JP2002230836A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk where flatness can be improved and then which can be held with excellent positional precision by eliminating an unevenness in thickness of clamp areas even if a disk structure is modified. SOLUTION: In the optical disk having a supporting substrate 2 at the central part of which clamp areas 8 are formed and a transparent reading layer thinner than the supporting substrate, the reading layer is not coated in the clamp areas of the supporting substrate. Thus, the unevenness in thickness of the clamp areas is eliminated even if the disk structure is modified, the flatness is improved and positioned precision is also improved.

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 obtaining good signal quality during reproduction.

[0002]

2. Description of the Related Art In an optical disk, an information signal composed of pit rows and grooves composed of fine irregularities is recorded on a support substrate composed of a transparent plastic substrate, and the information signal of the transparent support substrate is engraved on the information signal. This is a system that irradiates light such as laser light from the opposite surface and reads out information by changing the amount of reflected light according to the information signal on the support base. This optical disk is, for example, a compact disk (CD) using a recording / reproducing laser beam wavelength of 780 nm and a numerical aperture of an objective lens of an optical pickup of 0.45.
It has become widely used in general. The types of this compact disk include a reproduction type disk (ROM) for reproducing recorded information, a recording type disk (CD-R) capable of recording only once, and a recording type disc (recordable / reproducible and erasable multiple times). CD-RW). There are also magneto-optical recording disks having the same form as the compact disk.

Recently, a laser element for emitting short-wavelength laser light has become inexpensive, and the disk manufacturing technology has been improved.
DVD (Digital Versatile) using a 5 nm optical pickup objective lens with a numerical aperture of 0.6
Discs are becoming mainstream, and high density is achieved by shortening the wavelength of laser light and increasing the numerical aperture of the objective lens. As next-generation optical disks, optical disks using a recording / reproducing laser beam wavelength of 400 nm and a numerical aperture of an objective lens of an optical pickup of 0.7 or more have been actively developed. The appearance of optical disks is becoming possible.

The thickness of a transparent support base for reading out an information signal from an optical disk is, for an optical disk such as a CD, the wavelength of a recording / reproducing laser beam is 7 mm.
80 nm, the thickness of the transparent support base from which information is read is 1.2 mm, and an information recording layer such as a pit row or a recording groove is engraved on the transparent support base. Is read from the information recording layer. That is, the transparent readout layer has a structure also serving as a support base having the information recording layer. The above CD
In an optical disk represented by a DVD having a higher density, the wavelength of a recording / reproducing laser beam is 635 nm,
In the single-layer plate, the thickness of the transparent support base from which information is read is 0.6 mm, and information recording layers such as pit rows and recording grooves are engraved on the transparent support base. The information on the information recording layer is read from the opposite side. That is, like the CD, the transparent readout layer has a structure also serving as a support base having the information recording layer. Then, a disc called a 0.6 mm dummy disc is adhered on the information recording layer to increase the disc strength.

In an optical disk called a next-generation disk, the wavelength of a recording / reproducing laser beam is 400 nm, and information recording such as pit rows and recording grooves is carried out on a supporting substrate having a thickness of 1.1 mm to 1.2 mm. In this system, a layer having a thickness of 0.2 mm or less, called a transparent readout layer, is adhered to the surface of the layer, and recording / reproduction is performed from the sheet surface side. In this next-generation disc,
In some cases, an information recording layer is formed on a transparent readout layer.

When recording and reproducing information on and from these optical disks, these optical disks are mounted on a turntable of a recording and reproducing apparatus. The turntable of this recording / reproducing machine has a high degree of perpendicularity and parallelism with respect to the optical pickup, and when optical and mechanical misalignment occurs, optical aberration occurs and deterioration of reproduction signal quality is caused. Therefore, a device is devised so that the quality of the reproduced signal is not deteriorated as much as possible. The optical disk mounted on the turntable is also devised so that it has sufficient verticality and parallelism so that information signals can be recorded and reproduced correctly. By devising such mechanical precision, it is possible to shorten the wavelength of the recording / reproducing laser beam and increase the numerical aperture of the objective lens of the optical pickup, and the recording capacity of the disk has been dramatically improved.

