JP4098592B2 - Optical recording medium, molding die for optical recording medium, and substrate for optical recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bonded optical recording medium, an optical recording medium manufacturing apparatus, and an optical recording medium substrate, and in particular, bonded with improved substrate warpage (R-Tilt) and inner quality. Type optical recording medium.
[0002]
[Prior art]
In recent years, optical recording media have attracted attention as large-capacity, high-speed memory media. For example, read-only optical discs (CD, DVD, CD-ROM, etc.), recording / playback optical discs (write-once type), recording, playback, and erasing. A rewritable optical disc (rewritable type) and the like are known.
[0003]
In general, a resin substrate (polycarbonate resin, acrylic resin, or the like) is used as a substrate constituting these optical recording media. Such a substrate is usually formed by an injection molding method or an injection compression molding method from the viewpoint of productivity.
Specifically, a stamper made of an annular thin metal plate is disposed in a cavity formed between a fixed mold and a movable mold, and a molten resin is injected and injected into the cavity. Disk substrates on which (pits), laser guide grooves and the like are transferred are manufactured.
[0004]
The optical disk substrate molded as described above has a flat shape immediately after molding. However, when a recording layer is formed on the substrate or a protective layer is formed on the substrate in the subsequent process, the film is formed. The substrate is warped due to stress relaxation or surface film stress based on thermal changes during formation.
[0005]
In particular, in the case of a thin substrate having a thickness of 1 mm or less, since the rigidity of the substrate is small, the effects of stress relaxation and surface film stress due to thermal changes during film formation increase, and warping increases. In addition, since the fluidity of the resin during molding is poor, there is a problem that the birefringence of the substrate is deteriorated.
[0006]
Such warpage of the substrate causes occurrence of surface vibration or the like in an optical disc that rotates at a high speed in order to perform high-density recording, resulting in malfunction.
In order to solve such a problem, an attempt has been proposed to increase the thickness by increasing the thickness of the peripheral portion (inner peripheral side) of the central hole of the substrate to reduce the vibration during disk rotation. (See, for example, Patent Document 1 below).
[0007]
However, the above method has a problem that optical characteristics, particularly birefringence, are deteriorated because the substrate is thick, and an excellent effect on thermal deformation cannot be obtained.
[0008]
There has also been proposed a method for reducing the warpage of a substrate to be molded by controlling the temperatures of a molding die and a stationary die during molding (see, for example, Patent Document 2 below). ).
However, only by controlling the temperature of such a molding machine, the control range of the warpage of the substrate is limited, and it is difficult to stably and accurately control the warpage.
[0009]
Further, a substrate in which a thin portion of a specific range is provided in a signal non-formation recording area near the center hole of the substrate and another substrate in which a thick portion is provided at a position corresponding to the thin portion are each thin-walled. There has also been a proposal to control the warp of the entire disk as a configuration in which the portion and the thick portion face each other (see, for example, Patent Document 3 below).
[0010]
However, according to the above method, as shown in FIG. 1, the inner peripheral portion (near the center hole 11 h) of the thin substrate 11 is warped and deformed as indicated by the broken line in the figure, and thus deformed. When the substrates are bonded to each other as shown in FIG. 2, the mutual bending occurs, so that a gap is generated in the vicinity of the center hole of the optical disc 100 as shown in FIG. Arise.
[0011]
[Patent Document 1]
JP-A-60-261042 [Patent Document 2]
JP-A-1-273244 [Patent Document 3]
Japanese Patent Laid-Open No. 10-40582
[Problems to be solved by the invention]
Accordingly, as a result of intensive studies on a substrate for a bonded optical recording medium, the present inventor has increased the flatness (R-Tilt) of the substrate, and has excellent optical characteristics (birefringence) and inner quality. An optical recording medium, an apparatus for manufacturing the optical recording medium, and a substrate for the optical recording medium are provided.
[0013]
[Means for Solving the Problems]
The optical recording medium of the present invention is an optical recording medium having a structure in which a disk substrate having a center hole is opposed to and bonded to a signal non-forming region in the vicinity of the center hole of the substrate over the entire circumference. A convex portion and a concave portion with respect to the surface are formed, the convex portion is formed along the outer periphery of the central hole, and the concave portion is formed adjacent to the outer peripheral side with respect to the convex portion. It is characterized by that.
