JP2003303444A - Optical disk and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the variation of a warp due to moisture absorption and loss in an optical disk where information is read and written by emitting a laser beam from a protective layer side. <P>SOLUTION: A substrate 1 indicated in the figure 2A is formed by an injection molding method and an information signal part 2 is formed on one main surface having recessed and projected parts of the substrate 1 as indicated in the figure 2B. As indicated in the figure 2C, on the other main surface of the substrate 1 on the opposite side of the one where the information signal part 2 is formed, a moisture-proof film 4 composed of the metal or semiconductor of 10 nm to 60 nm preferably, and 20 nm to 30 nm more preferably, is formed. As indicated in the figure 2D, a protective film 3 is formed on the information signal part 2 by a spin coating method and the protective film 5 is formed on the moisture-proof film 4. On the protective film 5, a printing layer 6 is formed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc and a method for manufacturing the same, and particularly to an optical disc having a recording layer and a protective layer provided on a substrate, irradiating a laser beam from the side provided with the protective layer. This is suitable for application to an optical disc on which information signals are recorded and / or reproduced.

[0002]

2. Description of the Related Art In recent years, compact discs (hereinafter referred to as C
The method D) is widely used because it has the advantage of being able to record a large amount of data and being compatible with respective memory types such as a read-only type, a write-once type, and a rewritable type.

FIG. 5 shows the structure of a CD. As shown in FIG. 5, the CD includes a reflective film 102 made of a metal thin film such as an aluminum (Al) film on a light-transmissive disk substrate 101 on which a concavo-convex pattern such as pits or grooves indicating information signals is formed. And a protective layer (not shown) for protecting the reflective film from moisture (H ₂ O) and oxygen (O ₂ ) in the atmosphere. Then, at the time of reproducing the information signal on the CD, as shown in FIG. 5, reproducing light such as laser light is irradiated from the side of the disk substrate 101 toward the concavo-convex pattern, and the incident light and the returning light by this reproducing light are combined. The information signal is detected by the difference in reflectance.

When manufacturing such a CD, first,
A disk substrate 1 having an uneven pattern by an injection molding method
01 is formed. Next, a reflective film 1 made of a metal thin film is formed on the optical disk substrate by vacuum vapor deposition or sputtering.
02 is formed. Next, a protective layer is formed by applying an ultraviolet curable resin to the upper layer of this reflective film.

In recent years, there has been a demand for an optical disc having a higher recording density than such a CD. In order to meet the demand for higher recording density, a technique is proposed to reduce the spot diameter of the reproduction light by increasing the numerical aperture (NA) of the objective lens used when the reproduction light of the optical pickup is irradiated with the reproduction light. Has been done.

That is, while the NA of the objective lens used in reproducing a conventional CD is 0.45,
DVD having a recording capacity of 6 to 8 times that of the conventional CD
For optical video discs such as (Digital Versatile Disc), the NA of the objective lens used during playback is 0.6.
By setting it to about 0, the spot diameter can be reduced.

As the NA of such an objective lens is increased, in order to transmit the reproduced light emitted,
It is necessary to make the disc substrate of the optical disc thinner. This is because the allowable amount of the angle (tilt angle) deviated from the vertical direction of the disc surface with respect to the optical axis of the optical pickup becomes smaller, and further, this tilt angle is influenced by aberration and birefringence due to the thickness of the disc substrate. This is because they are easily affected. Therefore, the tilt angle is made as small as possible by thinning the disc substrate.

In consideration of future demand for higher recording density, it is necessary to make the substrate thinner.
Therefore, an unevenness is formed on one main surface of the substrate to form an information signal section, and a reflective film and a protective layer made of a thin film capable of transmitting light are sequentially laminated on the information signal section, and reproduced from the protective layer side. There has been proposed an optical disc configured to reproduce an information signal by irradiating light. In such an optical disc that reproduces the information signal by irradiating the reproducing light from the protective layer side, the NA of the objective lens can be increased by thinning the protective layer.

[0009]

By the way, it is known that in the above-mentioned optical disc, the optical disc is warped due to a change in humidity of the surrounding environment. The CD is
Since the disk substrate has an asymmetric structure in which the reflective film is coated only on one side, moisture is absorbed and released mainly from the surface on which the reflective film is not formed, and as a result, the disk substrate is warped.

FIG. 6A shows the shape of the CD when absorbing moisture, and FIG. 6B shows the shape of the CD when releasing moisture. Figure 6
As shown in A, while the surface on the side opposite to the side on which the reflective film is provided extends and the CD has a concave shape, when moisture is released, the reflective film is provided as shown in FIG. 6B. The surface opposite to the side contracts, and the CD has a convex shape. On the CD,
The amount of change in the warp (Skew) due to such moisture absorption and desorption is within the permissible range, and thus was not a problem.

