WO2002049015A1

WO2002049015A1 - Magnetic-disk substrate, and method for manufacturing the same

Info

Publication number: WO2002049015A1
Application number: PCT/JP2001/010783
Authority: WO
Inventors: Shinya Abe; Kiyoshi Tada; Masahiro Miyazaki; Hirofumi Hatakeyama
Original assignee: Showa Denko K.K.
Priority date: 2000-12-13
Filing date: 2001-12-10
Publication date: 2002-06-20
Also published as: AU2002221105A1; MY135730A

Abstract

A magnetic-disk substrate is manufactured by conducting Ni-P plating to an aluminum substrate to form a Ni-P plated aluminum substrate, heat-treating the Ni-P plated aluminum substrate in a non-oxidizing atmosphere to form a heat-treated aluminum substrate, and polishing the heat-treated aluminum substrate. The heat-treating is performed in a vacuum of 6.7 Pa or less, or in an inert gas atmosphere having an oxygen density of 100 ppm or less and a moisture concentration of 200 ppm or less. Thereby, the growth of oxide film at the time of heat-treating is suppressed, and the generating of PED due to polishing is also suppressed.

Description

DESCRIPTION

MAGNETIC-DISK SUBSTRATE, AND METHOD FOR MANUFACTURING THE SAME

Cross Reference to Related Applications

This application is an application filed under 35 U.S.C. ^§ 111(a) claiming the benefit pursuant to 35 U.S.C. ^§ 119(e)(1) of the filing data of Provisional Application No.60/310, 835 filed August 9, 2001 pursuant to 35 U.S.C. § 111(b) .

Technical Field

The present invention relates to a method for manufacturing a magnetic-disk substrate, especially a Ni-P plated magnetic-disk substrate, used as a storage medium substrate for a magnetic disk device. It also relates to a magnetic-disk substrate manufactured by the aforementioned method.

Background Art In accordance with an increased recording density of a magnetic-disk unit, a magnetic-disk substrate before forming a magnetic-film thereon is required to have small surface roughness and no defect. Accordingly, it became necessary to eliminate even minute defects that did not cause any problem in the past . For example, in a magnetic-disk substrate to which Ni-P metal plating is performed, minute defects called polished enhanced defects (hereinafter referred to as "PED") are generated. The aforementioned Ni-P plated magnetic-disk substrate is manufactured by the following processes: conducting Ni-P plating to an aluminum substrate to obtain a Ni-P plated aluminum substrate, heat-treating the Ni-P plated aluminum substrate to eliminate the stress, and then polishing it . The polishing is usually performed with a disc having an abrasive cloth including organic high polymer while supplying polishing liquid containing abrasive grains such as alumina. The aforementioned PED are defects which appear after the polishing process as a final process, and the configuration thereof is indefinite and the depth is about several nm. Furthermore, the defects will appear after the final polishing process, resulting in a deteriorated product yield, which in turn lowers the productive efficiency. It is supposed that the generation of PED is affected by the moisture adhered to the substrate and the temperature at the time of heat-treating the substrate. Therefore, it is supposed that the generation of PED can be eliminated by avoiding the adherence of the moisture and lowering the heat-treating temperature. In a general mass-production plating process, the substrate is immersed in a treatment liquid together with a jig. Therefore, the treatment liquid adheres and remains on the jig and/or the substrate even after the plating process. Furthermore, the components of the treatment liquid evaporated due to the high temperature thereof and condensed on the jig will fall down to adhere to the substrate. Therefore, it is very difficult to completely eliminate the adherence of moisture to the substrate in the current plating process.

Furthermore, the heat-treatment after the plating process is also indispensable to remove the stress. The heat-treatment is currently performed in an atmospheric air. When the heat-treatment is performed at the temperature of 150 °C or below, almost no PED will be generated even in cases where moisture is adhered to the substrate. However, at the temperature of 200 °C or above, the PED incidence rate increases. When the temperature is 250 °C or above, the PED will generate at the PED incidence rate of nearly 100 % in cases where moisture is adhered to the substrate. In many cases, the heating temperature is decided in accordance with the conditions of the magnetic-film spattering process which will be performed after the plating process. Furthermore, in order to increase the recording density, the temperature tends to be set to a high temperature of 200 °C or above so that minute crystals of the magnetic film can be obtained. Accordingly, in practice, it is impossible to lower the heating temperature.

