JP3709349B2 - Optical disc substrate, optical disc - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk substrate on which at least a light transmission layer is laminated.
[0002]
[Prior art]
Conventionally, there are CDs (compact discs), MDs (mini discs), DVDs (digital versatile discs), etc. as optical discs for recording various types of information such as audio, video, and computer. Accordingly, it is necessary to further improve the recording density of these optical discs.
[0003]
In order to improve the recording density of an optical disk or the like, it is necessary to reduce the focused spot diameter of the laser beam to be used. For this purpose, the wavelength of the laser beam is shortened or the objective lens in the laser optical system has a high NA (numerical aperture). ) Is required.
[0004]
The laser light as described above is condensed on the information recording surface through the light transmission layer covering the information recording surface, but the optical aberration becomes noticeable as the wavelength is shortened and the NA is increased as described above. . Therefore, in order to suppress optical aberration, the light transmission layer must be made as thin as possible.
[0005]
In CD and MD, the wavelength of the laser beam used is 780 nm, NA is 0.45, and the thickness of the light transmission layer is 1.2 mm. The wavelength is 650 nm, NA is 0.6, and the thickness of the light transmission layer is 0.6 mm. Within these ranges, a substrate formed by injection molding using a transparent material can usually be used as the light transmission layer.
[0006]
In order to further increase the recording density in the future, when the wavelength of the laser beam is further shortened and the NA is further increased, the light transmission layer as the substrate must be further thinned. However, it has become extremely difficult to produce a substrate that is thinner and more accurate than conventional injection molding methods (including injection compression). In other words, in a conventional optical disk using a substrate as a light transmission layer, a technique for improving the recording density by shortening the wavelength of the laser light and increasing the NA has reached the limit in terms of manufacturing technology.
[0007]
On the other hand, as disclosed in, for example, Japanese Patent Laid-Open No. 10-289489, a protective plate that does not need to transmit light is formed thick by injection molding as a substrate, and a recording film / reproduction is recorded on the information recording surface of the substrate. There is an optical disc having a structure in which a thin light transmission layer is formed on a reflective film after forming a reflective film for use. In this way, the light transmission layer can be formed thin, and the overall strength can be ensured on the substrate side. Therefore, it is possible to flexibly cope with the shorter wavelength and higher NA of the laser beam. become able to do.
[0008]
As a method for forming the light transmission layer, a method of curing after applying an ultraviolet curable resin liquid on a substrate by a spin coating method, or a separately formed transparent sheet using an ultraviolet curable resin or an adhesive material as an adhesive. There is a method of bonding and integrating on a substrate. However, the method of adhering the transparent sheet to the substrate has a problem that the manufacturing cost is high because the optical properties and thickness accuracy of the light transmission layer are required to be strict. On the other hand, the spin coat method is relatively easy to satisfy the required characteristics. For example, the specific spin coat described in JP-A-10-289489, JP-A-11-73691, JP-A-11-203724, etc. Means for forming a light transmission layer by the method is disclosed.
[0009]
[Problems to be solved by the invention]
As described above, an optical disk having a structure using the protective plate side as a substrate can improve the recording density, but has the following problems in terms of manufacturing technology.
[0010]
(1) Problem of substrate shrinkage error When a substrate is manufactured by injection molding, the vicinity of the outer periphery of the substrate may be thicker than the center side due to a difference in cooling rate during molding. That is, as shown in FIG. 6, there may be a raised portion 2 called a ski jump on the outer periphery of the resin substrate 1 by injection molding, and the incident and reflection angle of the laser beam deteriorates as it is, or There is a possibility that a laser optical system such as an objective lens may collide with the raised portion 2. Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-200791, the raised portion 2 has to be removed by post-processing, resulting in an increase in manufacturing cost.
