JPH08300388A - Molding of substrate for recording medium - Google Patents

Abstract

PURPOSE: To prevent not only transfer inferiority such as pit deformation generated when a substrate for a recording medium is released from a stamper but also the warpage deformation of the substrate by releasing the substrate while keeping the temp. of a molded resin material lower than that of a mold. CONSTITUTION: Polycarbonate is injected into clamped molds 2a, 2b by using a stamper 4 to mold a substrate for a recording medium. Subsequently, the molds 2a, 2b are opened and release gas with temp. of 0--30 deg.C is sprayed on the substrate for the recording medium made of polycarbonate being the molded resin material in a flow rate of about 10l/min from the gas blowoff passage 5 of the movable mold 2a. By this constitution, the molded substrate is released from the stamper 4 while polycarbonate is held to 10-130 deg.C. The deformation of a pit is not generated in the released substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a substrate for a recording medium such as an optical disk by injection molding, and more particularly to a method for molding a substrate for a recording medium characterized by a releasing process.

[0002]

2. Description of the Related Art Most of transparent substrates for disk-shaped recording media such as optical disks are manufactured by heating and melting PC (polycarbonate) or PMMA in an injection molding apparatus equipped with a stamper.
It is molded by injecting a resin material such as (polymethylmethacrylate). This injection molding method is widely used for molding a recording medium because of its short molding time, excellent transferability, and long stamper life.

FIG. 2 shows a mold part in a conventional molding apparatus used for molding an optical disk substrate. Mold 2
Is configured by coaxially combining the fixed mold 2a and the movable mold 2b. An eject pin 22 is inserted into the movable mold 2b at a central axis position thereof, and a punch 23, an ejector 24, a fixed sleeve 25, and an inner peripheral stamper retainer 21 are concentrically inserted toward the outer side in the radial direction. Has been done. A gas outlet passage is formed between the fixed sleeve 25 and the inner stamper retainer 21 (see FIG. 3).
As a result, the gas is blown toward the molded product at the time of mold release, which facilitates the mold release. During the molding operation, the stamper 4 has an inner surface of the movable mold 2b, that is, the fixed mold 2b.
It is placed on the surface facing the and is fixed by the inner peripheral stamper holder 21 and the outer peripheral stamper holder 20 of the movable mold 2b. The fixed mold 2a has a spool 16 formed along the central axis thereof toward the movable mold 2b.

At the time of injection molding, the movable mold 2b having the stamper 4 mounted thereon is clamped to the fixed mold 2a, and then the synthetic resin which is heated and melted flows from the spool 16 of the fixed mold 2a into the cavity 19. The recording information of the stamper 4 is ejected and transferred to the resin surface, that is, one surface of the optical disk substrate to be formed. After this, the mold is opened and the mold is released.

In FIG. 3, after the injection molding is completed, the movable mold 2b is released from the fixed mold 2a (mold open), and the movable mold 2 is opened.
The step of releasing the molded optical disk from the stamper 4 fixed to b is shown. As shown in FIG. 3, when the optical disc substrate 3 which is a molded product is released from the stamper, a predetermined flow rate of gas is ejected from the gas outlet passage 5 in the direction of arrow d, and at the same time, the ejector 24 fixes the optical disc substrate 3 to a fixed metal. It is performed by protruding in the direction of the mold 2a. Here, as the gas used, air or nitrogen gas heated to the mold temperature, or gas heated to the mold temperature or higher as described in JP-A-2-150327 is used.

[0006]

According to the above-mentioned conventional mold releasing method, when the optical disk substrate 3 is peeled from the stamper 4,
Transfer defects were liable to occur in areas where peeling was difficult, especially in the vicinity of pits. FIG. 4 shows the cross-sectional shape of the pits 33 of the substrate obtained by normal transfer (FIG. 4 (a)) and the cross-sectional shape of the pits 33 when the deformation A occurs in the pit peripheral portion due to the transfer failure from the stamper. (Fig. 4 (b)). When an optical disk is manufactured by laminating a recording film on an optical disk substrate in which such a transfer failure has occurred, the unevenness caused by the transfer failure changes the amount of reflected light, which deteriorates the recording / reproducing characteristics. Therefore, there is a demand for a method of effectively preventing transfer defects when an optical disk substrate is molded by injection molding.

By the way, as a next-generation large-capacity optical disc, a magneto-optical disc having a thickness of 0.8 mm, which is thinner than the conventional 1.2 mm-thick single plate, has been proposed. When such a thin single plate disc is ejected from the inner peripheral side of the substrate by an ejector and released from the stamper as seen in the mold release step, the warp deformation of the optical disc substrate is 1.2 mm compared with the conventional one.
There is a problem that it becomes considerably larger than a thick single-plate magneto-optical disk substrate.

Therefore, an object of the present invention is to provide an injection molding method for a recording medium capable of preventing transfer defects such as pit deformation that occur when the recording medium is released from the stamper side.

Another object of the present invention is to provide an injection molding method for a recording medium which can effectively prevent the warp deformation of the substrate even when a thin substrate having a thickness of 0.8 mm is used. is there.