Further, in the DVD, the permissible range of the change amount of the Skew is about 1/2 of the change amount of the Skew of the CD, but a symmetrical structure in which 0.6 mm discs are stuck with the pit surface inside is bonded. Since it has, Skew was canceled, and the amount of change in Skew was within the allowable range, which was not a big problem.

However, in the optical disc in which the laser beam is irradiated from the protective layer side to read and write information, the warp caused by moisture absorption and desorption (S
This is a problem because the amount of change in (kew) may exceed the allowable range.

In a disk having a high density and an asymmetric structure such as the SACD (Super Audio CD) hybrid disk shown in FIG. 7, an amorphous polyolefin material (manufactured by Zeon Corporation) having a low hygroscopic property is used to prevent warping of the optical disk. Is used as a substrate material. However,
Since such a substrate material is extremely expensive, the price of the optical disc is increased.

Therefore, the problem to be solved by the present invention is that the amount of change in warp caused by moisture absorption and desorption in an optical disc in which laser light is irradiated from the protective layer side to read and write information. An object of the present invention is to provide an optical disc and a manufacturing method thereof that can reduce the noise.

[0015]

In order to solve the above-mentioned problems, a first invention of the present application is an information signal section configured to record and / or reproduce an information signal on one main surface of a disc substrate. In an optical disc which is formed by sequentially laminating a protective layer capable of transmitting a laser beam, and which records and / or reproduces an information signal by irradiating a laser beam from the protective layer side, the side where the information signal section of the substrate is formed. An optical disk having a moisture-proof film made of metal or semiconductor provided on the opposite surface.

In the second invention of the present application, an information signal portion configured to record and / or reproduce an information signal and a protective layer capable of transmitting a laser beam are sequentially laminated on one main surface of a disk substrate. Configured, irradiating a laser beam from the protective layer side,
A method of manufacturing an optical disc for recording and / or reproducing an information signal, characterized by including a step of forming a moisture-proof film made of metal or semiconductor on a surface of a substrate opposite to a side where an information signal portion is formed. It is a method of manufacturing an optical disc.

In the optical disc of the present invention configured as described above, since the moisture-proof film made of metal or semiconductor is provided on the surface of the substrate opposite to the side where the protective layer is formed, the protective layer of the substrate is provided. It is possible to prevent moisture absorption and desorption from the surface opposite to the side provided with.

[0018]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the structure of the optical disc of the present invention.

The substrate 1 has a planar annular shape with a center hole formed in the center thereof, and a concavo-convex pattern is formed concentrically around the center hole on the surface on which the protective layer 3 is formed. Has been done. As the material of the substrate, a resin having a low hygroscopicity such as polycarbonateate (PC) or cycloolefin polymer is used. This board 1
Has a diameter (outer diameter) of, for example, 120 mm, and the center hole opening diameter (inner diameter) thereof is, for example, 15 mm.

The information signal section 2 is a reflective film made of a material such as Al or Ag. The thickness of this reflective film is, for example, 10
It is selected from the range of nm to 60 nm. The information signal section 2 is not limited to the reflective film, but may be a film made of a magneto-optical material, a film made of a phase change material, a film made of an organic dye, or the like.

The protective layer 3 includes, for example, a light transmissive sheet,
An adhesive layer made of a pressure-sensitive adhesive material (PSA) attached to one surface of the light-transmissive sheet, and the sheet has a flat ring-shaped stamped shape like the substrate, A through hole is formed in the center. This protective layer 3
Has a thickness of 0.1 mm, for example.

The moisture-proof film 4 is for preventing moisture absorption and release from the surface of the substrate 1 opposite to the surface on which the protective layer is provided. A metal such as Al or Ag, or a semiconductor such as Si is used as the material of the moisture-proof film 4. The thickness of the moisture-proof film is preferably selected from the range of 10 nm to 60 nm, and more preferably 20 nm to 30 nm.

The protective layer 5 includes, for example, a light transmissive sheet,
An adhesive layer made of a pressure-sensitive adhesive material (PSA) attached to one surface of the light-transmissive sheet, and the sheet has a flat ring-shaped stamped shape like the substrate, A through hole is formed in the center.

In the optical disc having the above-mentioned structure, with respect to the substrate 1, from the surface on which the information signal section 2 is formed,
It is an optical disc of a type in which information signals are recorded and / or reproduced by irradiating the information signal section 2 with laser light.

Next, a method of manufacturing an optical disc according to an embodiment of the present invention will be described.

First, the substrate 1 shown in FIG. 2A is formed by, for example, an injection molding method. When the substrate 1 is formed by injection molding, a stamper provided with predetermined irregularities
Pits and grooves are formed on one main surface of the substrate 1 in a spiral shape, for example.

