JP2006225572A - Lubricant, magnetic recording medium and manufacturing method of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant, especially a lubricant for a magnetic recording medium, having excellent lubricating characteristic and sustaining lubricating effects even after long hours use by attaching well to an object to be lubricated. <P>SOLUTION: This lubricant is made of at least one compound selected from compounds expressed by general formula (a), wherein R<SP>1</SP>and R<SP>2</SP>each represents hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group; a is an integer of 1-12; v is an integer of 1-12; w is an integer of 1-6; z is an integer of 1-5; and h and k each is an integer of 0-30. A lubricant layer of the magnetic recording medium is formed with this lubricant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel compound useful as a lubricant for use in precision machines or precision parts that require high-precision lubricity, a lubricant containing the compound, a magnetic recording medium using the lubricant, and a magnetic The present invention relates to a method for manufacturing a recording medium.

  In recent years, in the field of magnetic recording, high-performance magnetic recording media suitable for it have been actively developed along with digital recording / reproducing equipment with higher performance such as downsizing and longer usage time. Yes. Recently, a metal thin film type magnetic recording medium, which is extremely advantageous for short wavelength recording, has been put into practical use in place of a coating type magnetic recording medium. In general, a metal thin film type magnetic recording medium refers to a tape, a disk, or the like in which a magnetic layer made of a ferromagnetic metal thin film is provided as a recording layer on a nonmagnetic support. Further, examples of the magnetic recording medium system used for recording / reproducing of the high-density magnetic recording medium include a digital video deck and a hard disk drive.

  In a metal thin film type magnetic recording medium represented by digital video tape, the magnetic layer has a very good surface property, that is, the roughness of the surface of the magnetic layer is small. For this reason, the contact area between the magnetic layer and the magnetic head increases, so that the magnetic layer is easily worn by receiving a large frictional force during high-speed sliding with the magnetic head in the signal recording / reproducing process. The wear of the magnetic layer greatly affects the running durability or the still durability of the magnetic recording medium. Therefore, reducing it is a major issue in the research and development of metal thin film magnetic recording media.

  Therefore, attempts have been made to reduce wear and improve running durability and still durability by providing a protective film and a lubricant layer in this order on the surface of the magnetic layer. When providing a lubricant layer, the protective layer and lubricant layer provided on the surface of the magnetic layer should be thin so as to increase output by minimizing the decrease in output due to spacing loss between the magnetic recording medium and the magnetic head. Is required. In particular, the lubricant layer is required to exhibit lubricating properties with a thickness of only a few nm.

  A general hard disk drive employs a CSS (contact start / stop) system. In the CSS system, when the hard disk, which is a high-density magnetic recording medium, is stopped, the magnetic head comes into contact with the disk, and when the hard disk starts rotating at startup, the magnetic head is It is a system that floats from the surface of the disk and performs recording / reproduction in this state. Then, the rotation of the disk is decelerated when stopped, and the magnetic head comes into contact with the hard disk again.

  In this CSS system, the magnetic head rubs against the surface of the hard disk when the disk is stopped or started, so the frictional force applied at that time is a big problem. In order to maintain the reliability of the hard disk drive, it is desirable that the friction coefficient of the medium after the CSS running test is the same as the initial one. However, it is difficult to satisfy this requirement with a magnetic disk with high surface flatness, that is, with a low roughness. In addition, a so-called head crash, in which the head and the medium collide when the hard disk rotates at a high speed, is one of the problems to be solved. One of the factors that cause the head crash is that the magnetic recording medium does not have an appropriate protective film and lubricant layer.

  Therefore, lubricants suitable for magnetic recording media have been widely studied. One of them is a fluorine compound. Since fluorine-based compounds exhibit excellent lubricating properties, use of various fluorine-based compounds has been proposed (see, for example, Patent Documents 1, 2, and 3).

However, as the recording density of media increases further, it is necessary to consider measures for new technologies such as mounting of MR heads or GMR heads and the use of contact recording methods. For this purpose, it is necessary to further improve the characteristics of the lubricant used in the magnetic recording medium.
JP 2003-113389 A Japanese Patent Laid-Open No. 2004-253110 JP 2002-241349 A

  A characteristic required for the lubricant used in the magnetic recording medium is that the lubricant adheres firmly to the protective film, that is, the adhesive force (or adsorption force) of the lubricant to the protective film is high. Maintaining the state in which the lubricant is firmly adsorbed or adhered to the protective film indicates that the lubrication characteristics are maintained even when used for a long time.

  In Patent Documents 1 and 2, it is proposed to use a compound in which a nitrogen atom is introduced into a fluorine-containing compound. Lubricants containing these compounds have some improved adhesion to the protective film due to their nitrogen atoms. However, as the performance of magnetic recording media is improved, the required level for lubricants has become higher. For this reason, in the field of magnetic recording media, there is a constant demand for lubricants having better characteristics. That is to say, there is a demand for a compound having characteristics more excellent than the compounds proposed in Patent Documents 1 and 2.

  Patent Documents 1 and 2 propose compounds suitable for application to a disk-shaped magnetic recording medium, and do not particularly mention application of these compounds to a tape-shaped magnetic recording medium. Therefore, when the present inventors applied a lubricant containing these compounds to a tape-shaped magnetic recording medium, none of the lubricants simultaneously satisfy the high adhesion to the protective film and the high lubrication characteristics. It was. That is, those having a high adhesion to the protective film have low lubrication characteristics, and those having a high lubrication characteristic have a low adhesion to the protective film.

  The present invention has been made in view of the above circumstances, and is a lubricant having excellent lubrication characteristics, particularly in the case of forming a lubricant layer of a magnetic recording medium, adhesion force (adsorptive power) to a protective film. And a lubricant that provides a magnetic recording medium that maintains a lubricating effect even when used for a long time, a magnetic recording medium using the lubricant, and a method of manufacturing a magnetic recording medium using the lubricant The issue is to provide.

（式中、Ｒ^１、Ｒ^２はそれぞれ水素、脂肪族アルキル基または脂肪族アルケニル基を示し、ａは１〜１２の整数であり、ｖは１〜１２の整数であり、ｗは１〜６の整数であり、ｚは１〜５の整数であり、ｈおよびｋはそれぞれ０〜３０の整数である。） In order to solve the above problems, the present invention provides, in the first aspect, a lubricant containing a compound having a specific structure. Specifically, the lubricant of the present invention contains at least one compound selected from fluoroether compounds represented by the following general formula (a).

Wherein R ¹ and R ² each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, a is an integer of 1 to 12, v is an integer of 1 to 12, and w is 1 to 6 Z is an integer of 1 to 5, and h and k are each an integer of 0 to 30.)

  The fluoroether compound represented by the general formula (a) has a fluoroalkyl ether chain as a main chain, each of which has nitrogen, the nitrogen atom is bonded to one hydroxyalkyl group, and hydrogen, And a structure bonded to either an alkyl group or an aliphatic alkenyl group. This compound can also be called an amino alcohol. Due to this structure, when the compound of the present invention is contained as a lubricant, particularly in the lubricant layer of a magnetic recording medium, the magnetic recording medium exhibits excellent lubricating properties, and the lubricant layer is located below it. In order to adsorb well to the protective film, the lubricant layer exhibits a good lubricating effect over a long period of time. The lubricant of the present invention is particularly suitable for forming a lubricant layer of a metal thin film type magnetic recording medium, and is preferably used for both disk-shaped and tape-shaped magnetic recording media.

