JPH05303768A - Optical disk - Google Patents

Abstract

PURPOSE:To enable the easy and good formation of a protective film for covering and protecting a signal recording part and to control the double refractive characteristic of a disk substrate in accordance with the molding conditions for the disk substrate. CONSTITUTION:This optical disk is constituted by having the disk substrate 100 which is flattened in the one main surface part formed with the signal recording part over the entire surface thereof and is fed with an annular groove part 101 in the position on the side inner than the signal recording part 103 of the other main surface part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc constructed as a recording medium capable of writing and / or reading information signals.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an optical disc having a disc substrate formed of a constituent resin material such as a polycarbonate resin having a light transmitting property. Such optical disks include read-only disks used exclusively for reproducing information signals, and recording / reproducing disks such as so-called magneto-optical disks capable of rewriting information signals once recorded. ..

The read-only disc is, for example, a disc substrate having a concave-convex pattern corresponding to an information signal formed on one main surface portion, and is attached to the one main surface portion of the disc substrate by means such as vapor deposition or sputtering. It is configured to have a formed reflection film made of aluminum or the like. In this read-only disc, the concave-convex pattern and the reflection film form a signal recording portion.

Further, in the above-described recording / reproducing disc, a disc substrate having a pre-groove constituting a recording track for recording an information signal is formed on one main surface portion, and the disc substrate is attached to the one main surface portion. And a signal recording layer formed of a magnetic material. In this recording / playback combined disc, the pre-groove and the signal recording layer constitute a signal recording section.

By the way, a disk substrate made of a synthetic resin material which constitutes the above-mentioned optical disk is formed by using a mold device for injection molding. As shown in FIG. 10, a mold device for molding this disk substrate is provided with a mold 3 composed of a fixed mold 1 and a movable mold 2 which are arranged to face each other. A disk substrate 30 formed between the fixed mold 1 and the movable mold 2 when the fixed mold 1 and the movable mold 2 are butted against each other.
The molding cavity 4 corresponding to is formed.

An insertion hole is formed at the center of the fixed mold 1. In the insertion hole formed in the fixed mold 1, a stamper holder support 10 having a substantially annular shape is formed.
Is inserted into the stamper holder support 10, and the sprue bush 5 is inserted into the stamper holder support 10. The sprue bush 5 is formed in a substantially cylindrical shape and has a resin injection hole 6 formed along the central axis thereof, such as a molten polycarbonate resin supplied from an injection device (not shown). A synthetic resin material is caused to flow into the molding cavity 4 through the resin injection hole 6. That is, the sprue bush 5 faces the inside of the molding cavity 4 at the tip side. The stamper holder support 10 has a flanged flange portion 13 having a stepped diameter on the front end side facing the molding cavity 4 and a flange shape on the rear end side.
Has been done.

Further, the surface of the fixed mold 1 on the side forming the molding cavity 4, that is, the surface of the side facing the movable mold 2 has a concavo-convex pattern corresponding to an information signal or the recording. A stamper 7 for forming a pre-groove forming a track is attached. The stamper 7 is formed in a disk shape having a center hole 7a at the center.

The stamper 7 is supported by an inner peripheral side stamper holder 8 formed in a substantially annular shape on the inner peripheral edge of the center hole 7a, and an outer peripheral side stamper formed on the outer peripheral edge side in a substantially annular shape. It is supported by a holder 9 and attached to the fixed mold 1. That is, the inner peripheral side stamper holder 8 that supports the peripheral edge of the center hole 7a that is the inner peripheral edge side of the stamper 7 is the stamper holder support 1
0 is fitted on the outer peripheral side of the sprue bushing 5, is positioned on the tip side of the sprue bush 5, and is mounted on the fixed mold 1. A stamper supporting claw portion 11 is formed in a flange shape on the outer periphery of the front end side of the stamper holder 8.
The stamper supporting claw portion 11 supports the peripheral edge of the center hole 7 a of the stamper 7.

