JPH11120553A - Production of substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a substrate having excellent adhesion property between a glass substrate and a NiP electroless plating layer and having high shock resistance and surface smoothness, and to stably obtain low floating height of a head by controlling the temp. of a NIP plating bath to a specified range in a NiP electroless plating process. SOLUTION: A glass substrate having fine recesses on the surface is used so as to obtain adhesion with a NiP electroless plating layer. The glass substrate is dipped in a NiP electroless plating bath at a temp. between >=60 deg.C and <70 deg.C C for NiP electroless plating. If the bath temp. is <60 deg.C, the film forming rate significantly decreases, which is not desirable for industrial purpose. If the temp. is >=70 deg.C, Pd adsorbed to the glass substrate in the treatment to add susceptibility reacts with the plating liquid to decrease the adhesion of the NiP plating film when the substrate is immersed in the plating bath. By this method, the obtd. magnetic recording medium has enough adhesion which does not cause peeling between the glass substrate and the NiP electroless plating film and the medium is excellent in shock resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a substrate for a magnetic recording medium. More specifically, the present invention relates to a method for manufacturing a substrate in a high-density magnetic recording medium such as a fixed-type thin-film magnetic recording disk used in the information industry and the like. In particular, the present invention relates to a method for forming a NiP electroless plating layer having high adhesion to a glass substrate.

[0002]

2. Description of the Related Art In recent years, fixed magnetic disk devices have been widely used as external storage devices of information processing devices such as computers. The magnetic disk mounted on this fixed magnetic disk device generally has a NiP electroless plating layer formed on the surface of a non-magnetic substrate made of an aluminum alloy, and performs a required smoothing process, texturing process, and the like.
A nonmagnetic metal underlayer, a magnetic layer, a protective layer, a lubricating layer, and the like are sequentially formed thereon.

In a magnetic disk drive, a recording / reproducing head moves over a magnetic recording medium at a constant flying height. In recent years, with the rapid increase in surface recording density of a magnetic recording medium,
This flying height is extremely small. In addition, the miniaturization and weight reduction of magnetic disk drives are also rapidly progressing, and in order to cope with these, it is necessary to further reduce the surface roughness of the magnetic recording medium, and the medium surface roughness has already been reduced. Is reduced to about several Å in Ra. Furthermore, since the impact resistance required for a magnetic disk for supporting a portable fixed magnetic disk device has also become a high value of 400 G to 800 G, a substrate made of a conventional aluminum alloy is used for the impact resistance. Then it is difficult to respond. Therefore, from the viewpoint of impact resistance and surface smoothness, glass substrates that can achieve extremely small surface roughness and have excellent mechanical strength have begun to be used instead of aluminum alloy substrates.

[0004] In many cases, an aluminum alloy substrate subjected to NiP electroless plating has its surface subjected to concentric texturing in the circumferential direction of the substrate by polishing. This is intended mainly to improve the friction characteristics between the recording / reproducing head and the magnetic recording medium and to ensure durability. In recent years, as the flying height of the head during the operation of the magnetic disk drive has become extremely small, instead of texturing by polishing, CS
Attempts have been made to texturing with a laser beam only in the S zone, that is, to form projections with the laser beam. (Japanese Unexamined Patent Publication No. 8-129949)

However, unlike an aluminum alloy substrate subjected to NiP electroless plating, it is extremely difficult to form projections by directly irradiating a glass plate with a laser beam due to poor control of the projection shape. Therefore, in order to apply laser texture technology to glass substrates,
It is necessary to form a NiP electroless plating layer on the substrate in advance.

Japanese Patent Application Laid-Open No. Sho 61-54018 proposes a method of forming a NiP electroless plating film on a glass substrate. However, it is technically difficult to form a NiP layer on a glass substrate with good adhesion by electroless plating. Therefore, in order to improve the adhesion between the glass substrate and the NiP electroless plating film, a method of mechanically or chemically roughening the surface of the glass substrate used for plating and a method of performing a pretreatment of the electroless plating are proposed. Have been. For example,
As a mechanical roughening method, the surface roughness is adjusted to a center line average roughness Ra of 10 using a grindstone using an abrasive such as Al ₂ O _3.
A method of polishing by 0 ° or more is known, and as a method of chemically polishing the surface, a method of performing an alkaline degreasing and then etching with hydrofluoric acid or the like is known.

Further, as a method of performing a pretreatment for electroless plating, Japanese Patent Application Laid-Open Nos. 7-272263 and 6-2
No. 12440, etc., after sensitizing a glass substrate with a solution of stannous chloride, performing an activation treatment with a palladium chloride solution,
Next, a method has been proposed in which the glass substrate is subjected to NiP electroless plating at a high temperature of 70 ° C. or higher, or 80 ° C. or higher.

