KR100438253B1 - Water soluble perfluoro polyether topcoat lubricants - Google Patents

Abstract

A water soluble or aqueous soluble salt of perfluoro polyether alcohol is applied to form a lubricant topcoat on the magnetic recording medium. Suitable water soluble salts include the sodium salt of perfluoro polyether diols.

Description

Water Soluble Perfluoro Polyether Topcoat Lubricant {WATER SOLUBLE PERFLUORO POLYETHER TOPCOAT LUBRICANTS}

Thin film magnetic recording disks and disk drives are commonly used to store large amounts of data in a magnetizable form. In operation, a typical contact start / stop (CSS) method is disclosed when the data conversion head begins to slide toward the surface of the disk as the disk rotates. When a certain high rotational speed is reached, the head is suspended in air at a predetermined distance from the surface of the disc held during the read and write operation. When the operation of the disk drive is terminated, the head starts to slide back to the surface of the disk, and eventually comes into contact with the disk and stops pressing the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats a circulating operation consisting of interruption, sliding toward the surface of the disk, floating in air, sliding toward the surface of the disk and stopping.

For optimal consistency and predictability, it is necessary to keep each transducer head as close as possible to the recording surface associated with it, i.e. to minimize the flying height of the head. Thus, it is desirable for the recording surface and the facing surface of the associated transducer head to be flat. However, if the head surface and the recording surface are too flat, an exact match of these surfaces will cause excessive stiction and friction during the start and stop phases, resulting in abrasion of the head and recording surface and eventually "head crash". Leads to a state referred to as ". Thus, there is a competing purpose of reducing head / disk friction and minimizing transducer flying heights.

Typical examples for solving these apparent competing purposes include providing a magnetic disk having a rough recording surface by a technique commonly referred to as "texturing" to reduce head / disk friction. Conventional texturing techniques include mechanically polishing or laser texturing the surface of the disk substrate to provide texture on the surface prior to subsequent deposition of layers such as underlayers, magnetic layers, protective overcoats and lubricant topcoats, Here the textured surface on the substrate is substantially reproduced in the subsequent deposition layer.

A representative longitudinal recording medium is shown in FIG. 1 and includes an aluminum (Al) alloy, such as an aluminum-magnesium (Al-Mg) alloy plated with a substrate 10, typically a layer of amorphous nickel-phosphorus (NiP). do. Alternative substrates include glass, glass-ceramic materials, and graphite. Substrate 10 contains chromium (Cr) or Cr-alloy underlayers 11 and 11 ', cobalt (Co) based alloy magnetic layers 12 and 12', generally carbon, deposited sequentially on each side. It is common to contain a protective overcoat 13, 13 ', and a lubricant topcoat 14, 14'. The lower chromium layers 11 and 11 'may be applied as a composite including a plurality of lower lower layers 11A and 11A'. Lower chromium layers 11 and 11 ', cobalt based alloy magnetic layers 12 and 12' and protective overcoats 13 and 13 'containing carbon in general are usually sputtered in a device with a continuous deposition chamber. deposited by a sputtering technique. Conventional aluminum alloy substrates are provided with NiP plating to primarily increase the hardness of the aluminum substrate, acting as a suitable surface that provides a texture that is substantially reproduced on the disk surface.

According to a typical example, a lubricant topcoat is applied evenly on the protective layer to prevent wear between the interface of the disk and the head during drive operation. Excessive wear of the protective overcoat, which typically includes carbon, increases the friction between the head and the disk, causing severe drive failure. Excessive lubricant at the head-disk interface causes high stiction between the head and the disk. If the stiction is excessive, the drive will not be able to start and severe failure will occur. Therefore, the lubrication layer thickness should be optimized for stiction and friction. Conventional materials used in lubricant topcoats include perfluoro polyethers (PFPE) which essentially comprise carbon, fluorine and oxygen atoms.

In view of the importance of lubricant topcoats, there is a continuing need to improve the adhesion of lubricants to protective carbon overcoats. Typical examples for controlling the degree of adhesion include heat treatment and UV curing of the lubricant.

