JPH07105042B2 - Method for improving corrosion resistance of base metal plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of use" The present invention relates to a treatment method for improving the corrosion resistance of an aluminum plate, which is a base material, in the production of a magnetic disk after the undercoating.

“Prior Art” A magnetic disk device is becoming more and more important as a storage device in a computer system year by year, and there is a demand for higher density of a magnetic recording medium for the purpose of downsizing and cost reduction.

For magnetic disks, the surface of the base aluminum plate is a magnetic medium (CoNiP for the plating method, CoNi, CoN for the sputtering method).
It is manufactured by coating with iCr, etc., but an underplating layer is interposed between them in order to improve the adhesion between them.

The base plating layer is usually NiP electroless plated to a thickness of 2
Although it is formed to have a thickness of 0 to 100 μm, Ni contains 8 to 12 wt% of P, is nonmagnetic, and has high corrosion resistance. Improving the corrosion resistance of this underplating is extremely important in extending the life of the magnetic disk, and it is necessary to improve the technology for performing the underplating. Has a big impact,
Energetic research is underway to develop even better base plating.

Conventionally, the baking process has been
Clean oven is used, atmospheric atmosphere, under normal pressure, 10
It is carried out under conditions of 0 to 200 ° C and 1 to 3 hours. By this treatment, the stored hydrogen is removed, the stress of plating is made uniform, and the corrosion resistance is improved, but the baking conditions are changed within the above range depending on the P content of the undercoat.

"Problems to be solved by the invention" By the way, unlike a floppy disk, a hard disk does not need to take out a magnetic disk from a computer.
Used as part of a computer, the life of a magnetic disk is directly linked to the life of the computer. In addition, the computer using the hard disk,
Since it is used in ordinary households as well, it must be able to withstand the environmental conditions of each country in the world.

Corrosion of the magnetic disk may occur from the surface, but often occurs due to corrosion of the undercoat. For example, a small amount of acid used in the pretreatment remains in pinholes, etc., which causes corrosion to start and when it reaches the base aluminum, since aluminum is weak against acid, corrosion easily spreads and adheres to the base plating. Becomes defective. If the adhesion is poor, a bulge occurs due to the stress of the undercoat, and the magnetic medium also bulges and cannot be used. However, the conventional baking method is not sufficiently effective in preventing the corrosion of the undercoat.

The present inventor, as a result of earnest research to solve the above problems, discovered that the corrosion resistance of the undercoating is improved when baking is performed under reduced pressure.

The present invention has been made based on the above findings, and provides a method for improving the corrosion resistance of a base plating, which allows a base aluminum and a magnetic medium to be in close contact with each other, and further, a base plating without substantially permanent corrosion can be obtained. The purpose is to provide.

"Means for Solving Problems" The present invention has been made to achieve the above-mentioned object, and its gist is to perform baking after subjecting the surface of the base aluminum to undercoating in the manufacture of a magnetic disk. ,Ten
It is a method of improving the corrosion resistance of undercoating performed under a vacuum of ^-4 to 10 ^-7 Torr.

[Operation] In the present invention, the base plating is baked under a vacuum of 10 ⁻⁴ to 10 ⁻⁷ Torr, so that the acid used for the pretreatment and the factors that cause the initiation of corrosion are completely removed.

[Examples] In the present invention, it is necessary to perform baking after performing electroless plating of NiP on the base aluminum, at a vacuum degree of ^10-4 to ^10-7 . At this time, the corrosion resistance increases as the degree of vacuum during baking increases, but 10 ^-4
The effect is not sufficient in the following degree of vacuum Torr, 10 ^-7 Torr
Even if the degree of vacuum is higher than that, the effect is not improved and it is not economical.

In addition, the baking temperature and time are the same as those in the conventional baking method using a clean oven.
It is carried out under the conditions of ~ 200 ° C and 1-3 hours. Temperature is 100 ℃
If it is less than 200 ° C., the effect of improving the corrosion resistance is small, and if it exceeds 200 ° C., it may cause magnetism when a commercially available plating bath for hard disk is used.

In addition, the baking time, when using the above temperature range,
Even if the temperature is low, if the time is increased, the same effect as when the temperature is increased and the time is shortened is obtained. For example, 3 hours at 150 ℃
The base plating treated for 6 hours has a higher corrosion resistance than that for the treatment, but there are some that can obtain the same corrosion resistance even if treated for 3 hours at 200 ° C. However, the shorter the baking time, the higher the use efficiency of the oven and the more economical.

Also, after baking under vacuum, the effect of improving the corrosion resistance is remarkable even if it is returned to room temperature and normal pressure in an air atmosphere, but the surface may be oxidized and the magnetic properties may become poor. After baking in the atmosphere, it is preferable to introduce an inert gas such as N ₂ or Ar, maintain this atmosphere, return the inside of the oven to normal temperature and pressure, and then take it out.