[0007]

By the way, on an optical disk called a next-generation disk, recording and reproduction are performed by the following system as described above. The wavelength of the recording / reproducing laser beam is 400 nm, and a recording layer such as a pit row or a recording groove is engraved on a support base having a thickness of 1.1 mm to 1.2 mm, and is called a transparent reading layer. In this system, recording and reproduction are performed by bonding a sheet having a thickness of 0.2 mm or less and irradiating a laser beam from the sheet surface side. On the other hand, since an optical pickup for performing recording and reproduction uses an objective lens having a numerical aperture of 0.7 or more, the distance between the readout layer of the optical disk and the objective lens of the pickup is 1 mm or less. If the configuration is easy to obtain the above performance, the distance between the disk and the objective lens becomes as small as 0.1 mm, resulting in a very close configuration.

A drive for recording and reproducing information on and from an optical disk is provided with a turntable for holding and rotating the optical disk. There is a clamp area in the center of the optical disk, and this area is held by the clamp mechanism so that it is held on this turntable and is highly accurate between the optical pickup and the optical pickup installed at a location away from the turntable. I'm dripping. The size of the information signal of the next-generation optical disc is, for example, a track pitch of 0.4 μm to 0.3 μ
m and the shortest pit length is from 0.22 μm to 0.1
Between 8 μm. In other words, an optical pickup must accurately trace such a small information unit,
The positional relationship between the optical disc and the pickup needs to be maintained with high precision.

Also, the optical disk must be mounted on the turntable accurately in position, and when the innermost circumference of the disk is reproduced, the number of rotations reaches 1800 or more. In order to allow the disk to accurately follow the acceleration until it reaches, a clamp mechanism that firmly holds and fixes the disk must also be formed with high precision, and the adhesion to the disk must be maintained sufficiently high. . Therefore, a sufficiently high tolerance is required for the tolerance and precision of the optical disc clamping mechanism. For this reason, in the case of a conventional CD or DVD disc, a place where the disc should be mounted on the turntable is determined as a clamp area, and the thickness and flatness of the support base of the clamp area are stricter differently from other parts. Tolerances are required.

FIG. 4 is a sectional view schematically showing an example of the next-generation optical disk as described above. The optical disk D1 has the circular support base 2 having a thickness of about 1.1 mm as described above, a recording layer is formed on the surface thereof, and a circular readout layer 4 made of a transparent sheet is formed on the surface side. It is attached with an adhesive layer interposed. A clamp hole 6 is formed at the center of the support base 2. A donut-shaped clamp area 8 having a constant width is formed around the clamp hole 6 on the upper surface and the lower surface. As shown in FIG. The clamp area 8 is directly sandwiched between the ring-shaped clamp members 10A of the optical disc D.
1 is firmly held and fixed. Here, the readout layer 4
Is provided so as to cover the portion of the clamp area 8.

There are various types of discs, such as a single-layer disc, a double-layer disc, a double-sided disc, and a double-sided two-layer (total of four layers) discs. Similarly, not only are a large number of disk structures prepared, but also due to advances in technology, multi-layer structures such as a three-layer disk and a four-layer disk and double-sided optical disks are being studied. When producing a next-generation optical disk having such a large number of structures, the thickness of the support base produced by injection molding is kept constant, and the sectional structure of the disk is as shown in FIG. In FIG. 6, the thickness H3 of each layer of the intermediate layer 12 is set to 50 μm (0.05 mm) so as to sufficiently reduce reproduction interference between the layers in the optical disc having a multilayer structure. The thickness H1 of the support base 2 is set to 1.1 mm, and the thickness H2 of the readout layer 4 is set to 0.1 mm.

The thickness of the entire optical disc, that is, the total thickness H
Is 1.2 mm in the single-layer board shown in FIG.
6A, the layer thickness H is 1.25 mm in a two-layer disc including one intermediate layer 12, and as shown in FIG. 6B, a two-layer master including two intermediate layers 12 and FIG. As shown in FIG. 6C, in the case of a double-sided disc having the readout layer 4 on both sides, the total thickness H is 1.3 mm each, and the intermediate layer 12 and the readout layer 4 are formed on both sides as shown in FIG. Both sides 2 provided
In the case of a layered board, the total thickness H is 1.4 mm. As described above, as the number of information surfaces of the disc increases, the total thickness H of the disc including the clamp area 8 gradually increases.

