JPH07272324A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain an optical disk which improves transferability with easy constitution and improves signal characteristics by molding a replica substrate by such a stamper that forms signal marks of a prescribed track pitch, etc., to a projecting shape. CONSTITUTION:This optical disk 1 is constituted of the single replica substrate 2 or by sticking these substrates. The signal marks 4 which are information pits are formed by means of the stamper on the information region 3 of the substrate 2. The marks 4 are formed to the projecting shape and the track pitch P is <=2 times the width W and is specified to P<=2W. The min. adjacent distance between the marks 4 is set smaller than the width W. The signal marks are formed to the projecting shape, by which the transferability of the signal marks is easily enhanced as compared with the case of the pit shape. The high-density optical disk having the good signal characteristics is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc capable of recording and reproducing information, and more particularly to an optical disc capable of obtaining good tracking and information signals.

[0002]

2. Description of the Related Art There are three types of optical discs: a read-only type, an additional recording type, and a rewritable type.

Among them, the reproduction-only type includes a CD in which audio information is recorded, a video disk in which image information is recorded, and a CD-ROM in which character information is recorded. In order to reproduce a large amount of recorded information on these optical discs, signal marks serving as information bits are formed on the disc surface.

Further, the additional recording type and rewritable type optical discs have been put to practical use for document files and video files. There are two tracking methods for these optical discs: a continuous groove servo method and a sample servo method. The continuous servo method is a method of performing tracking with a guide groove, and the sample servo method is to provide a signal mark at some places of the track and perform the tracking while detecting the signal mark. Then, information is recorded on the recording film formed on the surface of the disk by the laser light of high power, and the information is reproduced by the laser light of weak power.

A conventional optical disk 8 is shown in FIGS.
An outline of (CD or CD-ROM etc.) is shown. Figure 4
As shown in (b), a signal mark 10 serving as an information bit is formed in a pit shape in the information area 3 of the replica substrate 9 and a reflective film 11 is vapor-deposited on the signal mark 10 to reproduce the information signal. . The optical depth of the pit of the signal mark 10 is λ / 4 (λ is the reading laser wavelength).

The substrate forming the optical disk 8 is a plastic replica substrate 9 formed by injection molding, and is molded by the optical disk substrate molding die 12 shown in FIG. As shown in the figure, the die 12 is provided with a stamper 13, and by casting molten resin into the cavity, the projections 14 formed on the surface of the stamper 13 are transferred as concave pits 10 and the replica substrate 9 of the optical disc is A signal mark 10 serving as a pit-shaped information bit is formed on the surface.

Among the above-mentioned conventional optical discs, in order to reproduce a tracking signal with high precision and to accurately perform tracking control, for example, one described in Japanese Patent Laid-Open No. 2-166642 is known.

[0008]

In the conventional optical disc, the track pitch is 1.5 to 1.6 μm, the width of the signal mark which becomes the information bit in the CD is 0.5 μm, and the width of the signal mark for tracking in the sample servo type optical disc. Is 0.6 μm (in this case, the track pitch is more than twice the signal mark width). Therefore, the distance between the adjacent signal marks in the radial direction is 0.9 μm at the minimum. However, as the density of information becomes higher, the track pitch tends to become narrower, which reduces the distance between adjacent signal marks. For example, when the track pitch is 0.8 μm and the width of the signal mark is 0.5 μm, the minimum distance between the adjacent signal marks in the radial direction is 0.3 μm, which is smaller than the signal mark width. In this way, as the track pitch becomes narrower and the distance between the signal marks becomes smaller, it becomes difficult to form the signal marks as the information bits in the pit shape on the surface like the replica substrate of the conventional optical disc. . That is, the pits on the replica substrate surface are formed by transferring the protrusions by pushing the resin between the protrusions on the stamper surface. Therefore, if the track pitch becomes narrow and the interval between the adjacent protrusions on the stamper surface becomes small, it becomes difficult to push the resin between the protrusions.
As a result, accurate pits cannot be transferred to the surface of the replica substrate, and there is a problem that the information of the signal mark cannot be read accurately.

Similarly, even in an optical disc in which the minimum adjacent distance between signal marks serving as information bits is smaller than the signal mark width, it becomes difficult to form the signal marks serving as information bits in the form of pits on the replica substrate surface. However, there is a problem in that accurate pits cannot be transferred and the information of the signal mark cannot be read accurately.

Further, in the method described in Japanese Patent Laid-Open No. 2-166642, it is disadvantageous to form the signal mark in the described range, and it is not effective in manufacturing an optical disc as described later. .

An object of the present invention is to provide an optical disk which can accurately read the information of the signal mark by transferring the signal mark more accurately than the conventional product.

