JPH06176400A - Optical disk substrate and optical disk formed by using the substrate - Google Patents

Abstract

PURPOSE:To provide the optical disk substrate having good flatness of a reference plane and high quality. CONSTITUTION:The optical disk substrate having a level difference between the reference plane formed on the inner peripheral part of the optical disk substrate and the reading surface formed on the outer side thereof is produced by an injection molding method using metallic molds designed in accordance with shrinkage at the time of molding. The thickness of the reference plane may be thinner than the thickness of the reading surface at this time. For example, the mold surface 14a of a sleeve 14 corresponding to the reference plane of the molds constituted of a stationary part 5 and a moving part 6 is formed as a surface inclining from a punch 15 toward a moving mirror 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk substrate and an optical disk using the same, and more particularly to the shape of a mold used for manufacturing the optical disk substrate.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a magnetic thin film is partially heated above a Curie point or a temperature compensation point to eliminate the coercive force of this portion and magnetize in the direction of a recording magnetic field applied from the outside. The basic principle is to invert the direction of the, and it is being put to practical use in an optical file system, an external storage device of a computer, a recording device of audio and video information, and the like.

The magneto-optical recording method is roughly divided into an optical modulation method and a magnetic field modulation method. Among them, the magnetic field modulation method has attracted attention because it can be overwritten and corresponds to the magnetic field modulation method. For example, a small magneto-optical disk having a diameter of about 64 mm has been developed as a recording medium.

The small-sized magneto-optical disk as described above has a recording magnetic layer (magneto-optical effect) which has an easy axis of magnetization in the direction perpendicular to the film surface on one main surface of a transparent optical disk substrate made of polycarbonate or the like. For example, a recording portion is formed by laminating a rare earth-transition metal alloy amorphous thin film), a reflection layer, and a dielectric layer, and is formed on the recording portion so as to cover a protective film made of an ultraviolet curable resin or the like. It is a thing.

The optical disk substrate is disk-shaped and has a reference surface 21 on the inner peripheral portion and a reading surface 22 on the outer side thereof, as shown in FIG. The reference surface 21 is a mounting surface for a recording / reproducing apparatus, and for convenience of mounting, a hole called a center hole 23 is formed in the center of the reference surface 21, and the reading surface 22 records information. The reference surface 21 and the reading surface 2 are formed as reproduction surfaces.
A step is formed between the two. Therefore, it goes without saying that the small magneto-optical disk described above also has the shape shown in FIG. In addition, normally, the reference surface 2 of the optical disk substrate 24
1 is formed thinner than the reading surface 22.

Such an optical disk substrate is manufactured by an injection molding method because it has good mass productivity and dimensional accuracy. That is, the resin melted in a mold that can form an optical disk substrate having a step between the reference surface and the reading surface and a center hole in the center of the reference surface is injected into the mold under high pressure. It is poured, solidified and molded to obtain an optical disk substrate.

[0007]

However, when the optical disk substrate is manufactured by injection molding as described above, there is a problem that the flatness of the reference surface of the obtained optical disk substrate is impaired. As a matter of course, when molding is performed by the injection molding method, the resin is melted and then injected into the mold under high pressure to be solidified, so that the resin slightly contracts during solidification. At this time, the shape of the manufactured optical disk substrate has a step between the reference surface 21 and the reading surface 22 and a center hole 23 at the center of the reference surface 21, as shown in FIG. When a shaped optical disk substrate is molded by injection molding, the solid-state optical disk substrate shown in FIG.
As shown in FIG. 3, the resin shrinks on the disk substrate 24 in the direction indicated by the arrow P in the figure, and the central portion of the reference surface 21, that is, the center hole 23 is depressed, and the reference surface 21
Becomes an inclined surface and impairs the flatness of the reference surface 21. When the reference surface 21 of the optical disk substrate is thinner than the reading surface, resin contraction is more likely to occur and the flatness of the reference surface 21 is likely to be impaired.

