JPH0831024A - Production of plastic substrate for recording medium - Google Patents

Abstract

PURPOSE:To produce a plastic substrate for a recording medium having improved performance as a recording medium by eliminating warp and wave which are generated at the time of molding. CONSTITUTION:Each molded plastic substrate 1 for an optical or magnetic disk as a recording medium is heated to a specified temp, under pressure applied from both sides with a pressing member 5 which comes into contact with only the inner and outer circumferential parts of the substrate 1 with no signal groove and has flat pressing faces. The heated substrate 1 is then slowly cooled. By this slow cooling, warp and wave generated at the time of molding are eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plastic substrate for a recording medium.

[0002]

2. Description of the Related Art Plastic substrates such as polycarbonate for optical recording media are widely used because they are inexpensive and lightweight. The plastic substrate is formed by injection molding or the like, but at that time, warpage or undulation occurs due to residual stress. If the substrate warps or waviness is severe, the results will not satisfy the conditions such as the axial acceleration and tilt angle defined by the International Organization for Standardization, resulting in poor followability of the optical pickup and eventually poor reproduction signal quality. Will be invited. On the other hand, magnetic recording media (hard disk)
Is conventionally manufactured as an aluminum or glass substrate,
In recent years, with the aim of mass productivity and improvement of recording density, development of a plastic molded substrate is under way. However, as with the optical recording medium, the warpage and undulation that occur during molding of the magnetic recording medium increase the runout (disk surface runout due to circumferential distortion), which hinders the stable flying of the magnetic head, which results in reproduction signals and recording. This leads to deterioration of signal quality.

[0003]

However, the conventional methods for producing plastic substrates for optical discs and magnetic discs have not been able to sufficiently prevent warpage and undulation of the substrate that occur during molding. An object of the present invention is to provide a method for manufacturing a plastic substrate for a recording medium, which is capable of removing warpage and undulation generated during molding of the plastic substrate and improving performance as a recording medium.

[0004]

The object of the present invention is achieved by the following constitutions. That is, it is a method of manufacturing a plastic substrate for a recording medium, in which after the substrate is molded, the substrate is heat-treated at a predetermined temperature for a predetermined time while being pressed from both sides by a pressing member, and then gradually cooled. In the present invention, it is desirable that the heat treatment temperature is set to a temperature at which the signal groove is not thermally deformed, for example, a temperature slightly lower than the glass transition point of the plastic material of the substrate. Further, it is desirable to use, as the pressure applying means, a pressure applying member having a flat pressure applying surface which is in contact only with the inner and outer peripheral substrates without signal grooves. As the plastic substrate used in the present invention, an amorphous polyolefin-based material or another plastic material can be used.

[0005]

The molded plastic substrates for recording media for optical disks and magnetic disks contact only the inner and outer peripheral portions having no signal groove, and are pressed from both sides by a flat pressing member for a predetermined time, and in the meantime. It is heated to a specific temperature. After that, the substrate is gradually cooled by natural heat radiation, so that the warp and undulation of the substrate generated at the time of molding can be removed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1, 2, 3 and 4. As shown in FIG. 1, a center hole 2 is formed in an injection-molded amorphous polyolefin-based plastic substrate 1 and has a disk shape. At the time of molding, the signal groove portion 3 is formed at the same time. After the substrate 1 is molded, if necessary, fine dust and dust are blown off with clean air, and then the stock columns 4 are stacked through the center holes 2 as shown in FIG.

Next, as shown in FIG. 3, a pressing member 5 which is in contact only with the substrate 1 in the inner and outer peripheral portions of the signal groove portion 3 where there is no signal groove and which has a flat pressing surface is alternately arranged with the substrate 1 for supporting columns for stock. Four
Stack on. The pressure member 5 is made of stainless steel, and is shown in FIG.
By stacking as described above, the substrate 1 can be pressed from both sides. In that state, the stock columns 4, the substrate 1 and the pressing member 5 are placed upright in a heating furnace (not shown) and held at a temperature slightly lower than the glass transition point of the amorphous polyolefin plastic substrate for a predetermined time. , Keep the heat release and radiate heat naturally. By the above heat treatment, the warp and undulation generated in the substrate 1 due to the residual stress during molding can be removed. Since the magnetic head of a magnetic recording disk (hard disk) comes into contact with the disk unlike an optical pickup for an optical disk, the standard of the warp amount required for the substrate is strict.

FIG. 4 is a graph showing a curve of a warp amount with respect to a radial position of a plastic substrate for a magnetic recording disk (hard disk) before the heat treatment (broken line) and a curve after the heat treatment (solid line) in the present embodiment. However, it can be seen that the amount of warpage of the substrate is clearly reduced by the heat treatment. In addition,
The present invention can also be applied to optical recording media such as compact discs, video discs, magneto-optical discs, and other types of optical recording media other than those described above that use a plastic substrate.

[0009]

As described above, according to the method of the present invention, it is possible to remove the warp and undulation of the plastic substrate caused by residual stress at the time of molding, which has been a problem in the past. It is possible to obtain a disk for a magnetic recording medium by a simple method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an injection-molded amorphous polyolefin-based plastic substrate according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which injection-molded amorphous polyolefin-based plastic substrates according to an embodiment of the present invention are stacked on a support column for stock.

FIG. 3 is a cross-sectional view showing a state in which an injection-molded amorphous polyolefin-based plastic substrate and a pressure member according to one embodiment of the present invention are alternately stacked on a stock strut.

FIG. 4 is a diagram showing curves of a warp amount with respect to a radial position of an injection-molded amorphous polyolefin-based plastic substrate according to an embodiment of the present invention before and after heat treatment.

[Explanation of symbols]

1 ... Amorphous polyolefin plastic substrate, 2 ... Center hole, 3 ... Signal groove part, 4 ... Stock support, 5
... Pressurizing member

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yasuyuki Imai 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (3)

[Claims] 1. A method of manufacturing a plastic substrate for a recording medium, which comprises heat-treating a substrate at a predetermined temperature for a predetermined time while pressing the substrate from both sides after molding the substrate, and then gradually cooling the substrate. 2. The method for producing a plastic substrate for a recording medium according to claim 1, wherein the heat treatment temperature is equal to or lower than a temperature at which the signal groove is not thermally deformed. 3. The method for producing a plastic substrate for a recording medium according to claim 1, wherein a pressure member having a flat pressure surface is used which is in contact only with the substrate in the inner and outer peripheral portions having no signal groove.