[0008]

However, these methods cannot form a NiP layer having sufficient adhesion and smoothness on a glass substrate by an electroless plating method to obtain a good magnetic disk. Was. The present invention has been made in view of the above points, and has as its object to provide excellent adhesion between a glass substrate and a NiP electroless plating layer, high impact resistance, surface smoothness, and a head. An object of the present invention is to provide a method of manufacturing a substrate for a magnetic recording medium capable of stably obtaining a low flying height.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies in view of the above-mentioned circumstances, and as a result, by controlling the temperature of the NiP plating bath in the NiP electroless plating step, an excellent NiP satisfying the above-mentioned various requirements has been obtained. The inventors have found that a layer is formed on a substrate and arrived at the present invention. That is,
The gist of the present invention is a method of manufacturing a substrate for a magnetic recording medium, which comprises sequentially providing a sensitization step, an activation step, and a NiP electroless plating step on a glass substrate, wherein the NiP plating bath is used in the NiP electroless plating step. A method for manufacturing a substrate for a magnetic recording medium, wherein the temperature is 60 ° C. or higher and lower than 70 ° C.

Hereinafter, the present invention will be described in detail. Although the glass substrate of the present invention is not particularly limited, for example, crystallized glass or aluminosilicate glass is preferably used. Among them, crystallized glass is preferable, and in particular,
SiO ₂ —Li ₂ O-based crystallized glass is preferred. As the glass substrate, it is preferable to use a glass substrate having a fine concave portion on the substrate surface in order to secure adhesion to the NiP electroless plating layer. More specifically, fine recesses having a maximum width of the recesses of 20 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less are suitably used.
This is because, when a fine concave portion is formed on the plate surface, the NiP film is formed in the fine hole, thereby enhancing the physical anchoring effect, thereby strengthening the adhesion between the glass substrate and the NiP plating layer. It seems to be.

The fine concave portions on the surface of the glass substrate are subjected to a chemical etching treatment using, for example, a hydrofluoric acid-based etching agent such as hydrofluoric acid, potassium fluoride or ammonium fluoride in a crystallized glass substrate. Thereby, it can be formed. The use of crystallized glass is preferable because the amorphous region on the substrate surface can be selectively etched by chemical etching, so that the concave portion can be appropriately formed without impairing the surface smoothness to some extent. The size of the concave portion depends on the concentration of the etching solution, the processing temperature,
It is possible to control by appropriately selecting the processing time and the like. In the case of a high-hardness aluminosilicate substrate, a concave portion can be formed by processing with free abrasive grains or grinding.

According to the present invention, a glass substrate is subjected to a sensitizing step and an activating step, and then NiP under specific conditions.
By performing electroless plating, the glass substrate and NiP
A substrate for a magnetic recording medium having excellent adhesion to the electroless plating layer can be obtained. And usually, before the sensitization step, a degreasing step is provided. Further, a water washing step is provided between each step, and as the washing water, ion exchange water or ultrapure water is used as appropriate.

The degreasing step is a step of cleaning the surface of the glass substrate, and includes, for example, a method using ultrapure water, an alkaline cleaning agent, an acid cleaning agent, a surfactant and the like. The sensitizing step and the activating step are steps for providing a catalytic activity necessary for starting NiP electroless plating on the glass substrate. That is, since the glass surface has no catalytic activity, it is necessary to form a catalytic nucleus of a noble metal such as Au, Pt, Pd, or Ag on the glass surface in order to start electroless plating.

Each of the above steps is performed as follows by a known method. (Surface Technology Vol.44 No.1
0, 1993, "Adhesion between glass and electroless nickel plating", Shinichi Hotta et al. In the sensitization step, first, Sn, Ti, Pd, Hg
And the like. Usually, 0.
A tin chloride aqueous solution of about 05 g / l is suitably used, and is immersed in a tin chloride aqueous solution at room temperature for about 1 to 3 minutes. Next, as an activation step, the above-mentioned glass substrate is immersed in an activation treatment solution containing a noble metal serving as the above-mentioned catalyst nucleus, and the catalyst nucleus is placed on the surface of the glass substrate by a reducing action of the adsorbed divalent metal ions. Is formed. Usually, an aqueous solution of palladium chloride of about 0.05 g / l is suitably used, and immersed in an aqueous solution of palladium chloride for about 1 to 3 minutes at room temperature.

