JPH11320616A - Manufacture of disk substrate and disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform high recording and reproducing characteristic by changing stepwise a reduced pressure of an injection molding pressure after the injection molding. SOLUTION: A stamper 26 is mounted on a surface of a signal face mirror member 11, and a cavity 14 is closed by moving a read face mirror member 12 so that a molten resin is injected into the cavity 14 through a gate 15. The injection molding pressure is applied, e.g. in five stages: in a first step the injection molding pressure is 13 tons or more and the injection molding pressure time is 0.4 sec or more; the switching time to a second step is 0-5 sec, the reduced pressure is 0-13 ton and the reduced pressure time is 0-3 sec; the switching time to a third, fourth, and fifth steps 0-5 sec respectively, the reduced pressure 0-13 ton respectively and the reduced pressure time 0-5 sec respectively. This results in substantial uniformity in an each CNR in the inner circumferential portion, intermediate circumferential portion, and outer circumferential portion of a magneto-optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of manufacturing a substrate used for a disk for recording information and a disk substrate.

[0002]

2. Description of the Related Art One of information recording disks, for example, C
A substrate used for an optical disk such as a D-ROM is generally manufactured by injection molding a plastic material such as polycarbonate. This injection molding method employs a stamper in which pits and grooves necessary for recording information on an optical disk are formed in an inverted manner, and is called a stamper of about 0.3 mm thickness.
A (nickel) master is mounted on the surface of one of a pair of mirror members constituting a molding die of an injection molding machine, and molten resin is placed in a cavity formed between the stamper and the other mirror member. Pits from the stamper
This is a method of forming an optical disc substrate by transferring a groove.

Here, the required characteristics of the optical disk substrate include mechanical characteristics such as dimensions, warpage, and roundness, optical characteristics such as birefringence, transfer characteristics such as pits and grooves, foreign matter, scratches, and molding defects. And other defect characteristics. Of these properties, the birefringence, with or without annealing,
Prior to film formation, it is desirable that all radial positions from the inner peripheral portion to the outer peripheral portion of the optical disk substrate be close to 0 nm.

Conventionally, a molding cycle represented by a resin temperature and a mold temperature, an injection speed, an injection molding pressure (mold clamping force), a pressure reduction (mold clamping force), a mold clamping time, etc., so as to satisfy each characteristic. By controlling the parameters of the injection molding conditions such as the above, the optical disk substrate is molded. For example, by molding the optical disc substrate by the injection molding cycle shown in FIG. 7, the birefringence at each radial position in the inner, middle and outer peripheral portions of the optical disc substrate is substantially reduced as shown in FIG. It can be 0 nm.

[0005]

According to the optical disk substrate molding method described above, one of the information recording disks, for example, a recording / reproducing mini disk (Recordable) is used.
e MD (registered trademark)), etc., a substrate used for a magneto-optical disk is formed, and the birefringence at each radial position in the inner, middle and outer peripheral portions of the magneto-optical disk substrate is set to approximately 0 nm. As shown in FIG. 9, it was found that a CNR (recording sensitivity characteristic), which is one of the electrical characteristics after film formation, had a difference of 1 dB or more between the inner and outer peripheral portions of the magneto-optical disk. did. As described above, when the CNR at the outer peripheral portion of the magneto-optical disk substrate is lower than the CNR at the inner peripheral portion by 1 dB or more, the recording / reproducing characteristics of information on the outer peripheral portion when the magneto-optical disk is formed is such that the recording of information on the inner peripheral portion is performed. Since the read / write characteristics are worse than the read / write characteristics, there is a problem that the magneto-optical disk has a variation in the read / write characteristics.

The present invention has been made in view of the above circumstances, and provides a method of manufacturing a disk substrate and a disk substrate capable of forming a disk having uniform high recording / reproducing characteristics over the entire surface. Aim.

[0007]

According to the present invention, there is provided a method for manufacturing a substrate used for a disk for recording information by injection molding, the method comprising the steps of reducing the injection molding pressure after the injection molding. This is achieved by changing the shape. Further, in the present invention, the above object is achieved by forming a substrate used for a disc for recording information such that a birefringence from an inner peripheral portion to an outer peripheral portion is changed.

According to the above construction, the birefringence from the inner peripheral portion to the outer peripheral portion of the disk substrate can be changed by changing the pressure of the injection molding pressure after the injection stepwise. The electrical characteristics can be made uniform over the entire surface of the substrate. That is, the difference in the electrical characteristics between the inner and outer peripheral portions of the disk substrate is caused by the trend of the birefringence from the inner peripheral portion to the outer peripheral portion of the disk substrate and the subtle shape change such as pits and grooves. In order to make the electrical characteristics uniform over the entire surface of the disk substrate, the pressure drop of the injection molding pressure after injection is changed in a step-like manner, and the birefringence index from the inner peripheral portion to the outer peripheral portion of the disk substrate is reduced. It is possible to respond by changing.