The inner stamper holder 8 has a stamper fixing rod 14 which is inserted into a first tunnel portion which is bored from the outer surface of the fixed mold 1 toward the center side. It is pressure-bonded and supported on the front surface portion 13 a of the collar portion 13 of the support body 10. That is, the stamper fixing rod 14 has a front end side facing a side surface portion of a front end side portion of the stamper holder support 10, and a rear end side thereof is the first side.
It faces the outside of the tunnel. The stamper fixing rod 14 has a screw portion 15 formed on the outer peripheral surface of the rear end side portion thereof, and a photographing portion 16 provided on the rear end portion. The screw portion 15 is screwed into a screw portion formed on the inner wall portion near the entrance of the first tunnel portion. That is, the stamper fixing rod 14 rotates the screw portion 15 by using the photographing portion 16 so that the stamper fixing rod 14 extends along the first tunnel portion as shown by arrows A and B in FIG. The fixed mold 1 can be moved back and forth. An engagement support portion 17 is formed on the tip end side of the stamper fixing rod 14. The engagement support portion 17 is provided with the collar portion 13 described above.
Is formed in a wedge shape in which the side facing the is an inclined surface portion and the tip side is reduced in diameter. Then, the engagement support portion 17 is
The stamper holder 8 is fitted into and engaged with the engaging recess 18 formed on the outer surface of the stamper holder 8.

When the stamper fixing rod 14 is advanced to the center side of the fixed mold 1 and moved to the stamper holder 8 side, the stamper holder 8 is moved through the engaging concave portion 18 to It is pressed against the inclined surface portion of the engaging support portion 17, and as shown by an arrow C in FIG.
Is pressed and supported by the front surface portion 13a of the.

Further, the fixed mold 1 is provided with a stamper fixing release rod 20 for removing the stamper holder 8 from the fixed mold 1. The stamper releasing rod 20 is inserted into a second tunnel portion that is bored from the outer side surface portion of the fixed mold 1 toward the center side, and is disposed at a position facing the stamper fixing rod 14. .. The tip end side of the stamper fixing release rod 20 faces the side surface portion of the front end side portion of the stamper holder support 10, and the rear end side faces the outer side of the second tunnel portion. The stamper fixing / releasing rod 20 has a threaded portion 21 formed on the outer peripheral surface of the rear end side portion thereof, and a grip 22 provided on the rear end portion. The screw portion 21 is screwed into a screw portion formed on the inner wall portion near the entrance of the second tunnel portion. That is, the stamper fixing release rod 20 rotates the screw portion 21 by using the photographing portion 22 so that the stamper fixing release rod 20 extends along the second tunnel portion as shown by arrows E and D in FIG. The advancing / retreating operation can be performed with respect to the fixed mold 1. A fixing releasing portion 23 is formed on the tip end side of the stamper fixing releasing rod 20.
The fixing releasing portion 23 is formed in a wedge shape in which the side facing the molding cavity 4 is an inclined surface portion and the tip side is reduced in diameter. Then, the fixing releasing portion 23 is fitted into the engaging concave portion 24 formed on the outer side surface portion of the stamper holder 8.

When the stamper fixing release rod 20 is advanced to the center side of the fixed mold 1 and moved to the stamper holder 8 side, the stamper holder 8 passes through the engaging recessed portion 24. It is pressed by the inclined surface portion of the fixing releasing portion 23 and is moved and operated in a direction away from the front surface portion 13a of the collar portion 13 as shown by an arrow F in FIG.

On the other hand, an insertion hole is formed at the center of the upper movable fixed mold 2. A sleeve 25 having a cylindrical shape is inserted and arranged in an insertion hole formed in the movable mold 2, and a cylindrical punch 26 is inserted in the sleeve 25 and arranged therein. .. This sleeve 25
Are supported by the movable mold 2 so as to be movable back and forth with respect to the molding cavity 4. The sleeve 25 has a front end face facing the molding cavity 4 slightly retracted into the movable mold 2. The punch 26 has a front end face facing the molding cavity 4 slightly projected from the front end face of the sleeve 25.

In order to form the disk substrate 30 in the mold apparatus having the above structure, first, the movable mold 2 is used.
Are abutted against the fixed mold 1 to form the molding cavity 4. Then, the synthetic resin material such as melted polycarbonate is injected and filled into the molding cavity 4 through the resin injection hole 6 of the sprue bush 5 by the injection device. At this time, the synthetic resin material flows in the molding cavity 4 from the central portion toward the outer peripheral side. Then, after moving the movable mold 2 to the fixed mold 1 side and performing mold clamping for compressing the synthetic resin material filled in the molding cavity 4,
By cooling and solidifying the synthetic resin material, the disk substrate 30 corresponding to the molding cavity 4 is formed.

Then, the punch 26 is attached to the fixed mold 1.
By forming a center hole by projecting the movable mold 2 away from the fixed mold 1 while projecting the sleeve 25 toward the fixed mold 1. The disk substrate 30 is the mold 3
More released. Then, by separating the disk substrate 30 from the fixed mold 1, the molding of the disk substrate 30 is completed as shown in FIG.

