Lubricant compound for magnetic disk and magnetic disk

Abstract

A lubricant compound is contained in a lubrication layer of a magnetic disk in which at least a magnetic layer, a protective layer, and a lubrication layer are sequentially provided on a substrate, and the lubricant compound contains a component A represented by Chemical formula 1 and a component B represented by Chemical formula 2: ##STR00001##
wherein X in Chemical formula 1 represents OH ##STR00002##
wherein X in Chemical formula 2 represents OCH.sub.2CH(OH)CH.sub.2OH,
and the lubricant compound further contains a component C made of a specific compound having a phosphezene ring in the structure thereof.

Claims

1. A lubricant compound for a magnetic disk contained in a lubrication layer of a magnetic disk in which at least a magnetic layer, a protective layer, and a lubrication layer are sequentially provided on a substrate, characterized in that the lubricant compound contains a component A represented by Chemical formula 1 and a component B represented by Chemical formula 2: ##STR00013## wherein X in Chemical formula 1 represents OH ##STR00014## wherein X in Chemical formula 2 represents OCH.sub.2CH(OH)CH.sub.2OH, and the lubricant compound further contains at least one type of a component C, wherein the component C is selected from compounds C-1 and C-2 represented by the following formulae: ##STR00015## wherein Rf represents (OC.sub.2F.sub.4)m(OCF.sub.2)n-, and m and n each represents an integer of not less than 1, and PN is represented from one of the following formulae: ##STR00016## ##STR00017## wherein x and y each is an integer of 5 when C is compound (C-1) and an integer of 4 when C is compound (C-2), wherein the lubricant compound does not contain a component D represented by the following Chemical formula ##STR00018##

2. The lubricant compound for a magnetic disk according to claim 1, wherein in the lubricant compound, the ratio of the component C among the component A, the component B, and the component C is 5 to 20 weight %.

3. A magnetic disk in which at least a magnetic layer, a protective layer, and a lubrication layer are sequentially provided on a substrate, characterized in that the lubrication layer contains the lubricant compound according to claim 1.

4. The magnetic disk according to claim 3, wherein the protective layer is a carbon protective layer formed by a plasma CVD method.

5. The magnetic disk according to claim 3, wherein the magnetic disk is mounted on a magnetic disk device whose start/stop mechanism is a load-unload type and used under the head floating amount of 5 nm or less.

6. The magnetic disk according to claim 3, wherein a thickness of the lubrication layer is 10 to 13 .

7. The lubricant compound for a magnetic disk according to claim 1, wherein a weight ratio between the components A and B is between 1:3 and 1:10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph illustrating a fixed-point floating test result after silicon exposure.

(2) FIG. 2 is a graph illustrating a fixed-point floating test result after silicon exposure.

BEST MODE FOR CARRYING OUT THE INVENTION

(3) The present invention will be described below in detail by using an embodiment.

(4) A lubricant compound for a magnetic disk of the present invention is, as described in the composition 1, a lubricant compound contained in a lubrication layer of a magnetic disk in which at least a magnetic layer, a protective layer, and the lubrication layer are sequentially provided on a substrate, and the lubricant compound contains a component A represented by Chemical formula 1 and a component B represented by Chemical formula 2:

(5) ##STR00009## wherein X in Chemical formula 1 represents OH

(6) ##STR00010## wherein X in Chemical formula 2 represents OCH.sub.2CH(OH)CH.sub.2OH, and the lubricant compound further contains at least one type of a component C, wherein the component C is selected from compounds C-1, C-2 and C-3 represented by the following formulae:

(7) ##STR00011## wherein Rf represents (OC.sub.2F.sub.4)m(OCF.sub.2)n-, and m and n each represents an integer of not less than 1, and PN is represented from one of the following formulae:

(8) ##STR00012## wherein x and y each is an integer of 5 when C is compound (C-1) and an integer of 4 when C is compound (C-2).

