JPH11185305A - Disk substrate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove the moisture and gases in a resin material and to suppress the occurrence of defects by previously superheating and preserving the resin material for a prescribed time at a prescribed temp. under a reduced pressure, then using the resin material. SOLUTION: A moving mold is moved in proximity to a stationary mold and both molds are clamped to constitute a cavity closed at the circumference and thereafter the resin material in the molten state superheated and preserved under the reduced pressure is injected and packed into the cavity through a nozzle of a sprue bushing. Next, the resin material is cooled to a half-molten state by a temp. control mechanism built in a mold device for injection molding and in this state a punch is projected and moved toward the stationary mold to form the center hole of the molded disk substrate. The resin material injected into the cavity is then cooled to cured. After the resin material cures completely, the mold opening action is carried out by moving the moving mold apart from the stationary mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin disk substrate used for a recording medium such as an optical disk, a magneto-optical disk, a phase change disk, and a magnetic disk, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a recording medium such as an optical disk, a magneto-optical disk, a phase change disk, and a magnetic disk, a resin disk substrate formed by an injection molding method in which a molten resin is injected into a mold, cooled, and taken out is used. Have been. A resin disk substrate molded by such an injection molding method is advantageous in terms of manufacturing cost because it is not necessary to perform a polishing step unlike a disk substrate made of aluminum or glass.

However, in the disk substrate 100 molded by using such an injection molding method, if moisture or gas is contained in the resin pellets, which are raw materials, the moisture or gas is dissipated during injection molding. And a groove-shaped or annular concave portion called a silver streak as shown in FIG. 5 is formed on the surface of the disk substrate 100.

[0004] Here, the groove-shaped concave portions are formed when moisture and gas occluded in the resin pellets gather and move along the flow of the resin by injection molding. Further, the annular concave portion is formed by collecting moisture and gas occluded in the resin pellet and generating bubbles. Hereinafter, the groove-shaped or annular concave portion is referred to as a defect.

Conventionally, in order to prevent such defects from occurring, a method of heating resin pellets as a raw material in a heating oven to remove moisture and gas from the resin pellets and then molding the resin pellets has been used. Above all, when molding lenses or the above-described disk substrates that require higher surface accuracy, the generation of defects is prevented by heating the resin pellets in heated air whose humidity is controlled.

[0006]

By the way, in a recording medium using a resin-made disk substrate, with a further increase in recording density, a defect smaller than ever before affects an error rate. I have. In particular, in a disk substrate used in a hard disk, the presence of such a defect directly leads to an increase in an error rate. Therefore, it is strongly desired to further reduce defects on the disk substrate surface.

However, the above-described conventional method of heating resin pellets cannot completely prevent the above-mentioned defects.

Therefore, the present invention has been proposed in view of the conventional circumstances, and provides a resin-made disk substrate having good surface properties without defects on the surface, and a method of manufacturing such a disk substrate. The purpose is to do.

[0009]

DISCLOSURE OF THE INVENTION A disk substrate according to the present invention, which has been completed to achieve the above-mentioned object, comprises a resin material which has been stored for a predetermined time while being heated to a predetermined temperature under a predetermined pressure, and It is characterized by being injection-molded using a material. The resin material is
It is preferably a thermoplastic norbornene-based resin.

In the disk substrate according to the present invention having the above-described structure, since the resin material is used after being heated and stored at a predetermined temperature under a predetermined pressure for a predetermined time, moisture and gas in the resin material are removed. It is effectively removed, and the occurrence of defects causing an increase in the error rate is effectively suppressed.

In addition, in the disk substrate according to the present invention, when injection molding is performed, the use of a thermoplastic norbornene-based resin having a small water absorption or a small amount of deformation due to moisture absorption as a resin material allows more effective generation of defects. Can be suppressed.

Further, a method of manufacturing a disk substrate according to the present invention, which has been completed to achieve the above-mentioned object, comprises: storing a resin material at a predetermined temperature under a predetermined reduced pressure for a predetermined time; It is characterized by injection molding using a material. Note that the resin material is preferably a thermoplastic norbornene-based resin.

