WO2013054393A1 - Lubricant and magnetic disk device using same - Google Patents

Abstract

The purpose of the present invention is to provide: a lubricant which enables long-term stabilization of a head-disk interface by means of a lubricant structure wherein the bulk of the polymer of the lubricant is decreased, while maintaining the fluidity as the lubricant; and a magnetic disk device which uses the lubricant. A lubricant of the present invention is a polymer having two or more polar groups, and is characterized in that a monomer unit having an oxygen/carbon ratio of less than 1/2 and a monomer unit having an oxygen/carbon ratio of 1/2 or more, one or more side chains selected from among -(CH₂)_p-CH₃, -O-(CH₂)_p-CH₃ and -(CH₂O)_p-CH₃ (wherein p represents an integer of 0 or more, and one or more hydrogen atoms may be substituted by fluorine atoms), or one or more alicyclic hydrocarbon groups are contained at least between two of the polar groups of the polymer.

Description

Lubricant and magnetic disk device using the same

The present invention relates to a lubricant and a magnetic disk device using the lubricant.

In recent years, in a magnetic disk device, the flying height of a magnetic head has been reduced to about 10 nm or less with an increase in recording density. In the future, the flying height tends to decrease year by year, and the chance that the magnetic head directly contacts the magnetic disk is expected to increase rapidly. When the magnetic head frequently contacts and slides on the magnetic disk, damage due to friction and wear occurs. Therefore, a protective film and a lubricating film are usually formed on the surface of the magnetic disk. As a protective film for preventing friction and wear, a diamond-like carbon (DLC) film having high hardness is often used. When a DLC film is used as the protective film, its surface is covered with a thin oxide film having a functional group such as a reactive carbonyl group, carboxyl group, or hydroxy group, and contaminants are easily adsorbed here. Therefore, by covering the surface of this protective film with a lubricant, it is possible to obtain a magnetic disk device with improved durability and stability, without causing harmful gas and organic contaminants to be adsorbed on the surface, and having excellent durability. Yes.

The lubricant film for improving the lubrication characteristics of the magnetic disk surface must be stably formed with a uniform film thickness on the surface of the protective film, and it is important that the adhesion and bonding with the protective film are high It is. In order to enhance this adhesion, a perfluoropolyether lubricant having a polar group such as a hydroxy group or a piperonyl group at the terminal is generally used. However, it is becoming difficult to keep the lubricant uniformly on the magnetic disk surface as the rotational speed of the magnetic disk is increased and the thickness of the lubricant film is reduced. Further improvement of the lubricant is an important issue. ing.

Specifically, when the molecular weight of the lubricant is small, the film thickness is significantly reduced due to rotational scattering, and in the worst case, a head crash occurs. On the other hand, when the molecular weight is large, the rotational molecular radius of one molecule of the lubricant becomes large, which may hinder the reduction of the flying height.

(Patent Document 1) proposes a molecular structure having an aromatic ring in addition to the polymer end as a lubricant, thereby reducing the bulk of the lubricant molecule and forming a lubricating film with a high coverage. .

JP 2010-250929 A

However, as in the lubricant of (Patent Document 1), if the aromatic ring is arranged at a position other than the end of the polymer, the bulkiness of the molecule is reduced, and rotation scattering is prevented by improving the adsorptivity to the magnetic disk. However, there is a problem that the damage to the head when the magnetic head comes into contact with the head due to the decrease in fluidity is large.

Therefore, the present invention proposes a lubricant structure that maintains fluidity as a lubricant while reducing the bulkiness of the polymer of the lubricant, and realizes stabilization of the head-disk interface over a long period of time, An object of the present invention is to provide a magnetic disk device using the same.

As a result of intensive studies by the present inventors, the polymer used as a lubricant has polar groups that can be adsorbed and bonded to the substrate side such as a protective film at both ends and / or molecular chains. The inventors have found that the above problems can be solved when the plurality of polar groups include a predetermined molecular structure, and have completed the present invention.

That is, the lubricant of the present invention is a polymer having two or more polar groups, of which at least two polar groups have a monomer unit having an oxygen / carbon ratio of less than 1/2 and an oxygen / carbon ratio. Or more than half monomer units, or — (CH ₂ ) _p —CH ₃ , —O— (CH ₂ ) _p —CH ₃ and — (CH ₂ O) _p —CH ₃ (wherein p is It is an integer of 0 or more, and one or more hydrogen atoms may be substituted with fluorine atoms), or one or more alicyclic hydrocarbon groups. Features.

