JP2006328418A - Fluorine-based lubricant for magnetic recording medium and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine-based lubricant for magnetic recording medium having controlled molecular weight and molecular weight distribution and having high introducing ratio of functional group and provide a magnetic recording medium having good sliding properties and durability. <P>SOLUTION: The fluorine-based lubricant for magnetic recording medium and having introduced functional group has an average introduction ratio of functional group of ≥95%. The invention provides the lubricant produced by the production method and a magnetic recording medium produced by directly or indirectly applying the lubricant to a magnetic layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fluorine-based lubricant having a high average functional group introduction rate and a magnetic recording medium using the lubricant.

  In the magnetic recording medium, a protective film such as carbon or silicon dioxide is provided on the magnetic layer and a lubricant layer is provided on the protective film in order to prevent damage due to contact wear with the magnetic head. The lubricant layer needs to be stably present on the protective film, and therefore, the lubricant is required to have a large adsorbing force with the protective film. Therefore, in general, a perfluoropolyether into which a polar group such as a hydroxyl group or an aromatic ring is introduced as a functional group for increasing the adsorptive power with the protective film is used as a lubricant.

  However, commercially available perfluoropolyether has a molecular weight of several hundred to several tens of thousands and a very broad molecular weight distribution. In addition, functional groups have not been completely introduced, and commercially available functional group-introduced perfluoropolyethers contain a mixture of non-functional group-introduced products in which no functional groups have been introduced. The mixing ratio of non-functional group-introduced products is usually around 10%. Furthermore, the mixed amount such as molecular weight distribution and functional group non-introduced substance varies between product lots.

  Low molecular weight substances having a molecular weight of several hundreds or functional group non-introduced substances have low adsorptive power with the protective film, and thus cause aging of the film thickness and contamination of the magnetic head due to volatilization and migration. Therefore, when such a lubricant containing a low molecular weight substance or a functional group non-introduced substance is used, troubles such as damage to the magnetic recording medium and magnetic head, head crash, and data error are likely to occur. In addition, variations in molecular weight distribution and mixed amounts of unintroduced functional groups among product lots make the quality of magnetic recording media such as sliding characteristics and durability unstable.

  Therefore, in view of such circumstances, a commercially available functional group-introduced perfluoropolyether is used as a lubricant for magnetic recording media to obtain a magnetic recording medium having good sliding characteristics and durability. Needs to be further purified before use.

As a method for purifying a commercially available functional group-introduced perfluoropolyether, a gel permeation chromatography (GPC) method has been proposed (Japanese Patent Laid-Open No. 5-20673) and is widely used. The GPC method is a method in which an organic solvent is used as a moving layer and a polymer gel is used as a fixed layer, and molecules having different molecular weights are separated mainly by size exclusion to remove unnecessary components. In the GPC method, perfluoropolyether from which low molecular weight substances have been removed can be obtained by fractionating only the eluate having a predetermined elution time.
JP-A-5-20673

  However, the GPC method requires a large amount of an organic solvent for dissolving the perfluoropolyether as the moving layer. However, perfluoropolyether is mainly soluble only in fluorine-based solvents such as chlorofluorocarbons, and these fluorine-based solvents have a great risk of adversely affecting workers and the environment. Further, since the GPC method requires several tens of minutes for one elution, it takes a lot of time to obtain a target amount of purified perfluoropolyether. Furthermore, since the GPC method is mainly separated due to the size exclusion effect, separation based on the presence or absence of a functional group is difficult in principle. That is, it is possible to improve the uniformity of the molecular weight distribution, but it is not possible to reduce the mixing ratio of the functional group-unintroduced product.

  In addition to the GPC method, it has also been proposed to fractionate commercially available functional group-introduced perfluoropolyethers using a supercritical fluid fractionation method (Japanese Patent Laid-Open No. 9-120524). The supercritical fluid fractionation method is superior to the GPC method in that it does not require the use of a fluorinated solvent. However, Japanese Patent Application Laid-Open No. 9-120524 does not describe details such as what kind of substance is used as a supercritical fluid under what conditions, and simply shows the molecular weight distribution of the obtained fraction. Only the narrowness is described. From this, it is doubtful whether the description of JP-A-9-120524 is sufficiently disclosed as a specification, but in any case, the supercritical fluid fractionation method described in JP-A-9-120524 is This is a method for improving the uniformity of the molecular weight distribution, and does not reduce the mixing ratio of functional group-unintroduced products.

