KR100457729B1 - Polymerizable Perfluoropolyether Phosphate Lubricant Topcoat - Google Patents

Abstract

In the present invention, the binding degree of the perfluoro polyether lubricant topcoat 14, 14 'to the magnetic recording medium is improved by forming its high molecular weight phosphate derivative. In an embodiment of the present invention, the perfluoropoly Ether phosphate polymers have a molecular weight of about 1000 to about 5000, and are applied to a magnetic recording medium to exceed a lubricant binding ratio of 0.9.

Description

Polymerizable Perfluoro Polyether Phosphate Lubricant Topcoat

FIELD OF THE INVENTION The present invention relates to magnetic recording media, in particular rotatable magnetic recording media such as lubricant topcoats and thin film magnetic disks for cavity magnetic transducer head contacts. The invention is particularly applicable to textured magnetic recording media comprising a lubricant topcoat with a high lubricant binding ratio.

Thin film magnetic recording disks and disk drives are commonly used to store large amounts of data in magnetizable form. In operation, a general contact start / stop (CSS) method is initiated when the data conversion head begins to slide relative to the disk surface as the disk begins to rotate. When a certain high rotational speed is reached, the head floats in air at a predetermined distance from the disk surface, and this state is maintained during read and write operations on the disk surface. In order to finish the work of the disc drive, the head starts to slide against the disc surface again and eventually comes into contact with the disc and stops by pressing. Each time the head and disk assembly is actuated, the running surface of the head repeats a cycle of stops, sliding to the disk surface, floating in air, sliding and stopping to the disk surface.

For optimum consistency and predictability, keeping each transducer head as close as possible to the relevant recording surface, i.e. minimizing the float height of the head, is essential. Therefore, it is desirable that not only the recording surface be smooth, but also that the facing surface of the associated transducer head is smooth. However, if the head surface and the recording surface are too flat, this exact matching of the surface will cause excessive wear and friction during start and stop conditions, causing wear to the head surface and the recording surface, and ultimately a "head crash". Cause. Accordingly, efforts have been made to reduce head / disk friction and minimize the floating height of the transducer.

A common practice for addressing this clear purpose is to reduce the head / disk friction by providing a rough recording surface on the magnetic disk by a technique generally referred to as "texturing". Conventional texturing methods involve mechanically polishing or laser texturing the surface of a disk substrate to provide a texture over the substrate prior to subsequent deposition layers such as underlayers, magnetic layers, protective overcoats and lubricant topcoats. Where the textured surface on the substrate is substantially replicated in the subsequently deposited layer. The underlying layer surface may also be textured, which texture is substantially replicated in the subsequently deposited layer.

A representative longitudinal recording medium is shown in FIG. 1, which forms the substrate 10 as an aluminum (Al) alloy such as an aluminum-magnesium (Al-Mg) alloy plated with an amorphous nickel-phosphorus (NiP) layer. Include. Still other substrates include glass, glass-ceramic materials, and graphite. Substrate 10 typically has a chromium (Cr) or Cr-alloy underlayer (11, 11 '), a cobalt (Co) based alloy magnetic layer (12, 12'), a protective overcoat generally deposited on each side. Troughs 13 and 13 'and generally include carbon and lubricant topcoats 14 and 14'. The chromium bottom layer 11, 11 ′ may be applied as a composite comprising a plurality of sub sublayers 11A, 11A ′. Cr underlayers 11, 11 ′, Co based alloy magnetic layers 12, 12 ′ and protective overcoats 13, 13 ′, typically comprising carbon, are usually sputtered in a device comprising a continuous deposition chamber. It deposits by implementing the sputtering method. Conventional Al alloy substrates are formed with NiP plating, which primarily increases the hardness of the Al substrate, thereby serving as a suitable surface to provide a texture that is substantially reproduced on the disk surface.