[0009]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the embodiments described below are preferred specific examples 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 in the following description. It is not limited to these forms unless otherwise stated.

FIG. 1 is a sectional plan view showing an example of an injection molding machine used in an embodiment of the method of manufacturing a disk substrate according to the present invention. The injection molding machine 10 includes a signal surface mirror member 11 on a fixed mold side and a reading surface mirror member 12 on a movable mold side, which are molding means. Signal surface mirror member 11
A stamper 26 is attached to the one end face of the substrate through a stamper retainer 13. On one end surface of the reading surface mirror member 12, there is provided a cavity 14 in which a molten resin is injected to form a disk substrate. Further, a gate 15 is provided that penetrates from the other end surface of the receiving plate to the center of the cavity 14 and guides the molten resin into the cavity 14. The reading surface mirror member 12 has a cut punch 16 for cutting a portion to be a center hole of the disk substrate.
Is provided.

An example of an injection molding process of a substrate for a magneto-optical disk by the injection molding machine 10 having such a configuration will be described with reference to FIG. FIG. 3 shows the electrical characteristics after film formation when the birefringence, which is the optical characteristic at the inner, middle, and outer peripheral portions of the magneto-optical disk substrate, is changed.
It is a figure showing change of NR. Thus, the birefringence and CN
Since there is a correlation with R, the inner, middle, and middle portions of the magneto-optical disk substrate are adjusted by setting the respective birefringence indices at the inner, middle, and outer peripheral portions of the magneto-optical disk substrate to appropriate values. Each CNR in the peripheral portion and the outer peripheral portion can be made substantially uniform.

That is, the standard value of the birefringence is ± 100 nm.
Since the standard value of CNR is 47 dB or more, the birefringence of the inner periphery is 30 nm to -50 nm, the birefringence of the middle is 20 nm to -60 nm, and the birefringence of the outer periphery is 0 nm. By setting it within the range of -100 nm, the CNR of each part can be set within the range of 47 dB to 48.5 dB.

As described in the prior art, the optical characteristics such as the birefringence of the substrate for a magneto-optical disk include resin temperature and mold temperature, injection speed, injection molding pressure (clamping force), and pressure reduction (clamping force). It can be changed by controlling parameters of injection molding conditions such as a molding cycle represented by a mold clamping force) and a mold clamping time. Therefore, for example, in order to make the CNR 48 dB over the entire surface of the magneto-optical disk substrate, the birefringence index of the inner peripheral portion of the magneto-optical disk substrate is approximately −10 nm and the birefringence index of the middle peripheral portion is approximately −10 nm. It is sufficient to set the birefringence of the outer periphery to about -60 nm, for example, by changing the injection molding pressure after injection into a step shape as shown in FIG. It should be a cycle.

That is, the injection molding pressure after injection is reduced in five stages. Injection molding pressure P1 in the first step
Is 13 ton or more in consideration of transfer characteristics, the injection molding pressure time T1 is 0.4 sec or more, the switching time t1 from the first step to the second step is 0 sec to 5 sec, and the pressure reduction P2 in the second step is 0 ton. １３13 ton, decompression time T2 is 0 secｓｅ3 sec, and switching time t2 from the second step to the third step is 0 sec〜5 sec.
It has become.

Further, the pressure reduction P3 in the third step is 0t
on to 13 ton, decompression time T3 is 0 sec to 5 sec
c, switching time t3 from the third step to the fourth step
Is 0 sec to 5 sec, the decompression P4 in the fourth step is
0 to 13 tons, decompression time T4 is 0 sec to 5
The switching time t4 from the fourth step to the fifth step is 0 sec to 5 sec.
Is 0 to 13 ton, and the decompression time T5 is 0 sec
５5 sec. When the pressure reduction time after the pressure reduction switching is 0 sec, it indicates that there is no step. Therefore, the ratio P1 / P5 of the injection molding pressure P1 after the injection molding to the final stage pressure P5 is 1 or more.

In forming the magneto-optical disk substrate having the above-described structure, first, a stamper 26 is attached to the surface of the signal surface mirror member 11, the reading surface mirror member 12 is moved to close the cavity 14, and the metal is closed. Mold temperature 100 ° C ~
The temperature is raised to 120 ° C and the resin temperature is raised from 270 ° C to
The temperature is raised to 320 ° C. (FIG. 2A). Then, the molten resin is injected into the cavity 14 through the gate 15 by 80 mm /
Inject and fill at an injection speed of s ^{2 to} 120 mm / s ² (FIG. 2B).

As a first step, the injection molding pressure P1 is 1
At 3 tons, 0.8 sec injection molding pressure time T
Hold at 1. If the resin is in a semi-molten state after filling the molten resin during that time, the cut punch 16 is projected into the cavity 14 to cut the inner diameter of the semi-molten resin (FIG. 2).
(C)). As a second step, immediately after the injection molding pressure time T1 elapses, the pressure reduction P2 is reduced by 10 with a switching time of 0.4 sec.
decompression until the pressure reaches ton, and a decompression time T2 of 0.8 sec.
Hold with.