  Thus, until now, no method has been proposed that can reduce the mixing ratio of non-introduced functional groups in commercially available functional group-introduced perfluoropolyethers, and currently it is used as a lubricant for magnetic recording media. Is a perfluoropolyether in which a functional group non-introduced product is mixed.

  Accordingly, an object of the present invention is to provide a fluorine-based lubricant for a magnetic recording medium having a controlled molecular weight and molecular weight distribution and a high functional group introduction rate. A further object of the present invention is to provide a magnetic recording medium having good sliding characteristics and durability.

  The present invention relates to a functional group-introduced fluorine-based lubricant for magnetic recording media, wherein the average functional group introduction rate is 95% or more. In addition, the present invention relates to a magnetic recording medium in which the lubricant of the present invention is applied directly or indirectly on a magnetic layer.

  According to the present invention, a highly purified fluorine-based lubricant having a high functional group introduction rate, a controlled molecular weight and molecular weight distribution, and the like can be provided. In addition, the method for producing the lubricant of the present invention requires a short time for its production (purification) compared to the prior art method, and does not use a fluorinated solvent. High environmental safety. By using the highly purified fluorine lubricant of the present invention, a magnetic recording medium having improved sliding characteristics and durability can be provided.

Method for Producing Fluorine-Based Lubricant for Magnetic Recording Medium The fluorine-based lubricant for magnetic recording medium of the present invention comprises a functional group-introduced fluorine-based lubricant, supercritical carbon dioxide as a mobile phase, and silica gel as a stationary phase. Manufactured by chromatography. A supercritical fluid continuously changes greatly from an extremely dilute low density state to a high density state close to a liquid by a slight change in temperature and pressure. The solute dissolution capacity of the supercritical fluid depends on this density. Therefore, the solute dissolving ability can be freely changed by controlling the temperature and pressure. Carbon dioxide has a critical temperature of 31.3 ° C. and a critical pressure of 75.3 kgf / cm ² , and can be in a supercritical fluid state under milder conditions than other substances.

  The solute dissolution capacity of carbon dioxide in the supercritical fluid state with such characteristics is controlled by changing the temperature and pressure, and using the difference in solubility due to slight structural differences such as molecular weight and functional group, Fluorine-based lubricants can be molecular weight fractionated and / or functional group fractionated. Supercritical fluids have a diffusion coefficient that is 2 to 3 orders of magnitude higher and a viscosity that is 2 orders of magnitude lower than liquids. Therefore, compared with the fractionation method using an organic solvent etc., fractionation is possible in a short time required.

  Examples of the functional group-introduced fluorine-based lubricant include a functional group-introduced perfluoropolyether-based lubricant. As the functional group-introduced fluorine-based lubricant, in addition to the functional group-introduced perfluoropolyether lubricant, for example, a functional group-introduced fluoropolyether, a functional group-introduced perfluoroalkyl, a functional group-introduced fluoroalkyl, and a functional group Examples thereof include an introduced perfluoroalkylated silicon system and a functional group-introduced fluoroalkylated silicon system. Examples of the functional group possessed by the functional group-introduced fluorine-based lubricant include a piperonyl group, a hydroxyl group, a carboxyl group, an ester group, and an amino group.