Conventional lubricant topcoats formed from PFPE are very nonpolar molecules and therefore exhibit solubility only in fluorinated solvents. Over the years, Freon® solvents have been commonly used to form lubricant topcoats on magnetic recording media. However, most freons have been found to severely pollute the environment and are therefore banned in the United States. Current solvent substitutes for freon solvents include very expensive perfluorinated hexanes.

Accordingly, there is a need for a lubricant that is readily soluble in inexpensive solvents, especially aqueous solvents such as water or aqueous alcohol solutions, and which can be effectively used as a lubricant topcoat on magnetic recording media.

The present invention relates to a rotating magnetic recording medium, such as a thin film magnetic disk having a lubricant topcoat and a surface textured to contact, record and store magnetic data, particularly interlocking magnetic transducer heads. The present invention is particularly suitable for a method for applying a lubricant topcoat to a magnetic recording medium.

1 is a schematic diagram of a magnetic recording medium structure to which the present invention can be applied.

Detailed description of the invention

Conventional methods of producing magnetic recording media have a concomitant economic effect on manufacturing costs and include forming a lubricant topcoat by applying a lubricant dissolved in a fluorinated hydrocarbon, in particular perfluorinated hexane. Conventional methods for forming lubricant topcoats of magnetic recording media also include the use of emulsified fluorinated formulations, and Langmuir-Blogt, which places a lubricant solution in a fluorinated solvent on a disk containing water. Blodgget) technology. However, this conventional technique is disadvantageous because it requires the use of a fluorinated solvent.

In accordance with the present invention, there is provided a water soluble and aqueous alcohol soluble lubricant which is inexpensive, time saving and easily applied in a convenient manner to form a lubricant topcoat on a magnetic recording medium. The present invention enables the formation of a lubricant topcoat by a cost-effective technique of immersing a magnetic recording medium in an aqueous solution of a lubricant, while avoiding the use of environmentally harmful fluorinated solvents. Thus, by applying the lubricant topcoat 14 as a solution of a lubricant dissolved in water and / or an aqueous alcohol and drying, for example, by heating, a magnetic recording medium such as that shown in FIG. 1 can be advantageously produced. Can be.

Water-soluble lubricants according to the invention include salts of perfluoro polyether compounds having at least one hydroxyl group, for example salts of perfluoro polyether alcohols, for example salts of perfluoro polyether diols. Lubricants of the present invention may be prepared by reacting a perfluoro polyether alcohol with a metal cation base, a suitable organic cation or a basic metal by one of the following schemes:

^{_{PFPE-CH 2 OH + M +}} -OH - → PFPE-CH 2 O - M + + H 2 O

^{_{PFPE-CH 2 OH + M +}} H - → PFPE-CH 2 O - M + + H 2

PFPE-CH₂OH + M^+-(CH₂CH₂CH₂CH₃) → PFPE-CH₂O^-M⁺+ CH₃CH₂CH₂CH₃

2PFPE-CH ₂ OH + 2M ⁰ → 2PFPE-CH ₂ O ^- M ⁺ + H ₂

Wherein M is an alkali metal, alkaline earth metal, transition metal or organic cation.

It will be apparent to those skilled in the art that any perfluoro polyether alcohol can be used to prepare the salts used in the practice of the present invention. Indeed, the PFPE in the reaction may be of any type, including PFPE-1, PFPE-2, PFPE-3 and PFPE-4, provided that at least one free hydroxyl group is required to form a metal salt. Del Pesco, Perfluoralkylpolyethers, CRC Handbook of Lubrication and Tribology, Vol. III, pp. 287-303, 1994, Booser, E.R. ed., CRC Press, Boca Ration, FL.

In this regard, when used throughout this specification, the product obtained from the reaction of PFPE with a cation will be described as a "salt," although it may not conform to the classical definition of salt. In addition, perfluoro polyether alcohols are intended to include corresponding compounds in which the terminal methylene group containing hydroxyl is not perfluorinated.

In addition to the above general structures, perfluoro polyethers may have one or more hydroxyl groups for reaction with cations. In an embodiment of the invention, the perfluoro polyether is a linear polymer, such as PFPE-3 or PFPE-4, wherein at least one hydroxyl group is located at the end.

