JP2001334562A - Method for molding optical disk board, optical disk board, and optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding an optical disk board for molding the optical disk board of a large capacity and thin type with good mechanical and optical characteristics, the optical disk board, and an optical disk. SOLUTION: The method for molding an optical disk board comprises a metering and melting step of metering and melting a resin in an injection cylinder, a filling step of casting a molten resin from a nozzle 10 of the cylinder in a cavity of a mold 1 for molding the board via a sprue 3, a cooling step of solidifying the cast resin, a taking-out and mold clamping step of taking out the molded board by opening the mold 1 and again clamping the mold 1, thereby molding the board by sequentially conducting the respective steps in such a manner that the cooling step is finished in the case of transferring to next molding cycle immediately after a metering operation of the resin for the next molding cycle is completed. A cooling medium is introduced into a cooling circuit 4 and a special cooling circuit 5 during this cooling step, and the resin filled in the sprue 3 part is cooled. Accordingly, the board having the good characteristics can be molded while preventing occurrence of a 'stringing' molding trouble.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk substrate molding method, an optical disk substrate, and an optical disk. More specifically, the present invention relates to an optical disk substrate having a larger capacity such as a DVD system and an optical disk substrate having a thinner thickness, In particular,
The present invention relates to an optical disk substrate molding method, an optical disk substrate, and an optical disk, which are required to have excellent mechanical characteristics such as a write-once type or a rewritable type, as well as a signal and an optical characteristic such as transferability and birefringence.

[0002]

2. Description of the Related Art Conventionally, CD (Compact Disc) systems and M
Various types of optical disks such as an O (magneto-optical disk) system have been used for read-only, additional recording, or rewriting purposes.

However, recently, in the information society, 1
It has become necessary to mount a larger capacity of information on a single optical disc at a higher density, for example,
Development of a DVD or a new optical disk having a larger capacity than the DVD is being promoted.

In order to increase the capacity of such an optical disk, a condition required for the optical disk substrate is to read out information on the optical disk or to narrow down the laser light of a pickup for writing information on the optical disk. (For example, the thickness of a DVD-based substrate is 0.6 mm compared to the thickness of a conventional CD or MO-based optical disc substrate (1.2 mm)). .), And a pit row for recording information and a guide groove for tracking of a pickup are more precisely transferred onto the substrate.

[0005] Substrates used for such optical discs are molded and produced by injection molding or injection compression molding using a resin mainly composed of polycarbonate in view of production efficiency and cost. .

In any of the above optical disk substrate molding methods, a cavity formed by closing a mold is filled with a molten material resin, and the molten resin is filled with the resin until a temperature at which the resin can be taken out of the mold. It is cooled and solidified in a mold to form a predetermined substrate shape. In the cavity, a stamper in which information necessary for the optical disk is engraved as a pit row or a guide groove is set. During the process from the time when the molten resin is filled into the cavity to the time when the resin is solidified, the stamper is placed on the optical disk substrate. Then, necessary information engraved on the stamper is transferred. After the cooling step in the mold is completed, the optical disc substrate molded in the mold is taken out of the mold and transferred to the next step after molding.

However, in the DVD system, the cavity is filled with a molten resin and the substrate is formed in the same manner as in the CD or MO optical disk, but the optical disk is compared with the CD or MO optical disk. Because the thickness of the substrate is thin,
The filling of the molten resin itself becomes difficult, and not only can the pit rows and guide grooves with higher density be faithfully transferred onto the optical disc substrate, but also the small birefringence and good mechanical properties required for the optical disc substrate. It is difficult to realize.

As a method of improving the filling property of the resin in the cavity and improving the transfer property, there is a method of setting the mold temperature and the resin temperature to higher temperatures.

However, this method has limitations in the material properties of the material used, such as the occurrence of decomposition and carbonization of the resin used by setting the resin temperature high.
Further, when the mold temperature is set high, there is a problem that the cooling of the filled resin does not sufficiently proceed, and the mechanical properties of the molded optical disk substrate are deteriorated, and the birefringence is also deteriorated.

[0010] As a method of solving the problem caused by increasing the temperature setting in order to solve the problem associated with poor filling as described above, the cooling time after filling the molten resin into the cavity is lengthened. There is a way to set.

However, if the cooling time is set to be appropriately long, the mechanical properties and the birefringence of the molded optical disk substrate can be improved, but not only the molding cycle becomes longer and the productivity decreases, but also the actual temperature of the cavity increases. Also falls,
There is a problem that the filling property and the transfer property of the molten resin are reduced.

As described above, in an optical disk substrate which is required to transfer a pit row and a guide groove having a smaller thickness and a higher density, appropriate characteristics are obtained not only in transferability but also in mechanical characteristics and birefringence. It is becoming clear that it is very difficult to provide, that is, to satisfy the entire characteristics required for the optical disc substrate comprehensively.

As a method of forming an optical disk substrate by solving the above-mentioned problems, conventionally, temperature settings relating to setting of molding conditions such as a temperature setting of a mold and a temperature of a resin are determined by changing material properties, mechanical properties, and birefringence. When filling the molten resin into the cavity, reduce the pressure applied to the cavity, and after the filling is completed, apply a large pressure to the cavity (filled resin in the cavity). Is generally performed.