As the perfluoropolyether lubricant, for example, — (C (R) F—CF ₂ —O) _p — (where R is a group such as F, CF ₃ , CH ₃ ), particularly HOOC-CF ₂ ( OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCF ₂ -COOH, F- (CF ₂ CF ₂ CF ₂ O) _n -CF ₂ CF ₂ COOH and other carboxyl group-modified perfluoropolyethers, HOCH ₂ -CF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCF ₂ -CF ₂ OH, HO- (C ₂ H ₄ -O) _m -CH _2- (OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCH Alcohol-modified perfluoropolyethers such as _2- (OCH ₂ CH ₂ ) _n -OH and F- (CF ₂ CF ₂ CF ₂ O) _n -CF ₂ CF ₂ CH ₂ OH, RO-CH ₂ -CF _2- (OC ₂ F ₄ ) _p (OCF ₂ ) _q —OCF ₂ —CH ₂ —OR (wherein R represents a piperonyl group). Perfluoropolyether-based lubricants introduced with these functional groups are commercially available, for example, Fomblin Z-Dol, Fomblin AM2001, Fomblin Z-DIAC (Audimont), Demnum ( Daikin Corporation) and Krytox (DuPont) are commercially available.

The supercritical carbon dioxide used as the mobile phase can have a pressure in the range of 80 to 350 kgf / cm ² and a temperature in the range of 35 to 300 ° C., for example. However, the pressure and temperature of carbon dioxide in the supercritical state can be appropriately determined from the above range in consideration of the separation state of the fluorine-based lubricant in the column. The silica gel used as the stationary phase can be appropriately selected from known or commercially available silica gels. In the present invention, molecular weight fractionation and / or functional group fractionation of a fluorine-based lubricant using carbon dioxide in a supercritical fluid state is mainly a supercritical fluid feeding device, a temperature control device, and a back pressure control device in addition to the silica gel column. By using this, it can be carried out easily.

  Chromatography is performed by flowing a functional group-introduced fluorine-based lubricant alone or dissolved in a solvent through a column packed with a predetermined amount of silica gel, and then flowing supercritical carbon dioxide as an elution medium. This is done by monitoring the group-introduced fluorine-based lubricant. Monitoring can be performed, for example, by absorbing ultraviolet light. While monitoring, a plurality of fractions are obtained, and a fraction having a high functional group introduction rate is selected from the obtained fractions. Selection of a fraction having a high functional group introduction rate can be performed by obtaining a retention time of a fraction having a high functional group introduction rate in advance and using this retention time as a guide.

  Temperature and pressure are set according to the type of fluorine-based lubricant and the purpose of purification. If necessary, a gradient such as a temperature gradient or a pressure gradient may be applied. In order to adjust the solubility of the fluorine-based lubricant in the supercritical fluid carbon dioxide, a small amount of an organic solvent may be added to the supercritical fluid carbon dioxide. Organic solvents to be added include alcohol solvents such as methanol and ethanol, hydrocarbon solvents such as n-hexane and cyclohexane, aromatic solvents such as benzene and phenol, ketone solvents such as acetone and methyl ethyl ketone, and alternative chlorofluorocarbons. Fluorinated solvents, mixed solvents of these organic solvents, mixed solvents such as water and alcohol solvents, and the like.

  The fraction is preferably selected so that the functional group introduction rate in the functional group-introduced fluorine-containing lubricant contained in the fraction is 95% or more, preferably 99% or more. By removing the functional group-introduced fluorine-based lubricant from the obtained fraction having a high functional group-introducing rate (containing the functional group-introduced fluorine-based lubricant), the fluorine having a high functional group-introducing rate and suitable for magnetic recording media -Based lubricant is obtained. The purification in the production method of the present invention may be repeated two or more times under different conditions depending on the type of fluorine-based lubricant and the purpose of purification. Moreover, the fluorine-type lubricant refine | purified previously with another refinement | purification method can also be used as a raw material of the manufacturing method of this invention.

Functionalizing fluorolubricant present invention for a magnetic recording medium is a functional group introduced fluorine-based lubricant for magnetic recording medium, including a lubricant average functional group introduction rate is 95% or more. Conventionally, functional group-introduced fluorine-based lubricants that have been used as lubricants in magnetic recording media have an average functional group introduction rate of about 90%. On the other hand, the functional group-introduced fluorine-based lubricant of the present invention has an average functional group introduction rate of 95% or more. More preferably, the functional group-introduced fluorine-based lubricant of the present invention has an average functional group introduction rate of 99% or more.