[0016]

By the way, in the mold apparatus as described above, the stamper supporting claw portion 11 is provided.
Through the center hole 7a, the molding cavity 4
Of the stamper 7 which faces the disk substrate molding surface. Therefore, the stamper 7 cannot be effectively used over the entire molding surface of the disk substrate. That is, in the disc substrate 30, as shown in FIG.
Since the ring-shaped groove portion 31 corresponding to the above is formed, the pit and the pre-groove are formed and the arrow S in FIG.
The formable area of the signal recording area shown by ₁ cannot be extended to the innermost side of the disk substrate 30.

In the optical disc constructed by using the disc substrate 30, as shown in FIG. 12, on the main surface portion which is the signal recording area in which the pits 32 shown by the arrow S in FIG. 12 are formed. , Reflection film or signal recording layer 33
Is deposited, and a protective film 34 made of a synthetic resin material or the like is deposited to cover the reflective film 33 and the like. The protective film 34 is for blocking the contact of the moisture or the like in the air with the reflective film 33 or the like to prevent corrosion of the reflective film 33 or the like.

The protective film 34 has a thickness sufficient to block contact of moisture in the air with the reflective film 33 and the like so that the protective film 34 cannot be easily peeled off from the disk substrate 30. It is necessary that the disk substrate 30 is surely adhered to and formed on the disk substrate 30. On the other hand, in particular, when the disk substrate 30 has a small diameter, the signal recording area needs to be formed as far as possible on the innermost side in order to increase the amount of recordable information signals. Therefore, the width of the adhered area of the protective film 34 to the disk substrate 30 shown by the arrow W ₁ in FIG. 12, that is, the width from the inner peripheral edge of the signal recording area to the outer peripheral part of the groove 31 is narrow. It will be done. If the width of the area where the protective film 34 is attached to the disk substrate 30 becomes narrow, the protective film 34 may not be able to reliably protect the reflective film 33 and the like.

In the above optical disc, the protective film 34 is formed by a so-called spin coating method. In this spin coating method, a synthetic resin such as an uncured ultraviolet curable resin is dropped on the inner peripheral side portion on the main surface portion of the disc substrate 30, and the disc substrate 30 is rotated to operate the disc substrate 30. The synthetic resin is caused to flow onto the main surface portion by the centrifugal force caused by the rotation and applied over the entire main surface portion, and then the synthetic resin is cured to form the protective film 34.

In the disk substrate 30, when the protective film 34 is formed by the spin coating method, the width between the groove 31 and the signal recording is narrow, so that the uncured portion is uncured. It is difficult to drop the synthetic resin. Then, when the uncured synthetic resin is dropped on the inner peripheral side of the groove portion 31 on the disc substrate 30, the synthetic resin is applied to the disc substrate 3.
When the synthetic resin flows on the main surface portion 0, the groove portion 31 hinders smooth flow of the synthetic resin, and there is a possibility that unevenness on the streak is generated on the surface portion. If the synthetic resin is cured with such unevenness, the surface portion of the protective film 34 will not be a smooth surface. This protective film 3
In the case where the optical disc is a magneto-optical disc, a magnetic head or the like may slide on the surface of the optical disc, and if the surface is not smooth, the signal recording characteristics of the optical disc will be deteriorated. ..

Here, it is conceivable to mold the disk substrate 30 so that the groove 31 is not formed. For example, in the mold apparatus, if the stamper 50 is attracted and supported by the fixed mold 1 by a magnet or the like, the stamper supporting claw portion 11 is provided.
It becomes unnecessary to provide. In this case, the groove portion 31 is not formed on the disc substrate 30. As described above, in the disk substrate 30 not having the groove portion 31, the protective film 34 can be adhered to the disk substrate 30 with a sufficient area, and the protective film 34 is spin-coated. Even when it is formed by, the good protective film 34 can be formed.

However, in the disk substrate 30 having no groove 31 as described above, the disk substrate 3
The birefringence characteristic of 0 is deteriorated as compared with the disk substrate 30 having the groove 31.

