Method of producing information recording medium, production...

Details Method of producing information recording medium, production... Method of producing information recording medium, production...

2002-10-29

2004-07-20

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C430S270110, C264S328140, C425S547000

Reexamination Certificate

active

06764737

ABSTRACT:

This application claims priority to Japanese Patent Application Number JP2001-333328 filed Oct. 30, 2001, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing an information recording medium, a production apparatus for the information recording medium, and an information recording medium produced by the production method.
2. Description of the Related Art
Recently, in the field of information recording, research on optical information recording systems is being conducted everywhere.
Optical information recording systems have numerous advantages such as the capability of non-contact recording and reproduction and the ability to handle various forms of memories such as read only types, write-once types, and rewritable types. Broad applications from industrial use to consumer use are being considered as systems enabling realization of inexpensive and large size files.
Increased capacity of optical recording media (hereinafter also referred to “optical disks”) for the above various types of optical information recording systems has been achieved mainly by shortening the wavelength of the laser light serving as the light source used in optical information recording systems and adopting objective lenses having high numerical apertures to reduce the spot size on a focal plane.
For example, in a CD (compact disk), the thickness of the disk substrate forming a light transmitting layer is about 1.2 mm, the wavelength of the laser light is 780 nm, the numerical aperture (NA) of the objective lens is 0.45, and the capacity is 650 MB, while in a DVD-ROM (digital versatile disk read-only memory), the thickness of the disk substrate forming a light transmitting layer is about 0.6 mm, the wavelength of the laser light is 650 nm, the NA is 0.6, and the capacity is 4.7 GB. A DVD is for example obtained by bonding together two disk substrate of about 0.6 mm thickness to form a disk having a thickness of 1.2 mm.
Furthermore, in the next generation optical disk systems, it is possible to increase the capacity to 22 GB or more by using an optical disk comprising an optical recording layer over which is formed a protection layer, that is, a light transmitting coating layer, reduced in thickness to about 0.1 mm, and making the laser light wavelength 450 nm or less and the NA 0.78 or greater.
FIG. 1A
is a schematic perspective view of an optical disk for the above next generation optical disk system.
An optical disk DC forms an approximately disk shape with a center hole CH formed at a center portion thereof and is driven to rotate in a drive direction DR.
When recording or reproducing information, light LT such as a laser light of a blue to blue-violet color region is focused on the optical recording film in the optical disk DC by an objective lens OL having a numerical aperture of for example 0.8 or greater.
FIG. 1B
is a schematic sectional view of the above optical disk.
Grooves for dividing track regions are provided in one surface of a disk substrate
30
having a thickness of about 1.1 mm formed of polycarbonate resin etc. An optical recording layer
31
comprised of for example a reflection film, a dielectric film, a recording film, another dielectric film, etc. stacked in that order is formed on this surface. The layer configuration and the number of layers of the optical recording layer
31
differ according to the type of recording material and the design.
The above recording film is for example a phase change type recording film, a magneto-optical recording film, or a recording film containing an organic dye.
Further, a light transmitting protection layer (coating layer)
32
having a film thickness of 0.1 mm comprised of for example an adhesive layer and a polymer film is formed on the optical recording layer
31
.
When recording on or reproducing from the above optical disk, light LT such as laser light is focused by the objective lens OL to the optical recording layer
31
from the protection layer
32
side.
At the time of reproduction from the optical disk, returned light reflected at the optical recording layer
31
is received by a light-receiving element, a predetermined signal is generated by a signal processing circuit, and a reproduction signal is extracted.
A production method of the above optical disk shown in
FIGS. 1A and 1B
will be explained next.
First, for example, a disk substrate
30
comprised of for example polycarbonate resin is formed by injection molding using injection mold described below having a stamper for disk substrate which has a relief pattern for optical recording layer.
Next, an optical recording layer
31
is formed on the disk substrate.
Next, polycarbonate film is bonded to the optical recording layer
31
by adhesive layer to form the light transmitting protection layer (coating layer)
32
of 0.1 mm thickness.
The optical disk shown in
FIGS. 1A and 1B
can thus be formed.
FIG. 2
is a schematic view of the configuration of an injection molding mold for forming a disk substrate according to a conventional method.
An outer circumferential ring
61
, a fixed side mirror
62
, a fixed side temperature adjusting circuit
63
, a stamper
64
, and a sprue
65
are provided as fixed side mold parts at a fixed side attachment plate FT. On the other hand, a movable side mirror
67
, a center pin
68
, and a gate cut punch
69
are provided as movable side mold parts in movable side attachment plate MT. Resin is injected into a cavity
66
composed of the above parts to form a disk substrate.
However, in information recording medium including CDs, DVDs, and other optical disks, including next generation optical disks of the above configuration, and further hard disks, the disk substrates are generally formed by injection molding. In this case, however, a mold for the injection molding is configured by a plurality of parts. Clearance is inevitable between the parts. Therefore, burrs occur in the disk substrate formed.
Further, it is difficult to achieve a uniform surface precision of the parts or stamper. If step differences occur between the parts, the steps will also end up being transferred to the disk substrate formed.
Further, as shown in
FIG. 3A
, a bulge RD easily occurs at the outer circumferential ends of a disk substrate
30
formed by injection molding. In this case, the optical recording layer
31
is formed along the surface of the bulge RD.
If for example the protection layer film is bonded at the upper layer thereof by an adhesive layer to form the protection layer
32
, as shown in
FIG. 3B
, an air bubble layer AL ends up occurring between the protection layer
32
and the optical recording layer
31
, so use of the outer circumferential region RG becomes difficult.
Even when coating ultraviolet curing resin or other protection layer on the optical recording layer by spin coating, etc., the bulge of the outer circumferential end region is further accentuated and therefore it becomes impossible to use this region.
By adjusting the pressure for injecting the molten resin so as to suppress the occurrence of the bulge in the injection molding of the disk substrate, a recess where part of the substrate becomes thinner easily occurs and hence a new problem arises.
Disk substrates for optical disks were produced by the above injection molding and were examined for planarity.
Here, the disk substrates formed had the shape shown in
FIGS. 4A
to
4
C, where
FIG. 4A
is a plan view of a signal surface,
FIG. 4B
is a side view thereof, and
FIG. 4C
is a plan view of a read surface.
In the figure, the positions of an innermost diameter (A), a sprue bushing (B), an air groove (C), a stamper holder (D), a signal portion (stamper) (E), an ejector (F), an ejector sleeve guide (G), a stacking rib (H), a mirror (I), and an outer circumferential end (Z) are shown.
FIG. 5A
is a view showing the measurement results of the planarity in the vicinity of an outer circumferential end of a signal surface of the disk substrate according to the conventional method. T

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