Method of and apparatus for forming transparent layer on disc substrate, and disc therefrom

A disc is produced using a method of and an apparatus for forming a transparent layer on a disc substrate. The method for forming the transparent layer on the disc substrate includes covering an axial hole formed at a center of the disc substrate with a cover element by inserting a protrusion of the cover element in the axial hole of the disc substrate so that a resin does not leak through the axial hole, dispensing the resin toward the center of the disc substrate from an upper side of the disc substrate, and removing the cover element. A more uniform transparent layer can be obtained throughout the disc substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2001-49032, filed Aug. 14, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a disc, and more particularly, to a method of and an apparatus for forming a transparent layer on a disc substrate, and a disc therefrom.

2. Description of the Related Art

FIG. 1is a cross-sectional view of a convention optical disc. Referring toFIG. 1, the disc includes a disc substrate10, a transparent layer15, and an axial hole14formed at a center of the disc. In a case of a high density digital versatile disc (HD-DVD), a thickness T of the disc substrate10is 1.1 mm, and a thickness “d” of the transparent layer15is 0.1 mm, and thus a total thickness of the optical disc is 1.2 mm. In particular, in order to precisely focus a laser beam, which is radiated from a reproducing apparatus, on a surface of the transparent layer15, the thickness “d” of the transparent layer15should be within a range of 100 μm±3 μm. Methods of forming the thin transparent layer15include a spin coating method.

FIG. 2is a reference view illustrating a conventional spin coating method of forming a transparent layer15on a substrate10. In the conventional spin coating method, a liquid ultraviolet hardening resin13is dropped at a point of a surface of the disc substrate10, which rotates at a low speed, as shown inFIG. 2, and then, the disc substrate10is rotated at a high speed. The liquid ultraviolet hardening resin13is spread out along the surface of the disc substrate10in a radial direction by a centrifugal force to coat the disc substrate10. Next, ultraviolet light is radiated onto the coated ultraviolet hardening resin13, thereby hardening the ultraviolet hardening resin13.

When forming the thin transparent layer15by the spin coating method, the thickness “d” of the transparent layer15depends on processing conditions such as a spinning speed, a spinning time, a dispensing position of the ultraviolet hardening resin13, and a dispensing amount, and a property of the resin13, such as viscosity. In particular, in order to coat the transparent layer15to the thickness T of 100 μm, the viscosity of the ultraviolet hardening resin13should be more than several centi-poise (cps). As the viscosity of the resin13increases, uniformity of the thickness “d” of the transparent layer15increases, and simultaneously, a molecular attraction increases, thereby affecting the discharged position of the ultraviolet hardening resin13on the disc substrate10.

FIG. 3is a graph illustrating a relationship between the dispensing position of a resin and the uniformity of the thickness of a layer.FIG. 3presents the uniformity of the thickness of the transparent layer15, which is generated when the ultraviolet hardening resin13is dispensed at the axial hole (center) and at 20 mm, 30 mm, 40 mm, and 45 mm of a radius, respectively, of the disc substrate10under conditions of the viscosity of 5000 cps, the dispensing amount of 5 g, and the spinning speed of 700 rpm. As shown inFIG. 3, the thickness of the transparent layer15is most uniform when the ultraviolet hardening resin13is dispensed at the center (axial hole14) of the disc substrate10.

However, as mentioned above, in the conventional spin coating method, the ultraviolet hardening resin is not dispensed at a center of the disc substrate but at a point of the surface of the disc substrate.

SUMMARY OF THE INVENTION

To solve the above and other problems, it is an object of the present invention to provide a method of and an apparatus for forming a transparent layer on a disc substrate, in which a resin is dispensed at a center of the disc substrate, thereby forming a transparent layer having higher uniformity, and a disc therefrom.

It is another object of the present invention to provide a method of and an apparatus for forming a transparent layer on a disc substrate, in which a wider recording surface can be obtained, and a disc therefrom.

Accordingly, to achieve the above and other objects, there is provided a method of forming a transparent layer on a disc substrate. The method includes (a) covering an axial hole formed at a center of the substrate with a cover element by inserting a protrusion of the cover element in the axial hole of the disc substrate so that a resin does not leak through the axial hole, (b) dispensing the resin toward the center of the disc substrate from an upper side of the disc substrate, and (c) removing the cover element from the substrate.

According to an aspect of the present invention, the method further includes (a0) inserting an central axle protruding from a spindle table in the axial hole of the disc substrate and mounting the disc substrate in a rotation support board installed around the central axle, wherein a first sum of a height of the rotation support board and a thickness of the disc substrate is equal to or greater than a second sum of a length of the central axle and a length of the protrusion of the cover element.