As described above, when the thickness of the portion of the clamp area 8 changes, the mounting position of the disk by the clamp mechanism 10 (see FIG. 5), which is manufactured with high precision, changes slightly, and the disk turns. There was a problem that it could not be mounted properly on the table. In order to solve the above problem, in order to keep the total thickness H of the disk including the clamp area 8 always constant, for example, when forming a single-layer disk as shown in FIG. Using a mold designed so that the height H1 is 1.1 mm,
For example, when molding a double-sided disc as shown in FIG. 6 (C), it is conceivable to use a mold designed so that the thickness H1 of the support base 2 is 1.0 mm. As described above, preparing the dies corresponding to the number of recording surfaces increases the number of dies to be managed, and the dies need to be replaced according to the contents of the order. The drawback is that it leads to up, which is not practical.

Further, since the readout layer 4 is not integrally formed with a mold or the like, but is provided by laminating and laminating a thin sheet on the support base 2, the readout layer 4 is formed between the disk surface and the back surface in the clamp area 8. There is also a disadvantage that the degree of parallelism and the flatness of the disk surface cannot be sufficiently obtained, and the vertical deflection of the disk recording surface during disk reproduction increases. FIG. 7 is a graph showing an example of the influence of the flatness of the clamp area on the surface runout of the outermost periphery of the disk. According to this graph, if the flatness in the clamp area 8 deteriorates by about 10 μm in one round of the disk. , 36μ
The vertical deflection of the recording surface increases by about m, and in a system in which the reproduction is performed while maintaining the distance between the disk reading surface and the objective lens of the pickup at 100 μm, the reading surface is as vertical as 36 μm per rotation of the disk. The change in the direction is a major problem from the viewpoint of ensuring the reliability of the system. The present invention has been made in view of the above problems, and has been made in order to effectively solve the problems. The purpose of the present invention is to eliminate the change in the thickness of the clamp area even when the disc structure is different, and to further reduce the flatness. Degree can be improved,
Accordingly, it is an object of the present invention to provide an optical disk capable of holding a position with high accuracy.

[0015]

According to a first aspect of the present invention, there is provided an optical disc having a support base having a clamp area formed in a center portion and a transparent readout layer thinner than the support base. An optical disk characterized in that an area is not covered with the readout layer. In this case, for example, as defined in claim 2, the clamp area is formed on both surfaces of the support base. According to this, even if the disc structure is different, the change in the thickness of the clamp area can be eliminated, and the flatness can be improved, so that the position can be held with high accuracy.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical disk of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view schematically showing an optical disk of the present invention, and FIG. 2 is a sectional view showing the optical disk held by a clamp mechanism.
The same parts as those described in the conventional example will be described with the same reference numerals. The difference between the optical disc D2 of the present invention and the conventional optical disc D1 shown in FIG. 4 is that a thin transparent readout layer 4 is not provided in the ring-shaped clamp area 8 of the support base 2.

The reason will be described below. First, the higher the precision of the optical disk becomes, the higher the required accuracy is due to the smaller information unit recorded. In order to reproduce such a small information unit with high accuracy, as described above, the optical disk is accurately held at an appropriate position, and a high-quality signal is obtained only when the optical disk is rotated at that position. You can play it. Therefore, in order to maintain high precision during disc reproduction, it is necessary to use the most accurate location on the disc as the clamp area 8 of the disc. And
The disk support base 2 is generally formed by injection molding using a disk molding die. On the support base 2 thus formed by injection molding, a recording functional film, a reflective film, and the like are formed, an adhesive layer is laminated thereon, and a transparent readout layer 4 made of a thin sheet is further formed thereon. Are laminated and finished. Since all of these laminated films pass through the laminating process, it is inevitable that the thickness of the layers varies within a certain range. And the final thickness of the optical disk is
In addition to the thickness variation of the support base 2, the thickness variation of the laminated film in each lamination process is added.