[0011]
(2) Non-uniform thickness problem of light transmitting layer The spin coating method is to apply a coating solution so that the coating solution spreads uniformly according to the rotation of the substrate while the substrate is rotated by a spindle and the coating solution flows down to the surface. . In this case, the thickness of the coating liquid can be adjusted by controlling the rotation speed of the spindle, the coating time, and the viscosity of the coating liquid. However, the bias of the coating liquid inevitably occurs on the outer peripheral portion of the substrate, resulting in swell. There is a problem that it is easy. This state is shown below.
[0012]
For example, the substrate 1 shown in FIG. 7 is provided with a signal recording area 4 inside a constant width area (blank area 3) on the outermost periphery of the surface (upper surface), and the surface of the blank area 3 and the signal recording area 4 ( The upper surface is covered with the light transmission layer 5. As a result of forming the light transmission layer 5 by applying and curing the resin by spin coating, a raised portion 5A is formed from the outermost peripheral portion of the signal recording region 4 to the blank region 3. In particular, as an application example of the spin coating method, when the light transmission layer 5 (for example, 100 μm) that falls into a relatively thick class is formed, the thickness T and the width W of the raised portion 5A become very large, so that the raised portion 5A has a signal. There is a problem that the information recording area is reduced because it overlaps the recording area 4.
[0013]
Further, since the raised portion 5A has a sufficient possibility that the laser optical system will collide, as described in, for example, JP-A-11-86355, JP-A-11-86356, etc. There was a problem that the upstream portion 5A had to be removed by post-processing, leading to an increase in manufacturing cost.
[0014]
Further, in the above-mentioned Japanese Patent Application Laid-Open No. 11-86356, as shown in FIGS. 8A and 8B, a light transmitting layer 5 is used by using a substrate 1 having an outer diameter slightly larger than that in the case of FIG. A method of removing the outer peripheral portion including the raised portion 5 </ b> A by cutting or the like after coating is disclosed.
[0015]
However, if the processing accuracy when removing the outer periphery of the substrate 1 is poor, the concentricity (eccentric gravity) of the outer diameter (outer peripheral side surface) with respect to the inner diameter of the substrate is lowered. There is a problem that the dynamic imbalance becomes large and a defect occurs in recording / reproduction. In addition, there is a problem that the yield of the material is poor as much as the outer peripheral portion is removed.
[0016]
The present invention has been made in view of the above-described conventional problems, and can suppress the expansion of the non-uniform portion of the outer periphery of the substrate or the light transmission layer at a low cost and without reducing the concentricity. An object of the present invention is to provide an optical disk substrate and an optical disk formed from the optical disk substrate.
[0017]
[Means for Solving the Problems]
As a result of diligent efforts by the inventor regarding the structure and the like of the optical disk, it has become clear that the nonuniformity of the outer peripheral portion can be suppressed by devising the shape of the substrate. That is, the above object is achieved by the following invention.
[0018]
(1) An optical disk substrate that can be configured as an optical disk by laminating at least a light transmission layer on one surface side, and a circumferential recess is formed on the outer peripheral side of the signal recording area on the one surface. The radially outer end of the recess on the one surface is set lower in the thickness direction than the radially inner end of the recess and higher in the thickness direction than the deepest part of the recess , Further, the concave portion is set to be gradually shallower from the deepest portion toward the radially outer side and is substantially continuous with the peripheral portion, and the radial cross section of the peripheral portion has a substantially serrated shape . substrate.
[0021]
( 2 ) An optical disk substrate in which an optical disk can be configured by laminating at least a light transmission layer on one surface side, and a circumferential recess is formed on the outer peripheral side of the signal recording area on the one surface. The recessed portion is formed to be gradually shallower from the deepest portion toward the radially outer side and is substantially continuous with the peripheral portion, and the radial cross section of the peripheral portion has a substantially serrated shape. Optical disk substrate.
[0022]
( 3 ) In the above (1) or (2) ,
When the radius of the outermost peripheral surface of the substrate is d, the radially inner end of the circumferential recess is on the outer peripheral side from the position of 0.965 × d, preferably 0.975 × d from the center of the substrate. An optical disk substrate characterized in that it is set on the outer peripheral side, more preferably on the outer peripheral side from a position of 0.983 × d.
