JPH0863807A - Manufacturing method of plastic substrate for optical disk - Google Patents

Abstract

PURPOSE: To prevent the local abnormality of birefringence by receiving the self-weight of a plastic substrate for optical disc at one point at the time of annealing. CONSTITUTION: A plastic substrate 1 for optical disc is held by a holding case 2. At the time of annealing, the plastic substrate 1 held by the holding case 2 is mounted on a spacer 3 preset in a heating furnace. Consequently, the self- weight of the plastic substrate 1 is prevented from being received at two points on the bottom part of the holding case and the plastic substrate 1 is annealed while being received at one point. This method eliminates local abnormality of birefringence thus realizing uniform birefringence.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plastic substrate for an optical disk, and more particularly for removing distortion in a method for manufacturing a plastic substrate used for an optical disk for recording / reproducing information by optical means such as laser light. The present invention relates to a method of annealing treatment performed on.

[0002]

2. Description of the Related Art A plastic substrate is generally used as a so-called optical disc substrate for recording or reproducing information according to changes in optical characteristics. This plastic substrate has advantages that it is lightweight, easy to process, and can be manufactured at low cost. However, the plastic substrate has a drawback that the birefringence is large due to the molecular orientation strain during injection molding. The large birefringence, which is a drawback of this plastic substrate, causes deterioration of the quality of the recording / reproducing signal or the servo signal, which becomes a problem in the quality of the optical disc. Therefore, efforts are being made to reduce birefringence by optimizing the manufacturing conditions during injection molding.

Further, since this birefringence changes due to heat received in a later step of manufacturing an optical disk, a so-called annealing process, that is, a process of heating the plastic substrate for an optical disk after injection molding for a predetermined period of time to remove strain and stabilize it, is performed. It is common to do.

FIG. 5 is a schematic view showing a conventional method for supporting a plastic substrate for an optical disc during an annealing process. The optical disk plastic substrate 11 is housed in the holding case 12 and stored in this state. FIG. 5 (A) is a side view showing this supported and stored state, and FIG. 5 (B) is FIG.
It is a BB line sectional view of (A).

In the conventional annealing treatment, in this state, it is placed in a heating furnace (oven) and heated at a constant temperature for a predetermined time, and then cooled or gradually cooled. For example, when the plastic substrate is made of polycarbonate, the annealing condition is heating at a temperature of about 100 ° C. for 2 to 3 hours and then gradually cooling.

As another supporting method, Japanese Patent Laid-Open No. 3-2 is known.
Japanese Patent No. 48345 discloses a method of penetrating a support through a center hole provided in a plastic substrate and supporting the plastic substrate with the support.

[0007]

However, in the conventional annealing treatment method shown in FIG. 5, the weight of the plastic substrate 11 for the optical disk is equal to the outer peripheral surface of the holding case 12.
Start at points (11a and 11b). When heated in this state, the plastic substrate 11 for the optical disk and the holding case 1
Due to the difference in thermal expansion of No. 2 and the weight of the plastic substrate being received at two points, a local force is applied to the contact portions 11a and 11b.

More specifically, the plastic substrate 11 for the optical disk and the holding case 12 are thermally expanded by being heated by the annealing treatment, but the plastic substrate for the optical disk is thermally expanded in the outer diameter direction, whereas the plastic substrate is held. The case 12 is thermally expanded as a whole. for that reason,
At the contact portions 11a and 11b, due to the frictional force between the optical disk plastic substrate 11 and the holding case 12, the optical disk plastic substrate loses its escape area, and a local force equal to or more than its own weight is applied in the inner circumferential direction. .

Due to the local force at the contact portions 11a and 11b, a portion where the birefringence is locally large is generated on the outer peripheral portion of the plastic substrate 11 for an optical disc. When an optical disc is manufactured by using the plastic substrate 11 for an optical disc having a portion having a large local birefringence, there is a problem that a problem occurs in a recording / reproducing signal and a servo signal.

FIG. 6 shows a plastic substrate 1 for an optical disk which has been annealed by the conventional supporting method shown in FIG.
3 is a graph showing a servo signal of an optical disc manufactured by using No. 1. The material of the plastic substrate for optical disks is polycarbonate, and the annealing condition is that the temperature in the furnace is 90 ° C. for 3 hours, followed by slow cooling. The measurement of the servo signal shows the tracking signal as a ratio when the track jump signal is set to 100% in an actual optical disk drive device, and is a graph of a radius of 61 mm of a 5.25 inch optical disk.