[0016]
According to the present invention, high flatness of the substrate (R-Tilt), and the optical properties (birefringence), and excellent optical recording medium body inner quality is provided.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
FIG. 4 shows a schematic sectional view of the optical recording medium of the present invention.
In the optical recording medium 10, the first substrate 1 on which the predetermined signal 3 is formed and the second substrate 2 having the same shape as the first substrate and on which no signal is formed have the signal surface on the inside. Thus, the structure is bonded together.
Information recording and / or reproduction with respect to the optical recording medium 10 is performed, for example, by irradiating a laser beam having a predetermined wavelength from the first substrate 1 side.
[0018]
As shown in FIG. 5, the first substrate 1 and the second substrate 2 constituting the optical recording medium 10 of the present invention are disk-shaped having a center hole 4, and are light transmissive such as polycarbonate. It is produced by injecting resin into an injection mold.
The substrate 1 (2) is a signal non-formation region 6 of the optical recording medium finally obtained, and a convex portion 20 and a concave portion 30 are formed over the entire circumference in the vicinity of the center hole 4 of the substrate. .
[0019]
Here, the height a based on the surface 5f of the signal forming region 5 of the convex portion 20 of the substrate is 0 to 40 μm, and the depth b based on the surface 5f of the signal forming region 5 of the concave portion 30 is It shall be 5-20 micrometers.
[0020]
For example, in the case of a conventional DVD + RW / + R book standard substrate, if the thickness of one substrate is 600 ± 20 μm, the thickness of the concave portion 30 is 580 ± 20 μm, and the thickness of the convex portion 20 is 600 ± 20 μm. It is preferable to form.
If the concave portion 30 is formed wide, the birefringence of the optical disk is reduced. However, if the concave portion 30 is formed too wide, the deformation of the substrate in the inner peripheral portion is increased and the warpage (R-Tilt) of the substrate is deteriorated. Is preferably formed in a region having a diameter of 21 ± 1.0 mm from the center, and the concave portion 30 is formed in a region having a diameter of 36 ± 2 mm from the center.
[0021]
Next, FIG. 6 shows a schematic diagram of an optical recording medium manufacturing apparatus 50, and the manufacturing process of the substrate 1 (2) and the optical recording medium 10 will be described with reference to this.
The manufacturing apparatus 50 includes a movable mold 52 made of, for example, a stainless steel metal that constitutes a cavity 51 for molding a substrate, and a fixed mold 53 on which a stamper 54 for transferring a signal to the substrate surface is installed. It is comprised by.
The fixed mold 53 is provided with a sprue bush 55 to which a gate for sending out a light-transmitting resin, for example, polycarbonate, which is melted in the cavity 51 is connected.
[0022]
In the movable mold 52, a cut punch 56 for finally punching and forming the center hole 4 of the substrate at the center is arranged so as to project and thrust.
[0023]
A stamper 54 for transferring predetermined fine irregularities constituting a signal when the first substrate 1 is formed is held on the fixed-side mold 53 by a stamper pressing means 57 in a vacuum chuck manner.
The wedge-shaped small protrusions 70 of the stamper pressing means 57 have a height of 0 to 200 μm, preferably 0 to 100 μm. If the concave portion formed by the small protrusions 70 is shallow when the substrate is molded, the deformation of the substrate is reduced. However, if it is 0 μm, the substrate 1 (2) is burred, resulting in poor bonding.
[0024]
An area corresponding to the non-signal forming area near the center hole of the substrate in the movable mold 52 of the optical recording medium manufacturing apparatus 50 has a recess 58 with respect to the surface corresponding to the signal forming area. And a convex portion 59 are formed.
The concave portion 58 is a portion corresponding to the convex portion 20 of the substrate shown in FIG. 5, and as shown in the partial enlarged view of the movable side mold 52 in FIG. 7, the depth c is on the surface corresponding to the signal forming region. On the other hand, the convex portion 59 is a portion corresponding to the concave portion 30 of the substrate, and the height d is 5 to 20 μm with respect to the surface corresponding to the signal forming region.
