JPH097227A - Composite optical disc structure - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a composite optical disc structure having less warpage and deformation and suitable for high density recording. [Structure] A pair of single-sided optical discs in which a data recording area 3 formed on one surface of a plastic disk 1 having a central hole is provided with an aluminum reflection film 4 and a protection film 6 is provided on the aluminum reflection film 4 are provided. The present invention relates to a composite optical disc in which these protective films 6 are made to face each other and are integrally bonded. In this composite optical disk, the bonding surface of the single-sided optical disk is the surface 6a of the protective film 6 and the protective film 6
And a transparent disc base surface 1c between the center hole and the center hole. Then, a step portion D having a depth step d that makes the transparent disk substrate surface 1c and the protective film surface 6a flush with each other is provided on each of the pair of single-sided optical disks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite optical disc made by laminating two single-sided discs such as an optical video disc.

[0002]

2. Description of the Related Art As an optical disc for reading recorded information by using a laser beam or the like, there is a disc made by laminating two disc substrates. Examples thereof include laser disks and DVDs. As a representative of these, a conventional laser disk will be described below.

First, in the conventional laser disk manufacturing method, a mold (called a stamper) in which pits to be recorded information are formed in advance is attached to a resin molding machine such as an injection molding machine, and polycarbonate or A transparent plastic substrate (single-sided disc), which is a transparent plastic disc with pits transferred, is created by injection-molding or pressure-molding a transparent plastic resin such as acrylic (base molding process). The actual plastic disk (single-sided disk) produced in this substrate molding process has a concave processed groove (hereinafter, referred to as a stamper clamp portion for fixing the stamper to the resin molding machine).
It is called a stamper clamp groove) and remains in a ring shape.

Next, a metal such as aluminum is attached to the pit surface of the disk by a sputtering method or a vacuum deposition method to form a reflection film (reflection film forming step). Then, a hot-melt type protective film is applied to the surface of the reflective film by a roll coater or the like, and the protective film (5 to 10 μm) for preventing scratches and corrosion is formed by irradiating this with an ultraviolet ray (protective film). Coating process).

As described above, A to be bonded
After making a pair of single-sided discs for side B and side B separately, apply a thermoplastic adhesive called hot melt to the bonding surface of each single-sided disc with a roll coater (coating thickness 15 to 30 μm / both sides). ) (Adhesive applying step).

Then, the pair of single-sided disks coated with the adhesive are bonded together by a method as shown in FIG. 7 (bonding step). That is, the adhesive surfaces of the pair of single-sided disks 10a and 10b coated with the adhesive are abutted against each other and placed on the lower pressure table 51 composed of a flat press surface, and then the upper pressure table 52 is pressed by the pressure cylinder 53. Is lowered and the pair of single-sided disks 10a and 10b are press-bonded with the flat press surface to bond them to one laser disk.

Recently, a small type called DVD (diameter 12c
A dual-sided recording type digital video disc capable of high-density recording with a disc base thickness of 0.6 mm on one side) is being developed. This DVD is manufactured by the same method as described above except that the ultraviolet curable resin is applied to the surface of the reflective film by a spinner or the like in the protective film applying step.

Since such a composite optical disc is a high-density recording disc, it is required to reduce warpage and deformation and make it as flat as possible. That is, not only making the disk substrates themselves flat before bonding, but also a highly accurate bonding technique in the bonding process is required.

The single-sided disk constituting the composite optical disk has a central hole as shown in, for example, the plan view of the single-sided disk of FIG. 4A and the cross-sectional view of the single-sided disk after the adhesive application step of FIG. 4B. A stamper clamp groove 2 around 1a, a disc clamp area 2c between the center hole 1a and the stamper clamp groove 2, and a data recording area 3 which is an information recording area around the stamper clamp groove 2
And a no-signal area 5 around the data recording area 3.

A protective film 6 is attached on the reflective film 4 in order to maintain the reliability (life) of the reflective film 4. That is, the protective film 6 is attached to prevent a thin oxide film from being formed on the surface of the reflective film 4 to lose the gloss. To attach the protective film 6, a method of coating an ultraviolet curable resin or the like by a spin coating method is used.

However, in order to apply the protective film 6 on the entire recording surface of the plastic disk 1, if the protective film 6 is applied around the disk center hole 1a having a large concave portion called the stamper clamp groove 2 on the surface, 5 (a), the air 6a is accumulated in the protective film 6 in the recessed portion, and as shown in FIG.
b, and coating unevenness occurs.

Therefore, as shown in FIG. 5 (c), in order to avoid coating unevenness due to the stamper clamp groove 2, a few millimeters before the data recording area 3 having no large unevenness, that is, the data recording area 3 is formed. The protective film 6 was applied from between the stamper clamp groove 2 and the outer circumference of the disk.