Specifically, in the conventional molding method, for example, when an optical disk substrate is molded by an injection molding method, a mold is opened slightly without completely closing the mold, or an extremely low pressure is applied. A method in which the molten resin is filled into the cavity while the mold is closed by setting, and after the filling is completed, the mold is completely closed and a mold clamping force is applied (Japanese Patent Laid-Open No. 8-17078).
Reference). When molding an optical disc substrate by the injection compression molding method, first, the mold is closed and a mold clamping force is applied, while the cavity thickness is expanded by a predetermined compression allowance with almost no compression force applied. In this method, the molten resin is filled, and after the filling is completed, a compressive force is applied to the cavity.

Conventionally, based on the above molding method,
For the purpose of further improving the characteristics of the substrate to be molded, it has a plurality of independent heating means for heating the surface on the cavity side of the fixed mold and the movable mold, and the heating means can independently control the temperature. There has been proposed a disk substrate molding die (see Japanese Patent Application Laid-Open No. 5-212765).

That is, this disk substrate molding die is
The temperature of the mold for forming the disk substrate is compensated by a plurality of heating means capable of independently adjusting the temperature, the temperature of the mold constituting the cavity is kept constant, and the cooling rate of the molten resin filled in the cavity is kept constant. Trying to mold a disk substrate without distortion.

[0017]

However, such a conventional technique has the following problems.

That is, in the above conventional molding method, the cavity is filled with the molten resin while the cavity is being filled, or the cavity is filled with a very low mold clamping force, so that the cavity is filled. The cavity is “expanded” by the pressure of the resin, which reduces the flow resistance of the resin and improves the fillability, reduces the amount of distortion that occurs inside the resin during filling, and allows The aim is to reduce the residual stress strain and improve the birefringence and mechanical properties.

Further, it is intended to improve the transferability of the pit rows and the guide grooves by filling the resin with better fluidity.

Further, after the filling of the resin is completed, the internal pressure of the resin in the cavity is increased by applying a large pressure to the cavity, and the resin in the cavity is set in the cavity by the high internal pressure of the resin. The pit rows and guide grooves are intended to be precisely transferred onto a molded substrate by strongly adhering to a stamper. In addition, a large pressure is applied to the cavity after the filling of the resin is completed, so that the variation in the internal pressure of the resin generated at the time of filling is also made uniform.

However, the above-mentioned conventional method has a main object of "maintaining a large amount of distortion inside the resin filled in the cavity and suppressing the amount of distortion generated inside the resin". Although effective effects can be recognized for each, the above conventional methods all focus on devising how to treat the molten resin filled in the cavity. The method of filling the molten resin, which does not leave large distortion inside and keeps the distortion generated inside small, is not considered much.

Then, regarding the molding of the optical disk substrate,
The method adopted as "the method of filling the molten resin that does not leave large distortion inside the resin filled in the cavity and suppresses the distortion generated inside" is "set the resin temperature to the highest possible temperature". Or “high-speed injection filling”.

However, setting the entire injection cylinder, which melts the resin to be used, to the upper limit temperature by, for example, a method of “setting the resin temperature to the maximum limit” is called “stringing”.
The temperature of the tip of the injection cylinder must be set lower, depending on the setting of the weighing process before the injection process. There is a problem that the set effect is lost. Regarding the “high-speed injection filling” method, simply setting the screw advance speed at the time of the injection process to a high speed cannot not only obtain the effect of high-speed filling but also conversely, the characteristics of the optical disc substrate. Has been previously found to worsen.

Therefore, the invention according to claim 1 provides a measuring and melting step of measuring and melting an extremely thin resin for an optical disk substrate in an injection cylinder, and injecting the resin into a cavity of a mold for an optical disk substrate. A filling step of injecting the molten resin from the nozzle of the cylinder through the introduction passage of the mold, and a cooling step of solidifying the injected resin,
The mold is opened, the molded optical disc substrate is taken out from the mold, and the take-out / clamping step of clamping the mold again is sequentially performed to mold the optical disc substrate, and the next molding cycle is performed. In the transition to the molding operation, the cooling process is completed immediately after the completion of the measurement operation of the resin for the next molding cycle, so that the filling is completed in the next cycle in which the measurement is completed and the nozzle remains in the injection cylinder. The molten resin to be cooled is prevented from being excessively cooled before the start of the injection process, so that the molten resin is filled while maintaining its fluidity in a good state, and distortion occurs inside the optical disk substrate to be molded. It is an object of the present invention to provide an optical disk substrate forming method capable of forming an optical disk substrate having good characteristics while suppressing occurrence thereof.

According to the second aspect of the present invention, the interval from the completion of the metering operation to the end of the cooling step and the start of the mold opening operation is set to a time of 0.2 sec or less, so that the nozzle portion of the injection cylinder can be used. The molten resin to be filled in the next cycle that has remained is more appropriately prevented from being excessively cooled before the start of the injection process, and the molten resin is filled while maintaining its fluidity in a better state. So that
It is an object of the present invention to provide an optical disc substrate forming method capable of forming an optical disc substrate having better characteristics by further suppressing generation of distortion inside an optical disc substrate to be formed.

