JPH06166074A - Manufacture of optical disk base - Google Patents

Abstract

PURPOSE:To control a skew of an optical disk base within a fixed value on a pulse side. CONSTITUTION:The manufacture of an optical disk base is constituted so that molten resin material 14 is injected within a cavity 29 constituted between a movable mold 21 and stationary mold 22 to which fixed mold clamping force is applied after completion of an injection process, the foregoing mold clamping force is released suddenly and release of the mold clamping pressure is performed within 5 seconds after completion of the injection process. Then a temperature difference is provided on the movable mold 21 and stationary mold 22 constituting the cavity 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical disk substrate for forming an optical recording medium formed of polycarbonate resin or the like, for example, an optical disk such as a magneto-optical disk or a write-once type magneto-optical disk.

[0002]

2. Description of the Related Art An optical recording system for optically recording an information signal is capable of recording and reproducing the information signal in a non-contact state with a recording medium, and is easy to handle, and is free from stains and scratches. It has features such as strength, and because it can record a large amount of information, it is used for compact discs with digitally recorded audio signals and video discs with recorded image signals, as well as code information and images. It is used as a large-capacity file for information.

As the optical recording medium of this optical recording system, in addition to the compact disc and the video disc described above, various systems such as a write-once optical disc capable of additionally recording an information signal and a magneto-optical disc capable of erasing recorded information are available. Optical discs are available. In this specification, these various discs are collectively referred to as an optical disc. These optical discs are generally PO (polycarbonate), PMM.
An optical information recording layer is formed on a transparent optical disk substrate formed of a synthetic resin such as A (polymethylmethacrylate).

Since this optical disc reads a minute rotation of the plane of polarization of the emitted laser light as a signal, the optical disc substrate is incident mainly for reading an information signal of the optical disc due to internal distortion. Little birefringence, which is the degree of phase shift between light and reflected light, good transferability, little contamination,
Then, various conditions such as a small disc return (skew) are required. For example, if the skew is large, the disc surface and the optical axis of the pickup for reading the recorded information will not intersect at right angles, making it unreadable.
For a 3.5-inch optical disc, it is regulated to be within 5 mrad.

By the way, the optical disk substrate is generally small in thickness with respect to the diameter, and is required to have a molding die having a large projected area and a clamping pressure for a single injection resin amount. Therefore, the injection resin amount and the cylinder capacity are not balanced,
The molten resin material stays in the cylinder for a long time under the molding conditions, and the heat history becomes excessive, so that various molding strains are likely to occur. Therefore, when injection-molding an optical disk substrate, the molecular weight of the resin material is reduced to lower the melting temperature, the cylinder temperature is increased, the mold temperature is increased and the temperature unevenness is reduced, or the injection speed is increased and the injection pressure is decreased. Etc. are taken.

Although injection molding of the optical disk substrate is performed by taking such various measures, for example, the skew is generated in the minus direction in the normal injection molding method. In the present specification, the polarity of the skew is defined as a negative direction when the molded optical disk substrate is heated at 100 ° C. and the concave side is the disk signal surface side where the information recording layer of the molded disk is formed, and vice versa. Define as positive direction.

On the optical disk substrate, a process such as vapor deposition of a metal film for reflection or formation of a transparent protective film on the disk signal surface to which pits or pregroups are transferred by a stamper incorporated in a molding die. Is applied. Through these steps, in the optical disc substrate, a tensile force in the direction of the center as a whole is generated on the disc signal surface, and the negative skew becomes larger and the standard may be exceeded.

Therefore, in the injection molding, it is considered to adopt the injection molding method in which a skew in the plus direction in which the disk signal surface side is convex is previously generated on the optical disk substrate. As an example of this method, there is a method of making a temperature difference between a movable mold and a fixed mold which cooperate to form a cavity of an optical disk substrate. In this method, the temperature of the movable mold forming the disk signal surface side is set to be higher than the temperature of the fixed mold forming the information signal reading side, so that the solidification time on the disk signal surface side of the optical disk substrate is determined. This is to delay the solidification time on the signal reading side to generate a skew in the positive direction.