Disclosure of Invention An object of the present invention is to provide a method for manufacturing a magnetic-disk substrate which can eliminate a generation of PED without changing a plating method and/or lowering a heating temperature. Another object of the present invention is to provide a magnetic-disk substrate having no PED.

In this specification, the wording "aluminum" denotes aluminum and its alloy. The inventor has investigated the generation process of PED and found a method by which no PED is generated irrespective of the temperature of the heat treatment of the substrate, and thus completed the present invention.

In manufacturing a magnetic-disk substrate, when moisture is unevenly adhered to the substrate after the Ni-P plating of the substrate, a thicker oxide film will be created at the portion where moisture was adhered by subsequently heat-treating the plated substrate, as compared with the portion where no moisture was adhered. When the oxide film includes a partially thick portion, the partially thick portion will be stripped off during the polishing process of the plated substrate, causing a dented portion as PED. Accordingly, even if moisture is unevenly adhered to the substrate, if no thick portion of the oxide film is generated at the portion where moisture was adhered during an annealing process, it is possible to prevent the generating of PED in the subsequent polishing process .

According to the first aspect of the present invention, a method for manufacturing of a magnetic-disk substrate, includes the steps of conducting Ni-P plating to an aluminum substrate to obtain a Ni-P plated aluminum substrate, heat-treating the Ni-P plated aluminum substrate in a non-oxidizing atmosphere to obtain a heat-treated aluminum substrate, and polishing the heat-treated aluminum substrate .

In the present invention, it is preferable that the aforementioned heat-treating is performed in a vacuum of 6.7 Pa or less, more preferably, in a vacuum of 6.7 X 10^"2 Pa or less.

It is preferable that the heat-treating is performed in an inert gas atmosphere having an oxygen density of 100 ppm or less and a moisture concentration of 200 ppm or less. Preferably, the oxygen density is 10 ppm or less, and the moisture concentration of 100 ppm or less, more preferably 10 ppm or less.

Furthermore, the heat-treating is performed preferably at a temperature of 300 °C or below. More preferably, the lower limit is 200 °C or above. It is preferable that the aluminum substrate is made of AA 5086 aluminum alloy.

According to the second aspect of the present invention, a magnetic-disk substrate includes an aluminum substrate and a Ni-P plating layer formed on the aluminum substrate, wherein the magnetic-disk substrate is manufactured by conducting Ni-P plating to the aluminum substrate in a non-oxidizing atmosphere and then polishing the aluminum substrate.

In this magnetic-disk substrate, it is preferable that the aluminum substrate is made of AA 5086 aluminum alloy. In the present invention, the growth of oxide film resulting from adhered moisture on the aluminum substrate to which the Ni-P plating was conducted can be suppressed by conducting the heat-treatment in the non-oxidizing atmosphere. Before the heat-treating as well as after the heat-treating at the temperature of 150 °C or below, almost no oxide film will be generated, and the Ni-P plated film is covered by a hydroxylation film. If the heat-treatment is performed to the aluminum substrate in an atmospheric air, the oxidation thereof will begin at around 200 °C , and an oxide film will be generated notably at around 250 °C or above . To the contrary, when the heat-treatment is performed in the predetermined non-oxidizing atmosphere, even if moisture is adhered to the Ni-P plated substrate, the growth of oxide film can be suppressed assuredly.

In the present invention, the heating temperature is not limited to a specific value. However, when the temperature exceeds 300 °C , the crystallization of the Ni-P film formed at the previous process will start, resulting in an inappropriate magnetic-disk substrate irrespective of the existence of oxide film. Accordingly, it is preferable that the heat-treatment is performed at 300 °C or below. It is required that an oxide film is not formed at the heat-treating temperature of 300 °C or below in the below-mentioned non-oxidizing atmosphere. Furthermore, in order to obtain minute crystals of the magnetic film to be formed later, it is preferable to perform the heat-treating at the temperature of 200 'C or above. Furthermore, although the heating time is not limited to a specific value in the present invention, it is preferable that the heating time falls within the range of from 30 to 60 minutes.