According to another aspect of the present invention, the method further includes (a1) closely placing the disc substrate and the rotation support board on the spindle table. In the closely placing of the disc substrate on the rotation support, air contained in a first space between the disc substrate and the rotation support board flows out through at least one hollow formed in the rotation support board to form a vacuum state in the first space between the disc substrate and the rotation support board in order to closely place the disc substrate on the rotation support board on the spindle table, or air contained in a second space between the cover element and the rotation support board flows out through at least one hollow formed in the central axle to form a vacuum state in the second space between the cover element and the central axle in order to closely place (attach) the disc substrate and the rotation support board on the spindle table. The method may include attaching the cover element and the central axis using a magnet, which is mounted in an internal side of the central axle. With this feature, the disc substrate and the rotation support board are closely placed on the spindle table.

According to still another aspect of the present invention, the method further includes rotating the disc substrate to uniformly coat the resin onto the disc substrate and hardening the coated resin.

To achieve the above and other objects, there is provided an apparatus for forming the transparent layer on the disc substrate. The apparatus includes a supporting portion which supports the disc substrate so that the disc substrate is mounted and rotates, and a resin dispensing portion which dispenses the resin toward the center of the disc substrate.

According to yet another aspect of the present invention, the supporting portion includes the cover element having the protrusion formed to cover the axial hole so that the resin dose not leak through the axial hole formed at the center of the disc substrate.

According to still yet another aspect of the present invention, the supporting portion includes a spindle motor, the spindle table having a side connected to the spindle motor, and the central axle connected to the spindle motor through the spindle table to pass through the spindle table and to protrude from an opposite side of the spindle table, and a rotation support board arranged around the central axle of the spindle table, on which the disc substrate is mounted.

According to a further aspect of the present invention, the first sum of the height of the rotation support board and the thickness of the disc substrate is equal to or greater than the second sum of the length of the central axle and the length of the protrusion.

According to another an aspect of the present invention, at least one hollow through which air flows out to form the vacuum state in a first space between the disc substrate and the rotation support board in order to closely attach the disc substrate and the rotation support board each other, is formed in the rotation support board, or at least one hollow through which air flows out to form the vacuum state in the second space between the cover element and the central axle in order to closely attach the disc substrate and the rotation support board to each other, is formed in the central axle. A magnet attaching the cover element and the central axle to closely attach the disc substrate and the rotation support board each other, may be mounted in the internal side of the central axle. In particular, it is possible that the rotation support board is coated with a predetermined material so that a residue is easily removed from the rotation support board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 4A and 4Bare partial sectional views of an apparatus for forming a transparent layer according to a first embodiment of the present invention. Referring toFIGS. 4A and 4B, the apparatus for forming a transparent layer includes a resin dispensing portion dispensing a resin43and a supporting portion supporting a rotating disc substrate40. The resin dispensing portion includes a dispensing header41and a dispensing nozzle42through which the resin43is dispensed. The supporting portion includes a spindle motor (not shown), a spindle table44connected to the spindle motor through a central axle47, and a rotation support board46, which surrounds the central axle47on the spindle table44. The rotation support board46is not limited to a specific material, and plastics and metals may be used for the rotation support board46.

In the first embodiment, the central axle47is projected to an external side of the rotation support board46so that the central axle47is inserted in an axial hole49, which is formed in a center of the disc substrate40, and the rotation support board46supports the disc substrate40. A radius of the rotation support board46is smaller than that of the disc substrate40. A cover element48is installed in an axial hole, which is formed at the center of the disc substrate40. The cover element48covers the axial hole49so that the resin43does not leak into the axial hole49when the resin43is dispensed. The cover element48includes a header48aand a protrusion48b. When the cover element48is mounted on the disc substrate40, a lower side of the header48ais closely attached onto a surface of the disc substrate40, and the protrusion48bis inserted in the axial hole49. A radius of the header48ais greater than that of the axial hole49so as to cover the axial hole49. The protrusion48bprevents the disc substrate40from shaking when the disc substrate40rotates at a high speed.

In particular, in the first embodiment, a first sum of a height h of the rotation support board46and a thickness d of the disc substrate40is equal to or greater than a second sum of a length l of the central axle47and a length p of the protrusion48b, and the length p of the protrusion48bis equal to or smaller than the thickness d of the disc substrate40. This is expressed by Equation 1.
h+d≧l+p,
and
d≧p  (1)

In order to rotate the disc substrate40by the spindle motor at a high speed, the disc substrate40, the rotation support board46, and the spindle table44are closely attached to one another. In order to closely attach the disc substrate40to a spindle table44during rotation of the spindle motor, air between the disc substrate40and the spindle table44flows out to obtain a vacuum state. The method can be applied to the present invention, and thus a configuration implementing the method is as below.

