JP2512113B2 - Thin film magnetic disk - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film magnetic disk suitable for high density recording used in a magnetic storage device of a computer.

Conventional technology As a thin-film magnetic disk that uses a metal thin film or metal oxide thin film for the magnetic layer, a vacuum deposition method or plating is usually used on a substrate whose surface is an aluminum alloy plate that has been subjected to alumite treatment, nickel-phosphorus plating treatment, or the like. A thin film magnetic layer formed by a method or the like has been put into practical use. In general, a so-called contact start stop (CSS) method is adopted in which the magnetic head floats above the disk surface when the magnetic disk is in operation and contacts the disk surface when stopped. In this case, in order to withstand the sliding contact between the magnetic head slider and the disk surface at the time of start or stop, the magnetic head normally formed on the disk surface by the texturing of the substrate surface is provided with a groove substantially parallel to the running direction. The magnetic thin film is provided with a protective film mainly containing graphite, SiO ₂ or the like, and a lubricant layer is provided on the surface of the protective film.

Problems to be Solved by the Invention In order to improve the recording density, it is necessary to reduce the flying distance of the magnetic head. At that time, the height of the projection shape generated by the texturing is reduced to improve the surface shape. As a result, CSS durability is sacrificed, and it becomes difficult to secure practical performance.

Further, the texturing is usually a process in which minute scratches are generated in the disk circumferential direction due to abrasive wear caused by abrasive grains, and the projection shape is a gradient such as a mountain range ridge in the circumferential direction. It's very loose. Such a gentle slope is easily deformed and destroyed by the impact force of the magnetic head slider,
Further, when the magnetic head slider slides, surface contact is likely to occur, and the coefficient of friction tends to be higher than in the case of point contact.

The present invention has been made in view of the above-mentioned problems, and it is possible to solve the above-mentioned problems by allowing a large number of small protrusions having a steep gradient to exist on the disk surface and making the contact with the magnetic head slider a point contact. An object is to provide a solved thin film magnetic disk.

Means for Solving the Problems In order to achieve the above object, the present invention provides a substrate having a height of 100 μm on a hard non-magnetic smoothing layer having a thickness of 5 μm or more made of a material having a Vickers hardness of 100 or more.
~ 500Å, height: length ratio in the plane direction 0.1 or more, areal density 1 × 10
A microprojection group of ⁷ to 1 × 10 ⁹ pieces / mm ² is provided, on which a magnetic thin film layer, a protective layer, and a lubricant layer are sequentially provided. Desirably, the microprojection group occupies the entire surface area. The area ratio is 1 to 50%.

Here, in the thin film magnetic disk, the thickness of the magnetic thin film is about 500 in the metal system such as CoP, CoNi, CoNiP, CoNiCr and CoCr.
Å, γ-Fe ₂ O ₃ is about 1000Å for oxides, and the total thickness is 2000Å even if an underlayer and a surface protection layer are added to these, so the shape of the substrate surface is almost the same as the disk surface shape. Reflected. The greatest feature of the present invention resides in that micro-projections having a steep gradient are arranged on the surface of the substrate, instead of the protrusions having an average gentle slope as seen in the conventional texturing process.

In addition, as a substrate for a thin film disk, generally, a substrate having a hard alumite layer having a thickness of 10 μm or more or a NiP alloy plating layer having a thickness of 20 μm or more on the surface of Al alloy is used, and the hardness of the surface material is Hundreds or more are needed by Vickers. And its thickness is at least 10μ
m or more is required.

The second feature of the present invention is that the substrate surface has a Vickers hardness of 10
It is to be 0 or more, and the thickness of the hard surface layer may be 5 μm or more. The reason why the hardness and the thickness can be reduced is that the minute projections having the steep gradient are arranged on the substrate surface.

First, the substrate used in the present invention has a thickness of 5 μm, at least the surface of which has a Vickers hardness of 100 or more.
It is necessary to be composed of the above hard non-magnetic smooth layer, and when the surface is made of a material with a Vickers hardness of 100 or less, or even if the surface has a Vickers hardness of 100 or more and its thickness is 5 μm or less. It is difficult to obtain the desired CSS life. Secondly, on the non-magnetic smooth layer, a height of 100-5
00Å, height: length ratio in the plane direction of 0.1 or more, areal density 1 × 10 ⁷ 〜
It is necessary to provide a group of microprotrusions of 1 × 10 ⁹ pieces / mm ² , and it is appropriate that the height of the group of protrusions is in the range of 100 to 500Å as an average value of the maximum height. Durability deteriorates, and conversely, at 500 Å or higher, output decreases greatly and it is difficult to obtain high recording density. Also, the ratio of the height of the protrusion to the surface length is 0.
When it is 1 or less, CSS durability is deteriorated. CSS when the surface density is 1 × 10 ⁷ / mm ² or less, or 1 × 10 ⁹ pieces / mm ² or more
Durability decreases.

