JPH0536058A - Magnetic disk substrate - Google Patents

Abstract

PURPOSE:To improve the extremely good surface state and CSS characteristics of the magnetic disk substrate formed with a resin layer on a titanium material and to enhance the adhesion between the titanium material and the resin layer. CONSTITUTION:The magnetic disk substrate is formed by forming the resin layer consisting of a synthetic rein on a disk-shaped core material consisting of the titanium material. The thickness of the resin layer, designated as t1 (mu), is t1<300mum and the t1 and the surface roughness RmaxS (mum) of the core material satisfy the relation t1/RmaxS>3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk substrate having a titanium material as a core material, and more particularly to a magnetic disk substrate having excellent surface accuracy.

[0002]

2. Description of the Related Art A high-performance magnetic disk used in a magnetic disk device is required to be a thin film magnetic recording medium having a high coercive force, but such a thin film magnetic recording medium is smooth. In order to form without defects, the surface accuracy of the substrate itself on which the magnetic recording medium is formed needs to be good.

However, in the Al alloy substrates currently used, it is impossible to cause defects due to inclusions inevitably included in the substrates and to eliminate scratches and the like remaining in the polishing process. Due to such inconveniences, a method has recently been proposed in which an organic material is applied onto a substrate and the surface accuracy is obtained by the organic material layer (for example, JP-A-58-18).
9836, Sho 60-167110, Sho 61-10572.
5). In these methods, types of synthetic resins and coating methods are proposed, and examples in which the thickness of the resin layer is 0.5 to 500 μm are shown.

By the way, the conventional magnetic disk substrate made of Al alloy lacks heat resistance against high temperature sputtering when a magnetic film (magnetic medium) is formed on the magnetic disk substrate, and the substrate is thinned. Insufficient rigidity for the request. In order to meet these requirements, new materials such as ceramics, glass and titanium are being used as magnetic disk substrates. Among them, titanium is suitable as a magnetic disk substrate material because it has excellent heat resistance, high rigidity, high strength, and high cleaning degree.

However, since titanium is a difficult-to-process material, it is difficult to manufacture it with good surface properties with good stability, which limits the use of titanium as a magnetic disk substrate. ..

On the other hand, the above-mentioned method of applying an organic substance on the Al alloy substrate is a method of obtaining a good surface texture regardless of the surface texture of the Al alloy core material, and therefore this method is directly applied to the titanium magnetic disk substrate. If it can be applied, the mirror finishing of titanium will be unnecessary, and it is expected to be a very effective method for producing a magnetic disk substrate made of titanium.

However, at present, a magnetic disk substrate in which a titanium material is used and an organic material is applied thereon has not yet been developed. The inventors of the present application have been studying a method of applying a resin to a titanium material to obtain a magnetic disk substrate, but the optimum application method could not be determined. This is because if the resin layer is thick,
This is because the titanium substrate is peeled off from the resin layer, and when the resin layer is thin, the CSS characteristics are deteriorated.

The present invention has been made in view of the above circumstances, and in a magnetic disk substrate in which a resin layer is formed on a titanium material, the surface state and CSS characteristics are extremely good, and the titanium material and the resin layer are combined. It is an object of the present invention to provide a magnetic disk substrate having high adhesion.

[0009]

In order to solve such a problem, the present invention provides a disc-shaped core material made of a titanium material, and a resin layer made of a synthetic resin provided thereon. And a thickness of the resin layer is t ₁ (μm), t ₁ <300 μm, and t ₁ and the surface roughness R _{maxS of the} core material satisfy the following relationship. A magnetic disk substrate characterized by the above. t ₁ / R _maxS > 3

The inventors of the present application have made a detailed study in order to obtain a magnetic disk substrate having a resin layer formed on a titanium material and having a good surface roughness without peeling of these layers, and as a result, the following conclusions have been reached.

The peeling of the resin layer from the titanium substrate and the resin layer occurs due to the difference in linear expansion coefficient between the two when the resin layer is thick, and there is an upper limit to the thickness of the resin layer in order to prevent peeling. To do. This is because the linear expansion coefficient of the resin is several 10 to 100 ×
10 ^-6 / ° C, the linear expansion coefficient of Al alloy is 23.0 × 10 ^-6
/ ° C., the linear expansion coefficient of titanium is 8.4 × 10 ⁻⁶ / ° C., and this is because the difference in linear expansion between titanium and resin is larger than the difference in linear expansion between Al alloy and resin. That is, the temperature of the substrate rises during the curing treatment of the resin layer and the sputtering,
At that time, peeling occurs due to the difference in expansion amount between the titanium material and the resin layer.

