JPH07326041A - Magnetic recording medium and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a magnetic recording medium having an excellent lubricating function even in a wide range of use environments and having little deterioration in CSS durability over time, and a manufacturing method thereof. A substrate, a recording film provided on the substrate, a protective film provided on the recording film, and a lubricant layer provided on the protective film, wherein the lubricant layer is An adsorption lubricant layer provided on the protective film and a free lubricant layer provided on the adsorption lubricant layer, wherein the adsorption lubricant layer is
Structural _{unit, - (C n F 2n O} ) m - ( where, n in the formula represents 1, 2 or 3, m is 1 or more an integer), and and a molecular end or a molecular chain functional groups in the And the free lubricant layer is formed of a compound represented by the general formula [1], a compound represented by the general formula [2] and a general formula [3]. A magnetic recording medium formed of a perfluoroalkylpolyether lubricant selected from the group consisting of compounds represented by: [Chemical 1]

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic disk whose CSS durability is less deteriorated with time and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic disk or a magnetic tape is prepared by forming a magnetic layer on a substrate. In the medium, there is a problem that tribological characteristics and electromagnetic conversion characteristics are deteriorated due to friction at the head / magnetic recording medium interface during recording and reproduction.

In order to solve the above problems, a perfluoroalkylpolyether-based lubricant layer is provided on the magnetic layer on the surface of the magnetic recording medium to impart wear resistance (lubricity) to the head / magnetic recording medium interface. A method has been proposed (US Pat. No. 3,778,308, US Pat. No. 3,919,71).
No. 9)), in the magnetic recording medium obtained by the above method, the perfluoroalkylpolyether-based lubricant is lost by scattering and the head is easily adsorbed to the magnetic recording medium, so that the durability with time is improved. There is a problem of being inferior.

Therefore, in order to improve such a problem,
A method of strengthening the binding force between the lubricant molecule and the protective film surface by using a lubricant having a functional group such as a hydroxyl group, a carboxyl group, or a piperonyl group introduced at the molecular end of the above-mentioned perfluoroalkyl polyether lubricant. US Patent 426
No. 8556, U.S. Pat. No. 4,267,238, and Japanese Patent Publication No. 60-10368) are proposed. The lubricant layer formed using such a lubricant is
Lubricant molecules (hereinafter referred to as "adsorbed lubricant") bound to the disk surface with a strength that prevents them from being washed off by washing with a fluorine-based solvent, and lubricant molecules that are bound to the extent that they are washed off ( Hereinafter referred to as "free lubricant").

As a result of a detailed study by the present inventors,
It has been found that the contact start / stop (CSS) durability, which has been most required in recent years as the durability of magnetic recording media, is controlled only by the amount of free lubricant molecules (tribology conference proceedings, Nagoya 1993-1).
1, P. 427).

On the other hand, in recent years, due to the widespread use of notebook computers and the installation of hard disk drives in laser printers, etc., the operating environment of the hard disk drives is not only in a normal environment but also in a wide range from low temperature low humidity to high temperature high humidity Therefore, the magnetic recording medium used in the hard disk drive is also required to have good CSS durability under a wide range of usage environments. However, since a conventional hard disk uses a magnetic recording medium having a lubricant layer formed of the above-mentioned functional group-containing lubricant as a magnetic recording medium, water molecules adsorbed on the disk surface from the surrounding environment. It has been found that the free lubricant changes to an adsorbed lubricant layer by binding with a functional group in the molecule of the free lubricant, the CSS durability deteriorates, and it is not possible to cope with the widening of the usage environment.

Accordingly, it is an object of the present invention to provide a magnetic recording medium which has an excellent lubricating function even in a wide range of use environments and has little deterioration in CSS durability over time, and a method for producing the same.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned deterioration of durability, the present inventors have found that the above-mentioned lubricant layer is formed on the above-mentioned protective film at the molecular end or in the molecular chain. And an adsorbent lubricant layer formed by using a specific fluorine compound having a functional group, and a free lubricant layer formed on the adsorbent lubricant layer by using a specific perfluoroalkylpolyether lubricant It has been found that a magnetic recording medium can achieve the above object.