  In the compound represented by the general formula (a), the hydroxyalkyl group bonded to both nitrogen atoms is considered to play a role of improving the adhesion of the lubricant to the object (for example, a protective film of a magnetic recording medium). It is done. The compound represented by the general formula (a) is characterized in that one hydroxyalkyl group is bonded to each nitrogen atom and is limited to two in one molecule. Due to this feature, the compound represented by the general formula (a) is excessively adsorbed on a counterpart object (for example, a magnetic head of a magnetic recording / reproducing apparatus) in sliding contact with an object applied as a lubricant. Accordingly, it is possible to prevent the lubrication characteristics of the object from being deteriorated, and it is possible to prevent the lubricant adsorbed on the other object (for example, the magnetic head) from aggregating to generate a powdery material. Further, when an aliphatic alkyl group or an aliphatic alkenyl group is bonded to at least one nitrogen atom, these groups are considered to particularly contribute to the improvement of the lubricating properties. Therefore, in addition to the high adhesion provided by nitrogen atoms and the lubrication properties provided by fluoroalkyl ether chains, this compound exhibits excellent properties for the groups bonded to the nitrogen atoms. It is inferred to give a balanced lubricant. However, the present invention is not limited by this inference.

  In the second aspect, the present invention provides a ferromagnetic metal film formed as a magnetic layer on a nonmagnetic support, a protective film formed on the magnetic layer, and a lubricant formed on the protective film. There is provided a magnetic recording medium having a layer, wherein the lubricant layer contains at least one lubricant of the present invention. The magnetic recording medium in which the lubricant layer is formed with the lubricant of the present invention has an excellent lubricating effect over a long period of time because the adsorbing force of the lubricant to the protective film is large. As will be described later, the adsorption force of the lubricant to the protective film can be confirmed by comparing the amount of lubricant on the protective film before and after the solvent cleaning.

  In the third aspect, the present invention provides a method for producing the magnetic recording medium of the present invention. The method for producing a magnetic recording medium of the present invention is characterized by the formation of the lubricant layer, and the other steps may be steps used in the conventional method for producing a magnetic recording medium. The formation process of the lubricant layer in the production method of the present invention includes a coating solution prepared by dissolving a compound constituting the lubricant layer (ie, lubricant) in a mixed organic solvent of a hydrocarbon solvent and an alcohol solvent. And a step of coating the protective film on the protective film. By using a mixed solvent in which a hydrocarbon solvent and an alcohol solvent are combined, a uniform thin lubricant layer with very little coating unevenness can be formed. Therefore, according to the method for manufacturing a magnetic recording medium of the present invention, it is possible to obtain a magnetic recording medium having excellent lubricating performance and high practical reliability.

  The lubricant of the present invention comprises a fluoroether compound having a specific structure. In this compound, a hydroxyalkyl group is bonded to a nitrogen atom, and preferably an aliphatic alkyl group or an aliphatic alkenyl group is bonded. It adheres well to the surface of the carbon film and exhibits excellent lubricity. In addition, when hydrogen is bonded to a nitrogen atom, although it is slightly inferior in terms of lubrication characteristics, appropriate adhesion to the surface of the target to be lubricated is ensured by the two hydroxyalkyl groups. From the viewpoint of maintaining the lubricity due to the fluoroether chain, it is preferably used. Therefore, since the lubricant of the present invention containing this compound exhibits excellent lubrication characteristics over a long period of time, the lubricant of the present invention is useful as a lubricant for various machines, devices or parts, and particularly a magnetic recording medium. It is useful as a lubricant.

  The lubricant of the present invention is particularly suitable for constituting a lubricant layer of a magnetic recording medium. The magnetic recording medium in which the lubricant layer is formed with the lubricant of the present invention has a large adsorbing power to the protective film of the lubricant, and thus exhibits an excellent lubricating effect over a long period of time, and is difficult to cause self-aggregation. Therefore, there is little powdering. Therefore, the magnetic recording medium of the present invention is particularly suitable for use in a digital video tape recorder or a hard disk drive.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described.
The fluoroalkyl ether compound necessarily contained in the lubricant of the present invention is represented by the general formula (a). This compound contains two nitrogen atoms and two hydroxyalkyl groups in the molecule, preferably at least one, more preferably two aliphatic alkyl or alkenyl groups.

In the general formula (a), R ¹ and R ² each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, a is an integer of 1 to 12, v is an integer of 1 to 12, and w is It is an integer of 1-6, z is an integer of 1-5, h and k are integers of 0-30, respectively.

R ¹ and R ² are generally the same, but may be different from each other. When R ¹ and R ² are different from each other, one may be hydrogen. Alternatively, R ¹ and R ² may both be hydrogen. The compound in which R ¹ = R ² = H is slightly inferior in terms of lubricity compared to the compound in which R ¹ and / or R ² is an aliphatic alkyl group or an aliphatic alkenyl group, but two hydroxyalkyl groups Therefore, it is preferably used as a compound constituting the lubricant of the present invention.

In the general formula (a), the aliphatic alkyl group or the aliphatic alkenyl group (that is, R ¹ and / or R ² has preferably 1 to 30 carbon atoms, more preferably 6 to 20 carbon atoms. When the number of carbon atoms is less than 6 or the number of carbon atoms exceeds 30, the lubricating performance exhibited by the compound may be reduced.The aliphatic alkyl group or the aliphatic alkenyl group may be either linear or branched. It may be.

  In the general formula (a), w is an integer of 1 to 6, z is an integer of 1 to 5, and h and k are integers of 0 to 30, respectively. More preferably, w is an integer of 2-5. z is more preferably an integer of 1 to 4. A preferred combination of (w, z) is (2,1) or (1,2). h is more preferably an integer of 2 to 6, and k is more preferably an integer of 2 to 6. a is an integer of 1 to 12, and v is an integer of 1 to 12.

In the general formula (a), when the moiety _{represented by-} (OC _w F _2w ) _h (OC _z F _2z ) _k- consists of only one kind of oxyfluoroalkylene, k = 0 in the general formula (a) And the compound represented by the general formula (a) contains only (OC _w F _2w ). In this case, w is preferably 2.

  When both h and k are 0, the compound represented by the general formula (a) contains one ether bond, and therefore includes a so-called fluoroether. When h ≠ 0 and k = 0, or when both h and k are integers of 1 or more, the number of ether bonds in the compound represented by the general formula (a) is 2 or more, and the compound is a fluoropolyether. Will contain chains.

In the general formula (a), the moiety represented by — (OC _w F _2w ) _h (OC _z F _2z ) _k — corresponds to a moiety in which two kinds of oxyfluoroalkylene units are copolymerized. h and k represent the number of each oxyfluoroalkylene unit in the copolymer. A copolymer composed of oxyfluoroalkylene units (OC _w F _2w ) and oxyfluoroalkylene units (OC _z F _2z ) is composed of h (OC _w F _2w ) blocks and k (OC _z F _2z ). It may be a block copolymer consisting of these blocks, or another block copolymer, a random copolymer, or an alternating copolymer. Therefore, formula _(a) - include moieties represented by the block copolymer, those which are random copolymers and alternating copolymers _{- (OC w F 2w) h} (OC z F 2z) k.

