halogen groups represented by X in the compound shown in formula (10) below (second reaction). In formula (10), X is one of a chloro group, a bromo group, or an iodo group.

[0087] By carrying out the second reaction, R in equation (1) 3 The corresponding group is bonded to a carbon atom located in the center of the chain structure, and the carbon atom is the R 3 Intermediate compound 2 is obtained, which forms a double bond with the carbon atom in the corresponding group. In intermediate compound 2, R 3 The carbon atom in the chain structure to which the corresponding group is bonded is R 2 (=R 4 It is bonded to two perfluoropolyether chains corresponding to ) via linking groups. R contained in intermediate compound 2 2 At the end of the corresponding perfluoropolyether chain, via a methylene group, R 1 The corresponding group is bonded. Also, R 4 At the end of the corresponding perfluoropolyether chain, via a methylene group, R 5 The corresponding group is bonded to it.

[0088] The compound represented by formula (10), used in the second reaction when producing the fluorine-containing ether compound of this embodiment, can be synthesized by the following method. The compound represented by formula (10) is the fluorine-containing ether compound represented by formula (1), which is the target product. 3 A product having the corresponding group is manufactured. Specifically, a-1 in the compound represented by formula (10) is R of the fluorine-containing ether compound represented by formula (1), which is the target product. 3 The goal is to produce something that is one less than the value of 'a' in equation (2).

[0089] To produce the compound shown in formula (10), first, R 3 A compound represented by formula (11) is synthesized by a Knoevenagel condensation reaction between a carbonyl compound having the corresponding structure and a malonic acid ester. In the carbonyl compound used to produce the compound represented by formula (11), R in formula (1) 3 It is preferable to protect the hydroxyl group in the corresponding structure with a protecting group such as a tetrahydropyranyl (THP) group before reacting it with the malonic acid ester.

[0090] Next, the compound shown in formula (12) is synthesized by reducing the ester of the compound shown in formula (11). Subsequently, the hydroxyl group of the compound represented by formula (12) is halogenated by an Appel reaction. The halogenation may be chlorination, bromination, or iodization. Through the above steps, the compound represented by formula (10) is obtained.

[0091] [ka] (In formula (10), X represents one of the following: a chloro group, a bromo group, or an iodine group. 6 represents a protecting group. a-1 is the R of the fluorine-containing ether compound shown in formula (1). 3 It is a number that is 1 less than a in equation (2). (In formula (11), R 6 represents a protecting group. a-1 is the R of the fluorine-containing ether compound shown in formula (1). 3 It is a number that is 1 less than a in equation (2). (In formula (12), R 6 represents a protecting group. a-1 is the R of the fluorine-containing ether compound shown in formula (1). 3 It is a number that is 1 less than a in equation (2).

[0092] Subsequently, the double bond in intermediate compound 2 obtained by the second reaction is converted to a saturated bond by catalytic hydrogenation (third reaction). By performing the above steps, R in equation (1) 1 and R 5 and are the same, R 2 , R 4 Compounds can be produced in which the two PFPE chains shown are the same.

[0093] (Second manufacturing method) In equation (1), R 1 and R 5 Unlike, R 2 , R 4When producing a compound in which the two PFPE chains indicated by are the same, the following production method can be used. In the second production method, only the method that differs from the first production method will be described, and the method that is the same as the first production method will not be described. In the second manufacturing method, in the first reaction, R 1 Intermediate compound 1a having a corresponding group, and R 5 Intermediate compound 1b having the corresponding group is synthesized.

[0094] Subsequently, the intermediate compound 1a obtained in the first reaction is reacted with an excess amount of the compound represented by formula (10), and the by-product is removed by silica gel column chromatography to obtain intermediate compound 2a. Next, intermediate compound 2a and intermediate compound 1b are reacted to obtain intermediate compound 2ab (second reaction). Subsequently, the double bond in intermediate compound 2ab obtained by the second reaction is converted to a saturated bond by a catalytic hydrogenation reaction (third reaction). By performing the above steps, R in equation (1) 1 and R 5 Unlike, R 2 , R 4 Compounds can be produced in which the two PFPE chains shown are the same.

[0095] (Third manufacturing method) In equation (1), R 1 and R 5 Unlike, R 2 and R 4 When producing compounds different from those described above, the following production methods can be used. In the third production method, only methods different from the first production method will be described, and the same methods as the first production method will not be described. In the third manufacturing method, in the first reaction, R 2 A fluorinated compound having a perfluoropolyether chain corresponding to the R 1 Intermediate compound 1c is synthesized by reacting it with an epoxy compound having a group consisting of . 4The hydroxyl group of the hydroxymethyl group located at one end of the fluorine-based compound having a perfluoropolyether chain corresponding to, and R 5 React with an epoxy compound having a group composed of to synthesize intermediate compound 1d.

[0096] Thereafter, an excessive amount of the compound represented by the formula (10) is allowed to act on the intermediate compound 1c obtained by the first reaction, and the by-products are removed by silica gel column chromatography to obtain the intermediate compound 2c. Subsequently, the intermediate compound 2c and the intermediate compound 1d are reacted to obtain the intermediate compound 2cd (second reaction). Thereafter, the double bond in the intermediate compound 2cd obtained by the second reaction is converted to a saturated bond by a catalytic hydrogenation reaction (third reaction). By performing the above steps, in the formula (1), R 1 and R 5 are different, and R 2 and R 4 are different, a compound can be produced.

[0097] Here, the function of the lubricating layer formed on the protective layer will be described using the lubricant containing the fluorine-containing ether compound of the present embodiment. Since the fluorine-containing ether compound of the present embodiment is a compound represented by the formula (1), the lubricating layer containing this can enhance the chemical resistance of the magnetic recording medium. This effect is based on the synergistic effect that the lubricating layer formed on the protective layer using the lubricant containing the fluorine-containing ether compound of the present embodiment has excellent adhesion to the protective layer, has an appropriate surface energy, and is formed on the protective layer in a uniform coating state.

[0098] More specifically, the lubricating layer formed on the protective layer is adhered to the protective layer by the hydroxyl group (-OH) of R 3 of the fluorine-containing ether compound represented by the formula (1), and the hydroxyl groups contained two or three in each of R 1 and R 5 . Moreover, R 1 and R 5Since the number of hydroxyl groups contained in it is three or less, the surface energy of the fluorine-containing ether compound is lower compared to the case where the number of hydroxyl groups exceeds three, and the surface energy of the fluorine-containing ether compound becomes appropriate. From this, the lubricating layer containing the fluorine-containing ether compound represented by the formula (1) is less likely to have chemical substances adhering to it, and can suppress chemical substance contamination of the magnetic recording medium.