[0009]

The state of skew and the change in basic shape of the optical disc substrate obtained by the injection molding method in which the temperatures of the movable mold and the fixed mold are different from each other are shown in FIGS. 9 and 10, respectively. Explained by. FIG. 9 shows an optical disk in which the vertical axis shows the skew inclination and the horizontal axis shows the temperature difference between the movable mold and the fixed mold, and the state where the temperature difference is gradually changed from the state where the temperature difference is not formed. 3 shows the skew of the substrate 1. In the figure, in the case of the minus region, the skew appears in the minus direction.

The optical disc substrate 1a molded without a temperature difference has a small difference in skew between the inner and outer peripheral portions, but has a large negative skew as a whole. From this state, in the optical disk substrate 1b formed by making the temperature difference between the two molds, the skew is slightly shifted to the plus side, but is still in the minus direction, and the difference between the inner peripheral portion and the outer peripheral portion is still different. Also grows. Then, by performing molding at a temperature difference of a certain temperature or more, as shown in the optical disc substrate 1c, it shifts to the plus side, but the amount of change is extremely small, and the difference between the inner peripheral portion and the outer peripheral portion is small. It will be extremely large.

FIG. 10 shows changes in the basic shape of the optical disk substrate 1 formed by gradually increasing the temperature difference between the movable mold and the fixed mold as described above. In addition,
In the figure, the upper surface side is the reading surface of the information signal.
Optical disc substrate 1a molded without temperature difference
Has a flat shape as a whole, but the reading surface side of the information signal is concave due to the skew in the negative direction. Then, in the optical disk substrate 1b formed by applying a temperature difference between the two molds, the reading surface side of the information signal is still concave, and the optical disc substrate 1b is curved due to the skew difference between the inner peripheral portion and the outer peripheral portion.

Further, when the movable mold and the fixed mold are molded at a temperature difference above a certain temperature, the skew shifts in the plus direction and the information signal reading surface has a slightly convex shape. Since the skew difference between the inner peripheral portion and the outer peripheral portion is extremely large, the overall curved shape is exhibited. In this way, by forming a temperature difference between the movable mold and the fixed mold to perform molding, a certain amount of skew positive direction can be secured, but molding distortion and the difference between the inner and outer circumferences become large, which is a very effective method. No

Therefore, an object of the present invention is to provide a method for molding an optical disk substrate, which can control the skew of the optical disk substrate to a predetermined value on the plus side, thereby forming a reflective film, a protective film and the like. It is possible to manufacture an optical disc that can sufficiently meet the skew standard even after the film process.

[0014]

In the method of manufacturing an optical disk according to the present invention, which achieves the above object, a molten resin material is applied between a movable mold and a fixed mold to which a predetermined mold clamping pressure is applied. In the manufacturing method of the optical disc, the decompression operation is performed by injecting into the cavity configured as described above, and after the injection process is completed, the decompression operation is performed to rapidly release the mold clamping pressure before the resin material is solidified. The feature is that it is performed within 5 seconds after the completion of the injection process.

Further, in the optical disc manufacturing method according to the present invention, the molten resin material is injected into the cavity formed between the movable mold and the fixed mold to which a predetermined mold clamping pressure is applied, and the injection is performed. After the process is completed, before the resin material is solidified, in the optical disc manufacturing method in which the decompression operation for rapidly releasing the mold clamping pressure is performed, in the movable mold and the fixed mold that form the cavity, The feature is that a difference is provided.

[0016]

According to the above-described optical disk manufacturing method of the present invention, the molten resin material is injected into the cavity formed between the movable mold and the fixed mold to mold the optical disk substrate. By performing a decompression operation for rapidly releasing the mold clamping pressure within an extremely short time of 5 seconds after the completion of the process, the skew of the optical disk substrate can be largely changed in the positive direction. Immediately after the molten resin material is injected into the cavity, a predetermined mold clamping pressure exerts a uniform force on the entire surface of the optical disc substrate, so that the transferability of the pits or pregroups of the stamper is sufficiently ensured, and the compounding force is maintained. Refractive properties are also maintained well.