[0023]
( 4 ) An optical disc, wherein at least a light transmission layer is laminated on the one surface side of the optical disc substrate according to any one of (1) to ( 3 ).
[0024]
Here, the “signal recording area” is an area in which signals are recorded substantially continuously from the inner circumference side, or a state in which signals can be recorded substantially continuously from the inner circumference side. Indicates the area that has been marked. Here, the substrate center is a position obtained by an intersection of virtual lines representing the diameters of at least two locations.
[0025]
At first glance, the concave portion formed on the optical disk substrate is considered to be unreasonable because the smooth spreading of the coating liquid during spin coating is inhibited. However, when actually tried, the coating solution spreads and rises to the peripheral edge (or the radially outer end of the recess) by the centrifugal force due to the rotation of the substrate, and rises when the rotation of the substrate stops. The applied coating solution flows back into the recess.
[0026]
As a result, the rising of the periphery of the optical disk due to the coating liquid is positively prevented. In addition, the radial width of the recess can be set to be relatively narrow, and the internal information recording area can be expanded if the bulge can be suppressed within the range. In addition, if the recesses are formed in this way, the vicinity of the periphery of the substrate itself can be prevented from becoming thick due to heat shrinkage after injection molding, and so-called ski jumps need not be formed.
[0027]
Furthermore, if the concave portion is used to make the peripheral edge of the substrate substantially saw-tooth shape (cross section), the coating liquid during spin coating will be well out, the amount of liquid pool will be reduced, and the rise can be further reduced. Become.
[0028]
As described above, the simple structure of forming the recess in the substrate suppresses both the thickening of the vicinity of the periphery of the substrate itself and the rising of the vicinity of the periphery of the light-transmitting layer to be laminated by a rational idea. Cost can be greatly reduced.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0030]
As shown in FIG. 1, an optical disc 10 according to a first example of an embodiment of the present invention is obtained by sequentially forming an information recording surface 14 and a light transmission layer 16 on the surface of a substrate 12.
[0031]
When the optical disk 10 is a read-only type, data pits are formed on the substrate 12 itself, and a reflective film such as aluminum or aluminum alloy is formed thereon to form the information recording surface 14. When the optical disk 10 is a recordable type, the information recording surface 14 is formed by laminating a reflection film and a recording film, a dielectric film, etc. whose reflectance can be modulated by a recording laser beam.
[0032]
The light transmission layer 16 is formed by applying an ultraviolet curable resin solution to the surface on the information recording surface 14 side by spin coating and then irradiating it with ultraviolet rays.
[0033]
In the vicinity of the peripheral edge of the substrate 12 on the information recording surface 14 side, a circumferential recess 50 is formed. The concave portion 50 is gradually shallower toward the outer side in the radial direction and is substantially continuous with the peripheral portion 52. As a result, the radial cross section of the peripheral portion 52 has a substantially saw-tooth shape with a sharp tip 52A. It has become.
[0034]
In more detail, when the radius of the outermost peripheral surface of the substrate 12 is d, the position of the radially inner end 50A of the recess 50 is set outside 0.965 × d from the substrate center, more preferably It is set outside 0.975 × d from the substrate center, and more preferably set outside 0.983 × d from the substrate center.
[0035]
Furthermore, the radially outer end 50C of the recess 50 (here, coincides with the tip 52A) is lower by H1 in the thickness direction than the radially inner end 50A of the recess 50 and is thicker than the deepest portion 50B of the recess 50. The direction is set higher by H2. That is, the outer end 50C is located between the inner end 50A and the deepest portion 50B in the thickness direction. Here, the deepest portion 50B is set so as to be located radially inward from the intermediate position M of the width W of the recess 50.