According to a third aspect of the present invention, the introduction passage portion of the optical disk substrate formed in the previous cycle is cooled by cooling the introduction passage portion of the mold in contact with the nozzle of the injection cylinder by a predetermined cooling means during the cooling step. Solidify,
An object of the present invention is to provide an optical disk substrate molding method capable of preventing the occurrence of a "stringing" molding trouble with a molten resin to be filled in a next cycle and appropriately molding an optical disk substrate having good characteristics. And

According to the fourth aspect of the present invention, the operation of filling the molten resin into the cavity is completed only by the injection step, so that excessive internal distortion is generated in the molded substrate, especially in the inner peripheral portion of the substrate. It is an object of the present invention to provide an optical disk substrate forming method capable of forming an optical disk substrate having better characteristics while preventing the occurrence of the optical disk substrate.

According to a fifth aspect of the present invention, the gate cutting operation for closing the gate of the cavity and forming the inner hole of the optical disk substrate with the gate cutter is performed by performing the pressure holding from the injection step of filling the cavity with the molten resin. By simultaneously performing the switching to the pressure holding step to be applied, the pressure holding effect by the operation of the injection screw during the pressure holding step is limited to the introduction passage portion, and excessive pressure is applied to the resin in the cavity forming the optical disk substrate. To provide a method for molding an optical disc substrate that can further prevent the occurrence of distortion and further suppress the occurrence of distortion inside the optical disc substrate to be molded, and can mold an optical disc substrate having better characteristics. It is an object.

According to a sixth aspect of the present invention, there is provided an apparatus for moving a gate cutter used in a gate cutting operation from a predetermined position during an injection process to a gate closing position in a time required for a forward movement of 0.015 sec or less. The optical disk which can prevent deformation and distortion from occurring in the inner peripheral portion of the optical disk substrate formed by the forward movement of the gate cutter, and can form an optical disk substrate having better characteristics. It is an object of the present invention to provide a substrate molding method.

According to a seventh aspect of the present invention, there is provided an optical disk substrate in which internal distortion and shape distortion are suppressed by molding the optical disk substrate by the optical disk substrate molding method according to any one of the first to sixth aspects. It is intended to be.

An object of the present invention is to provide an optical disk having excellent signal characteristics by forming an optical disk using the optical disk substrate of the present invention.

[0032]

According to a first aspect of the present invention, there is provided a method for molding an optical disk substrate, comprising: measuring and melting a resin for an optical disk substrate having an extremely thin thickness in an injection cylinder; A filling step of injecting the molten resin from the nozzle of the injection cylinder into the cavity of the mold for the substrate through an introduction passage of the mold; a cooling step of solidifying the injected resin; and opening the mold. The optical disk substrate molded from the mold is removed, and the removal and mold clamping step of clamping the mold again is sequentially performed to mold the optical disk substrate, and molding in the next molding cycle An optical disc substrate molding method which shifts to an operation, wherein the cooling step is ended immediately after the resin measuring operation for the next molding cycle is completed. Ri, has achieved the above object.

According to the above construction, the resin for the optical disk substrate having a very small thickness is measured and melted in the injection cylinder, and the resin is injected into the cavity of the mold for the optical disk substrate from the nozzle of the injection cylinder. A filling step of injecting the molten resin through the introduction passage of the mold, a cooling step of solidifying the injected resin, and opening the mold to take out the optical disk substrate molded from the mold,
Again, the removal / clamping step of clamping the mold is sequentially performed to mold the optical disc substrate, and when moving to the molding operation of the next molding cycle, the cooling step is performed by the resin for the next molding cycle. Since the measurement is completed immediately after the completion of the weighing operation, the molten resin filled in the next cycle, which is completed in the weighing operation and remains at the nozzle portion of the injection cylinder, is prevented from being excessively cooled before the start of the injection process. As a result, the molten resin can be filled while maintaining its fluidity in a good state, and the occurrence of distortion inside the optical disk substrate to be molded can be suppressed, and an optical disk substrate having good characteristics can be formed. Can be molded.

In this case, for example, in the optical disk substrate molding method, the interval from the completion of the weighing operation to the end of the cooling step and the start of the mold opening operation is zero. .2 sec or less.

According to the above configuration, the interval from the completion of the weighing operation to the end of the cooling step and the start of the mold opening operation is defined as:
Since the time is set to 0.2 sec or less, the molten resin charged in the next cycle remaining in the nozzle portion of the injection cylinder is more appropriately prevented from being excessively cooled before the start of the injection step, and Can be filled while maintaining its fluidity in a better state, and further suppressing the occurrence of distortion inside the optical disk substrate to be molded, and an optical disk with better characteristics A substrate can be formed.

Also, for example, in the above-mentioned optical disk substrate molding method, in the above-described method, the introduction passage portion of the mold in contact with the nozzle of the injection cylinder is provided with a predetermined cooling means during the cooling step. May be cooled.

