JPH11283245A - Magnetic recording medium and its evaluating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion strength between a protective layer and a lubricant and wear resistance by specifying the adhesion work amt. between the protective layer and the lubricant layer. SOLUTION: The adhesion work amt. between the protective layer and the lubricant layer is specified to 20 to 35 mNm<-1> . As for the substrate, a disk nonmagnetic substrate such as aluminum, aluminum alloy and glass is used. After a base layer is formed on the surface processed layer of the substrate, a magnetic layer is deposited thereon. As for the base layer, for example, a chromium base film having about 50 to 2000 Å film thickness is formed, on which a metal magnetic layer having 50 to 600 Å thickness is formed by using a Co alloy such as Co-Cr and Co-Ni. The protective layer consists of a carbon film, hydrogenated carbon film, carbon nitride film, nitride film such as TiC, SiN and TiN or oxide film such as SiO, Al2 O3 and ZrO, and is formed by vapor deposition or the like. As for lubricant, a compd. having hydroxyl groups at the molecular ends or in the side chains and having a fluorocarbon skeleton in the skeleton of the molecule is used.

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 having a protective layer and a lubricant layer formed on a magnetic layer, and more particularly to a magnetic recording medium having excellent durability and a method for evaluating the same. It is.

[0002]

2. Description of the Related Art A magnetic recording medium such as a magnetic disk is formed by depositing a magnetic thin film layer (magnetic layer) made of a metal or an alloy thereof on a substrate by a plating method, a vacuum evaporation method or a sputtering method. Manufactured. The magnetic recording medium is required to have sufficient abrasion resistance to withstand physical contact with the magnetic head and to have sufficient corrosion resistance to withstand the magnetic layer in a corrosive environment such as water vapor. Therefore, in order to satisfy the required characteristics, a protective layer is provided on the magnetic layer of the magnetic recording medium.

[0003] As this protective layer, a carbonaceous film is usually used because of its excellent wear resistance with the head. The carbonaceous protective layer is usually formed on the magnetic layer by a normal sputtering method using graphite or amorphous carbon as a target in a rare gas atmosphere such as argon. However, even a magnetic recording medium in which a carbonaceous protective layer is formed on a magnetic layer does not have sufficient abrasion resistance in actual use. For this reason, conventionally, a method of applying various lubricants such as fluorocarbon on the protective layer In the above, the surface of the protective layer is polarized by plasma treatment, ultraviolet light, ozone treatment, etc. to improve the adhesion between the protective layer and the lubricant. Attempts have been made to improve the abrasion resistance between the magnetic recording medium and the head by a method (Japanese Patent Laid-Open Publication No. Hei 4-6624) or the like.

[0004]

In the above method, however, it is necessary to increase the thickness of the lubricant layer so that the magnetic recording medium is attracted when the thickness of the lubricant layer is increased.
With such a film thickness, the abrasion resistance cannot be sufficiently improved.
Further, although the adhesion between the protective layer and the lubricant is improved by the above method, it cannot be said that the abrasion resistance is not necessarily sufficiently satisfied.

[0005]

Means for Solving the Problems The present inventors have made intensive studies in view of the above prior art, and as a result, have grasped the interfacial chemical properties of the protective layer and the lubricant layer. It has been found that the work of adhesion (polar component) is an important factor in durability. That is, the magnetic recording medium of the present invention is a magnetic recording medium in which a protective layer and a lubricant layer are formed on a magnetic layer, and the work of adhesion (polar component) between the protective layer and the lubricant layer is 20. ３５35 mNm ⁻¹ .

The method for evaluating a magnetic recording medium according to the present invention comprises:
In a magnetic recording medium having a protective layer and a lubricant layer, the work of adhesion (polar component) between the protective layer and the lubricant layer is used as an index of durability.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The magnetic recording medium of the present invention has at least a magnetic layer on a substrate,
Other configurations are optional as long as they have a protective layer and a lubricant layer, but the following description is a current general configuration, a magnetic recording medium having a base layer, a magnetic layer, and a protective layer in order on a substrate. Will be described.