As for the non-oxidizing atmosphere in which the heat- treating is performed, a vacuum or an inert gas atmosphere is preferably used. In cases where the heat-treating is performed in a vacuum, it is necessary that the vacuum degree is 6.7 Pa or less. If the vacuum degree exceeds 6.7 Pa, it becomes difficult to suppress the growth of oxide film because of the moisture adhered during the plating process. More preferably, the vacuum degree is 6.7XlO^"2Pa or less.

In cases where the heat-treating is performed in an inert gas atmosphere, the oxygen density is set to 100 ppm or less and the moisture concentration is set to 200 ppm or less. If each of value exceeds the upper limit, it becomes difficult to suppress the growth of oxide film because of the moisture adhered during the plating process. The heat-treating is preferably performed in the inert gas atmosphere having oxygen density of 10 ppm or less . Furthermore, the heat-treating is preferably performed in the inert gas atmosphere having moisture concentration of 100 ppm or less, more preferably 10 ppm or less. Although the kind of inert gas is not limited to a specific one, nitrogen or argon can be preferably used as the inert gas .

In the present invention, the materials of the aluminum substrate, the Ni-P plating method and the polishing method are not limited to a specific one, but may be a conventional material of the aluminum substrate, a conventional plating method and a conventional polishing method, respectively. Furthermore, a pretreatment and/or an after-treatment may be added.

Concretely, as the aforementioned aluminum substrate, it is recommended to use AA 5086 aluminum alloy. This aluminum substrate can be manufactured by, for example, grinding, washing and then heating the material alloy plate.

Furthermore, as a pretreatment for the aluminum substrate before conducting the Ni-P plating thereto, a degreasing washing, etching and zincate treatment may be exemplified. Furthermore, as an after-treatment to be conducted after the plating process, a hot water rinsing and drying can be exemplified. The aluminum substrate to which the aforementioned processes were performed is subjected- to the aforementioned heat-treating in accordance with the aforementioned method, and then polished. The polishing may include rough polishing and finish polishing. The Ni-P plated aluminum substrate after the heat-treatment does not have an oxide film, especially a partially thick oxide film. Accordingly, no PED will be generated even if the substrate is polished. Thus, a flat and smooth surface can be obtained.

The magnetic-disk substrate manufactured by the method according to the present invention can be used as a magnetic-disk. If desired, the magnetic-disk may have a magnetic film formed on a stacking-tendency control film, and further a protective film and a lubricating film thereon. Since the obtained magnetic-disk substrate has an excellent flat surface with no PED, it can be used as a high-density recordable magnetic disk.

Furthermore, in the present invention, since it is merely required to control the heating atmosphere for the heat-treatment after the Ni-P plating process, the growth of PED can be suppressed without changing a plating method and/or lowering the temperature for the heat-treatment restrained by the magnetic-film forming conditions.

Best Mode for Carrying Out the Invention

First, an AA 5086 aluminum alloy plate was prepared. The plate was rolled, then punched, and subjected to surface grinding, washing and annealing, to thereby obtain a plurality of aluminum substrates each having a diameter of 84 mm X a thickness of 0.8 mm.

These aluminum substrates were etched after the degreasing washing by a conventional method, and then subjected to a zincate treatment. Subsequently, these substrates were Ni-P plated in a nickel sulfate bath including a hypophosphite as a reducing agent under the conditions of a bath temperature of 90 °C, pH 4.5 and a processing time of 2.0 hours, and then dried after a hot water rinsing. On the surface of these Ni-P plated substrates, liquid-dried spots which may cause PED were visually confirmed.

These Ni-P plated substrates were heat-treated for 60 minutes in the atmospheric air or the vacuum as shown in Table 1, or in the nitrogen atmosphere as shown in Table 2. The heating temperature were set to 150 °C , 200 °C , 250 °C , and 300 °C , respectively.

Subsequently, these Ni-P plated substrates were roughly polished, washed, and then subjected to a finish polishing to thereby obtain magnetic-disk substrates. On the other hand, as comparative examples, non-Ni-P plated substrates were prepared and subjected to the same polishing to thereby obtain magnetic-disk substrates . As for each of the aforementioned magnetic-disk substrates, the existence of PED was observed by an optical interference type shape measuring apparatus and evaluated. The observation was performed as follows : both sides of ten pieces every each sample were observed, i.e., a total of 20 surfaces were observed every each sample. Then, the incidence rate of PED was calculated based on the number of the surfaces on which PED were generated.