Further, according to the optical disk manufacturing method of the present invention, when the molten resin material is injected into the cavity formed between the movable mold and the fixed mold to mold the optical disk substrate, By providing a temperature difference between the movable mold and the fixed mold, and by performing a decompression operation to release the mold clamping pressure rapidly within an extremely short time after the completion of the injection process, the skew of the optical disk substrate is increased in the positive direction. Can vary greatly, and also
Immediately after injecting the molten resin material into the cavity,
Since a predetermined mold clamping pressure exerts a uniform force on the entire surface of the optical disk substrate, the transferability of the pits of the stamper or the pregroup is sufficiently secured, and the birefringence characteristic is also maintained well.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a schematic configuration of an injection molding machine used for carrying out the present embodiment. When roughly classified, a resin injection section 10 for melting and sending a resin material to a mold, and an optical disc. Mold part 20 that constitutes a cavity according to the shape of the mold, and this mold part 20
It is composed of a mold clamping mechanism section 30 for applying pressure to and a control section 40 for controlling each mechanism section.

The resin injection section 10 is provided with a charging hopper 11 for charging resin pellets as a raw material, a heating heater for melting the raw material resin supplied from the charging hopper 11, and the inside thereof. A heating cylinder 1 provided with a screw for sequentially sending out molten resin
2 and a nozzle 1 for injecting the melted resin into the mold part 20.
3 and 3.

As shown in FIG. 2, the mold unit 20 has a movable mold 21 and a fixed mold 22 as main constituent elements. A stamper 23 is fixed to the cavity forming surface side of the movable mold 21 by an inner peripheral stamper retainer 24 and an outer peripheral stamper retainer 25, respectively. In addition, the fixed mold 22
Is fixed plate 26 so as to face the movable mold 21.
A sprue 27, which is connected to the nozzle 13 of the resin injection unit 10 and has an opening 27a at its tip, is arranged in the center.

A die retainer 28 fixed to a stationary platen 26 is provided on the outer peripheral portion of the fixed die 22, and the outer peripheral portion of the movable die 21 abuts on the tip surface 28a of the die retainer 28. The movable mold 21
A cavity 29 for molding the optical disk substrate 1 is formed between the facing surfaces of the fixed mold 22.

The mold clamping mechanism 30 drives the movable mold 21 in the left-right direction in FIG. 1. In this example, a so-called booster ram type mold clamping mechanism is adopted as the mold clamping mechanism 30. This booster ram type mold clamping mechanism is a mechanism that incorporates a booster ram with a diameter smaller than the diameter of the main ram coaxially with the center axis of the main ram in order to advance the main ram at high speed, and is used in relatively medium-sized injection molding machines. There is.

The mold clamping mechanism 30 includes a control unit 4
Controlled by 0. The control unit 40 includes a servo valve mechanism 41 for controlling the mold clamping operation and the mold clamping pressure of the mold clamping mechanism 30, a mold clamping pressure adjuster 42, and a mold clamping pressure detector 43. , Movable mold 2
The heater controller 4 controls the temperature of both the movable mold 45 and the fixed mold heater 46 by controlling the movable mold heater 45 and the fixed mold heater 46, respectively.
4 and a mold setting control unit 47 for controlling the operations of the mold clamping pressure control unit and the mold temperature control unit.

The mold clamping pressure adjuster 42 is connected to the mold clamping mechanism 30 via a mold clamping pressure detector 43,
The servo valve mechanism 41 is adjusted and controlled by the output of the mold clamping pressure detector 43 which detects the mold clamping pressure applied to the movable mold 21 by the operation of the mold clamping mechanism 30. Further, the heater adjuster 44 is connected to the mold section 20 via a movable mold heater 45 and a fixed mold heater 46, and operates both heaters 45 and 46 to move the movable mold 21 and The fixed mold 22 is maintained at the set temperature.