As the substrate of the magnetic recording medium in the present invention, a normal disk-shaped non-magnetic substrate made of aluminum, aluminum alloy, glass or the like is used. Normally, these non-magnetic substrates are processed to a predetermined thickness, the surfaces thereof are mirror-finished, and then a non-magnetic metal, for example, Ni-P alloy, N
Approximately 5 to 5
It is used after forming a film with a film thickness of 20 μm to form a surface layer. The surface layer formed on the substrate in this manner is subjected to texture processing as necessary, and fine grooves or irregularities are processed and formed with high precision to obtain a surface processed layer finished to a specific surface roughness. By this texture processing, adsorption between the magnetic head and the magnetic recording medium can be prevented, CSS characteristics are improved, and magnetic anisotropy is further improved.

Further, after forming a base layer on the surface processing layer, a magnetic layer is formed by adhesion. The underlayer is usually formed by a sputtering method, for example, by forming a chromium underlayer with a thickness of about 50 to 2000 °. The magnetic layer formed on the underlayer is usually made of Co-C
r, Co-Ni, Co-Cr-X, Co-Ni-X, C
A magnetic thin film layer of a Co-based alloy represented by oWX or the like is preferable. Here, X is Li, Si, Ca,
Ti, V, Cr, Ni, As, Y, Zr, Nb, Mo,
Ru, Rh, Ag, Sb, Hf, Ta, W, Re, O
s, Ir, Pt, Au, La, Ce, Pr, Nd, P
One, two or more elements selected from the group consisting of m, Sm and Eu.

The metal magnetic layer made of such a Co-based alloy is usually formed on a base layer of a substrate by means such as sputtering. As the film thickness of the metal magnetic layer,
Usually, it is in the range of 50 to 600 °.

The protective layer includes a carbon film, a hydrogenated carbon film, a nitrogenated carbon film, a carbonized film such as TiC and SiC, SiN,
It is composed of a nitride film such as TiN, an oxide film such as SiO, Al ₂ O ₃ , ZrO and the like.
It is formed by a sputtering method, an ion plating method, a wet method, or the like. As the protective layer, a carbon film, a hydrogenated carbon film, and a nitrogenated carbon film are preferable.

For example, the hydrogenated carbon film is not particularly limited as long as it is a film containing hydrogen and carbon. For example, sputtering is performed in a plasma containing a rare gas and hydrogen gas with carbon as a target. It is formed by doing. As a target used here, diamond-like, graphite-like, or amorphous carbon is used.

Examples of the rare gas include argon, helium, neon, xenon, radon, and krypton. Of these, argon is particularly preferably used. The content of hydrogen gas in a sputtering atmosphere containing a rare gas such as argon gas and hydrogen gas is usually 2 to 2 times.
0 volume%, desirably in the range of 5 to 10 volume%. As the sputtering method, a DC magnetron sputtering method is usually employed, but a high-frequency magnetron sputtering method can also be used.

The pressure in the chamber during sputtering is generally 0.5 to 20 mTorr, preferably 1 to 1 mTorr.
The pressure is set to 0 mTorr, and the temperature of the substrate is usually 300 ° C. or lower, and preferably in a range from room temperature to 250 ° C. The distance between the substrate and the target, the sputtering time, the input power, and the like are appropriately determined according to the thickness of the hydrogenated carbon protective film to be formed. The thickness of the hydrogenated carbon protective film is usually 5
It is in the range of 0-1000 °, preferably 100-600 °.

A lubricant layer is provided on the surface of the protective layer. As the lubricant, for example, a fluorine-based liquid lubricant is used, and is usually formed on the surface of the protective layer by a dip coating method, a spin coating method, a spray coating method, or the like.
The thickness of the lubricant layer is typically in the range of about 15-50 °. After the formation of the lubricant layer, a heat treatment may be performed.
The heating temperature may be appropriately selected within a range of 50 ° C. or higher and lower than the decomposition temperature of the lubricant.

As the lubricant, a compound having a hydroxyl group at a terminal or a side chain and having a fluorocarbon skeleton in a molecular skeleton, such as perfluorocarboxylic acid ester, perfluorothiol carboxylic acid ester, perfluorodicarboxylic acid ester, Perfluoroalkyl esters of fluorocarboxylic acids, perfluorobenzoic esters,
Carboxylic acid perfluoroalkyl ester, dicarboxylic acid perfluoroalkyl ester, carboxylic acid perfluoroalkoxyalkyl ester, perfluorocarboxylic acid amide, perfluoropolyether, perfluoropolyethercarboxylic acid, perfluoropolyether alcohol, perfluoropolyether Esters and the like can be used. Such lubricants include Ausi
Fomblin-Z-DOL (trade name) and Fomblin-Z-Tetraol (trade name) manufactured by Mont Corporation
And the like.