The present invention has been made on the basis of the above findings, and includes a substrate, a recording film provided on the substrate, a protective film provided on the recording film, and an protective film provided on the protective film. In the magnetic recording medium having a lubricant layer formed on the protective film, the lubricant layer includes an adsorption lubricant layer provided on the protective film and a free lubricant layer provided on the adsorption lubricant layer. The structural unit of the adsorptive lubricant layer is-(C _n F
_2nO ) _m- (wherein n represents 1, 2 or 3 and m represents an integer of 1 or more) and is formed by a fluorine compound having a functional group at the molecular end or in the molecular chain. ,
The free lubricant layer is a compound represented by the following general formula [2] (same as the above [chemical formula 1]) and a general formula [2].
A magnetic recording medium comprising a compound represented by or a perfluoroalkylpolyether lubricant selected from the group consisting of compounds represented by the general formula [3]. is there.

[0010]

[Chemical 2]

The present invention also provides, as a preferred method for producing the above magnetic recording medium, a step of providing a recording film on a substrate,
A step of providing a protective film on the recording film, a step of forming a adsorptive lubricant layer on the protective film by binding the fluorine compound to the protective film through the functional group, and the adsorptive lubrication And a step of forming the free lubricant layer by applying the above-mentioned perfluoroalkylpolyether-based lubricant on the agent layer.

The magnetic recording medium of the present invention will be described in more detail below.

Examples of the magnetic recording medium of the present invention include a magnetic disk, a magnetic tape and a magneto-optical disk.

The substrate used in the present invention is
Examples thereof include aluminum alloy substrates, glass substrates, non-magnetic substrates such as carbon substrates, plastic substrates or films. Regarding the shape and thickness of the substrate, the shape and thickness usually required can be appropriately selected according to the application.

The aluminum alloy substrate may have a surface plated with nickel, phosphorus or the like,
In addition, in order to improve the flying characteristics of the head and control the magnetic anisotropy, the diamond abrasive grains and polishing tape are pressed against the substrate while rotating it to create a concentric minute groove on the substrate. A processed product may be used.

Further, the glass substrate is one in which the surface is etched with a chemical such as strong acid to form fine irregularities, and the area of the magnetic recording medium that contacts the head is reduced to reduce the frictional force during sliding. May be used.

Further, particularly when the magnetic recording medium of the present invention is a magnetic disk, in order to improve the magnetic characteristics of the recording film on the above-mentioned substrate, chrome or the like is formed before forming the recording film. The underlying film may be formed by a sputtering method or the like.

In the present invention, the recording film provided on the substrate is not particularly limited as long as it can be used as a recording film of a magnetic recording medium.
A film made of Co-Ni or Co-Cr, or Co-N
Examples thereof include a film formed by adding a small amount of Pt, Ta, V, Sm or the like to i or Co-Cr. The thickness of the recording film is preferably 15 to 80 nm.

In the present invention, examples of the protective film provided on the recording film include an inorganic oxide film such as SiO ₂ and a carbon-based film, and a carbon-based film is preferable.
Above all, a carbon-based film formed using glassy carbon is particularly preferable. It is also possible to use, for example, a cubic boron nitride film formed by a plasma CVD method using borohydride, ammonia and hydrogen as raw materials. The thickness of the protective film is preferably 10 to 25.
nm.

In the present invention, the lubricant layer provided on the protective film includes an adsorbent lubricant layer formed of a specific fluorine compound on the protective film, and a specific perfluoro on the adsorbent lubricant layer. And a free lubricant layer formed of an alkyl polyether lubricant. Here, the adsorbed lubricant layer is a layer which is not removed by washing with a fluorine-based solvent such as “CFC113”, and the free lubricant layer is
This layer is removed by the above washing. The thickness of the adsorption lubricant layer is preferably 3 to 10Å, and
The thickness of the free lubricant layer is preferably 6 to 18Å.