Referring toFIG. 5, at least one hollow46acommunicates with the rotation support board46and the spindle table44. As a result, air flows out to an external side of the spindle table44, and the vacuum state is formed between the cover element48and the rotation support board46, and thus the disc substrate40and the rotation support board46are closely placed on the spindle table44.

Referring toFIG. 6, at least one hollow47acommunicates with the central axle47and the spindle table44. As a result, air flows out toward the external side of the spindle table44, and the vacuum state is formed between the cover element48and the central axle47, and thus the disc substrate40and the rotation support board46are closely placed on the spindle table44.

FIG. 7illustrates another method of closely attaching the disc substrate40and the rotation support board46to the spindle table44. Referring toFIG. 7, a magnet70is mounted in an internal side of the central axle47. In order to increase a magnetic force of the mounted magnet70, the magnet70is preferably an electromagnet. As a result, the cover element48and the central axle47is closely attached to each other, and thus, the disc substrate40and the rotation support board46are closely placed on the spindle table44.

FIGS. 8A and 8Bare partial cross-sectional views of another apparatus for forming the transparent layer according to a second embodiment of the present invention. Referring toFIGS. 8A and 8B, the apparatus for forming the transparent layer includes a resin dispensing portion dispensing a resin83and a supporting portion supporting a disc substrate80so that the disc substrate80is mounted and rotates. The resin dispensing portion includes a dispensing header81and a dispensing nozzle82through which the resin83are dispensed. The supporting portion includes a spindle motor (not shown), a spindle table84connected to the spindle motor through a central axle87, and a rotation support board86surrounding the central axle87on the spindle table84.

In the second embodiment, the central axle87is mounted in an internal side of the rotation support board86. An insertion hole90is formed at a center of the rotation support board86. A radius of the rotation support board86is smaller than that of the disc substrate80. A cover element88is installed in the insertion hole90after the disc substrate80is mounted so that an axial hole89formed at a center of the disc substrate80is connected to the insertion hole90formed in the rotation support board86. The cover element88covers the axial hole89so that the resin83does not leak through the axial hole89when the resin83is dispensed. The cover element88also includes a header88aand a protrusion88b. When the cover element88is mounted on the disc substrate80, a lower side of the header88ais closely placed on an upper surface of the disc substrate80, and the protrusion88bis inserted in the axial hole89, which is formed on the disc substrate80, and in the insertion hole90, which is formed in the rotation support board86. A radius of the header88ais greater than that of the axial hole89so as to cover the axial hole89. The protrusion88bpasses through the disc substrate80to be inserted into the rotation support board86, thereby preventing the disc substrate80from shaking when the disc substrate80rotates at a high speed.

Also, in the second embodiment, the first sum of the height h of the rotation support board86and the thickness d of the disc substrate80is equal to or greater than the second sum of the length l of the central axle87and the length p of the protrusion88b, and the length p of the protrusion88bis greater than the thickness d of the disc substrate80. This is expressed by Equation 2.
h+d≧l+p,
and
p>d  (2)

In order to rotate the disc substrate80by the spindle motor at the high speed, the disc substrate80, the rotation support board86, and the spindle table84is closely placed on one another. The configuration of the supporting portion is the same as that of the supporting portion of the first embodiment described inFIGS. 5 through 7.

FIGS. 9A through 9Dare various cross-sectional views of a cover element according to another embodiment of the present invention. Referring toFIGS. 9A through 9D, unlike the above-mentioned cover element of the first and second embodiments, the cover element can be manufactured in various shapes. Referring toFIG. 9A, the header of the cover element has a disc shape as an isosceles trapezoid. Referring toFIGS. 9B and 9C, the header of the cover element has a disc shape, in which a cross-section of the header has a semi-ellipse shape.FIG. 9Dshows the cover element in which only a protrusion without a header is formed.

The material of the cover element is not limited, and plastics and metals may be used for the cover element. In order to reduce a barr of a transparent layer occurring when the cover element is removed by minimizing the amount of a resin remaining in the cover element, the cover element is preferably coated with a material minimizing a surface tension of the cover element, i.e., Teflon.

FIG. 10is a cross-sectional view illustrating a disc formed using the cover element according to the present invention. Referring toFIG. 10, respective size of a lead-in region and a clamping region of the disc is one of critical factors affecting the size of the cover element. In other words, a surface of the clamping region should be uniform, and thus, a starting portion of the transparent layer should not be included in the clamping region. The clamping region of the disc is clamped by a clamper when the disc is rotated by a spindle motor. Since data should be recorded in the lead-in region, the transparent layer should be formed on the lead-in region. Considering this, an end of the transparent layer may be formed at a point A in which a stamping region begins from the center of the disc substrate100or at a point B between the stamping region and the lead-in region.