The magnetic recording medium of the present invention is characterized in that the work of adhesion (polar component) between the protective layer and the lubricant layer is from 20 to 35 mNm ^-1 . In the present invention, the work of adhesion (polar component) between the protective layer and the lubricating layer is determined from the surface energy of the protective layer and the lubricant layer. As a method for analyzing the surface energy, a method using a contact angle with a test solution is generally known.

The contact angle θ, the surface free energy γ _S of the solid, the surface free energy γ _{L of} the liquid, the surface free energy γ _SL of the solid-liquid interface, and the work of adhesion W _SL have the following relationships (Young-Dupre Relation). ).

[0019]

Γ _S = γ _L · cos θ + γ _SL ... Γ _S + γ _L = γ _SL + W _SL ... W _SL = γ _L (1 + cos θ) Also, the surface free energy γ is a dispersive force component γ ^d , a dipole It is represented by the sum of a force component γ ^p and a hydrogen bond component γ ^h .

[0020]

## EQU2 ## γ = γ ^d + γ ^p + γ ^h The surface free energy γ _S (= γ _S ^d + γ _S ^p + γ _S ^h ) of a solid whose surface free energy is unknown is the contact angle with a test solution whose surface free energy is known. Can be obtained from The surface free energy of the test solution (A, B, C)

[0021]

Assuming that γ _LA = γ _LA ^d + γ _LA ^p + γ _LA ^h γ _LB = γ _LB ^d + γ _LB ^p + γ _LB ^h γ _LC = γ _LC ^d + γ _LC ^p + γ _LC ^h (Fowkes's theory, extended Fowkes by Kitazaki and Hata et al.
Theory).

[0022]

(Equation 4)

By solving this simultaneous equation, the surface free energy γ _{S of the} solid to be obtained and its three components γ _S ^d ,
γ _S ^p, it is possible to obtain the γ _S ^h. According to the above method, the surface free energies of the protective layer and the lubricant layer are obtained respectively. Further, since the contact between the protective layer and the lubricant layer is also considered to be a contact at the solid-liquid interface, the work of adhesion W between the protective layer and the lubricant layer is expressed as follows by applying the Fowkes' theory. .

[0024]

(Equation 5)

In the present invention, the polar component (W ^h ) of the work of adhesion refers to the sum of a dipole force component and a hydrogen bond component.

[0026]

(Equation 6)

As described above, the work of adhesion (polar component) can be determined. In the present invention, the work of adhesion (polar component) is preferably in the range of 20 to 35 mNm ^-1 . If the amount of adhesion work (polar component) is smaller than the above range, the adhesion between the protective layer and the lubricant layer is weak and the lubricating performance is deteriorated. Become. Thus, the work of adhesion is also very useful as a guideline for evaluating the durability of a magnetic recording medium.

In the present invention, the type of the protective layer and the type of the lubricant layer may be appropriately selected so that the adhesive work (polar component) in the above range can be obtained. For example, when the protective layer is made of hydrogenated carbon, DOL2000 is used as a lubricant.
It is preferable to use By setting the work of adhesion (polar component) between the protective layer and the lubricant layer within the range of the present invention, a magnetic recording medium having excellent durability can be provided.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. FIG. 3 is a schematic diagram showing the configuration of the contact angle measuring device used in the present invention. That is, the sample liquid dropped from the micro syringe contacts the surface of the object to be measured (protective layer, lubricant) on the stage,
A curved liquid surface is formed by surface tension. The contact surface between the sample liquid and the surface of the object is photographed by a CCD camera in a direction facing the light source and in a horizontal direction. The amount of the sample liquid dropped from the syringe varies depending on the surface tension of the liquid, but is 1 to 2 ml.

(1) Measurement of Surface Free Energy of Protective Layer On an Al disk-shaped substrate provided with a Ni-P plating layer, a Cr underlayer and a Co-based magnetic layer were formed on a disk, and hydrogenated by sputtering. Carbon protective layer (film thickness 15
0 °). The sputtering conditions are shown below.

[0031]

[Table 1] Water (γ ^d + γ ^p + γ ^h ), ethylene glycol (γ ^d + γ ^h ), formamide (γ ^d + γ ^p + γ ^h ) as a test solution
Angle (°) of the hydrogenated carbon protective layer obtained by using
Is shown below.

[0032]

[Table 2] The surface free energy (mNm ^-1 ) of the protective layer calculated from the measured contact angle is shown below.