  Examples of the functional group-introduced fluorine-based lubricant include a functional group-introduced perfluoropolyether-based lubricant. As the functional group-introduced fluorine-based lubricant, in addition to the functional group-introduced perfluoropolyether lubricant, for example, a functional group-introduced fluoropolyether, a functional group-introduced perfluoroalkyl, a functional group-introduced fluoroalkyl, and a functional group Examples thereof include an introduced perfluoroalkylated silicon system and a functional group-introduced fluoroalkylated silicon system. Examples of the functional group possessed by the functional group-introduced fluorine-based lubricant include a piperonyl group, a hydroxyl group, a carboxyl group, an ester group, and an amino group.

More specifically, the perfluoropolyether lubricant is — (C (R) F—CF ₂ —O) _p — (where R is a group such as F, CF ₃ , CH ₃ ), particularly HOOC. Carboxyl-modified perfluoropolyethers such as -CF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCF ₂ -COOH, F- (CF ₂ CF ₂ CF ₂ O) _n -CF ₂ CF ₂ COOH, HOCH ₂ -CF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCF ₂ -CF ₂ OH, HO- (C ₂ H ₄ -O) _m -CH _2- (OC ₂ F ₄ ) _p (OCF ₂ ) _q -OCH _2- (OCH ₂ CH ₂ ) _n -OH, alcohol-modified perfluoropolyether such as F- (CF ₂ CF ₂ CF ₂ O) _n -CF ₂ CF ₂ CH ₂ OH, RO-CH _{2 -CF 2 - (OC 2 F 4} ) p (OCF 2) q -OCF 2 -CH 2 -OR ( where, R represents piperonyl represents a group) and the like.

  Furthermore, the functional group-introduced fluorine-based lubricant for magnetic recording media of the present invention does not contain a low molecular weight substance having a molecular weight of 500 or less and / or impurities. Here, “does not contain” means that the content is 1% or less.

Magnetic Recording Medium The magnetic recording medium of the present invention is a magnetic recording medium having at least a magnetic layer and a lubricant layer on a nonmagnetic substrate, more preferably a protective layer on the magnetic layer, and a lubricant thereon. It has a layer. Nonmagnetic substrates include, for example, polyesters such as polyethylene terephthalate (PET), polyamides, polyimides, polysulfones, polycarbonates, olefinic resins such as polypropylene, polymer materials such as cellulose resins and vinyl chloride resins, Glass, ceramics, inorganic materials such as glass ceramics and carbon, and metal materials such as aluminum alloys can be used. However, it is not limited to these.

  The magnetic layer can be one layer or two or more layers, and in the case of two or more layers, a nonmagnetic intermediate layer can be provided between each magnetic layer. The material constituting the magnetic layer is not particularly limited, but for example, metals such as Fe, Co, Ni, Co-Ni alloys, Co-Ni-Cr alloys, Co-Ni-Cr-Ta alloys, Co- Pt alloy, Co-Pt-Cr alloy, Co-Ni-Pt-Cr alloy, Co-Ni-Pt alloy, Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Co-B alloy, Co-Ni-Fe-B alloys, Co-Cr alloys, Co-Pt-Cr-Ta alloys, or alloys containing these metals such as Al, oxygen, nitrogen, oxides, nitrides, etc. Can be mentioned. These magnetic layers can be formed by various methods such as vapor deposition, direct current sputtering, alternating current sputtering, high frequency sputtering, direct current magnetron sputtering, high frequency magnetron sputtering, and ion beam sputtering. The magnetic layer can be provided directly on the non-magnetic substrate or via an underlayer such as Cr.

  Examples of the protective film layer include carbon films such as amorphous carbon films, diamond-like carbon films, and hydrogenated carbon films, and oxide films such as silicon dioxide films and zirconia films. However, the protective film layer is not limited to these. Incidentally, the carbon film has a lower number of functional groups on the surface like the oxide film, so that the adsorptivity of the lubricant is worse than that of the oxide film, and the present invention provides a magnetic recording having the carbon film as a protective film layer. It is particularly effective in the medium. Further, it is preferable that the surface of the magnetic recording medium is uneven from the viewpoint of preventing the head from adsorbing to the lubricant layer. The uneven surface of the protective film layer can also be formed by making the surface of the substrate or the base layer on the substrate uneven (textured), or by adding fine particles to the protective film layer. As for the unevenness on the surface of the magnetic recording medium, it is appropriate that the maximum height Rmax is, for example, in the range of 1 to 30 nm, preferably in the range of 3 to 10 nm. The unevenness on the surface of the magnetic recording medium is particularly useful when the magnetic recording medium is a hard disk.