According to the method of manufacturing a disk substrate according to the present invention having the above-described structure, the resin material is heated and stored at a predetermined temperature under a predetermined pressure for a predetermined time before use. Moisture and gas are effectively removed, and the occurrence of defects that cause an increase in the error rate on the disk substrate after injection molding is effectively suppressed.

Further, in the method for manufacturing a disk substrate according to the present invention, by using a thermoplastic norbornene-based resin having a small water absorption or a small amount of deformation due to moisture absorption as a resin material,
The occurrence of defects is more effectively suppressed on the disk substrate after injection molding.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, a disk substrate to which the present invention is applied will be described. FIG. 1 is a perspective view showing an example of a disk substrate to which the present invention is applied.

The disk substrate 1 to which the present invention is applied is one in which a resin material is stored under a predetermined reduced pressure at a predetermined temperature while being stored for a predetermined time, and then injection molded using the resin material. As a material of the disk substrate 1,
Any synthetic resin such as polycarbonate may be used, but a thermoplastic norbornene-based resin is preferred in view of a small water absorption and a small amount of deformation due to moisture absorption.

As described above, the disk substrate 1 to which the present invention is applied is used after the resin material is pre-heated and stored at a predetermined temperature under a predetermined pressure for a predetermined time, so that moisture and gas in the resin material are not effectively used. And the occurrence of defects that cause an increase in the error rate can be effectively suppressed. Therefore,
The disk substrate 1 to which the present invention is applied has good surface properties as shown in FIG.

Hereinafter, a method of manufacturing the disk substrate 1 will be described in detail. The method of manufacturing a disk substrate to which the present invention is applied is applied as a method of manufacturing a resin disk substrate used for an optical disk, a magneto-optical disk, a phase change disk, a magnetic disk, and the like. FIG. 2 is a sectional view showing an injection molding die apparatus for injection molding a disk substrate.

In the method of manufacturing a disk substrate to which the present invention is applied, first, a resin material is stored for a predetermined time while being heated and maintained at a predetermined temperature in an environment in which the pressure is reduced from atmospheric pressure by 500 mmHg or more to about 260 mmHg or less. I do. Here, assuming that the predetermined temperature is t [° C.] and the glass transition temperature of the resin material is _TG [° C.], _TG− 50 <t < _TG− 10
[° C.] is preferable.

As described above, in the method of manufacturing a disk substrate to which the present invention is applied, since the resin material, which is a raw material pellet for injection molding, is heated and stored under reduced pressure in advance, the resin material is heated under atmospheric pressure. Than the conventional method of storing and using,
After molding, moisture, gas, and the like that cause defects on the disk substrate 1 can be more effectively removed from the resin material.

When a thermoplastic norbornene-based resin is used as the resin material, it is preferable to store the resin at the above-mentioned predetermined temperature for about 4 hours or more, preferably for 8 hours or more.

Next, the resin material previously heated and stored under reduced pressure is injected into the injection molding die apparatus 2 as shown in FIG.
To form the disk substrate 1. Hereinafter, as the injection molding apparatus 2, an injection molding apparatus for a magnetic disk substrate will be described.

Here, the structure of the injection molding die apparatus 2 will be described. As shown in FIG. 2, the injection molding die apparatus 2 includes a fixed die 3 forming one main surface of the disk substrate 1, and a disk substrate 1 disposed opposite to the fixed die 3. Of the disk substrate 1 and an outer peripheral die 5 that forms the outer peripheral side surface of the disk substrate 1.

The movable mold 4 is supported by guide means (not shown), and moves toward and away from the fixed mold 3 by a driving mechanism. Further, the outer peripheral mold 5 is incorporated on the movable mold 4 side. The fixed mold 3 and the movable mold 4
The outer peripheral mold 5 forms a cavity 6 that forms the disk substrate 1 in cooperation with each other in a mold clamped state. And
At the time of molding, the cavity 6 is filled with a resin material that is a material of the disk substrate 1.