[0021] The above specific fluorine compounds to form the adsorbent lubricant layer, a structural _{unit, - (C n F 2n O} ) m -
(However, in the formula, n represents 1, 2 or 3, and m is an integer of 1 or more) and is a fluorine compound having a functional group at the molecular end or in the molecular chain. The average molecular weight of the fluorine compound is preferably 1,000 to 8,000 in terms of number average molecular weight. Preferred examples of the functional group contained in the fluorine compound include a hydroxyl group, a carbonyl group and a piperonyl group.

Specific examples of the above-mentioned fluorine compound include the following compounds, and the trade name "Fomblin ZDO
L "(functional group: -CH ₂ OH), product name" Fomblin ZDIAC "
(Functional group: -COOH), trade name "Fomblin AM2001" (functional group: functional group represented by the following [Chemical Formula 3]) (above manufactured by Montecatini); trade name "Demnum SA" (functional group: -CH ₂ OH)
, Product name "Demnum SH" (functional group: -COOH), product name "D
Commercial products such as "emnum SP" and trade name "Demnum SY" (all manufactured by Daikin Industries, Ltd.) can also be used.

[0023]

[Chemical 3]

Specific examples of the above fluorine compound: HOCH ₂ CF ₂ O- (CF ₂ CF ₂ O) _m- (CF ₂ O) _m -CF ₂ CH ₂ OH HOOCCF ₂ O-(CF ₂ CF ₂ O) _m- (CF ₂ O) _m -CF ₂ COOH Compound F (CF ₂ CF ₂ CF ₂ O) _m -CF ₂ CF ₂ CH ₂ OH F (CF ₂ CF ₂ CF ₂ O) _m −CF ₂ CF ₂ COOH

[0025]

[Chemical 4]

The above-mentioned specific perfluoroalkylpolyether-based lubricant forming the above-mentioned free lubricant layer is represented by the compound represented by the general formula [1] and the general formula [2] of the above [Chemical formula 2]. Or a perfluoroalkylpolyether lubricant selected from the group consisting of compounds represented by the general formula [3]. Here, in the general formula [1], [2] or [3], a, b, c and d are each such that the number average molecular weight of the perfluoroalkyl polyether lubricant satisfies 2000 to 10,000. It is an integer.

Further, the following commercially available products can be used as the perfluoroalkylpolyether type lubricant. "Krytox", a commercial product corresponding to the perfluoroalkyl polyether lubricant represented by the above general formula [1].
Product name, manufactured by DuPont. Commercial products corresponding to the perfluoroalkylpolyether lubricant represented by the above general formula [2]; "Fomblin Z03", "Fomblin Z15" (both are trade names _, manufactured by Montecatini) and the like. The above general formula [3]
Commercially available products corresponding to the perfluoroalkyl polyether lubricants represented by: "Demnum S20", "Demnum S65",
"Demnum S100" (Brand name _, manufactured by Daikin Industries)
etc.

[Operation] In the magnetic recording medium of the present invention, a lubricant layer is formed by bonding the above-mentioned fluorine compound to the surface of the protective film through a functional group of the fluorine compound, and the above-mentioned adsorption lubricant layer, Since the free lubricant layer is formed by adsorbing the perfluoroalkyl polyether lubricant on the adsorption lubricant layer by the intermolecular interaction force with the fluorine compound, the free lubricant in the free lubricant layer The molecules do not migrate to the adsorptive lubricant layer, and the free lubricant molecules are adsorbed to the adsorptive lubricant layer by the intermolecular interaction force, so that the free lubricant molecules scatter with use. It never disappears. Therefore, the magnetic recording medium of the present invention does not cause deterioration in durability over time.