On the other hand, when the resin layer is thin, the head crush resistance is lowered. This is because the titanium material has a lower head crush resistance than the NiP plating type Al alloy substrate due to its softness (it is easily deformed and easily becomes burr), and when the resin layer is too thin, This is because the head crash resistance of the titanium material becomes dominant. That is, since the magnetic disk of the present invention improves the head crush resistance of the titanium material due to the cushioning property of the resin layer, the minimum thickness necessary for obtaining good CSS characteristics exists.

As described above, the resin layer in the present invention improves the surface roughness of the titanium substrate and also acts as a kind of cushion to improve the CSS characteristics. Therefore, the larger the thickness of the resin layer, the more the surface roughness and CSS characteristics are improved. On the other hand, on the other hand, since the linear expansion coefficient of the resin layer and that of titanium are greatly different from each other as described above, it is necessary to set the thickness of the resin layer to less than 300 μm in order to prevent the two from peeling. Further, in order to ensure the cushioning property, the thickness of the titanium core material is 3 of R _maxS in relation to the surface roughness R _maxS of the titanium core material.
Must be more than double.

The synthetic resin constituting the resin layer is not particularly limited as long as it has excellent adhesiveness to the titanium core material, but urethane type, epoxy type, melanin type, methacrylic type, ABS type, polycarbonate type is used. , Dialphtalate type, etc. are applicable. In the present invention, the term "titanium" is intended to include both pure titanium and titanium alloy.

[0015]

[Example] CP of 3.5 inch size and 0.5 mm in plate thickness
Both surfaces of the two kinds of pure titanium disk substrate material were polished by a double-sided polishing machine using # 400 grindstone to _obtain a substrate having a surface roughness of R _maxS 2.1 μm.

Next, after washing and drying this substrate, the substrate was set on a double-sided simultaneous spin coater at room temperature of 25 ° C. and rotation speed of 20.
The melamine resin solution was spin coated at 00 rpm. The spin coating thickness was changed by adjusting the viscosity by increasing or decreasing the solvent component of the melamine resin solution. Then, while rotating the spin-coated substrate in an oven, 150 ° C. × 3
Pre-baking was performed for 0 minutes to evaporate the solvent, and the heat treatment temperature was raised to 275 ° C. and main baking was performed for 10 minutes to complete the curing reaction. The resin thickness after spin coating and the surface roughness R _maxR of the resin were measured by an ellipsometer and a surface roughness meter, respectively. As a result, the resin thickness is 5μ
m to 400 μm, and the surface roughness R _maxR of the resin was 0.03 to 0.05 μm, which was good.

Next, a required magnetic medium and a protective film were formed by sputtering, and a lubricant was applied by spin coating to prepare a magnetic disk. First, a Cr underlayer is formed to a thickness of 150 nm, and then a CoNiCr film is formed to a thickness of 4 nm.
A magnetic layer was formed by forming a film with a thickness of 0 nm, and an aC layer was further formed thereon as a protective and lubricating layer by sputtering to form a magnetic disk. The above layers are examples, and the layer structure of the ferromagnetic metal thin film magnetic disk is not limited to this.

The test results of this sputter disk are shown in Table 1. In the table, the CSS characteristic is represented by the number of contact between the head and the disk, and is a measure of the head strength of the disk. That is, the number of times of CSS is the number of times until the head is damaged due to the peeling of the magnetic film or the dent deformation of the titanium magnetic disk substrate. In the current magnetic disk substrate, the number of CSS times of 30,000 or more is a criterion. In addition, the presence or absence of peeling was determined by visually observing the bonded portion after the magnetic disk was created.

[0019]

[Table 1]

As is clear from Table 1, t ₁ / R
_If the value of _maxS is 3 or less, the number of CSS is small and CSS
It was confirmed that the characteristics were poor. Moreover, the thickness of the resin layer is 30
It was confirmed that peeling occurred in the case of 0 μm or more. On the other hand, it was confirmed that when t ₁ / R _maxS > 3 and the thickness of the resin layer is less than 300 μm, the CSS characteristics are good and the resin layer does not peel off.

[0021]

According to the present invention, since the resin layer having a specific thickness is provided on the titanium plate, good surface roughness can be obtained, and the magnetic head can be formed on the recording layer formed thereon. The resin layer absorbs the impact force even if it collides, and the head crushing resistance can be greatly improved.

That is, according to the present invention, it is possible to easily improve the surface roughness and the head crushing resistance when the titanium material is used as the magnetic disk substrate, which has a great industrial effect.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Morita, 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masanori Omura, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A magnetic disk substrate having a disk-shaped core material made of a titanium material and a resin layer made of a synthetic resin provided on the disk-shaped core material. T ₁ (μ
m), t ₁ <300 μm, and t ₁ and the surface roughness R _maxS (μm) of the core material satisfy the following relationship. t ₁ / R _maxS > 3