According to the above configuration, the introduction passage portion of the mold in contact with the nozzle of the injection cylinder is cooled by the predetermined cooling means during the cooling step, so that the introduction passage portion of the optical disk substrate formed in the previous cycle can be reliably formed. By solidifying, it is possible to prevent the occurrence of "stringing" molding trouble with the molten resin to be filled in the next cycle, and it is possible to appropriately mold an optical disk substrate having good characteristics.

Furthermore, for example, in the optical disk substrate molding method, the operation of filling the cavity with the molten resin may be completed only by the injection step.

According to the above configuration, since the operation of filling the cavity with the molten resin is completed only by the injection step, it is possible to prevent the occurrence of excessive internal distortion in the molded substrate, especially in the inner peripheral portion of the substrate. As a result, an optical disk substrate having better characteristics can be formed.

For example, as set forth in claim 5, in the optical disk substrate molding method, the gate cutting operation of closing a gate of the cavity and forming an inner hole of the optical disk substrate with a gate cutter is performed by the following method. The process may be performed simultaneously with the switching from the injection step of filling the cavity with the molten resin to the pressure-holding step of applying a pressure-holding force to the cavity.

According to the above configuration, the gate cut operation for closing the gate of the cavity and forming the inner hole of the optical disk substrate with the gate cutter is performed by applying a pressure to the cavity from the injection step of filling the cavity with the molten resin. Since it is performed simultaneously with the switching to the pressure-holding step, the pressure-holding effect of the operation of the injection screw during the pressure-holding step is limited to the introduction passage portion, and excessive pressure is applied to the resin in the cavity forming the optical disk substrate. It is possible to prevent the occurrence of distortion inside the optical disk substrate to be molded, and to mold an optical disk substrate having better characteristics.

Further, for example, as described in claim 6, the gate cutter has a forward speed and a time required for a forward operation of moving forward from a predetermined position during the injection step to a gate closing position to be 0.015 sec or less. The cutting pressure may be set.

According to the above arrangement, the time required for the forward movement of the gate cutter used in the gate cutting operation to advance from the predetermined position during the injection process to the gate closing position is 0.0.
Since the operation is performed at a forward speed and a cut pressure of 15 sec or less, it is possible to prevent the inner peripheral portion of the optical disk substrate formed by the forward operation of the gate cutter from being deformed and distorted, and to further improve the characteristics. A good optical disk substrate can be formed.

The optical disk substrate of the invention according to claim 7 is:
The above object is attained by being molded by the optical disk substrate molding method according to any one of claims 1 to 6.

According to the above configuration, the present invention is characterized in that:
Since the optical disk substrate is molded by the optical disk substrate molding method according to any one of the above, an optical disk substrate with reduced internal distortion and shape distortion can be molded.

An optical disk according to an eighth aspect of the present invention achieves the above object by being formed by the optical disk substrate according to the seventh aspect.

According to the above configuration, since the optical disk is formed using the optical disk substrate according to claim 7, an optical disk having excellent signal characteristics can be formed.

[0048]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

1 to 3 show an embodiment of the optical disk substrate forming method, optical disk substrate and optical disk of the present invention. FIG. 1 shows the optical disk substrate forming method, optical disk substrate and optical disk of the present invention. FIG. 2 is a front sectional view of a main part of a sprue part of an optical disk substrate forming mold 1 to which one embodiment is applied.

In FIG. 1, an optical disk substrate molding die 1 is shown.
Has a sprue bush 2 and a sprue bush 2
Is formed with a sprue 3 which is a resin introduction passage. A cooling circuit 4 is formed at an inner end of the optical disc substrate molding die 1 of the sprue bush 2 so as to surround the sprue 3. An outer end of the sprue bush 2 of the optical disc substrate molding die 1 is formed. , A special cooling circuit 5 is formed so as to surround the sprue 3. In the cooling step of the molding step, a cooling medium is introduced into the cooling circuit 4 and the special cooling circuit 5 to cool the sprue 3, particularly the resin filled in the sprue 3, and function as a cooling unit. .

A nozzle 10 of an injection cylinder of a molding machine is joined to the sprue bush 2 in accordance with the sprue 3, and molten resin is injected into the sprue 3 from the nozzle 10 of the injection cylinder. The molten resin injected and filled into the sprue 3 is introduced into a cavity (not shown) defined by the optical disc substrate molding die 1 through the sprue 3.

Next, the operation of the present embodiment will be described. In order to mold an optical disc substrate using the optical disc substrate molding die 1 of the present embodiment, first, a resin is weighed in an injection cylinder of a molding machine, and a light weight / melting process for sufficiently heating and melting is performed. After that, the nozzle 10 at the tip of the injection cylinder is pressed with a predetermined pressure (nozzle touch) against the inlet at the outer tip of the sprue 3 which is the resin introduction path of the optical disc substrate molding die 1 (nozzle touch). The mold 1 is closed, and the molten resin of the injection cylinder is injected into the nozzle 10.
Through the sprue 3 into the sprue 3 of the optical disk substrate molding die 1 to fill the cavity of the optical disk substrate molding die 1 through the sprue 3.