[0099] Also, in the fluorine-containing ether compound represented by the formula (1), R 3 The hydroxyl group contained in, and R 1 And R 5 Between the terminal groups represented by, R 2 R, 4 The PFPE chain represented by is arranged. Therefore, the distance between the hydroxyl group contained in R 3 And the hydroxyl group of the terminal group represented by R 1 And R 5 Is appropriate. As a result, the hydroxyl group contained in R 3 Is less likely to aggregate with the hydroxyl groups of the terminal groups represented by R 1 And R 5 And adheres to the protective layer. Therefore, the fluorine-containing ether compound represented by the formula (1) easily spreads and wets on the protective layer, and the lubricating layer containing this is easily formed in a uniform coating state. The lubricating layer formed in a uniform coating state has a high coating rate, so the chemical substance resistance of the magnetic recording medium can be increased.

[0100] Also, the fluorine-containing ether compound represented by the formula (1) has R 2 R, 4 The PFPE chain represented by. The PFPE chain represented by R 2 R, 4 Contained in the lubricating layer covers the surface of the protective layer and imparts chemical substance resistance to the lubricating layer due to its low surface energy. Furthermore, in the fluorine-containing ether compound represented by the formula (1), since R 3 Has the structure represented by the formula (2), R 3 The distance between the hydroxyl group contained in and the PFPE chain represented by R 2 R, 4 Is appropriate. As a result, R3 The hydroxyl group contained in R 2 and R 4 It can approach the protective layer without being hindered by the PFPE chain represented by [the symbol]. Therefore, it becomes a lubricating layer that exhibits excellent adhesion to the protective layer.

[0101] [Lubricant for magnetic recording media] The lubricant for magnetic recording media of this embodiment contains a fluorine-containing ether compound represented by formula (1). The lubricant of this embodiment can be mixed with known materials used as lubricants, as long as the properties are not impaired by the inclusion of a fluorine-containing ether compound represented by formula (1).

[0102] Specific examples of known materials include, for example, FOMBLIN® ZDIAC, FOMBLIN ZDEAL, FOMBLIN AM-2001 (all manufactured by Solvay Solexis), and Moresco A20H (manufactured by Moresco). The known materials used in combination with the lubricant of this embodiment preferably have a number-average molecular weight of 500 to 10000.

[0103] If the lubricant of this embodiment contains other materials of the fluorine-containing ether compound represented by formula (1), the content of the fluorine-containing ether compound represented by formula (1) in the lubricant of this embodiment is preferably 50% by mass or more, and more preferably 70% by mass or more. The content of the fluorine-containing ether compound represented by formula (1) may be 80% by mass or more, or 90% by mass or more.

[0104] The lubricant of this embodiment contains a fluorine-containing ether compound represented by formula (1), and therefore exhibits excellent adhesion to the protective layer. Even with a thin thickness, it can cover the surface of the protective layer with a high coverage rate, forming a lubricating layer with good coverage. Thus, with the lubricant of this embodiment, a lubricating layer that can increase the chemical resistance of the magnetic recording medium can be obtained even with a thin thickness.

[0105] [Magnetic recording medium] The magnetic recording medium of this embodiment has at least a magnetic layer, a protective layer, and a lubricating layer sequentially provided on a substrate. In the magnetic recording medium of this embodiment, one or more underlay layers may be provided between the substrate and the magnetic layer, as needed. Furthermore, an adhesive layer and / or a soft magnetic layer may be provided between the underlay layer and the substrate.

[0106] Figure 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 adhesion 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.

[0107] "substrate" As the substrate 11, for example, a non-magnetic substrate can be used, which has a film made of NiP or NiP alloy formed on a base made of a metal or alloy material such as Al or an Al alloy. Furthermore, the substrate 11 may be a non-magnetic substrate made of a non-metallic material such as glass, ceramics, silicon, silicon carbide, carbon, or resin, or a non-magnetic substrate in which a film of NiP or NiP alloy is formed on a substrate made of one of these non-metallic materials.

[0108] "Adhesion layer" The adhesive layer 12 prevents the progression 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 placed in contact with each other. The material of the adhesion layer 12 can be appropriately selected from, for example, Cr, Cr alloy, Ti, Ti alloy, CrTi, NiAl, AlRu alloy, etc. The adhesion layer 12 can be formed, for example, by sputtering.

[0109] "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 sequentially laminated. That is, the soft magnetic layer 13 preferably has a structure in which the soft magnetic films above and below the intermediate layer are anti-ferro-coupling (AFC) coupled by sandwiching an intermediate layer made of a Ru film between the two soft magnetic films.

[0110] Examples of materials for the first and second soft magnetic films include CoZrTa alloy and 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 becomes possible to improve the orientation of the first underlayer (seed layer) and reduce the amount of levitation of the magnetic head. The soft magnetic layer 13 can be formed, for example, by a sputtering method.

[0111] "First base layer" The first sublayer 14 is a layer that controls the orientation and crystal size of the second sublayer 15 and the magnetic layer 16 which are placed on top of it. Examples of the first subsoil layer 14 include a Cr layer, a Ta layer, a Ru layer, or a CrMo alloy layer, a CoW alloy layer, a CrW alloy layer, a CrV alloy layer, a CrTi alloy layer, and so on. The first subsoil layer 14 can be formed, for example, by a sputtering method.

[0112] "Second base layer" The second underlayer 15 is a layer that controls the orientation of the magnetic layer 16 to a good degree. The second underlayer 15 is preferably a layer made of Ru or a Ru alloy. The second sublayer 15 may consist of one layer or multiple layers. If the second sublayer 15 consists of multiple layers, all layers may be made of the same material, or at least one layer may be made of a different material. The second subsoil layer 15 can be formed, for example, by sputtering.

[0113] "Magnetic layer" The magnetic layer 16 is composed of a magnetic film whose easy axis of magnetization is perpendicular or horizontal to the substrate surface. The magnetic layer 16 is a layer containing Co and Pt. The magnetic layer 16 may be a layer containing oxides, Cr, B, Cu, Ta, Zr, etc. in order to improve the SNR characteristics. Examples of the oxide contained in the magnetic layer 16 include SiO2, SiO, Cr2O3, CoO, Ta2O3, TiO2, etc.

[0114] The magnetic layer 16 may be composed of one layer, or may be composed of a plurality of magnetic layers made of materials with different compositions. For example, when the magnetic layer 16 is composed of three layers of a first magnetic layer, a second magnetic layer, and a third magnetic layer laminated in order from the bottom, the first magnetic layer preferably has a granular structure made of a material containing Co, Cr, Pt, and further containing an oxide. As the oxide contained in the first magnetic layer, for example, oxides of Cr, Si, Ta, Al, Ti, Mg, Co, etc. are preferably used. Among them, in particular, TiO2, Cr2O3, SiO2, etc. can be preferably used. Also, the first magnetic layer preferably consists of a composite oxide containing two or more kinds of oxides. Among them, in particular, Cr2O3 - SiO2, Cr2O3 - TiO2, SiO2 - TiO2, etc. can be preferably used.

[0115] In addition to Co, Cr, Pt, and the oxide, the first magnetic layer can contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re. The same material as the first magnetic layer can be used for the second magnetic layer. The second magnetic layer preferably has a granular structure. [[ID=​​​​

[0117] When the magnetic layer 16 is formed of multiple magnetic layers, it is preferable to provide a non-magnetic layer between adjacent magnetic layers. When the magnetic layer 16 consists of three layers, 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.