Next, a preferable method for manufacturing the magnetic recording medium of the present invention will be described in detail. A preferred method for producing a magnetic recording medium of the present invention is the step of providing the recording film on the substrate, the step of providing the protective film on the recording film, and the fluorine compound being functionalized on the protective film. Forming a adsorption lubricant layer on the protective film by bonding via a base, and applying the perfluoroalkylpolyether lubricant on the adsorption lubricant layer to form the free lubricant layer. And the step of performing can be carried out sequentially.

The step of providing the recording film can be carried out by appropriately adopting a dry plating means such as a sputtering method or a vapor deposition method and a wet plating means which are usually used.

In the step of providing the protective film, various methods can be appropriately adopted depending on the kind of the protective film to be formed. For example, in the case of forming a carbon-based protective film, it may be formed by the following methods. it can. Method: 2mTorr using an opposing target composed of glassy carbon and an inert gas as an introduction gas
A method of forming a glassy carbon film on the recording film by sputtering under the following gas pressure. Method: A method in which glassy carbon is used as a carbon source, and a glassy carbon film is formed on the recording film by means such as three-pole direct current glow discharge sputtering, two-pole high-frequency glow discharge sputtering, or magnetron sputtering. Method: A method of forming a graphite-like carbon film or a diamond-like carbon film by applying a voltage between carbon electrodes in a vacuum atmosphere to cause a carbon atom or a carbon ion generated by causing a discharge to adhere to the recording film. Method: A method for forming a carbon-based film on the recording film by sputtering with a target of graphite in an inert gas or a mixed gas of an inert gas and a hydrocarbon gas such as methane, Method: hydrocarbon A method of forming a carbon-based film on the recording film by plasma CVD by mixing an organic compound such as gas, alcohol or acetone alone or with hydrogen gas, an inert gas or the like. Method: A method of forming a carbon-based film by ionizing an organic compound, accelerating it by applying a voltage thereto, and colliding it with the recording film on the substrate.

When the cubic boron nitride film is formed as the protective film, it can be formed, for example, by a plasma CVD method using boron hydride, ammonia and hydrogen as raw materials.

The step of forming the adsorption lubricant layer can be carried out by applying the fluorine compound on the protective film. The above-mentioned application can be carried out by a usual spin coating method, a dip coating method, a spray method or the like,
The temperature at this time can be room temperature. Further, after the coating is completed, cleaning for removing unreacted fluorine compound molecules not bound to the protective film surface, heat treatment for binding the unreacted fluorine compound molecules to the protective film, and the like are performed. Is preferred. The above cleaning is performed using "Flon 1,
1, 3 "(trade name, made by Sumitomo 3M)," Fluorinert PF
5080 "(trade name, manufactured by Sumitomo 3M) or the like, and can be performed by a method usually used as a method for cleaning a magnetic recording medium. Moreover, the said heat processing can be performed by processing at 100-180 degreeC for 1 to 5 hours. In addition, by leaving at room temperature for a long time (24 to 300 hours) after the above application,
It is possible to obtain the same effect as when the above heat treatment is performed.

The step of forming the free lubricant layer can be carried out by applying the perfluoroalkyl polyether lubricant as it is or by dissolving a solution such as "Fluorinert PF5080" in a solvent. The above-mentioned application can be carried out by a usual spin coating method, a dip coating method, a spraying method or the like, and the temperature at this time can be room temperature.

[0035]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

Example 1 A Ni-P plated aluminum substrate was polished and textured to obtain a substrate having a center line average surface roughness Ra of 4 nm. On the obtained substrate, DC magnetron sputtering was carried out in an Ar gas atmosphere with a thickness of 50 nm of C.
An underlayer film was formed, and then a 40 nm thick CoCrTa-based magnetic film was formed on the underlayer to provide a recording film.

Then, a protective film was provided on the above recording film by a sputtering method using a facing target type sputtering apparatus. At this time, a target made of glassy carbon was used as the target, and the gas pressure was such that after exhausting the chamber of the sputtering apparatus, Ar gas was introduced and the gas pressure was 2 mTorr for sputtering. The thickness of the obtained protective film (glassy carbon film) was 150Å.