Some specifications of discs, which are being manufactured or to be manufactured, are as follows.

In a case that the transparent layer having the thickness of 0.1 mm is formed on respective ones of the disc substrates by using a ultraviolet hardening resin having 5000 cps of viscosity in consideration of the above conditions in the case of the point A, preferably, the header of the cover element has a diameter of less than φ22 mm and the thickness of less than 0.35 mm. In the case of the point B, preferably, the diameter of the header of the cover element is less than φ27–32 mm, and the thickness of the header of the cover element is less than 0.35 mm. The cover element becomes thicker when the viscosity of the ultraviolet hardening resin decreases, and on the contrary, the cover element becomes thinner when the viscosity of the ultraviolet hardening resin increases.

A method of forming the transparent layer of the disc substrate according to another embodiment of the present invention will be described below.

FIG. 11is a flow chart illustrating the method of forming the transparent layer. Referring toFIG. 11, in operation1101, the disc substrate40,80is mounted on the spindle table44,84such that a major surface of the disc substrate40,80on which the transparent layer is to be formed faces upward, and then, the axial hole49,89, which is formed at the center of the disc substrate40,80, is covered with the cover element48,88. Next, in operation1102, the disc substrate40,80is rotated at a low speed by using a rotating force of the spindle motor, and the predetermined amount of an ultraviolet hardening resin43,83is dispensed toward the center of the disc substrate40,80through the dispensing nozzle42,82of the dispensing header41,81. Next, the disc substrate40,80, which is mounted on the spindle table44,84, is rotated at a high speed by controlling the spindle motor. In operation1103, the ultraviolet hardening resin43,83is spread out the disc substrate40,80in the radial direction by centrifugal force caused by rotation to uniformly coat the entire surface of the disc substrate40,80. In operation1104, ultraviolet is radiated on the resin43,83after the cover element48,88is removed, thereby hardening the resin43,83, or the cover element48,88is removed after the resin43,83is hardened.

FIGS. 12A and 12Bare cross-sectional views illustrating a section of a transparent layer formed according to conventional apparatus and method and the section of a transparent layer formed according to the present invention, respectively.FIG. 12Aillustrates a conventional transparent layer, andFIG. 12Billustrates a transparent layer according to the present invention. InFIG. 12A, the resin is dispensed at a point of the surface of a disc substrate1100without using the cover element, and thus, the thickness of the starting portion of a transparent layer111is not uniform. However, according to the present invention, the cover element is mounted on the disc substrate1100, and then, the resin is dispensed toward the axial hole (central hole) of the disc substrate1100, and then, the cover element is removed, and thus, the thickness of the transparent layer112is uniform.

Measured values required to form the disc using the method of manufacturing the disc according to the present invention are as follows.

<Conditions for Manufacturing a Disc>

Stamper:Track pitch in-groove type 0.32 μm; andThe stamper records tracks at the radius of 22–60 mm to check transfer property.

Transfer is good to 58.5 mm of a radius when the disc substrate having 120 mm of a diameter and 1.1 mm of a thickness shown inFIG. 1is injected.

Condition for InjectionTemperature of fixing mold: 125° C., temperature of moving mold: 125° C.;Temperature of sprue bush: 90° C., temperature of a resin: maximum 380° C.;Forces such as 35 ton/sec, 25 ton/sec, and 10 ton/sec, are required to make the form of mold; andInjection molding is performed on these conditions. As a result of injection molding, the property of a molding machine is less than 0.3° C., and the streaming flow of a resin is stable to edges of a mask.

Spin Coating:The axial hole of a disc substrate is covered by a cover element having 22–44 mm of a diameter and 0.24–0.78 mm of a thickness having various shapes, spin coating is performed on the axial hole on the same conditions, and in most cases, the thickness of 100 μm±2 μm and uniformity are obtained to 17–57 mm of a radius.

Result of Recording and Reproducing Experiment:The uniform property is obtained to 17–58 mm of a radius.

As described above, the present invention can provide the cover element, thereby enabling a central dispensing method of dispensing the resin at the axial hole of the disc substrate. As a result, the thickness of the transparent layer becomes more uniform on the entire region of the disc substrate. Moreover, as a recording region increases, a recording capacity increases. When the rotation support board is installed and when the cover element is provided to the conventional spin coating apparatus, the apparatus and method according to the present invention can be implemented in conventional equipment, thereby increasing a using efficiency of the conventional equipment.

Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and sprit of the invention, the scope of which is defined in the claims and their equivalents.