[0118] The non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16 can preferably be made of, for example, Ru, Ru alloy, CoCr alloy, CoCrX1 alloy (where 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, B).

[0119] For the non-magnetic layer provided between adjacent magnetic layers of the magnetic layer 16, it is preferable to use an alloy material containing an oxide, metal nitride, or metal carbide. Specifically, as oxides, for example, SiO2, Al2O3, Ta2O5, Cr2O3, MgO, Y2O3, TiO2, etc. can be used. As metal nitrides, for example, AlN, Si3N4, TaN, CrN, etc. can be used. As metal carbides, for example, TaC, BC, SiC, etc. can be used. The non-magnetic layer can be formed, for example, by sputtering.

[0120] To achieve a higher recording density, the magnetic layer 16 is preferably a perpendicular magnetic recording layer in which the easy magnetization axis is oriented perpendicular to the substrate surface. The magnetic layer 16 may also be an in-plane magnetic recording layer. The magnetic layer 16 may be formed by any conventional known method, such as vapor deposition, ion beam sputtering, or magnetron sputtering. The magnetic layer 16 is usually formed by sputtering.

[0121] "Protective layer" The protective layer 17 protects the magnetic layer 16. The protective layer 17 may consist of one layer or multiple layers. Examples of materials for the protective layer 17 include carbon, nitrogen-containing carbon, and silicon carbide. A carbon-based protective layer can preferably be used as the protective layer 17, and an amorphous carbon protective layer is particularly preferred. A carbon-based protective layer is preferable because it further enhances the interaction with the hydroxyl groups contained in the fluorine-containing ether compound in the lubricating layer 18.

[0122] The adhesion between the carbon-based protective layer and the lubricating layer 18 can be controlled by using hydrogenated carbon and / or nitrated 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 to 20 atomic percent when measured by hydrogen forward scattering (HFS). Furthermore, the nitrogen content in the carbon-based protective layer is preferably 4 to 15 atomic percent when measured by X-ray photoelectron spectroscopy (XPS).

[0123] The hydrogen and / or nitrogen contained in the carbon-based protective layer do not need to be uniformly distributed throughout the entire layer. Preferably, the carbon-based protective layer is a compositionally graded layer, for example, in which nitrogen is contained on the lubrication layer 18 side of the protective layer 17 and hydrogen is contained on the magnetic layer 16 side of the protective layer 17. In this case, the adhesion between the magnetic layer 16 and the lubrication layer 18 and the carbon-based protective layer is further improved.

[0124] The thickness of the protective layer 17 should be between 1 nm and 7 nm. If the thickness of the protective layer 17 is 1 nm or more, sufficient performance as a protective layer 17 can be obtained. If the thickness of the protective layer 17 is 7 nm or less, it is preferable from the viewpoint of thinning the protective layer 17.

[0125] As a method for forming the protective layer 17, sputtering using a carbon-containing target material, CVD (chemical vapor deposition) using hydrocarbon raw materials such as ethylene and toluene, and IBD (ion beam deposition) can be used. When forming a carbon-based protective layer as the protective layer 17, it can be deposited by, for example, DC magnetron sputtering. In particular, when forming a carbon-based protective layer as the 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 and low roughness.

[0126] "Lubricant layer" The lubricating layer 18 prevents contamination of the magnetic recording medium 10. Furthermore, the lubricating layer 18 reduces the frictional force of the magnetic head of the magnetic recording / reproducing device sliding on the magnetic recording medium 10, thereby improving the durability of the magnetic recording medium 10. As shown in Figure 1, the lubricating layer 18 is formed in contact with the protective layer 17. The lubricating layer 18 contains the fluorine-containing ether compound described above.

[0127] The lubricating layer 18 is bonded with a particularly strong bond to the protective layer 17, especially when the protective layer 17 located beneath the lubricating layer 18 is a carbon-based protective layer. As a result, even with a thin lubricating layer 18, it becomes easier to obtain a magnetic recording medium 10 in which the surface of the protective layer 17 is covered with a high degree of coverage, and contamination of the surface of the magnetic recording medium 10 can be effectively prevented.

[0128] The average thickness of the lubricating layer 18 is preferably 0.5 nm (5 Å) to 2.0 nm (20 Å), and more preferably 0.5 nm (5 Å) to 1.0 nm (10 Å). When the average thickness of the lubricating layer 18 is 0.5 nm or more, the lubricating layer 18 is formed with a uniform thickness without forming island-like or mesh-like structures. Therefore, the surface of the protective layer 17 can be covered with a high coverage rate by the lubricating layer 18. Furthermore, by making the average thickness of the lubricating layer 18 2.0 nm or less, the lubricating layer 18 can be sufficiently thinned, and the amount of levitation of the magnetic head can be sufficiently reduced.

[0129] If the surface of the protective layer 17 is not covered with a sufficiently high degree of coverage by the lubricating layer 18, environmental substances adsorbed on the surface of the magnetic recording medium 10 will pass through the gaps in the lubricating layer 18 and penetrate beneath it. Environmental substances that penetrate beneath the lubricating layer 18 will adsorb and combine with the protective layer 17 to generate contaminants. Then, during magnetic recording and playback, these contaminants (aggregated components) will adhere to (transfer) the magnetic head as a smear, damaging the magnetic head or degrading the magnetic recording and playback characteristics of the magnetic recording and playback device.

[0130] Examples of environmental substances that generate pollutants include siloxane compounds (cyclic siloxanes, linear siloxanes), ionic impurities, relatively high molecular weight hydrocarbons such as octacosane, and plasticizers such as dioctyl phthalate. Examples of metal ions contained in ionic impurities include sodium ions and potassium ions. Examples of inorganic ions contained in ionic impurities include chloride ions, bromide ions, nitrate ions, sulfate ions, and ammonium ions. Examples of organic ions contained in ionic impurities include oxalate ions and formate ions.

[0131] "Method for forming a lubricating layer" One method for forming the lubricating layer 18 is to prepare a magnetic recording medium in the process of being manufactured, in which each layer up to the protective layer 17 has been formed on the substrate 11, apply a lubricating layer forming solution to the protective layer 17, and dry it.

[0132] The lubricating layer forming solution is obtained by dispersing and dissolving the lubricant for magnetic recording media of the above embodiment in a solvent as needed, and adjusting the viscosity and concentration to be suitable for the coating method. Examples of solvents used in lubrication layer-forming solutions include fluorine-based solvents such as Bartrell® XF (trade name, manufactured by Mitsui DuPont Fluorochemicals).

[0133] The method for applying the lubricating layer-forming solution is not particularly limited, but examples include the spin coating method, spray method, paper coating method, and dip method. When using the dip 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 lubricating layer forming solution placed in the immersion tank of the dip coating apparatus. Next, the substrate 11 is withdrawn from the immersion tank at a predetermined speed. This coats the surface of the protective layer 17 of the substrate 11 with the lubricating layer forming solution. By using the dipping method, the lubrication layer-forming solution can be uniformly applied to the surface of the protective layer 17, and a lubrication layer 18 can be formed on the protective layer 17 with a uniform film thickness.

