JPH07282470A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain an optical disk which lessens generation of defective products and has a good yield by considering in what way the warpage of the optical disk is changed by a change in relative humidity. CONSTITUTION:Such warpage as to attain -A/2+ or -0.5[mrad] in warpage quantity at the time of allowing the optical disk produced by using a synthetic resin substrate as a disk substrate 11 to leave for three days in an enviromnent to maintain relative humidity of 50% and 23 deg.C when the max. change in the warpage at the outermost periphery of the disk at the time of a change of 20% in relative humidity in the environment of relative humidity of 3 to 85% and 5 to 55 deg.C is A[mrad] is previously applied to the optical disk described above. The control of the warpage quantity to be previously applied to the optical disk is executed by, for example, applying and forming a UV curing resin layer 16 on the surface of the optical disk and controlling the warpage quantity by the thickness of this UV curing resin layer 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk which uses a hygroscopic synthetic resin substrate as a disk substrate and in which the disk substrate warps due to changes in relative humidity.

[0002]

2. Description of the Related Art An optical disc has a recording layer formed on a transparent disc-shaped disc substrate to optically record and / or reproduce information signals.

When manufacturing the above-mentioned optical disc, it is difficult to make the disc into a completely flat surface, and a certain degree of warpage occurs. Usually, this warp is controlled so as to be within a certain range in the manufacture of an optical disk, that is, within a range of 0 ± B [mrad] with reference to the state where there is no warp. Here, B is a warp control value in the optical disc manufacturing process.

By the way, a synthetic resin such as polycarbonate is usually used for a disc substrate of an optical disc. And, this synthetic resin has hygroscopicity (water absorption is 0
Therefore, when the relative humidity changes, the optical disc may warp. Then, due to this warp, the optical system for optical recording and reproduction may be tilted, and normal recording and reproduction may not be possible.

However, in the optical disks that have been commercialized so far, this warpage has not been a serious problem. This is because the optical discs that have been commercialized so far have a large flexural rigidity due to the thick disk substrate, or are less likely to warp, or have a large flexural rigidity and are less likely to warp because two disc substrates are bonded together. Or, since the diameter is small, a large warp is unlikely to occur. Specifically, the ISO standard 5.25-inch magneto-optical disk has a large bending rigidity and is less likely to warp because two disk substrates are bonded together. Since the diameter is small, large warpage is unlikely to occur.

[0006]

However, the needs for optical recording / reproducing have become more sophisticated and diversified, and an optical disk having a thin disk substrate or magnetic field modulation to support optical recording / reproducing by a short wavelength laser. The use of a single-plate type optical disc composed of one disc substrate having a thickness of about 1.2 mm suitable for magneto-optical recording, a large-diameter optical disc, or an optical disc having a plurality of these conditions is considered. . In such an optical disc, warpage caused by a change in relative humidity becomes a problem.

As described above, in an optical disk which is warped due to a change in relative humidity, it is necessary to take into consideration the warp due to a change in relative humidity. Must. Therefore, it is expected that the number of defective products will increase and the yield will deteriorate. However, the warpage caused by changes in relative humidity has never been discussed.

In view of the above, the present invention provides an optical disk which is warped due to a change in relative humidity and has a good yield in consideration of how the warp changes due to a change in relative humidity. The purpose is to do.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies on the warpage caused by a change in relative humidity of an optical disk using a disk substrate having a hygroscopic property and a water absorption rate of not 0, and as a result, By preliminarily imparting a warp of half the maximum change in the opposite direction of the warp, it is possible to suppress the inclination of the optical system due to the warp to a half of the maximum change of the warp even at the maximum. The present invention has been completed based on this.

That is, the optical disc of the present invention uses a synthetic resin substrate as the disc substrate and has a relative humidity of 3 to
When the maximum change of the warp at the outermost circumference of the disk is A [mrad] when the relative humidity changes by 20% under the environment of 85% and the temperature of 5 to 55 ° C., the relative humidity is 50% and the temperature is 23.
The amount of warpage when left for 3 days in an environment of ℃ is -A / 2
A warp of ± 0.5 [mrad] is given in advance.

The reason why the relative humidity change amount is 20% is that the rapid relative humidity change occurs when the optical disk is set in the optical disk drive, and the relative humidity change changes. This is because the amount is always about 20%.

In the above optical disk, the method of controlling the warp amount is arbitrary, but for example, an ultraviolet curable resin layer is formed by coating on the surface, and the thickness of this ultraviolet curable resin layer
It is possible to control the amount of warpage given in advance.

[0013]

In an optical disk using a hygroscopic disk substrate, which warps due to a change in relative humidity, a warp of half the maximum change in the warp is applied in the opposite direction of the warp in advance, The inclination of the optical system due to the warp can be suppressed to a half of the maximum change in the warp even at the maximum.