[0012]

In order to achieve the above object, the present invention provides an optical disc in which a signal mark serving as an information bit has a track pitch of not more than twice the signal mark width or a minimum distance between signal marks serving as information bits. In an optical disc in which the distance between adjacent signals is smaller than the signal mark width, the signal marks have a protrusion shape.

[0013]

In conventional optical disks (including magneto-optical disks), signal marks for information and tracking are formed as pits. In order to form such pits on the replica substrate, the stamper is provided with protrusions corresponding to the pits. The projections on the stamper surface are formed as pits on the replica substrate by the injection molding method, and the injection molding process will be described. The resin that is the material of the replica substrate is melted, and this molten resin is injected and filled into the mold to which the stamper is attached. The resin pressure in the mold rises due to injection and filling, and then the holding pressure (pressure applied to compensate for the solidification shrinkage of the resin) holds this pressure and moves to the cooling process, and the holding pressure is released. After cooling, the mold is released and taken out to form a replica substrate. In order to form the signal marks for information and tracking as concave pits on the replica substrate surface, it is necessary to press the resin between the convex protrusions on the stamper surface by the holding pressure. If the track pitch is 1.6 μm and the signal mark width is about 0.5 μm like the conventional optical disc (in this case, the track pitch is more than twice the signal mark width),
The distance between the protrusions of the stamper was at least about 1.1 μm, the resin could be easily pushed in, and pits with high precision could be formed on the replica substrate surface. However, as the track pitch becomes narrower as the density of optical disks becomes higher, the distance between the protrusions of the stamper becomes smaller, making it difficult to push the resin in, and it becomes impossible to form pits with high precision on the replica substrate surface.

The present invention relates to an optical disc in which the track pitch of signal marks serving as information bits is less than twice the signal mark width or an optical disc in which the minimum adjacent distance between signal marks serving as information bits is smaller than the signal mark width. The signal marks for information and tracking are formed in a protrusion shape, and concave pits are formed in the stamper in order to form the protrusion on the replica substrate. As a result, as described above, the track pitch becomes narrower as the density of the optical disc becomes higher, and the track pitch of the signal marks is less than twice the signal mark width or the minimum distance between adjacent signal marks becomes smaller than the signal mark width. In this case, when molding the replica substrate by injection molding, it is easier to form the signal mark as a protruding shape than to form the signal mark as a concave pit as in a conventional optical disc, and it is possible to transfer the signal mark with high accuracy. it can. Therefore, a defective signal mark does not occur, and an optical disc with good information and tracking signals can be obtained. In addition, the range of molding conditions for injection molding of the replica substrate is widened, and it is possible to easily find molding conditions that can obtain a replica substrate with good transferability without impairing optical characteristics and shape accuracy.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to FIG.
A description will be given using (a) and (b). FIG. 1A is a schematic diagram of an optical disc 1 which is an embodiment of the present invention. This shows a read-only optical disk such as a CD or a CD-ROM, or an optical disk including a read-only area and an information recording area for recording data and the like. FIG. 1B is a partially enlarged view showing a part of the reproduction-only area of the replica substrate 2. This optical disc 1
Is constructed by laminating a plastic replica substrate 2 or a single plate. In the information area 3 in which data and the like are recorded in advance on the replica substrate 2, a signal mark 4 serving as an information bit for reading data is formed. The signal mark 4 serving as an information bit for reading information in the information area 3 of the replica substrate 2 is shown in FIG.
As shown in the enlarged view of the portion A of FIG. The track pitch on the optical disc 1 is less than twice the mark width of the signal mark 4 (that is, P ≦ 2 where P is the track pitch and W is the signal mark width).
W). The height of the protrusion of this signal mark 4 is calculated by λ
/ 4 (λ is the reading laser wavelength) is optimum, and the length is, for example, 0.3 to 2.0 μm. The projection of the signal mark 4 may have any projection shape as long as it does not deteriorate the tracking and information signal characteristics. Then, the reflective recording film 5 is formed on the replica substrate, and recording and reproduction of information signals are performed.

In the above description, the signal mark serving as the information bit in the reproduction-only area has been described, but the present invention also includes a signal mark for addressing or tracking in the information recording area in the form of a protrusion (here, the track. The pitch is less than twice the signal mark width).

2A and 2B are a partial plan view and a partial sectional view of an optical disc 1 showing another embodiment of the present invention. As shown in the figure, in the replica substrate 2 of the optical disc 1 in which the minimum distance L between signal marks for data, addresses, and tracking, which are information bits in the information area 3, is smaller than the mark width W of the signal mark, The mark 4 has a protruding shape (L ≦ W, where L is the minimum distance between adjacent signal marks and W is the signal mark width). The protrusions of the signal mark 4 may have any protrusion shape as long as they do not deteriorate the tracking signal characteristics.