Next, a cooling process for cooling and solidifying the resin filled in the cavity of the optical disk substrate molding die 1 is performed, and when the resin is cooled and solidified, the optical disk substrate molding die 1 is opened and molded. The optical disk substrate is taken out and transferred to a subsequent process. Then, the optical disk substrate molding die 1 is closed again, and the take-out / clamping step processing for shifting to the next molding cycle is performed.

In the above molding step, the nozzle 10 of the injection cylinder keeps the nozzle touching the optical disk substrate molding die 1 and, during the cooling step, weighs the resin charged in the injection cylinder and filled in the next molding cycle. Perform the operation. The reason why the metering operation of the next molding cycle is performed during the cooling process while the nozzle is being touched in this manner is that the resin of the sprue 3 which has been filled in the previous molding cycle and has already been cooled closes the mouth of the nozzle 10. It acts as a "plug" to prevent resin from leaking from the tip of the nozzle 10 during metering,
This is because accurate measurement of the resin can be performed.

However, when a thinned optical disk substrate is molded, the resin to be filled is generally heated to almost the upper limit temperature due to its characteristics. If the temperature is set to a very high temperature, the optical disk substrate molding
The resin in the sprue 3 filled in the side nozzle touch portion is not sufficiently cooled, and causes molding troubles such as "stringing" and "dropping".

Therefore, conventionally, the temperature of the nozzle 10 of the injection cylinder is generally set to a relatively low temperature.

As a result, when the measuring operation of the resin to be charged in the next cycle is performed at an earlier timing during the cooling process, the time during which the measured resin stays at the nozzle 10 set at a lower temperature is reduced. It becomes longer and the resin temperature drops before filling the cavity, and the intended effect cannot be obtained.

Therefore, in the present embodiment, when the timing of starting the weighing operation is set, immediately after the completion of the weighing operation,
The timing of the start of the weighing operation is set so that the cooling process is completed, the mold opening, the removal of the molded substrate, and the mold clamping operation are sequentially performed, and the process moves to the molding operation of the next molding cycle. That is, the cooling step is terminated immediately after the measurement operation of the resin for the next molding cycle is completed.

Therefore, the time during which the measured resin in the injection cylinder stays in a lower temperature atmosphere can be shortened, and the width of the resin temperature that decreases before filling can be suppressed. As a result, the effect of heating the resin filled in the injection cylinder to the upper limit temperature can be sufficiently obtained.

The relationship between the time from the completion of filling of the resin into the cavity to the start of the mold opening operation and the characteristics of the molded optical disk substrate (birefringence of the optical disk substrate) is as shown in FIG. In addition, in FIG.
sec, 0.20 sec, 0.25 sec and 0.30
“sec” indicates the time from the completion of filling the cavity into the resin to the start of the mold opening operation. As can be seen from FIG. 2, the time from the completion of filling to the start of the mold opening operation is 0.2
It is necessary to keep the time to less than sec in order to improve the characteristics of the optical disk substrate.

Therefore, in the present embodiment, the interval from the completion of the weighing operation to the end of the cooling step and the start of the mold opening operation is set to a time of 0.2 sec or less.

Accordingly, it is possible to more appropriately prevent the molten resin charged in the next cycle, which remains in the nozzle 10 of the injection cylinder, from being excessively cooled before the start of the injection step. Can be filled while maintaining an even better state, further suppressing the occurrence of distortion inside the optical disk substrate to be molded, and forming an optical disk substrate with better characteristics. be able to.

If the timing of the start of the weighing operation is further delayed in order to further shorten the interval from the completion of the weighing of the resin in the injection cylinder to the start of the filling, the weighing operation will be performed after the completion of the cooling step. -It will be performed during the mold clamping operation.

However, if the metering operation is performed during this time, the end face of the sprue 3 serving as a “plug” for closing the opening of the tip of the nozzle 10 on the nozzle 10 side is taken out of the mold together with the forming substrate taking-out operation. As a result, the resin leaks from the opening at the tip of the nozzle 10 during the measurement, and accurate measurement cannot be performed.

Therefore, it is necessary to set the metering operation so that it is always completed during the cooling process.

Further, in order to improve the characteristics of the thinned optical disk substrate, the resin to be used is heated to near the upper limit temperature in the characteristics of the resin in the injection cylinder. When the temperature of the nozzle 10 is set to a lower temperature, the temperature of the resin remaining in this portion decreases from the completion of the metering of the resin to the start of filling into the cavity, and the state of the resin deteriorates. Characteristics may be degraded.

However, in the present embodiment, the optical disc substrate molding die 1 to which the injection cylinder makes nozzle touch.
A cooling circuit 4 is formed at an inner end of the sprue 3 which is a resin introduction passage, in a state surrounding the sprue 3, and an outer end of the sprue bush 2 of the optical disc substrate molding die 1. , A special cooling circuit 5 is formed so as to surround the sprue 3. Then, in the cooling step of the molding step, a cooling medium is introduced into the cooling circuit 4 and the special cooling circuit 5 to cool the sprue 3, particularly, the resin filled in the sprue 3 portion.