(9) In the lubricant compound for a magnetic disk of the present invention, since the component D is not contained, aggregation or pickup of the lubricant hardly occurs, as compared with the FOMBLIN Z-TETRAOL (product name) lubricant, which has been used in general, and since the component C having an adsorption force to the protective film to the same degree as the component D, a function of reducing abrasion of the protective film or physical damage to the magnetic recording medium during LUL or in head contact is provided.

(10) That is, since the prior-art component D has three hydroxyl groups for one terminal part, it can bind to the protective film extremely strongly, and thus, removal of the lubricant hardly occurs even in head contact, and abrasion of the protective film or physical damage to the magnetic recording medium can be reduced. However, since the positions of the hydroxyl groups in the molecule are close to the ends and they are close to each other in the component D, interactions such as hydrogen bonding can easily occur in the molecule or between the molecules, and aggregation of the lubricant can easily occur on the disk surface.

(11) On the other hand, the component C contained in the lubricant of the present invention has fewer hydroxyl groups close to the end of the molecule than the component D, and aggregation between the molecules hardly occurs. Also, since it has a hydroxyl group not only at the end but also at the center part of the molecule as the compound C-3, the interaction between the molecules can be favorably suppressed. Also, by providing a phosphazene ring at the center part or end part of the molecule as a polar group (functional group) instead of the hydroxyl group as in the compounds C-1 and C-2, the interaction between the molecules can be favorably suppressed. Such component C can adsorb to the protective film not only at the end group but also at the center part of the molecule and has the adsorption force to the protective film equal to or larger than that of the component D, and thus, removal of the lubricant hardly occurs even in head contact, and abrasion of the protective film or physical damage to the magnetic recording medium can be reduced.

(12) The lubricant compound for a magnetic disk of the present invention is a mixture of the component A, the component B, and the component C, and there is no particular need to restrict its mixing ratio in the present invention, but in order for the working effects by the present invention to exert better, the ratio of the component C is preferably 5 to 20 weight %. The component A and the component B can be also obtained by removing the component D from the commercially available FOMBLIN Z-TETRAOL (product name) lubricant, by appropriate refining, for example. Also, FOMBLIN Z-TETRAOL GT (product name) not containing the D component is also commercially available.

(13) The content ratio between the components A and B is preferably anywhere between 1:3 and 1:10 (weight ratio).

(14) Also, the component C is at least one type selected from the above compounds C-1, C-2, and C-3, but each compound may be used singularly or these compounds may be used at the same time as appropriate. Also, if these compounds are used at the same time, at least one type of the compounds C-1 and C-2 may be used at the same time with the compound C-3, for example. In the present invention, particularly the compounds C-2 and C-3 are preferable.

(15) Each molecular weight of the component A, the component B, and the component C contained in the lubricant compound of the present invention is not particularly limited, but the number average molecular weight (Mn) is preferably within a range of 1000 to 10000, for example, and more preferably within a range of 1000 to 6000. That is because repairability by appropriate viscosity is provided, and favorable lubrication performances are exerted.

(16) The lubricant compound of the present invention has the number average molecular weight (Mn) within a range of 1000 to 10000, for example, by an appropriate molecular weight fractionation. The method of molecular weight fractionation is not particularly limited in this case, and molecular weight fractionation using a gel permeation chromatography (GPC) method or molecular weight fractionation using a supercritical extraction method can be used, for example.

(17) Also, the present invention is a magnetic disk in which at least a magnetic layer, a protective layer, and a lubrication layer are sequentially provided on a substrate, and the lubrication layer is also provided for the magnetic disk characterized by containing the lubricant compound for a magnetic disk of the present invention.

(18) In forming the lubrication layer using the lubricant compound of the present invention, a film can be formed by application using a dip method, for example, using a solution in which the lubricant compound is dispersed and dissolved in a fluorine solvent or the like.

(19) The film forming method of the lubrication layer is naturally not limited to the above dip method and a film forming method such as a spin coating method, a spraying method, a paper coating method and the like may be used.