Table 1

* PED incidence-rate ¹ : 10% or less 0:11-30%

Δ:31-89% X : 90% or more

Table 2

* PED incidence-rate ':10% or less 0:11-30%

Δ:31-89^ X : 90% or more

From these results, it is confirmed that a magnetic-disk substrate with almost no PED, which is equivalent to a non-heating substrate, can be manufactured by heat-treating the substrate in a vacuum or an inert gas atmosphere in which the amount of oxygen and the moisture content are controlled.

This application claims priority to Japanese Patent

Application No. 2000-378672 filed on December 13, 2000, the disclosure of which is incorporated by reference in its entirety.

The terms and descriptions in this specification are used only for explanatory purposes and the present invention is not limited to these terms and descriptions . It should be appreciated that there are many modifications and substitutions without departing from the spirit and the scope of the present invention which is defined by the appended claims. A present invention permits any design-change, unless it deviates from the soul, if it is within the limits by which the claim was performed.

Industrial Applicability

As will be apparent from the above, since the magnetic-disk substrate manufactured by the method of the present invention is excellent in surface flatness and smoothness, the substrate ^"can be used as a high-density recordable magnetic disk by forming a magnetic film thereon. This magnetic-disk substrate can be suitably used for a magnetic disk unit which is required to have a high storage capacity.

Claims

1. A method for manufacturing of a magnetic-disk substrate, comprising the steps of : conducting Ni-P plating to an aluminum substrate to obtain a Ni-P metal plated aluminum substrate; heat-treating said Ni-P plated aluminum substrate in a non-oxidizing atmosphere to obtain a heat-treated aluminum substrate; and polishing said heat-treated aluminum substrate.

2. The method for manufacturing of a magnetic-disk substrate as recited in claim 1, wherein said heat-treating is performed in a vacuum of 6.7 Pa or less .

3. The method for manufacturing of a magnetic-disk substrate as recited in claim 2, wherein said heat-treating is performed in a vacuum of 6.7 X 10^"2 Pa or less.

4. The method for manufacturing of a magnetic-disk substrate as recited in claim 1, wherein said heat-treating is performed in an inert gas atmosphere having an oxygen density of 100 ppm or less and a moisture concentration of 200 ppm or less.

5. The method for manufacturing of a magnetic-disk substrate as recited in claim 4, wherein said heat-treating is performed in an inert gas atmosphere having an oxygen density of 10 ppm or less.

6. The method for manufacturing of a magnetic-disk substrate as recited in claim 4, wherein said heat-treating is performed in an inert gas atmosphere having a moisture concentration of 100 ppm or less.

7. The method for manufacturing of a magnetic-disk substrate as recited in claim 5, wherein said heat-treating is performed in an inert gas atmosphere having a moisture concentration of 100 ppm or less.

8. The method for manufacturing of a magnetic-disk substrate as recited in claim 6, wherein said heat-treating is performed in an inert gas atmosphere having a moisture concentration of 10 ppm or less.

9. The method for manufacturing of a magnetic-disk substrate as recited in claim 7, wherein said heat-treating is performed in an inert gas atmosphere having a moisture concentration of 10 ppm or less.

10. The method for manufacturing of a magnetic-disk substrate as recited in any one of claims 1 to 9 , wherein said heat-treating is performed at a temperature of 300 °C or below.

11. The method for manufacturing of a magnetic-disk substrate as recited in claim 10, wherein said heat-treating is performed at a temperature of 200 °C or above.

12. The method for manufacturing of a magnetic-disk

0 substrate as recited in claim 1, wherein said aluminum substrate is made of AA 5086 aluminum alloy.

13. A magnetic-disk substrate, comprising: an aluminum substrate; and a Ni-P plating layer formed on said aluminum substrate, wherein said magnetic-disk substrate is manufactured by conducting Ni-P plating to said aluminum substrate in a non- oxidizing atmosphere and then polishing said aluminum substrate.

14. The magnetic-disk substrate as recited in claim 13, wherein said aluminum substrate is made of AA 5086 aluminum alloy.