In order to reproduce such an optical disk,
The optical disc D2 is mounted on a turntable, and is supported and fixed to a turntable (not shown) in a clamp area 8 by a clamp member 10A of a clamp mechanism 10 as shown in FIG. It is only necessary that the variation does not affect the clamp area. For this purpose, if the film formation in such a laminating step is performed outside the clamp area 8, this leads to the solution of the problem. Therefore, the readout layer 4 is not provided in the clamp area 8 as shown in FIG. Like that.
As described above, the clamp area 8 is not provided with other recording functional films, reflective films, adhesive layers, and the like.

That is, only the support base 2 forms the clamp area 8, and the innermost periphery of the transparent readout layer 4 may be prevented from entering the clamp area 8.
It is convenient to provide the clamp area 8 of the optical disc D2 on the inner peripheral side of the optical disc D2 because reproduction compatibility with CDs and DVDs can be performed. Then, it is preferable to set the inner side of the inner peripheral portion lead-in area of the optical disk D2. DV
Considering compatibility with D disk, etc., the clamp area 8
Is preferably in the range of 22 mm to 33 mm in diameter of the disk. In addition, since the clamp mechanism 10 needs to be precise, it is better to minimize the variation in the thickness of the support base 2 to be clamped.
Considering compatibility with VD and the like, the thickness of the support base 2 is 1.
2 mm ± 0.1 mm is appropriate. However, if you mainly consider high-density discs, make them even more rigorous.
Is suitably 1.2 mm ± 0.05 mm. This numerical value has been achieved for DVD disks and the like, and is an appropriate value for studying next-generation optical disks, and is a sufficiently achievable value.

As described above, a new effect is produced by not forming the transparent readout layer 4 in the clamp area 8. That is, even when producing a single-layer disc as shown in FIG. 1 or a double-sided disc as shown in FIG. 3, that is, when producing optical discs having different structures, the thickness of the support base 2 can be made the same. It is possible to keep the thickness of the clamp area 8 at the above-mentioned 1.2 mm ± 0.1 mm, preferably 1.2 mm ± 0.05 mm, and it is possible to produce various optical discs with one mold. It is easy to manage and the cost can be reduced. Naturally, the present invention can be applied to all types of optical disks shown in FIG.

Next, the optical disk according to the present invention was specifically manufactured and evaluated, and the evaluation results will be described. Example 1 First, an optical disk support base 2 was formed by injection molding using a next-generation optical disk mold. This mold is a type that can mount stampers for information signals on both sides of the mold.When manufacturing a single-layer board, one side is equipped with a stamper without information signals, and the other side is equipped with information signals. I attached a stamper. The information signal density on the information recording surface is, for example, a track pitch of 0.4 μm when having information pits such as a ROM type.
From 0.3 μm to 0.32 μm. The shortest pit length is from 0.25 μm to 0.1
Since the thickness is 5 μm, a thickness of 0.19 μm was used. The diameter of the clamp hole 6 at the center of the support base 2 was 15 mm, and the thickness of the support base 2 was 1.2 mm. The material used was a polycarbonate resin. A 50 nm layer of aluminum was formed on the information recording layer on the support base 2 to form a reflective layer.

An adhesive layer having a thickness of 10 μm is provided on the reflective layer, and a transparent readout layer 4 having an inner diameter of 38 μm is provided thereon.
A sheet having a thickness of 100 μm and processed into a donut shape having an outer diameter of 119 mm and a diameter of 119 mm was adhered. The inner diameter of this sheet is not required to be in the range of 22 mm to 33 mm in diameter, which is the clamp area 8, and it is sufficient if it is located on the outer diameter side and further on the inner diameter side than the innermost circumference of the information signal. Can be arbitrarily selected from the range of 33 mm to 44 mm.
Since the clamp area 8 of the next-generation optical disk manufactured in this manner is not covered with the transparent readout layer 4, the thickness is 1.2 mm. The standard deviation was 10 μm, and the substrate thickness of the clamp area 8 sufficiently satisfied 1.2 mm ± 0.05 mm. The flatness of the clamp area surface is 20
μm or less, and sufficient flatness could be obtained. When this optical disk is mounted on a turntable of a recording / reproducing apparatus by a clamp mechanism and rotated, the optical disk can be held on the turntable with high accuracy, and the amount of surface deviation at the outer peripheral end of the disk is reduced to 0.
It was as good as 1 mmpp.