[0010]

According to the present invention, in order to achieve the above-mentioned object of the present invention, a substrate for a recording medium is molded by injecting a molten resin material into a mold equipped with a stamper. In the method, there is provided a method for molding a recording medium, characterized in that the molded resin material is released from the mold while maintaining the temperature lower than the mold temperature.

In the molding method of the present invention, the temperature lower than the mold temperature is preferably 10 to 130 ° C, more preferably 40 to 110 ° C. In order to maintain the temperature of the molded resin material lower than the mold temperature, it is preferable to bring a gas having a temperature lower than the mold temperature into contact with the molded resin material. It is preferable that the gas having a temperature lower than the mold temperature is blown onto the molded resin material in such a direction that the resin material is separated from the stamper. Further, it is preferable that a gas having a temperature lower than the mold temperature is brought into contact with the molded resin material during the mold opening and the period after the mold opening including the mold releasing step. The gas temperature is preferably −30 ° C. to 0 ° C. because the resin material can be easily cooled using an inexpensive device. In the molding method of the present invention, the mold temperature at the time of mold release is generally 100 to 13
The temperature is 0 ° C.

In the present specification, "at the time of mold opening" means a period from the start of mold opening to the end of mold opening, and "after mold opening" means from the end of mold opening to the end of a molding cycle through a releasing operation. Term of.

[0013]

The present inventor has found conditions suitable for mold release by changing the temperature of the pit and the pressure acting on the pit to various values and releasing the optical disk substrate. That is, it was found that pit deformation did not occur when the mold temperature was 90 ° C. or lower, that is, when the temperature of the pit portion at the time of mold release was 90 ° C. or lower. However, when molding a magneto-optical disk substrate, it is necessary to set the mold temperature as high as 120 to 130 ° C. for the purpose of increasing the fluidity of the resin during molding and decreasing the cross-sectional birefringence of the substrate. There is. Further, the sample servo type optical disk substrate is a CD-ROM,
Since the pit density is lower than that of a video disk or a continuous servo type optical disk substrate, multiple transfer is likely to occur when the mold temperature is low, that is, when the adhesion between the substrate and the stamper during molding is low. Therefore, at the time of molding, it is necessary to set the mold temperature to 120 ° C. or higher for the purpose of improving the adhesion between the substrate and the stamper and preventing multiple transfer. Therefore, in order to satisfy the two needs of improving the optical characteristics and preventing multiple transfer, the mold temperature at the time of molding must be set to 120 ° C. or higher. However, the temperature of the mold is maintained at the same temperature as the temperature at the time of molding also in the mold releasing step following the molding step, and such high temperature easily causes deformation of the pits. Therefore, in the present invention, in order to satisfy the molding condition and the releasing condition separately, the substrate temperature at the time of releasing is kept lower than the mold temperature, and the substrate temperature at the time of forming and the substrate temperature at the time of releasing are maintained. I decided to make my own adjustments.

Further, according to the present invention, the temperature of the substrate becomes lower than the thermal deformation temperature by blowing a low temperature gas onto the substrate at the time of releasing the mold, so that the warp deformation can be effectively prevented. Therefore, the present invention is also suitable for injection molding of a thinner optical disk substrate.

[0015]

EXAMPLE An example of the present invention will be described below with reference to FIG. FIG. 1 shows a schematic cross-sectional view of a mold portion of a molding apparatus used in the recording medium molding method of the present invention. The mold part of this apparatus comprises a fixed mold 2a and a movable mold 2b, which are substantially similar to those shown in FIGS. 2 and 3, and a fixed plate 1a and a movable plate 2a on two common support beams 100, respectively. It is held by 1b. The movable platen 1b has a beam 10 when the mold is clamped.
0 moves to the left side in FIG. 1 and moves to the fixed mold 2a Mold 2
When the mold b is clamped and the mold 100 is opened, the movable mold 2b is separated from the fixed mold 2a by moving to the right on the beam 100. Movable plate 1
b is driven by a mold clamping cylinder (not shown). FIG. 1 shows the movable mold 2 when the mold is opened, that is, the injection molding is completed.
It shows a state of being separated from the fixed mold 2a while holding the substrate 3 on which b is molded.

Inside the movable mold 2b, as shown in FIGS. 2 and 3, a gas blowing passage 5 for releasing the molded product is provided. The gas outlet, which is the end of the gas outlet passage 5, is formed in a portion of the recording medium 3 in the radial direction away from the recording area. Gas outlet passage 5
After extending in the axial direction from the outlet, it turns downward in the radial direction in the movable mold 2a, communicates with the gas flow pipe 11 from below the movable mold 2b, and communicates with the refrigerator 12. A temperature sensor 6 is provided at a connecting portion between the gas flow pipe 11 and the movable mold 2a.
Is mounted, and the heater 7 is wound around the gas flow path pipe 11 below it. The heater 7 and the temperature sensor 6 are connected to the temperature controller 8, and the temperature controller 8 receives the signal of the temperature sensor 6 and adjusts the heater 7. Gas flow pipe 11
Is covered with a heat insulating material 10.