The fine projection group is provided on the non-magnetic smooth layer, but it is most preferable that the area ratio of the fine projection group in the total surface area of the non-magnetic smooth layer is 1 to 50%. The CSS durability is further improved as compared with the case where this ratio is out of the above range.

Effect In the disk of the present invention, during CSS, the surface of the magnetic head slider makes point contact with the tips of the projections of the minute projections present on the disk surface, so the frictional resistance is reduced, and good adhesion and fracture characteristics do not occur. Is secured. Further, the lubricant which is usually applied to the surface of the disk is held between the minute projections on the surface of the disk and is supplied to the tips of the minute projections by the action of surface tension. As a result, a good CSS life can be obtained.

Embodiment FIG. 1 is a partially enlarged view of a cross section in the thickness direction of a magnetic disk according to an embodiment of the present invention. In the figure, 1 is a substrate, 2 is a hard non-magnetic smooth layer on the surface of the substrate 1, 3 is fine protrusions on the hard non-magnetic smooth layer 2, 4 is a magnetic thin film layer, 5 is a protective layer, and 6 is a lubricant layer. is there. Reference numeral 7 indicates a fine protrusion portion on the disk surface corresponding to the fine protrusion 3, and reference numeral 8 indicates a smooth portion on the disk surface corresponding to a smooth portion on which the fine protrusion 3 does not exist. As described above, the shape including the minute protrusions on the substrate surface is reflected on the disk surface as it is.

As the substrate 1 used in the present invention, an aluminum or aluminum alloy plate having a hard non-magnetic smooth layer 2 provided with an alumite treatment layer, a Ni or NiP plating treatment layer or the like, a plastic molded plate or a reinforced plastic plate is used. A Ni- or NiP-plated layer, a glass plate, a ceramic plate, or the like can be used, and their surfaces must be mirror-finished (for example, 0.001 μm in Ra).

As a method of forming the group of minute projections 3 on the hard non-magnetic smooth layer 2, for example, there is a method in which fine particles having a particle size of 100 to 500Å are fixed to the surface of the substrate 1 by a resin binder. , Inorganic particles such as alumina, silica, titanium oxide, polyester, polyamide, polyarylate, polysulfone, polyphenylene oxide, polyimide, epoxy, cross-linked styrene, cross-linked acrylic, cross-linked benzoguanamine, cross-linked melamine and other high-molecular compound particles, carbon fine particles, Fine particles of metal alkoxide hydrolyzate can be used. As the resin binder, saturated polyester such as polyethylene terephthalate and polybutylene terephthalate, polyamide such as nylon 6, nylon 66, nylon 610, nylon 11 and nylon 12, polystyrene, polycarbonate, polyarylate, polysulfone, polyether sulfone, Various resins such as polyacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, phenoxy resin, polyimide, polyamide imide, etc. can be used as a single substance, a mixture, a copolymer, etc., and also an epoxy resin, urethane resin A crosslinkable resin such as silicone resin or phenol resin can also be used. The hard non-magnetic smooth layer 2 of the substrate 1 is prepared by adding the above fine particles to a dilute solution of these resin binders.
By coating on top, a group of minute projections 3 is formed. It is suitable to add 50 to 300 parts by weight of fine particles to 100 parts by weight of the resin binder. A thin layer of the binder resin exists on the smooth portion 8 other than the protrusions 3 of the substrate 1 having the group of minute protrusions 3 thus obtained. If the thickness of this thin layer is 500 Å or less, the thin layer itself is formed. It does not directly affect disk performance. The method for forming the fine projections is not limited to the above, and a method of depositing metal, oxide or the like in an island shape by a method such as sputtering, ion beam vapor deposition or plating can be used.

As the magnetic thin film layer 4, Co-Ni, Co-Ni-Cr, Co-Cr, C
A well-known thin film layer obtained by a sputtering method such as o-Ni-P or γ-Fe ₂ O ₃ or a plating method can be used.
It is also possible to provide an underlayer such as i. A suitable thickness of the magnetic thin film layer 4 including the underlayer is 500 to 5000Å.

As the protective layer 5, thin films of various inorganic / organic non-magnetic materials with a thickness of 50 to 500 Å can be used. In particular, various carbon thin films obtained by sputtering, CVD, etc., SiO ₂ thin films obtained by wet method, etc. Is suitable.