The birefringence characteristic expresses the amount of birefringence that occurs when a light beam passes through a medium having a different refractive index depending on the direction in the same plane, that is, a medium having so-called refractive index anisotropy. It is a characteristic to do. That is, one direction in a medium is the x direction, and the refractive index in this direction is n _X ,
The refractive index in the y direction, which is the direction orthogonal to the x direction, is n _Y
Then, the light flux traveling in this medium in the z direction orthogonal to the x direction and the y direction is a component having a plane of polarization parallel to the x direction when n _X and n _Y are not equal, that is, the x component. And a component having a polarization plane parallel to the y direction, that is, the y component, a phase shift can be generated.
Letting δ be the phase difference, δ = 2π / λ · (n _X −n _Y ) d, where λ is the wavelength of the light beam and d is the travel distance of the light beam in the medium. The degree of birefringence can be expressed by the amount of the phase difference δ.

In molding the disc substrate 30, the birefringence characteristic is determined by the disc substrate 3
The pressure in the molding cavity 4 when the synthetic resin material forming 0 is cooled in the molding cavity 4, that is, the so-called clamping pressure, and the punch 26.
And the timing of hardening of the synthetic resin forming the disk substrate 30 and the like.
Therefore, in molding the disc substrate 30,
The birefringence characteristics can be controlled to have desired characteristics by appropriately variably adjusting the mold clamping pressure, the timing of forming the center hole, and the like.

However, in the disk substrate 30 which does not have the groove portion 31, the birefringence characteristic cannot be controlled by the mold clamping pressure, the timing of punching the center hole, and the like. Curve E in
As indicated by the curve F and the curve F, when the radius of the disc substrate 30 is 32 mm, the portion less than about 25 mm from the center has characteristics unsuitable for use as an optical disc. That is, in the optical disc configured by using the disc substrate 30 having no such groove portion 31, it is not possible to improve the recording and / or reproducing characteristics of the information signal.

Therefore, the present invention has been proposed in view of the above-mentioned circumstances, and the region where the signal recording region can be formed is a wide region extending to the innermost peripheral side, and the reflection film and the signal recording layer are provided. An object of the present invention is to provide an optical disc in which a protective film for protection is surely applied and a disc substrate has a good birefringence property and an information signal recording and / or reproducing property is good.

[0027]

In order to solve the above problems and achieve the above objects, an optical disk according to the present invention is a disk substrate made of a synthetic resin material having a light-transmitting property, and one of the main parts of the disk substrate. A signal recording portion formed on the surface portion for writing and / or reading an information signal through the disc substrate from the other principal surface portion side of the disc substrate, and a central portion of the other principal surface portion of the disc substrate. And a stepped portion for position reference provided in a protruding manner,
At a position on the other main surface portion serving as the writing and / or reading surface of the information signal, which is on the inner side of the area corresponding to the formation area of the signal recording portion and on the outer side of the position reference step portion, At least one continuous groove portion having an annular shape is provided, and the portion where the groove portion is provided is thinner than the portion corresponding to the formation region of the signal recording portion.

[0028]

In the optical disc according to the present invention, the disc substrate having the signal recording portion for writing and / or reading the information signal on one main surface portion serves as the writing and / or reading surface of the information signal. At least at a position on the other main surface portion that is on the inner side of the area corresponding to the formation area of the signal recording portion and on the outer side of the position reference step portion that is provided at the center of the main surface portion. Since there is one continuous groove portion having an annular shape, and the portion where the groove portion is provided is thinner than the portion corresponding to the formation region of the signal recording portion, the signal recording portion is formed. One of the main surface portions can be a flat surface over the entire surface, and birefringence characteristics can be controlled during molding.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 3, the optical disk according to the present invention is configured to have a disk substrate 100 formed of a constituent resin material such as a polycarbonate resin having a light transmitting property. This optical disc can be configured as a read-only disc used exclusively for reproducing information signals, and also serves as a recording / reproducing device such as a magneto-optical disc in which information signals once recorded can be rewritten. It can be configured as a disc.

Then, the disk substrate 100 is formed by so-called injection molding using a mold device.
As shown in FIG. 6, this mold device is configured to include a mold 43 including a fixed mold 41 and a movable mold 42, which are arranged to face each other. Between the lower surface 41a of the fixed mold 41 and the upper surface of the movable mold 42, when the fixed mold 41 and the movable mold 42 are butted against each other, the disk substrate 100 to be molded corresponds. A shaped molding cavity 44 is formed. That is, the forming cavity 44 has a substantially disc shape.