[0036]
In the present embodiment, the width W of the recess 50 is set to 1 (mm) or less, and specifically set to about 0.5 (mm). Accordingly, a range within 1 (mm) radially inward from the peripheral edge 52A of the substrate 12 is a blank area 20A where no information is recorded, and the signal recording area 20 is located on the inner peripheral side.
[0037]
The depth of the recess 50 (the difference in height between the inner end 50A and the deepest portion 50B (= H1 + H2)) is 0.02 (mm) <H1 + H2 <0.4 (mm), preferably 0.02 (mm ) <H1 + H2 <0.2 (mm), more preferably 0.02 (mm) <H1 + H2 <0.1 (mm). The height difference H1 between the inner end 50A and the outer end 50C is 0.01 (mm) <H1 <0.4 (mm), preferably 0.01 (mm) <H1 <0.2 (mm). More preferably, 0.02 (mm) <H1 <0.1 (mm) is set.
[0038]
Next, the state of the process of forming the light transmission layer 16 on the substrate 12 by spin coating will be described.
[0039]
As shown in FIG. 2, when the coating liquid (light transmission layer 16) flows down while the substrate 12 is rotating, a raised portion 16 </ b> A is temporarily formed near the peripheral edge 52. In addition, since the coating liquid (light transmission layer 16) in the recess 50 is drawn to the rising portion 16A side by the surface energy of the raised portion 16A, it is assumed that the coating liquid does not stay so much in the recessed portion 50. . That is, during the rotation of the substrate 12, a similar recessed space 16 </ b> B is formed in the light transmission layer 16 at a position corresponding to the recessed portion 50.
[0040]
When the rotation of the substrate 12 is stopped in this state, as shown in FIG. 3, the swelled portion 16A flows backward inward in the radial direction, and flows into the recessed space 16B using the inclination of the bottom surface of the recessed portion 50. As a result, the remaining of the raised portion 16A is suppressed, and the surface of the light transmission layer 16 can be made smoother than before. The optical disc 10 shown in FIG. 1 is obtained as described above.
[0041]
In the present embodiment, the rising of the peripheral edge of the light transmission layer 16 is positively prevented by the presence of the recess 50 as described above. In addition, the radial width W of the concave portion 50 can be set to be relatively narrow (for example, within 1 (mm)), and the rise can be suppressed within the range, so that the signal recording area 20 can be expanded as a result. Further, since a cutting step (for cutting the raised portion) after forming the light transmission layer 16 is not required, an increase in processing cost can be suppressed and deterioration of dynamic unbalance of the optical disc 10 due to processing errors can be prevented. it can.
[0042]
If the recess 50 is formed in this manner, a so-called ski jump does not need to be formed on the substrate 12 itself after injection molding.
[0043]
Furthermore, since the peripheral edge 52 of the substrate 12 has a substantially serrated shape (cross section) using the concave portion 50, the coating liquid in the spin coat is excellently drained, the amount of liquid pool is reduced, and the peripheral edge 52 is reduced. It is possible to further reduce the swell.
[0044]
The substrate 12 is formed by a normal injection molding method, a 2P (Photo-Polymer) method, or the like. In the injection molding method, acrylic or polycarbonate resin is melted by a plasticizer of a molding machine, and the molten resin is filled into a mold cavity equipped with a master having a micro uneven pattern for recording / reproducing signals, and cooled. This is a method of opening a mold after solidification and taking out the substrate.
[0045]
In the 2P method, an ultraviolet curable resin, a two-component mixed curable resin, or the like is interposed between a glass or resin substrate without a fine uneven pattern and a master having a fine uneven pattern, and the two are adhered to each other. In this method, the master is peeled off to form a substrate having a micro uneven pattern. Further, the reflective film or the like constituting the information recording surface 14 is formed on the fine uneven pattern for recording / reproducing signals by, for example, spin coating, sputtering, vapor deposition or the like.