As shown in FIG. 6, in the annealing process by the conventional supporting method, a local abnormality occurs in the servo signal in the circumferential direction. The portion of such birefringence abnormality also affects the recording / reproducing signal. This abnormal portion corresponds to the contact portions 11a and 11b in FIG. It should be noted that such an abnormal portion does not occur in all the plastic substrates for optical disks in the annealing treatment by the conventional supporting method, and the friction coefficient at the contact portions 11a and 11b, the plastic substrate 11 for optical disks and the holding case. 1
2 dimensional clearance is involved and the actual incidence is 2
~ 5%.

In the conventional example disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-248345, the problem is solved, but on the other hand, a new defect that the work for carrying out the annealing treatment is extremely troublesome occurs. ing. In addition, JP-A-3
In JP-A-248345, as shown in FIG. 5, the local birefringence anomaly that occurs in the conventional annealing method is not a problem if the distance from the disk edge to the outer circumference of the recording area is 4 mm. However, with respect to such a problem, the influence on the servo signal is larger than that on the recording / reproducing signal,
Actually, 2 to 5% of the optical discs are defective as described above.

In order for optical discs to further develop in the future and to be widely accepted in the market, it is indispensable to provide them at a low price, and it is necessary to easily improve yields and countermeasures in optical disc manufacturing without much effort. is there.

In view of the above problems, the present invention provides an annealing treatment for a plastic substrate for an optical disc,
An object of the present invention is to provide a method for manufacturing a plastic substrate for an optical disc in which local birefringence abnormality is eliminated by receiving the weight of the plastic substrate for an optical disc at one point.

[0015]

That is, the present invention provides a method for producing a plastic substrate for an optical disc, in which a plastic substrate for an optical disc is injection-molded and then annealed to the plastic substrate for the optical disc. The weight of plastic substrate for optical disk is 1 when annealing the substrate.
It is a method of manufacturing a plastic substrate for an optical disk, which is characterized in that it is received at points.

According to the manufacturing method of the present invention, when the plastic substrate for an optical disk is annealed, the plastic substrate for an optical disk is supported at one point while avoiding being subjected to its own weight at two points as shown in the conventional example. As a result, a local force due to thermal expansion and frictional force does not work on the plastic substrate for an optical disk, and it is always supported only by its own weight, so that the occurrence of local birefringence abnormality can be prevented.

[0017]

EXAMPLES The present invention will be described more specifically below with reference to examples. The present invention is not limited to this.

FIGS. 1, 2 and 3 show Embodiment 1, Embodiment 2 and Embodiment 3 of the present invention, respectively. In these drawings, 1 is a plastic substrate for optical discs, 2 is a holding case for holding the plastic substrate 1 for optical discs, 3
Is a spacer for floating the optical disk plastic substrate 1 in order to avoid contact between the optical disk plastic substrate 1 and the holding case 2, and 4 is annealed when the optical disk plastic substrate 1 and the holding case 2 are turned upside down. Further, the supporting members 5 for supporting the plastic substrate for the optical disc are arranged so that the plastic substrate for the optical disc is not outside the holding case 2 when the annealing treatment is performed with the plastic substrate 1 for the optical disc and the holding case 2 lying down. A stopper that plays a role in
The bottom surface of the heating furnace wall surface or the adjacent holding case is shown.

FIG. 4 is a graph showing servo signals of an optical disc manufactured by using the optical disc plastic substrate 1 annealed by the supporting method of the present invention. FIG. 5 shows a conventional method for supporting a plastic substrate for an optical disc. FIG. 6 is a graph showing a servo signal of an optical disc manufactured by using the plastic substrate 11 which is annealed by the conventional supporting method.

Embodiment 1 The embodiment shown in FIG. 1 is a drawing that best represents the features of the present invention. FIG. 1A shows a plastic substrate 1 for an optical disk.
Side view of the case 2 held by the holding case 2, FIG.
[Fig. 3] is a sectional view taken along line AA in Fig. 1 (A).