As described above, the reference surface 2 of the optical disk substrate
Since reference numeral 1 is a mounting surface for a recording / reproducing apparatus, the reference surface 2
When the flatness of 1 is impaired, when recording and reproducing information on a magneto-optical disk formed using this, eccentricity occurs at the time of rotation of the magneto-optical disk, and the magneto-optical disk rotates while fluttering up and down, It becomes impossible to accurately record and reproduce information.

Further, if such deformation occurs in the optical disk substrate, it cannot be used as a product, resulting in a decrease in manufacturing yield.

Therefore, the present invention has been proposed in view of the conventional circumstances, and does not impair the flatness of the reference surface of the optical disc substrate even if the resin shrinks during injection molding of the optical disc substrate. An object of the present invention is to provide a mold that does not reduce the manufacturing yield, and to provide an optical disk substrate having a good reference plane flatness and a high quality, and an optical disk using the same.

[0011]

In order to achieve the above object, the present invention provides an optical disk substrate having a step between a reference surface formed on the inner peripheral portion of the optical disk substrate and a reading surface formed outside the reference surface. Is manufactured by an injection molding method using a mold designed based on the shrinkage deformation amount at the time of molding.

Further, in the optical disc substrate of the present invention, the thickness of the reference surface of the optical disc substrate is smaller than the thickness of the reading surface, and further, the mold surface forming the reference surface of the mold is located from the center of the reference surface. It is characterized in that it is an inclined surface that is inclined toward the reading surface side. Further, the optical disc of the present invention is designed based on the shrinkage deformation amount at the time of molding the optical disc substrate having a step between the reference surface formed on the inner peripheral portion of the optical disc substrate and the reading surface formed outside the reference surface. An optical disk substrate manufactured by an injection molding method using a mold is used.

[0013]

The reference surface having the center hole formed at the center, which is the surface to be attached to the recording / reproducing apparatus, is provided on the inner peripheral portion, and the reading surface is provided outside the reference surface. A step is provided between the reference surface and the reading surface. When injection molding an optical disc substrate having the shape
When the resin is solidified, the resin shrinks toward the center of the optical disk substrate, which causes a problem of impairing the flatness of the reference surface.

In the optical disk substrate of the present invention, an optical disk substrate having a step between the reference surface formed on the inner peripheral portion of the optical disk substrate and the reading surface formed outside the reference surface is based on the shrinkage deformation amount at the time of molding. Since the resin is manufactured by the injection molding method using the designed mold, the flatness of the reference surface of the optical disk substrate is not impaired by the shrinkage of the resin.

Further, in the optical disk substrate of the present invention, the thickness of the reference surface of the optical disk substrate is thinner than the thickness of the reading surface, and further, the mold surface forming the reference surface of the mold is located from the center of the reference surface. Since the inclined surface is inclined toward the reading surface side, even if the resin shrinks toward the center of the optical disk substrate during solidification, it is offset by the inclination of the formed reference surface and the reference surface of the optical disk substrate There is no loss of flatness.

Therefore, by using such an optical disk substrate, it is possible to obtain an optical disk which can perform accurate recording / reproduction without causing eccentricity in recording and / or reproducing information or fluttering the disk vertically.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described below with reference to the drawings. In this embodiment, the case where the present invention is applied to a magneto-optical disk will be described as an example.

As shown in FIG. 1, the magneto-optical disk of this embodiment is a recording comprising an optical disk substrate 31, a first dielectric layer 32, a recording magnetic layer 33, a second dielectric layer 34, and a reflecting layer 35. The part 36 is formed, and the protective layer 37 is further formed so as to cover the recording part 36.