In addition, since the base plating has a considerably high corrosion resistance for the determination of the corrosion resistance of the undercoat, no difference is recognized in the salt spray test or the heat shock test used for judging the superiority or inferiority of the usual plating, which is not suitable. Therefore, instead of the salt spray test, an immersion test in which this is made harder is used.
As the immersion liquid used, an HCl aqueous solution or the like, which is likely to remain on the surface of the undercoat, is suitable.

The comparison method is that the base aluminum plate is subjected to undercoating, the surface is mirror-polished, and then baked, and this is immersed in an aqueous solution of HCl or the like of a predetermined concentration for a predetermined time and taken out,
Corrosion resistance was compared by visually observing the changed portion of the mirror surface and showing the ratio of the area to the total area by%.

Example 1 A base aluminum plate was immersed in a non-magnetic NiP plating bath for a magnetic disk for 3 hours so that the P content was 11.5 wt% and the thickness was 36 μm.
After undercoating and mirror polishing, this was baked in a vacuum oven at 150 ° C for 2 hours while changing the degree of vacuum. After baking the end, it introduced the N ₂ in the oven, N ₂
In the atmosphere, the temperature was returned to normal temperature and pressure. This underplated aluminum plate was immersed in a 2 wt% HCl aqueous solution for 48 hours to measure the corrosion resistance. The first is the relationship between each degree of vacuum and corrosion resistance.
Shown in the figure. As is clear from FIG. 1, it is found that the corrosion resistance is almost saturated between 10 ^{−4 and} 10 ⁻⁵ Torr.

Example 2 The same as Example 1, except that the degree of vacuum during baking was set to 10 ⁻⁶ Torr and the baking temperature was changed to 100 to 200 ° C.
The relationship between the baking temperature and the corrosion resistance was obtained. Second result
Shown in the figure. As is clear from FIG. 2, the corrosion resistance increases as the temperature rises. Further, at a temperature in this range, even if the degree of vacuum was set to 10 ^-6 Torr, the non-magnetic property of the undercoating was not deteriorated, and the surface was not hardened or cracked, and the surface condition was not deteriorated.

Example 3 A base aluminum plate was immersed in a non-magnetic NiP plating bath for a magnetic disk for 3 hours to carry out undercoating with a P content of 12.5 wt% and a thickness of 36 μm, and after mirror polishing, this was vacuumed in a vacuum oven. Was changed, and baking was performed at 150 ° C. for 2 hours. After completion of baking, N ₂ was introduced into the oven, and the temperature was returned to normal temperature and pressure in N ₂ atmosphere. This underplated aluminum plate was immersed in a 2 wt% HCl aqueous solution for 48 times to measure the corrosion resistance. The relationship between each degree of vacuum and corrosion resistance is shown in FIG. As is clear from FIG. 3, it was found that the corrosion resistance was almost saturated between 10 ^{−4 and} 10 ⁻⁵ Torr.

Example 4 The relationship between the degree of vacuum and the corrosion resistance was determined in the same manner as in Example 1 except that the corrosion resistance test was carried out by dipping it in a 5 wt% NaCl aqueous solution for 96 hours. Results are shown in FIG. As is clear from Fig. 4,
The tendency is the same as when using the HCl aqueous solution, but the result is that the corrosion resistance is high. Therefore, when comparing the difference in corrosion resistance, an aqueous HCl solution, which shows a large difference, is suitable.

Example 5 Except that the baking temperature was 100 ° C, 175 ° C, and 200 ° C,
In the same manner as in Example 1, the relationship between the degree of vacuum at each temperature and the corrosion resistance was determined, and each temperature is shown as a parameter in FIG. From FIG. 5, it can be seen that the higher the temperature, the higher the corrosion resistance, and that the corrosion resistance is almost saturated when the degree of vacuum is between 10 ^{−4 and} 10 ⁻⁵ Torr.

"Effects of the Invention" As described above, the method for improving the corrosion resistance of the undercoat according to the present invention, in which the baking after applying the undercoat to the base aluminum is performed in a vacuum of 10 ^-4 to 10 ^-7 Torr is Has the effect of greatly improving the corrosion resistance of the magnetic disk and making the life of the magnetic disk almost permanent, and it greatly contributes to the field of computer industry.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the degree of vacuum and corrosion resistance in Example 1, FIG. 2 is a diagram showing the relationship between baking temperature and corrosion resistance in Example 2, and FIG. 3 is a diagram corresponding to FIG. 1 in Example 3. FIG. 4 is a view corresponding to FIG. 1 in Example 4, and FIG. 5 is a view corresponding to FIG.

Claims (1)

[Claims] 1. A method for improving the corrosion resistance of an undercoating, characterized in that, in the production of a magnetic disk, baking after applying undercoating to the surface of a base aluminum plate is performed in a vacuum of 10 ⁻⁴ to 10 ⁻⁷ Torr. Method.