JPH0485734A - Optical disk - Google Patents

Abstract

PURPOSE:To suppress the warpage of the optical disk by providing an elastic part or flexible part which is easily deformed by centrifugal force in the inner peripheral part of a substrate. CONSTITUTION:The elastic part or flexible part which is easily deformed by centrifugal force is provided in the inner peripheral part of the synthetic resin substrate 4 of the optical disk 2 provided with a recording layer 8 on the substrate 4. The optical disk 12 is then warped when static. The elastic part or flexible part 2 is, however, deformed by the centrifugal force and the warpage is decreased if such disk is mounted to a drive and is rotated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to optical discs, and particularly to suppressing warping of discs.

[Prior Art 1] Glass, polycarbonate, epoxy, acrylic, amorphous polyolefin, and other synthetic resins are used for optical disc substrates. As the recording layer, a perpendicular magnetization type magneto-optical recording layer, a phase change type magneto-optical recording layer such as 5n-Te-3s, etc. are used. When a synthetic resin is used for the substrate, the disc warps due to the difference in thermal expansion coefficient and water absorption expansion coefficient between the substrate and the recording film. Warpage of the disk causes deterioration of tracking characteristics during driving and also leads to loss of recording power.

FIG. 5 shows a state in which a conventional single-plate optical disc 02 is mounted on a clamp 04 of a drive.

In the figure, 06 is a synthetic resin substrate such as polycarbonate, and 08 is a magneto-optical recording layer. Generally, the thermal expansion coefficient and water absorption expansion coefficient of the substrate 06 are larger than those of the magneto-optical recording layer 08, so that the disk 02 is warped due to the bimetallic effect. When the substrate 06 shrinks due to a decrease in temperature or dryness of the surrounding area, warping occurs in the opposite direction.

θ1 represents the warpage angle.

Generally, when the warpage angle θ1 exceeds 5 mRad, tracking becomes unstable, and at 7 mRad, the recording power is said to decrease by 10%. For optical disks with a diameter of 130 mm or more, the mainstream method is to bond two disks together to cancel the warpage, but for optical disks with a diameter of 90 mm, a single-plate type is the international standard, and warping cannot be suppressed by bonding. For this reason, the problem of disc warping is particularly problematic with single-temporary optical discs. In order to suppress warping due to water absorption, it has also been proposed to coat the entire disk with glass. However, glass coating complicates the disk manufacturing process and is not effective against warping due to the difference in thermal expansion coefficient between the substrate and the recording layer.

[Problem of the Invention] An object of the present invention is to suppress warping of an optical disc.

[Structure of the Invention] The optical disc of the present invention is an optical disc in which a recording layer is provided on a synthetic resin substrate, and is characterized in that an elastic portion or a flexible portion that is easily deformed by centrifugal force is provided on the inner peripheral portion of the substrate. do.

The optical disc of this invention is warped when it is at rest.

However, when this is mounted on a drive and rotated, the elastic or flexible portion deforms due to centrifugal force, reducing warpage.

The optical disc of the present invention is particularly suitable for single-plate optical discs, but is not limited thereto.

Further, the optical disk of the present invention is particularly suitable for magneto-optical disks, but it can also be used for other optical disks.

[Example] Fig. 1 shows a state in which an optical disk is used alone, and Fig. 2 shows a state in which it is installed in a drive. In the figure, 2 is an optical disk, 4
is, for example, a polycarbonate substrate with a diameter of 86 mm and a thickness of 1.2 mm. 6 is a hub with a diameter of 25mm,
It is provided at the center of the substrate 4.

8 is a magneto-optical recording layer, which is located on the inner circumference of the substrate 4 (diameter 36 mm).
It was not provided on the outside of the inner periphery with a diameter of 36 mm.

An example of manufacturing the magneto-optical recording layer 8 will be shown. On the substrate 4, an amorphous yttrium aluminum sialon layer was formed with a thickness of 920 layers and a layer of 200 layers with a thickness of 0 by magnetron sputtering.
Amorphous GdDyFe perpendicular magnetization film, 300mm thick O4 thutrium aluminum sialon film, 800mm thick 0AI
A metal layer was laminated and an ultraviolet curable resin was spin-coded to a thickness of 9 μm to form a magneto-optical recording layer 8.

Reference numeral 10 denotes a clamp portion, which uses a hub 6 to attract and hold the disk 2 to a clamp 04 of the drive. 1
Numeral 2 denotes a groove, which is used as a flexible part and is deformed by centrifugal force caused by rotation when attached to a drive, thereby reducing warping of the disk 2 during rotation. The depth of the groove 12 is preferably 0.5-1.1 mm (40-90% of the thickness of the substrate 2), more preferably 60-85% of the thickness of the substrate 2. Further, the width of the groove 12 is preferably 1 to 5 mm. Within this range, warping can be reduced while maintaining the mechanical strength of the disk 2. The groove 12 is provided in the inner peripheral portion of the substrate 4 where the magneto-optical recording layer 8 is not provided. Further, the groove 12 may be provided on the side of the hub 6, contrary to that shown in FIG.