[0134] In this embodiment, it is preferable to heat-treat the substrate 11 on which the lubricating layer 18 is formed. By heat-treating, the adhesion between the lubricating layer 18 and the protective layer 17 is improved, and the adhesion force between the lubricating layer 18 and the protective layer 17 is improved. The heat treatment temperature is preferably 100 to 180°C. A heat treatment temperature of 100°C or higher provides sufficient improvement in the adhesion between the lubricating layer 18 and the protective layer 17. Furthermore, a heat treatment temperature of 180°C or lower prevents thermal decomposition of the lubricating layer 18. The heat treatment time is preferably 10 to 120 minutes.

[0135] The magnetic recording medium 10 of this embodiment has at least a magnetic layer 16, a protective layer 17, and a lubricating layer 18 sequentially provided on a substrate 11. In the magnetic recording medium 10 of this embodiment, the lubricating layer 18 containing the above-mentioned fluorine-containing ether compound is formed in contact with the protective layer 17. This lubricating layer 18 has excellent adhesion to the protective layer 17, possesses appropriate surface energy, and can cover the surface of the protective layer 17 with a high coverage rate in a uniform coating state even when thin, resulting in good coverage. Therefore, in the magnetic recording medium 10 of this embodiment, environmental substances that generate contaminants such as ionic impurities are prevented from entering through gaps in the lubricating layer 18. In addition, the lubricating layer 18 in the magnetic recording medium 10 of this embodiment is less likely to generate foreign matter (smears), and pickup can be suppressed. As a result, the magnetic recording medium 10 of this embodiment has fewer contaminants on its surface, excellent chemical resistance, and good reliability and durability. [Examples]

[0136] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0137] [Example 1] The compound represented by formula (A) above was produced by the method described below. Under a nitrogen gas atmosphere, HOCH2CF2O(CF2CF2O) is added to a 200 mL round-bottom flask. x 20 g of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), 3.00 g of the compound represented by the following formula (13) (molecular weight 250.29, 12.0 mmol), and 20 mL of t-butanol were charged and stirred at room temperature until homogeneous. To this homogeneous solution, 0.67 g of potassium tert-butoxide (molecular weight 112.21, 6.0 mmol) was added and the mixture was stirred at 70°C for 16 hours to allow the reaction to proceed.

[0138] 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 with anhydrous sodium sulfate. After filtering off the drying agent, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 10.00 g (molecular weight 1250.29, 8.0 mmol) of the compound shown in formula (14) below as an intermediate.

[0139] [ka] (In formula (13), Ph represents a phenyl group.) (In formula (14), xa, which represents the average degree of polymerization, represents 7.1, and Ph represents a phenyl group.)

[0140] The compound represented by formula (13) was synthesized by the following method. A compound was synthesized by reacting 1,2,4-butanetriol with benzaldehyde dimethyl acetal to protect the hydroxyl groups bonded to the 2- and 4-position carbons of 1,2,4-butanetriol. By reacting this compound with epibromohydrin, the compound represented by formula (13) was synthesized.

[0141] Next, under a nitrogen gas atmosphere, 10.00 g of the compound represented by formula (14) (molecular weight 1250.29, 8.0 mmol), which was the intermediate obtained above, and 80 mL of N,N-dimethylformamide were charged into a 200 mL round-bottom flask and stirred at room temperature until homogeneous. This homogeneous solution was cooled to 0°C, 0.33 g of sodium hydride (purity 60%, molecular weight 24.00, 8.2 mmol) was added and stirred for 30 minutes, and then 1.31 g of the compound represented by formula (15) (molecular weight 328.04, 4.0 mmol) was gradually added. The suspension obtained in the above procedure was stirred at room temperature for 24 hours.

[0142] [ka] (In formula (15), THP represents a tetrahydropyranyl group.)

[0143] After the reaction, 10 mL of water was gradually added to the reaction solution obtained under ice cooling. The reaction solution was then gradually transferred to a separatory funnel containing 100 mL of saturated saline solution, and extracted three times with 200 mL of a mixed solvent of ethyl acetate and hexane. Each organic layer was washed with 100 mL of saline solution and dehydrated with anhydrous sodium sulfate. After filtering off the drying agent, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 4.27 g (molecular weight 2666.83, 1.6 mmol) of the compound shown in formula (16) as an intermediate.

[0144] [ka] (In formula (16), xa1 and xa2, which represent the average degree of polymerization, both represent 7.1. Ph represents a phenyl group, and THP represents a tetrahydropyranyl group.)

[0145] Under a nitrogen gas atmosphere, 4.27 g (molecular weight 2666.83, 1.6 mmol) of the compound shown in formula (16) above, 30 mL of ethanol, and 0.10 g of Pd / C (5% Pd) were added to a 200 mL round-bottom flask. After the reaction system was brought under a hydrogen atmosphere, it was stirred at room temperature for 16 hours. After removing Pd / C by Celite filtration, 30 mL of 5% hydrogen chloride methanol solution was added to the filtrate and it was stirred at room temperature for 2 hours. The reaction mixture was neutralized with 125 mL of saturated sodium bicarbonate aqueous solution and then extracted three times with 250 mL of ethyl acetate. Each organic layer was washed with 125 mL of saturated sodium chloride aqueous solution and dehydrated with anhydrous sodium sulfate. After filtering off the drying agent, the filtrate was concentrated, and the residue was purified by silica gel column chromatography to obtain 3.27 g (molecular weight 2408.53, 1.4 mmol) of compound (A) (in formula (A), xa1 and xa2, which indicate the average degree of polymerization, are both 7.1).

[0146] The compound represented by formula (15) used in the above reaction was synthesized by the following five-step reaction, from the first to the fifth reaction. One hydroxyl group of ethylene glycol was protected with a tetrahydropyranyl (THP) group (first reaction). Next, the other hydroxyl group of ethylene glycol was converted to an aldehyde group by Swarn oxidation (second reaction) to obtain the aldehyde compound shown in formula (17). The obtained aldehyde compound shown in formula (17) was subjected to a Knoevenagel condensation reaction with dimethyl malonate (third reaction) to obtain the compound shown in formula (18). The ester of the obtained compound shown in formula (18) was reduced (fourth reaction) to obtain the compound shown in formula (19). Subsequently, the hydroxyl group of the compound shown in formula (19) was brominated by an Appel reaction (fifth reaction) to obtain the compound shown in formula (15).

[0147] [ka] (In formula (17), THP represents a tetrahydropyranyl group.) (In formula (18), THP represents a tetrahydropyranyl group.) (In formula (19), THP represents a tetrahydropyranyl group.)

[0148] The obtained compound (A) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(7H), 3.4~4.3(41H) 19 F-NMR(CD3COCD3):δ[ppm]=-77~-80(8F), -88~-91(56F)

[0149] [Example 2] The procedure was the same as in Example 1, except that 2.76 g (molecular weight 230.30, 12.0 mmol) of the compound represented by formula (20) below was used instead of the compound represented by formula (13). 3.23 g of the compound represented by formula (B) above (wherein xb1 and xb2, which indicate the average degree of polymerization, are both 7.1) was obtained.