As a third step, immediately after the elapse of the decompression time T2, the decompression P3 is reduced to 8 tons with a switching time of 0.2 sec.
The pressure is reduced until the pressure is reduced, and the pressure is maintained for a reduced pressure time T3 of 1.4 sec. As a fourth step, immediately after the elapse of the decompression time T3,
The pressure is reduced until the reduction P4 becomes 6 tons in the switching time of 0.3 sec, and the pressure is maintained for the decompression time T4 of 1.2 sec.
As a fifth step, immediately after the elapse of the decompression time T4, 0.5
The pressure is reduced until the pressure reduction P5 becomes 4 tons in the switching time of sec, and is maintained for the pressure reduction time T5 of 1 sec. Then, immediately after the elapse of the decompression time T5, the pressure is reduced until the pressure becomes zero.

By the above steps, the semi-molten resin is cooled and solidified (FIG. 2 (D)).
Is returned into the reading surface mirror member 12 and the reading surface mirror member 12 is moved to open the cavity 14 (FIG. 2).
(E)). Finally, the magneto-optical disk substrate 30 and the sprue (portion of the inner diameter of the resin cut by the cut punch 16) 31 are taken out of the cavity 14, and the magneto-optical disk substrate 30 is transported to the next step, and the sprue 31 is removed. Discard (FIG. 2 (F)). In this example, the stamper 2
Although 6 is attached only to the signal surface mirror member 11, the process for injection molding by attaching it to the reading surface mirror member 12 is basically the same as the above process.

By the above-described injection molding process, the birefringence index at each radial position in the inner, middle and outer peripheral portions of the magneto-optical disk substrate 30 is substantially -5n, as shown in FIG.
Those that change in a quadratic curve from m to about -75 nm are obtained. Therefore, as shown in FIG. 6, the CNR after the film formation of the magneto-optical disk substrate 30 is substantially equal to 48 dB at the inner, middle and outer peripheral portions of the magneto-optical disk.
It is possible to obtain a magneto-optical disk having uniform information recording / reproducing characteristics over the entire surface and high characteristics.

[0021]

As described above, according to the present invention, it is possible to provide a disk having uniform high recording and reproducing characteristics over the entire surface.

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view showing an example of an injection molding machine used in an embodiment of a method for manufacturing a disk substrate of the present invention.

FIG. 2 is a view showing an example of an injection molding process of a disk substrate by the injection molding machine of FIG. 1;

FIG. 3 is a diagram showing a change in CNR, which is an electrical characteristic after film formation, when a birefringence, which is an optical characteristic, is changed in an inner peripheral portion, a middle peripheral portion, and an outer peripheral portion of a disk substrate.

FIG. 4 is a view showing an example of an injection molding cycle showing a relationship between molding pressure and molding time by the injection molding machine of FIG. 1;

FIG. 5 is a diagram showing each birefringence as an optical characteristic at a radial position of a disk substrate formed by the injection molding cycle of FIG. 4;

6 is a view showing CNR which is an electrical characteristic of an inner peripheral portion, a middle peripheral portion, and an outer peripheral portion of the disk substrate formed by the injection molding cycle of FIG. 4 after film formation.

FIG. 7 is a diagram showing an example of an injection molding cycle showing a relationship between molding pressure and molding time by a conventional injection molding machine.

FIG. 8 is a diagram showing each birefringence which is an optical characteristic at a radial position of a disk substrate molded by the injection molding cycle of FIG. 7;

9 is a diagram showing CNR which is an electrical characteristic of an inner peripheral portion, a middle peripheral portion, and an outer peripheral portion of the disk substrate formed by the injection molding cycle of FIG. 7 after film formation.

[Explanation of symbols]

10 ... injection molding machine, 11 ... signal surface mirror member,
12: reading surface mirror member, 26: stamper

Claims (5)

[Claims] 1. A method of manufacturing a substrate used for a disk for recording information by injection molding, wherein the pressure of the injection molding pressure after the injection molding is changed stepwise. . 2. The method for manufacturing a disk substrate according to claim 1, wherein a ratio of an injection molding pressure after the injection molding to a final stage pressure is 1 or more. 3. A substrate for a disk for recording information, wherein the substrate for a disk is formed so that the birefringence varies from an inner peripheral portion to an outer peripheral portion. 4. The disk substrate according to claim 3, wherein the birefringence is formed so as to gradually decrease from an inner peripheral portion to an outer peripheral portion. 5. The method according to claim 1, wherein the inner peripheral portion has a birefringence of 30 nm to-.
It is formed so that it may be set to 50 nm, the birefringence of the middle part may be set to be 20 nm to -60 nm, and the birefringence of the outer part may be set to be 0 nm to -100 nm. The disk substrate according to claim 4.