The fixed mold 3 and the movable mold 4 are provided with stampers 8a and 8b, respectively, on the molding surface side of the cavity 6. These stampers 8a and 8b
The disk substrate 1 has a disk shape whose diameter is larger than the outer diameter, and a center hole slightly larger than the inner diameter of the center hole of the disk substrate 1 is formed. The stampers 8a and 8b have, on one main surface thereof, a concentric concavo-convex pattern forming a recording track on which an information signal is recorded on a magnetic disk. Then, the stampers 8a and 8b transfer and form these uneven patterns to the disk substrate 1. And these stampers 8a, 8b
Are held between the fixed mold 3 and the movable mold 4, respectively.

On the fixed mold 3 side, a nozzle 10 is located at the center of the cavity 6 for molding the disk substrate 1 and injects and fills the cavity 6 with a molten resin material heated and stored under the above-described conditions. Is provided. Then, the resin material supplied from the injection material forming machine 30 is injected and filled into the cavity 6 through the nozzle 10 at a high pressure.

On the other hand, on the movable mold 4 side, a first ejecting member 15 provided at a position corresponding to the center of the cavity 6 is disposed so as to be movable in the axial direction. The first ejecting member 15 moves the disk substrate 1 to the movable mold 4 by driving means (not shown) during the releasing operation of the disk substrate 1.
Release from mold.

A punch 13 for forming a center hole of the disk substrate 1 to be formed is mounted on the inner peripheral side of the first ejecting member 15, and a driving mechanism (not shown) is coaxial with the first ejecting member 15. Is moved by

The inner peripheral side of the punch 13 is provided with a second
The eject member 12 is mounted to be able to move forward and backward by a hydraulic mechanism. The end face of the second eject member 12 on the side of the cavity 6 forms a bottom surface of the resin reservoir 14.

The outer peripheral mold 5 is fixed to the outer peripheral side of the movable mold 4 by a set screw 16. The outer peripheral die 5 forms an outer peripheral surface of the disk substrate 1 to be molded by being disposed so that an end is sandwiched by the fixed die 3 and the movable die 4.

The injection molding die apparatus 2 includes a first temperature adjustment mechanism 20 for adjusting the temperature of the fixed mold 3 and a second temperature adjustment mechanism 25 for adjusting the temperature of the movable mold 4. Is provided. These first temperature control mechanism 20 and second temperature control mechanism 20
The temperature adjustment mechanism 25 cools the resin material filled in the cavity 6 and independently adjusts the temperatures of the fixed mold 3 and the movable mold 4.

As described below, the resin material heated and stored under reduced pressure is injected into the disk substrate 1 by the injection molding die apparatus 2 for molding the disk substrate 1 configured as described above. Molded.

First, in the injection molding die apparatus 2, the movable die 4 is moved closer to the fixed die 3 by the operation of a drive mechanism (not shown), and the periphery is closed. The cavity 6 thus formed is constituted.

Thereafter, the molten resin material heated and stored under reduced pressure as described above is injected and filled into the cavity 6 in the mold clamped state through the nozzle 10 of the sprue bush 11. And this injection molding die apparatus 2
In a state where the resin material is cooled to a semi-molten state by the first temperature control mechanism 20 and the second temperature control mechanism 25 built in the punch, the punch 13 is fixed from the center hole of the first eject member 15 to the fixed mold. It protrudes in three directions to form a center hole of the disk substrate 1 to be formed.

Thereafter, the first temperature control mechanism 20 and the second
The resin material injected into the cavity 6 is cooled and hardened by the temperature control mechanism 25.

After the resin material in the cavity 6 is completely cured, a drive mechanism (not shown) is operated to move the movable mold 4 away from the fixed mold 3, thereby performing the mold opening operation. Will be

Finally, the disk substrate 1 molded in the cavity 6 is moved by the first ejecting member 15 which operates in a state where the fixed mold 3 and the movable mold 4 are opened. The disk substrate 1 is protruded from the movable mold 4 side, and the disk substrate 1 is removed by a disk substrate removal mechanism (not shown).