According to the present invention, conventional perfluoro polyether alcohol lubricants such as ZDOL® are modified by metal cations in the above scheme to render the perfluoro polyether alcohols water soluble. ZDOL (Ocimont USA, Toro Fair, NJ) is a linear perfluoro polyether diol having the following structure:

Wherein m and n are each 0 or an integer of about 100 or less.

Thus, one embodiment of the present invention comprises a water soluble linear perfluoro polyether diol salt having the structure:

Wherein M is a cation of an alkali metal, alkaline earth metal, transition metal or organic salt, and m and n are each 0 or an integer of about 100 or less.

ZDOL® of various molecular weights from about 100 to about 10,000, prepared from commercial sources by fractionation, are available, either of which may be used in the practice of the present invention. In one embodiment of the invention, an alcohol salt of ZDOL is produced having an average molecular weight of about 1000 to about 5000, for example 2000.

Another commercially available perfluoro polyether alcohol that may be used in the practice of the present invention is Denumnum SA (Nagase Co., Ltd.) having the following structure:

F (CF ₂ CF ₂ CF ₂ O) _n CF ₂ CF ₂ CH ₂ OH

Wherein n is an integer from about 15 to about 100.

Denumnum® SA is available in a molecular weight of about 1500 to about 8000, and molecular weights of about 100 to about 10,000 can be obtained by fractionation techniques such as flash chromatography or distillation. In another embodiment of the invention, Demnum® SA having an average molecular weight of about 1000 to about 5000, for example about 2000, is used.

In another embodiment of the present invention, the water soluble and / or aqueous alcohol soluble PFPE lubricants may be selected from perfluoro polyether alcohols for alkali metals, alkaline earth metals, cations or organic cations of transition metals (e.g. quaternary ammonium, phosphonium, It is produced by adding a basic source of sulfonium or the like to an aqueous solution containing an excess and mixing. In another embodiment of the present invention, the mixing is carried out by vigorous stirring to maximize the yield within a moderately short reaction time. Upon reaction with metal cations or organic cations, perfluoro polyether alcohols form precipitates that can be easily separated by standard techniques such as, for example, decantation, filtration and the like.

The separated perfluoro polyether alcohol salt precipitate is washed with deionized water such as 8 mPa water to remove excess salt reagent. The washed precipitate is dissolved in alcohol, for example alkanols of 1 to 5 carbon atoms, for example methanol, ethanol, propanol, isopropanol or butanol, and in an equal volume of Freon TF [Fluorinert®], or perfluorinated hexane Extraction is repeated repeatedly to remove any unreacted perfluoro polyether alcohol. The product PFPE, ie, the alcohol extract containing the alcohol salt product, is passed through a celite column, for example by gravity feed, and the solvent is removed under vacuum. The recovered product, which is a white precipitate, may be dissolved at a predetermined concentration suitable for aqueous alcohols, for example lower alkyl alcohols such as methanol, ethanol, propanol, butanol and the like. The recovered product can also be dissolved in the alcohol itself. Generally, the PFPE alcohol salt solution is reused at a concentration of about 0.01% (w / v) to about 100% (w / v), for example about 0.1% (w / v) to about 50% (w / v). Harm. In an embodiment of the invention, the PFPE alcohol salt solution is redissolved at a concentration of about 1% (w / v) to about 10% (w / v).

In the practice of the present invention, an amount of PFPE alcohol salt is diluted to the desired working concentration with water, for example deionized water, and / or a water soluble short chain alcohol solution. In general, useful working concentrations of PFPE alcohol salts in the practice of the present invention range from about 0.0001% (w / v) to about 10% (w / v), for example from about 0.001% (w / v) to about 1% (w). / v), for example about 0.01% (w / v) to about 0.5% (w / v). In one embodiment of the invention, the working concentration of the aqueous PFPE alcohol salt is about 0.1% (w / v) and the aqueous solution is heated to a temperature of about 40 ° C to about 100 ° C before use, and filtered using conventional techniques. do.

