Ionic perfluoropolyether lubricant

Abstract

An ionic lubricant includes a single lubricant compound having a perfluoropolyether main chain, wherein each end of the perfluoropolyether main chain is terminated by an end group, and at least one of the end groups includes an ionic bond and at least one functional group. The ionic perfluoropolyether lubricant has unique characteristics that allows its ultra-thin and uniform distribution over a protective overcoat layer of a magnetic recording medium, while at the same time providing its molecules with strong adhesion power to the protective overcoat layer of the magnetic recording medium compared to existing lubricants, so as to provide shorter magnetic spacing between the magnetic recording medium and the magnetic head, and enable longer operation hours for the magnetic recording medium.

Claims

1. An ionic lubricant, comprising: a single lubricant compound having a perfluoropolyether main chain and ends, each end of the perfluoropolyether main chain being terminated by an end group, and at least one end group consisting of an ionic bond, at least one functional group, and a hydrocarbon chain interposed between the ionic bond and the at least one functional group, wherein the perfluoropolyether main chain is represented by one of chemical formulae (A) through (D) as follows: ##STR00014## where m and n are positive integers,
O(CF.sub.2CF.sub.2CF.sub.2O).sub.m(B), where m is a positive integer,
O(CFCF.sub.2O).sub.m(C), where m is a positive integer, and
O(CF(CF.sub.3)CF.sub.2O).sub.m(D), where m is a positive integer, and wherein the ionic bond is positioned between a carboxylic acid group and a basic amino group, and wherein the at least one functional group is a hydroxyl group or a phenyl group.

2. The ionic lubricant according to claim 1, wherein the at least one end group comprises from 3 to 6 carbon atoms.

3. The ionic lubricant according to claim 1, wherein the ionic bond is positioned at least two chemical bonds from the end of the perfluoropolyether main chain.

4. An ionic lubricant represented by chemical formulae (1) through (5) as follows: ##STR00015## where m and n are positive integers, ##STR00016## where m and n are positive integers, ##STR00017## where m and n are positive integers, ##STR00018## where m and n are positive integers, and ##STR00019## where m and n are positive integers.

5. A magnetic recording medium, comprising: a substrate; a magnetic layer provided over the substrate; a protective layer provided over the magnetic layer; and a lubricating layer provided over the protective layer and being comprised of the single lubricant compound according to claim 1.

6. The magnetic recording medium according to claim 5, wherein the ionic bond is positioned at least two chemical bonds from the end of the perfluoropolyether main chain.

7. The magnetic recording medium according to claim 5, wherein the at least one end group comprises from 3 to 6 carbon atoms.

8. An ionic lubricant, comprising: a single lubricant compound having a perfluoropolyether main chain and ends, each end of the perfluoropolyether main chain being terminated by an end group, and at least one end group consisting of an ionic bond, at least one functional group, and a fluorocarbon chain interposed between the ionic bond and the at least one functional group, wherein the perfluoropolyether main chain is represented by one of chemical formulae (A) through (D) as follows: ##STR00020## where m and n are positive integers,
O(CF.sub.2CF.sub.2CF.sub.2O).sub.m(B), where m is a positive integer,
O(CFCF.sub.2O).sub.m(C), where m is a positive integer, and
O(CF(CF.sub.3)CF.sub.2O).sub.m(D), where m is a positive integer, and wherein the ionic bond is positioned between a carboxylic acid group and a basic amino group, and wherein the at least on functional group is a hydroxyl group or a phenyl group.

9. The ionic lubricant according to claim 8, wherein the end group comprises from 3 to 6 carbon atoms.

10. The ionic lubricant according to claim 8, wherein the ionic bond is positioned at least two chemical bonds from the end of the perfluoropolyether main chain.

11. A magnetic recording medium, comprising: a substrate; a magnetic layer provided over the substrate; a protective layer provided over the magnetic layer; and a lubricating layer provided over the protective layer and being comprised of the single lubricant compound according to claim 8.

12. The ionic lubricant according to claim 11, wherein the end group comprises from 3 to 6 carbon atoms.

13. The magnetic recording medium according to claim 11, wherein the ionic bond is at least two chemical bonds from the end of the perfluoropolyether main chain.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be described in conjunction with a single drawing which is only for the purpose of illustrating the embodiments of the present invention, and not for the purpose of limiting the present invention.

(2) FIG. 1 is a cross-sectional view of a magnetic recording medium according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) The invention is described in detail in reference to the Examples below and the accompanying FIG. 1.