  The molecular weight of the compound represented by the general formula (a) is preferably 500 to 3000 when the lubricant containing the compound is used in a tape-like magnetic recording medium. In the case of being used in the above, it is preferably 2000 to 20000. When the molecular weight of the compound constituting the lubricant used in the disk-shaped magnetic recording medium is small, the problem of lubricant spin-off occurs. Spin-off refers to a phenomenon in which the lubricant on the disk is scattered due to high-speed rotation of the disk. This phenomenon is likely to occur when a compound having a lower molecular weight is used. For this reason, the preferable lower limit of the molecular weight of the compound represented by the general formula (a) when constituting the lubricant for the disk-shaped magnetic recording medium is higher than the lower limit of those used in the tape-shaped magnetic recording medium. On the other hand, in the tape-like magnetic recording medium, the molecular weight itself of the compound constituting the lubricant does not cause a specific phenomenon, and an arbitrary molecular weight can be selected. However, in the case where the lubricant layer of the magnetic recording medium is formed using a coating solution in which the lubricant is dissolved in a hydrocarbon solvent, the lubricant is configured to improve the solubility of the lubricant. The compound is preferably of low molecular weight. Considering this point, the preferred molecular weight range of the compound represented by the general formula (a) when used as a lubricant for a tape-like magnetic recording medium is specified as described above.

The compound represented by the general formula (a) can be obtained by the synthesis method shown below. First, a carboxylic acid-modified fluoroalkyl ether compound is reacted with thionyl chloride to obtain a dicarboxylic acid chloride. Next, the dicarboxylic acid chloride is reacted with an alkanolamine having an aliphatic hydrocarbon chain to obtain an amide-modified fluoroalkyl ether compound. Next, the fluoroalkyl polyether compound of the present invention is obtained by reducing the amide-modified product with a catalyst such as LiAlH ₄ (lithium aluminum hydride). As the catalyst, for example, NaBH ₄ or Bu ₃ SnH can be used in addition to LiAlH ₄ .

  The lubricant of the present invention may contain only one type or two or more types of compounds represented by the general formula (a).

  The lubricant of the present invention may contain another compound exhibiting a lubricating effect in addition to the compound represented by the general formula (a). By combining the compound represented by the general formula (a) with a compound for other lubricant, a lubricant having more excellent lubrication characteristics can be provided.

  In the lubricant of the present invention, one of the compounds suitable for combining with the compound represented by the general formula (a) is a fluorine-containing carboxylic acid compound having a carboxyl group. While the nitrogen atom of the compound represented by the general formula (a) is easily adsorbed at the acidic point, the carboxyl group of the fluorinated carboxylic acid compound is easily adsorbed at the basic point. Therefore, by combining the compound represented by the general formula (a) and the fluorine-containing carboxylic acid compound, the lubricant exhibiting high adhesive force regardless of whether the object to which the lubricant is to be applied is acidic or basic. Can be provided. In addition, the fluorine-containing carboxylic acid compound is preferably used because it is a stable lubricant exhibiting excellent lubricating properties. When a lubricant layer of a magnetic recording medium is formed with a lubricant containing a combination of these two compounds, the lubricant layer is satisfactorily adsorbed to the magnetic layer even when the protective film is partially discontinuous. Therefore, the coverage with the lubricant can be further improved, and a more uniform layer is provided. Furthermore, the magnetic recording medium in which the lubricant layer is formed with a lubricant containing a combination of these two compounds has a lubricant even when a part of the magnetic layer is exposed due to breakage of the protective film during running of the tape. Since the surface state is restored by covering the magnetic layer, excellent durability is exhibited.

  Specifically, the fluorine-containing carboxylic acid compound is preferably at least one compound selected from the compounds represented by the following general formulas (b) and (c).

（式中、Ｒ^３、Ｒ^４、Ｒ^５、Ｒ^６はそれぞれ水素、脂肪族アルキル基または脂肪族アルケニル基を示し、Ｒ^３およびＲ^４の少なくとも一方が水素であり、Ｒ^５およびＲ^６の少なくとも一方が水素であり、ｍは１〜６の整数であり、ｎは１〜５の整数であり、ｐ、ｑはそれぞれ０〜３０の整数であり、ｒは１〜１２の整数である。）

^(Wherein, R ^3, R ^4, R 5, ^{R 6} each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, at least one of ^{R 3} and ^{R 4} are hydrogen, ^{R 5} and ^{R 6} At least one is hydrogen, m is an integer of 1 to 6, n is an integer of 1 to 5, p and q are each an integer of 0 to 30, and r is an integer of 1 to 12. )

（式中、Ｒ^７は脂肪族アルキル基または脂肪族アルケニル基を示し、Ｒ^８はフルオロアルキル基、またはフルオロエーテル基もしくはフルオロポリエーテル基を示し、ｂは０または１であり、ｃは０から２０の整数である）

(Wherein R ⁷ represents an aliphatic alkyl group or an aliphatic alkenyl group, R ⁸ represents a fluoroalkyl group, a fluoroether group or a fluoropolyether group, b is 0 or 1, and c is from 0 to (It is an integer of 20)

In the general formula (b), R ³ , R ⁴ , R ⁵ and R ⁶ each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, and at least one of R ³ and R ⁴ is hydrogen, and R ⁵ And at least one of R ⁶ is hydrogen. Therefore, in the compound represented by the general formula (a), i) R ³ is hydrogen, R ⁴ is an aliphatic alkyl group or an aliphatic alkenyl group, and R ⁵ is an aliphatic alkyl group or an aliphatic alkenyl group. A compound in which R ⁶ is hydrogen, ii) R ³ is an aliphatic alkyl group or an aliphatic alkenyl group, R ⁴ is hydrogen, R ⁵ is hydrogen and R ⁶ is an aliphatic alkyl group or A compound that is an aliphatic alkenyl group, iii) R ³ is an aliphatic alkyl group or an aliphatic alkenyl group, R ⁴ is hydrogen, R ⁵ is an aliphatic alkyl group or an aliphatic alkenyl group, and R ⁶ is hydrogen, compound, and iv) R ³ is a hydrogen R ⁴ is an aliphatic alkyl group or an aliphatic alkenyl group, R ⁶ R ⁵ is a hydrogen in an aliphatic alkyl group or an aliphatic alkenyl group That compound, and ^v) R 3 ^{~R 6} may include compounds which are all hydrogen.

In the general formula (b), the number of carbon atoms of the aliphatic alkyl group or aliphatic alkenyl group (that is, one or more groups out of R ³ , R ⁴ , R ⁵ and R ⁶ are aliphatic alkyl groups or aliphatic alkenyls). The number of carbon atoms of the group or groups in the case of a group is preferably 1 to 22, more preferably 8 to 18. The aliphatic alkyl group or the aliphatic alkenyl group may be either a straight chain or a branched chain. When a plurality of groups of R ³ , R ⁴ , R ⁵ and R ⁶ are aliphatic alkyl groups or aliphatic alkenyl groups, the plurality of groups may be the same group or different from each other. Also good.

  In general formula (b), m is an integer from 1 to 6, n is an integer from 1 to 5, and p and q are integers from 0 to 30, respectively. m is more preferably an integer of 2 to 5. n is more preferably an integer of 1 to 4. A preferred combination of (m, n) is (2, 1) or (1, 2). p is more preferably an integer of 2 to 6, and q is more preferably an integer of 2 to 6. r is an integer of 1-12.

In the general formula (b), when the moiety represented by — (OC _m F _2m ) _p (OC _n F _2n ) _q — consists of only one kind of oxyfluoroalkylene, q = 0 in the general formula (a) The compound represented by the general formula (a) includes only (OC _m F _2m ). In this case, m is preferably 2.

  When both p and q are 0, the compound represented by the general formula (b) contains one ether bond, and thus includes a so-called fluoroether. When p ≠ 0 and q = 0, or when p and q are both integers of 1 or more, the number of ether bonds in the compound represented by the general formula (a) is 2 or more, and the compound is a fluoropolyether. Will contain chains.