04 is a drive clamp that holds the hub 6 with a permanent magnet or the like and rotates the disk 2.

The warping angle θ2 of the optical disc 2 of the example at rest is 7 m.
It is about Rad. However, when this is rotated, the groove 12
Due to the bending deformation caused by the centrifugal force, the disk 2 tries to become a flat plate. At this time, although the curvature of the outer portion of the groove 12 (the portion where the recording layer 8 is provided) hardly changes, the warp angle decreases from θ2 to 03 due to the deflection of the groove 12.

FIG. 3 shows an embodiment in which the clamp portion 12 is made of hard rubber 22. In this case, the hard rubber 22 serving as an elastic portion is deformed by centrifugal force to reduce warping of the disk.

FIG. 4 shows that between the clamp part 12 and the magneto-optical recording layer 8,
This is an example using an elastic part 32 made of hard rubber. In this case as well, the warpage of the disk is corrected by the deformation of the hard rubber 32 due to the centrifugal force. The elastic parts 22.32 of FIGS. 3 and 4 are connected to the substrate 4, for example with adhesive.

FIG. 6 shows the depth and width of the groove for the embodiment shown in FIG.
The relationship with the reduction angle of warpage is shown. The reduction angle of warpage is the warpage angle θ2 when it is at rest and the warpage angle θ when it is rotating.

The rotation speed of the disk 2 was set to 1800 rpm using the difference between the two. The warpage angle decreases with the width and depth of the groove 12 due to centrifugal force.

FIG. 7 shows the relationship between the rotational speed and the angle of reduction in warpage of an optical disc 2 in which the width of the groove 12 is 3 mm and the depth is 0.8 mm.

The warpage angle decreases with the rotation speed.

FIG. 8 shows the relationship between the rotational speed of the substrate and the angle of reduction in warpage for the embodiments shown in FIGS. 3 and 4. The solid line shows the characteristics of Example 3 in FIG. 4, and the broken line shows the characteristics of Example 2 in FIG. In addition, the diameter of the hard rubber 22 in Fig. 3 is 30 mm,
The hard rubber 32 in the figure is an annular piece with a radial width of 3 mm.

Next, the inventor conducted a strength test on the embodiments shown in FIGS. 7 and 8. The optical disc of each example was assembled into a cartridge case, mounted on an optical disc drive, and continuously rotated at 3600 rpm for 240 hours. No abnormality occurred in any of the Examples. Furthermore, the optical disks of each example were assembled into a cartridge case, and 10 disks were allowed to fall freely 50 times from a height of 760 nm onto a concrete floor surface coated with vinyl chloride with a thickness of 2 mm.
Impact resistance was investigated. Originally, optical discs are susceptible to such tests because they may come into contact with the open end surface of the cartridge case and be damaged. This includes the groove 12 and the elastic part 22.3.
This can occur even if 2 is not provided. Therefore, a hemispherical protrusion with a height of 0.5 mm was provided inside the opening end surface of the cartridge case at a position relative to the outermost periphery of the optical disk to prevent the disk surface from touching the opening end surface. No scratches or abnormalities due to free fall were observed in any of the examples.

In the embodiment shown in FIG. 1, the inventor set the depth range of the groove 12 to 0.5 to 1.5 mm. Omm, the width of the groove 12 ranges from 1 to 5 mm
Continuous rotation for 240 hours at 3600 rpm, 76
Tests were conducted for 50 free falls from a height of 0 mm. No abnormalities were observed in either case. From this,
It can be said that the optical disc of the example has sufficient strength.

This invention is particularly effective for magneto-optical disks, but is also effective for any optical disk that has a recording layer having a coefficient of thermal expansion or a coefficient of water absorption expansion that is different from that of the substrate.

[Effect of the invention] In this invention, the deformation of the elastic part and the flexible part due to centrifugal force causes
To reduce warpage of an optical disc during use, facilitate tracking, and suppress loss of recording power.

[Brief explanation of the drawing]

1 and 2 are end views of the embodiment, FIGS. 3 and 4 are end views of other embodiments, and FIG. 5 is an end view of the conventional example.
6 and 7 are characteristic diagrams of the embodiment of FIG. 1. 8th
The figure is a characteristic diagram of the embodiment shown in FIGS. 3 and 4. In the figure, 2 optical disk, 4 synthetic resin substrate, 8 magneto-optical recording layer, 12 groove, 22.32 hard rubber, 01 to θ1 warp angle. Figure 8

Claims (1)

[Claims] (1) An optical disc having a recording layer provided on a synthetic resin substrate, characterized in that an elastic part or a flexible part that is easily deformed by centrifugal force is provided on the inner circumference of the substrate.