(4) The invention relates to an ionic type perfluoropolyether lubricant. The lubricant is especially suited for the lubrication of a magnetic recording medium (MRM). The lubricant is applied as a lubricating layer 4 over the top surface of the magnetic disk, which is typically a carbon coated protective overcoat layer 3. Due to its molecular structure, the lubricant can easily achieve a thin but uniform coverage over the entire surface of the MRM, which is preferred for example in an ultra compact portable hard disk drive with high storage capacities, for example, in the range of 1 to 3 terabytes (TB). The ultra thin lubrication layer 4 allows the MRM to rotate closer to the magnetic head, reduces wear and tear of the MRM, thus achieving high capacity storage while keeping the portable hard disk drive reliable and durable, despite its ultra compact dimensions.

(5) In an example of the present invention, the lubricant is PFPE type consisting of a main chain and two end groups each terminating the main chain. The main chain has the following chemical formula (A):

(6) ##STR00007##
where m, n are positive integers.

(7) The lubricant molecule has only one main chain of formula (A). This feature is preferable in obtaining the desired low viscosity of the lubricant. Formula (A) is the main chain of a common PFPE, commercially known as Fomblin PFPE. Fomblin lubricants are fluorinated lubricants most suitable in aggressive chemical environments, high temperatures or where wide working-temperature ranges are involved.

(8) Notwithstanding the above PFPE main chain, other types of PFPE main chain may also be used, such as O(CF.sub.2CF.sub.2CF.sub.2O).sub.m (Demnum), O(CFCF.sub.2O).sub.m, or O(CF(CF.sub.3)CF.sub.2O).sub.m.

(9) Preferably, each end group of the lubricant molecule has at least one ionic bond and at least one functional group.

(10) The ionic bond furnishes the lubricant with unique characteristics. The presence of ionic bond as a result of the strong electrostatic interaction between the cation and the anion in the salts could raise the boiling point of the ionic lubricant. Conventional lubricants which consist of mainly covalent bond may suffer the disadvantage of undergoing evaporation with time at high operating temperatures, hence reducing their protection effects over the MRM surface. The use of low-volatility ionic lubricant will help to reduce the evaporation rate and prolong the life of the MRM.

(11) The example of ionic bond is O.sup.N.sup.+ derived from carboxylic acid group (COOH) and amino group. Carboxylic acid can donate a hydrogen ion (H+) to the nitrogen lone pair of the amino group.

(12) The lubricant has at least one functional group in the end group. The first preferred functional group in an embodiment of the present invention is a hydroxyl group (OH). A second preferred functional group in an embodiment of the present invention is a phenyl group. It is of course to be appreciated that other functional groups may be used as well. The functional group will interact with the elements, such as carbon, of the protective overcoat layer 3 and anchor the lubricant molecule to the protective overcoat layer 3. This will give the lubricant molecules an adhesive force to latch onto the protective overcoat layer 3. The adhesive force will help to prevent the lubricant molecules from being scattered when the MRM is in use. Most hard disk drives spin their magnetic recording medium up to 7200 RPM when in use. Therefore, this adhesive characteristic is obviously advantageous when the lubricant molecules are subjected to such high centrifugal force by the spinning MRM.

(13) The examples of the end groups are represented by formula (E) to (I) which follow.

(14) ##STR00008##

(15) The number of carbons in the end group may be changed from the above examples. The preferred number of carbon atoms in the end group according to an embodiment of the present invention is from 3 to 6 carbon atoms. By increasing the carbon atoms of non-polar component (in case of the figures above, carbons disposed at right side of the ionic bond) in the end group, this could improve the solubility of the ionic salt in organic solvent. Apart from that, by introducing hydrocarbon chain into the lubricant is also beneficial in order to achieve a balance of the hydrophobic and hydrophilic properties of the lubricant to ensure better coverage and low friction coefficient of the lubricants.

(16) It is possible to adopt two or more functional groups in the lubricant.

EXAMPLE 1

(17) The lubricant material was obtained by reacting the Fomblin Z DIAC PFPE lubricant (manufactured by Solvay Specialty Polymers) with the amino-alcohol molecule. The mixture of Z DIAC and a 5% excess of the long chain amino-alcohol is warmed to 80-90 C. with constant stirring until complete dissolution is obtained. The salt formed after the reaction is then rinsed with hexane in order to remove the excess amino-alcohol. The chemical structure of the synthesized ionic salt can be characterized by infrared spectroscopy (FT-IR).