In formula _{(a) - (OC m F} 2m) p (OC n F 2n) q - moiety represented by the two oxyfluoroalkylene units corresponds to the portion that is copolymerized. p and q represent the number of each oxyfluoroalkylene unit in the copolymer. A copolymer composed of oxyfluoroalkylene units (OC _m F _2m ) and oxyfluoroalkylene units (OC _n F _2n ) is composed of p (OC _m F _2m ) blocks and q (OC _n F _2n ). It may be a block copolymer consisting of these blocks, or another block copolymer, a random copolymer, or an alternating copolymer. Therefore, formula _(a) - include moieties represented by the block copolymer, those which are random copolymers and alternating copolymers _{- (OC m F 2m) p} (OC n F 2n) q.

  The compound represented by the general formula (b) is produced by mixing and stirring an alkyl succinic anhydride, an alkenyl succinic anhydride, or a succinic anhydride and a fluoroalkyl dialcohol having a fluoroalkylene oxide group. Since the method of synthesizing the compound represented by the general formula (a) is known as described in Patent Document 3, for example, detailed description thereof is omitted here.

When the compound represented by the general formula (a) and the compound represented by the general formula (b) are used in combination,-(OC _w F _2w ) _h (OC _z F) of the compound represented by the general formula (a) _{2z) k} - and the portion represented by the general formula (b) at the indicated by the compound _{- (OC m F 2m) p} (OC n F 2n) q - and the portion represented by is preferably the same. That is, it is preferable that m = w, n = z, p = h, and q = k. In that case, since the basic skeletons of the two components are common, the compatibility of the two components becomes better.

  The compound represented by the general formula (c) contains, in one molecule, 1) one fluorine-containing end group, that is, a fluoroalkyl end group, a fluoroether end group or a fluoropolyether end group; 2) one aliphatic group Hydrocarbon end groups, that is, alkyl end groups or alkenyl end groups; 3) one carboxyl group; and 4) a fluorine-containing carboxylic acid having a structure having one ester bond.

In the general formula (c), R ⁷ is an aliphatic alkyl group or an aliphatic alkenyl group. R ⁷ preferably has 6 to 30 carbon atoms, and more preferably 10 to 24 carbon atoms. When the number of carbon atoms is less than 6, or when the number of carbon atoms is 30, the lubricating performance exhibited by the compound may be deteriorated.

In the general formula (c), R ⁸ is a fluoroalkyl group, a fluoroether group or a fluoropolyether group. When R ⁸ is a fluoroalkyl group, the number of carbon atoms is preferably 1 to 12, and more preferably 6 to 10. The fluoroalkyl group is preferably a perfluoroalkyl group.

When R ⁸ is a fluoroether group or a fluoropolyether group, the molecular weight is preferably about 200 to about 6000, and more preferably about 300 to about 4000. When the molecular weight is less than 200 or exceeds 6000, the lubricity and reliability of the magnetic recording medium may be lowered when the lubricant layer of the magnetic recording medium is formed with a lubricant containing this compound. . The fluoroether group or fluoropolyether group is preferably a perfluoroether group or a perfluoropolyether group.

  In the general formula (c), b is 0 or 1. c is an integer of 0 to 20, preferably an integer of 0 to 12.

  The compound represented by the general formula (a) and the fluorinated carboxylic acid compound are preferably mixed in a ratio of 1: 9 to 9: 1 (weight ratio), more preferably 3: 7 to 7: 3. It is mixed at a ratio of (weight ratio). When the proportion of either one of the compounds is less than 10% by weight of the total amount of both compounds, the effect of the compound cannot be sufficiently obtained.

  In the lubricant of the present invention, another compound suitable for combining with the compound represented by the general formula (a) is a fluorine-containing monoester compound containing one ester bond. When mixed with the compound represented by the general formula (a), the fluorine-containing monoester compound further improves the application state of the lubricant, that is, the wettability. Therefore, when a lubricant containing this is used as a lubricant for a magnetic recording medium, it contributes to a reduction in the initial friction coefficient of the magnetic recording medium.

（式中、Ｒ^９はフルオロアルキル基、フルオロアルケニル基、フルオロエーテル基もしくはフルオロポリエーテル基を示し、Ｒ^１０は脂肪族アルキル基または脂肪族アルケニル基を示し、ｓは１〜１２の整数である。） Specifically, the fluorine-containing monoester compound is preferably at least one compound selected from the compounds represented by the following general formula (d).

(In the formula, R ⁹ represents a fluoroalkyl group, a fluoroalkenyl group, a fluoroether group or a fluoropolyether group, R ¹⁰ represents an aliphatic alkyl group or an aliphatic alkenyl group, and s is an integer of 1 to 12. .)

In the general formula (d), R ⁹ is a fluoroalkyl group, a fluoroether group, or a fluoropolyether group.

When R ⁹ is a fluoroalkyl group or a fluoroalkenyl group, the number of carbon atoms is preferably 1 to 12, and more preferably 6 to 10. The fluoroalkyl group or fluoroalkenyl group may be either a straight chain or a branched chain. The fluoroalkyl group or fluoroalkenyl group is preferably a perfluoroalkyl group or a perfluoroalkenyl group.

When R ⁹ is a fluoroalkyl group or a fluoroalkenyl group, R ⁹ may have a fluorinated cyclic hydrocarbon group. The fluorinated cyclic hydrocarbon group is a substituent selected from an aromatic hydrocarbon group, an alicyclic hydrocarbon group, and a condensed polycyclic hydrocarbon group in which part or all of hydrogen is substituted with fluorine. And preferably an alicyclic hydrocarbon group (that is, a cycloalkyl group). In the fluorinated cyclic hydrocarbon group, it is preferable that all hydrogens are substituted with fluorine. The cyclic hydrocarbon group substitutes hydrogen or fluorine of the fluoroalkyl group or fluoroalkenyl group. The cyclic hydrocarbon group may be bonded to any carbon of the fluoroalkyl group or the fluoroalkenyl group, for example, may be bonded as a side chain group. The cyclic hydrocarbon group is preferably bonded to the terminal carbon of the fluoroalkyl group or fluoroalkenyl group. The carbon number of the fluorinated cyclic hydrocarbon group is preferably 4-8.

When R ⁹ is a fluoroether group or a fluoropolyether group, the molecular weight is preferably about 200 to about 6000, more preferably about 300 to about 4000. When the molecular weight is less than 200 or exceeds 6000, the lubricity and reliability of the magnetic recording medium may be lowered when the lubricant layer of the magnetic recording medium is formed with a lubricant containing this compound. The fluoroether group or fluoropolyether group is preferably a perfluoroether group or a perfluoropolyether group.

In the general formula (d), R ¹⁰ is an aliphatic alkyl group or an aliphatic alkenyl group. R ¹⁰ preferably has 6 to 30 carbon atoms, and more preferably 10 to 24 carbon atoms. When the number of carbon atoms is less than 6 or more than 30, the lubrication performance may be deteriorated. R ¹⁰ may be linear or branched.

  The compound represented by the general formula (d) can be synthesized by reacting a fluorinated alcohol and a fatty acid. This reaction can be conveniently carried out by mixing and stirring the fluorinated alcohol and the fatty acid while heating in a solvent in the presence of a catalyst. It is preferable to use heptane, octane or toluene as the solvent. Further, when the heating temperature is low, a large amount of unreacted material tends to remain, and when the heating temperature is high, a by-product tends to be generated. Therefore, the heating temperature is preferably 80 to 150 ° C, more preferably 120 to 130 ° C. As the catalyst, an acid catalyst or a base catalyst can be used. A preferable example of the acid catalyst is p-toluenesulfonic acid. A preferable base catalyst is, for example, pyridine. It is also possible to use fatty acid chloride in place of the fatty acid. In this case, there is no need for a catalyst.