Therefore, in the previous molding cycle, sprue 3
The resin loaded in the portion is sufficiently cooled during the cooling process to improve "cut" with the resin remaining in the injection cylinder nozzle 10 portion which is metered for subsequent molding. As a result, the temperature of the nozzle 10 can be set to a higher temperature than before. That is, conventionally, for the maximum temperature set in the injection cylinder, the nozzle 10
Although the temperature is set to a lower temperature of about 50 to 100 ° C., when the optical disk substrate molding die 1 of the present embodiment is used,
The temperature difference between the temperature of the nozzle 10 and the maximum temperature of the injection cylinder can be suppressed to 30 ° C. or less.

When the optical disk substrate is molded at such a high temperature of the nozzle 10, the cavity is filled with resin in a better state (at a higher temperature and in a more fluid state) and is molded. Therefore, the characteristics of the optical disk substrate are improved, and in particular, the birefringence characteristics of the inner peripheral portion are improved, as in the case where the time from the completion of filling to the start of the mold opening operation shown in FIG.

In general, in injection molding,
Dissolve the resin of the material. The melted resin flows into (the cavity of) the mold. The flowed resin is solidified in the mold (in the cavity). It is said to go through a three-step process.

However, the second “flow” process,
The third "consolidation" process cannot be completely separated, and the resin flowing into the mold starts cooling, solidifying, and shrinking from that moment. Therefore, even when the material resin is measured and filled so that the cavity is completely filled with the resin, when the cooling process is completed and the molded substrate is taken out of the mold, the molded product shrinks from a predetermined shape. In many cases, the shape is a bent shape (ie, a sink shape).

Therefore, conventionally, in general, “flowing a melted resin into a mold (filling step)” in injection molding is performed by measuring a material corresponding to a cavity capacity and then moving an injection screw at a predetermined speed at a predetermined speed. It is divided into two stages, an injection process of pouring the material resin into the cavity by advancing to the position, and a pressure-holding process of applying a predetermined pressure to the resin filled in the cavity by the injection screw having completed the advancing operation in the injection process. Control.

The screw position for switching the injection control from the injection control performed by the forward control of the injection screw to the holding pressure control performed by the pressure control or the timing of switching the control is generally called "VP switching".

The reason why the pressure applied to the resin injected / filled into the cavity in the pressure-holding step is continuously increased is that the resin filled in the cavity is prevented from contracting due to cooling and solidification. This is for filling (supplementally) filling the cavity with a resin sufficient to compensate for the volume decrease.

When a thin optical disk substrate is molded, it is difficult to inject and fill the resin into the cavity itself because the thickness of the cavity is extremely thin, and the resin filled in the cavity is difficult to inject. Cooling and solidification also proceed rapidly, and it is extremely difficult to perform an operation of (supplementally) filling the cavity with the resin during the pressure holding step. In a state where the cooling and solidification of the resin injected and filled in the cavity has already progressed for the most part, and the flow of the resin is almost impossible, the resin is forced into the cavity by the dwell control. When the resin is filled, uneven pressure is generated inside the resin in the cavity, which appears as distortion in the molded substrate. The relationship between the holding pressure filling amount and the amount of warpage (R-tilt) of the formed optical disk substrate is shown in FIG.
Is shown as

Therefore, in the present embodiment, the weighing value defining the amount of resin to be filled in the cavity is strictly set in consideration of the amount of shrinkage after filling, and further, the advancement of the injection screw during the injection process is performed. The setting and control to complete the operation of filling the cavity with the material resin by optimally controlling the operation are performed.

Therefore, the entire cavity is filled with the material resin in a state of good fluidity without receiving excessive pressure and resistance during the injection process, and the characteristics of the optical disk substrate to be molded can be improved. .

Further, in this embodiment, the gate of the cavity is closed at the same time as the VP switching at which the control of the injection screw operation is switched from the injection control to the holding pressure control, and the inner hole of the optical disk substrate is removed. The gate cut operation to form is performed.

This gate cutting operation is performed by advancing the gate cutter into the resin which has been cooled and solidified at the same time as filling the cavity. Therefore, when the gate cutter is advanced at a low speed to perform a gate cutting operation, "plastic deformation" occurs around the gate cutter, and a large distortion occurs in a clamp area around an inner hole formed by the gate cutting operation. There is a problem.

The optimal setting of the forward movement of the gate cutter for closing the gate of the cavity and performing the gate cut operation for forming the inner hole of the optical disk substrate was examined. The time required for the forward movement to move forward from the gate to the gate closing position is 0.015 sec.
If the forward speed and cut pressure are set so that
It has been found that a gate cut and an inner hole can be formed without causing distortion in a clamp area of a molded optical disk substrate.

Therefore, in the present embodiment, the forward speed and the cut pressure are set so that the time required for the forward operation to advance from the predetermined position during the injection process to the gate closing position is 0.015 sec or less. To perform a gate cut operation.