Further, by controlling the amount of warp given to the optical disc in advance by the thickness of the ultraviolet curable resin layer formed by coating on the surface of the optical disc, the above-mentioned warp can be easily controlled to an arbitrary amount. You can

[0015]

EXAMPLES The results of examining the warpage of optical discs caused by changes in relative humidity will be described below.

The target optical disk has a thickness of 1.2 m.
This is a single-plate type optical disc consisting of a single synthetic resin disc substrate having a diameter of 130 mm and a diameter of 130 mm.
The positions were separated by mm, that is, the position having a radius of about 60 mm. As shown in FIG. 1, the amount of warpage is positive when the optical disc 1 is warped on the side without the optical head 2 for recording and reproduction, and is warped on the opposite side. The case was negative.

First, with respect to the above optical disk, the amount of warpage caused by a change in relative humidity was examined.

FIG. 2 shows the results of measuring how the amount of warp changes with time when the relative humidity is changed from 50% to 30%. From this result, the amount of warp increases gradually after the change of relative humidity, and becomes about −3.0 [mrad] which is the maximum change of warp after about 3 hours, and then the amount of warp gradually decreases and returns to the initial state. You can see it coming back. Particularly, after about 2000 minutes or more, the amount of warpage has almost disappeared.

FIG. 3 shows the result of measurement of the relationship between the radial position of the optical disk and the maximum change in the warp when the relative humidity is changed by about 20%. The radial position is represented by the radius at each position. from this result,
It can be seen that the warp amount linearly increases toward the outside of the optical disc. That is, the largest amount of warp is
It is the outermost periphery of the optical disc.

FIG. 4 shows the results of measurement of the relationship between the amount of change in relative humidity change and the maximum change in warpage. From this result, it can be seen that the larger the change amount of the relative humidity change is, the larger the maximum change of the warp is.

Next, changes in relative humidity in an actual use environment were examined.

The relative humidity change in the actual use environment is
The main causes are (1) a change in climate and (2) a difference between the relative humidity inside the optical disk drive device and the relative humidity outside the device.

The change in relative humidity due to the change in climate of (1) may change by 50% or more, but since the change is gradual, it does not seem to cause a problematic warp. .

On the other hand, (2) the difference between the relative humidity inside the optical disk drive device and the relative humidity outside the device is the temperature inside the device due to the heat generation of the IC and the power transistor which are the components of the device. Is higher than the temperature outside the device by 10
It occurs because the temperature rises by about ℃. The relative humidity change due to this occurs when the optical disk is set in the optical disk drive, and since the change is abrupt, there is a possibility of causing a problematic warp.

Therefore, when the relative humidity inside and outside the device was measured when the environment outside the device was at a temperature of 5 to 60 ° C. and a relative humidity of 40 to 95%, the relative humidity inside the device was It was always about 20% lower than the relative humidity outside the device.

Therefore, as the warp of the optical disk caused by the change in the relative humidity, the warp of the optical disk due to the decrease of the relative humidity of about 20%, which occurs when the optical disk is set in the optical disk drive, may be taken into consideration. For example, when the change amount of the relative humidity change and the maximum change of the warp have a relationship as shown in FIG. 4, about -3 [mrad] may be considered as the warp due to the change of the relative humidity.

Next, the cause of the tilt of the optical system of the optical recording / reproducing and the influence of the tilt on the recording / reproducing were examined.

When the optical system for optical recording / reproducing tilts, coma aberration occurs, and normal recording / reproducing cannot be performed.
FIG. 5 shows the relationship between the tilt of the optical system and the error rate. Thus, as the tilt of the optical system increases, the error rate increases. Then, when the inclination of the optical system increases and the error rate exceeds a constant value, that is, the error threshold,
Recording / playback cannot be performed normally. (Hereinafter, the range of the tilt of the optical system that allows normal recording and reproduction is referred to as the "allowable range", and the range is referred to as -K to K [mrad].)

The first cause of the tilt of the optical system is the warp of the optical disc that occurs during the manufacture of the optical disc. When manufacturing an optical disk, particularly when manufacturing a single-plate optical disk composed of one disk substrate, it is difficult to make the disk a perfect flat surface, and warping occurs to some extent. Therefore, this warp is usually within a certain range in the manufacture of optical discs, that is, 0 is based on the condition that there is no warp.
It is managed to be within ± B [mrad]. Here, B is a warp control value in the optical disc manufacturing process. Therefore, an inclination of the optical system of −B to B [mrad] occurs due to the warp of the optical disc that occurs during the production of the optical disc. (Hereinafter, this inclination is referred to as "first inclination".)