(18) Scheme 1 below illustrates the synthetic scheme for the proposed ionic lubricant formula (1). Fomblin Z DIAC, i.e., COOHCF.sub.2O[CF.sub.2CF.sub.2O]m[CF.sub.2O]nCF.sub.2COOH, and 4-amino-1-butanol are used. The carboxylic acid end group (COOH) donates a hydrogen ion (H+) to the nitrogen lone pair of the amino group and forms ammonium ion. Both end groups have long chain hydrocarbon with an ester, amide, alcohol and carboxylate ammonium salt. The hydroxyl group (OH) in 4-amino-1-butanol anchors or adhere the resultant molecule to MRM's protective overcoat layer 3, which comprises carbon.

(19) ##STR00009##
where m, n are positive integers.

EXAMPLE 2

(20) The lubricant material was obtained by reacting the Fomblin Z DIAC PFPE lubricant (manufactured by Solvay Specialty Polymers) with 4-amino-2-propanol. The mixture of Z DIAC and a 5% excess of the long chain 4-amino-2-propanol is warmed to 80-90 C. with constant stirring until complete dissolution is obtained. The salt formed after the reaction is then rinsed with hexane in order to remove the excess amino-alcohol. The chemical structure of the synthesized ionic salt can be characterized by infrared spectroscopy (FT-IR).

(21) Scheme 2 which follows illustrates the synthetic scheme for the proposed ionic lubricant formula (2). Fomblin Z DIAC, i.e., COOHCF.sub.2O[CF.sub.2CF.sub.2O]m[CF.sub.2O]nCF.sub.2COOH, and 4-amino-2-propanol are used. The carboxylic acid end group (COOH) donates a hydrogen ion (H+) to the nitrogen lone pair of the amino group and forms ammonium ion. Both end groups have long chain hydrocarbon with an ester, amide, alcohol and carboxylate ammonium salt. The hydroxyl group (OH) in 4-amino-2-propanol anchors or adhere the resultant molecule to MRM's protective overcoat layer 3, which comprises carbon. The hydroxyl group acts as the branched group from the linear PFPE ionic molecule.

(22) ##STR00010##
where m, n are positive integers.

EXAMPLE 3

(23) The lubricant material was obtained by reacting the Fomblin Z DIAC PFPE lubricant (manufactured by Solvay Specialty Polymers) with 4-amino-1-fluorobutanol. The mixture of Z DIAC and a 5% excess of the long chain 4-amino-1-fluorobutanol is warmed to 80-90 C. with constant stirring until complete dissolution is obtained. The salt formed after the reaction is then rinsed with hexane in order to remove the excess amino-alcohol. The chemical structure of the synthesized ionic salt can be characterized by infrared spectroscopy (FT-IR). Replacing the hydrocarbon chain (CH.sub.2) with a fluorocarbon chain (CF.sub.2) improves the wettability and solubility of the resultant lubricant. The resultant lubricant is also chemically and thermally more stable than its hydrocarbon counterpart.

(24) Scheme 3 which follows illustrates the synthetic scheme for the proposed ionic lubricant formula (3). Fomblin Z DIAC, i.e., COOHCF.sub.2O[CF.sub.2CF.sub.2O]m[CF.sub.2O]nCF.sub.2COOH, and 4-amino-1-fluorobutanol are used. The carboxylic acid end group (COOH) donates a hydrogen ion (H+) to the nitrogen lone pair of the amino group and forms ammonium ion. Both end groups have long chain fluorocarbon with an ester, amide, alcohol and carboxylate ammonium salt. The hydroxyl group (OH) in 4-amino-1-fluorobutanol anchors or adhere the resultant molecule to MRM's protective overcoat layer 3, which comprises carbon.

(25) ##STR00011##
where m, n are positive integers.

EXAMPLE 4

(26) The lubricant material was obtained by reacting the Fomblin Z DIAC PFPE lubricant (manufactured by Solvay Specialty Polymers) with the amino-alcohol molecule. The mixture of Z DIAC and a 5% excess of the long chain amino-alcohol is warmed to 80-90 C. with constant stirring until complete dissolution is obtained. The salt formed after the reaction is then rinsed with hexane in order to remove the excess amino-alcohol. The chemical structure of the synthesized ionic salt can be characterized by infrared spectroscopy (FT-IR).