As the lubricant layer 6, perfluoroalkyl polyether and its derivative, a fluoroalkyl group-introduced fatty acid,
Suitable are fatty acid esters, fatty acid amides, metal soaps, silicone compounds, fluorine-based surfactants, etc., and the amount present is 0.1 to 100 mg per 1 m ² of the surface.

 Hereinafter, examples will be described more specifically.

Mirror surface buffed aluminum alloy plate with a diameter of 95 mm and a thickness of 1.2 mm 1
A hard non-magnetic smooth layer 2 is formed by forming a plating film with various hardnesses and various thin films made of Ni or NiP on the surface of nickel by electroplating or electroless plating, and then buffing the surface again to make it mirror-finished. And On this layer 2, fine projection groups of various shapes were formed by the following methods A to C.

(A) Polyvinyl alcohol aqueous solution containing 4 kinds of silica colloids with average diameters of 50Å, 100Å, 210Å, 400Å (silica colloid concentration 1000ppm, polyvinyl alcohol concentration
500 to 2000 ppm) was applied and dried.

(B) Polyacrylate emulsion (particle size 600
Å) diluted solution (particle concentration 3000ppm) is applied and dried at 150 ℃
Heat treatment was performed for 10 minutes.

(C) A solution of polyethylene terephthalate in dichloroacetic acid (concentration 2000 ppm) was applied and dried by heating at 150 ° C. for 30 minutes.

From the SEM photographs of the surface and the fractured surface of the sample obtained by these methods, the average height of the microprotrusions, the height: plane length ratio, and the areal density were determined. After that, the Cr underlayer (thickness 1000Å), CoNi magnetic layer 4 (see
00 Å) and carbon protective layer 5 (200 Å) were sequentially formed, and finally, a perfluoropolyether lubricant was applied so that 1 mg per 1 m ² of the surface was formed, and a lubricant layer 6 was formed as a sample. From the surface SEM photographs of each of these samples, the ratio of the area (occupied area) of the microprojections 3 to the entire surface was obtained. Then, the CSS durability of each sample was evaluated by performing CSS measurement. At that time, when the friction coefficient exceeds 1.0, or
The life was defined when the head crash occurred. The types and contents of the above samples and their CSS test results are summarized in Table 1. The prototype disc numbers in parentheses in the table are comparative examples.

From Table 1, it is necessary that the hardness of the hard non-magnetic smooth layer 2 be 100 Hv or more [see Comparative Examples (15) and (16)].
The thickness must be 5 μm or more [see Comparative Example (4)], the height of the microprojections 3 must be 100 Å or more [see Comparative Example (14)], and the ratio of height: length in the plane direction. Is 0.1
The above is required [see Comparative Example (19)], and the areal density is 1
× 10 ⁷ to 1 × 10 ⁹ pieces / mm ² is appropriate [Comparative example (2
0), (21)], and more preferably, the occupied area of the three groups of minute projections is 1 to 50% [see Examples 3, 7, and 17].

In view of the above, it is clear from Table 1 that all the CSS test results are good within the scope of the claims of the present application. In addition, in the configuration according to the above-described embodiment, the minute protrusions 3
When a protrusion is formed by the conventionally known texture processing instead of the group, the hardness of the hard non-magnetic smooth layer is 100Hv, 180H.
With v, the CSS durability was 5000 times or less even if the thickness was 20 μm. Even when the hardness was 550 Hv and the thickness was 20 μm, the CSS durability was 10,000 times or less when the texture protrusion height was 500 Å or less.

Effect of the Invention According to the present invention, it is possible to secure practical CSS durability in a region where high recording density with small surface roughness is possible by adopting a group of minute protrusions instead of the conventional texture shape. The present invention is industrially valuable.

[Brief description of drawings]

FIG. 1 is a sectional view in the thickness direction of a thin film magnetic disk according to the present invention. 1 ... Substrate, 2 ... Hard non-magnetic smooth layer, 3 ... Minute protrusions, 4 ... Magnetic thin film layer, 5 ... Protective layer, 6 ... Lubricant layer.

Claims (2)

(57) [Claims] 1. A height of 100 to 500Å, a height: plane length ratio of 0.1, on a substrate composed of a hard non-magnetic smooth layer having a thickness of 5 μm or more and made of a material having a Vickers hardness of 100 or more. As described above, the thin film magnetic layer is characterized in that a group of minute projections having an area density of 1 × 10 ⁷ to 1 × 10 ⁹ pieces / mm ² is provided, on which a magnetic thin film layer, a protective layer, and a lubricant layer are sequentially provided. disk. 2. A thin-film magnetic disk according to claim 1, wherein the ratio of the area of the microprojections to the total surface area is 1 to 50%.