[0150] [ka] (In formula (20), THP represents a tetrahydropyranyl group.)

[0151] The compound represented by formula (20) was synthesized by protecting one hydroxyl group of 1,4-butanediol with a tetrahydropyranyl (THP) group and reacting the other hydroxyl group with epibromohydrin.

[0152] The obtained compound (B) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.89(11H), 3.4~4.3(37H) 19 F-NMR(CD3COCD3):δ[ppm]=-77~-80(8F), -88~-91(56F)

[0153] [Example 3] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2CF2CF2O(CF2CF2CF2CF2O) z The compound represented by CF2CF2CF2CH2OH (where z, representing the average degree of polymerization, is 2.9) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 4.01 g (molecular weight 334.41, 12.0 mmol) of the compound represented by formula (21) below was used instead of the compound represented by formula (13); (iii) In Example 1, instead of the compound represented by formula (15), 1.37 g (molecular weight 342.07, 4.0 mmol) of the compound represented by formula (22) below was used. As a result, 3.41 g of the compound represented by formula (C) above (wherein formula (C), zc1 and zc2, which indicate the average degree of polymerization, are both 2.9) was obtained.

[0154] [ka] (In formula (21), THP represents a tetrahydropyranyl group, and MOM represents a methoxymethyl group.) (In formula (22), THP represents a tetrahydropyranyl group.)

[0155] The compound represented by formula (21) was synthesized by the following method. A compound obtained by oxidizing an ethylene glycol monoallyl ether protected with dihydropyran was reacted with the hydroxyl group of 3-buten-1-ol. The secondary hydroxyl group of the resulting compound was protected with a methoxymethyl (MOM) group, and the double bond of the resulting compound was oxidized to synthesize the compound represented by formula (21).

[0156] The compound represented by formula (22) was synthesized in the same manner as the compound represented by formula (15), except that 1,3-propanediol was used as the starting material instead of ethylene glycol.

[0157] The obtained compound (C) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(9H), 3.4~4.3(49H) 19 F-NMR (CD3COCD3): δ[ppm]=-83.7(31F), -120.5(4F), -122.8ppm(4F), -125.8(23F), -127.6(8F)

[0158] [Example 4] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2CF2O(CF2CF2CF2O) y The compound represented by CF2CF2CH2OH (where y, representing the average degree of polymerization, is 4.4) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 4.18 g (molecular weight 348.44, 12.0 mmol) of the compound represented by formula (23) below was used instead of the compound represented by formula (13); (iii) In Example 1, 1.37 g (molecular weight 342.07, 4.0 mmol) of the compound represented by formula (22) was used instead of the compound represented by formula (15). As a result, 3.45 g of the compound represented by the above formula (D) (wherein yd1 and yd2, which indicate the average degree of polymerization, are both 4.4) was obtained.

[0159] [ka] (In formula (23), THP represents a tetrahydropyranyl group and MOM represents a methoxymethyl group.)

[0160] The compound represented by formula (23) was synthesized by the following method. A tert-butyldimethylsilyl (TBS) group was introduced as a protecting group to the primary hydroxyl group of 3-allyloxy-1,2-propanediol, and a methoxymethyl (MOM) group was introduced as a protecting group to the secondary hydroxyl group of the resulting compound. Subsequently, the TBS group was removed from the compound, and the resulting primary hydroxyl group was reacted with 2-(4-bromobutoxy)tetrahydro-2H-pyran. The double bond of the resulting compound was oxidized. Through these steps, the compound represented by formula (23) was obtained.

[0161] The obtained compound (D) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(13H), 3.4~4.3(49H) 19 F-NMR (CD3COCD3): δ[ppm]=-84.3(36F), -86.4(4F), -124.2(4F), -130.1(18F)

[0162] [Example 5] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2CF2O(CF2CF2CF2O) yThe compound represented by CF2CF2CH2OH (where y, representing the average degree of polymerization, is 4.4) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 2.59 g (molecular weight 216.27, 12.0 mmol) of the compound represented by formula (24) below was used instead of the compound represented by formula (13); (iii) In Example 1, 1.42 g (molecular weight 356.1, 4.0 mmol) of the compound represented by formula (25) below was used instead of the compound represented by formula (15). As a result, 3.23 g of the compound represented by the above formula (E) (wherein formula (E), ye1 and ye2, which indicate the average degree of polymerization, are both 4.4) was obtained.

[0163] [ka] (In formula (24), THP represents a tetrahydropyranyl group.)

[0164] The compound represented by formula (24) was synthesized by protecting one hydroxyl group of 1,3-propanediol with a tetrahydropyranyl (THP) group and reacting the other hydroxyl group with epibromohydrin.

[0165] [ka] (In formula (25), THP represents a tetrahydropyranyl group.)

[0166] The compound represented by formula (25) was synthesized in the same manner as the compound represented by formula (15), except that 1,4-butanediol was used as the starting material instead of ethylene glycol.

[0167] The obtained compound (E) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(11H), 3.4~4.3(37H) 19 F-NMR (CD3COCD3): δ[ppm]=-84.3(36F), -86.4(4F), -124.2(4F), -130.1(18F)

[0168] [Example 6] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2CF2O(CF2CF2CF2O) y The compound represented by CF2CF2CH2OH (where y, representing the average degree of polymerization, is 4.4) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 3.84 g (molecular weight 320.38, 12.0 mmol) of the compound represented by formula (26) below was used instead of the compound represented by formula (13); (iii) In Example 1, 1.42 g (molecular weight 356.1, 4.0 mmol) of the compound represented by formula (25) was used instead of the compound represented by formula (15). As a result, 3.39 g of the compound represented by the above formula (F) (wherein formula (F), yf1 and yf2, which indicate the average degree of polymerization, are both 4.4) was obtained.

[0169] [ka] (In formula (26), THP represents a tetrahydropyranyl group, and MOM represents a methoxymethyl group.)

[0170] The compound represented by formula (26) was synthesized by the following method. A tert-butyldimethylsilyl (TBS) group was introduced as a protecting group to the primary hydroxyl group of 3-allyloxy-1,2-propanediol, and a methoxymethyl (MOM) group was introduced as a protecting group to the secondary hydroxyl group of the resulting compound. Subsequently, the TBS group was removed from the compound, and the resulting primary hydroxyl group was reacted with 2-(2-bromoethoxy)tetrahydro-2H-pyran. The double bond of the resulting compound was oxidized. Through these steps, the compound represented by formula (26) was obtained.

[0171] The obtained compound (F) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(7H), 3.4~4.3(49H) 19 F-NMR (CD3COCD3): δ[ppm]=-84.3(36F), -86.4(4F), -124.2(4F), -130.1(18F)

[0172] [Example 7] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2CF2O(CF2CF2CF2O) y The compound represented by CF2CF2CH2OH (where y, representing the average degree of polymerization, is 4.4) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 2.42 g (molecular weight 202.25, 12.0 mmol) of the compound represented by formula (27) below was used instead of the compound represented by formula (13); (iii) In Example 1, instead of the compound represented by formula (15), 1.48 g (molecular weight 370.13, 4.0 mmol) of the compound represented by formula (28) below was used. As a result, 3.21 g of the compound represented by the above formula (G) (wherein formula (G), yg1 and yg2, which indicate the average degree of polymerization, are both 4.4) was obtained.