As shown in FIG. 2, the optical disk substrate 31 is disk-shaped and has a reference surface 1 on the inner peripheral portion and a reading surface 2 on the outer side. The reference surface 1 is a mounting surface for a recording / reproducing apparatus. For convenience of mounting, a hole called a center hole 3 is formed in the center of the reference surface 1, and the reading surface 2 records information. An information signal such as a sector mark (not shown) is recorded as a pit on the surface for reproduction, and a step is formed between the reference surface 1 and the reading surface 2. Further, the reference surface 1 of the optical disk substrate 4 is formed thinner than the reading surface 2, and in the optical disk substrate of the present embodiment, the reference surface 1
Has a thickness a of 0.8 mm and the reading surface 2 has a thickness b of 1.2.
It is set to mm.

Such an optical disk substrate is manufactured by injecting a molten resin under high pressure into a mold as shown in FIG. 3 and solidifying it. The mold includes a fixed part 5 connected to the resin supply part and a movable part 6 facing the fixed part 5.
And a space 16 having the shape of an optical disk substrate is formed in the facing portion between the fixed portion 5 and the movable portion 6.

The fixed portion 5 is composed of a sprue bush 7 having a resin supply hole 8 formed therein and a fixed mirror 9 having an air suction hole 10 formed therein, and has a substantially cylindrical fixed mirror 9. The sprue bush 7 having a substantially columnar shape is arranged in the center. One main surface 9a of the fixed mirror 9
Ring-shaped stamper 11 for forming sector marks and the like at positions corresponding to the reading surface of the optical disk substrate
Is installed, in order to fix the stamper 11, a stamper inner circumference guide 9b is provided at a position corresponding to the inner circumference of the stamper 11 of the fixed mirror 9, and a stamper is provided at a position corresponding to the outer circumference of the stamper 11 of the fixed mirror 9. A stamper holder 12 for pressing and fixing 11 from the outer periphery is arranged. The movable portion 6 is formed by a movable mirror 13, a sleeve 14 and a punch 15, and a substantially cylindrical sleeve 14 is provided at the center of the substantially cylindrical movable mirror 13.
And a substantially cylindrical punch 15 is arranged. The movable mirror 13, the sleeve 14 at the position corresponding to the reading surface of the optical disk, the sleeve 14 at the position corresponding to the reference surface, and the punch 15 at the position corresponding to the center hole. It is provided. The punch 15 is movable.

At this time, the outer diameter of the movable mirror 13 of the movable portion 6 is sized to fit into the gap formed by the stamper holder 12 of the fixed mirror 9 of the fixed portion 5, and the sprue bush 7 of the fixed portion 5 is fitted. Is arranged so as to protrude from the fixed mirror 9, the tip 15a of the punch 15 of the movable portion 6 is fitted into the tip portion 8a of the resin supply hole 8 of the sprue bush 7, and the sleeve 14 is arranged more than the movable mirror 13. Since the movable mirror 13 is fitted in the gap formed by the stamper holder 12 so that the fixed portion 5 and the movable portion 6 face each other, the reference portion between the fixed portion 5 and the movable portion 6 is provided. A space 16 having the shape of an optical disk substrate having a step between the reading surface and the reading surface is formed. As shown in FIG. 4, after the resin is injected, the punch 15 is attached to the resin supply hole 8
The center hole can be formed by fitting to.

In the mold for manufacturing the optical disk substrate of this embodiment, the mold surface 14a corresponding to the reference surface of the sleeve 14 of the movable portion 6 is movable from the punch 15 side to the movable mirror 1 side.
It is formed so as to incline toward the 3 side. here,
As shown in FIG. 5, in the optical disk substrate obtained by the conventional mold in which the mold surface 18a corresponding to the reference surface of the sleeve 18 is a flat surface, when the mold surface 18a shrinks in the P direction as shown in FIG. Since the shrinkage rate differs between the area D ₁ over the entire surface and the area D ₂ corresponding to the center hole 23,
The center hole 23 is depressed and the reference surface 21 becomes an inclined surface. With respect to the inclination angle θ of this inclined surface, if the contraction rate of the area D ₁ over the entire reference surface 21 is S ₁ and the contraction rate of the area D ₂ corresponding to the center hole 23 is S ₂ ,
It is calculated by Equation 1.