In accordance with conventional practice, the lubricant topcoat is evenly applied on the protective overcoat to prevent wear between the disk and the head interface during drive operation. Excessive wear of the protective overcoat increases friction between the head and the disk, resulting in an unrecoverable drive failure. If excess lubricant is used in the head disk interface, the stiction between the head and the disk increases. If the stiction is excessive, the drive cannot be started, resulting in an unrecoverable failure. Therefore, lubricant thickness must be optimized for stiction and friction.

Conventional materials used for lubricant topcoats include perfluoro polyethers (PFPE) having carbon, fluorine and oxygen atoms as essential ingredients. However, the expression "perfluoro polyether" as used herein includes groups that are not fully perfluorinated, such as the terminal methylene groups attached to hydroxyl radicals do not contain any fluorine. Lubricants are usually applied to magnetic recording media by techniques such as heat treatment, UV irradiation and dipping to dissolve in the combined organic solvent. An important factor in the performance of the lubricant topcoat is the bonded lube ratio, which is the ratio of the amount of lubricant directly bonded to the magnetic recording medium to the amount of lubricant bound to itself or to the mobile lubricant. Preferably, the lubricant bonding ratio should be high to significantly improve the stiction and wear performance of the formed magnetic recording medium.

In view of the importance of lubricant topcoats in magnetic recording media, there is a continuing need for improved uniform bonding of lubricant topcoats to magnetic recording media, particularly protective carbon overcoats. There is also a need for an improved lubricant for use as a topcoat in the manufacture of magnetic recording media that can achieve high lubricant bonding ratios.

Fig. 1 schematically shows the structure of a magnetic recording medium to which the present invention can be applied.

Figure 2 shows Fourier modified infrared (FT-IR) spectra of the phosphate polymers of the present invention.

Figure 3 shows the FT-IR spectrum of ZDOL-4000 as a conventional polyether alcohol.

Figure 4 is a graph showing the test results comparing the efficacy of the lubricant top coat of the present invention and the efficacy of conventional lubricants.

5 is a graph showing the results of comparing the efficacy of the lubricant top coat of the present invention and the efficacy of the conventional lubricant.

6 shows lubricant binding to ZDOL-4000, Z4000 / POCl ₃ (1: 1), Z4000 / POCl ₃ (1: 2), Z4000 / POCl ₃ (1: 4) and 2400 / POCl ₃ (1: 6) It is a graph showing the ratio.

FIG. 7 shows the reaction taking place to form a perfluoropolyether phosphate polymer from a mixture of PFPE diol and PFPE alcohol, where the letters c-f are integers from about 0 to about 10.

Best Modes for Carrying Out the Invention

The present invention relates, in particular, to a group of lubricants which can advantageously be used as lubricant topcoats on magnetic recording media while having a high degree of bonding to protective overcoats such as carbon containing protective overcoats. A particularly advantageous feature of the lubricant group of the present invention is that it has a high affinity for carbon, so that the lubricant forms a strong adhesive bond to the carbon-containing protective overcoat. As a result, the lubricant topcoat of the present invention preferably not only reduces stiction, but also increases wear resistance and durability.

In accordance with the present invention, the phosphate polymer can be formed from any of a variety of perfluoro polyether alcohol lubricants such as those conventionally used to form lubricant topcoats on magnetic recording media. In an embodiment of the present invention, a perfluoro polyether phosphate polymerizable lubricant having the following structure is formed by the following series of reactions.

Wherein PFPE- {CH ₂ OH} ₂ is a perfluoro polyether diol, POCl ₃ is phosphorus oxychloride, and a to f are integers from about 0 to about 10.

The present invention also provides a series of lubricants that can adjust the lubricant binding ratio to greater than 0.4 and even greater than 0.9 by controlling the synthesis reaction chemistry. By controlling the reaction time, the reaction temperature and the ratio of reactants, the ratio of PFPE alcohol and phosphorus oxychloride, the lubricant binding ratio of the magnetic medium prepared from the series of lubricants formed can be adjusted to exceed about 0.4 to 0.9. Advantageously, the lubricants of the present invention are soluble in organic solvents such as conventional solvents such as Freon® and perfluorohexane. The lubricant of the present invention can be applied to the magnetic recording medium using an easy method such as dip-coating in a lubricant solution dissolved in a conventional organic solvent.