Next, by combining the dip coating method and the washing with a fluorine-based solvent ("Fluorinate PF5080"), "Fomblin AM2001" (trade name, manufactured by Montecatini, number average) having a functional group (piperonyl group) at the end is combined. A molecular weight of 2600) was applied on the protective film and bonded to form an adsorption lubricant layer having a film thickness of 5Å. Furthermore,
"Fo which does not have functional group of number average molecular weight 4000 in the molecule"
mblin Z03 "(trade name, made by Montecatini) is applied on the above-mentioned adsorption lubricant layer by dip coating method to obtain a film thickness of 1
A 5Å free lubricant layer was formed to obtain a magnetic disk as a magnetic recording medium of the present invention. The thickness of the free lubricant layer and the thickness of the adsorption lubricant layer are obtained by X-ray photoelectron spectroscopy (XPS).

Example 2 A disk having a protective film formed in the same manner as in Example 1 was
Dip coating method and heat treatment (120 ° C, 1 hour)
By combining and, "Fomblin AM2001" (trade name, made by Montecatini, number average molecular weight 2600) having a functional group at the end was applied onto the protective film and bonded to form an adsorption lubricant layer with a film thickness of 10 Å. . Furthermore, "Fomblin Z03" which does not have a functional group with a number average molecular weight of 4000 in the molecule
(Trade name, manufactured by Montecatini) was applied on the adsorption lubricant layer by a dip coating method to form a free lubricant layer having a film thickness of 15Å to obtain a magnetic disk as a magnetic recording medium of the present invention.

Example 3 A disk having a protective film formed in the same manner as in Example 1 was
Dip coating method and fluorinated solvent (“CFC 11
3)) and combined with washing with “Demnum SA” (functional group; —CH ₂ OH) having a functional group at the end (trade name, manufactured by Daikin Industries, Ltd., number average molecular weight 3500) is applied on the protective film. The layers were combined to form an adsorption lubricant layer having a film thickness of 6Å. Furthermore, "Demnum S65" (trade name, manufactured by Daikin Industries, Ltd.) does not have a functional group with a number average molecular weight of 4,500 in the molecule.
Was coated on the above-mentioned adsorption lubricant layer by a dip coating method to form a free lubricant layer having a film thickness of 15Å to obtain a magnetic disk as a magnetic recording medium of the present invention.

Comparative Example 1 A Ni-P plated aluminum substrate was polished and textured to obtain a substrate having a center line average surface roughness Ra of 4 nm. On the obtained substrate, DC magnetron sputtering was carried out in an Ar gas atmosphere with a thickness of 50 nm of C.
An underlayer film was formed, and then a 40 nm thick CoCrTa-based magnetic film was formed on the underlayer to form a recording film. Then, a protective film was provided on the recording film by a sputtering method using a facing target type sputtering device. At this time, a target made of glassy carbon was used as the target, and the gas pressure was set to 2 mTorr by introducing Ar gas after exhausting the chamber of the sputtering apparatus and performing sputtering. The thickness of the obtained protective film (glassy carbon film) was 150Å. Next, the number average molecular weight 4000
"Fomblin Z03" (trade name, manufactured by Montecatini Co.), which has no functional group in the molecule, was applied by the dip coating method to a thickness of 15Å to form a lubricant layer on the protective film. A magnetic disk as a magnetic recording medium was obtained.

Comparative Example 2 In the same manner as in Comparative Example 1, "Fomblin Z03" (trade name, manufactured by Montecatini Co.) having no functional group in the molecule having a number average molecular weight of 4000 was dipped on a disk having a protective film formed thereon. The coating method was applied to a thickness of 30Å to obtain a magnetic disk as a magnetic recording medium having a lubricant layer formed on the protective film.