[0046]
Although the board | substrate 12 in the example of the said embodiment was shown only when the recessed part 50 and the peripheral part 52 were continuing, this invention is not limited to it. For example, like the optical disc 60 shown in FIG. 4, the peripheral edge 52 and the recess 50 may be separated from each other. Further, the present invention includes the case where the cross section of the peripheral edge 52 is not a sawtooth shape as in the case of the present optical disk 60.
[0047]
Further, in the above embodiment, the case where the radially outer end 50C of the recess 50 is lower by H1 in the thickness direction than the inner end 50A is shown, but the present invention is not limited thereto, and for example, the optical disc 70 shown in FIG. Thus, the case where both are the same height or the outer end 50C is higher is included. These may be appropriately set in consideration of the smoothness required for the optical disc. As shown in FIG. 1, it can be said that setting the outer end 50C lower than the inner end 50A is preferable because it can absorb a slight rise of the light transmission layer 16 in the peripheral edge 52.
[0048]
In the example of the above embodiment, the case where the substrate 12 is manufactured by the injection molding method and the light transmission layer 16 is formed by the spin coating method is shown, but the present invention is not limited to this. Further, the concave portion 50 of the substrate 12 may be formed by pressing or cutting.
[0049]
The substrate (including the recess) and the optical disk shape of the present invention are not limited to the above examples, and should be appropriately changed without departing from the gist of the present invention.
[0050]
【The invention's effect】
Since the present invention is configured as described above, it has an excellent effect that it is possible to suppress non-uniformity of the shape of the outer region including the raised portion of the outer light transmitting layer while reducing the manufacturing cost. .
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a main part of an optical disc according to an example of an embodiment of the present invention. FIG. 2 is an enlarged view showing a main part in a state where a light transmission layer is formed by spin coating on the optical disc. Sectional view [FIG. 3] An enlarged sectional view showing the main part of the optical disc in a state where the light transmission layer is cured. [FIG. 4] An enlarged sectional view showing another example of the shape of the substrate on the optical disc. FIG. 5 is an enlarged cross-sectional view showing another example of the shape of the substrate in the optical disc. FIG. 6 is an enlarged cross-sectional view showing the main part of a conventional substrate having a raised portion formed on the outer periphery. FIG. 8 is an enlarged cross-sectional view showing a raised portion of the light transmitting layer in the substrate. Description】
10, 60, 70 ... optical disc 12 ... substrate 14 ... information recording surface 16 ... light transmission layer 16A ... raised portion 16B ... recessed space 20 ... signal recording region 20A .... Blank area 50 ... Concave part 50A ... Inner end 50B ... Deepest part 50C ... Outer end 52 ... Peripheral part 52A ... Tip

Claims (4)

An optical disk substrate in which an optical disk can be configured by laminating at least a light transmission layer on one surface side,
A circumferential recess is formed on the outer peripheral side of the signal recording area on the one surface,
The radially outer end of the recess on the one surface is set lower in the thickness direction than the radially inner end of the recess and higher in the thickness direction than the deepest portion of the recess ,
Further, the concave portion is set to be gradually shallower from the deepest portion toward the radially outer side and is substantially continuous with the peripheral portion, and the radial cross section of the peripheral portion has a substantially serrated shape . substrate. An optical disk substrate in which an optical disk can be configured by laminating at least a light transmission layer on one surface side,
A circumferential recess is formed on the outer peripheral side of the signal recording area on the one surface,
The optical disc substrate, wherein the concave portion is set to be gradually shallower from the deepest portion toward the radially outer side and is substantially continuous with the peripheral portion, and the radial cross section of the peripheral portion has a substantially serrated shape. In claim 1 or 2 ,
When the radius of the outermost peripheral surface of the substrate is d, the radially inner end of the circumferential recess is on the outer peripheral side from the position of 0.965 × d, preferably 0.975 × d from the center of the substrate. An optical disc substrate characterized by being set on the outer peripheral side, more preferably on the outer peripheral side from a position of 0.983 × d. Optical disc, wherein at least the light transmitting layer is laminated on the one surface of the optical disc substrate according to any one of claims 1 to 3.

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