JPH0528543A - Optical disk substrate manufacturing method - Google Patents

Abstract

(57) [Summary] When continuously manufacturing an optical disk substrate by injection molding, the mold temperature of the molding machine and the substrate temperature in the cavity of the molding machine are monitored, and the substrate temperature is A method for manufacturing an optical disk substrate, characterized in that when the values are equal to or less than a set value, the controller of the molding machine is operated to open the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for a plastic disk substrate used for an optical information recording medium capable of recording, reproducing and erasing information by a light beam.

[0002]

2. Description of the Related Art Polycarbonate (PC), polymethylmethacrylate (PMMA) as a substrate for optical disks
A transparent plastic material such as, for example, is generally used. Here, the injection molding process using polycarbonate will be described.

FIG. 3 shows the structure of a mold for an optical disk molding mold when the mold is clamped. In FIG. 3, 21 is a sprue, 23
Is a mirror surface of a fixed-side mold, 24 is a mirror surface of a movable-side mold, 28 is a substrate, 29 is a stamper, 30 is an ejector pin for sprue, 31 is an ejector pin for substrate, 32 is a stamper for holding an outer peripheral side, and 33 is an inner periphery. It is a side stamper presser. In the optical disk molding die, a stamper 29 having fine grooves and pits formed on the upper surface of the mirror surface 24 of the movable side die is attached by an inner peripheral side stamper retainer 33 and an outer peripheral side stamper retainer 32. A cavity is formed by the mirror surface 23 of the fixed-side mold that faces the mold 24.

Next, the resin melted in the plasticizer is
After filling the cavity through the sprue 21, the cavity is filled with pressure, and after the cooling time for the resin to solidify, the substrate 28 is taken out. The mold opening for taking out the solidified substrate is generally performed by the operation of the control device on the molding machine side after a preset time has elapsed. After the mold is opened, the sprue 21 is a sprue ejector pin 30 for releasing the substrate 28 from the movable side mold 24.
The substrate 28 is separated from the stamper 29 and separated from the outer peripheral stamper retainer 32 by the ejector pin 31 for the substrate, forcibly protruding the central portion, air blow, or a combination thereof, and taken out.

[0005]

However, in order to reduce the warp of the substrate, it was necessary to set the molding conditions (cooling time) in consideration of the following phenomenon. In the conventional optical disk manufacturing method, in ordinary injection molding, the substrate 2 immediately after molding is different due to the difference in linear expansion coefficient between the mold member and the resin.
8 has a force that expands in the radial direction and the plate thickness direction in the cavity. The force that works in the plate thickness direction is released by opening the mold, but the force that expands in the radial direction is 8 It is suppressed by the outer peripheral side stamper holder 32, and the substrate 28 and the outer peripheral side stamper holder 32 are in close contact with each other due to the pressure generated at this time.

On the other hand, the die temperature is usually heated to 100 to 120 ° C. so that the grooves and pits provided in the stamper 29 can be faithfully transferred, and the die temperature at that time and the cavity during cooling. Figure 4 shows the relationship with the substrate temperature in the tee.
As shown in, although the temperature decreases with time, the substrate temperature becomes much higher than the mold temperature when the cooling time setting is short. The mold is opened and taken out in the region or near the glass transition temperature (130 to 140 ° C).

Therefore, if the releasing operation is performed in such a state, the limit of the thermal deformation stress becomes small and the deformation becomes easy even though the adhesion between the outer peripheral side stamper holder and the substrate is large. Furthermore, deformation is likely to occur in the plastic region that cannot be removed even by the annealing process in the subsequent process. As a matter of course, when the setting of the cooling time is short, a substrate with less warp cannot be obtained, and the amount of warp is almost constant even by the annealing process.

As a means for suppressing the deformation in the plastic region, the cooling time is extended so that the substrate is taken out in the elastic region below the mold temperature (120 ° C. or below), and the substrate is sufficiently cooled in the cavity. A method of taking it out is also conceivable, but a method of easily extending the cooling time leads to an increase in molding cycle time, which eventually leads to an increase in the cost of the substrate.

An object of the present invention is to provide an optical disk substrate having good mechanical characteristics. Furthermore, it is necessary to accurately set the cooling time for obtaining a substrate with a small warp and to minimize the increase in cycle time.

[Means for Solving the Problems]

According to the present invention, when an optical disk substrate is continuously manufactured by an injection molding method, the mold temperature during molding and the substrate temperature in the cavity during molding are monitored,
The present invention relates to a method for manufacturing an optical disk substrate, which is characterized in that when a substrate temperature is equal to or lower than a mold temperature, a controller during molding is operated to open the mold. The present invention relates to a manufacturing method in which the temperature is a temperature at which the substrate does not deform due to the pressure generated by the difference in the linear expansion coefficient of the mold.

For the optical disk substrate material of the present invention, a thermoplastic resin such as the above-mentioned polycarbonate (PC) or polymethylmethacrylate (PMMA) having good transparency and a high heat distortion temperature is preferably used.

If the mold release temperature is not lower than the heat deformation temperature of the resin, the substrate is permanently deformed and residual stress and annealing for removing the deformation do not work.

Therefore, the temperature of the substrate resin and the temperature of the mold in the cavity of the molding machine are accurately and continuously monitored, and the absolute value of the temperature and the two temperatures are compared. And
The substrate temperature becomes the same as the mold temperature. The control symbol is issued at the set temperature and the mold is opened.

In order to accurately measure the substrate temperature and the mold temperature in the cavity, it is preferable that the mold surface or the substrate surface is separated as much as possible.