[0025]
A method for forming the substrate 1 (2) using the optical recording medium manufacturing apparatus 50 will be described.
First, the movable mold 52 and the fixed mold 53 are matched to form a cavity 51 between them. In this state, a light transmitting resin such as molten polycarbonate is fed into a gate (not shown). The light-transmitting resin poured into the cavity 51 is
After a predetermined signal is transferred and formed by the stamper 54, the temperature is lowered and cured. Next, the cut punch 56 is protruded, and the center hole 4 of the substrate 1 (2) is punched out.
[0026]
Through the steps as described above, the convex portion 20 and the concave portion 30 are formed over the entire circumference in the vicinity of the center hole of the substrate 1 (2).
[0027]
Thereafter, a predetermined material layer is formed on the signal surface transferred to the substrate, and a photo-curing resin is applied to at least one of the signal surfaces of the first substrate 1 and the second substrate 2. As shown in the figure, the signal surface is aligned and pressed, and, for example, ultraviolet rays are irradiated from the back surface of the first substrate 1 to cure the ultraviolet curable resin, and finally the target bonded light. The recording medium 10 is produced.
[0028]
As described above, the convex portion 20 thicker than the signal forming region 5 is formed in the vicinity of the center hole 4 of the disk-shaped substrate, so that the substrate 1 (2) has a warp which has been a problem in the past. It was confirmed that generation was effectively reduced. Thereby, in the case where the optical recording medium 10 is manufactured by bonding two substrates, an excellent flatness can be realized, and in particular, a multilayer in which the thickness of one substrate is reduced and the amount of information is increased. The quality of the optical recording medium can be improved.
[0029]
In addition, by forming the concave portion 30 thinner than the signal forming region 5, it was possible to satisfactorily ensure optical characteristics such as birefringence.
[0030]
Note that the optical recording medium substrate 1 (2) of the present invention has the above-described configuration in which the protrusions 20 are formed in the signal non-forming region near the center hole on the signal forming surface side as shown in FIG. As in the example, it was confirmed that the occurrence of warpage, which was a problem in the past, was effectively reduced.
The height of the convex portion 20 is 0 to 40 μm, preferably 0 to 20 μm, based on the surface of the signal forming region 5. The depth of the recess 30 is 5 to 20 μm with reference to the surface of the signal forming region 5.
[0031]
【The invention's effect】
According to the present invention, an optical recording medium having high surface accuracy, that is, flatness (R-Tilt) of a substrate constituting a bonded optical disc, and excellent optical characteristics (birefringence) and inner quality is obtained. It was.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a conventional optical disk substrate.
FIG. 2 is a schematic sectional view showing a state in which a conventional optical disk substrate is bonded.
FIG. 3 is a schematic plan view showing a state in which a conventional optical disk substrate is bonded.
FIG. 4 is a schematic cross-sectional view of an optical recording medium of the present invention.
FIG. 5 is a schematic sectional view of a substrate constituting the optical recording medium of the present invention.
FIG. 6 shows a schematic view of an optical recording medium manufacturing apparatus of the present invention and a substrate manufacturing process.
FIG. 7 is a schematic view of the main part of the optical recording medium manufacturing apparatus of the present invention.
FIG. 8 shows a schematic diagram of another example of the optical recording medium manufacturing apparatus of the present invention and a substrate.
DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 2nd board | substrate 3 Signal 4 Center hole 5 Signal formation area 5f Signal formation area surface 6 Signal non-formation area 10 Optical recording medium 11 Substrate 11h Center hole 20 Convex part 30 Concave part 50 Optical recording medium manufacturing apparatus 51 Cavity 52 Movable mold 53 Fixed mold 54 Stamper 55 Sprue bush 56 Cut punch 57 Stamper pressing means 58 Concave part 59 Convex part 70 Small protrusion

Claims (1)

In an optical recording medium having a structure in which a disk substrate having a central hole is bonded to face each other,
The signal non-formation region near the center hole of the substrate is formed with a convex portion and a concave portion with the signal forming region surface as a reference over the entire circumference .
The convex portion is formed along the outer periphery of the center hole,
The optical recording medium , wherein the concave portion is formed adjacent to the convex portion on the outer peripheral side .

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