JPH0626012B2 - Magnetic disk substrate - Google Patents

Description

The present invention relates to a substrate for a magnetic disk used as a storage medium.

<Prior Art> The substrate of a thin-film magnetic disk for high-density recording must have sufficient strength for convenience of handling, and should be able to withstand a temperature rise when forming a magnetic medium by sputtering. It is necessary to have high heat resistance and high surface accuracy and sufficient hardness so as to enable high-density magnetic recording and to secure required abrasion resistance against sliding contact of the magnetic head.

Conventionally, after mirror-polishing both surfaces of a thin plate of aluminum alloy, to form a surface layer by electroless nickel plating or alumite coating treatment, after polishing the surface, chromium, iron, nickel, cobalt A magnetic film made of, for example, is formed by coating, plating, sputtering or the like, and a protective film is further formed on the surface to complete a magnetic disk.

However, in order to form a good surface layer, the aluminum core plate is required to have a highly accurate surface roughness of about 0.015 μm, and therefore an expensive aluminum alloy material containing no non-metallic inclusions is required. In addition, since the aluminum alloy is relatively soft, it is difficult to process the surface thereof, which causes an increase in the cost of the magnetic disk substrate. Further, the electroless nickel plating layer has a thickness of about 10 to 20 μm, so that the strength is not always sufficient, and since magnetic transformation occurs at around 250 ° C., when a magnetic film is formed by sputtering, As the temperature rises, the magnetic characteristics are deteriorated, or a special sputtering process is required to suppress the temperature rise, which causes a large amount of time in the manufacturing process. Furthermore, when performing the alumite treatment, if the thickness of the surface layer is made sufficiently large so as to obtain sufficient strength, defects such as bores are likely to occur on the surface. Further, since the polishing process is required twice, the manufacturing cost rises, and the manufacturing requires a lot of time.

Therefore, as disclosed in Japanese Examined Patent Publication No. 53-37202, it has been proposed to attach a fine powder of a ceramic material to the surface of an aluminum core plate by sputtering to form a hard surface layer. When the surface layer is formed by sputtering or vapor deposition, it takes time to form the film and heat is dissipated.
It is difficult to increase the thickness to more than μm. If the hard coating is thin, the strength of the magnetic disk becomes insufficient, and the strength of the magnetic disk becomes insufficient when it comes into contact with the magnetic head, or handling problems such as damage when dropped on the floor are likely to occur.

In consideration of the above problems, the applicant of the present invention has disclosed in Japanese Patent Application No. 61-230910 dated Sep. 29, 1986 that a core material made of aluminum or an aluminum alloy has a surface made of a ceramic material or a glass material. By joining the layers, a magnetic disk substrate having sufficient strength, heat resistance, surface accuracy and surface hardness is proposed.

However, the shellac or glass layer used for the surface layer generally has a small coefficient of thermal expansion, whereas the aluminum or aluminum alloy forming the core material has a large coefficient of thermal expansion. Therefore, if both are pressed and heated to join,
Distortion may occur due to a difference in size between the two.
Also, when this substrate is incorporated into a magnetic disk device,
The reading accuracy may be deteriorated due to the temperature change.

<Problems to be Solved by the Invention> Therefore, an object of the present invention is to provide an improved magnetic disk substrate having strength, surface accuracy and surface hardness required for a magnetic disk substrate, and particularly excellent heat resistance. To do.

<Means for Solving the Problems> According to the present invention, such an object is a magnetic disk substrate, a core plate made of titanium or a titanium alloy, an insert material layer, nickel, titanium, a nickel alloy. Alternatively, it can be achieved by providing a magnetic disk substrate characterized by laminating a titanium alloy layer and a glass or ceramic layer in this order.

<Operation> By using titanium or a titanium alloy as the core material and using the ceramic or glass layer as the surface hardened layer in this way, particularly excellent heat resistance can be obtained together with sufficient strength, denseness and hardness. In particular, nickel, titanium or alloys thereof have good adhesion to glass-based materials.

<Embodiment> Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a magnetic disk substrate according to the present invention. First, the core plate 1 made of a titanium alloy or pure titanium is prepared, but unlike the case of the prior art, the surface roughness thereof does not pose a problem. Next, the thickness is about 50 μm
Glass thin plate made of soda-lime glass of ~ 500 μm 2
A nickel film 3 is formed on one surface of the substrate by PVD (physical vapor deposition) or plating to a thickness of 0.5 μm to 20 μm. The thin plate 2 may be made of a ceramic material such as alumina, zirconia, silicon carbide, or silicon nitride, or a glass material such as quartz glass or borosilicate glass,
The nickel film 3 may be made of titanium, a nickel alloy or a titanium alloy. Next, between the nickel film 3 and the surface of the core plate 1, a copper alloy thin plate 4 as an insert material having a thickness of 0.5 μm to 100 μm is inserted and placed 548.
They are pressed against each other at a temperature of from ℃ to 630 ℃.

The magnetic disk substrate thus obtained has a temperature of 350 ° C.
Even when the magnetic film is sputtered at the above temperature, there is no adverse effect. Further, even if the rapid cooling process of heating to 400 ° C. and immersing it in water was repeated 5 cycles, no abnormality such as cracking or deformation occurred. Further, regarding the sample obtained by chamfering the thin glass plate 2, no damage or cracking occurred even when it was dropped onto a vinyl chloride tile from a height of about 1 meter. In addition, when a cracking test was conducted on such a sample, it was found that even if a crack in the glass layer occurred, the bonding surface did not peel off and sufficient bonding strength was obtained.

As the insert material, pure copper or a copper-based (copper alloy) brazing material is suitable. Copper or copper alloy does not have good adhesion to glass, but nickel, titanium, etc. have good adhesion to glass. Therefore, as described above, using the insert material made of the copper alloy thin plate 4 sandwiching the nickel film 3,
As described above, a sufficient bonding force can be obtained by performing the pressure contact while heating to the temperature of 548 ° C to 630 ° C.

<Effects of the Invention> As described above, according to the present invention, by using titanium or a titanium alloy having a relatively small coefficient of thermal expansion as a core material, the heat resistance of the substrate itself is significantly improved and at the same time, the change over time is reduced. be able to. Therefore, even when incorporated in a magnetic disk, the dimensional change due to a rise in temperature is small, so that the reading accuracy can be improved. Furthermore, since titanium generally has relatively high rigidity, the core material can be made thinner, the weight of the substrate can be reduced, the moment of inertia can be reduced, and the time required to reach a predetermined rotation speed during use can be shortened. There are advantages such as getting.

[Brief description of drawings]

FIG. 1 is a sectional view of a magnetic disk substrate according to the present invention. 1 ... Core plate, 2 ... Glass thin plate 3 ... Nickel film, 4 ... Copper alloy thin plate

Claims (2)

[Claims] 1. A magnetic disk substrate comprising: a core plate made of titanium or a titanium alloy; an insert material layer; a nickel, titanium, nickel alloy or titanium alloy layer; and a glass or ceramic layer laminated in this order. A magnetic disk substrate characterized by being formed. 2. The magnetic disk substrate according to claim 1, wherein the insert material is made of copper or a copper alloy.