Since the metal mold has a high thermal conductivity, the mold temperature can be measured with sufficient accuracy on the metal mirror surface to which the stamper is attached. However, since the thermal conductivity of resin is relatively low, it is necessary to devise a measure for the substrate surface temperature. The temperature is measured indirectly in the bush that fixes the passage (spur) that fills the cavity with molten resin.
Adjust the sensor tip position so that it is flush with the substrate mirror surface position. The molten resin is a highly viscous fluid and it is difficult to measure it directly to solidify it. However, the distance between the actual fluid and the actual fluid is set to be as small as possible.

The upper limit temperature of the set value is the heat distortion temperature of the resin. The set value is arbitrary as long as it is below the upper limit temperature.

[0017]

EXAMPLES Example 1 of the present invention will be described below.
FIG. 1 shows a mold structure when the optical disk mold of the present invention is clamped. FIG. 2 shows the control process of the present invention.
In FIG. 1, 1 is a sprue, 2 is a fixed-side bush, 3 is a mirror surface of a fixed-side mold, 4 is a mirror surface of a movable-side mold, 5 is a temperature sensor, 6 is a screw, 7 and 7'are temperature sensors, and 8 is substrate,
9 is a stamper, 10 is an ejector pin for sprue, 11
Is an ejector pin for a substrate, 12 is an outer peripheral side stamper holder, and 13 is an inner peripheral side stamper holder.

First, the mold structure will be described. In FIG. 1, a fixed-side bush 2 provided to attach the sprue 1 used when the molten resin is filled into the cavity to the mirror surface 3 of the fixed-side mold holds the sprue 1 so that the fixed-side bush 2 holds the sprue 1. It is press-fitted and attached to the mirror surface 3 of the mold. Further, in order to monitor the temperature inside the cavity, a temperature sensor 5 was adjusted on the fixed side bush 2 so as to be flush with the fixed side bush 2 in contact with the cavity side, and attached by a screw 6. The trace of the temperature sensor generated during molding is located between the clamping zone and the recording area, and is outside the area normally used for the optical disk substrate. I set it so that it would not be a problem.

Next, the structure of the control unit will be described. When the substrate temperature in the cavity during the cooling process is monitored by the temperature sensor 5 and compared with the temperature sensors 7, 7'which monitor the mold temperature, when the substrate temperature falls to the mold temperature. Alternatively, the control unit is configured so that the mold opening signal is output from the external control device of FIG. 2 to the control device on the molding machine side at a temperature several degrees higher, and the mold opening is performed.

Next, an actual molding state will be described.
Polycarbonate is 330-350 ° C in plasticizer
The melting point of the polycarbonate is 2
Molten resin at 30 ° C. or higher is filled into the cavity through the sprue 1 and, after the filling is completed, it is pressurized and the grooves and pits provided on the surface of the stamper 9 are faithfully transferred to form the substrate 8. It After the mold was opened by a signal from the control unit that detects the substrate temperature and the mold temperature, the sprue ejector pin 10 and the substrate ejector pin 11 respectively took out the substrate 8 and the sprue 1 from the mold. The substrate manufactured in this manner is not deformed due to the thermal deformation caused by the close contact with the outer peripheral side stamper holder 12 when the temperature of the substrate 8 is close to the mold temperature (120 °).
Since it is C or less), the deformation was suppressed, and even if the deformation occurred, it could be sufficiently removed by the annealing treatment in the subsequent process.

Table 1 shows the results of the molding test by the conventional method and the method of the present invention. It is considered that the conventional method causes thermal deformation as compared with the method of the present invention.

[Table 1]

[0022]

As described above, according to the present invention, since the substrate is always taken out near the mold temperature, the thermal deformation at the time of taking out 1 can be suppressed, and thus the substrate having excellent mechanical characteristics can be easily manufactured. 2 Even if deformation occurs during extraction, it can be improved by annealing treatment in a later process. 3 By directly monitoring the substrate temperature, the temperature at the time of taking out is always constant and the cooling time can be optimized.
And so on.

[Brief description of drawings]

FIG. 1 is a die configuration diagram when an optical disc forming die of the present invention is clamped.

FIG. 2 is a control process diagram of the present invention.

FIG. 3 is a mold configuration diagram when a conventional optical disk molding mold is clamped.

FIG. 4 is a relationship diagram between a mold temperature and a substrate surface temperature.

[Explanation of symbols]

1 sprue 2 Fixed side bush 3 Mirror surface of fixed side mold 4 Mirror surface of movable mold 5 temperature sensor 6 screws 7,7 'temperature sensor 8 substrates 9 stampers 10 Sprue ejector pin 11 Ejector pin for board 12 Outer side stamper holder 13 Presser on inner circumference side 21 sprue 23 Mirror surface of fixed side mold 24 Mirror surface of movable mold 28 substrate 29 Stamper Ejector pin for 30 sprue 31 Ejector pin for board 32 Peripheral side stamper holder 33 Presser for inner stamper

Claims (2)

[Claims] 1. When continuously manufacturing an optical disk substrate by an injection molding method, the mold temperature during molding and the substrate temperature in the cavity during molding are monitored, respectively, and the substrate temperature is equal to the mold temperature. Alternatively, a method for manufacturing an optical disk substrate is characterized in that a controller during molding is operated to open the mold when the value becomes equal to or less than a set value. 2. The manufacturing method according to claim 1, wherein the set value is a temperature at which a critical stress at which the substrate is not deformed by a pressure generated due to a difference in linear expansion coefficient between the substrate and the mold is exhibited.