The PFPE alcohol salts produced according to the present invention can be applied to the magnetic recording medium by conventional techniques. For example, the working solution may be heated to a temperature of about 50 ° C to about 90 ° C. Using a lifter-type submerger, the magnetic disk is immersed in a lubricant solution and dipped for a time sufficient to completely cover the disk surface. It will be apparent to those skilled in the art that the time required to form the coating depends on the solution concentration and time, and the nature of the particular PFPE alcohol salt. For example, a immersion time of about 3 minutes was found to be sufficient to cover the disk surface using 0.1% (w / v) ZDOL sodium salt solution.

After a sufficient coating period has elapsed, the disk is slowly removed from the lubricant solution at a rate of about 0.01 mm / sec to about 10.0 mm / sec, for example about 0.1 mm / sec to about 1 mm / sec. The formed disk has a lubricant coating of about 15 kV to 30 kV as measured by Fourier transform infrared spectroscopy (FT-IR). The coated disc can then be dried at high temperature if it has not yet dried.

In another embodiment of the present invention, the disc is immersed for a time sufficient to form a coating thereon as described above, taken out of solution, and wiped excess lubricant solution by hand or with a mechanical wiping device. In this embodiment, low temperatures such as about 20 ° C. to about 40 ° C. may be used, and the immersion time may thus be varied. The disk formed contains a lubricant coating having a thickness of about 5 kPa to about 100 kPa depending on the lubricant solution formulation, the concentration of lubricant in the solution, the temperature of the lubricant solution and the structure of the thin film disk.

Surfactants may be added to the lubricant solution of the present invention to enhance the wetting of the thin film media. Suitable conventional surfactants include FLUORAD®, available from 3M Company, and other known surfactants may also be used. Surfactants are particularly useful in the low temperature application / wiping embodiments described above.

In another embodiment of the present invention, the wettability of the disk surface is increased to facilitate and improve the attachment and formation of lubricant topcoats. For example, the wettability can be increased by oxidizing the disk surface in a conventional manner such as plasma etching to provide a hydrophilic surface.

Lubricant topcoats on magnetic recording media formed in accordance with the present invention were evaluated in relation to static stiction, ie 1 RPM stiction on thin film and magnetic recording disks and SD-CSS performance, and are currently used such as AM2001 (Ausimont USA). It was shown to be as good or better as the lubricant. In addition, the PFPE alcohol salt lubricants according to the invention can advantageously use solvent systems which are much less expensive in applications which form lubricant topcoats. In addition, the present invention provides an excellent lubricant membrane that is free from the environmental problems associated with the use of conventional perfluorinated hydrocarbons and requires less operator effort.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a water soluble and / or aqueous alcohol soluble lubricant which can be easily applied to a magnetic recording medium to form a lubricant topcoat with excellent friction and stiction properties.

It is a further object of the present invention to provide a method of producing a water soluble lubricant for use as a lubricant topcoat in producing a magnetic recording medium.

Additional objects, advantages and other features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be derived from the embodiments of the invention. The objects and advantages of the invention may be realized or obtained as particularly pointed out in the appended claims.

According to the invention, this and other objects are achieved, in part, by a magnetic recording medium comprising a lubricant topcoat, wherein the lubricant is soluble in water, lower alkanols or solutions of lower alkanols and water.

Another aspect of the invention is a water soluble lubricant comprising a salt of a perfluoro polyether compound having at least one hydroxyl group.

Another aspect of the invention is a method of manufacturing a magnetic recording medium, comprising depositing a magnetic layer on a substrate and depositing a solution of a water soluble lubricant on the magnetic layer to form a lubricant top coat.

A further aspect of the present invention is to mix perfluoro polyether alcohols with alkali metal cations, alkaline earth metal cations, transition metal cations or organic cations to form precipitates; The resulting precipitate is washed with water; The washed precipitate is dissolved in a solvent; A method of producing a water-soluble perfluoro polyether alcohol, including recovering an alkali metal salt, alkaline earth metal salt, transition metal salt or organic salt of a perfluoro polyether alcohol.

Further objects and advantages of the invention will be readily apparent to those skilled in the art from the following detailed description, which is briefly described by way of illustration of the best mode contemplated for carrying out the invention embodiments of the invention. As will be appreciated, the invention may have different and different embodiments, and its several details may be modified in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded in an illustrative rather than a restrictive sense.