With the lubricant of the present invention, a lubricating film having a small molecular bulk can be formed, and at the same time, a lubricating film having high fluidity can be obtained. By using such a lubricant in the magnetic disk device, it is possible to stabilize the head-disk interface over a long period of time while contributing to further reduction of the flying height of the magnetic head. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a figure which shows typically the molecular structure of the lubricant in the 1st Embodiment of this invention. It is a figure which shows typically the molecular structure of the lubricant in the 2nd Embodiment of this invention. It is a figure which shows typically the molecular structure of the lubricant in the 3rd Embodiment of this invention. 1 is a diagram schematically showing a magnetic disk device of the present invention. It is sectional drawing of a magnetic disc. It is a figure which shows the adhesion form analysis result of the lubricant on the protective film in Example 1 of this invention. It is a figure which shows the adhesion form analysis result of the lubricant on the protective film in the comparative example 1. It is a figure which shows the adhesion form analysis result of the lubricant on the protective film in Example 2 of this invention. It is a figure which shows the adhesion form analysis result of the lubricant on the protective film in Example 3 of this invention.

Hereinafter, the present invention will be described in detail based on embodiments.
The lubricant according to the present invention, as a first embodiment, is a polymer having two or more polar groups, and a monomer having an oxygen / carbon ratio of less than 1/2 between at least two polar groups. It is characterized by containing monomer units of 1/2 or more in terms of unit and oxygen / carbon ratio.

The polar group is a functional group having polarity, and when a base material such as a protective film of a magnetic disk is covered with a lubricant, a polar group such as a carbonyl group, a carboxyl group, or a hydroxy group on the surface of the protective film. A group that can be firmly bonded to a hydrogen bond or a covalent bond. Specific examples include monovalent functional groups such as —OH, —COOH, —NH ₂ , and —CHO, and divalent functional groups such as —O—, —COO—, and —NH—. These polar groups are present at both ends of the polymer that is the lubricant, at the molecular chain other than the terminal, or at both sites, and are adsorbed to a substrate such as a protective film at multiple sites in the molecular chain. Can do.

A monomer unit having an oxygen / carbon ratio of less than 1/2 functions as a hard molecular skeleton because the proportion of oxygen atoms such as ether bonds (—O—) is small. Preferably it is 1/4 or less. However, when there is no ether bond or the like (when the oxygen / carbon ratio is 0), the interaction between the lubricant and the base material such as the protective film may be weakened. It is desirable to have an oxygen / carbon ratio of 12 or greater.

Examples of the monomer unit having an oxygen / carbon ratio of less than 1/2 include monomer units having a structure such as an alkylene group having 2 to 5 carbon atoms and an oxyalkylene group having 2 to 5 carbon atoms. One or more hydrogen atoms of these groups may be substituted with a halogen such as fluorine, and these groups may have one or more double bonds or triple bonds. In particular, — (CF ₂ ) _q — (wherein q is an integer of 2 or more), — (OCF ₂ CF ₂ CF ₂ ) _r — and — (OCF ₂ CF ₂ CF ₂ CF ₂ ) _r — (Formula Among them, a monomer unit containing one or more selected from r is an integer of 1 or more is preferable because of excellent lubricity.

A monomer unit having an oxygen / carbon ratio of 1/2 or more functions as a soft molecular skeleton because of a large proportion of oxygen atoms such as ether bonds. Examples of such a monomer unit include a monomer unit having a structure of an oxyalkylene group having 1 to 2 carbon atoms. One or more hydrogen atoms of these groups may be substituted with a halogen such as fluorine, and these groups may have one or more double bonds or triple bonds. In particular, the monomer unit containing one or more selected from — (OCF ₂ —CF ₂ ) _m — and — (OCF ₂ ) _n — (wherein m and n are each an integer of 1 or more) is a molecular chain. It is preferable because of its high flexibility and excellent lubricity.

As specific examples of the polymer containing a monomer unit having an oxygen / carbon ratio of less than 1/2 and a monomer unit having an oxygen / carbon ratio of 1/2 or more, the following chemical formulas (1) and (2) are used. And copolymers obtained from the monomers shown. The monomer of chemical formula (1) functions as a soft molecular skeleton, and the monomer of chemical formula (2) functions as a hard molecular skeleton. In chemical formulas (1) and (2), A represents a terminal structure having a polar group such as —CH ₂ OH, —COOH, —NH ₂ , —CH ₂ OCH ₂ CH (OH) CH ₂ OH, k and l are integers of 0 or more, and s is an integer of 1 or more. If s is too large, the lubricant tends to be separated from the base material such as the protective film and tends to float, and is preferably 10 or less, but is not limited thereto.