(20) In the present invention, in order to further improve an adhesion force of the formed lubrication layer to the protective layer, heating treatment or ultraviolet irradiation treatment may be conducted in which the magnetic disk is exposed to the atmosphere at 50 to 150 C. after the film formation.

(21) The film thickness of the prior-art lubrication layer has been usually 15 to 18 , but in the present invention, the film thickness can be made thinner to the film thickness of approximately 10 to 13 , for example. If the thickness is less than 10 , lubrication performances as the lubrication layer might be lowered.

(22) Also, as the protective layer in the present invention, a carbon protective layer can be favorably used. Particularly, an amorphous carbon protective layer is preferable. If the protective layer is a carbon protective layer, the interaction between the polar group (hydroxyl group or phosphazene ring) of the lubricant according to the present invention and the protective layer is further increased, and the working effect by the present invention is further exerted, which is a preferable mode.

(23) In the carbon protective layer in the present invention, it is preferable that nitrogen is contained in the lubrication layer side of the protective layer so as to have a composition graded layer in which hydrogen is contained in the magnetic layer side, for example.

(24) If the carbon protective layer is used in the present invention, a film can be formed by using a DC magnetron sputtering method, for example, but an amorphous carbon protective layer formed by the plasma CVD method is particularly preferable. By forming a film by the plasma CVD method, the surface of the protective layer is made uniform and closely formed. Therefore, formation of a lubrication layer according to the present invention on the protective layer formed by using the CVD method with smaller coarseness is preferable.

(25) In the present invention, the film thickness of the protective layer is preferably 20 to 70 . If the thickness is less than 20 , performances as the protective layer might be lowered. The thickness exceeding 70 is not preferable from the viewpoint of film thinning.

(26) In the magnetic disk of the present invention, the substrate is preferably a glass substrate. A glass substrate is rigid and is excellent in smoothness, which is preferable for higher recording density. As the glass substrate, an aluminosilicate glass substrate, for example, can be cited, and particularly a chemically-reinforced aluminosilicate glass substrate is preferable.

(27) In the present invention, regarding coarseness of the main surface of the above substrate, the surface is preferably supersmooth with Rmax at 3 nm or less and Ra at 0.3 nm or less. The surface coarseness Rmax and Ra here are based on the specification by JIS B0601.

(28) The magnetic disk obtained by the present invention is provided with at least a magnetic layer, a protective layer, and a lubrication layer on the substrate, but in the present invention, the magnetic layer is not particularly limited and may be either an in-plane recording type magnetic layer or a perpendicular recording type magnetic layer, but the perpendicular recording type magnetic layer is particularly preferable for realization of the recent rapid increase in recording density. Particularly, a CoPt magnetic layer is preferable since it can obtain both a high magnetic coercive force and a high reproduction output.

(29) In the magnetic disk of the present invention, an underlayer can be provided between the substrate and the magnetic layer as necessary. Also, an adhesion layer or a soft magnetic layer or the like may be provided between the underlayer and the substrate. In this case, as the underlayer, a Cr layer, a Ta layer, a Ru layer or an alloy layer of CrMo, CoW, CrW, CrV, CrTi and the like can be cited, for example, and particularly the Ru layer is preferable in the perpendicular magnetic recording medium. As the adhesion layer, an alloy layer of CrTi, NiAl, AlRu and the like can be cited, for example. Also, as the soft magnetic layer, a CoZrTa alloy film, for example, can be cited.

(30) According to the present invention, since the lubrication layer in which adhesion to the protective layer is high and aggregation or pickup of the lubricant, scratches and the like hardly occur can be formed, further reduction of the magnetic spacing can be realized, and moreover, under the circumstances of the super low floating amount (5 nm or less) of the magnetic head involved with the recent rapid increase in the recording density, a magnetic disk having high reliability under the extremely severe environmental resistance involved with diversification of applications can be obtained.

(31) The magnetic disk of the present invention is preferable as a magnetic disk mounted particularly on an LUL-type magnetic disk device. A further decrease of the magnetic-head floating amount realized by introduction of the LUL method has required the magnetic disk to operate stably even with an extremely low floating amount of not more than 5 nm, for example, and the magnetic disk of the present invention having high reliability under the circumstance of the low floating amount is preferable.