<Embodiment 2> A mold similar to that of Embodiment 1 was used, and a stamper for an information signal was mounted on both sides of the mold, and a support base 2 for a next-generation optical disk was formed by injection molding. In the case of a recording type such as a RAM type, the information signal density on the information recording surface is 0.32 μm because the track pitch is from 0.4 μm to 0.3 μm. Since the shortest mark length of the mark to be recorded is from 0.25 μm to 0.15 μm, it is 0.19 μm.
m. The diameter of the clamp hole 6 of the support base 2 was 15 mm, and the thickness of the support base 2 was 1.2 mm. The material used was a polycarbonate resin. The information recording layer on the support base 2 has a total thickness of 10 including a dielectric, a recording layer, and a reflective film.
An information recording layer of 0 nm was formed.

An adhesive layer having a thickness of 10 μm is provided on the information recording layer, and a transparent readout layer 4 is formed on the information recording layer to form a doughnut-shaped sheet having an inner diameter of 38 mm and an outer diameter of 119 mm. Was glued. The inner diameter of this sheet is from 33 mm to 22 mm in diameter, which is the clamp area 8.
The inner diameter of the sheet can be arbitrarily selected from a range of 33 mm to 44 mm as long as the sheet is located on the outer diameter side and further on the inner diameter side than the innermost circumference of the information signal. Since the optical disc to be manufactured was a double-sided disc, an information recording layer, an adhesive layer, and a transparent readout layer were formed on the other side in the same manner as described above. The total thickness of the substrate on the signal surface of the next-generation optical disk manufactured in this manner increased to 1.4 mm, but the thickness was 1. mm because the clamp area 8 was not covered with the transparent readout layer 4. 2 mm and 10
The thickness variation when molding 0 sheets is 10μ with standard deviation.
m, and the substrate thickness of the clamp area 8 is 1.2 mm ±
0.05 mm was sufficiently satisfied. The flatness of the surface of the clamp area 8 was 20 μm or less, and a sufficient flatness could be obtained. When this optical disk was mounted on a turntable of a recording / reproducing apparatus by a clamp mechanism and rotated, the optical disk could be held on the turntable with high accuracy, and the amount of runout at the outer peripheral edge of the disk was as good as 0.1 mmpp.

[0025]

As described above, according to the optical disk of the present invention, the following excellent operational effects can be exhibited. Even if the disc structure is different, the readout layer is not provided in the clamp area. Therefore, even if the disc structure is different, the thickness of the clamp area does not change, and the flatness can be improved. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an optical disk of the present invention.

FIG. 2 is a cross-sectional view showing the optical disc held by a clamp mechanism.

FIG. 3 is a cross-sectional view schematically showing an optical disc according to a modification of the present invention.

FIG. 4 is a cross-sectional view schematically showing an optical disc according to a modification of the present invention.

FIG. 5 is a diagram showing a state where the optical disk shown in FIG. 4 is held by a clamp mechanism.

FIG. 6 is a schematic sectional view schematically showing various optical disks.

FIG. 7 is a schematic sectional view schematically showing various optical disks.

[Explanation of symbols]

2 ... support base, 4 ... readout layer, 6 ... clamp hole, 8 ...
Clamp area, 10: clamp mechanism, 10A: clamp material, D2: optical disk.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takayuki Onizawa 3-12 Moriyacho, Kanagawa-ku, Yokohama-shi, Kanagawa Japan F-term (reference) 5D029 KB12 KB15 PA05

Claims (2)

[Claims] 1. An optical disc having a support base having a clamp area formed in the center thereof and a transparent readout layer thinner than the support base, wherein the clamp area of the support base is not covered with the readout layer. An optical disk characterized by comprising: 2. The optical disk according to claim 1, wherein the clamp areas are formed on both sides of the support base.