The program setting device 47 includes a movable mold 21.
The application timing of the mold clamping pressure or the mold temperatures of the movable mold 21 and the fixed mold 22 are programmed respectively. Therefore, by applying the output of the program setting device 47 to the mold clamping pressure adjuster 42 and controlling the output, the servo valve mechanism 41 is operated and the mold clamping mechanism 30 is operated.
Of the molten resin material into the cavity 29 between the movable mold 21 and the fixed mold 22 or the movable mold 21 after the injection process is completed
The mold clamping pressure of is changed.

Further, by applying the output of the program setting device 47 to the heater adjuster 44 and controlling it, the energizing time and the like to the movable mold heater 45 and the fixed mold heater 46 are controlled, respectively. Mold 21 and fixed mold 22
Are maintained at predetermined temperatures. The change of the mold clamping pressure or the mold temperature is preferably digitally controllable, and the one having quick response is preferable.

In order to mold the optical disk 1 made of a polycarbonate resin by using the injection molding machine having the above-described structure, as shown in FIG. 2, the outer peripheral portion 21a of the movable mold 21 is fixed to the fixed mold 22. The molten resin material 14 melted in the resin injection part 10 is injected from the sprue 27 into the cavity 29 through the nozzle 13 in the mold clamped state in which it is in contact with the tip surface 28a of the mold retainer 28 provided on the outer periphery of the mold. To do. In this case, the filling pressure of the molten resin material 14 is set to be slightly higher than the mold clamping pressure applied to both the molds 21 and 22.

When the molten resin material 14 is injected, if the temperature of the molten resin material is too high, the resin itself is decomposed to increase contamination. Therefore, the temperature of the molten resin material is increased by heating the resin injection part 10. It is preferable to make the temperature as low as possible if uniform kneading is possible in the cylinder 12. In addition, the mold temperature maintains the skew characteristics described later, accelerates the molding cycle, and improves the productivity.
It is preferable that the temperature is not higher than the heat distortion temperature of the optical disk, and the glass transition temperature Tg of the polycarbonate resin of the material is
Since it is about 24 ° C, 1
It is set in the range of 10 to 120 ° C.

When the molten resin material 14 is injected into the cavity 29, as shown in FIG. 3, the movable mold 21 is moved by ΔL in the mold opening direction indicated by the arrow B by the filling pressure of the molten resin material 14. When the movable mold 21 and the fixed mold 22 are moved backward, the gap between the movable mold 21 and the fixed mold 22 is opened by pushing from T1 in FIG. 2 to T2 in FIG. Therefore, the cavity 29
The internal pressure escapes from this gap, and the molten resin material 14 is filled evenly in the inside of the cavity 29 to enable highly accurate molding of the optical disc 1, and unnecessary stress is not given to the molten resin material 14. Therefore, it is also effective for improving birefringence.

When the filling of the molten resin material 14 is completed, the mold clamping pressure of the movable mold 21 is maintained at this stage, and a uniform predetermined pressure is applied to the entire surface of the molten resin material 14 to shrink due to cooling. As a result, the movable mold 21 is tightened toward the fixed mold 22 as shown by the arrow A in FIG. Therefore, the molten resin material 14 in the cavity 29 is press-molded to a desired plate thickness T1, and the signal (pit) and guide groove (pregroup) of the stamper 23 are transferred. In this state, the molten resin material 14
Is not completely solidified, the outer peripheral portion is solidified as a skin layer, and the inside is still in a molten state as a core layer.

In this state, the servo valve mechanism 31 is operated through the mold clamping pressure adjuster 32 to rapidly discharge the oil in the cylinder chambers of the main ram and booster ram, thereby adding the mold to the movable mold 21. A so-called decompression operation is performed in which the tightening pressure is rapidly released to zero or extremely low pressure. This decompression operation is performed within an extremely short time after the injection of the molten resin material, and the decompression operation and the movable mold 21 and the fixed mold 22 are performed.
The skew of the optical disk substrate 1 is largely shifted to the plus side by controlling the mold temperature difference between the and.

By controlling the heater 45 for the movable mold and the heater 46 for the fixed mold by the heater controller 44, an injection molding method in which a temperature difference is made between the movable mold 21 and the fixed mold 22 and a decompression operation is also used. 4A and 4B show changes in the skew state of the optical disc substrate 1 and changes in the basic shape of the optical disc 1 when the timing of the decompression operation is gradually advanced.
The timing adjustment of the decompression operation and the temperature adjustment of the movable mold 21 and the fixed mold 22 can be extremely easily performed by the control unit 40.