The glass substrate treated in the activation step is 6
The NiP electroless plating is performed by dipping in a NiP electroless plating bath at a temperature of 0 ° C. or more and less than 70 ° C.
If the temperature of the NiP plating bath is lower than 60 ° C., the film-forming speed becomes extremely low, which is not desirable in industrial production. If the temperature is higher than 70 ° C., Pd adsorbed on the surface of the glass substrate during the sensitization treatment reacts with the plating solution when immersed in the plating bath, and violently generates hydrogen. For this reason, the hydrogen enters between the glass substrate and the plating film, and lowers the adhesion of the NiP plating film.

That is, according to the findings of the present inventors, 7
By performing electroless plating at a low temperature of less than 0 ° C., a NiP film having stronger adhesion can be obtained. A commercially available NiP electroless plating bath is generally used, and a glass substrate is treated in the plating bath for a predetermined time. The thickness of the NiP electroless plating layer is arbitrarily selected, but is preferably in the range of 1 to 10 μm for a good magnetic recording medium.

The glass substrate on which the NiP electroless plating has been performed can be subjected to a polishing treatment as needed, or a texturing treatment such as a texturing with a laser beam or a mechanical texturing as appropriate. An underlayer, a magnetic layer, a protective layer, a lubricating layer, and the like are laminated. According to the present invention, NiP is applied to the glass substrate as described above.
By performing the electroless plating, it is possible to obtain a magnetic recording medium having a sufficient strength of adhesion that does not cause separation of the glass substrate and the NiP electroless plating film, and excellent in impact resistance. .

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to the following Examples without departing from the scope of the invention.

Example 1 A commercially available SiO ₂ —Li ₂ O-based crystallized glass was used.
After performing a grinding process using fixed abrasive grains, a grinding agent (manufactured by Fujimi Incorporated, trade name "artificial abrasive F0 (composite artificial emery)"): specific gravity 3.
90 or more: Al ₂ O ₃ 45% by weight or more, TiO 2.0% by weight or less, ZrSiO 49% by weight or less: Particle size classification # 10
00 (maximum particle diameter: 27 μm or less)).

Thereafter, an alkali detergent for glass (trade name "PK-LCG" manufactured by Parker Corporation) is used.
22 ”) at a bath temperature of 50 ° C. for 10 minutes, followed by washing with water, followed by ammonium acid fluoride (manufactured by Kanto Chemical Co., Inc., NH ₄ F.HF, JIS No. K8817) 50.
The crystallized glass was immersed in g / l at room temperature for 2 minutes to perform an etching treatment, followed by washing with water. Observation of the obtained glass substrate surface with a SEM at a magnification of 30,000 times revealed that the maximum length of the concave portion was 3.8 μm.

Next, a commercially available glass substrate of 0.05 g /
1 of SnCl ₂ aqueous solution at room temperature for 2 minutes, washed with water, and sensitized. Then, commercially available 0.05g
/ L of PdCl ₂ aqueous solution at room temperature for 2 minutes, washed with water and activated. Next, a plating bath temperature of 68 ° C.
16-hour NiP electroless plating with a thickness of 15 μm
The layer was deposited. Further, after plating, a baking treatment was performed at 150 ° C. for 1 hour to improve adhesion. As a result of evaluating the adhesion between the thus obtained NiP layer and the glass substrate, the evaluation score was 10, and it was confirmed that the NiP layer had good adhesion. The adhesion between the glass substrate and the NiP electroless plating layer was determined in accordance with JIS K54008.15.
Was evaluated by a cross cut test. An evaluation score of 10 indicates good adhesion.

Examples 2 and 3 The plating bath temperature of NiP electroless plating was 68 ° C.
An NiP electroless plating layer was formed on a glass substrate in the same manner as in Example 1 except that the temperature was changed to 2 ° C. Glass substrate and Ni
Evaluation score of adhesion to P electroless plating layer was 10
And has good adhesion.

Comparative Example 1 An NiP electroless plating layer was formed on a glass substrate in the same manner as in Example 1 except that the plating bath temperature of NiP electroless plating was set at 90 ° C. The evaluation score of adhesion was 5, and sufficient adhesion could not be obtained.

Claims (3)

[Claims] 1. A method for manufacturing a substrate for a magnetic recording medium, comprising a glass substrate sequentially provided with a sensitizing step, an activating step, and an NiP electroless plating step, wherein a temperature of a NiP plating bath in the NiP electroless plating step is set. Is 60 ° C or more and 7
A method for producing a substrate for a magnetic recording medium, wherein the temperature is lower than 0 ° C. 2. The temperature of a NiP plating bath is 65 to 69 ° C.
2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein 3. The glass substrate according to claim 1, wherein the glass substrate is made of SiO ₂ —Li ₂ O-based crystallized glass.
Method of manufacturing magnetic recording medium substrate