The lubricant used in the present invention is a perfluorinated polyether phosphate, and the synthetic reaction chemistry is adjusted to control the final direct amount of lubricant bound to the magnetic recording medium. One of ordinary skill in the art will readily be able to determine the optimal synthetic reaction chemistry after learning that the above object of the present invention is a result-effective variable that directly affects the degree of binding. According to the present invention, it has been found that as the PFPE diol / POCl ₃ ratio decreases and the reaction temperature and reaction time increase, the direct binding of polyether phosphate polymers to substrates such as protective carbon overcoats increases. For example, phosphate polymers prepared from ZDOL-4000 and POCl ₃ reacted at a ratio of 1/6 (mol / mol) for about 30 hours at a reaction temperature of about 70 ° C. with high binding such as lubricant binding ratios greater than 0.9 It has been found to provide a figure. Compare with FIG.

In embodiments of the invention, conventional perfluoro polyether alcohol compounds, such as ZDOL, can be reacted with phosphorus oxychloride, for example to prepare the lubricants of the invention. ZDOL (Ausimont USA, Thorofare, NJ) is a linear perfluoro polyether diol compound having the structure:

Where

m and n are independently integers of 0 or 100 or less.

ZDOLs are available in various molecular weights from about 100 to about 10,000, prepared from commercially available sources, any of which may be used to synthesize the lubricants used in the practice of the present invention.

It will be apparent to those skilled in the art that perfluoro polyether alcohols can be used to prepare the corresponding phosphate polymers used in the practice of the present invention. In fact, the PFPE used in the present invention may be of any type, including PFPE-1, PFPE-2, PFPE-3 and PFPE-4. See Del Pesco, Perfluoroalkylpolyethers, CRC Handbook of Lubrication and Tribology, Vol. III, pp. 287-303, 1994, Booser, E. R. ed. CRC Press, Boca Raton, FL].

Another commercially available perfluoro polyether alcohol compound that can be used to synthesize phosphate lubricants useful in 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

Where

n is an integer from about 15 to about 100.

Denumnum SA is available in molecular weights ranging from about 1,500 to about 8,000, and those having a molecular weight of about 200 to about 10,000 can be obtained by fractionation methods such as flash chromatography or distillation. In another embodiment of the invention, Demnum SA having an average molecular weight of about 1,000 to about 5,000, for example 2,000, can be used.

The lubricant topcoat of the present invention may be applied on either the magnetic layer of the magnetic recording medium or on a conventionally applied protective overcoat, in particular carbon overcoat. In an embodiment of the invention, the lubricant is from about 0.0001% to about 100% (weight / weight), preferably from about 0.001% to about 0.5% in conventional organic solvents such as Freon® or perfluorohexane Dissolves. A common magnetic recording medium, for example a composite comprising a nonmagnetic substrate on which each of the lower layers, the magnetic layer and the protective carbon overcoat are sequentially deposited, is immersed in a lubricant solution and then slowly recovered therefrom. In the practice of the present invention, a conventional lifter-type dipper may be used to immerse the composite in the lubricant solution.

One skilled in the art can easily optimize the immersion duration and recovery rate to achieve the desired coating thickness. Surprisingly, lubricants of the present invention, in particular lubricants prepared from PFPE alcohols having a molecular weight of about 1,000 to 5,000, can form lubricant topcoats with lubricant bond ratios greater than 0.9 at various thicknesses, such as about 8 kPa to about 25 kPa.

The lubricant of the present invention is characterized by forming a top coat that is uniformly bonded with a significantly high lubricant bonding ratio. In view of this high lubricant bonding ratio, under certain circumstances, for example, application of any thin mobile lubricant layer, for example from about 1 kPa to about 15 kPa, to the combined lubricant topcoat to further enhance stiction and wear performance It is advantageous. Magnetic recording media made in accordance with the present invention exhibit low static friction and increased durability during CSS testing.