As described above, in the present embodiment, the resin for the optical disk substrate having an extremely small thickness is measured and melted in the injection cylinder, and the resin is injected into the cavity of the optical disk substrate molding die 1. Cylinder nozzle 1
0, a filling step of injecting the molten resin through the sprue 3 of the optical disk substrate molding die 1, a cooling step of solidifying the injected resin, and opening of the optical disk substrate molding die 1 to open the optical disk substrate molding die 1. The optical disk substrate molded from the optical disk substrate is taken out of the mold, and a take-out / clamping step of clamping the optical disk substrate molding die 1 again is sequentially performed to mold the optical disk substrate, and then proceed to the molding operation of the next molding cycle. In doing so, the cooling step is completed immediately after the completion of the resin measuring operation for the next molding cycle.

Therefore, it is possible to prevent the molten resin filled in the next cycle, which has been measured and completed in the nozzle 10 of the injection cylinder, from being excessively cooled before the start of the injection step, so that the molten resin is prevented from flowing. It is possible to fill the optical disk substrate while maintaining good properties, to suppress the occurrence of distortion inside the optical disk substrate to be molded, and to mold an optical disk substrate having good characteristics.

In the present embodiment, the interval from the completion of the weighing operation to the end of the cooling step and the start of the mold opening operation is set to 0.2 sec or less.

Therefore, it is possible to more appropriately prevent the molten resin charged in the next cycle remaining in the nozzle 10 of the injection cylinder from being excessively cooled before the start of the injection step, so that the molten resin has its fluidity. Can be filled while maintaining an even better state, further suppressing the occurrence of distortion inside the optical disk substrate to be molded, and forming an optical disk substrate with better characteristics. be able to.

Further, in the present embodiment, the cooling circuit 4 and the special cooling circuit 5 apply the cooling of the molding process to the sprue 3 of the optical disk substrate molding die 1 in contact with the nozzle 10 of the injection cylinder during the cooling process. In the process, a cooling medium is introduced to cool the sprue 3, particularly the resin filled in the sprue 3 portion.

Therefore, it is possible to reliably solidify the sprue 3 portion of the optical disk substrate formed in the previous cycle and to prevent the occurrence of a "stringing" forming trouble with the molten resin to be filled in the next cycle. As a result, an optical disk substrate having good characteristics can be appropriately molded.

In this embodiment, the operation of filling the cavity with the molten resin is completed only by the injection step.

Therefore, it is possible to prevent the occurrence of excessive internal distortion in the molded substrate, particularly in the inner peripheral portion of the substrate, and to mold an optical disk substrate having better characteristics.

Further, in the present embodiment, the gate cutting operation of closing the gate of the cavity and forming the inner hole of the optical disk substrate with the gate cutter is performed by changing the injection step of filling the cavity with the molten resin and holding the cavity in the cavity. At the same time as switching to the pressure-holding step of applying the pressure.

Therefore, the injection screw during the pressure holding process is
Is limited to the sprue 3 portion, so that excessive pressure is prevented from being applied to the resin in the cavity forming the optical disk substrate, and distortion occurs in the molded optical disk substrate. In this case, it is possible to form an optical disc substrate having better characteristics.

In the present embodiment, the gate cutter used in the gate cutting operation is moved forward from the predetermined position during the injection step to the gate closing position in a forward speed / cutting time of 0.015 sec or less. Operated by pressure.

Therefore, it is possible to prevent the inner peripheral portion of the optical disk substrate formed by the forward movement of the gate cutter from being deformed and distorted, and to form an optical disk substrate having better characteristics. it can.

Further, the optical disk substrate molded by the optical disk substrate molding method of the present embodiment appears inside the optical disk substrate, and appears due to distortion at a microscopic level evaluated by birefringence or the like and deformation of the shape. Both distortions at the macro level are kept very small.

An optical disk manufactured using this optical disk substrate is superior not only in signal characteristics but also in a single disk as compared with an optical disk manufactured using a substrate formed by an ordinary method. The width of the characteristic fluctuation inside is also kept small.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the gist of the invention. It goes without saying that it is possible.

[0097]

According to the optical disk substrate molding method of the present invention, a measuring and melting step of measuring and melting resin for an optical disk substrate having an extremely thin thickness in an injection cylinder, A filling step of injecting the molten resin from the nozzle of the injection cylinder through the introduction passage of the mold into the cavity of the mold, a cooling step of solidifying the injected resin, and opening the mold to form the mold from the mold. Take out the optical disk substrate that has been taken out, again take out and mold clamping step of clamping the mold, and sequentially perform molding to form the optical disk substrate, and when moving to the molding operation of the next molding cycle, the cooling step, Immediately after the metering operation of the resin for the next molding cycle is completed, the process ends, so that the metering is completed and the resin is filled in the next cycle remaining at the nozzle of the injection cylinder. To prevent the molten resin from being excessively cooled before the start of the injection process, so that the molten resin can be filled while keeping its fluidity in a good state, and the inside of the optical disk substrate to be molded can be filled. The optical disk substrate having good characteristics can be formed while suppressing the occurrence of distortion in the optical disk.

