JPH0250529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for manufacturing a magnetic disk used as a recording medium in a magnetic disk device.

BACKGROUND TECHNOLOGY, PRIOR TECHNOLOGY AND PROBLEMS Recent magnetic disk devices aiming at high density use contact start and
Many of them use the stop (CSS) method. As the name suggests, the CSS method means that when the magnetic disk stops rotating, the magnetic head contacts the magnetic disk surface, and when the magnetic disk rotates, the magnetic head slides in contact with the magnetic disk surface, increasing the rotational speed. As the speed increases, it is floated by wind pressure, and when steady rotation is reached, a predetermined floating height is reached, and writing or reading is performed through this gap.
Alternatively, the magnetic head is brought into contact with the surface of the magnetic disk again when the magnetic disk stops rotating. In this case, it is desired that the magnetic disk has good electromagnetic properties, as well as good surface smoothness, abrasion resistance (or durability), etc. with respect to the contact sliding movement.

Conventionally, there is a CSS type magnetic disk whose surface is coated with a lubricant to improve durability. For example, magnetic powder and thermosetting resin such as epoxy resin are mixed with a binder diluted with a solvent, thoroughly kneaded and dispersed using a ball mill, etc., and then applied by spin coating or the like onto a non-magnetic substrate such as an aluminum alloy substrate. The resin is thermally cured in a heat treatment furnace, and further polished to a predetermined film thickness and surface roughness, and then a lubricant is applied to the surface. However, when the surface is simply coated with lubricant,
Due to the repetition of the above-mentioned contact and sliding, the lubricant is peeled off in a relatively short period of time, causing so-called lubrication failure, which causes scratches on the magnetic disk surface in a relatively short period of time.

In addition, in order to prevent the above-described loss of lubrication, other conventional techniques include making the surface layer of the magnetic disk somewhat rough to make it easier to retain the lubricant, or forming micropores in the surface layer of the magnetic disk to lubricate it. There are some that have been impregnated with a chemical. However, these
The production of the magnetic disk surface layer is complicated, and it is difficult to produce a magnetic disk surface layer of uniform quality. In addition, there is a problem that the magnetic disk surface layer is not sufficiently durable.

Purpose of the Invention In view of the above-mentioned problems with the conventional magnetic disk, the present invention improves the durability by increasing the lubricant absorption rate (or content) while maintaining the electromagnetic characteristics and surface hardness of the magnetic disk. Another object of the present invention is to provide a method for manufacturing a magnetic disk that can improve reliability.

The object of the present invention is that, as a result of systematic research by the inventor of the present application regarding the absorption of lubricant into the recording medium layer of a magnetic disk, the absorption rate (or amount) of lubricant is It has been found that when the heat treatment process for thermosetting the plastic resin is divided into an intermediate heat treatment process and a final heat treatment process, it is largely dependent on the heating temperature in the intermediate heat treatment process, and this can be achieved by appropriately performing this intermediate heat treatment process.

Structure of the Invention The present invention comprises a coating step of coating a magnetic material obtained by kneading magnetic powder, a lubricant, and a binder onto a non-magnetic substrate, and a heat treatment step of curing the binder after the coating step, and a heat treatment step of curing the binder. The heat treatment step includes an intermediate heat treatment step and a final heat treatment step performed thereafter, and the heat treatment temperature T1 in the intermediate heat treatment step is set lower than the heat treatment temperature T2 in the final heat treatment step, and the absorption rate of the lubricant is A method of manufacturing a magnetic disk is provided, characterized in that the temperature is set in a low temperature region near an inflection point where the temperature changes from a large value to a relatively small value.

Embodiment of the Invention An embodiment of the invention will be described below with reference to the accompanying drawings.

In the present invention, magnetic powder, a thermosetting resin such as an epoxy resin, and a lubricant are mixed into a binder diluted with a solvent, thoroughly kneaded and dispersed, and then applied onto a non-magnetic substrate such as an aluminum alloy substrate and subjected to the required surface treatment. After that, heat treatment is performed to produce a magnetic disk.

The heat treatment process is divided into an intermediate heat treatment process and a final heat treatment process.

A curve C1 in the drawing shows the relationship between the lubricant absorption rate a (left side of the vertical axis) and the intermediate heat treatment temperature T (horizontal axis). In this example, perchloroalkyl ether (trade name: Krytx) is used as the lubricant. The above absorption rate a is
230℃, which was previously heated at 230℃ for the first baking.
It is expressed as the ratio of the absorption amount (numerator) at an arbitrary intermediate heat treatment temperature T to the absorption amount (denominator) at . Further, the heat treatment time was 1 hour. This example shows that the absorption rate a is highly dependent on the intermediate heat treatment temperature T, and that there is an inflection point around about 195°C. That is, at about 200°C to 280°C, the absorption rate a is constant at approximately 1, and about
At temperatures below 190°, the absorption coefficient a is constant at approximately 1.78, but there is a large difference between these absorption coefficients, indicating that the absorption coefficient is large at low temperatures.