These monomers are dissolved in, for example, a fluorinated solvent to conduct a polymerization reaction, and then —OH in the middle of the molecular chain is replaced with —OCH _3, and unreacted products are separated using supercritical carbonic acid extraction. By performing the above, it is possible to obtain a polymer having a hard molecular skeleton at the intermediate part and a soft molecular skeleton at both ends, as shown by the following chemical formula (3). The chemical formula (3) shows a case where the terminal structure A is —CH ₂ OCH ₂ CH (OH) CH ₂ OH, and therefore Rf shows a structure obtained by removing A from the chemical formula (1).

FIG. 1 schematically shows a stable state of one molecule when a lubricant containing a polymer as described above is applied to the surface of a substrate such as a protective film having a polar group. As shown in FIG. 1, a polymer that serves as a lubricant is adsorbed on a substrate 1, and polar groups 2 are attached to both ends of the polymer. The polar group 2 has a property of being strongly bound to the polar group on the substrate 1 side by forming a hydrogen bond or a covalent bond. The main chain skeleton 3 near both ends of the polymer has a soft property, and the main chain skeleton 4 near the middle portion has a hard property. The molecular chain of a hard skeleton has a small vibration width (thermal fluctuation) due to heat and prevents the polymer from becoming thread-like, so that the bulk of the whole molecule can be kept low. In FIG. 1, the polar groups 2 are located at both ends of the polymer, but may be located in a molecular chain other than the ends. In that case, polar groups present between at least two polar groups, i.e., when there are a plurality of polar groups in the molecular chain other than the terminal or between the plurality of polar groups or in the molecular chain other than the terminal. And a polar group present at the terminal or both of them include a monomer unit having an oxygen / carbon ratio of less than ½ and a monomer unit having an oxygen / carbon ratio of ½ or more.

If the molecular weight of the polymer is too small, the lubrication characteristics may deteriorate or the lubrication film thickness may decrease due to rotational scattering / evaporation. If the molecular weight is too large, the film thickness increases, which hinders the reduction of flying height. Therefore, it is set appropriately in consideration of these balances. The number average molecular weight is preferably 500 or more and 6000 or less.

Next, the lubricant according to the present invention, as a second embodiment, is a polymer having two or more polar groups, and at least two polar groups are — (CH ₂ ) _p —CH ₃ , —O— (CH ₂ ) _p —CH ₃ and — (CH ₂ O) _p —CH ₃ (wherein p is an integer of 0 or more, and one or more hydrogen atoms are substituted by fluorine atoms) It is also characterized in that it contains one or more side chains selected from. If p is too large, the lubricating film thickness may increase, so it is preferably 0 to 5. Examples of such side chains include alkyl groups such as —CH ₂ CH ₂ CH ₃ , alkoxy groups such as —OCH ₂ CH ₂ CH ₃ , fluoroalkyl groups such as —CF ₂ CF ₂ CF ₃ , —OCF fluoroalkoxy group such as a ₂ CF ₂ CF ₃ and the like.

An example of such a polymer is a structure represented by the following chemical formula (3). The polymer of the chemical formula (3) has _four butoxy groups (—OC ₄ H ₉ ) as side chains in the vicinity of the center of the molecular chain, and hydroxy groups that are side chains (functional groups) at both ends of the polymer. The polarity is smaller than In the chemical formula (3), the meanings of Rf and s are the same as those in the first embodiment.

FIG. 2 schematically shows a stable state of one molecule when the lubricant containing the polymer according to the second embodiment is applied to the surface of a substrate such as a protective film having a polar group. As shown in FIG. 2, a polymer as a lubricant is adsorbed on the base material 1, and the structure of the polar group 2 at both ends of the polymer and the structure of the relatively soft main chain skeleton 3 near the ends is shown in FIG. Same as 1. There are many side chains 5 having a small polarity in the vicinity of the center of the molecular chain. For this reason, the polymer is less likely to have a string shape, and the bulk of the molecule can be kept low. The polar group 2 may be located in the molecular chain other than the terminal (or in addition to the terminal) of the polymer, the preferred molecular weight range of the polymer, etc. According to the embodiment.