Example

In the vial, ZDOL-4000 (5 g: 0.31 mm) and phosphorus oxychloride (0.05 mL; 0.53 mm) were mixed with vigorous stirring. After about 5 hours, the mixture was heated to about 70 ° C. and stirred for about 72 hours, then further phosphorus oxychloride (0.2 mL; 2.1 mm) was added and the mixture was further stirred at about 70 ° C. for about 24 hours. The mixture was then cooled and chromatographed on SiO ₂ . Elution with Freon TF (TM) gave a white semisolid. Further elution with Freon® TA gave 3.3 g (66%) of clear oil. The reaction taking place is as follows:

The FT-IR spectrum of the formed phosphate polymer is shown in FIG. 2, which shows two phosphates at 1292 cm ⁻¹ and a carbon fluorine of about 1200 to 1000 cm ⁻¹ . For comparison, the FT-IR spectrum of ZDOL-4000 is shown in FIG. 3.

The phosphate polymers of the ZDOL-4000 lubricant of the present invention were tested against ZDOL-4000 and Dermnum SP3 as commercial lubricants commonly used to form lubricant topcoats for magnetic recording media. In each case, the magnetic recording medium was made of the same structure, namely the substrate, the underlayer, the magnetic layer and the protective carbon overcoat except for the difference in the lubricant topcoat. The results shown in FIG. 4 demonstrate that the lubricant binding ratio of the phosphate polymer lubricants of the present invention is excellent and the stiction performance for each ZDOL-4000 and Dermnum SP3 is excellent.

In another comparison, phosphate polymers of ZDOL-4000 lubricants prepared according to the present invention were tested against HMW ZDOL-2000, another lubricant commonly used to form lubricant topcoats. As in the comparison, magnetic recording media of the same structure were compared except for the lubricant topcoat. The thickness of the lubricant topcoat of the magnetic recording medium according to the present invention was 18 kPa and 19 kPa while the ZDOL-2000 topcoat thickness of the comparative medium was 13 kPa, 16 kPa and 19 kPa. The results shown in FIG. 4 demonstrate that the lubricant topcoat of the present invention has superior stiction performance compared to conventional ZDOL-2000 lubricants.

The lubricant topcoat of the present invention advantageously achieves a high lubricant binding ratio and shows good stiction performance. The present invention is not limited to any particular type of lubricant in that the concept of forming phosphate polymers with controlled reaction chemistry to optimize direct lubricant binding can be applied to a wide variety of polymers.

The invention is not limited to any particular type of magnetic recording medium, but the substrate or subsequently deposited layer is textured, such as by mechanical processing or laser techniques, and the textured surface is substantially on the subsequently deposited layer. It can be used to form lubricant topcoats on any of a variety of types of magnetic recording media, including those that are reproduced. Therefore, the lubricant topcoat of the present invention can be applied as the topcoat 14 on the magnetic recording medium shown in FIG. 1, but is not necessarily limited thereto.

Preferred embodiments of the invention and some variations thereof are described herein. The invention can be used in a variety of different combinations and environments and can be varied or changed within the scope of the invention as expressed herein.

It is an object of the present invention to provide a magnetic recording medium comprising a lubricant topcoat bonded at a high lubricant bonding ratio.

It is another object of the present invention to provide a lubricant for use as a lubricant topcoat on a magnetic recording medium capable of bonding at high lubricant bonding ratios.

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 having become familiar with the description or may be learned from practice of the invention. The objects and advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.

According to the present invention, the above and other objects are achieved in part by a magnetic recording medium comprising a lubricant topcoat containing a perfluoro polyether phosphate polymer.