According to the optical disk substrate molding method of the second aspect of the present invention, the interval from the completion of the weighing operation to the end of the cooling step and the start of the mold opening operation is set to 0.2 sec or less. Prevents the molten resin filled in the next cycle remaining in the nozzle part of the injection cylinder from being excessively cooled before starting the injection process, and further improves the flowability of the molten resin. The optical disk substrate can be filled while maintaining the optical disk substrate, and the occurrence of distortion inside the optical disk substrate to be molded can be further suppressed, and an optical disk substrate having better characteristics can be molded.

According to the optical disk substrate molding method of the third aspect of the present invention, since the introduction passage portion of the mold contacting the nozzle of the injection cylinder is cooled by a predetermined cooling means during the cooling step, the molding is performed in the previous cycle. By properly solidifying the introduction path of the optical disk substrate, it is possible to prevent the occurrence of "stringing" molding troubles with the molten resin to be filled in the next cycle. Can be molded into

According to the optical disk substrate molding method of the present invention, the operation of filling the cavity with the molten resin is completed only by the injection step, so that the molded substrate, especially the inner peripheral portion of the substrate, is not excessively filled. The occurrence of internal distortion can be prevented, and an optical disc substrate having better characteristics can be formed.

According to the optical disk substrate molding method of the present invention, the gate cutting operation for closing the gate of the cavity and forming the inner hole of the optical disk substrate with the gate cutter is performed by injecting the molten resin into the cavity. Since the process is performed simultaneously with the switching from the process to the pressure holding process of applying a pressure to the cavity, the pressure holding effect due to the operation of the injection screw during the pressure holding process is limited to the introduction passage portion, and the inside of the cavity for forming the optical disc substrate is formed. It is possible to prevent an excessive pressure from being applied to the resin of the present invention, to further suppress the occurrence of distortion inside the optical disk substrate to be molded, and to mold an optical disk substrate having better characteristics. it can.

According to the optical disk substrate molding method of the present invention, the time required for the forward operation of moving the gate cutter used in the gate cutting operation from the predetermined position during the injection process to the gate closing position is 0.015 sec or less. Since the operation is performed at a forward speed and a cutting pressure as described below, it is possible to prevent the inner peripheral portion of the optical disk substrate formed by the forward operation of the gate cutter from being deformed and distorted, and to obtain more excellent characteristics. An optical disc substrate can be formed.

According to the optical disk substrate of the present invention, since the optical disk substrate is molded by the optical disk substrate molding method according to any one of the first to sixth aspects, internal distortion and shape distortion are suppressed to a small level. An optical disc substrate can be formed.

According to the optical disk of the present invention, since the optical disk is formed using the optical disk substrate of the present invention, an optical disk having excellent signal characteristics can be formed.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a main part of an optical disk substrate forming mold to which an embodiment of an optical disk substrate forming method, an optical disk substrate and an optical disk according to the present invention is applied.

FIG. 2 is a diagram showing the relationship between the time from the completion of filling of a resin into a cavity to the start of a mold opening operation and the birefringence characteristics of a molded optical disk substrate.

FIG. 3 is a diagram showing a relationship between a holding pressure filling amount and a warpage amount of a molded optical disk substrate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical disk substrate molding die 2 sprue bush 3 sprue 4 cooling circuit 5 special cooling circuit 10 nozzle

Claims (8)

[Claims] 1. A measuring and melting step of measuring and melting resin for an optical disk substrate having an extremely small thickness in an injection cylinder, and a step of inserting the resin from a nozzle of the injection cylinder into a cavity of a mold for the optical disk substrate. A filling step of injecting the molten resin through an introduction passage of a mold, a cooling step of solidifying the injected resin, and opening the mold to take out the optical disc substrate molded from the mold, and again, The take-out / clamping step of clamping the mold is performed sequentially to form the optical disc substrate,
An optical disc substrate molding method which shifts to a molding operation in a next molding cycle, wherein the cooling step is completed immediately after the resin weighing operation for the next molding cycle is completed. Method. 2. An optical disk substrate molding method according to claim 1, wherein an interval from completion of said measuring operation to completion of said cooling step and starting of said mold opening operation is a time of 0.2 sec or less. The method for forming an optical disk substrate according to claim 1. 3. The method of molding an optical disk substrate according to claim 1, wherein said introduction passage portion of said mold in contact with said nozzle of said injection cylinder is cooled by a predetermined cooling means during said cooling step. 3. The method for forming an optical disk substrate according to claim 2. 4. The optical disk substrate molding method according to claim 1, wherein the operation of filling the cavity with the molten resin is completed only by the injection step.
An optical disk substrate molding method according to any one of the above. 5. The optical disk substrate molding method according to claim 1, wherein a gate cutting operation of closing a gate of the cavity and forming an inner hole of the optical disk substrate with a gate cutter is performed from an injection step of filling the cavity with the molten resin. The method according to any one of claims 1 to 4, wherein the method is performed simultaneously with switching to a pressure holding step of applying a pressure to the cavity. 6. The gate cutter is set at a forward speed / cut pressure at which a time required for a forward operation for advancing from a predetermined position during the injection process to a gate closing position is 0.015 sec or less. The method for forming an optical disk substrate according to claim 5. 7. An optical disk substrate formed by the optical disk substrate forming method according to claim 1. 8. An optical disk formed of the optical disk substrate according to claim 7.