The central position of the fixed mold 41, that is,
An insertion hole is formed perpendicularly to the lower surface portion 41a at the center position of the lower surface portion 41a which constitutes the molding cavity 44 of the fixed mold 41. A sprue bush support ring 51 having a substantially annular shape is inserted and arranged in an insertion hole formed in the fixed mold 41. A substantially cylindrical sprue bush 48 is fitted and disposed on the sprue bush support ring 51. The sprue bush 48 has a resin injection hole 49 formed along the central axis.
have. The sprue bush 48 allows a synthetic resin material such as a molten polycarbonate resin supplied from an injection device (not shown) to flow into the molding cavity 4 through the resin injection hole 49. The sprue bush 48 is arranged such that the tip side portion thereof is slightly projected from the lower surface portion 41a of the fixed mold 1. That is, the tip end side of the sprue bush 48 enters the molding cavity 44, and the tip end surface where the opening end of the resin injection hole 49 is formed faces the molding cavity 44. The sprue bush support ring 51 is
The front end side facing the molding cavity 44 is reduced in diameter in a step shape, and the rear end side is a flange-shaped collar portion. The front end portion of the sprue bush support ring 51 has the fixed mold 4
1 is flush with the lower surface portion 41a of the first molding portion 1 and forms a part of the inner surface portion of the molding cavity 44. The front end portion of the sprue bush support ring 51 has the fixed mold 41.
A slight space is separated from the lower surface portion 41a of the.
The void portion is formed in an annular shape surrounding the front end portion of the sprue bush support ring 51.

Then, a stamper 50 for forming a concavo-convex pattern corresponding to an information signal or a pre-groove constituting the recording track is formed on the lower surface portion 41a constituting the molding cavity 44 of the fixed mold 41. It is installed. The stamper 50 is made of a material such as nickel and is formed in a thin disk shape having a center hole 50a in the center.

In the stamper 50, the center hole 50a is externally fitted to the tip end side portion of the sprue bush 48,
Positioned. That is, the inner diameter of the center hole 50a corresponds to the outer diameter of the sprue bush 48.
The outer peripheral edge side of the stamper 50 is fixed by the outer peripheral side stamper holder 54 attached to the fixed mold 41.
It is sandwiched between and supported by the fixed mold 41. The outer peripheral side stamper holder 54 is formed in a substantially annular shape, is attached to the outer peripheral side portion on the lower surface side of the fixed mold 41, and forms the outer peripheral edge portion of the molding cavity 44.

The fixed mold 41 is provided with a stamper suction mechanism for sucking and holding the stamper 50. This stamper suction mechanism includes a front end portion of the sprue bush support ring 51 and a lower surface portion 41 of the fixed mold 41.
The air between the fixed mold 41 and the stamper 50 is discharged to the outside by a vacuum pump (not shown) via a suction slit 55 which is a space between the fixed die 41 and a. That is, the suction slit 55 is formed on the outer surface of the sprue bush support ring 51 and the fixed mold 41.
The air discharge passage 56, which is a space formed between the inner wall of the insertion hole and the inner wall of the insertion hole. And this air discharge path 5
6 is communicated to the outside through a tunnel 57 formed in the fixed mold 41. The tunnel portion 57 is bored in the radial direction of the molding cavity 44 from the center side of the fixed mold 41 to the outer side surface portion.

The upper end of the air discharge path 56, that is, the gap 60 between the rear end of the sprue bush support ring 51 and the upper surface of the fixed mold 41 is provided with an O-ring 61. And is closed by the upper lid member 46.

A suction hose 58 is attached to the outer surface of the fixed mold 41 so as to communicate with the tunnel 57. The suction hose 58 is connected to the vacuum pump via a valve device 59. That is, this vacuum pump has a lower surface of the fixed mold 41 through the suction hose 58, the tunnel 57, the air discharge path 56, and the suction slit 55 when the valve device 59 is in the open state. Air between the portion 41a and the stamper 50 is sucked and discharged to the outside. When the valve device 59 is closed, the space between the lower surface portion 41a of the fixed mold 41 and the stamper 50 is closed to the outside. At this time, the stamper 50 has the lower surface portion 41a.
Against, it is suction-held.