The lubricant according to the present invention is a polymer having two or more polar groups as a third embodiment, and at least two polar groups among them are one or more alicyclic hydrocarbon groups. It is characterized by including.

Examples of the alicyclic hydrocarbon group include 5- to 7-membered cycloalkylene groups, and these alicyclic hydrocarbon groups include — (CH ₂ ) _p —CH ₃ , —O— (CH ₂ ). _p -CH ₃ and _{- (CH 2 O) p -CH} 3 ( wherein, p is an integer of 0 or more, one or more hydrogen atoms may be substituted by fluorine atoms) one or more selected from It may have one or more side chains.

An example of such a polymer is a structure represented by the following chemical formula (4). The polymer of the chemical formula (4) has a 1,4-cyclohexylene group near the center of the molecular chain. In the chemical formula (4), the meaning of Rf is the same as that in the first embodiment.

The alicyclic hydrocarbon group may be a heterocyclic ring in which one or more carbon atoms are substituted with a heteroatom such as oxygen, nitrogen, or sulfur. Furthermore, the alicyclic hydrocarbon group may have one or more unsaturated bonds. As the following formula (5), an example of an alicyclic hydrocarbon group having one double bond and having one carbon atom substituted with nitrogen is shown. By having one or more unsaturated bonds, the flatness of the ring structure is improved. However, it should be noted that when there are many unsaturated bonds, an aromatic ring having a conjugated bond can be formed, in which case the adsorptivity between the lubricant and the substrate is increased, and the lubrication characteristics may be deteriorated. .

FIG. 3 schematically shows a stable state of one molecule when a lubricant containing a polymer according to the third embodiment is applied to the surface of a substrate such as a protective film having a polar group. As shown in FIG. 3, a polymer as a lubricant is adsorbed on the substrate 1, and the structure of the polar group 2 at both ends of the polymer and the structure of the relatively soft main chain skeleton 3 near the ends is shown in FIG. Same as 1. The alicyclic hydrocarbon group 6 is contained in the vicinity of the center of the molecular chain, and this cyclic hydrocarbon prevents the polymer from becoming thread-like, so that the bulk of the molecule is kept low. Can do. The polar group 2 may be located in the molecular chain other than the terminal (or in addition to the terminal) of the polymer, the preferred molecular weight range of the polymer, etc. According to the embodiment.

FIG. 4 is a top view schematically showing one embodiment of a magnetic disk device according to the present invention. As shown in FIG. 4, the magnetic disk device normally has a magnetic disk 7 for recording / holding data, a motor 8 for rotating the magnetic disk, and a magnetic head 9 for reading / writing magnetic data from / to the magnetic recording layer on the surface of the magnetic disk. And an arm 10 for supporting the magnetic head, and a positioning device 11 for controlling the position of the magnetic head. As shown in the cross-sectional view of FIG. 5, the magnetic disk 7 includes a base material 12 (nonmagnetic support), a base film 13, a magnetic film 14, a protective film 15, a lubricating film 16, and the like. The base film 13 and the protective film 15 may be omitted. The lubricating film 16 is formed from the lubricant of the present invention and is applied on the protective film 15.

The surface of diamond-like carbon (DLC) or the like that forms the protective film 15 is modified with a polar group such as a reactive carbonyl group, a carboxyl group, or a hydroxy group, and these polar groups are the polar groups on the lubricant side. By bonding, a strong bonding force is generated at the interface between the protective film and the lubricating film. The lubricating film may be formed not on the surface of the magnetic disk 7 or on the surface of the magnetic head 9 in addition to the surface of the magnetic disk 7.

Next, the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to these examples.

Example 1
In the case of using the lubricant according to the first embodiment, the adhesion form of the lubricant on the protective film was examined by molecular dynamics simulation. Molecular dynamics simulation is a method that solves the motion of each atom over time according to Newton's equation of motion, and has been used many times to analyze the adhesion form of lubricant polymers on the magnetic disk surface as computers have developed. (See, for example, Myung S. Jhon et al., “Simulation of Nanostructual Lubricant Films”, IEEE TRANSACTIONS ON MAGNETICS, MARCH 2003, VOL. 39, NO. 2, pp 754-758). As shown in FIG. 6, the analysis model considers a base material in which polar groups (hydroxy groups) 17 are randomly arranged on the surface of the protective film 15 (diamond-like carbon film), and a molecular weight of about a lubricant on the base material. A model in which 3000 g / mol of polymer 18 was attached was used. As the polymer 18, a structure in which s is 6, k is 6, and l is 6 in the chemical formula (2) was examined. In the adhesion morphology analysis, the polymer 18 was placed on a substrate, and molecular dynamics calculation was performed until the energy of the entire system was stabilized at room temperature. From the result of FIG. 6, it can be seen that the polymer 18 has a flat shape on the substrate.