  The compound represented by the general formula (a) and the fluorine-containing monoester compound are preferably mixed in a ratio of 1: 9 to 9: 1 (weight ratio), more preferably 3: 7 to 7: 3. It is mixed at a ratio of (weight ratio). When the proportion of either one of the compounds is less than 10% by weight of the total amount of both compounds, the effect of the compound cannot be sufficiently obtained.

  In addition to the specific compound described above, the lubricant of the present invention may optionally contain other lubricants, rust preventives, extreme pressure agents, and the like. In that case, the proportion of the compound represented by the general formula (a) is preferably 5% by weight or more based on the total amount of the lubricant. The compound represented by the general formula (a) imparts good adsorbability to the lubricant even when the proportion of the lubricant in the lubricant is as small as 5% by weight. Therefore, even when the lubricant layer of the magnetic recording medium is formed with a lubricant in which the proportion of the compound represented by the general formula (a) is about 5% by weight, the lubricant layer is well adsorbed on the protective film and lubrication is performed. The effect can last for a long time. The proportion of the compound represented by the general formula (a) is more preferably 30% by weight or more, and still more preferably 50% by weight or more. When the lubricant contains the fluorine-containing carboxylic acid compound, the fluorine-containing compound is used so that the ratio of the compound represented by the general formula (a) is 5% by weight or more and the mixing ratio of both is within the above range. The mixing amount of the carboxylic acid compound is determined. The same applies to the case where the lubricant contains the fluorine-containing monoester compound.

  The lubricant of the present invention described above is suitable for forming a lubricant layer of a magnetic recording medium. Therefore, the magnetic recording of the present invention will be described below together with its manufacturing method. In the present specification including the following description, the “surface” of each layer or film constituting the magnetic recording medium is a surface exposed when each layer or film is formed, that is, a nonmagnetic support of each layer or film. It means the surface far from the body. The term “on the surface” of each layer refers to a position in contact with the surface unless otherwise specified. Furthermore, in this specification including the following description, regarding the configuration of the magnetic recording medium, the term “on” each layer or film constituting the magnetic recording medium refers to the nonmagnetic support of each layer or film unless otherwise specified. It means that it touches the surface on the side far from the body. Therefore, for example, “on the magnetic layer” means “at a position adjacent to the surface of the magnetic layer far from the nonmagnetic support”.

The magnetic recording medium of the present invention comprises a ferromagnetic metal film formed as a magnetic layer on a nonmagnetic support, a protective film formed on the magnetic layer, and a lubricant layer formed on the protective film. And a lubricant layer containing the compound of the present invention as a lubricant. That is, the lubricant layer contains a lubricant comprising at least one fluoroether compound represented by the general formula (a). The amount of the compound represented by the general formula (a) contained in the lubricant layer is preferably 0.05 to 100 mg, more preferably 0.1 to 50 mg per 1 m ² of the surface of the lubricant layer. . In order to make such a small amount of compound uniformly exist in the lubricant layer, it is desirable to form the lubricant layer of the magnetic recording medium of the present invention by the following method.

  The lubricant layer is formed on the protective film after forming a ferromagnetic metal film and a protective film in this order on the nonmagnetic support using conventional materials and means. The step of forming the lubricant layer includes a step of applying a coating solution prepared by dissolving the lubricant of the present invention in a mixed solvent of a hydrocarbon solvent and an alcohol solvent on the protective film, and drying the applied coating solution. And evaporating the mixed solvent. Finally, when the mixed solvent evaporates, the lubricant dissolved in the solvent remains on the protective film to form a lubricant layer. Therefore, even if the coating solution is applied thickly, the solvent evaporates to form a uniform and very thin lubricant layer on the protective film, that is, a lubricant layer with a small amount of lubricant uniformly covering the protective film. Is done.

  Examples of the hydrocarbon solvent that can be used in the present invention include toluene, hexane, heptane, octane, nonane, xylene, and ketone. Examples of alcohol solvents that can be used in the present invention are lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. Specifically, the mixed organic solvent is preferably a mixed solvent of toluene and isopropyl alcohol, a mixed solvent of hexane and isopropyl alcohol, or a mixed solvent of heptane and isopropyl alcohol. If the proportion of the alcohol solvent is too large, coating unevenness is likely to occur. On the other hand, if the proportion of the hydrocarbon solvent is too large, it is disadvantageous in terms of cost. It is preferable to use the mixture so as to be in the range of 1, preferably in the range of 3: 7 to 7: 3.

  The concentration of the coating solution and the coating thickness are applied so that the lubricant layer formed on the protective film after the solvent evaporates has a desired thickness. Generally, it is preferable to apply a coating solution having a lubricant concentration of 100 to 10000 ppm so as to have a thickness of 10 to 100 μm.

  As a method of forming a lubricant layer using the above mixed solvent, wet coating methods such as bar coating method, gravure coating method, reverse roll coating method, die coating method, dip coating method, and spin coating method, or organic vapor deposition methods may be used. Yes, either method may be adopted.

  After applying the coating solution, the lubricant layer is formed on the protective film by drying and evaporating the organic solvent. The drying process can be performed by heating or natural drying. The thickness of the finally obtained lubricant layer is preferably about 3 to 5 nm. However, since there is an optimum range of the thickness of the lubricant layer depending on the composition of the lubricant, the thickness of the lubricant layer is not necessarily limited to this range.

  In this way, by using a predetermined mixed organic solvent, a uniform thickness lubricant layer without application unevenness is obtained, and after the solvent has finally evaporated, a very thin lubricant layer of several nm is formed. Can be formed. As a result, a magnetic recording medium having excellent lubrication performance and high practical reliability can be obtained.

  As described above, the magnetic recording medium of the present invention can be formed using conventional materials and means for the layers other than the lubricant layer.

  For example, the nonmagnetic support is a film made of polyethylene terephthalate, polyethylene naphthalate, aromatic polyamide, or aromatic polyimide; a film made of vinyl resin such as polyvinyl chloride or polyvinylidene chloride; polycarbonate, glass, ceramic, carbon A substrate made of a metal such as aluminum or copper, a light metal such as an aluminum alloy or a titanium alloy, or single crystal silicon; or paper. When using a rigid substrate such as an aluminum alloy substrate or glass substrate as the non-magnetic support, an oxide film or Ni-P film is formed on the substrate surface by anodizing to harden the surface. May be.

The surface of the non-magnetic support on which the ferromagnetic metal film is formed (that is, the surface that is in direct contact with the magnetic layer or in some cases through the underlayer, etc.) has practical reliability and good RF output value. In order to achieve both, it is desirable that a protrusion forming process having a diameter of 20 to 700 nm and a height of 5 to 70 nm is performed. Specifically, for example, the protrusions are formed by dispersing and fixing ultrafine particles made of an inorganic material such as SiO ₂ or ZnO or ultrafine particles made of an organic material such as imide on the surface of the nonmagnetic support. . Alternatively, the protrusions are formed by forming a polymer material containing such fine particles into a film.

  In the magnetic recording medium of the present invention, the magnetic layer is a ferromagnetic metal film. Ferromagnetic metals suitable for the magnetic layer include Fe-based metals, Co-based metals, and Ni-based metals. In the present invention, it is particularly preferable to form the magnetic layer with a Co-based metal. Here, “Co-based metal” refers to cobalt and an alloy containing cobalt as a main component and preferably 50 atomic% or more. The same applies to “Fe-based metal” and “Ni-based metal”.