[0033]

[Table 3]

(2) Measurement of Surface Free Energy of Lubricant Layer The surface free energy when the lubricant is present as a bulk, not the surface on which the lubricant is applied, is determined.
It is considered that the lubricating film has an adsorbed layer adsorbed on the interface of the protective film and a free lubricating layer having fluidity on the adsorbing layer.
Assuming that the Lub layer has the same properties as the bulk,
The surface free energy on the formed thick film was defined as the bulk surface free energy. Lubricants are available from Ausimont Dol 2000, Dol 4000, Tetraol
2000S (each trade name) was used. The structure and properties of each lubricant are shown below.

[0035]

X-CH ₂ -CF ₂ -[(O-OF ₂ -CF ₂ ) _p- (O-CF ₂ )
_{q] -O-CF 2 -CH 2} -X Fomblin Z dol X = -OH

[0036]

[Table 4] An undiluted solution of a lubricant was dropped on the disk, spread over the surface with a nonwoven fabric, and a thick film was formed. The actually applied film thickness was 50 to 100 times the thickness of the lubricant layer of a normal magnetic recording medium.

The test solution contained n-hexadecane (γ ^d
Type) and water (γ ^d + γ ^p + γ ^h type). First, n-H
The contact angle of exadecane is measured. n-Hexa
Decane is a liquid having only a γ ^d component. Since it is a good approximation that dispersive force and polar force are additive and that they do not interact with each other, applying Fowkes's theory, the interface free energy becomes

[0038]

(Equation 7) It is expressed as Applying this, Young's formula and Dupre's formula to each component,

[0039]

Γ _S ^d is determined as an unknown from γ _S = γ _SL + γ _L · cos θ γ _L + γ _S = γ _SL + W _SL . Similarly, using the obtained value of γ _S ^d

[0040]

(Equation 9) Γ _S ^Ph is obtained. The measured contact angle values are shown below.

[0041]

[Table 5] The surface free energy (mN
m ^-1 ) are shown below. Here, γ ^ph is the sum of the dipole force component and the hydrogen bond force component.

[0042]

[Table 6]

(3) Calculation of adhesion work The adhesion work calculated for the combination of the hydrogenated carbon protective layer and the lubricant from the respective surface energies obtained in the above (1) and (2) is shown below. (Here, the polar component γ ^ph of the lubricant layer is assumed to be γ ^h = γ ^ph because the hydrogen bonding force component caused by the hydroxyl group is considered to be the majority.) W ^d is the dispersive force of the adhesive work. component, W ^h represents a polar component of the adhesion amount of work.

[0044]

[Table 7] FIG. 1 shows the relationship between W ^h and hydrogen gas Flow.

(4) Durability At a hydrogen concentration of 9% in the atmosphere, Dol was deposited on the hydrogenated carbon protective film.
FIG. 2 shows the results of evaluating the CSS characteristics of a magnetic recording medium on which 2000 (●) and Dol 4000 (○) were formed as lubricant layers. The magnetic recording medium was assembled in an actual drive under the conditions of 32 ° C. and 80% RH, and drive torque after repeated start and stop was measured, and evaluated by the relationship between the number of CSSs and the drive torque.

As described above, the work of adhesion (polar component) W ^h in this case is Dol 2000: 23.4 mN.
m ^-1 and Dol 4000: 15.6 mNm ^-1 . Dol whose work of adhesion (polar component) is within the scope of the present invention
It can be seen that in the case of 2000, stable CSS characteristics are exhibited.

[0047]

As described above, according to the present invention,
In addition to obtaining a magnetic recording medium having excellent durability, effects such as easy selection of a lubricant suitable for the protective layer and estimation of durability can be realized in a short time.

[Brief description of the drawings]

Figure showing adhesion workload W ^h in the embodiment of the present invention; FIG.

FIG. 2 is a diagram showing CSS characteristics according to the embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a contact angle measuring device used in the present invention.

Claims (3)

[Claims] 1. A protective layer and a lubricant layer are formed on a magnetic layer.
A magnetic recording medium comprising a protective layer and a lubricant layer.
Adhesion work (polar component) is 20 to 35 mNm ^-1Is
And a magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the protective layer is a hydrogenated carbon protective layer. 3. A method for evaluating a magnetic recording medium having a protective layer and a lubricant layer, wherein the work of adhesion (polar component) between the protective layer and the lubricant layer is used as an index of durability.