The second cause of the tilt of the optical system is a tilt of the optical disk drive such as a setting error of the optical system and a tilt of the axis of the turntable that rotates the optical disk. (Hereinafter, this inclination is referred to as "second inclination", and its range is defined as -C to C [mrad].) Then, the first inclination and this second inclination are added,
That is, -B-C to B + C [mrad] is the range of the initial slope that is the slope that originally exists in the system. In Figure 6,
An example is shown in which the range of the initial tilt is shown on the graph of the relationship between the tilt of the optical system and the error rate.

The third cause of the inclination of the optical system is the warp of the optical disc caused by the change in relative humidity. As described above, when the optical disk is set in the optical disk drive, the relative humidity decreases by about 20%, the optical disk warps, and the optical system tilts. (Hereinafter, this inclination is referred to as "third inclination".
Say. ) For example, the maximum change of this warp is A [mrad]
When the warp occurs in the optical disc, an inclination of A [mrad] is generated in the optical system, and the entire inclination range in which the third inclination is added to the initial inclination is -BC + A to B + C + A [mrad].
FIG. 7 shows an example in which the range of the entire tilt is shown on a graph of the relationship between the tilt of the optical system and the error rate.

Usually, in order to keep the above-mentioned tilt of the optical system within the allowable range, the first tilt is reduced. That is, the management value B of the warp in the manufacturing process of the optical disc is made small, and the control regarding the warp of the optical disc that occurs during the optical disc manufacturing is made strict.

As a warp of an optical disk due to a change in relative humidity, a change in relative humidity is 20 as described above.
It suffices to consider the maximum amount of warpage when it decreases by%. Therefore, the maximum warp amount A of the optical disk due to the change in relative humidity can be known in advance. Therefore, if the warp of the optical disc during the optical disc manufacturing is controlled so as to be within the range of −A / 2 ± B [mrad] with the warp of −A / 2 [mrad] as a reference, the optical disc manufacturing process The control value B of the warp in the optical disc can be increased to loosen the control regarding the warp of the optical disc that occurs during the optical disc manufacturing.

That is, the range of the first inclination is (-A / 2
-B) to (-A / 2 + B) [mrad], and the range of the initial gradient obtained by adding the second gradient to this is (-A / 2-BC) to
(-A / 2 + B + C) [mrad]. Then, the range of the entire gradient in which the gradient of A [mrad] is added to the initial gradient as the third gradient is (A / 2-BC) to (A / 2 + B +).
C) It becomes [mrad]. FIG. 8 shows an example in which the range of this inclination is shown on the graph of the relationship between the inclination of the optical system and the error rate.

That is, as in the conventional case, when the warp of the optical disk produced during the manufacture of the optical disk is set within the range of 0 ± B [mrad] with reference to the state where there is no warp, −
It is necessary to set the warp management value B in the optical disc manufacturing process so that K <A−B−C and A + B + C <K. On the other hand, as in the present embodiment, the warp of the optical disc that occurs during the optical disc manufacturing is -A / 2 [mrad].
When the warp is set to be within the range of −A / 2 ± B [mrad], the optical disc is set to −K <A / 2−B−C and A / 2 + B + C <K. The control value B of the warp in the manufacturing process of
Therefore, it is possible to loosen the management regarding the warp of the optical disc that occurs during the optical disc manufacturing.

A more specific embodiment will be described below.

Example 1 The optical disk of this example has a thickness of 1.2 mm and a diameter of 130.
This is a magneto-optical disk using a polycarbonate disk substrate of mm, and as described above, -3 [mrad] may be considered as the maximum change A of the warp caused by the change in relative humidity, and -A / 2 [mrad]. That is, a warp of 1.5 [mrad] is given in advance.

First, mark length recording was performed on the above optical disk by 2-7 modulation. The mark length recording condition is 4.8 m / s and the shortest carrier frequency is 2.88 MH.
z, laser wavelength 780 nm, NA 0.55. After that, the turntable that rotates the optical disk is tilted to reproduce the recording, and the byte error rate is measured.
The relationship between the tilt of the optical system and the error rate was investigated. The results are shown in Fig. 9. The error threshold for this system is 5 x 10
^Since it is ^-4 , the allowable range of the tilt of the optical system is about -1.
It becomes 1.5 to 11.5 [mrad].

Next, the second inclination, that is, the setting error of the optical system, the inclination of the axis of the turntable, and the like existing in the optical disk drive, was measured and found to be ± 4.9 [m].
rad]. This value was obtained by measuring the slope at 8 points and doubling the standard deviation of the χ ² distribution of these data.

In order to keep the tilt of the optical system within the allowable range in the above optical disk, the warp of the optical disk, which is the cause of the first tilt, which occurs during the manufacture of the optical disk is managed as follows. Just go.