In the annealing treatment shown in FIG. 1, when the plastic substrate for an optical disk stored in the holding case shown in FIG. 5 is put into a heating furnace (oven), it is placed on the spacer 3 already installed in the heating furnace. Holds the weight of plastic substrate 1 for optical disk by placing it on Case 2
It is possible to avoid receiving at two points on the bottom of the substrate, and receive the own weight of the plastic substrate for optical disk 1 at one point with the spacer 3 to perform the annealing treatment.

The spacer 3 may be of any type as long as it can receive the weight of the plastic substrate 1 for an optical disc at one point on the outer periphery. In this embodiment, a plate material of polycarbonate having a thickness of 10 mm is used as the bottom surface of the holding case 2. What was processed according to the opening was used.

After holding the injection-molded plastic substrate for an optical disk in the state shown in FIG. 1, it was held at a furnace temperature of 90 ° C. for 3 hours, and then annealed under annealing conditions for slow cooling. FIG. 4 shows servo signals of a radius of 61 mm of the annealed 5.25 inch optical disk. The measurement of the servo signal is a ratio of the tracking signal when the track jump signal is 100% in the actual optical disk drive device. At 4 mm from the outer circumference, the local abnormality was obviously improved as compared with the conventional servo signal of FIG. No abnormal birefringence was observed up to the outermost circumference of the plastic substrate for optical disks.

Embodiment 2 FIG. 2 shows a second embodiment of the present invention. The injection-molded optical disk plastic substrate is held in the state shown in FIG. 2, that is, the optical disk plastic substrate 1 and the holding case 2 are turned upside down, and the self-weight of the optical disk plastic substrate 1 is received at one point of the support member 4. By performing the annealing treatment, the same effect as that of the first embodiment can be obtained even in the holding case having no opening on the bottom surface.

The supporting member 4 may be of any type as long as it can receive the weight of the plastic substrate 1 for optical disc at one point when the plastic substrate 1 for optical disc and the holding case 2 are turned upside down.

Embodiment 3 FIG. 3 shows a third embodiment of the present invention. The annealing process in FIG. 3 uses the member by laying the optical disk plastic substrate 1 and the holding case 2 sideways and receiving the weight of the optical disk plastic substrate 1 at one point on the side surface of the holding case 2 and performing the annealing process. Without doing so, the same effect as that of the first embodiment can be obtained.

Reference numeral 5 in FIG. 3 denotes a stopper which serves to prevent the optical disk plastic substrate 1 from being outside the holding case 2 when the optical disk plastic substrate 1 and the holding case 2 are laid sideways. It may be the wall surface or the bottom surface of the adjacent holding case.

In all of the above three examples, a remarkable improvement in local birefringence anomaly was observed, and as a result of the test of the sample of 100 plastic substrates for optical disks obtained in each example, the local birefringence was locally improved. The effect of 0% in refractive error was confirmed.

[0029]

According to the present invention, when the plastic substrate for an optical disk is annealed, the plastic substrate for an optical disk receives its own weight at one point, thereby eliminating local birefringence abnormality of the plastic substrate for an optical disk. It is possible to obtain a plastic substrate for an optical disc with uniform birefringence.

An optical disk manufactured by using the plastic substrate for an optical disk can be an optical disk in which the recording / reproducing signal and the servo signal do not locally change.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a method for supporting a plastic substrate for an optical disc during an annealing process in the present invention.

FIG. 2 is a schematic view showing another example of a method of supporting a plastic substrate for an optical disc at the time of annealing treatment according to the present invention.

FIG. 3 is a schematic view showing another example of a method of supporting a plastic substrate for an optical disc at the time of annealing treatment according to the present invention.

FIG. 4 is a graph showing a circumferential distribution of servo signals in the outer peripheral portion of an optical disc manufactured according to the present invention.

FIG. 5 is a schematic view showing a conventional method of supporting a plastic substrate for an optical disc during annealing treatment.

FIG. 6 is a graph showing the circumferential distribution of servo signals in the outer peripheral portion of the conventional optical disc corresponding to FIG.

[Explanation of symbols]

 1, 11 Optical disk plastic substrate 2, 12 Holding case 3 Spacer 4 Support member 5 Stopper 11a, 11b Contact part

Claims (1)

[Claims] 1. A method of manufacturing a plastic substrate for an optical disc, wherein the plastic substrate for an optical disc is molded by injection molding, and then the plastic substrate for an optical disc is annealed. A method of manufacturing a plastic substrate for an optical disk, characterized in that the weight of the substrate is received at one point.