JPS629926A - Molding method for optical disk base - Google Patents

Abstract

PURPOSE:To mold an optical disk base whose index of birefringence is small, by controlling compression force in a releasing direction after the compression force has been applied to resin in a cavity. CONSTITUTION:When an injection compression molding device is turned ON, resin heated and melted within an injection cylinder is injected into a cavity 4 through a sprue and gate 3 and the cavity 4 is filled with the same. Hydraulic pressure is applied to the inside of a compression hydraulic cylinder 17a through an action of a servovalve 28 and the force is applied to the resin in the cavity 4 through a compression ram 18 and compression core 16. Resin pressure applied to the resin is detected by a pressure sensor 10 and controlled according to the applied resin pressure. After the lapse of a preset period of time, a mold is demolded by moving a movable mold 8A backward by a toggle type mold clamping mechanism 12 and a desired optical disc base is released through the inside of the cavity 4.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a method for molding an optical disc substrate, and particularly to a method for molding an optical disc substrate.

The present invention relates to an optical disc substrate molding method suitable for molding an optical disc substrate with a small birefringence index.

[Background of the invention]

Optical disc substrates are usually molded by injection molding. However, an injection compression molding method is known as a molding method that is said to be suitable for molding an optical disk substrate with lower strain and lower birefringence than injection molding (Japanese Patent Laid-Open No. 57-123031). Public bulletin).

This molding method is characterized in that the joint surface of the mold is opened in advance by a certain compression stroke amount, and in the compression process immediately after injection and filling of the resin into the cavity, the compression stroke is instantaneously compressed and molded. It is something to do.

This method will be explained below using the drawings.

FIG. 5 is a schematic diagram of an injection compression molding mold used in the conventional injection compression molding method, and FIG. 6 is a schematic diagram of an optical disk substrate made of polycarbonate resin molded by the injection compression molding mold according to FIG. FIG. 3 is a birefringence phase difference diagram showing an example of refractive index.

The injection compression mold 1 has a fixed mold 6 attached to a fixed mold mounting plate 13 and a movable mold 8 mounted to a movable mold mounting plate 14, and is formed by the fixed mold 6 and the movable mold 8. A stamper 5 on which information pits or information recording grooves are transferred is mounted on the movable mold 8 side of the cavity 4 with the transfer formation surface facing the fixed mold 6 side.

In the injection compression mold l configured in this way, the toggle type mold clamping mechanism 12 holds the mold joint surface open by a constant compression stroke δ0.

In this state, when the injection compression molding device is turned on, the resin heated and melted in the injection cylinder (not shown) is transferred to the fixed mold 6.
It is injected and filled into the cavity 4 through the gate 3 via the sprue 2 located at . At the same time as this injection filling is completed, the gate cutting cylinder 7 moves forward to cut the gate part, make a hole in the center, and prevent the resin from flowing back. Then, the toggle type mold clamping mechanism 12 is activated, and the movable mold 8 moves forward by a certain compression stroke δ0 and closes the mold, compressing the resin in the cavity. After a predetermined period of time has elapsed, the movable mold 8 is moved back and opened by the toggle type mold clamping mechanism 12, and a desired optical disk substrate 9 is released from the cavity 4. Thereafter, the above operation is repeated.

The birefringence of the optical disc substrate 9 molded in this manner was smaller when molded with PMMA resin than that with injection molding, but was almost unchanged when molded with polycarbonate resin.

For example, an optical disk substrate 9 having an outer diameter of 200 mm and a thickness of 1.25 mm is molded from polycarbonate resin using the injection compression mold 1 shown in FIG. When measured, the result was as shown by the broken line connecting the circles in FIG. Compared to injection molding (dotted chain line connecting the x marks in Figure 6), the 1 distribution has moved to the negative side, but the absolute value of the birefringence phase difference remains almost unchanged. .

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc substrate molding method that can improve the problems of the prior art described above and can mold an optical disc substrate with a small birefringence index.