Example 1

10 ml of ZDOL 2,000, available from Ossimmont, was vigorously mixed with 30 ml of 50% sodium hydroxide solution in a Ernmeyer flask with a stir bar. A large amount of white precipitate formed and continued stirring by hand for 5 minutes. The excess sodium hydroxide solution was decanted and the white precipitate washed five times with deionized water. The white precipitate was then dissolved in 300 ml of methanol and extracted five times with Freon TF® to remove unreacted ZDOL. The methanol layer was filtered through celite by gravity and removed under vacuum to afford 12 g of ZDONa® as a white solid. ZDONa®, a white solid formed, was found to be soluble in aqueous methanol, isopropanol, water and alcohol solutions, but insoluble in Freons®, hexane, methylene chloride, acetone and perfluorinated hexane.

Lubricant solutions for forming lubricant topcoats on magnetic recording media can be prepared by simply dissolving the PFPE alcohol salts produced in accordance with the present invention in alcohol to prepare a solution and diluting the solution with water.

Example 2

5 g of ZDONa was dissolved in 10 ml of methanol by heating. The methanolic solution formed was diluted to 1 L with deionized water. This solution was then heated to 60 ° C. to 80 ° C. and filtered through cotton cloth filter paper. The solution formed can be used to form a lubricant topcoat on a magnetic recording medium.

Example 3

The procedure of Example 2 was followed except that ultrasonic energy was used to form the ZDONa solution in 10 ml of methanol.

Advantageously, the water soluble lubricant solution prepared according to the present invention can be easily applied to the magnetic recording medium to form the lubricant topcoat 14 on the magnetic recording medium, for example as shown in FIG. According to the present invention, the lubricant topcoat can be advantageously applied by immersing the disk in the lubricant solution and wiping by hand to remove excess lubricant for a time sufficient to form a lubricant topcoat on the disk. Although high temperatures are not necessarily required, it has been found to be convenient to form lubricant topcoats at high temperatures.

Example 4

The ZDONa lubricant solution prepared according to Example 2 was heated to about 50 ° C to 90 ° C. Using a lifter type submerger, the disc was immersed in the lubricant solution for 3 minutes and slowly removed from the solution at a rate of 0.1 mm / sec to 1.0 mm / sec. The disk formed was free of water stains and measured by FT-IR to have a uniform lubricant coating of about 15 kPa to about 30 kPa. In this example, ZDONa was used to test 1 rpm stiction and SD-CSS performance on thin-film disks lubricated with lubricant thicknesses of 10-11 kPa and 21-26 kPa. It has been shown to have a degree or better performance.

Those skilled in the art will appreciate that the lubricant coating thickness will vary depending on the particular lubricant solution formulation, the concentration of lubricant in the solution, the temperature of the lubricant solution and the structure of the thin film disc. Those skilled in the art will be able to easily adjust the relevant process parameters to achieve the desired lubricant coating thickness.

As described above, the lubricant solution according to the invention can be applied at high temperatures by immersing the disc in the lubricant solution and then wiping it with a hand or a machine. The disc prepared for application to the lubricant topcoat is immersed in the lubricant solution, removed from the solution and wiped by hand or machine, using a clean cotton handkerchief. In this way, a lubricant thickness of about 10 kPa to about 100 kPa may be obtained depending on the formulation and the wiping process.

The present invention is not limited to ZDOL alcohol salts. Rather, a variety of PFPE alcohols can be purchased, which will be similarly useful through the salt conversion. For example, Nammase's Denumnum® SA PFPE alcohol, available with a molecular weight of about 1,500 to about 8,000, can be used in the present invention. In an embodiment of the invention, Denumnum SA® alcohol having a molecular weight of about 1,000 to about 5,000 has been used successfully.

The PFPE alcohol salts according to the invention are not limited to sodium. Rather, alkali metal cations such as lithium, sodium, potassium, cesium and rubidium can be conventionally used. In addition, various alkaline earth metal cations such as beryllium, magnesium, calcium, strontium and barium can be used to form water soluble PFPE alcohol salts. In addition, various transition metal cations may be used, as well as organic cations such as quaternary ammonium (R ₄ N ⁺ ), sulfonium (R ₃ S ⁺ ) and phosphonium cations.