  As the lubricant, the lubricant produced by the production method of the present invention or the lubricant of the present invention is used. The film thickness of the lubricant layer is suitably in the range of 0.5 to 2.0 nm, for example.

  The lubricant obtained by the production method of the present invention and the fluorine-based lubricant of the present invention have high adsorptive power with the protective film of the magnetic recording medium since the low molecular weight substance and the functional group non-introduced substance are removed. Therefore, by applying the obtained fluorine-based lubricant on the protective film, a lubricant layer with excellent stability is formed, and a magnetic recording medium having good sliding characteristics and durability can be obtained.

<Example>
Piperonyl-introduced perfluoropolyether lubricant FOMBLINAM2001 manufactured by Augmont Co., Ltd. is used as a high pressure silica gel for supercritical fluid application equipment consisting of a supercritical fluid pumping device, temperature control device, back pressure control device and UV-visible spectroscopic detector A column was attached and chromatographic fractionation with mobile phase carbon dioxide. The chromatography conditions were a carbon dioxide flow rate of 5 ml / min, a back pressure of 210 to 220 kgf / cm ² , and a column temperature of 80 ° C. The eluate was detected at a wavelength of 200 nm. As a result, five peaks were observed in the elution time of 5 to 420 sec, and the eluate corresponding to each peak was fractionated to obtain five fractions. The obtained fractions were designated as F1, F2, F3, F4, and F5 in the order of elution time.

¹ H-NMR spectrum measurement was performed on F2, and the introduction rate of the piperonyl group was evaluated from the chemical shift value of the peak and the integrated intensity ratio. As a result, F2 had a piperonyl group introduction rate of 99.6%. Furthermore, the molecular weight and molecular weight distribution of F2 were evaluated by the GPC method. As a result, F2 had an average molecular weight of 2030 and a molecular weight dispersion of 1.39, and impurities having a molecular weight of 500 or less were not detected. From these results, it was found that F2 was a purified AM2001 fraction in which piperonyl group was almost completely introduced and low molecular weight molecules having a molecular weight of 500 or less were not mixed. The time required to obtain 20 g of the same fraction was 40 minutes.

On the glass substrate on which the protective layer made of amorphous carbon is formed on the underlayer, the magnetic layer, and the outermost surface, the F2 lubricant layer (film thickness of about 1 nm), which is a fraction of the purified AM2001 obtained above. A magnetic recording medium was obtained by dipping. The obtained magnetic recording medium was subjected to a CSS test using an Al ₂ O ₃ —TiC magnetic head. The test conditions were a head load of 3 gf, a temperature of 25 ° C., a humidity of 40%, a measurement radius of 20 mm, and a disk rotation speed of 3600 rpm. As a result of the measurement, the maximum friction coefficients of the first CSS and up to 30000 times were 0.3 and 0.6, respectively.

<Comparative example>
FOMBLIN AM2001 was subjected to molecular weight fractionation using Asahi Clin AK225 manufactured by Asahi Glass Co., Ltd., which is a fluorinated solvent, as an eluent using a GPC apparatus. Chromatographic conditions were performed at an eluent flow rate of 5 mL / min and a column temperature of room temperature. As a result, in FOMBLIN AM2001 before fractionation, one broad peak with a molecular weight of 300 to 30000 was observed during the elution time of 440 to 1730 sec. Of this broad peak, the eluate having an elution time of 880 to 1000 sec was fractionated to obtain one fraction. About this fraction, the introduction rate of the piperonyl group was evaluated under the same measurement conditions and evaluation method as in the Examples using ¹ H-NMR spectrum measurement. From this evaluation, the fraction had a piperonyl group introduction rate of 90.8%.