[0024]

[Equation 1]

For example, the thickness a of the reference surface 1 is 0.8 mm,
When the thickness b of the reading surface 2 is 1.2 mm, S
₁ is 0.6%, S ₂ is 0.58 to 0.59%, and the inclination angle θ of the inclination generated by the depression is 0.8 ° to
The degree of depression d is 1.6 °, and the amount of depression d reaches about 30 to 50 μm.

On the other hand, in the present embodiment, in consideration of such a depression deformation of the optical disc substrate reference surface in advance, an inclination opposite to the inclination formed by the depression deformation on the mold surface 14a corresponding to the reference surface, That is, as shown in FIG. 4, an inclination angle of 0.8 ° to 1.6 ° such that the height difference C between the die surface 14a of the sleeve 14 on the punch 15 side and the movable mirror 13 side is 0.03 mm. Is attached. Therefore, when the resin injected and injected into the space 16 is solidified, the resin contracts in the central direction of the optical disk substrate, and the reference surface 1
Even if the center hole 3 of the mold is depressed, in the optical disk substrate of the present embodiment, the mold surface 1 corresponding to the reference surface of the sleeve 14 in the mold forming the optical disk substrate.
This is offset by the fact that 4a is an inclined surface, and it is possible to obtain the reference surface 1 having good flatness. In the optical disc substrate of this embodiment, the flatness of the reference plane can be set to 30 μm or less.

Therefore, when manufacturing an optical disk substrate using the above-mentioned mold, the air in the space 16 is degassed from the air suction hole 10 provided in the fixed mirror 9, and the resin is supplied under high pressure. The molten resin 17 is injected and injected into the space 16 from the portion through the resin supply hole 8 of the sprue bush 7,
5 is fitted in the resin supply hole 8 to form a center hole and solidified to manufacture an optical disk substrate.

The magneto-optical disk of this embodiment, as shown in FIG. 1, is an optical disk substrate 31 manufactured in this way.
A recording section 36 composed of a first dielectric layer 32, a recording magnetic layer 33, a second dielectric layer 34, and a reflective layer 35 is laminated on top, and the surface of the recording section 36 is covered with a protective layer 37. To be done. Oxides and nitrides can be used as the first dielectric layer 32 and the second dielectric layer 34 of the functional film forming the recording portion 36. Nitride is more preferable because it may adversely affect the layer, and silicon nitride, aluminum nitride, or the like is preferable as a substance that does not allow oxygen and moisture to pass therethrough and allows the used laser beam to pass sufficiently.

The recording magnetic layer 33 is an amorphous magnetic thin film having an easy magnetization direction in a direction perpendicular to the film surface, and it has excellent magneto-optical characteristics and has a large coercive force at room temperature. It is desirable to have a Curie point near 200 ° C. As a recording material satisfying such conditions, a rare earth-transition metal alloy amorphous thin film and the like can be mentioned, and among them, a TbFeCo based amorphous thin film is preferable. An additive element such as Cr may be added to the recording magnetic layer 33 for the purpose of improving corrosion resistance.

The reflective layer 35 is preferably composed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric layer 34, and a non-magnetic metal vapor deposition film is suitable. . Further, it is desirable that this reflective layer is a good conductor in terms of heat, and aluminum is suitable in view of availability and film formation.

Each of these layers 32, 33, 34, 35 is
It is formed by a so-called vapor phase plating technique such as vapor deposition or sputtering. At this time, the film thickness of each layer can be set arbitrarily, but is usually set to several hundreds to several thousands Å. It is preferable that these film thicknesses are determined in consideration of not only the optical properties of the individual layers but also the effects of the combination. This is because, for example, when the thickness of the recording magnetic layer 33 is thinner than the wavelength of the laser light, the laser light causes multiple interference with the light transmitted through the recording magnetic layer 33 and reflected at each layer boundary, and the combination of the thicknesses causes This is because the effective optical and magneto-optical characteristics of the recording magnetic layer 33 greatly change.

