JPH05138700A - Mold for disk molding - Google Patents

Abstract

PURPOSE:To mold a disk substrate without surface fault. CONSTITUTION:A stamper 20 which forms a cavity 10 for disk molding, a mirror plate 30, and the face of a peripheral ring 40 facing the cavity 10 are covered with Ta thin membranes 21, 31, and 41, respectively. In this way, adhesion between a mold and a disk substrate is reduced so that the disk substrate can be released from the mold smoothly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk molding die used for injection molding of a disk substrate such as an optical disk.

[0002]

2. Description of the Related Art For injection molding of a disk substrate such as an optical disk, a mold which is a combination of a movable mold and a fixed mold is used as in other general injection molding. A characteristic of the disk molding die is that a stamper 62 is attached to the surface of the movable die 61 as shown in FIG. 2, and this stamper 62 and a mirror surface plate of a fixed die opposed to the movable die 61. A cavity 60 is formed by 63 and the outer peripheral ring 64 held between the movable mold 61 and the mirror surface plate 63.

Of these cavity forming members, the stamper 62 forms the signal surface of the disk substrate, and the surface is provided with predetermined information in the form of pits or grooves. Then, in a general disc molding die, the surface of the stamper 62 is made of Ni formed as a conductive film for electroforming.
It is covered with a film (Ni sputtered film or electroless Ni film). The mirror surface plate 63 and the outer peripheral ring 64 are made of corrosion-resistant alloy steel capable of mirror surface polishing, and the surface on the cavity side is mirror surface polished.

[0004]

When a disk substrate is injection-molded with such a disk molding die, stain-shaped surface defects or cloudy surface defects may occur on the molded disk substrate. When these surface defects are observed in detail, fine streaks are lined up, and it is considered that they occurred at the time of mold release after injection molding.

That is, when the disk substrate is taken out of the mold after the injection molding, compressed air for mold release is made to flow between the mold and the disk substrate to promote the separation of the disk substrate from the mold. If the adhesive force between the mold and the disk substrate is high, peeling by compressed air does not proceed smoothly and becomes discontinuous, so the traces when the mold release speed is slow or the mold release is stopped It is presumed that it appears as a pattern.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a disc molding die capable of smoothly releasing a disc substrate and molding a disc substrate having no surface defect. To aim.

[0007]

DISCLOSURE OF THE INVENTION A disk molding die according to the present invention is characterized in that a cavity forming member for forming a disk molding cavity is covered with a Ta thin film at least on a surface facing the cavity.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional side view showing an enlarged part of an example of a disk molding die according to the present invention.

The cavity 10 into which the resin is injected at the time of molding the disk substrate is formed by a stamper 20, a fixed mirror mirror plate 30 and an outer peripheral ring 40. The stamper 20 has a disk shape and is attached to the central portion of the surface of the movable mold 50, and a predetermined gap corresponding to the thickness of the disk substrate is secured between the stamper 20 and the mirror plate 30. The outer ring 40 is
The inner edge of the end face is the surface of the stamper 20 in order to be fitted into the convex portion 32 provided in the central portion of the surface of the mirror plate 30 and to form the disk molding cavity 10 between the stamper 20 and the convex portion 32 of the mirror plate 30. It is held close to the outer edge.

Here, the stamper 20 has a known stamper constituent material such as Ni as a base material, and the entire surface on the cavity side of the base material is covered with a Ta thin film 21. Mirror plate 3
0 and the outer peripheral ring 40 also use a corrosion-resistant alloy steel or the like that can be mirror-polished as a base material, and in the specular plate 30, the entire surface of the convex portion 32 is covered with the Ta thin film 31, and in the outer peripheral ring 40, A region slightly wider than the cavity on the inner peripheral surface is covered with the Ta thin film 41. Therefore, the entire surface of the member forming the cavity 10 facing the cavity 10 is covered with the Ta thin film.

The Ta thin film is formed by a known film forming method such as a sputtering method or a vapor deposition method. When using the sputtering method,
The reverse sputtering has the advantages that the surface of the base material is cleaned, the adhesion of the Ta thin film to the base material is increased, and the smoothness of the base material surface is improved by sputter etching.
The film thickness of the Ta thin film can be appropriately selected within the range of 10 angstrom to 1 μm, but the Ta thin film of the stamper does not significantly change in pits and grooves.
0-3000 Angstroms are particularly suitable.

To mold the disk substrate, resin is injected into the cavity 10 of the disk molding die. When taking out the disc substrate from the disc molding die, compressed air for release is flown between the die and the disc substrate. Since the surface of the disk molding die facing the cavity 10 is covered with the Ta thin film, the adhesion between the die and the disk substrate is reduced,
Mold release with compressed air proceeds smoothly. for that reason,
A disk substrate having no surface defect can be obtained.

The same molding is performed by using the mold of the present invention in which all the surfaces facing the cavity 10 are coated with the Ta thin film, the conventional mold not having the Ta thin film, and the comparative mold in which only the surface of the stamper is coated with the Ta thin film. The disk substrate was molded under the conditions. The Ta thin film was formed by a sputtering method and had a thickness of 300 Å. Table 1 shows the surface condition of the molded disk substrate. ◯ indicates no surface defect, and x indicates the occurrence of surface defect. However, when the mold of the present invention was used, no defect occurred on either the movable side or the fixed side of the disk substrate.

[0014]

[Table 1]

[0015]

As described above, in the case of the disk molding die according to the present invention, the surface of the cavity forming member facing the cavity is covered with the Ta thin film, so that the adhesion force between the die and the disk substrate is lowered, and the disk substrate is reduced. Since the mold can be released smoothly, a disk substrate having no surface defect can be obtained. Further, as a secondary effect, the Ta thin film is chemically stable and hard, so that the life of the mold can be expected to be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an enlarged part of an example of a disk molding die according to the present invention.

FIG. 2 is a vertical sectional side view showing a part of a conventional disk molding die in an enlarged manner.

[Explanation of symbols]

 10 Disk-forming Cavity 20 Stamper 30 Fixed Mold Mirror Plate 40 Outer Ring 50 Movable Mold 21, 31, 41 Ta Thin Film

Claims (1)

[Claims] 1. A disk molding die, characterized in that at least a surface of a cavity forming member for forming a disk molding cavity facing the cavity is covered with a Ta thin film.