  Specifically, the ferromagnetic metal film includes Fe, Co and Ni, and Co—Ni, Co—Fe, Co—Cr, Co—Cu, Co—Pt, Co—Pd, Co—Sn, Co—Au, Selected from alloys such as Fe-Cr, Fe-Co-Ni, Fe-Cu, Ni-Cr, Fe-Co-Cr, Co-Ni-Cr, Co-Pt-Cr and Fe-Co-Ni-Cr It is made of one or more materials. The ferromagnetic metal film may contain oxygen, which may be contained in the form of oxides of these metals or alloys. The ferromagnetic metal film may be in the form of a single layer film or in the form of a multilayer film.

  The ferromagnetic metal film can be formed by an ion plating method, a sputtering method, an electron beam evaporation method, or the like. If the ferromagnetic metal film is formed in an oxygen atmosphere, oxygen is contained in the ferromagnetic metal film. The thickness of the ferromagnetic metal film is generally 10 nm to 300 nm.

The protective film is preferably a carbon film. The carbon film has a high Vickers hardness of about 2.45 × 10 ⁴ N / mm ² (about 2500 kg / mm ² ) and prevents damage to the magnetic recording medium together with the lubricant layer. Considering the balance between practical reliability and output, the thickness is preferably 1 to 20 nm.

  The carbon film is preferably graphitic carbon or diamond-like carbon. Diamond-like carbon is the most preferable material because it has an appropriate hardness and can suppress damage to the magnetic recording medium without damaging the magnetic head. A carbon film made of graphite-like carbon or diamond-like carbon is formed by a plasma CVD method using only a hydrocarbon gas or a mixed gas of a hydrocarbon gas and an inert gas, or by a sputtering method using a carbon target. It is formed.

  Specifically, the carbon film is a vacuum in a state where a hydrocarbon gas or a mixed gas of hydrocarbon gas and an inert gas such as argon is introduced into a vacuum vessel and the pressure in the vessel is maintained at 0.13 to 130 Pa. It is formed on the ferromagnetic metal film by generating a discharge inside the container and generating a plasma of hydrocarbon gas. The discharge type may be either an external electrode type or an internal electrode type, and the discharge frequency can be determined experimentally. In addition, by applying a voltage of 0 kV to -3 kV to the electrode disposed on the nonmagnetic support side, the hardness of the carbon film can be increased, and the adhesion between the carbon film and the ferromagnetic metal film is improved. Can be made. As the hydrocarbon gas, methane, ethane, propane, butane, pentane, hexane, heptane, octane, benzene, or the like can be used.

  In order to form a hard carbon film, it is desirable to increase the discharge energy, and it is also desirable to maintain the temperature of the nonmagnetic support at a high temperature. For example, it is desirable that the discharge energy has an effective value of 600 V or more by superimposing an alternating current, for example, a high frequency current and a direct current.

  In the present invention, it is preferable that a nitrogen-containing plasma polymerized film is formed on the surface portion of the carbon film, and the lubricant layer is formed on the nitrogen-containing plasma polymerized film of the carbon film. Nitrogen-containing plasma polymerization results in the presence of amino groups in the surface layer of the carbon film, resulting in greater adhesion strength between the lubricant layer and the carbon film, and further improving the durability of the magnetic recording medium. It becomes. Combined with the inclusion of a specific fluoroalkyl ether compound in the lubricant layer, the running durability, the still durability and the corrosion resistance are improved with excellent lubrication performance without impairing the electromagnetic conversion characteristics. A highly reliable magnetic recording medium can be obtained.

  The nitrogen-containing plasma polymerized film is obtained by gasifying and introducing an amine compound such as propylamine, butylamine, ethylenediamine, propylenediamine or tetramethylenediamine into a vacuum vessel, and maintaining the pressure in the vessel at 0.13 to 130 Pa. The high frequency discharge is generated inside the vacuum vessel. By forming the nitrogen-containing plasma polymerized film, the chemical adsorption force of the lubricant of the present invention is improved, and as a result, the adhesion strength between the lubricant layer and the carbon film is improved. The film thickness of the nitrogen-containing plasma polymerized film is suitably less than 3 nm. If the nitrogen-containing plasma polymerized film is thicker than this, the protective effect of the carbon film is lowered. Incidentally, methods for forming a nitrogen-containing plasma polymerized film on the surface layer of the carbon film are disclosed in US Pat. Nos. 5,540,957 and 5,637,393, and the contents disclosed in these patents by this reference are described in this specification. Part of it.

  The magnetic recording medium of the present invention may have a backcoat layer on the surface opposite to the surface on which the magnetic layer of the nonmagnetic support is formed. The backcoat layer may be a layer formed of one or more materials selected from polyurethane, nitrocellulose, polyester, carbon, calcium carbonate, etc., or a thin film made of metal, metal oxide, or alloy. It's okay. The thickness of the backcoat layer is preferably about 50 to 500 nm.

  The magnetic recording medium of the present invention is not limited to the above configuration. For example, the magnetic recording medium of the present invention has a reinforcing layer formed by vapor deposition of metal on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed, and the backcoat layer is formed on the reinforcing layer. It may be of a formed configuration. Alternatively, the magnetic recording medium of the present invention has a configuration in which a nonmagnetic support has a reinforcing layer on the surface subjected to the protrusion treatment and the magnetic layer is formed on the reinforcing layer, or on the reinforcing layer. The underlayer and the magnetic layer may be stacked in this order.

  FIG. 1 is a sectional view schematically showing an example of the magnetic recording medium of the present invention. In FIG. 1, a magnetic layer (2) is formed on one surface of a nonmagnetic support (1), a protective film (3) is formed on the magnetic layer, and a lubricant is formed on the protective film (3). A magnetic recording medium (100) is shown in which a layer (4) is formed and a backcoat layer (5) is formed on the other surface of the nonmagnetic support (1).

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by this Example.
Example 1
As a nonmagnetic support, a polyester film having granular protrusions on the surface was prepared. Specifically, (1) having a plurality of gently-gradient protrusions (average height 7 nm, diameter 1 μm) per 100 μm ² formed by forming a polymer material containing silica fine particles into a film, and ( 2) colloidal silica particles having a diameter of 15nm was used a polyester film having ² per 1 × 10 ⁷ cells 1mm steep projections formed is fixed to the polyester film surface with ultraviolet curable epoxy resin. The polyester film used in this example had a very small number of relatively large protrusions formed on the film surface by fine particles derived from the residue of the polymerization catalyst.

  A ferromagnetic metal film (thickness: 100 nm) made of Co was formed on the surface of the polyester film on which the granular protrusions were formed by continuous vacuum oblique deposition in the presence of a small amount of oxygen. The oxygen content in the ferromagnetic metal film was 5% in atomic fraction.

  Next, a protective film having a thickness of 5 nm made of diamond-like carbon was formed on the ferromagnetic metal film by plasma CVD. The protective film introduces a gas in which hexane gas and argon gas are mixed at a ratio of 4: 1 (pressure ratio) into a vacuum vessel, and keeps the total gas pressure at 39 Pa, while the frequency is 20 kHz, the voltage is 1500 V AC and 1000 V. The direct current was superimposed and applied to the electrode in the discharge tube. Further, propylamine gas is introduced onto the carbon film, and a high frequency plasma treatment of 10 kHz is performed while maintaining a pressure of 6.5 Pa to form a nitrogen-containing plasma polymerization film having a thickness of 2.5 nm on the surface layer of the carbon film. did.