Next, as shown in FIG. 2B, the information signal section 2 is formed on one main surface of the substrate 1 on which the unevenness is formed. Next, as shown in FIG. 2C, a moisture-proof film 4 is formed on the other main surface of the substrate 1 opposite to the surface on which the information signal section 2 is formed.

Next, as shown in FIG. 2D, the protective layer 3 is formed, and the protective layer 5 is formed on the moisture-proof film 4. The protective layer 3 and the protective layer 5 are formed by coating the information signal portion 2 and the moisture-proof film 4 with an ultraviolet curable resin so as to have a uniform thickness by a spin coating method.

The method for forming the protective layers 3 and 5 is not limited to the spin coating method. For example,
The sheet with the pressure-sensitive adhesive is pressed and bonded to the information signal section 2 and the moisture-proof film 4, so that the protective layer 3 is formed.
Also, the protective layer 5 may be formed.

Further, the protective layer 3 and the protective layer 5 may be formed on the information signal portion 2 and the moisture-proof film 4 by pressurizing the dry photopolymer sheet and ultraviolet curing.

Further, the protective layer 3 and the protective layer 5 may be formed by bonding a sheet made of polycarbonate or the like on the information signal portion 2 and the moisture-proof film 4 with an ultraviolet curable resin and then curing the same. Absent.

Finally, the print layer 6 is formed on the protective layer 5. As a result, the target optical disc is manufactured.

The inventor measured the amount of moisture absorption and the amount of Skew change (R-Skew change amount) of the optical disc of the present invention manufactured as described above and the conventional optical disc and compared them. Here, the conventional optical disc is an optical disc in which the formation of the moisture-proof film 4 in the optical disc of the present invention is omitted, that is, an optical disc manufactured by omitting the step of forming the moisture-proof film 4 in the above-described optical disc manufacturing method. is there. The material of the moisture-proof film of the optical disk of the present invention used for this measurement is Ag, and the film thickness is 3
It is 0 nm. The material of the substrate 1 in the present invention and the conventional optical disc is polycarbonate, and the thickness thereof is 1.1 mm. The material of the information signal section 2 is Ag and the thickness thereof is about 30 nm.

The measured value of the skew change amount is at a position 58 mm from the center of the optical disk. In addition, in the measured value of the Skew change amount, “+” is the Skew change amount when the substrate is warped upward, and “−” is the change amount when the substrate is warped upward in the state where the signal surface is downward. "

The measurement results of the moisture absorption amount (moisture increase amount) and Skew change amount of the optical disc when the optical disc is held for 70 hours in an environment of temperature 30 ° C. and humidity 90% are shown below. Moisture absorption amount Conventional optical disk: 0.032 g Optical disk of the present invention: 0.010 g (about 1/3) Skew change amount Conventional optical disk: -0.28 deg Optical disk of the present invention: -0.04 deg (about 1/7)

Next, the measurement result of the skew change amount of the optical disk when the optical disk is held for 100 hours in the environment of temperature 70 ° C. and humidity 30% is shown. Skew change amount Conventional optical disc: +1.15 deg Optical disc of the present invention: -0.18 deg (about 1/6)

From the above-mentioned measurement results, the optical disc of the present invention can reduce the moisture absorption amount of the optical disc when the ambient environment changes to about 1/3 as compared with the conventional optical disc,
It can be seen that the amount of change in w can be reduced to about 1/7. Further, the optical disc of the present invention is
The amount of moisture released from the substrate when the ambient environment changes can be reduced
It can be seen that the amount of change in ew can be reduced to about 1/6.

Next, the present inventor formed a reflective film of Ag on the surface of the substrate on which the unevenness was formed, and bonded a pressure-sensitive adhesive sheet (PSA sheet) on this reflective film. Five samples were prepared and environmental tests were conducted on these samples. And 2 after finishing the environmental test
R-Skew was measured after 2 days and after 2 weeks. In addition,
The environmental test was carried out by holding the sample for 10 days in an environment of a temperature of 80 ° C. and a humidity of 85%. here,
The thickness of the substrate used for the measurement is 1.1 mm. Also,
The film thicknesses of the reflection films of the five samples are different from each other. Table 1 shows the film thickness of each sample and the measurement results.

[0039]

[Table 1]

In Table 1, Δ1 is the amount of change in R-Skew after the lapse of 48 hours from the measurement of the initial value, Δ
2 is the amount of change in R-Skew from 48 hours to 2 weeks.

FIG. 3 shows a graph prepared based on the R-Skew measurement values shown in Table 1. From Table 1 and FIG. 3, sample 1 has a small amount of change in R-Skew and recovery is fast, whereas samples 2, 3, 4 and 5 have large amount of change in R-Skew and recovery is slow. I understand. This is because Sample 1 has water in and out through the reflective film, and there is a good balance between water in and out through the reflective film and water in and out of the surface opposite to the side where the reflective film is formed. Against samples 2, 3, 4
In Nos. 5 and 5, there is almost no ingress / egress of water through the reflective film, and there is a poor balance between ingress / egress of water through the reflective film and ingress / egress of water on the surface opposite to the side where the reflective film is formed.