In such a coating method, the portion without the protective film 6, that is, the inner portion between the data recording area 3 and the stamper clamp groove 2 and the outer portion with the protective film 6 are around the central hole 1a. And the thickness t of the protective film 6
The difference in height caused by the difference occurs as a step difference of several micrometers to several tens of micrometers.

In this state, when the adhesive 7 is applied to the disk by means of a roll coater or the like, the thickness of the coating film of the adhesive 7 is applied evenly over the entire surface of the disk.
The adhesive 7 having a uniform thickness rides on the step d, so that the adhesive 7 is pasted with the step d formed by the protective film 6 remaining.

[0015]

However, in the above-mentioned conventional composite optical disc, a gap S is formed in the portion bonded together with the step d formed by the protective film 6 remaining, as shown in FIG. 6 (a). If the bonding accuracy is reduced,
As shown in (b), it is difficult to stably manufacture a highly accurate bonded disc with less warpage or deformation because one disc substrate deforms H in a manner that follows the other disc substrate. There was a problem.

In general, in the case of a small-sized bonded disc having a small diameter, most of the flat disc portion from the center hole 1a of the disc to the information recording start area is used as the clamp zone of the player. This flat portion will function as a reference surface for the optical system when the disc is placed on the turntable of the player and held by the clamper.

Particularly, in a small-sized and high-density recording type disc such as a DVD, an optical system having a large numerical aperture (NA) is used, so that the depth of focus is small. Therefore, even if a slight warp or deformation occurs, reproduction is performed. This will significantly degrade the signal. There is a problem that the load of the pickup servo that tries to prevent this deterioration by the pickup servo becomes too large. Therefore, since the warp or deformation of the disk in the clamp zone directly affects the reference surface for the optical system, it is desired to flatten the disk with high accuracy.

Therefore, an object of the present invention is to provide a composite optical disk structure which is less warped or deformed and is suitable for high density recording.

[0019]

In order to achieve the above object, in a composite optical disk structure of the present invention, a reflective film is provided in an information recording area formed on one surface of an optical disk substrate having a central hole. In a composite optical disc in which a pair of single-sided optical discs each having a protective film provided on a reflection film are adhered and integrated by making these protective films face each other, the bonding surface of the single-sided optical disc is the protective film surface and the protective film. A step of a depth composed of a translucent disc substrate surface between the film and the central hole, and making the translucent disc substrate surface and the protective film surface flush between the protective film and the central hole. But,
It is characterized in that each of the single-sided optical disks is provided.

[0020]

In the composite optical disk structure of the present invention having the above-mentioned structure, the bonding surface of the composite optical disk is provided with a step portion having a depth such that the surface of the protective film is flush with the bonding surface without the protective film. Therefore, after applying the protective film on the reflective film, the surface of the protective film and the bonding surface on which the protective film is not applied are flush with each other. In addition, the compressive force is applied uniformly over almost the entire surface of the single-sided disk, and there is no gap between the bonding surfaces or deformation.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk structure according to the present invention will be described below with reference to the accompanying drawings. FIG.
(A) is a cross-sectional view of a plastic disk that is a part of a composite optical disk according to one embodiment, (b) is a cross-sectional view of a protective disk formed on the plastic disk of (a), and (c) is (b). FIG. 3 is a cross-sectional view in which an adhesive is formed on the plastic disc of FIG. FIG. 2 is a cross-sectional view of a mold used for molding a plastic disc.

The mold 20 is mainly formed by attaching a stamper 21 having a data recording area transfer portion 23 for transferring pits to the data recording area 3 of the plastic disk 1 and attaching the stamper 21. A first mold part 22 and a second mold part 25 that cooperates with the first mold part 22 to form the mold 20 and mainly mold the adhesive application surface are provided. Then, the stamper 21 is attached to the second mold part 25 in the first mold part 2
A stamper clamp 26, which is sandwiched and held between the two, projects, and the stamper clamp 26 forms a stamper clamp groove 2 in the plastic disk 1.

Further, a depth corresponding to the thickness t of the protective film 6 is provided between the surface of the stamper 21 which is the molding surface 24 of the first mold part 22 and the molding surface 27 of the second mold part 25. Step T is formed. Therefore, as shown in FIG. 1A, the molded plastic disk 1 has a protective film 6 with an outer upper surface 1b and an inner upper surface 1c of the stamper clamp groove 2.
A step d having a depth corresponding to the thickness of is formed. Further, the reflection film 4 is formed on the pit portion transferred to the outer upper surface 1b of the stamper clamp groove 2 by the reflection film forming step. As the reflective film 4, for example, a metal film of aluminum, nickel, gold or the like or a dielectric film of silicon nitride, silicon oxide or the like can be used.