That is, in FIG. 4, the vertical axis shows the skew inclination, and the horizontal axis shows the timing time of the decompression operation on the horizontal axis, and there is no temperature difference between the movable mold 21 and the fixed mold 22 and melting is performed. Since the resin material was molded by releasing the mold clamping pressure for a sufficient time after injection, a temperature difference was provided between the movable mold 21 and the fixed mold 22 and the decompression operation was gradually advanced in the molding. The figure shows the state of skew that occurs in the optical disk substrate 1 in this case. In the figure, in the case of the minus region, the skew appears in the minus direction.

As described above, in the optical disk substrate 1a formed without making the temperature difference between the movable mold 21 and the fixed mold 22 and without performing the decompression operation, the skew in the inner and outer peripheral parts is Although the difference is small, a large negative skew appears as a whole. From this state, the optical disc substrate 1b molded by providing a temperature difference between the two molds and performing a decompression operation,
The skew shifts to the positive side rapidly.

Then, the skew is further shifted in the positive direction as shown in the optical disk substrate 1c by molding the decompression operation with a shorter time while the temperature difference is provided between the two dies. Further, as shown in FIG. 4, in this case, the skew inclination amount between the inner peripheral portion and the outer peripheral portion of the optical disc substrate 1c hardly changes.

FIG. 5 shows a change in the basic shape of the optical disk substrate 1 obtained by performing the decompression operation with the temperature difference provided between the movable mold and the fixed mold as described above. In the figure, the upper surface side is the reading surface of the information signal of the optical disk. An optical disk substrate 1a formed by molding a movable mold and a fixed mold without making a temperature difference and without performing a decompression operation has a flat shape as a whole, but an information signal due to a skew in the negative direction. The reading surface side of is concave.

Then, an optical disk substrate 1 is formed by providing a temperature difference between both molds and performing a decompression operation.
In the case of b, as shown in FIG. 5, the skew rapidly changes from the minus direction to the plus direction,
As a whole, the information signal reading surface has a convex shape. Furthermore, since the skew is further shifted in the positive direction by forming the decompression operation with a shorter time in the state where the temperature difference is provided between the two dies, as shown in the optical disc substrate 1c,
The reading surface side of the information signal has a convex shape, and the change in curvature is small.

In the optical disc substrate 1, by gradually advancing the timing of the decompression operation, the birefringence on the inner circumference side becomes higher and the birefringence on the outer circumference side becomes lower, but this birefringence can be adjusted by, for example, melting. The birefringence on the inner peripheral side can be lowered by lowering the temperature of the resin material, and the secondary mold clamping pressure can be extended or the birefringence on the outer peripheral side can be increased by using a slope together.

6 to 8 show the movable mold temperature of 120.degree.
In the condition of fixed mold temperature 110 ℃, temperature difference 10 ℃,
The decompression operation was performed 5 seconds (FIG. 6), 4 seconds (FIG. 7) and 7 seconds (FIG. 8) after injecting the molten resin material 14 and an annealing treatment was performed.
It is a figure in which the skew of the 5-inch optical disc substrate 1 is actually measured in the radial direction. In addition, when 7 seconds or more have passed after injecting the molten resin material 14, the solidification of the molten resin material 14 almost proceeds, and the effect of the decompression operation cannot be expected.

Decompression operation is performed on the molten resin material 1
When 7 seconds have passed after 4 is ejected, a skew in the negative direction appears as a whole on the optical disc substrate 1 as shown in FIG. 8, and the effect of the decompression operation cannot be expected so much. Further, when the decompression operation is performed after 5 seconds, a skew in the negative direction appears on the innermost peripheral portion of the optical disc substrate 1 as shown in FIG. 6, but a value largely shifted in the positive direction as a whole. Becomes Further, as shown in FIG. 7, when the decompression operation is performed after 4 seconds, it is possible to obtain the optical disk substrate 1 having a value in which the skew is largely shifted in the plus direction.