EXAMPLES

(32) The present invention will be described below in more detail by referring to examples.

Example 1

(33) A magnetic disk of the present example has an adhesion layer, a soft magnetic layer, an under layer, a magnetic recording layer, a carbon protective layer, and a lubrication layer sequentially formed on a disk substrate.

(34) (Manufacture of Magnetic Disk)

(35) A 2.5-inch glass disk (outer diameter of 65 mm, inner diameter of 20 mm, and disk thickness of 0.635 mm) made of chemically reinforced aluminosilicate glass was prepared and used as a disk substrate. The main surface of the disk substrate was mirror-polished so as to have R max of 2.13 nm and Ra of 0.20 nm.

(36) On this disk substrate, films of a Ti adhesion layer, a FeCoTaZr alloy thin-film soft magnetic layer, a NiW first underlayer, a RuCr second underlayer, and a CoCrPtSiO.sub.2 alloy thin-film magnetic recording layer were formed sequentially in an Ar gas atmosphere by the DC magnetron sputtering method. This magnetic recording layer was a perpendicular magnetic recording type magnetic layer.

(37) Subsequently, a film of an amorphous diamond-like carbon protective layer was formed with the film thickness of 60 by the plasma CVD method using a lower straight-chain hydrocarbon gas.

(38) Subsequently, a lubrication layer was formed as follows.

(39) As the lubricant, a lubricant in which FOMBLIN Z-TETRAOL (product name) by Solvay Solexis, Inc. containing the component A and the component B (however, the component D is removed) and the compound C-2 (component C) (however, in the compound C-2, PN ring=P.sub.3N.sub.3(OC.sub.6H.sub.4CF.sub.3)x (x=4)) are mixed at 9:1 (weight ratio) and adjusted as above was dispersed and dissolved with concentration of 0.2 weight % in VERTREL XF UP (product name) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD., which is a fluorinated solvent, to prepare a solution.

(40) By using this solution as an application liquid, the magnetic disk on which films were formed up to the protective layer was immersed and the liquid was applied by the dip method, and a film of the lubrication layer was formed.

(41) After the film formation, the magnetic disk was subjected to heating treatment in a vacuum firing furnace at 100 C. for 60 minutes. The film thickness of the lubrication layer was measured by a Fourier transform infrared spectrophotometer (FTIR), and the result was 12 . A magnetic disk of Example 1-1 was obtained as above.

(42) A magnetic disk of Example 1-2 fabricated similarly except that the film thickness of the lubrication layer was 14 and a magnetic disk of Example 1-3 fabricated similarly except that the film thickness of the lubrication layer was 16 were obtained.

Example 2

(43) The lubrication layer was formed as follows.

(44) As the lubricant, a lubricant in which FOMBLIN Z-TETRAOL (product name) by Solvay Solexis, Inc. containing the component A and the component B (however, the component D is removed) and the compound C-3 (component C) are mixed at 5:1 (weight ratio) and adjusted as above was dispersed and dissolved with concentration of 0.2 weight % in VERTREL XF UP (product name) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD., to prepare a solution. The compound C-3 was manufactured by reacting 2 equivalent weight of the perfluoropolyether compound having a perfluoropolyether main chain in the molecule and having a hydroxyl group at the end with 1 equivalent weight of a diepoxy compound having a hydroxyl group in the molecule and an epoxide structure at the end.

(45) By using this solution as an application liquid, the magnetic disk on which films were formed up to the protective layer was immersed and the liquid was applied by the dip method, and a film of the lubrication layer was formed. After the film formation, the magnetic disk was subjected to heating treatment in a vacuum firing furnace at 100 C. for 60 minutes. The film thickness of the lubrication layer was measured by a Fourier transform infrared spectrophotometer (FTIR), and the result was 14 .