Subsequently, the fluoroether compound represented by the chemical formula (a1) was dissolved in a mixed organic solvent (weight ratio 1: 1) of isopropyl alcohol and toluene to prepare a coating solution. The prepared coating solution was applied onto the protective film by a wet coating method using a reverse roll coater, and then dried to evaporate the solvent. Finally, a lubricant layer containing 8 mg of lubricant per 1 m ² of the surface was formed on the protective film. This was cut into a predetermined width to produce a magnetic tape.

In the compound represented by the chemical formula (a1), in general formula (a), R ¹ and R ² are octadecyl groups, and a = 2, v = 1, w = 2, z = 1, h = 6, k Corresponds to a compound with = 5.

(Examples 2 to 7)
Instead of the compound represented by the chemical formula (a1), the compounds represented by the following chemical formulas (a2) to (a7) were used, respectively, and six types of magnetic tapes (Examples 2 to 7) were prepared in the same manner as in Example 1. ) Was produced.

(Example 8)
Instead of the compound represented by the chemical formula (a1), a magnetic tape was produced in the same manner as in Example 1 using a compound represented by the following chemical formula (a8).

Example 9
A lubricant was prepared by mixing the compound represented by the chemical formula (a1) and the compound represented by the following chemical formula (b1) at a weight ratio of 1: 1. Using this lubricant, a magnetic tape was produced in the same manner as in Example 1.

(Example 10)
A lubricant was prepared by mixing the compound represented by the above chemical formula (a1) and the compound represented by the following chemical formula (c1) in a weight ratio of 1: 1. Using this lubricant, a magnetic tape was produced in the same manner as in Example 1.

(Example 11)
A lubricant was prepared by mixing the compound represented by the chemical formula (a1) and the compound represented by the following chemical formula (d1) at a weight ratio of 1: 1. Using this lubricant, a magnetic tape was produced in the same manner as in Example 1.

(Comparative Example 1)
Instead of the compound represented by the chemical formula (a1), a magnetic tape was produced in the same manner as in Example 1 using a compound represented by the following chemical formula (e1) as a lubricant.

(Comparative Example 2)
Instead of the compound represented by the chemical formula (a1), a magnetic tape was produced in the same manner as in Example 1 using a compound represented by the following chemical formula (e2) as a lubricant.

(Comparative Example 3)
Instead of the compound represented by the chemical formula (a1), a known tape represented by the following chemical formula (e3) was used as a lubricant, and a magnetic tape was produced in the same manner as in Example 1.

(Comparative Example 4)
A coating liquid was prepared by dissolving the compound represented by the chemical formula (a1) only in isopropyl alcohol, and a magnetic tape was produced in the same manner as in Example 1.

  The magnetic tape samples obtained in Examples 1 to 10 and Comparative Examples 1 to 4 were evaluated as follows.

(I) Running test Each sample was wound around a guide pin made of stainless steel (SUS420J2, surface roughness 0.2S), outer diameter 6 mm) at a winding angle of 90 ° in an environment of 23 ° C. and 50% RH. The sample was unwound at a speed of 18 mm / sec under 2N conditions, wound at the same speed, and the tension was measured on the winding side. The dynamic friction coefficient was calculated from the ratio of the tension on the winding side and the tension on the winding side using the Euler equation. The coefficient of friction was calculated by calculating the coefficient of friction in the first pass, the 100th pass, and the 1000th pass, with unwinding and winding taken as one pass.

(II) Still Life Test Still life was measured in a 3 ° C., 5% RH environment using a commercially available digital VTR (made by Matsushita Electric Industrial Co., Ltd., trade name NV-DJ1) modified for still life measurement. . The still life is indicated by the time (minutes) from the beginning until the output drops by 6 dB.

(III) Durability test Durability was evaluated by clogging the head. Using a commercially available digital VTR (NV-DJ1 manufactured by Matsushita Electric Industrial Co., Ltd.) modified for RF (high frequency) output measurement, each sample was repeatedly reproduced for 1330 hours in an environment of 23 ° C. and 60% RH. The head clogging was measured from the RF output during reproduction. During this repeated reproduction, head clogging occurred when the RF output decreased by 6 dB or more, and the total time for which such reduction was measured was defined as head clogging.

  Further, the magnetic head after repeated reproduction was observed using an optical microscope, and the dust attached to the magnetic head was observed. Evaluate powder with 5 levels, 5 is the level at which almost no powder is seen, 4 is the level when powder is less than 30% of the head area and does not affect the output, and the level with powder is less than 50% of the head area The level at which the output does not affect the output is 3, the level at which the dust is 50% or less of the head area and the level at which the output is affected is 2, and the level at which the powder is 50% or more the head area is 1.

(IV) Adsorption test The adsorption test was performed by immersing the sample in which the lubricant layer was formed by immersing the sample in the solvent used for preparing the coating liquid when forming the lubricant layer for 10 seconds. The residual ratio of the lubricant was determined. According to this test, the larger the residual ratio, the higher the adsorptivity is evaluated. The residual rate of the lubricant was determined from the amount of change in the amount of fluorine atoms before and after washing with a solvent by detecting fluorine atoms by ESCA analysis.
The evaluation results of each test are shown in Table 1.

As is clear from Table 1, all of the samples of Examples 1 to 10 containing the compound represented by the general formula (a) in the lubricant layer have a friction coefficient in an environment such as normal temperature and normal humidity and low temperature and low humidity. Good results were obtained in all tests such as little increase, long still life, short head clogging time, and high residual rate. The sample of Example 8 in which the compound represented by the general formula (a), in which R ¹ and R ² are both hydrogen, was used as a lubricant, compared with the samples of Examples 1 to 7, The coefficient was slightly higher. This is nothing but to show that the lubricity is improved when R ¹ and R ² are aliphatic alkyl groups or aliphatic alkenyl groups. Further, a mixture of the compound represented by the general formula (a) and the fluorinated carboxylic acid compound represented by the general formula (b) or (c) (Examples 9 and 10) has a very low friction coefficient and is stable. Met. Moreover, what mixed the compound shown by General formula (a), and the fluorine-containing monoester compound shown by General formula (d) (Example 11) is shown by Example 1 (General formula (a)). The initial coefficient of friction (first pass) was lower than that of the compound alone used as a lubricant. This is because the presence of the compound of the formula (d1) improves the wettability of the lubricant, so that the compound of the formula (a1) having good lubricating properties (ie, a low coefficient of friction) is more uniform. This is probably due to the distribution on the surface. On the other hand, the samples of Comparative Examples 1 to 3 generally had a high coefficient of friction and were inferior in terms of still life and durability. Since the compound used as a lubricant in Comparative Example 2 is a compound in which only a hydroxyalkyl group is bonded to a nitrogen atom, the lubricant is also adsorbed to the magnetic head, resulting in more head clogging and head dusting. As a result, the friction coefficient is considered to have increased. In the sample of Comparative Example 4, since only isopropyl alcohol was used as a solvent when forming the lubricant layer, a uniform lubricant layer was not formed. Therefore, the sample of Comparative Example 4 was not obtained as an appropriate level for the evaluation test, and all the characteristics were inferior.

(Example 12)
Next, another embodiment of the magnetic recording medium (disk-shaped medium) of the present invention will be described.
In this example, a nonmagnetic NiAl alloy layer having a thickness of 30 nm was formed on the surface of an aluminum alloy plate having a diameter of 2.5 mm as a nonmagnetic support for a magnetic recording medium. In addition, a texture formed with protrusions having an average roughness of 5 nm and a maximum height of 20 nm was used. A base layer made of a CrMo alloy having a thickness of 8 nm is formed on the nonmagnetic NiAl alloy layer of the support by a sputtering method, and a CoPt alloy made of CoCrPtB having a thickness of 15 nm is further formed on the base layer by a sputtering method. A magnetic layer was formed. Further, a protective film made of diamond-like carbon having a thickness of 5 nm was formed on the magnetic film by plasma CVD. Subsequently, the fluoroalkyl ether compound represented by the chemical formula (a9) was dissolved in HFE-7200 (manufactured by Sumitomo 3M), which is a fluorocarbon solvent, to prepare a coating solution. Using this coating solution, a lubricant layer was formed by a dip coating method so that the final amount of the lubricant was 5 mg per 1 m ² , thereby producing a magnetic disk.