  Furthermore, the molecular weight and molecular weight distribution of the same fraction were evaluated by the GPC method using the same measurement conditions and evaluation method as in the examples. As a result, this fraction had an average molecular weight of 2120 and a molecular weight dispersion of 1.41, and impurities with a molecular weight of 500 or less were not detected. The required time for obtaining 20 g of the same fraction was 190 minutes.

  The same lubricant layer (film thickness) of AM2001 obtained as described above on a glass substrate on which an underlayer, a magnetic layer, and a protective film made of amorphous carbon were formed on the outermost surface, similar to those used in the examples. About 1 nm) was formed by a dipping method to obtain a magnetic recording medium. The obtained magnetic recording medium was subjected to a CSS test using the same apparatus and conditions as in the example. As a result of the measurement, the maximum friction coefficients of CSS first time and 30000 times were 0.4 and 2.5, respectively.

  Table 1 shows the piperonyl group introduction rate, average molecular weight, and molecular weight dispersion of fraction F2 obtained in Examples, fractions obtained in Comparative Examples, and AM2001 before purification.

  The piperonyl group introduction rate of AM2001 before purification was 90.6%, and about 10% of functional group non-introduced products were mixed. In the comparative example, the piperonyl group introduction rate of the fraction obtained by the conventional GPC method was 90.8%, and the functional group non-introduced product was not removed. On the other hand, in the examples, the introduction rate of piperonyl group in fraction F2 obtained by chromatographic fractionation using carbon dioxide in a supercritical fluid state was 99.6%, and the functional group unintroduced product was almost removed. . The average molecular weight and molecular weight dispersion of the fraction F2 were 2030 and 1.39, respectively, which were almost the same as those of the fraction obtained by the conventional GPC method. Low molecular weight compounds having a molecular weight of 500 or less were removed. As described above, a highly purified perfluoropolyether lubricant having a high functional group introduction rate, low molecular weight contaminants removed, and molecular weight / molecular weight distribution controlled by the production method of the present invention. Could get.

Table 2 shows the time required to obtain 20 g and the amount of eluent used for fractionation in Examples and Comparative Examples.

  The required time for obtaining 20 g of the fraction F2 in the example and the fraction in the comparative example was 40 minutes and 190 minutes, respectively. In the examples, it was not necessary to use a fluorinated solvent, whereas the amount of the fluorinated solvent used as the eluent in the comparative example was about 1000 ml. As described above, the production method according to the present invention has a short required time of about 1/5 compared with the conventional GPC method, and a fluorine-based solvent was not used.

  Table 3 shows the results of the CSS test of the magnetic recording medium in which the lubricating layer was formed using the fraction F2 obtained in the example and the fraction obtained in the comparative example.

  In the medium using the fraction F2 obtained in the example, the maximum friction coefficient at the initial stage of CSS was 0.3, and after 30000 times, it was 0.6, an increase of about twice. On the other hand, the maximum friction coefficient of the CSS first time of the medium using the fraction obtained in the comparative example was 0.4, and that after 30000 times was 2.5, an increase of 6 times or more. Therefore, the magnetic recording medium using the purified fluorine-based lubricant obtained by the production method of the present invention has higher sliding characteristics and durability than the medium using the one purified by the prior art method.

Claims (6)

A functional group-introduced fluorine-based lubricant for magnetic recording media, having an average functional group introduction rate of 95% or more. The lubricant according to claim 1, wherein the functional group-introduced fluorine-based lubricant is a perfluoropolyether-based lubricant. The lubricant according to claim 1 or 2, wherein the functional group of the functional group-introduced fluorine-based lubricant is at least one selected from the group consisting of a piperonyl group, a hydroxyl group, a carboxyl group, and an amino group. The lubricant according to any one of claims 1 to 3, which contains no low molecular weight substance having a molecular weight of 500 or less and / or no impurities. The magnetic recording medium which apply | coated the lubricant of any one of Claims 1-4 directly or indirectly on the magnetic layer. The magnetic recording medium according to claim 5, wherein a lubricant is applied on the protective layer on the magnetic layer.