In the method of manufacturing a disk substrate to which the present invention is applied by the above manufacturing steps, a step of heating and storing at a predetermined temperature under a predetermined pressure for a predetermined time is performed in advance on the resin material as a raw material. Moisture, gas, and the like can be more effectively removed from the raw resin material than by the conventional method of heating and storing the resin material under atmospheric pressure. For example, when a thermoplastic norbornene-based resin is used as the resin material, the thermoplastic norbornene-based resin is usually about 0.0
1% by weight of water and a similar amount of gas are absorbed, but by using the method for manufacturing a disk substrate to which the present invention is applied, such water and gas can be effectively removed.

Therefore, according to the method of manufacturing a disk substrate to which the present invention is applied, injection molding is performed using a resin material from which moisture and gas have been effectively removed, and the occurrence of defects on the substrate surface is significantly suppressed. Thus, a highly reliable disk substrate 1 having good surface properties can be formed.

That is, the disk substrate 1 to which the present invention is applied
Is manufactured by the manufacturing process described above,
The occurrence of defects on the substrate surface is significantly suppressed, and a highly reliable disk substrate having good surface properties is obtained.

As a result, according to the disk substrate 1 to which the present invention is applied, it is possible to provide a recording medium having improved recording and reproducing characteristics.

Next, in order to verify whether or not the occurrence of defects on the disk substrate surface can be effectively suppressed by the above-described method for manufacturing a disk substrate to which the present invention is applied, the following evaluation was performed. went.

<Examples> The following experiments were conducted to evaluate the effects of the disk substrate manufacturing method to which the present invention was applied.

First, the pressure of the thermoplastic norbornene resin is reduced by at least 500 mmHg from the atmospheric pressure to a pressure of about 260 mHg.
The heating and drying were continued in an environment of mHg and a set temperature of 100 ° C., using a thermoplastic norbornene-based resin after drying for 1 hour, using a mold apparatus for injection molding to have a radius of 2.5 inches and a thickness of 1.2 mm. A plurality of disk substrates were formed.

Next, the optical disk was used to focus on the position of a 25 mm radius of the molded disk substrate at a magnification of 5 times the objective lens and 10 times the eyepiece.

Each of these disk substrates is rotated 360 degrees on a rotary stage to search for defects, and it is determined whether the found defect is a defect caused by moisture or gas occluded in the resin material. After the discrimination was made by double or 1000 times, the number of those defects was counted.

Next, the thermoplastic norbornene-based resin was dried under the same environment for 3, 4, 6, 8 hours, and a plurality of disk substrates were similarly formed using the respective thermoplastic norbornene-based resins. The number of defects caused by moisture or gas occluded in the resin material was counted.

FIG. 3 shows the above results. FIG. 3 shows, for each heating and drying time, the number of defects of a plurality of disk substrates manufactured with the same heating and drying time, and the average value and the range of variation.

<Comparative Example> Next, the following experiment was conducted to evaluate the surface condition of the disk substrate when the disk substrate was manufactured using a conventional method of heating a resin material under atmospheric pressure.

First, the thermoplastic norbornene resin was heated and dried under atmospheric pressure at a set temperature of 100 ° C.
Using a thermoplastic norbornene-based resin after drying for a period of time, a radius of 2.5 inches and 1.2 mm was obtained using an injection molding die apparatus.
A plurality of thick disk substrates were formed.

Next, the number of defects caused by the resin on the substrate surface was counted for each of the molded disk substrates in the same manner as in the example.

Further, the thermoplastic norbornene-based resin was dried in a similar environment for 72 hours, and a disk substrate was similarly formed using the thermoplastic norbornene-based resin.
The number of defects caused by an increase in the error rate was counted.

FIG. 4 shows the above results. FIG. 4 shows, for each heating and drying time, the number of defects of a plurality of disk substrates manufactured with the same heating and drying time, and the average value and the range of variation.

<Comparative Evaluation between Example and Comparative Example> As is clear from the results in FIG. 3, in the example in which the resin material was heated and stored under reduced pressure, the resin material after heating and drying for 4 hours was used. The number of defects on the disk substrate molded using the resin material is reduced to about one tenth of the number of defects on the disk substrate molded using the resin material after heating and drying for one hour. Moreover,
No defects were found on the disk substrate molded using the resin material after heating and drying for 8 hours.

