JPS63308743A - Optical disk - Google Patents

Abstract

PURPOSE:To enable formation of a stable disk which is less burred by forming dents to the corner parts in the inside diameter part of a plastic substrate having optical transparency. CONSTITUTION:This optical disk consists of the plastic substrate of polycarbonate or the like having the optical transparency and is formed by injection- molding the disk 1 in metallic molds and cutting the inside diameter part by a cutting means. The dents are formed in the corner parts P, Q in the inside diameter part at the time of this injection molding, by which the inside diameter having the high accuracy of the eccentricity to prevent burring by the movement of a gate cutting punch and the flawing of the disk surface by the burring is prevented in spite of stacking the disks. The stable disk resistant to the burring is formed by this forming method.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Use> The present invention relates to the shape of an optical disk on which information is recorded, which is made of a plastic base with excellent optical transparency such as polycarbonate or polymethyl methacrylate.

<Conventional technology and its problems> Conventionally, an optical disc base has a center hole for mounting it on a player, and the cross section of the inner diameter of this hole is a second hole.
As shown in the figure, it has a single vertical shape, the overall thickness is H, and the corner P of the inner diameter part where the horizontal surface of the disk intersects with the vertical side surface, and the horizontal surface of the disk Corner Q of the inner diameter part where the back surface intersects with the vertical side surface
Both had right-angled cross-sectional shapes.

That is, in this shape, in the molding process as shown in FIG. 5, the resin passes through the resin runner 2 and is filled into the disk substrate l from the resin gate 3, but the thickness H of the disk substrate 1 is suddenly filled from the narrow flow channel gate 3. Since the disk is expanded in size and filled, uneven filling occurs at the corners of the disk shown at P and Q, and as a result, the packing density tends to decrease.

As a result, the shape of the end face becomes unstable and the dimensional accuracy of the inner diameter tends to be difficult to achieve.In the case of optical discs, the inner diameter dimension is determined by rotating the disc based on the inner diameter as described above, which can lead to eccentricity. Tracking servo fluctuations on the player affect the quality of thick rediscs.

In addition, conventionally, the second
If a burr 5 is generated as shown in the figure, it exceeds the thickness H of the disk, so there is a problem that it tends to scratch or damage other disks when stacking disks.

Means for Solving the Problems> The present invention has been made in view of the current situation as described above, and is an optical disc made of an optically transparent plastic base such as polycarbonate or polymethyl methacrylic. The inner diameter was pressed out with a mold by forming depressions at the corner A of the inner diameter part where the front surface and the vertical side surface intersect, and at the corner B of the inner diameter part where the horizontal back surface of the disk and the vertical side surface intersect. The present invention provides an optical disc that can stably produce discs because it is difficult for the edges to appear, and maintains the accuracy of the inner diameter of the optical disc, thereby ensuring reliable tracking.

<Example> The present invention will be described in detail below with reference to the drawings.

The shape of the disk according to the present invention is as shown in FIG. 1, where H represents the thickness of the disk base and a(φ) represents the inner diameter of the disk. The dimensional accuracy of this inner diameter a(φ) tends to affect the performance of the disk, and if the dimensional accuracy of this inner diameter a(φ) is poor, eccentricity during reproduction becomes large and tracking errors are likely to occur. In the present invention, in order to maintain the dimensional accuracy of a(φ), as shown in FIG. 4, a means is used for cutting the disk base in the mold at the same time as the injection molding. In the same figure, the disk base of the inner diameter portion of the mold shape has the shape of a disk base having depressions P and Q as shown in FIG.

A shows the state of the mold during disk molding, and B shows the state of the mold when cutting the inner diameter gate. That is, when cutting the inner diameter, the sprue and the gate cut bunch 4 of the movable cavity in the gate section move to cut the resin gate section 3 at the entrance to the disk base 1 to create a disk having an inner diameter of a predetermined size.

During molding, resin passes through the resin runner 2 and the resin gate part 3 and is filled into the disk base 1 by injection molding. At this time, in the shape of the disk substrate according to the present invention having a recess at the inner diameter corner, the filling of the inner diameter end of the disk substrate gradually changes from d − * d + e + f − * H shown in FIG. 1 in the disk thickness direction. By enlarging the dimensions and making the filling of the resin at the end of the inner diameter smoother and more uniform as shown in Figure 4, we were able to improve the maintenance of the dimensional accuracy of the inner diameter and eliminate burrs by cutting the inner diameter gate. 5 is difficult to come out, and even if it does come out, it will not exceed the thickness H of the disk base as shown in FIG.

<Effects> By using the optical disc shape according to the present invention, it is possible to stably produce discs because it is difficult to produce burrs when the inner diameter is pressed out with a mold, and it is possible to maintain the accuracy of the inner diameter of the optical disc. Tracking becomes more reliable, and the fit between the player and the inner diameter of the disc also improves.

[Brief explanation of the drawing]

1 and 3 are explanatory diagrams showing a cross section of the inner diameter portion of a disk according to the present invention, FIG. 2 is an explanatory diagram showing a cross section of the inner diameter portion of a conventional disk, and FIG. 4 is an explanatory diagram showing a cross section of the inner diameter portion of a disk according to the present invention. FIG. 5 is an explanatory diagram showing the molding process for obtaining a conventional disk. 1-m-disc base 2-m-runner 3-m-gate portion 4-m-gate cut punch 5-m-Paris patent applicant Toppan Printing Co., Ltd. Representative Kazuo Suzuki Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) In an optical disc made of an optically transparent plastic base such as polycarbonate or polymethylmethacrylic, a corner P of the inner diameter portion where the horizontal surface of the disc intersects with the vertical side surface and a corner P that is perpendicular to the horizontal back surface of the disc An optical disc characterized in that a recess is formed at a corner Q of an inner diameter portion where the side surface intersects with the inner diameter part.