[Summary of the invention]

The structure of the optical disc substrate molding method according to the present invention is as follows.

A stamper on which information pits or information recording grooves have been transferred is installed into the cavity of an injection compression mold.
An optical disk is formed by injecting and filling a resin into the cavity, applying compressive force to the resin, and transferring the information pits or information recording grooves of the stamper to the resin to form an optical disk substrate. In the substrate molding method, after compressive force is applied to the resin in the cavity.

The compressive force is controlled in the direction of release immediately or after a short period of time.

More details are as follows.

One of the main factors governing the birefringence of a molded article is the compression force during the compression process. Theoretically, the smaller the compressive force, the smaller the birefringence of the molded product. So 1
In the present invention, in the compression process of 1-injection compression molding, a compression force that is not necessary for transferring information pits or information recording grooves that are essential for an optical disk substrate is applied to the resin in the cavity, and then the compression force is immediately reduced. This is how it was done.

[Embodiments of the invention]

The present invention will be explained below by way of examples.

FIG. 1 is a schematic diagram (at the start of injection) showing the main parts of an injection compression molding apparatus used to carry out the optical disk substrate molding method according to an embodiment of the present invention, and FIG. It is a schematic diagram of an injection compression mold (at the time of completion of compression).

In FIGS. 1 and 2, the same parts as in FIG. 5 are denoted by the same numbers.

First, the injection compression molding mold IA will be explained. Reference numeral 16 denotes a compression core that is slidably fitted into the movable mold 8A and has a through hole 16a in the center thereof, and the cavity 4 is formed by the compression core 16 and the fixed mold 6A. And on the front side of this compression core 16.

The stamper 5 can be mounted using the center fixing jig 11 and the outer peripheral fixing jig 21.

Reference numeral 19 denotes a punch 20 that is slidably fitted into the through hole 16a and that slides on the inner circumference of the center fixing jig 11 at the tip.
This is the gate cutting rod with the attached. The fixed mold 6A can be moved back by pressing the compression core 16. A compression core return hydraulic cylinder 15 equipped with a return ram 15a, and a pressure sensor 10 capable of detecting the resin pressure of the resin filled in the cavity 4.
is built-in.

17 is a hydraulic cylinder consisting of a compression hydraulic cylinder 17a and a gate cutting hydraulic cylinder 17b, and the movable mold 8A of the injection compression molding mold IA is fastened to this hydraulic cylinder 17, and the movable mold 8A is still connected to the hydraulic cylinder 17. A toggle type mold clamping mechanism 12 is installed which can move the mold forward and backward to perform mold closing and mold opening operations. 18 is slidably fitted into the compression hydraulic cylinder 17a.

This is a compression ram with a through hole 18a bored in the center, and this compression ram 18 contacts and presses the compression core 16, and applies compression force to the resin in the cavity 4 via the compression core 16. This is what is used to load. 22 denotes the gate cutting hydraulic cylinder 17b and the through hole 18a.
A rod ram 22 is slidably fitted inside the rod ram 22, and the rod ram 22 is in contact with the rear end of the gate cutting rod 19, and a punch provided at the tip of the gate cutting rod 19. 20 is moved forward to cut the gate portion of the resin filled in the cavity 4, thereby preventing the resin from flowing back into the cavity.

Next, a compression force control circuit for controlling the compression force applied to the resin filled into the cavity 4 of the injection compression mold IA will be explained.

23 inputs the gate cutting completion signal from the screw position sensor of the injection cylinder (not shown), and sends this to the CPU.
The molding machine r/o interface 24 outputs the resin pressure signal detected by the pressure sensor 10 to the A/D converter 25.31 (details will be described later). This is an amplifier that outputs to the CPU 31 via the i10 interface 30. The CPU 31 sets the resin pressure profile in advance, and connects it to the molding machine I/O interface 2.
When the gate cutting completion signal is input from 3, the compression cylinder oil pressure is calculated from the set resin pressure corresponding to the elapsed time j = jo from the gate cutting completion, and r
/o interface 3o to 4H]'a Pressure signal When pressure is applied, deviation Δp from the set resin pressure corresponding to elapsed time t=jo and elapsed time 1+=j6+Δt
The compression cylinder hydraulic pressure to be applied the second time can be calculated from the set resin pressure corresponding to the set resin pressure. 27 is.