(46) A magnetic disk of Example 2 fabricated similarly to Example 1 except the lubrication layer was obtained.

Example 3

(47) The magnetic disk of Example 3 was obtained similarly to Example 1 except that as the lubricant, a lubricant in which FOMBLIN Z-TETRAOL (product name) by Solvay Solexis, Inc. containing the component A and the component B (however, the component D is removed) and the compound C-2 (component C) (however, in the compound C-2, PN ring=P.sub.3N.sub.3(OCH.sub.2CF.sub.3)y (y=4)) are mixed at 9:1 (weight ratio) and prepared was used. The film thickness of the lubrication layer was 14 .

Comparative Example 1

(48) As the lubricant, a solution in which FOMBLIN Z-TETRAOL 2000S (product name) by Solvay Solexis, Inc. refined by the supercritical extraction method was dispersed and dissolved in VERTREL XF UP (product name) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD. was used as an application liquid, the magnetic disk on which films were formed up to the protective layer was immersed therein and the liquid was applied by the dip method, and a film of the lubrication layer was formed. The film thickness of the lubrication layer was 14 . It was found that, as the result of NMR analysis, the lubricant has the component A at approximately 15%, the component B at approximately 70%, and the component D at approximately 15% (weight ratio).

(49) A magnetic disk manufactured similarly to Example 1 except this point was obtained as Comparative Example 1.

Comparative Example 2

(50) As the lubricant, a solution in which FOMBLIN Z-TETRAOL GT (product name) by Solvay Solexis, Inc. refined by the supercritical extraction method was dispersed and dissolved in VERTREL XF UP (product name) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD. was used as an application liquid, the magnetic disk on which films were formed up to the protective layer was immersed therein and the liquid was applied by the dip method, and a film of the lubrication layer was formed. The film thickness of the lubrication layer was 14 . The concentration of the application liquid was adjusted, and those with the film thicknesses of the lubrication layer at 12 and 16 were also manufactured, respectively. It was found that, as the result of NMR analysis, the lubricant has the component A at approximately 85% and the component B at approximately 15% (weight ratio).

(51) A magnetic disk manufactured similarly to Example 1 except this point was obtained as Comparative Example 2.

(52) In FIG. 2, Comparative Examples 2-1 to 2-3 are illustrated and they indicate respective lots of the above tetraol GT.

(53) Subsequently, the magnetic disks in Examples and Comparative Examples were evaluated by using the following test methods.

(54) (Fixed-Point Floating Test)

(55) After each magnetic disk is exposed to a silicon gas for 24 hours, a back-off amount was set to 1.5 nm by using DFH of magnetic head under a high-temperature condition at 75 C. and then, a fixed-point floating test at a position of 20 mm of the disk radius was conducted for continuous two hours. The result is shown in FIGS. 1 and 2. The results of Examples 2 and 3 are not illustrated in FIG. 1 but the result similar to Example 1 was obtained. Also, the magnetic disk manufactured similarly to Example 1 except that as the lubricant, the compound C-1 (however, in the compound C-1, PN ring=P.sub.3N.sub.3(OC.sub.6H.sub.4CF.sub.3)x (x=5)) was used instead of the compound C-2 was also evaluated similarly, and it was found that the head contamination level was approximately 1.0, which is poorer than Example 1.

(56) In Examples 1, 2, and 3 and Comparative Example 1, a scratch was not observed in the medium but in Comparative Example 2, a crush failure occurred in the middle or a large number of scratches were observed in the medium.

(57) Subsequently, regarding aggregation of the lubricant after the above fixed-point floating test, observation was made by using an optical surface analyzer (OSA). As a result, in Comparative Example 1, a large number of aggregated spots (Mogul spots) of 2000 or more were observed but in Examples 1, 2, and 3 and Comparative Example 2, the number of aggregated spots (Mogul spots) was 500 or less, which showed a favorable characteristic.

(58) That is, the examples of the present invention show high abrasion properties represented by prevention of scratches and favorable characteristics in which the lubricant does not aggregate at the same time.