Further, the protective layer 37 is formed on the recording portion 36. The protective layer 37 is provided on the recording unit 36.
Is provided to insulate water from oxygen and water in the atmosphere. An ultraviolet curable resin such as an acrylic ultraviolet curable resin is used for the protective layer 36.

In the magneto-optical disk having such a structure, since the reference surface of the optical disk substrate is a precisely flat surface, there is no eccentricity or fluttering of the disk when recording / reproducing information, and the disk is accurate. Recording and reproduction can be performed.

In this embodiment, the case where the optical disk substrate of the present invention is applied to a magneto-optical disk has been described as an example, but the present invention is not limited to the magneto-optical disk and can be applied to various optical disks. For example, in a CD-ROM or the like, a metal reflective film of Al or the like is formed on the disk substrate. In the write-once type optical disc, a low melting point metal thin film, a phase change film, a film containing an organic dye, etc. are formed on the optical disc substrate.
In any of the optical discs, if the optical disc substrate manufactured by using the above-mentioned mold is used, the reference plane is precisely a flat plane, and therefore, accurate recording / reproducing can be performed similarly.

[0035]

As is apparent from the above description, according to the present invention, an optical disk substrate having a step between the reference surface formed on the inner peripheral portion of the optical disk substrate and the reading surface formed outside the reference surface is formed. Since it is manufactured by an injection molding method using a mold designed based on the shrinkage deformation amount at the time, the shrinkage of the resin does not impair the flatness of the reference surface of the optical disk substrate, and the manufacturing yield is good and high quality is achieved. An optical disk substrate can be obtained.

Further, in the optical disk substrate of the present invention, the thickness of the reference surface of the optical disk substrate is thinner than the thickness of the reading surface, and further, the mold surface forming the reference surface of the mold is located from the center of the reference surface. Since it is an inclined surface that inclines toward the reading surface side, even if resin shrinks toward the center of the optical disk substrate during solidification, it is offset, and the flatness of the reference surface of the optical disk substrate is not compromised. It is possible to obtain a high-quality optical disk substrate with a good yield.

Therefore, by using the above optical disk substrate, it is possible to obtain an optical disk capable of performing accurate recording / reproduction without causing eccentricity in recording and / or reproducing information or fluttering the disk vertically.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an essential part showing a configuration example of an optical disc to which the present invention is applied.

FIG. 2 is a sectional view showing an optical disk substrate to which the present invention is applied.

FIG. 3 is a cross-sectional view showing one structural example of a mold for manufacturing an optical disc substrate to which the present invention is applied.

FIG. 4 is an enlarged sectional view of an essential part showing a mold for manufacturing an optical disc substrate to which the present invention is applied.

FIG. 5 is an enlarged sectional view of an essential part showing a conventional mold.

FIG. 6 is a cross-sectional view showing an optical disk substrate manufactured by a conventional mold.

FIG. 7 is a cross-sectional view showing an optical disk substrate.

[Explanation of symbols]

 1 ・ ・ Reference surface 2 ・ ・ Reading surface 3 ・ ・ ・ ・ ・ ・ Center hole 4 ・ ・ ・ ・ ・ ・ Optical disk substrate 5 ・ ・ ・ ・ ・ ・ Fixing part 6 ・ ・ ・ ・..Movable part 13 ... Movable mirror 14 ... Sleeve 15 ... Punch 16 ... Space

Claims (4)

[Claims] 1. A mold designed based on a shrinkage deformation amount when molding an optical disk substrate having a step between a reference surface formed on an inner peripheral portion of the optical disk substrate and a reading surface formed outside the reference surface. An optical disk substrate characterized by being used and manufactured by an injection molding method. 2. The optical disk substrate according to claim 1, wherein the reference surface has a thickness smaller than that of the reading surface. 3. The optical disk substrate according to claim 2, wherein the mold surface forming the reference surface is an inclined surface inclined from the center of the reference surface toward the reading surface side. 4. An optical disc using the optical disc substrate according to claim 1 as a substrate for forming a recording portion.