CPU31 to i10 ear 3l-7x chair 3Q, D/A
This is a servo amplifier that inputs the compression cylinder oil pressure signal via the converter 26 and operates the servo pulp 28. Due to this operation of the servo pulp 28, the hydraulic pressure is loaded into the compression hydraulic cylinder 17a, and the compression ram 18
．． A set resin pressure is applied to the resin in the cavity 4 via the compression core 16. 29, hydraulic pump for increasing the oil pressure of the compression force control circuit, 32°33
34. is a keyboard used to set the resin pressure profile in the CPU 31, a floppy disk, and 34.
35 is a CRT and a printer used to output the resin pressure detected in the compression process.

An optical disc substrate molding method according to an embodiment of the present invention will be described using the injection compression molding apparatus configured as described above.

The injection compression mold IA is opened by the toggle type mold clamping mechanism 12, and the stamper 5 is mounted on the front surface of the compression core 16 by the center fixing jig 11 and the outer peripheral fixing jig 21, and then the mold is closed. Hydraulic cylinder 15 for compression core return
is operated, and the return ram 15a compresses the compression core 1.
6 from the contact surface with the fixed mold 6A δ2 (however, δ2>
δ0, where δ0 is the compression stroke). At this time, the rear end surface of the compression core 16 and the compression ram 18 are in contact with each other.

With the keyboard 32 or floppy disk 33,
After applying a compressive force to the resin in the cavity 4, the CPU 31 sets a resin pressure profile (details will be described later on the body side) for immediately releasing this compressive force.

When the injection compression molding apparatus is turned on, the resin heated and melted in the injection cylinder is injected and filled into the cavity 4 through the sprue 2° gate 3.

At the same time as this injection filling is completed, the rod ram 22 is driven, and the gate cutting rod 19. The punch 20 moves forward and the gate portion is cut. This prevents the molten resin from flowing back in the first compression step. When the gate portion is cut, a gate cutting completion signal from the screw position sensor of the injection cylinder is inputted to the CPU 31 via the molding machine I/O interface 23. [CPU 3] calculates the compression cylinder hydraulic pressure from the set resin pressure corresponding to the elapsed time 1=1o from the completion of gate cutting, and this hydraulic pressure signal is sent to the r/o interface 30. The signal is input to a servo amplifier 27 via a D/A converter 26, and a servo valve 28 is operated. Due to the operation of this servo valve 28, the hydraulic pressure is applied to the compression hydraulic cylinder 17a, and the force is transferred to the compression ram 18. A load is applied to the resin in the cavity 4 via the compression core 16. The resin pressure applied to the resin is detected by the pressure sensor 10, and this resin pressure signal is sent to the amplifier 24. CPU 3 via A and /D converter 25
1. The CPU 31 calculates the load for the first time based on the deviation Δp from the set resin pressure corresponding to the elapsed time 1-1o from the start of compression, that is, the completion of gate cutting, and the set resin pressure corresponding to the elapsed time 1=io+Δt. Calculate the compression cylinder oil pressure. This hydraulic pressure signal is the same as last time.

I/O interface 30. The elapsed time t=t is inputted to the servo valve 28 via the D/A converter 26°-IJ--ho amplifier 27 and passes through the 1 compression core 18.

The resin pressure at +Δt is controlled. This control is repeated, and the resin pressure is controlled in accordance with the set resin pressure.