Next, a method for forming the projection-shaped signal mark 4 in the information area 3 of the replica substrate will be described.
The plastic replica substrate 2 forming the optical disc 1 of the present invention is molded by an injection molding method. An outline of the stamper used at this time is shown in FIGS. 3 (a) and 3 (b). By using this stamper 6, it is possible to form the signal mark 4 having a projection shape in the information area 3. As shown in FIG. 3B, a concave pit 7 is formed on the surface of the stamper 6 at a portion corresponding to the signal mark 4 in order to form the signal mark 4 in the information area 3 of the replica substrate 2 in a projection shape. ing. By molding the replica substrate 2 using this stamper 6 by an injection molding method, the projection-shaped signal mark 4 is formed.
Can be formed. Further, this stamper 6 can be easily manufactured by the same method as the conventional stamper.

In the optical disc in which the track pitch of the signal marks is less than twice the signal mark width or the minimum distance between adjacent signal marks is smaller than the signal mark width as in the present invention, the signal marks are formed in a protruding shape. Due to
It is possible to form a signal mark with higher accuracy than in the case where the signal mark has a pit shape as in the conventional product. In the case of the conventional product, the signal mark on the surface of the replica substrate is formed as a pit shape, but this is transferred as a concave pit by pushing resin between the convex protrusions formed on the stamper surface. As the track pitch becomes narrower as the optical disc capacity increases and the pitch becomes narrower, the spacing between the protrusions on the stamper surface also becomes narrower, and it becomes more difficult for resin to enter into this narrow portion. Can no longer be formed. As a result, the information of the signal mark cannot be read accurately.

According to the present invention, as shown in FIG. 1, the signal mark 4 to be an information bit is formed in a projection shape, and in order to form the projection, a concave pit 7 is formed on the stamper surface as shown in FIG. The protrusions are transferred by pushing resin into the pits. Here, when the track pitch of the signal mark is less than twice the signal mark width or the minimum distance between adjacent signal marks is smaller than the signal mark width, the signal mark 10 is formed into a pit shape as in the conventional product shown in FIG. It is more advantageous to press the resin into the pits 7 on the stamper surface to form the signal mark 4 in the shape of a protrusion, as in the present invention, than to press the resin between the protrusions on the stamper surface for higher precision. Signal marks can be formed. As a result, it is possible to obtain an optical disc from which the information of the signal mark can be accurately read.

In the replica substrate molding of the optical disc of the present invention, by raising the mold temperature and the resin temperature, and increasing the injection rate and the holding pressure, an optical disc having good signal characteristics of signal marks can be obtained. For example, as molding conditions, mold temperature 125 ℃, resin temperature 330 ℃, injection rate 75 cm ³ /
By molding the replica substrate of the present invention at s, holding pressure of 50 MPa, and holding time of 1.0 s, an optical disc having good signal characteristics of signal marks could be obtained.

By molding the replica substrate of the optical disc of the present invention by injection compression molding, it is possible to form a highly precise signal mark having a protruding shape and obtain an optical disc having good signal characteristics.

[0023]

According to the present invention, the minimum adjacent distance between the optical discs in which the track pitch of signal marks serving as information bits is less than twice the signal mark width or the signal marks serving as information bits is smaller than the signal mark width. In the case of a small optical disc, a resin having a protrusion shape can be more easily pushed into a resin than a signal mark having a pit shape, and the transferability of the signal mark can be improved. This makes it possible to obtain an optical disc having good signal characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical disc showing an embodiment of the present invention.

FIG. 2 is a partial plan view and a partial cross-sectional view of an optical disc showing another embodiment of the present invention.

FIG. 3 is a schematic view of a stamper for molding a replica substrate of an optical disc of the present invention.

FIG. 4 is a schematic diagram of a conventional optical disc.

FIG. 5 is a schematic diagram of a mold for molding an optical disk substrate.

[Explanation of symbols]

 1, 8 ... Optical disc, 2, 9 ... Replica substrate, 3 ... Information area, 4 ... Projection-shaped signal mark, 5 ... Reflective recording film, 6, 13 ... Stamper, 7 ... Stamper surface pit, 10 ... Pit-shaped Signal mark, 11 ... Reflective film, 12 ... Mold for molding optical disk substrate, 14 ... Projection on stamper surface.

Claims (2)

[Claims] 1. An optical disc capable of recording / reproducing information and having a track pitch of signal marks as information bits less than twice the signal mark width, wherein the signal marks have a protrusion shape. Optical disc. 2. An optical disk capable of recording / reproducing information and having a minimum adjacent distance between signal marks serving as information bits smaller than a signal mark width, wherein the signal marks have a protrusion shape. Optical disc.