Therefore, when a disk substrate is formed using a thermoplastic norbornene-based resin, the thermoplastic norbornene-based resin is decompressed at a pressure of about 260 mmHg by reducing the pressure from atmospheric pressure to 500 mmHg or more.
It was found that the use of the substrate after heating at 0 ° C. and storing it for at least 4 hours, preferably at least 8 hours can greatly suppress the occurrence of defects on the disk substrate.

As described above, according to the disk substrate manufacturing method to which the present invention is applied, the generation of defects is effectively suppressed by pre-heating and preserving the resin material to be pellets under reduced pressure and then molding. be able to.

On the other hand, as is apparent from the results shown in FIG. 4, in the comparative example in which the resin material was heated and stored under atmospheric pressure and used, the disk substrate formed by using the resin material after heating and drying for 24 hours was used. The number of defects was almost the same as the number of defects on the disk substrate molded using the resin material after heating and drying for 4 hours in the above example. In addition, the number of defects of the disk substrate using the resin material after heating and drying for 72 hours was almost the same as that of the disk substrate using the resin material after heating and drying for 6 hours in the above example.

Therefore, in the method of the comparative example in which the resin material is heated and stored under the atmospheric pressure, the resin material must be dried for a long time to minimize defects on the disk substrate.
It turned out that the production efficiency was very bad.

From the above results, it can be seen that the occurrence of defects can be more effectively suppressed by using the resin material after heating it under reduced pressure in advance when molding the disk substrate as in this embodiment. found.

[0061]

As described in detail above, according to the disk substrate of the present invention, the resin material is used after being heated and stored at a predetermined temperature under a predetermined pressure for a predetermined time before use. Is effectively removed, and the occurrence of defects causing an increase in the error rate is effectively suppressed, so that a highly reliable disk substrate having good surface properties can be obtained.

In the disk substrate according to the present invention, the use of a thermoplastic norbornene-based resin having a small water absorption or a small amount of deformation due to moisture absorption as a resin material allows the generation of defects to be suppressed more effectively, and Good reliability.

As described in detail above, according to the method for manufacturing a disk substrate of the present invention, the resin material is heated and stored at a predetermined temperature under a predetermined pressure for a predetermined time before use. Moisture and gas in the material are effectively removed, the generation of defects can be effectively suppressed, and a highly reliable disk substrate with good surface properties can be manufactured.

In the method of manufacturing a disk substrate according to the present invention, a thermoplastic norbornene-based resin having a small water absorption and a small amount of deformation due to moisture absorption is used as a resin material.
The occurrence of defects can be more effectively suppressed on the disk substrate after the injection molding, and a highly reliable disk substrate having good surface properties can be manufactured.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a disk substrate to which the present invention is applied.

FIG. 2 is a cross-sectional view showing an example of an injection mold apparatus for injection-molding a disk substrate to which the present invention is applied.

FIG. 3 is a diagram showing the results of Examples.

FIG. 4 is a diagram showing the results of a comparative example.

FIG. 5 is an enlarged sectional view showing a surface of a disk substrate formed by a conventional injection molding method.

[Explanation of symbols]

1 disk substrate, 2 injection molding die apparatus, 3
Fixed mold, 4 Movable mold, 5 Outer mold, 6 Cavity, 7 Resin material

Claims (5)

[Claims] 1. A disk substrate obtained by storing a resin material for a predetermined time while heating it to a predetermined temperature under a predetermined pressure, and then performing injection molding using the resin material. 2. The disk substrate according to claim 1, wherein the resin material is a thermoplastic norbornene-based resin. 3. A method for manufacturing a disk substrate, comprising: storing a resin material for a predetermined time while heating the resin material to a predetermined temperature under a predetermined reduced pressure; and performing injection molding using the resin material. 4. The method according to claim 3, wherein the resin material is a thermoplastic norbornene resin. 5. A pressure of 260 mm due to the predetermined pressure reduction.
5. The method according to claim 4, wherein the predetermined time is not more than Hg and the predetermined time is not less than 4 hours.