Further, the present inventor prepared four samples having the same structure, and carried out an environmental test and R-Skew measurement on these samples. Table 2 shows the film thickness and measurement results of these samples.

[0043]

[Table 2]

In Table 2, Δ1 is the amount of change in R-Skew 48 hours after the measurement of the initial value, Δ1
2 is the amount of change in R-Skew from 48 hours to 2 weeks.

FIG. 4 shows a graph prepared based on the R-Skew measurement values shown in Table 1. From Table 2 and FIG. 4, sample 1 has a small amount of change in R-Skew and recovers quickly, while samples 2, 3 and 4
Indicates that the amount of change in R-Skew is large and the recovery is slow.

From the above-mentioned measurement results, the film thickness of the moisture-proof film 4 formed on the surface of the substrate 1 opposite to the information signal portion 2 is 10
It turns out that it is preferable that it is nm or more.

According to one embodiment of the present invention, the following advantages can be obtained. Since the moisture-proof film 4 made of metal or semiconductor is provided on the other main surface of the substrate 1 opposite to the side where the information signal unit 2 is formed, it is opposite to the side where the information signal unit 2 of the substrate 1 is provided. It is possible to prevent the absorption and release of moisture from the surface. Therefore, it is possible to reduce the amount of change in the warp of the optical disk due to moisture absorption and desorption.

Further, unlike the case of forming a light-transmitting film such as SiO 2 by sputtering, there is no need to use sputtering using a reactive gas, so that the moisture-proof film 4 can be formed using a simple device. Can be formed. Further, since it is not necessary to perform sputtering using a dangerous gas such as O2, the moisture-proof film 4 can be easily formed unlike the case of forming a film having optical transparency such as SiO2 by sputtering. .

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-mentioned one embodiment, and various modifications can be made based on the technical idea of the present invention. is there.

For example, the numerical values given in the above-mentioned one embodiment are merely examples, and different numerical values may be used if necessary.

[0051]

As described above, according to the present invention, on the surface of the substrate opposite to the side where the information signal portion is formed,
Since the moisture-proof film made of metal or semiconductor is provided, it is possible to prevent moisture absorption and release from the surface of the substrate opposite to the side provided with the protective layer. Therefore, it is possible to reduce the amount of change in the warp of the optical disk due to moisture absorption and desorption.

Further, since the amount of change in the warp of the optical disk due to the change in humidity of the surrounding environment is small, the disk shape is stable. Therefore, the stability of the reproduction signal and the recording signal can be improved.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view for explaining an example of the optical disc manufacturing method according to the embodiment of the present invention.

FIG. 3 is a graph showing the amount of change in R-Skew over time.

FIG. 4 is a table showing the amount of change in R-Skew over time.

FIG. 5 is a cross-sectional view showing a configuration of a conventional compact disc.

FIG. 6 is a cross-sectional view showing the shape of an optical disc when absorbing and releasing moisture.

FIG. 7 is a cross-sectional view showing the structure of a conventional SACD.

[Explanation of symbols]

1 ... Substrate, 2 ... Information signal part, 3, 5 ... Protective layer, 4 ... Moisture-proof film, 6 ... Printing layer

Claims (6)

[Claims] 1. A disc substrate is provided with an information signal portion capable of recording and / or reproducing an information signal and a protective layer capable of transmitting a laser beam, which are sequentially laminated on one main surface of the disc substrate. In an optical disc for irradiating a laser beam from the layer side to record and / or reproduce the information signal, on the surface of the substrate opposite to the side where the information signal portion is formed,
An optical disc having a moisture-proof film made of metal or semiconductor. 2. The optical disk according to claim 1, wherein the metal is Al or Ag and the semiconductor is Si. 3. The film thickness of the moisture-proof film is 10 nm or more and 60.
The optical disc according to claim 1, wherein the optical disc has a thickness of not more than nm. 4. An information signal section capable of recording and / or reproducing an information signal and a protective layer capable of transmitting a laser beam are sequentially laminated on one main surface of a disk substrate, and the above-mentioned protection is provided. In a method of manufacturing an optical disc in which a laser beam is irradiated from a layer side to record and / or reproduce the information signal, a surface of the substrate opposite to a side where the information signal portion is formed,
A method for manufacturing an optical disc, comprising a step of forming a moisture-proof film made of metal or semiconductor. 5. The method of manufacturing an optical disk according to claim 4, wherein the metal is Al or Ag and the semiconductor is Si. 6. The film thickness of the moisture-proof film is 10 nm or more and 60.
The method for producing an optical disk according to claim 4, wherein the thickness is not more than nm.