On the other hand, at the center position of the upper movable mold 42,
An insertion hole is formed vertically on the upper surface of the movable mold 42. That is, this insertion hole is provided at a position facing the front end surface of the sprue bush 48 supported by the fixed mold 41. A substantially cylindrical groove portion forming ring 70 is fitted and disposed in the insertion hole formed in the movable mold 42. The groove forming ring 70 is fixedly disposed on the movable mold 42. The upper end surface of the groove forming ring 70 is flush with the upper surface of the movable mold 42 and forms a part of the inner surface of the molding cavity 44. On the upper end surface portion of the groove portion forming ring 70, a groove portion forming protrusion 53 is provided so as to have an annular shape coaxial with the groove portion forming ring 70. The groove forming projection 53 is provided on the fixed mold 41 side, that is, the molding cavity 4 side.
4 is provided so as to project inward.

Further, a sleeve 65 having a cylindrical shape is inserted and disposed in the groove forming ring 70. The sleeve 65 has a cylindrical punch 66.
Are inserted and disposed. The punch 66 and the sleeve 65 can be moved back and forth so that the sleeve 6
It is supported by 5. The sleeve 65 is supported by the movable mold 42 so as to be movable back and forth with respect to the groove forming ring 70. And this sleeve 65
Has the front end face facing the molding cavity 44 slightly retracted into the movable mold 42 rather than the upper surface of the groove forming ring 70. The punch 66 has a front end face facing the molding cavity 44 slightly projected from the front end face of the sleeve 65.

In order to form the disc substrate 100 in the mold device thus constructed, first, the movable mold 42 is butted against the fixed mold 41 to form the molding cavity 44. .. Then, by the injection device, the resin injection hole 4 of the sprue bush 48 is formed.
The molten synthetic resin material such as polycarbonate is injected and filled into the molding cavity 44 through 9. At this time, the synthetic resin material is used in the molding cavity 44.
Flows from the center toward the outer circumference. Then, the movable mold 42 is moved to the fixed mold 41 side, the synthetic resin material filled in the molding cavity 44 is compressed by a predetermined mold clamping pressure, so-called mold clamping is performed, and then cooled. .. Then, the synthetic resin material filled in the molding cavity 44 is solidified, and the disk substrate 100 having a shape corresponding to the molding cavity 44 is formed as shown in FIG. On the other hand, the punch 66
The center hole 100a is formed by projecting to the fixed mold 41 side.

In this mold apparatus, when molding the disk substrate 100, the mold clamping pressure, the punching of the center hole 100a by the punch 66 and the timing of curing the synthetic resin forming the disk substrate 100, etc. It is possible to control the birefringence characteristic of the disk substrate 100 to have a desired characteristic by appropriately adjusting the value. That is, since the disk substrate 100 has the annular groove portion 101 formed by the groove portion forming projection 53, the disc substrate 100 has a curved line in FIG. 4 depending on the mold clamping pressure, the timing of forming the center hole 100a, and the like. As shown by A to curve D, the birefringence characteristics are controlled. This disk substrate 100
When the radius is set to 32 mm and molded,
As shown by the curve B or the curve C therein, it can be formed with a birefringence characteristic suitable for use as an optical disk over substantially the entire surface.

The birefringence characteristic is a characteristic expressing the amount of birefringence that occurs when a light beam passes through a medium having so-called refractive index anisotropy, and is orthogonal to the traveling direction of the light beam. And the phase difference δ between the polarization components of the light beam in the x direction and the y direction orthogonal to each other.
When the phase difference [delta], where the wavelength of the light flux lambda, this travel distance in the medium of the light beam d, the medium quality of the x-direction of the refractive index n _X, the refractive index in the y-direction respectively and n _Y, It can be represented by δ = 2π / λ · (n _X −n _Y ) d.

In the mold apparatus, molding is performed by opening the movable mold 42 from the fixed mold 41 while projecting the sleeve 65 toward the fixed mold 41 side. The disk substrate 100 is released from the mold 43. Then, by separating the disc substrate 100 from the fixed mold 41,
As shown in FIG. 2, the molding of the disc substrate 100 is completed.

In this disc substrate 100, one main surface portion serves as a signal recording portion forming surface formed by the stamper 50. This signal recording portion formation surface is formed as a flat surface over the entire surface shown by arrow S ₂ in FIG. A chuck plate mounting recess 100c is formed in the center of one main surface of the disk substrate 100. This chuck plate mounting recess 10
0c is formed by the tip side portion of the sprue bush 48 that has entered the molding cavity 44. A position reference step 100b is formed in the center of the other main surface of the disc substrate 100. The position reference step 100b is formed by the insertion hole in the center of the movable mold 42 and the upper end of the sleeve 65, and is formed so as to include the chuck plate mounting recess 100c. ing. The lower end surface 100d formed by the outer peripheral surface of the position reference step 100b and the upper end of the sleeve 65.
Serves as a reference plane for positioning an optical disc constructed by using the disc substrate 100.