The present invention is not limited to a particular type of magnetic recording medium, but includes those in which the substrate or subsequently deposited layer is textured by, for example, mechanical treatment or laser technology, and the textured surface is almost reproduced on the later deposited layer. It can be used in many magnetic recording media. Thus, the lubricant produced according to the present invention forms, but is not necessarily limited to, a topcoat, for example a topcoat 14 on the magnetic recording medium shown in FIG.

Preferred embodiments of the present invention and some modified embodiments are described for the present invention. It is to be understood that the present invention can be used in a variety of different combinations and environments, and that it can be varied or modified within the scope of the invention presented herein.

Claims (31)

A magnetic recording medium comprising a lubricant topcoat, wherein the lubricant is soluble in water, lower alkanols, or a solution of lower alkanols and water, and is a salt of a fluoropolyether alcohol. 2. The magnetic recording medium of claim 1, wherein the salt of the fluoro polyether alcohol is a salt of the perfluoro polyether alcohol. The magnetic recording medium of claim 1, wherein the lubricant is a salt of a perfluoro polyether alcohol having at least one hydroxyl group. delete 2. The magnetic recording medium of claim 1, wherein the lubricant is a sodium salt of perfluoro polyether diol. 4. The magnetic recording medium of claim 3, wherein the salt of perfluoro polyether alcohol is a salt of linear perfluoro polyether diol of the structure: Wherein M is an alkali metal, an alkaline earth metal, a cation of a transition metal or a cation of an organic salt, and m and n are each 0 or an integer of 100 or less. delete A solvent selected from the group consisting of water, lower alkanols, and mixtures of water and lower alkanols; And a salt of a perfluoro polyether alcohol dissolved in the solvent. 9. The lubricant solution of claim 8 wherein the salt of perfluoro polyether alcohol is a salt of linear perfluoro polyether diol of the structure: Wherein M is an alkali metal, an alkaline earth metal, a cation of a transition metal or a cation of an organic salt, and m and n are each 0 or an integer of 100 or less. 10. The lubricant solution of claim 9 wherein the average molecular weight of the linear perfluoro polyether diol is between 1000 and 5000. delete 9. The lubricant solution of claim 8 wherein the salt of perfluoro polyether alcohol is a sodium salt of linear perfluoro polyether diol. The lubricant solution of claim 8 wherein the perfluoro polyether alcohol has the following structural formula: F (CF ₂ CF ₂ CF ₂ O) _n CF ₂ CF ₂ CH ₂ OH Wherein n is an integer from 15 to 100. delete delete Depositing a magnetic layer on the substrate; And depositing a lubricant solution of water, lower alkanol, or a salt of fluoro polyether alcohol dissolved in a solution of water and lower alkanol on a magnetic layer to form a lubricant top coat. How to manufacture. 17. The method of claim 16, wherein a protective overcoat is deposited on the magnetic layer and a lubricant topcoat is deposited on the protective overcoat. 18. The method of claim 17, wherein the salt of the fluoro polyether alcohol is a salt of the perfluoro polyether alcohol. 19. The method of claim 18, wherein the salt of the perfluoro polyether alcohol is a salt of the perfluoro polyether alcohol formed by an alkali metal, an alkaline earth metal, a cation of a transition metal or a cation of an organic salt. delete delete 19. The process of claim 18, wherein the salt of the perfluoro polyether alcohol is a salt of the linear perfluoro polyether diol of the structure: Wherein M is an alkali metal, an alkaline earth metal, a cation of a transition metal or a cation of an organic salt, and m and n are each 0 or an integer of 100 or less. delete delete delete delete delete 2. The magnetic recording medium of claim 1, comprising a substrate, a magnetic layer on the substrate, a protective overcoat on the magnetic layer, and a lubricant topcoat on the protective overcoat. 19. The method of claim 18, wherein the substrate comprising the magnetic layer and the protective overcoat is immersed in a solution, immersed, and slowly removed and dried. 30. The method of claim 29, wherein the solution is heated to 50 ° C to 90 ° C. delete