JPS625824A - Manufacture of base plate for disk - Google Patents

Abstract

PURPOSE:To manufacture the base plate for disk, excellent in the properties of birefringence and transfer, by a method wherein a stamper is attached to the molding surface of core of a mold through a sheet upon injection molding or injection and compression molding the base plate for disk. CONSTITUTION:The sheet 13 is provided between the stamper 8 and the moving side core 4. A metal or a synthetic resin may be considered as the sheet 13. When molten resin, injected from an injection device, flows into the cavity of the mold, heat conduction from the molten resin to a cooling medium for cooling the molten resin, which is provided in the mold, is reduced, the cooling speed of the molten resin is also reduced and the transfer property, important for the base plate for disk, may be improved while the solidifying speed is slowed and a power is applied while solidifying is not advanced whereby strain may be reduced and the birefringence may be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a disk substrate such as an optical disk or a magneto-optical disk.

Substrates for video discs, compact discs, recordable and erasable optical discs, and magneto-optical discs are being manufactured or developed using 2ft, 4-way injection molding or injection compression molding. Molding of disk substrates involves thin-wall precision molding, and important issues include improving the precision of the mold, developing resin materials, and developing molding conditions such as mold temperature, cylinder temperature, injection pressure, and injection speed. . There are many requirements for an optical disc substrate, among which are low birefringence caused by the orientation of molecular chains and residual strain during molding, and good transferability of signal pits or guide grooves for tracking holes. Being good is important. These items include the development of resin materials (small photoelastic coefficient and good melt flow characteristics) and molding conditions, such as ■
Increase the cylinder temperature to improve the fluidity of the resin material. ■Increase the mold temperature. ■Keep the injection pressure as low as possible. ■Make the injection speed as fast as possible. This can be improved by setting the following.

However, each of the above-mentioned conditions (1) to (2) has its limits; for example, (2) causes problems with thermal deterioration of the resin material, and (2) causes problems such as prolonged cooling time, which becomes an obstacle to shortening the cycle, and increases warping of the disk substrate.

In case (2), birefringence improves, but the internal pressure of the resin decreases and signal transfer deteriorates. In case (2), there is a problem that overfilling tends to occur and control is difficult, and it has been difficult to find a perfect solution. (Plastic Age Mar, 1984P 103
~P 106) On the other hand, with regard to the structure of molds, as with general molded products, attention is paid only to increasing the cooling and solidification rate of the molten resin as much as possible in order to improve mass productivity. This is the current situation. FIG. 3 shows a schematic cross-sectional view of a conventional disk substrate molding die.

(Unexamined Japanese Patent Publication No. 68-151223) Referring to FIG. 3, 1 is a fixed die plate, 2 is a movable die plate, 3 is a fixed core, 4 is a movable core, 5 is a member for tightening the stamper, and 6 is a member for tightening the stamper. A stamper holding ring, 7 is a cavity, 8 is a stamper, 9 and 1Q are cooling medium passage grooves for cooling the molten resin, 11 is a part of a sprue, and 12 is an injection cylinder.

For example, in injection molding, a disk substrate is placed in a mold as shown in FIG. 3, and molten resin injected from an injection cylinder 12 passes through a sprue portion 11 and fills a cavity. The die plate on one side of this mold (moving die plate 2 in FIG. 3) has a stamper 8 engraved with a signal pit or a guide groove for tracking, a stamper clamping member 5 on the inner periphery, and a stamper on the outer periphery. It is held using a presser ring 6. With this structure, as the molten resin is filled, the internal pressure of the cavity increases, signal transfer is performed, and the stamper 8 immediately comes into close contact with the movable core 4, so that the molten resin solidifies. In order to remove heat as quickly as possible from the resin material filled into the mold by injection and shorten the cooling time until the mold is opened, it is effective to have nothing interposed between the stamper and the core so that they can be in close contact with each other. There will be.