Then, as shown in FIG. 3, on the surface of the disc substrate 100 on which the signal recording portion is formed, an information signal is written and written through the disc substrate 100 from the other main surface side thereof. The read / write signal recording unit 103 is formed over a predetermined area indicated by an arrow S in FIG.

That is, when this optical disc is constructed as a read-only disc, a concavo-convex pattern corresponding to an information signal is formed on the surface of the disc substrate 100 on which the signal recording portion is formed. By means of the means, a reflection film made of aluminum or the like is deposited and formed so as to cover the uneven pattern. The concavo-convex pattern is formed by the stamper 50. The concavo-convex pattern and the reflection film form the signal recording unit 103.

When this optical disk is configured as a recording / playback disk, pregrooves forming recording tracks for recording information signals are formed on the surface of the disk substrate 100 on which the signal recording portion is formed. Further, a signal recording layer made of a magnetic material is deposited and formed so as to cover the pre-groove. The pregroove is formed by the stamper 50. The pre-groove and the signal recording layer serve as the signal recording unit 103.

Then, on the disk substrate 100, on the other main surface portion serving as the writing and / or reading surface of the information signal, and on the inner side of the area corresponding to the formation area of the signal recording section 103 and at the position. One continuous annular groove portion 101 is provided at a position on the outer side of the reference step portion 100b. This disk substrate 100
Since the signal recording portion formation surface is flat over the entire surface, the portion where the groove portion 101 is provided is thinner than the portion corresponding to the formation region of the signal recording portion 103. The depth of the groove portion 101 can be appropriately set in consideration of the molding condition of the disk substrate 100 in the mold device, but is set to, for example, about 50 μm or more.

In the mold device, the stamper 5 is used.
0 is effectively used over the entire surface of the disk substrate molding surface facing the molding cavity 44. That is,
In the disk substrate 100, the entire one main surface portion shown by the arrow S ₂ in FIG. 3 extending from the outer peripheral edge portion to the peripheral edge portion of the chuck plate mounting recess 100c is a flat surface having a flat surface. The area is a formable area of the signal recording unit 103 in which the signal recording unit 103 can be formed.
That is, in the disc substrate 100, the area where the signal recording unit 103 can be formed is the disc substrate 1
It extends to the innermost side of 00.

In this optical disc, a protective film 104 made of a synthetic resin material or the like is formed on one main surface portion so as to cover the signal recording portion 103. This protective film 1
Reference numeral 04 is for blocking the contact of moisture or the like in the air with the signal recording unit 103 to prevent corrosion of the reflection film or the like forming the signal recording unit 103.

The protective film 104 is provided on the signal recording portion 10
3 has a thickness sufficient to block the contact of moisture in the air with the disk substrate 3 and is firmly adhered to the disk substrate 100 so that it cannot be easily peeled off from the disk substrate 100. Needs to be formed. In this disc substrate 100, the protective film 1 indicated by an arrow W ₂ in FIG.
The width of the area 04 of the adhesion to the disk substrate 100, that is, the width from the inner peripheral edge of the signal recording portion 103 to the peripheral edge of the chuck plate mounting recess 100c is made wider. Disk substrate 10
It is possible to secure the close contact with 0 and secure the protection of the signal recording portion 103 by the protective film 104.

In this disc substrate 100, even when the protective film 104 is formed by a so-called spin coating method, the width from the inner peripheral edge of the signal recording portion 103 to the peripheral edge of the chuck plate mounting recess 100c is increased. And the signal recording portion forming surface is flat over the entire surface, a good protective film 104 can be formed.

Then, in this optical disc, the chuck plate 102 is fitted and disposed in the chuck plate mounting recess 100c. This chuck plate 1
02 is formed in a disk shape by a magnetic material such as metal. The chuck plate 102 is for holding the optical disk by being attracted by a magnet that constitutes a so-called magnet chuck mechanism in a recording and / or reproducing apparatus using the optical disk.

In the optical disc according to the present invention, the groove portion 101 may be formed continuously with the outer peripheral wall portion of the position reference step portion 100b as shown in FIG. Further, in the optical disc according to the present invention, the number of the groove portions 101 is not limited to one, and as shown in FIG. 9, the first groove 101a and the second groove 101a formed in two concentric annular shapes. It may be configured by the groove 101b. Further, the groove portion 101 may be formed by three or more annular groove portions that are concentric with each other. In these cases as well, the groove portion 101 is on the other main surface portion of the disc substrate 100 on the inner side of the area corresponding to the formation area of the signal recording portion 103 and more than the position reference step portion 100b. It is formed at a position on the outer side.