[0173] [ka] (In formula (27), THP represents a tetrahydropyranyl group.) (In formula (28), THP represents a tetrahydropyranyl group.)

[0174] The compound represented by formula (27) was synthesized by oxidizing a compound in which ethylene glycol monoallyl ether was protected with dihydropyran. The compound represented by formula (28) was synthesized in the same manner as the compound represented by formula (15), except that 1,5-pentanediol was used as the starting material instead of ethylene glycol.

[0175] The obtained compound (G) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(9H), 3.4~4.3(37H) 19 F-NMR (CD3COCD3): δ[ppm]=-84.3(36F), -86.4(4F), -124.2(4F), -130.1(18F)

[0176] [Example 8] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2O(CF2O) w (CF2CF2O) xThe compound represented by CF2CH2OH (where w, representing the average degree of polymerization, is 4.5, and x, representing the average degree of polymerization, is 4.5) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 4.47 g (molecular weight 372.51, 12.0 mmol) of the compound represented by formula (29) below was used instead of the compound represented by formula (13); (iii) In Example 1, instead of the compound represented by formula (15), 1.54 g (molecular weight 384.16, 4.0 mmol) of the compound represented by formula (30) below was used. As a result, 3.46 g of the compound represented by the above formula (H) (wherein formula (H), wh1 and wh2, which represent the average degree of polymerization, are both 4.5, and xh1 and xh2, which also represent the average degree of polymerization, are both 4.5) was obtained.

[0177] [ka] (In formula (29), THP represents a tetrahydropyranyl group.) (In formula (30), THP represents a tetrahydropyranyl group.)

[0178] The compound represented by formula (29) was synthesized by the following method: An epoxy compound was obtained by oxidation of a compound in which the hydroxyl group of 6-hepten-1-ol was protected with a tetrahydropyranyl (THP) group. The obtained epoxy compound was reacted with allyl alcohol, and then the secondary hydroxyl group was protected with a THP group, followed by an oxidation reaction to obtain the compound represented by formula (29). The compound represented by formula (30) was synthesized in the same manner as the compound represented by formula (15), except that 1,6-hexanediol was used as the starting material instead of ethylene glycol.

[0179] The obtained compound (H) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(23H), 3.4~4.3(45H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(4F), -80.3(4F), -91.0~-88.5(36F)

[0180] [Example 9] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2O(CF2O) w (CF2CF2O) x The compound represented by CF2CH2OH (where w, representing the average degree of polymerization, is 4.5, and x, representing the average degree of polymerization, is 4.5) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 2.59 g (molecular weight 216.28, 12.0 mmol) of the compound represented by formula (31) below was used instead of the compound represented by formula (13); (iii) In Example 1, 1.54 g (molecular weight 384.16, 4.0 mmol) of the compound represented by formula (30) was used instead of the compound represented by formula (15). As a result, 3.27 g of the compound represented by formula (I) above (wherein formula (I), wi1 and wi2, which represent the average degree of polymerization, are both 4.5, and xi1 and xi2, which also represent the average degree of polymerization, are both 4.5) was obtained.

[0181] [ka] (In formula (31), THP represents a tetrahydropyranyl group.)

[0182] The compound represented by formula (31) was synthesized by the following method: by reacting 3-buten-1-ol with 2-(2-bromoethoxy)tetrahydro-2H-pyran and oxidizing the double bond of the resulting compound.

[0183] The obtained compound (I) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.8(15H), 3.4~4.2(37H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(4F), -80.3(4F), -91.0~-88.5(36F)

[0184] [Example 10] Except for (i) to (iii) below, the same procedures as in Example 1 were followed. (i) In Example 1, HOCH2CF2O(CF2CF2O) x Instead of the compound represented by CF2CH2OH (where x, representing the average degree of polymerization, is 7.1) (number average molecular weight 1000, molecular weight distribution 1.1), use HOCH2CF2O(CF2O) w (CF2CF2O) x The compound represented by CF2CH2OH (where w, representing the average degree of polymerization, is 4.5, and x, representing the average degree of polymerization, is 4.5) (number-average molecular weight 1000, molecular weight distribution 1.1) was used in 20g. (ii) In Example 1, 2.76 g (molecular weight 230.30, 12.0 mmol) of the compound represented by formula (32) below was used instead of the compound represented by formula (13); (iii) In Example 1, instead of the compound represented by formula (15), 1.64 g (molecular weight 412.22, 4.0 mmol) of the compound represented by formula (33) below was used. As a result, 3.34 g of the compound represented by the above formula (J) was obtained (in formula (J), wj1 and wj2, which represent the average degree of polymerization, are both 4.5, and xj1 and xj2, which represent the average degree of polymerization, are both 4.5).

[0185] [ka] (In formula (32), THP represents a tetrahydropyranyl group.)

[0186] The compound represented by formula (32) was synthesized by the following method: by reacting 3-buten-1-ol with 2-(3-bromopropoxy)tetrahydro-2H-pyran and oxidizing the double bond of the resulting compound.

[0187] [ka] (In formula (33), THP represents a tetrahydropyranyl group.)

[0188] The compound represented by formula (33) was synthesized in the same manner as the compound represented by formula (15), except that 1,8-octanediol was used as the starting material instead of ethylene glycol.

[0189] The obtained compound (J) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(23H), 3.4~4.2(37H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(4F), -80.3(4F), -91.0~-88.5(36F)

[0190] [Comparative Example 1] The compound represented by the following formula (K) was synthesized by the method described in Patent Document 3. The compound represented by the following formula (K) is the product of Example 2 in Patent Document 3.

[0191] [ka] (In formula (K), yk1 and yk2, which represent the average degree of polymerization, are both 4.4.)

[0192] The obtained compound (K) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=3.4~4.2(28H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(8F), -80.3(8F), -91.0~-88.5(36F)

[0193] [Comparative Example 2] The compound represented by the following formula (L) was synthesized by the method described in Patent Document 4. The compound represented by the following formula (L) is compound 9 of Patent Document 4.

[0194] [ka] (In formula (L), yl1 and yl2, which represent the average degree of polymerization, are both 4.4.)

[0195] The obtained compound (L) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=3.4~4.4(41H)2.2 (1H) 19F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(8F), -80.3(8F), -91.0~-88.5(36F)

[0196] [Comparative Example 3] The compound represented by the following formula (M) is HOCH2CF2CF2O(CF2CF2CF2O) ym The compound represented by CF2CF2CH2OH (where ym, representing the average degree of polymerization, is 10.4) (number average molecular weight 2000, molecular weight distribution 1.1) was synthesized by reacting a tetrahydropyranyl (THP) protected form of glycidol with the compound (M) and then deprotecting the THP group. The compound represented by the following formula (M) is compound (1) of Patent Document 1.