On the other hand, even at the above intermediate heat treatment temperature, if the heat treatment time is increased, the absorption rate changes. For example 190
Even in the temperature range below .degree. C., when the heat treatment time is increased, the absorption rate decreases from 1.78 to 1, and the characteristic curve C1 in the drawing also changes.

The physical phenomenon of showing such absorption rate is
The amount of lubricant absorbed is related to the hardening reaction state of the binder; that is, under predetermined heat treatment conditions, the internal structure of the recording medium layer of the magnetic disk is such that it is easy to contain the lubricant, which will be discussed later. It is understood that the lubricant continues to be contained within the recording medium layer even when the final heat treatment is performed. Incidentally, the fact that the amount of lubricant absorbed is related to the hardening reaction state of the binder is thought to be due to brittle cracks inside the recording medium layer due to overheating when the heat treatment temperature is 280℃ or higher, as shown in the figure. This is also supported by the phenomenon of increased absorption rate.

Considering that the amount of lubricant absorbed varies depending on the intermediate heat treatment conditions (temperature, time), in this example, the heat treatment temperature T1 = 185°C, the heat treatment time is approximately 1 hour, and the absorption rate is high. I'm trying to get that.

Note that although the intermediate heat treatment conditions differ depending on the lubricant, since the tendency of change depending on the drawings and the heat treatment time described above is generally the same, it can be handled in the same manner as above. Here, the characteristics of the above intermediate heat treatment conditions are that the intermediate heat treatment temperature T1 is set slightly lower than the inflection point shown in the drawing (this temperature is lower than the final heat treatment temperature described later), and the absorption rate does not decrease during the heat treatment time. The goal is to do it within the appropriate range.

After the above intermediate heat treatment, the heat treatment temperature T2 is approximately 220 ~
A final heat treatment is carried out in the range of 280°C, preferably 260°C for about 10 minutes (the lubricant is perchloroalkyl ether as before). This final heat treatment step mainly consists of
It is understood that this contributes to raising the temperature near the surface and thermosetting the surface portion of the magnetic disk to a predetermined hardness. The above temperature T2 is the intermediate heat treatment temperature T1 (=185
℃) higher. However, the heat treatment time is set within a range that does not reduce the amount of lubricant absorbed.

The characteristic curve of surface hardness after heat treatment as described above is shown as C2 in the drawings. This surface hardness is generally close to the actual operating condition when evaluating the durability based on the scratch depth d (μm) as shown in the figure on the right side.
It is specified by CSS number of times, but it takes a lot of time. Therefore, as an accelerated test, the surface hardness was evaluated based on the number of times of sliding with a high-load head (continuous sliding using a head that applies a load approximately 4 times the load normally used) and the depth of scratches made with a needle release needle. However, the curve C2 indicates the depth d. Curve C2 is approximately constant over a wide temperature range, indicating that the surface hardness is determined by the final heat treatment conditions and is independent of intermediate heat treatment conditions. The hardness of this surface is equivalent to that of the conventional one.

The final heat treatment conditions are defined by a range in which the resin is not decomposed and only the surface portion is hardened. It goes without saying that these conditions, like the intermediate heat treatment conditions, vary depending on the binder.

In the above description, the heat treatment temperature and time have been described in a steady state. Strictly speaking, it involves the temperature distribution on the surface and inside, and depending on the structure of the heat treatment furnace and the flow of the manufacturing process, there are elements in which the characteristics may vary slightly due to the temperature rise period until reaching a steady state and the subsequent temperature fall period. However, it is assumed here that these processes are carried out in the same way as conventional processes using conventional equipment.

The electromagnetic characteristics of the magnetic disk according to the present invention are the same as those of the conventional disk because the bars on which the electromagnetic characteristics are defined are the same as those of the conventional disk.

It is clear that the magnetic disk according to the present invention is not limited to the CSS type, and can also be used for non-contact type and constant contact type.

Effects of the Invention As described above, according to the present invention, the heat treatment process is separated into at least an intermediate heat treatment process and a final heat treatment process, and the intermediate heat treatment temperature is set to a low temperature near the inflection point of the absorption rate characteristic curve of the lubricant. By setting it on the side, it is possible to increase the absorption amount and manufacture a magnetic disk with improved durability.

[Brief explanation of drawings]

The drawing is a characteristic curve diagram as an embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. A coating step of coating a magnetic material obtained by kneading magnetic powder, a lubricant, and a binder onto a non-magnetic substrate, and a heat treatment step of hardening the binder after the coating step, and the heat treatment The step includes an intermediate heat treatment step and a final heat treatment step performed thereafter, the heat treatment temperature T1 in the intermediate heat treatment step.
, the heat treatment temperature T2 in the final heat treatment step
A method for manufacturing a magnetic disk, characterized in that the absorption rate of the lubricant is set at a lower temperature in a low temperature region near an inflection point where the absorption rate of the lubricant changes from a large value to a relatively small value.