Comparative Example 3 A disk having a protective film formed in the same manner as in Comparative Example 1,
"Fombli having a functional group at the end with a number average molecular weight of 2500"
n AM2001 ”(trade name, manufactured by Montecatini) was applied by a dip coating method so as to have a thickness of 40 Å to obtain a magnetic disk as a magnetic recording medium having a lubricant layer formed on the protective film. .

Test Examples The magnetic disks obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following tests to evaluate the performance. [Test] For the magnetic disks obtained in the above examples, C
SS test [Thin film head made of sintered body of Al ₂ O ₃ and TiC for slider material (US GLIDE / WRITE
Head load 6g, head flying height 0.1μ
m, 3600 rpm for 15 seconds-stop for 15 seconds] a predetermined number of times, and the CSS resistance characteristics (friction coefficient and presence / absence of adsorption) after the predetermined number of times are determined by a disc friction / wear tester "PT101" (trade name, Patty). (Manufactured by Tech Co.). Further, the change in the film thickness of the adsorbent lubricant layer when left for 1 month in an environment of temperature 30 ° C./humidity 80% was examined. The above results are shown in [Table 1].

[0045]

[Table 1]

As is clear from the results shown in [Table 1],
Magnetic disks of Examples 1 to 3 (magnetic recording medium of the present invention)
Has extremely high durability, whereas the magnetic disk of Comparative Example 2 in which the lubricant layer was formed only with the perfluoroalkyl polyether lubricant having no functional group caused head adsorption. Further, in Comparative Example 3 in which the lubricant layer is formed only with the perfluoroalkyl polyether lubricant having the functional group, there is a problem that the thickness of the adsorbed lubricant changes.

[0047]

The magnetic recording medium of the present invention has an excellent lubricating function even in a wide range of use environments and has little deterioration in CSS durability over time. More specifically, the magnetic recording medium of the present invention is characterized in that the perfluoroalkylpolyether-based lubricant is provided between a protective film and a free lubricant layer comprising a perfluoroalkylpolyether-based lubricant having no polar group in the molecule. Since an adsorbing lubricant layer made of a fluorine compound having a structure similar to the molecular skeleton of the lubricant is interposed, the interaction force between the lubricant layer and the surface of the protective film is strong, and the durability is high. Since it is used, the thickness of the adsorption lubricant layer does not change with time and stable durability can be obtained, and the magnetic recording medium is a perfluoroalkyl polyether lubricant that does not have a polar group in the molecule. Since the free lubricant layer located on the outermost surface of the magnetic recording medium is formed, adsorption of water molecules from the use environment to the magnetic recording medium can be suppressed, and head adsorption is less likely to occur.

Claims (3)

[Claims] 1. A magnetic recording medium having a substrate, a recording film provided on the substrate, a protective film provided on the recording film, and a lubricant layer provided on the protective film, The lubricant layer is composed of an adsorbent lubricant layer provided on the protective film and a free lubricant layer provided on the adsorbent lubricant layer, and the adsorbent lubricant layer has a structural unit of − (C _n F _2n O) _m
-(Wherein n represents 1, 2 or 3 and m represents an integer of 1 or more) and is formed by a fluorine compound having a functional group at the molecular end or in the molecular chain, and the above-mentioned free lubrication The agent layer is selected from the group consisting of a compound represented by the following general formula [1], a compound represented by the general formula [2], and a compound represented by the general formula [3]. A magnetic recording medium formed of a fluoroalkyl polyether lubricant. [Chemical 1] 2. The magnetic recording medium according to claim 1, wherein the functional group is a hydroxyl group, a carbonyl group or a piperonyl group. 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein a step of providing a recording film on a substrate, a step of providing a protective film on the recording film, and A step of forming a adsorptive lubricant layer on the protective film by binding a fluorine compound through the functional group, and a free lubricant by applying the above-mentioned perfluoroalkylpolyether lubricant on the adsorptive lubricant layer A method of manufacturing a magnetic recording medium, comprising the step of forming a layer.