[0197] [ka] (In equation (M), ym, which represents the average degree of polymerization, is 10.4.)

[0198] The obtained compound (M) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=3.4~4.2(18H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(21F), -77.7(4F), -80.3(4F), -91.0~-88.5(42F)

[0199] [Comparative Example 4] The compound represented by the following formula (N) was synthesized by the method described in Patent Document 5. The compound represented by the following formula (N) is compound 1 of Patent Document 5.

[0200] [ka] (In equation (N), both yn1 and yn2, which represent the average degree of polymerization, are 4.4.)

[0201] The obtained compound (N) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=3.4~4.4(30H)1.3(8H) 19 F-NMR (CD3COCD3): δ[ppm]=-55.6~-50.6(18F), -77.7(8F), -80.3(8F), -91.0~-88.5(36F)

[0202] [Example 11] The same procedure as in Example 1 was followed, except that 3.17 g (molecular weight 264.32, 12.0 mmol) of the compound represented by formula (34) below was used instead of the compound represented by formula (13). 3.26 g of the compound represented by the above formula (O) (wherein formula (O), xo1 and xo2, which indicate the average degree of polymerization, are both 7.1) was obtained.

[0203] [ka] (In formula (34), Ph represents a phenyl group.)

[0204] The compound represented by formula (34) was synthesized by the following method. A compound was synthesized in which the hydroxyl groups bonded to the 2- and 4-carbon atoms of 1,2,4-butanetriol were protected by reacting 1,2,4-butanetriol with benzaldehyde dimethyl acetal. By reacting this compound with 2-(2-bromoethyl)oxirane, the compound represented by formula (34) was synthesized. The obtained compound (O) 1 H-NMR measurement and 19 The structure was identified by performing 1F-NMR measurements, based on the following results. 1 H-NMR(CD3COCD3);δ[ppm]=1.5~1.9(11H), 3.4~4.3(41H) 19F-NMR(CD3COCD3):δ[ppm]=-77~-80(8F), -88~-91(56F)

[0205] The compounds obtained in Examples 1 to 11 in this way, when applied to formula (1), give R 1 and R 5 The structure of (i and j in equation (3-1), k and l in equation (3-2), m in equation (3-3), n in equation (3-4)), R 2 and R 4 The structure (average degree of polymerization in equations (5) to (9)), R 3 The structure (a in equation (2)) is shown in Table 1.

[0206] [Table 1]

[0207] Furthermore, the number-average molecular weight (Mn) of the compounds in Examples 1-11 and Comparative Examples 1-4 is as described above. 1 H-NMR and 19 The molecular weight was determined by 1F-NMR measurement. The results are shown in Table 2. It is estimated that there is a variation of approximately 1 to 5 in the average molecular weight of the synthesized compound due to differences in the molecular weight distribution of the fluoropolyether used as a raw material for the compound and differences in the procedure during compound synthesis.

[0208] Next, lubricating layer-forming solutions were prepared using the compounds obtained in Examples 1-11 and Comparative Examples 1-4 by the method described below. Then, using the obtained lubricating layer-forming solutions, a lubricating layer was formed on the magnetic recording medium by the method described below, obtaining the magnetic recording media of Examples 1-11 and Comparative Examples 1-4.

[0209] "Lubricant layer forming solution" The compounds obtained in Examples 1-11 and Comparative Examples 1-4 were each dissolved in Bartrell® XF (trade name, manufactured by Mitsui DuPont Fluorochemicals), a fluorine-based solvent, and then diluted with Bartrell XF to a film thickness of 9 Å to 10 Å when applied to a protective layer, to prepare a lubricating layer forming solution.

[0210] "Magnetic recording medium" A magnetic recording medium was prepared by sequentially layering an adhesive layer, a soft magnetic layer, a first underlayer, a second underlayer, a magnetic layer, and a protective layer on a substrate with a diameter of 65 mm. The protective layer was made of carbon. The lubricating layer-forming solutions of Examples 1-11 and Comparative Examples 1-4 were applied to the protective layer of the magnetic recording medium, which had each layer up to the protective layer formed, using the dipping method. The dipping method was performed under the following conditions: dipping speed of 10 mm / sec, dipping time of 30 sec, and withdrawal speed of 1.2 mm / sec. Subsequently, the magnetic recording medium coated with the lubricating layer-forming solution was placed in a constant temperature bath at 120°C and heated for 10 minutes to remove the solvent in the lubricating layer-forming solution, thereby forming a lubricating layer on the protective layer and obtaining a magnetic recording medium.

[0211] (Film thickness measurement) The thickness of the lubricating layer on the magnetic recording media obtained in Examples 1-11 and Comparative Examples 1-4 was measured using FT-IR (product name: Nicolet iS50, manufactured by Thermo Fisher Scientific). The results are shown in Table 2.

[0212] [Table 2]

[0213] Next, the magnetic recording media of Examples 1-11 and Comparative Examples 1-4 were subjected to the following chemical resistance tests.

[0214] (Chemical resistance testing) The contamination of magnetic recording media by environmental substances that generate pollutants under high-temperature conditions was investigated using the method described below. Si ions were used as the environmental substance, and the amount of Si adsorbed was measured as the amount of pollutant generated by the environmental substance that contaminates the magnetic recording media.

[0215] Specifically, the magnetic recording medium to be evaluated was kept in a high-temperature environment of 85°C and 0% humidity for 240 hours in the presence of siloxane-based Si rubber. Next, the amount of Si adsorbed on the surface of the magnetic recording medium was analyzed and measured using secondary ion mass spectrometry (SIMS), and the degree of contamination by Si ions was evaluated as the amount of Si adsorbed. The evaluation of the amount of Si adsorbed was performed using a value with the result of Comparative Example 1 set to 1.00, as follows. The results are shown in Table 2. ◎: Less than 0.70 ○: 0.70 or higher, less than 0.80 △: 0.80 or higher, less than 1.00 ×: 1.00 or higher

[0216] As shown in Table 2, the Si adsorption amount of all magnetic recording media in Examples 1 to 11 was less than 0.80. From this, it was confirmed that the magnetic recording media in Examples 1 to 11 exhibit excellent chemical resistance even with a thin lubrication layer. In particular, in Examples 5, 6, 7, and 8, which used compounds in formula (2) where a is 4 to 6, the Si adsorption amount was less than 0.70, confirming excellent chemical resistance. This is explained below. <1> and <2> It is presumed that this is due to the following reason.

[0217] <1> It is presumed that the good coverage of the lubricating layer is due to the strong interaction between the compounds in the substituent represented by formula (2) where a is an integer between 4 and 6, and the protective layer. <2> In Examples 5, 6, 7, and 8, the number of hydroxyl groups not involved in the bonding between the lubricating layer and the active sites on the protective layer is smaller compared to the other examples. Therefore, it is presumed that the attraction of environmental substances that generate pollutants by hydroxyl groups not involved in the interaction between the lubricating layer and the active sites on the protective layer is suppressed.