Another aspect of the invention is a step of forming a magnetic layer on a nonmagnetic substrate, optionally forming a protective overcoat on the magnetic layer and a lubricant topcoat on the magnetic layer or, if present, the protective overcoat. The method relates to a method of manufacturing a magnetic recording medium, wherein the lubricant topcoat contains a perfluoro polyether phosphate polymer, including forming a polymer.

Further objects and advantages of the invention will be readily understood by those skilled in the art from the following detailed description, wherein embodiments of the invention are described by simply illustrating the best mode contemplated for carrying out the invention. As will be appreciated, the invention may have other and different embodiments, and some details may be modified in various obvious respects, without departing from the invention. Accordingly, the drawings and detailed description are by way of example and should not be regarded as limiting.

Claims (20)

A magnetic recording medium comprising a lubricant topcoat, A magnetic recording medium characterized in that the lubricant topcoat comprises a phosphate polymer of the formula: Where R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are independently fluoroalkylether-phosphate repeating units or groups, or fluoroalkylether groups, PFPE is a perfluoroalkyl ether group, a to f are integers from 0 to 10, and at least one of a to f is 1 or more. The magnetic recording medium of claim 1, wherein the lubricant topcoat comprises a phosphate polymer as an essential component. 2. The magnetic recording of claim 1 comprising a nonmagnetic substrate, an underlayer on the nonmagnetic substrate, a magnetic layer on the underlayer, a protective overcoat on the magnetic layer and a lubricant topcoat on the protective overcoat. media. The magnetic recording medium of claim 1, wherein the PFPE has the formula: Where m and n are each 0 or an integer of 100 or less. The magnetic recording medium of claim 1, wherein the fluoroalkylether group has the formula: Where n is an integer of 15 to 100. 2. The magnetic recording medium of claim 1, wherein the lubricant top coat exhibits a lubricant bonding ratio of greater than 0.4. 2. The magnetic recording medium of claim 1, wherein the phosphate polymer has a molecular weight of about 1,000 to about 50,000. A method of making a magnetic recording medium comprising forming a magnetic layer on a nonmagnetic substrate and forming a lubricant topcoat comprising a phosphate polymer of the formula: Where R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are independently fluoroalkylether-phosphate repeating units or groups, or fluoroalkylether groups, PFPE is a perfluoroalkyl ether group, a to f are integers from 0 to 10, and at least one of a to f is 1 or more. 9. The lubricant topcoat of claim 8, further comprising: forming a bottom layer on a nonmagnetic substrate, forming a magnetic layer on the bottom layer, forming a protective overcoat on the magnetic layer, and a lubricant topcoat on the protective overcoat. Forming a process. The method of claim 8 wherein the PFPE has the formula: Where m and n are each 0 or an integer of 100 or less. The process of claim 8 wherein the fluoroalkylether group has the formula: Where n is an integer of 15 to 100. 9. The method of claim 8 including controlling the amount of phosphate polymer bound to the magnetic medium. 13. The method of claim 12, wherein the phosphate polymer is bonded directly to the magnetic recording medium with a lubricant bond ratio of greater than 0.4. 9. The method of claim 8, wherein the phosphate polymer has a molecular weight of about 1,000 to about 50,000. 9. The method of claim 8, comprising forming a composite of a magnetic layer on a nonmagnetic substrate and immersing the composite in a solution of phosphate polymer and a solvent. Phosphate polymers having the formula: Where R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are independently fluoroalkylether-phosphate repeating units or groups, or fluoroalkylether groups, PFPE is a perfluoroalkyl ether group, a to f are integers from 0 to 10, and at least one of a to f is 1 or more. The phosphate polymer of claim 16 wherein the PFPE is represented by the formula: Where m and n are each 0 or an integer of 100 or less. 17. The phosphate polymer of claim 16 wherein the fluoroalkylether group has the formula: Where n is an integer of 15 to 100. 17. The phosphate polymer of claim 16 wherein the molecular weight is about 1,000 to about 50,000. A process for preparing a phosphate polymer according to claim 16 comprising reacting a fluoroalkylether alcohol compound with phosphorus oxychloride.