During this time, the compression core 16 has a compression stroke δ0−δ2−
The compressible stroke δl is maintained when the compression is completed (the state shown in FIG. 2). After a predetermined period of time has elapsed, the movable mold 8A is moved back and opened by the toggle type mold clamping mechanism 12, and the desired optical disc substrate 9A is released from the cavity 4. Thereafter, the above operation is repeated. Furthermore, the resin pressure detected by the pressure sensor 10 during the compression process is outputted from the CPU 31 by the CRT 34 or the printer 35.

A specific example will be explained.

According to the optical disk substrate molding method shown in FIG. 1, polycarbonate resin is used, and the outer diameter is 200 mm.

A specific example of molding an optical disc substrate with a thickness of 1.25 mm will be described.

FIG. 3 is a resin pressure profile diagram showing an example of the set resin pressure in the optical disc substrate molding method according to FIG. 1;
FIG. 4 is a birefringence phase difference diagram of an optical disk substrate made of polycarbonate resin molded by the resin pressure profile shown in FIG. 3. FIG.

The resin pressure profile 36A (see FIG. 3) is determined by determining in advance the resin pressure profile 36 loaded on the resin in the cavity 4 of the conventional injection compression mold 1 shown in FIG. The maximum value of the resin pressure profile 36 is set as the maximum value of the resin pressure, and after that, the resin pressure is immediately controlled in a direction smaller than the resin pressure profile 36, that is, in the direction of releasing the resin pressure. It was designed so that

This resin pressure profile 36A is set in the CPU 31, resin temperature is 320C, mold temperature is 90C, compression stroke δo = 0.1. It was molded under the conditions of mm.

The resin pressure actually applied to the resin in the cavity 4 is:
The difference was as shown by the dashed line 368', and the error with respect to the set value was within ±5 coefficients. The birefringence retardation of the molded optical disk substrate 9A is as shown in the solid line connecting the marks in FIG. , the same as the broken line in FIG. 6), and an optical disk substrate 9A having an extremely small birefringence was obtained.

According to the embodiment described above, by controlling the resin pressure applied to the resin in the cavity 4 in the direction of release immediately after the loading, an optical disk substrate 9A having a small birefringence index can be molded. .

In this example, the compressive force was applied in the direction of releasing the bacteria immediately after the compressive force was applied, but the compressive force was maintained for a certain amount of minute time (for example, held for 0.2 seconds). Even if the optical disc substrate is controlled in the release direction by using the optical disc, it is possible to obtain an optical disc substrate with a small birefringence.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide an optical disc substrate molding method that can mold an optical disc substrate with a small birefringence index.

[Brief explanation of drawings]

FIG. 1 is a schematic view (at the start of injection) showing the main parts of an injection compression molding apparatus used to carry out an optical disk substrate molding method according to an embodiment of the present invention, and FIG. Schematic diagram of the injection compression mold in Figure 1 (when compression is completed)
, FIG. 3 is a resin pressure profile diagram showing an example of the resin pressure setting in the optical disc substrate molding method according to FIG. 1, and FIG. 4 is a polycarbonate resin optical disc molded by the resin pressure profile according to FIG. 3. Birefringence phase difference diagram of the substrate 1 FIG. 5 is a schematic diagram of an injection compression molding mold used in the conventional injection compression molding method, and FIG.
FIG. 6 is a birefringence phase difference diagram showing an example of the birefringence of an optical disk substrate made of polycarbonate resin molded by the injection compression mold according to FIG. 5; IA...Injection compression mold, 4...Cavity, 5.
...stander, 8A...movable type, 9A...optical disk board. 16... Compression core, 18... Compression ram, 31...
CPU.

Claims (1)

[Claims] 1. Mount the stamper on which the information pits or information recording grooves have been transferred into the cavity of the injection compression mold, inject and fill the cavity with resin, and apply compression force to the resin to form the stamper. In an optical disc substrate molding method in which an optical disc substrate is molded by transferring information pits or information recording grooves to the resin, compressive force is applied to the resin in the cavity, and then the resin is compressed immediately or after a short period of time. An optical disk substrate molding method characterized by controlling compressive force in a releasing direction.