[0218] In contrast, Comparative Example 1 used compound (K) in which a glycerin structure was placed in the center of the chain structure, with perfluoropolyether chains and terminal groups having two hydroxyl groups bonded to both sides in that order, and hydroxyl groups positioned at both ends of the chain structure. Comparative Example 1 showed a higher amount of Si adsorption compared to Examples 1 to 11. This is presumed to be due to insufficient coverage of the lubricating layer because the interaction between the hydroxyl groups positioned between the perfluoropolyether chains in compound (K) used in Comparative Example 1 and the protective layer was weak. It is also possible that the hydroxyl groups positioned between the perfluoropolyether chains in compound (K), as hydroxyl groups that do not participate in the interaction between the lubricating layer and the active sites on the protective layer, attracted environmental substances that generate pollutants, thus reducing chemical resistance.

[0219] In Comparative Example 2, a compound (L) was used in which one primary hydroxyl group and two secondary hydroxyl groups were arranged in the center of the chain structure, with perfluoropolyether chains and terminal groups having two hydroxyl groups bonded in this order on both sides, and hydroxyl groups positioned at both ends of the chain structure. In Comparative Example 2, the amount of Si adsorption was greater than in Examples 1 to 11. This is presumed to be because the hydroxyl groups between the perfluoropolyether chains in compound (L) used in Comparative Example 2 are hydroxyl groups that do not participate in the interaction between the lubricating layer and the active sites on the protective layer, thus attracting environmental substances that generate pollutants.

[0220] In Comparative Example 3, compound (M) was used, in which terminal groups having two hydroxyl groups were bonded to both ends of the perfluoropolyether chain, with hydroxyl groups positioned at both ends of the chain structure. In Comparative Example 3, the amount of Si adsorption was higher compared to Examples 1 to 11. This is presumed to be because compound (M) used in Comparative Example 3 has a structure that does not have a hydroxyl group in the center of the chain structure, resulting in insufficient interaction between the lubricating layer and the protective layer, and thus insufficient coverage of the lubricating layer.

[0221] Furthermore, Comparative Example 4 used compound (N) in which two secondary hydroxyl groups were positioned in the center of the chain structure, with perfluoropolyether chains and terminal groups having two hydroxyl groups bonded in that order on both sides, and hydroxyl groups positioned at both ends of the chain structure. Comparative Example 4 showed a higher amount of Si adsorption compared to Examples 1 to 11. This is presumed to be because the two secondary hydroxyl groups between the perfluoropolyether chains in compound (N) used in Comparative Example 4 are hydroxyl groups that do not participate in the interaction between the lubricating layer and the active sites on the protective layer, thus attracting environmental substances that generate pollutants. [Industrial applicability]

[0222] By using the lubricant for magnetic recording media containing the fluorine-containing ether compound of the present invention, a lubricating layer with excellent chemical resistance can be formed even with a thin thickness. [Explanation of Symbols]

[0223] 10...Magnetic recording medium, 11...Substrate, 12...Adhesion layer, 13...Soft magnetic layer, 14...First underlayer, 15...Second underlayer, 16...Magnetic layer, 17...Protective layer, 18...Lubricating layer.

Claims

1. A fluorine-containing ether compound characterized by being represented by the following formula (1). R １ -CH ２ -R ２ -CH ２ -OCH ２ -CHR ３ -CH ２ O-CH ２ -R ４ -CH ２ -R ５ (1) (In formula (1), R ２ and R ４ This is a perfluoropolyether chain. １ and R ５ Each of these is independently a terminal group represented by the following formulas (3-1) to (3-5). ３ This is expressed by the following formula (2). -(CH ２ ) ａ -OH (2) (In equation (2), a represents an integer between 2 and 8.) 【Chemistry 1】 (In equation (3-1), i is an integer between 0 and 1, and j is an integer between 1 and 4.) (In equation (3-2), k is an integer between 1 and 2, and l is an integer between 1 and 3.) (In equation (3-3), m is an integer between 1 and 3.) (In equation (3-4), n is an integer between 1 and 2.)

2. The fluorine-containing ether compound according to claim 1, wherein a in formula (2) is an integer from 3 to 6.

3. R in formula (1) ２ and R ４ The fluorine-containing ether compound according to claim 1, wherein each is independently represented by the following formula (4). -(CF ２ ) ｖ O-(CF ２ O) ｗ -(CF ２ CF ２ O) ｘ -(CF ２ CF ２ CF ２ O) ｙ -(CF ２ CF ２ CF ２ CF ２ O) ｚ -(CF ２ ) ｖ’ - (4) (In equation (4), w, x, y, and z represent the average degree of polymerization and are independent real numbers between 0 and 20. It is impossible for all of w, x, y, and z to be 0 at the same time. v and v' are -CF) ２ This represents the average number of negative values, and each is an independent real number between 1 and 3. There are no particular restrictions on the order of the repeating units in equation (4).

4. R in formula (1) ２ and R ４ However, each is independently represented by one of the following formulas (5) to (9), the fluorine-containing ether compound according to any one of claims 1 to 3. -CF ２ O-(CF ２ O) ｗ５ -(CF ２ CF ２ O) ｘ５ -CF ２ - (5) (In equation (5), w5 and x5 represent the average degree of polymerization, and each independently represents a real number between 1 and 20.) -CF ２ O-(CF ２ CF ２ O) ｘ６ -CF ２ - (6) (In equation (6), x6 represents the average degree of polymerization and is a real number between 1 and 20.) -CF ２ CF ２ O-(CF ２ CF ２ CF ２ O) ｙ７ -CF ２ CF ２ - (7) (In equation (7), y7 represents the average degree of polymerization and is a real number between 1 and 20.) -(CF ２ ) ｖ８ O-(CF ２ CF ２ O) ｘ８ -(CF ２ CF ２ CF ２ O) ｙ８ -(CF ２ ） ｖ８’ － （８） (In equation (8), x8 and y8 represent the average degree of polymerization and each independently represents a real number from 1 to 20. v8 and v8' are -CF) ２ (This represents the average value of the number of negative signs, and each sign independently represents a real number between 1 and 2.) -CF ２ CF ２ CF ２ O-(CF ２ CF ２ CF ２ CF ２ O) ｚ９ -CF ２ CF ２ CF ２ - (9) (In equation (9), z9 represents the average degree of polymerization and is a real number between 1 and 20.)

5. In the above formula (1), R １ and R ５ A fluorine-containing ether compound according to any one of claims 1 to 3, wherein the same

6. In the above formula (1), R ２ and R ４ A fluorine-containing ether compound according to any one of claims 1 to 3, wherein the same

7. A fluorine-containing ether compound according to any one of claims 1 to 3, wherein the number average molecular weight is in the range of 500 to 10,000.

8. A lubricant for magnetic recording media, characterized by containing a fluorine-containing ether compound as described in any one of claims 1 to 3.

9. 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 characterized in that the lubricating layer contains a fluorine-containing ether compound according to any one of claims 1 to 3.

10. The magnetic recording medium according to claim 9, wherein the average thickness of the lubricating layer is 0.5 nm to 2.0 nm.

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