(Examples 13 to 18)
Instead of the compound represented by the chemical formula (a9), the compounds represented by the following chemical formulas (a10) to (a15) were used, respectively, in the same manner as in Example 12, and six types of magnetic disks (Examples 13 to 18). ) Was produced.

(Example 19)
A lubricant was prepared by mixing the compound represented by the chemical formula (a9) and the compound represented by the chemical formula (b1) (see Example 9) in a weight ratio of 1: 1. Using this lubricant, a magnetic disk was produced in the same manner as in Example 12.

(Example 20)
A lubricant was prepared by mixing the compound represented by the chemical formula (a9) and the compound represented by the chemical formula (c1) (see Example 10) at a weight ratio of 1: 1. Using this lubricant, a magnetic disk was produced in the same manner as in Example 12.

(Example 21)
A lubricant was prepared by mixing the compound represented by the chemical formula (a9) and the compound represented by the chemical formula (d1) (see Example 11) at a weight ratio of 1: 1. Using this lubricant, a magnetic disk was produced in the same manner as in Example 12.

(Comparative Example 5)
Instead of the compound represented by the chemical formula (a9), a known compound (see Comparative Example 1) represented by the chemical formula (e1) was used as a lubricant, and a magnetic disk was produced in the same manner as in Example 12. .

(Comparative Example 6)
Instead of the compound represented by the chemical formula (a9), a known compound (see Comparative Example 2) represented by the chemical formula (e2) was used as a lubricant, and a magnetic disk was produced in the same manner as in Example 12. .

(Comparative Example 7)
Instead of the compound represented by the chemical formula (a9), a known compound (see Comparative Example 3) represented by the chemical formula (e3) was used as a lubricant, and a magnetic disk was produced in the same manner as in Example 12. .

  The magnetic disk samples obtained in Examples 12 to 21 and Comparative Examples 5 to 7 were evaluated as follows.

(I) Dynamic friction coefficient measurement test A friction coefficient was measured when a magnetic head having a load of 10 gf was contacted and slid at a rotational speed of 10 rpm at a disk radius of 20 mm on the surface of a magnetic disk.

(II) Durability test In a high-temperature and high-humidity environment of 60 ° C. and 80% RH, a magnetic head with a load of 10 gf was slid in contact with the magnetic disk surface at a rotational speed of 300 rpm at a disk radius of 20 mm. The number of revolutions until a visible scratch was generated was measured.

(III) Adsorption test The adsorption test was performed by immersing the sample in which the lubricant layer was formed by immersing the sample in the solvent used for preparing the coating solution for 10 seconds when forming the lubricant layer. The residual ratio of the lubricant was determined. According to this test, the larger the residual ratio, the higher the adsorptivity is evaluated. The residual rate of the lubricant was determined from the amount of change in the amount of fluorine atoms before and after washing with a solvent by detecting fluorine atoms by ESCA analysis.
The evaluation results of each test are shown in Table 2.

As is clear from Table 2, all the samples of Examples 12 to 21 containing the compound represented by the general formula (a) in the lubricant layer have a friction coefficient in an environment such as normal temperature and normal humidity and high temperature and high humidity. Good results were shown for all tests, such as small, good durability, and high residual rate. On the other hand, the samples of Comparative Examples 5 to 7 generally had a high coefficient of friction and were inferior in durability.
In the examples, the protective film on the magnetic layer was formed by the plasma CVD method. However, a protective film made of diamond-like carbon was formed by the sputtering method, and the lubricant of the present invention was used on the protective film. Similar effects were obtained even when the layer was formed.

  Since the lubricant of the present invention has the characteristics of having a large adhesion to an object (particularly a carbon film) and exhibiting excellent lubricity by using a specific fluoroether compound, this lubricant is particularly Suitable for configuring a lubricant layer of a magnetic recording medium, for example, a lubricant layer of a magnetic recording medium used in a digital video tape recorder, a hard disk drive, etc., and configured to rub against a magnetic head or the like Suitable for doing.

Schematic sectional view showing an example of the magnetic recording medium of the present invention

Explanation of symbols

1 Non-magnetic support 2 Magnetic layer (ferromagnetic metal film)
3 Protective film 4 Lubricant layer 5 Backcoat layer 100 Magnetic recording medium

Claims (11)

A lubricant comprising at least one compound selected from fluoroether compounds represented by the following general formula (a).

Wherein R ¹ and R ² each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, a is an integer of 1 to 12, v is an integer of 1 to 12, and w is 1 to 6 Z is an integer of 1 to 5, and h and k are each an integer of 0 to 30.)   The lubricant according to claim 1, further comprising at least one fluorine-containing carboxylic acid compound having a carboxyl group. The lubricant according to claim 2, wherein the fluorine-containing carboxylic acid compound is at least one compound selected from compounds represented by the following general formulas (b) and (c).

^(Wherein, R ^3, R ^4, R 5, ^{R 6} each represent hydrogen, an aliphatic alkyl group or an aliphatic alkenyl group, at least one of ^{R 3} and ^{R 4} are hydrogen, ^{R 5} and ^{R 6} At least one is hydrogen, m is an integer of 1 to 6, n is an integer of 1 to 5, p and q are each an integer of 0 to 30, and r is an integer of 1 to 12. )

Wherein R ⁷ represents an aliphatic alkyl group or an aliphatic alkenyl group, R ⁸ represents a fluoroalkyl group, a fluoroether group or a fluoropolyether group, b is 0 or 1, and c is 0 to 0 (It is an integer of 20)   The lubricant according to claim 1, further comprising at least one fluorine-containing monoester compound containing one ester bond. The lubricant according to claim 4, wherein the fluorine-containing monoester compound is selected from compounds represented by the following general formula (d).

(In the formula, R ⁹ represents a fluoroalkyl group, a fluoroalkenyl group, a fluoroether group or a fluoropolyether group, R ¹⁰ represents an aliphatic alkyl group or an aliphatic alkenyl group, and s is an integer of 1 to 12. .)   The lubricant for magnetic recording media containing the lubricant of any one of Claims 1-5.   A magnetic recording medium having a ferromagnetic metal film formed as a magnetic layer on a nonmagnetic support, a protective film formed on the magnetic layer, and a lubricant layer formed on the protective film, A magnetic recording medium, wherein the lubricant layer contains at least one lubricant according to claim 6.   The magnetic recording medium according to claim 7, wherein the protective film is diamond-like carbon.   9. The magnetic recording medium according to claim 7, wherein the protective film is a carbon film having a nitrogen-containing plasma polymerized film on a surface layer portion, and the lubricant layer is formed on the nitrogen-containing plasma polymerized film of the carbon film.   10. The method of manufacturing a magnetic recording medium according to claim 7, wherein the step of forming a lubricant layer on the protective film is a mixed organic solvent of a hydrocarbon solvent and an alcohol solvent. A method for producing a magnetic recording medium, comprising: applying a coating solution prepared by dissolving a lubricant on a protective film.   The method for producing a magnetic recording medium according to claim 10, wherein a mixing ratio of the hydrocarbon solvent and the alcohol solvent is in a range of 1: 9 to 9: 1 by weight.

Images