In the above-described embodiment, the molding method for the 3.5-inch optical disk substrate is such that a temperature difference is provided between the movable mold and the fixed mold and the decompression operation is performed in an extremely short time. However, the present invention is not limited to this embodiment. For example, a very short time within 5 seconds after injection of the molten resin material without providing a temperature difference between the movable mold and the fixed mold. Needless to say, by performing the decompression operation in advance, the skew can be positively directed.

Further, it is needless to say that the skew can be directed in the positive direction by forming a temperature difference between the movable mold and the fixed mold on the assumption that the decompression operation is performed. Further, the type of injection molding machine used, the shape of the molding die, etc. may be arbitrary, and it goes without saying that the dimensions of the optical disc, the mold clamping pressure, etc. are appropriately set.

[0043]

As described in detail above, according to the present invention, the molten resin material is placed in the cavity formed between the movable mold and the fixed mold to which a predetermined mold clamping pressure is applied. After the injection process is completed, the decompressing operation of rapidly releasing the mold clamping pressure before the resin material is solidified is performed within 5 seconds after the completion of the injection process, or the movable mold and the fixed mold for performing the decompressing operation. By providing a temperature difference between the mold and the mold, it is possible to control the initial value skew of the molded optical disk substrate to a predetermined value on the plus side, and even through a film forming process for forming a reflective film or a protective film. It is possible to obtain an optical disc that conforms to the specifications. Therefore, by using the above method together, skew adjustment can be performed with higher precision, the molding conditions can be expanded, and the present invention can be applied to a mold having any configuration.

[Brief description of drawings]

FIG. 1 is a side view illustrating a schematic configuration of an injection molding machine used in implementing the present invention.

FIG. 2 is a diagram illustrating an injection molding process, and is a schematic cross-sectional view of a mold clamping state in which a molten resin material is filled.

FIG. 3 is a schematic cross-sectional view of a state in which the molten resin material is filled.

FIG. 4 is a characteristic diagram illustrating a taming time of a decompression operation and a state of skew generated on an optical disc substrate obtained.

FIG. 5 is a characteristic diagram illustrating a state of a basic shape of the optical disc substrate.

FIG. 6 is a diagram in which the skew of a 3.5-inch optical disk substrate obtained by performing a decompression operation and performing an annealing treatment 5 seconds after the injection of the molten resin material is actually measured in the radial direction.

FIG. 7 is an actual measurement diagram of the skew in the radial direction when a decompression operation is performed after 4 seconds.

FIG. 8 is a radial actual measurement diagram of a skew when a decompression operation is performed 7 seconds later.

FIG. 9 is a characteristic diagram for explaining a state of skew occurring in an optical disc substrate injection-molded with a temperature difference between a movable mold and a fixed mold.

FIG. 10 is a characteristic diagram illustrating a basic shape of the optical disc substrate.

[Explanation of symbols]

 1 ... Optical disc substrate 10 ... Resin injection part 20 ... Mold part 21 ... Movable mold 22 ... Fixed mold 29 ... Cavity 30 ... Clamping mechanism 40 ...・ Control unit 41 ・ ・ ・ Servo valve mechanism 42 ・ ・ ・ Clamping pressure regulator 44 ・ ・ ・ Heater regulator 47 ・ ・ ・ Program setter

Claims (2)

[Claims] 1. A molten resin material is injected into a cavity formed between a movable mold and a fixed mold to which a predetermined mold clamping pressure is applied, and after the injection step is completed and before the resin material is solidified. In the method of manufacturing an optical disk substrate in which the mold clamping pressure is rapidly released, the method of manufacturing an optical disk substrate is characterized in that the mold clamping pressure is released within 5 seconds after completion of the injection step. 2. A molten resin material is injected into a cavity formed between a movable mold and a fixed mold to which a predetermined mold clamping pressure is applied, and after the injection process is completed and before the resin material is solidified. In the method for manufacturing an optical disk substrate in which the mold clamping pressure is suddenly released, a temperature difference is provided between a movable mold and a fixed mold that form a cavity.