However, in the molding of disk substrates, in order to improve the transferability of the aforementioned birefringence, signal pits, or guide grooves, it is necessary to remove the heat from the molten resin until the internal pressure of the injected molten resin is sufficiently transmitted to the cavity. It's better not to have it. In normal molding, the mold temperature is set at a temperature approximately 10 to 40'C lower than the heat distortion temperature, so the surface layer of the resin material that comes into contact with the cavity surface in the mold during injection solidifies immediately. This is obvious from the fact that the transferability deteriorates, and as a result of applying force while solidifying, distortion remains and the birefringence worsens.

Problems to be Solved by the Invention The present invention solves the above-mentioned drawbacks of the prior art in cooling the injected molten resin within the cavity, and solves the problem of birefringence, which is an important characteristic of disk substrates such as optical disks and magneto-optical disks. It is also an object of the present invention to provide a method for manufacturing a disk substrate that can provide good transferability.

Means for Solving the Problems The method for manufacturing a disk substrate of the present invention is such that when injection molding or injection compression molding a disk substrate, a stamper is placed on the molding surface of a mold core through sorting to achieve a target. be.

Function: The method of manufacturing a disk substrate of the present invention is such that when the injected molten resin flows into the cavity of the mold, a sorter is provided under the stamper to prevent the molten resin from entering the mold. , reduce the heat conduction to the cooling medium for cooling the molten resin, slow down the cooling rate of the molten resin, and increase the apparent cylinder temperature to improve the fluidity of the molten resin.
The same effect as raising the mold temperature is obtained, improving transferability, which is important for disk substrates, and slowing down the solidification rate. By applying force before solidification progresses, strain is reduced and birefringence is improved. be done.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a sectional view of a mold for manufacturing a disk substrate according to the present invention.

This corresponds to FIG. 3 showing a conventional example. This example is provided. The sheet may be made of metal or synthetic resin.

As for the metal, it must fit between the nickel stand bar and the steel moving core.

Aluminum and copper, which have low hardness, can be used, and these metal sheets are processed to have the same inner and outer diameters as the stub bar. Further, the synthetic resin may be in sheet form as long as it satisfies heat insulation properties, such as a polyimide film.

FIG. 2 is an enlarged partial cross-sectional view of the structure of the stand bar 8, seat 13, and moving core shown in FIG. By adopting this configuration, the progress rate of assimilation of the molten resin is slowed down, and the birefringence and
It becomes possible to manufacture products with excellent transferability. Furthermore, the presence of this sheet does not increase the cooling time.

As described in detail, the disk substrate manufacturing method according to the present invention attaches a stand bar to the molding surface of the mold core via a sheet when injection molding or injection compression molding a disk substrate. This is especially noticeable when using a heat-insulating synthetic resin sheet compared to those made using the same manufacturing method. Although the mirror surfaces of the surfaces were in direct contact, the presence of a sheet in between has the ripple effect of extending the life of the mirror surfaces of the standber and mold core. Furthermore, fine irregularities on the back surface of the methane disk are also absorbed to some extent by sorting, and have the effect of not being transferred as irregularities to the surface of the disk substrate.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a partially enlarged sectional view thereof, and FIG. 3 is a diagram showing a conventional embodiment. 1... Fixed die plate, 2... Moving die plate, 3... Fixed side core, 4...
・Moving side core, 5...Stand bar tightening member, 6
...Stand bar holding ring, 7...Cavity, 8...Stand bar, 9゜10...
・Cooling medium passage groove for cooling molten resin, 11...
Part of the sprue, 12... Injection cylinder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (4)

[Claims] (1) A method for manufacturing a disk substrate, which comprises attaching a stamper to the molding surface of a core of a mold via a sheet when injection molding or injection compression molding a disk substrate. (2) The method for manufacturing a disk substrate according to claim 1, wherein the sheet is a metal sheet. (3) The method for manufacturing a disk substrate according to claim 2, wherein the metal sheet is selected from aluminum or copper. (4) The method for manufacturing a disk substrate according to claim 1, wherein the sheet is a synthetic resin sheet.