(27) Scheme 4 which follows illustrates the synthetic scheme for the proposed ionic lubricant formula (4). Fomblin Z DIAC, i.e., COOHCF.sub.2O[CF.sub.2CF.sub.2O]m[CF.sub.2O]nCF.sub.2COOH, and the diol of NH.sub.2CH.sub.2CHOHCH.sub.2OH (3-aminopropan-1,2-ol) are used. The carboxylic acid end group (COOH) donates a hydrogen ion (H+) to the nitrogen lone pair of the amino group and forms ammonium ion. Both end groups have long chain hydrocarbon with an ester, amide, alcohol and carboxylate ammonium salt. The hydroxyl group (OH) in 3-aminopropan-1,2-ol anchors or adhere the resultant molecule to MRM's protective overcoat layer 3. It is note that the terminal ends have two hydroxyl groups, and thereby providing stronger anchoring/adhesive power to the MRM's protection layer, which comprises carbon.

(28) ##STR00012##
where m, n are positive integers.

EXAMPLE 5

(29) The lubricant material was obtained by reacting the Fomblin Z DIAC PFPE lubricant (manufactured by Solvay Specialty Polymers) with 4-phenylbutylamine. The mixture of Z DIAC and a 5% excess of the long chain 4-phenylbutylamine is warmed to 80-90 C. with constant stirring until complete dissolution is obtained. The salt formed after the reaction is then rinsed with hexane in order to remove the excess phenylbutylamine. The chemical structure of the synthesized ionic salt can be characterized by infrared spectroscopy (FT-IR). Replacing the hydroxyl group (OH) with phenyl group (C.sub.5H.sub.5) improves lubricant coverage, as phenyl rings are flatter than hydroxyls. This results in a thinner lubrication layer, and thus reduces the magnetic spacing further.

(30) Scheme 5 which follows illustrates the synthetic scheme for the proposed ionic lubricant formula (5). Fomblin Z DIAC, i.e., COOHCF.sub.2O[CF.sub.2CF.sub.2O]m[CF.sub.2O]nCF.sub.2COOH, and 4-phenylbutylamine are used. The carboxylic acid end group (COOH) donates a hydrogen ion (H+) to the nitrogen lone pair of the amino group and forms ammonium ion. Both end groups have long chain hydrocarbon with an ester, amide, benzene and carboxylate ammonium salt. The phenyl group (C.sub.6H.sub.5) in 4-phenylbutylamine can lie flatter and adhere the resultant molecule to MRM's protective overcoat layer 3, which comprises carbon.

(31) ##STR00013##

EXAMPLE 6

(32) The magnetic recording medium with the cross-sectional view as shown in FIG. 1 with the lubricant represented by the formulae (1) through (5) is prepared.

(33) The substrates used are 65 mm diameter rigid magnetic disks 5 composed of glass substrates 1. A magnetic layer 2 comprised of chromium and cobalt-based recording layer is sputter-deposited onto the substrate followed by the deposition of protective nitride carbon overcoat layer 3 through plasma-enhanced chemical vapor deposition (PECVD) process. The lubricant 4 is applied onto the protective overcoat layer 3 by using a dip-coating method. Each of the ionic lubricant material of formulae (1) through (4) is mixed with fluorinated solvent. The solvent was Vertrel/methanol (manufactured by Dupont). The concentration of the lubricant material in the solution was 0.5% by weight. The film thickness after dipping was quantified using FT-IR spectroscopy method (grazing angle). Each sample showed satisfactory results.

(34) The number of main chains in every embodiment of the present invention is kept to a minimum, which resulted in small, uncomplicated lubricant molecules. The presence of an ionic bond at the end group gives the lubricant physical properties that are typical of ionic bonds including high boiling point, and partial solubility in water when combined with the hydrophobic properties of the hydrocarbon and fluorocarbon end groups. The presence of the functional group, hydroxyl, anchors/adheres the lubricant molecule to the carbon-based protective overcoat layer 3 (protective layer), and this maintains the lubricant molecules firmly over the protective overcoat layer 3.

(35) Therefore, it can be surmised that ionic PFPE lubricants of the kind represented by the five types of ionic PFPE lubricants described in examples 1 through 5 of the description have the potential to provide advantageous results and properties over existing PFPE lubricants, in terms of distribution uniformity, protection/operation longevity, and improved recording density as a result of reduced magnetic spacing when applied to a magnetic recording medium (MRM).

(36) It is understood that the invention may be embodied in numerous other ways without departing from the scope of the invention.