The refrigerator 12 has a cooling capacity capable of cooling the internal gas to -30 ° C. or lower, and the gas input from the gas source 14 passes through the coiled copper pipe 13 having high thermal conductivity and -30 ° C. or lower. Is cooled down. The cooled gas passes through the gas flow path pipe 11 covered with the heat insulating material 10, and the flow rate of the gas is adjusted by the flow meter 9 provided on the way. To control the temperature of the gas, the cooling gas is controlled by the heater 7 under the control of the temperature controller 8.
The temperature is adjusted to 0 to -30 ° C by heating at. In this example, nitrogen gas was used as the low temperature gas.

Injection molding was performed under the following conditions using the molding apparatus as described above. Mold temperature 120 ° C., resin temperature 350 ° C., holding pressure 50 MPa, holding time 0.5 sec, injection speed 60 mm / s and cooling time 10 sec. A stamper with an inner diameter of 35 mm and an outer diameter of 108 mm is used as the stamper.
Polycarbonate for a magneto-optical disk substrate was injected as a melted resin into a clamped mold.

Then, the mold is opened as shown in FIG.
The mold releasing gas having a temperature of 0 to −30 ° C. lower than room temperature was blown from the gas blowing passage 5 of the movable mold 2a toward the molded resin material at a flow rate of about 10 liters / minute. By this operation, the molded substrate 3 was released from the stamper 4 while maintaining the molding material at a temperature of 60 to 80 ° C. No deformation of pits was observed on the released substrate.

In the above embodiment, nitrogen gas was used as the releasing gas, the temperature was cooled to -30 ° C or lower, and the temperature of the gas was controlled to 0 to -30 ° C by the heater. However, the gas and gas temperature that bring about the effect of the present invention can be appropriately selected.

Further, in the above embodiment, the case where the temperature-controlled release gas is injected from the stamper side has been described. However, in addition to this, when the mold is opened and after the mold is opened or when the mold is released, it is not the stamper side but the substrate. A method of blowing a gas having a temperature lower than the mold temperature from the side to the entire substrate may be used.

[0022]

According to the molding method of the present invention, it is possible to prevent transfer defects such as pit deformation and substrate warp deformation that occur when the recording medium is released from the stamper side.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a mold part in a molding apparatus used in a recording medium molding method of the present invention.

FIG. 2 is a schematic sectional view of a conventional mold used for injection molding of an optical recording medium.

FIG. 3 is an enlarged cross-sectional view showing the state of the mold of FIG. 2 at the time of mold release.

FIG. 4 is an enlarged cross-sectional view of the pit portion of the substrate obtained after molding, (a) shows the cross-sectional shape of the pit of the substrate obtained from normal transfer, and (b) shows the transfer failure from the stamper. The cross-sectional shape of the pit when the deformation A occurs in the peripheral portion of the pit is shown.

[Explanation of symbols]

 1a Fixed plate 1b Movable plate 2a Fixed mold 2b Movable mold 3 Optical disk substrate 4 Stamper 5 Air blowout hole 6 Temperature sensor 7 Heater 8 Temperature controller 9 Flowmeter 10 Insulation material 11 Gas flow pipe 12 Refrigerator 13 Copper pipe 14 Gas Source 15 Nozzle 16 Spool 17 Spool Bush 18 Fixed Mirror Surface Plate 19 Cavity 20 Outer Perimeter Stamper Press 21 Inner Perimeter Stamper Press 22 Eject Pin 23 Punch 24 Ejector 25 Fixed Sleeve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Ohta 1-88, Tora-Tora, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd. (72) Masaki Yoshii, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa (72) Inventor Hiroki Kuramoto, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd.

Claims (7)

[Claims] 1. A method of molding a substrate for a recording medium by injecting a molten resin material into a mold equipped with a stamper, wherein the molded resin material is maintained at a temperature lower than the mold temperature. A method for molding a substrate for a recording medium, which comprises releasing the mold. 2. The molding method according to claim 1, wherein the molded resin material is released from the mold while being maintained at a temperature of 10 to 130 ° C. 3. The molded resin material is maintained at a temperature lower than the mold temperature by bringing a gas having a temperature lower than the mold temperature into contact with the molded resin material. 1. The method for forming a recording medium substrate according to 1 or 2. 4. A recording medium according to claim 3, wherein a gas having a temperature lower than the mold temperature is sprayed onto the molded resin material in a direction such that the resin material is separated from the stamper. Substrate molding method. 5. The recording according to claim 3, wherein a gas having a temperature lower than the mold temperature is brought into contact with the molded resin material during mold opening and after mold opening including a mold releasing step. A method of molding a substrate for a medium. 6. The method for molding a recording medium substrate according to claim 3, wherein the gas temperature is −30 ° C. to 0 ° C. 7. The method for molding a recording medium substrate according to claim 1, wherein the mold temperature is a mold temperature at the time of molding.