The mold device for molding the disc substrate of the optical disc according to the present invention is not limited to the one having the stamper suction mechanism using the vacuum pump as shown in the above embodiment. That is, as shown in FIG. 7, this mold device has a magnet 68 arranged so as to be flush with the lower surface part 41a so as to form a part of the lower surface part 41a of the fixed mold 41. It may be configured as. In the mold device having such a magnet 68, the sprue bush support ring 51 and the fixed mold 41 are in close contact with each other and seal the molding cavity 44. In this mold apparatus, the stamper 50 is supported on the outer peripheral side by the outer peripheral side stamper holder 54, and the main surface portion is attracted and held by the magnet 68, so that the fixed mold 4 is held.
It is attached to 1. If the magnet 68 is an electromagnet, it becomes easier to remove the stamper 50 from the fixed mold 41.

[0055]

As described above, in the optical disc according to the present invention, information signals are written and / or written on one main surface portion.
Alternatively, the disc substrate on which the signal recording portion to be read is formed is on the other main surface portion serving as the writing and / or reading surface of the information signal, and is on the inner side of the area corresponding to the formation area of the signal recording portion. Further, at least one continuous groove portion having an annular shape is provided at a position on the outer side of the position reference step portion projectingly provided in the central portion of the main surface portion, and the portion where the groove portion is provided is It is made thinner than the portion corresponding to the formation area of the signal recording portion.

Therefore, in this optical disc, one main surface portion of the disc substrate on which the signal recording portion is formed can be a flat surface over the entire surface. Therefore, in this optical disc, the protective film formed on one main surface of the disc substrate to cover the signal recording portion can be surely applied to the disc substrate.

The disc substrate of this optical disc is
The birefringence property can be controlled during molding, and the birefringence property can be formed to have good birefringence properties.

That is, according to the present invention, the formable area of the signal recording area is a wide area extending to the innermost peripheral side, and the protective film for protecting the reflection film, the signal recording layer and the like is surely deposited, and It is possible to provide an optical disk in which the disk substrate has good birefringence characteristics and recording and / or reproducing characteristics of information signals are good.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an optical disc according to the present invention.

FIG. 2 is a vertical cross-sectional view showing a disk substrate that constitutes the optical disk.

FIG. 3 is a vertical sectional view showing a configuration of the optical disc.

FIG. 4 is a graph illustrating a control situation of birefringence characteristics during molding of the disc substrate.

FIG. 5 is a graph illustrating a control state of birefringence characteristics during molding of a conventional disk substrate.

FIG. 6 is a vertical cross-sectional view showing a configuration of a mold device for molding a disc substrate of an optical disc according to the present invention.

FIG. 7 is a vertical cross-sectional view showing another example of the configuration of a mold device for molding the disc substrate of the optical disc.

FIG. 8 is a vertical cross-sectional view showing another example of the configuration of the optical disc.

FIG. 9 is a vertical sectional view showing still another example of the configuration of the optical disc.

FIG. 10 is a vertical cross-sectional view showing the configuration of a mold device for molding a disc substrate of a conventional optical disc.

FIG. 11 is a vertical cross-sectional view showing a disk substrate that constitutes a conventional optical disk.

FIG. 12 is a vertical sectional view showing the structure of a conventional optical disc.

[Explanation of symbols]

 Reference numeral 100 ... Disk substrate 100b ... Position reference step portion 101 ... Groove portion 101a ... ...... First groove portion 101b ...... Second groove portion

Claims (1)

[Claims] 1. A disk substrate made of a synthetic resin material having a light-transmitting property, formed on one main surface portion of the disk substrate, and the information is transmitted through the disk substrate from the other main surface portion side of the disk substrate. A signal recording portion for writing and / or reading a signal, and a position reference step portion projecting in the central portion of the other main surface portion of the disc substrate are provided. And / or at least one continuous line at a position on the other main surface portion serving as a read surface, which is on the inner side of the area corresponding to the formation area of the signal recording portion and on the outer side of the position reference step portion. An optical disc having a circular ring-shaped groove portion, and a portion where the groove portion is provided is thinner than a portion corresponding to the formation area of the signal recording portion.