A protective film 6 is formed on the reflective film 4 as shown in FIG. The protective film 6 is formed by coating an ultraviolet curable resin or the like by a spin coating method. Here, as described above, since the surface 1b on which the protective film 6 is formed has the step portion D formed in advance lower than the surface 1c on which the protective film 6 is not formed by the step d, the protective film 6 is formed.
The adhesive application surface 6a on the upper surface and the adhesive application surface 1c on the inner side of the stamper clamp groove 2 of the plastic disc 1 are flush with each other. The protective film surface 6a and the plastic disk surface 1c between the protective film 6 and the center hole 1a form a bonding surface.

As shown in FIG. 1C, the adhesive 7 is applied to the thus prepared single-sided disk by a roll coater. The adhesive 7 is formed on the upper surface of the protective film 6,
It is applied to the upper surface of the plastic disk 1 without the protective film 6 in a uniform thickness.

FIG. 3 is a sectional view showing before and after the bonding of the disks. As shown in the upper diagram of FIG. 3, the above-mentioned single-sided disks are arranged with their protective film 6 sides facing each other. When pressure is applied in this state, the surface of the protective film 6 which is the bonding surface and the bonding surface of the plastic disc 1 without the protective film 6 are flush with each other at the same height. It is uniformly transmitted to almost the entire surface of the sheet, and it is possible to prevent warpage and deformation after bonding.

Since the prevention of the warp and the deformation can be achieved only by providing a step having a depth equal to the thickness of the protective film on the disc side, it is sufficient to change the shape of the mold and other Conventional manufacturing equipment can be used.

In the above embodiment, the step is formed inside and outside the stamper clamp groove, and the protective film is attached from the outer edge of the stamper clamp groove. However, for example, the outer edge of the stamper clamp groove and the inner edge of the data recording area are formed. A step d may be provided on the upper surface 1b between and, and the adhesion start position of the protective film may be the step portion.

[0029]

As is apparent from the above description, according to the composite optical disk structure of the present invention, the reflective film is provided in the information recording area formed on one surface of the optical disk substrate having the central hole. In a composite optical disc in which a pair of single-sided optical discs provided with a protective film thereon are adhered and integrated by making these protective films face each other, the bonding surface of the single-sided optical disc has the protective film surface and the protective film. It is composed of a transparent disk base surface between the central hole and a transparent disk base surface between the protective film and the central hole, and a step portion having a depth that makes the protective film surface flush with each other, Since it is provided on each of the single-sided optical disks, there is no gap or deformation between the bonding surfaces when bonding the pair of optical disks during manufacturing, and it is suitable for high density recording. It has the effect of providing a disk.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part showing a single-sided disc of a composite optical disc according to an embodiment of the present invention in the order of manufacturing steps,
(A) is a cross-sectional view of a plastic disk that is a part of a composite optical disk according to one embodiment, (b) is a cross-sectional view of a protective disk formed on the plastic disk of (a), and (c) is (b). FIG. 3 is a cross-sectional view in which an adhesive is formed on the plastic disc of FIG.

FIG. 2 is an enlarged cross-sectional view of a main part of a mold used for molding a plastic disc of a composite optical disc according to an embodiment.

FIG. 3 is an enlarged sectional view of an essential part before and after the bonding of the composite optical disc in one example.

FIG. 4A is a plan view of a single-sided disk, and FIG. 4B is a cross-sectional view of the single-sided disk after the adhesive application process is completed.

5A and 5B are enlarged cross-sectional views of a main part for explaining a coating state of a conventional protective film, FIG. 5A is a diagram showing air pockets in the protective film, and FIG. It is a figure which shows, (c) is a figure which shows the level | step difference of a protective film.

FIG. 6 is an enlarged cross-sectional view of a main part showing a pasted state of a conventional composite optical disc, (a) showing a state in which a gap is formed between the pasted discs, and (b) showing the pasted discs. It is a figure which shows the state which the disk deform | transformed.

FIG. 7 is a diagram for explaining a bonding step.

[Explanation of symbols]

 1 plastic disk (translucent disk substrate) 1a center hole 1c bonding surface 3 information recording area (data recording area) 4 reflective film 6 protective film 6a bonding surface 7 adhesive D step d step

Claims (1)

[Claims] 1. A pair of single-sided optical discs in which a reflective film is provided in an information recording area formed on one surface of an optical disc substrate having a central hole, and a protective film is provided on the reflective film. In the composite optical disc in which the two are opposed to each other and integrally bonded, the bonding surface of the single-sided optical disc is composed of the protective film surface and a translucent disc substrate surface between the protective film and the central hole. A composite optical disc structure characterized in that each of the single-sided optical discs is provided with a step portion having a depth such that the surface of the transparent disc substrate between the protective film and the center hole is flush with the surface of the protective film. .