(Comparative Example 1)
The adhesion form was analyzed in the same manner as in Example 1 except that a polymer having s of 0, k of 6, and l of 6 in the chemical formula (2) was investigated as the lubricant. As shown in the results of FIG. 7, it was found that the adhesion form of the polymer 19 in the case where s is 0 becomes a string shape and becomes bulky.

(Example 2)
The adhesion form was analyzed in the same manner as in Example 1 except that the polymer having chemical formula (3) in which s was 3, k was 6, and l was 6 was investigated. As shown in the results of FIG. 8, it became clear that the bulk of the polymer 20 is suppressed.

(Example 3)
The adhesion form was analyzed in the same manner as in Example 1 except that the polymer having the chemical formula (4) where k is 6 and l is 6 was investigated. As shown in the results of FIG. 9, the bulk of the polymer 21 is somewhat larger due to the influence of the soft main chain skeleton, but the tendency to become stringy is suppressed. Increasing the number of alicyclic hydrocarbon groups to 2 to 3 can further suppress the formation of a string.

According to the above examples and comparative examples, it is possible to keep the bulk of the molecules low without increasing the adsorption force of the polymer as the lubricant more than necessary, and to reduce the flying height of the magnetic head. Thus, it is possible to obtain a magnetic disk apparatus that realizes formation of a lubricating film that is advantageous for improving the lubrication characteristics when contacting the magnetic head, and improvement of the reliability of the head-disk interface over a long period of time.

Note that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

All publications, patents and patent applications cited in this specification shall be incorporated into the present specification as they are.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Polar group 3 Main chain skeleton 4 Main chain skeleton 5 Side chain 6 Alicyclic hydrocarbon group 7 Magnetic disk 8 Motor 9 Magnetic head 10 Arm 11 Positioning device 12 Base material 13 Underlayer film 14 Magnetic film 15 Protective film 16 Lubricating film 17 Polar group 18-21 Polymer

Claims (8)

A polymer having two or more polar groups, and at least two of the polar groups have a monomer unit having an oxygen / carbon ratio of less than 1/2 and a monomer unit having an oxygen / carbon ratio of 1/2 or more. — (CH ₂ ) _p —CH ₃ , —O— (CH ₂ ) _p —CH ₃ and — (CH ₂ O) _p —CH ₃ (wherein p is an integer of 0 or more, 1 or more A hydrogen atom in which the fluorine atom may be substituted with a fluorine atom), or a lubricant containing one or more alicyclic hydrocarbon groups. Monomer units having an oxygen / carbon ratio of less than 1/2 are — (CF ₂ ) _q — (wherein q is an integer of 3 or more), — (OCF ₂ CF ₂ CF ₂ ) _r — and — (OCF ₂ CF ₂ CF ₂ CF ₂ ) _r — (wherein r is an integer of 1 or more), and a monomer unit having an oxygen / carbon ratio of ½ or more is — (OCF _{2 2.} The lubricant according to claim 1, comprising one or more selected from —CF ₂ ) _m — and — (OCF ₂ ) _n — (wherein m and n are each an integer of 1 or more). The lubricant according to claim 1, wherein at least one carbon atom of the alicyclic hydrocarbon group is substituted with a hetero atom. The lubricant according to claim 1 or 3, wherein the alicyclic hydrocarbon group has one or more unsaturated bonds. The alicyclic hydrocarbon group is — (CH ₂ ) _p —CH ₃ , —O— (CH ₂ ) _p —CH ₃ and — (CH ₂ O) _p —CH ₃ (wherein p is an integer of 0 or more) The lubricant according to claim 1, 3 or 4 having one or more side chains selected from the group consisting of: one or more hydrogen atoms may be substituted with fluorine atoms. Polar group, the lubricant according to any one of claims 1 to 5, which is a group selected -OH, from -COOH and -NH _2. The lubricant according to any one of claims 1 to 6, wherein the polymer has a number average molecular weight of 500 or more and 6000 or less. 8. A magnetic disk device in which a lubricating film is formed on at least one of a magnetic disk surface and a magnetic head surface, wherein the lubricating film contains the lubricant according to claim 1.

Images