That is, it is controlled so as to be within the range of -A / 2 ± B [mrad] with reference to the state where there is a warp of -A / 2 [mrad]. At this time, the value of B, which is the warp control value in the optical disc manufacturing process, is −K <A / 2−B−C, that is, −11.5 <−3 / 2−B−4. It should be set to 9. Therefore, it suffices to manage so that B <5.1.

Therefore, the control of the warp in the manufacturing process of this optical disc which has been previously given a warp of 1.5 [mrad] may be 1.5 ± 5.1 [mrad]. As described above, in the optical disc of the present embodiment, warp management in the manufacturing process may be loose, so that defective products rarely occur and the yield is improved.

COMPARATIVE EXAMPLE 1 The optical disk of this comparative example is a magneto-optical disk manufactured without warping in advance, and is otherwise the same as the optical disk of Example 1.

In the above optical disc, in order to keep the inclination of the optical system within the allowable range, the warp of the optical disc, which is the cause of the first inclination, which occurs at the time of manufacturing the optical disc must be managed as follows. There is.

That is, 0 is used as a reference when there is no warp.
It is managed to be within ± B [mrad]. At this time,
The value of B, which is a warp control value in the optical disc manufacturing process, is set to −K <A−B−C, that is, −11.
It should be set to 5 <-3-B-4.9. Therefore, it suffices to manage so that B <3.6.

Therefore, the control of the warp in the manufacturing process of this optical disk which is manufactured without giving the warp in advance is as follows.
It becomes 0 ± 3.6 [mrad]. As described above, in the optical disc of this comparative example, it is necessary to strictly control the warpage in the manufacturing process, many defective products are generated, and the yield is deteriorated.

Example 2 In this example, a method for controlling the amount of warp given to an optical disk in advance will be described.

As shown in FIG. 10, the optical disk of the present example has a polycarbonate disk substrate 11 having a thickness of 1.2 mm and a diameter of 130 mm and a Si-N film having a thickness of 100 nm as a recording layer for magneto-optical recording. Layer 12, thickness 22 nm
M-O layer 13, a Si-N layer 14 having a thickness of 40 nm, and an Al layer 15 having a thickness of 70 nm are laminated in this order, and an ultraviolet curable resin layer 16 is further applied and formed thereon to form a single plate type light. It is a magnetic disk. The characteristics of the disk substrate and the ultraviolet curable resin are as shown in Table 1.

[0049]

[Table 1]

The optical disc is warped due to the shrinkage of the ultraviolet curable resin when it is cured. The amount of warp depends on the thickness of the ultraviolet curable resin layer. FIG. 11 shows the results of measuring how the warp of the optical disk changes when the thickness of the ultraviolet curable resin layer is changed within the range of 5 to 30 μm.

As is clear from the measurement results, the amount of warp of the optical disk depends on the thickness of the ultraviolet curable resin layer, and the amount of warp applied to the optical disk in advance is controlled by changing the thickness of the ultraviolet curable resin layer. You can see that you can. .

[0052]

EFFECTS OF THE INVENTION Warpage occurs due to changes in relative humidity,
In an optical disk using a disk substrate having a hygroscopic property, by preliminarily imparting a warp of half the maximum change in the warp caused by a change in relative humidity in the opposite direction of the warp, the inclination of the optical system due to the warp is reduced. The maximum change can be suppressed to half the maximum change.

Therefore, the deflection disk of the present invention can loosen the warp management in the manufacturing process, reduce the number of defective products, and improve the yield.

Further, by controlling the warp amount of the warp applied to the optical disc in advance by the thickness of the ultraviolet curable resin layer formed on the surface of the optical disc, the warp can be easily controlled to an arbitrary amount. You can

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a warp direction of an optical disc.

FIG. 2 is a diagram showing an example of measurement results of changes over time in the amount of change in warp when the relative humidity is changed from 50% to 30%.

FIG. 3 shows the radial position of the optical disc and the relative humidity of 20.
It is a figure which shows an example of the measurement result of the relationship with the maximum change of the warp when changing%.

FIG. 4 is a diagram showing an example of measurement results of the relationship between the amount of change in relative humidity change and the maximum change in warpage.

FIG. 5 is a graph showing an example of the relationship between the tilt of the optical system and the error rate.

FIG. 6 is a graph showing an example of the relationship between the tilt of the optical system and the error rate and the range of the initial tilt.

FIG. 7 is a graph showing an example of the relationship between the tilt of the optical system and the error rate and the range of the entire tilt.

FIG. 8 is a graph showing an example of the relationship between the inclination of the optical system and the error rate and the range of the entire inclination when the present invention is applied.

FIG. 9 is a diagram showing an example of the measurement result of the relationship between the tilt of the optical system and the error rate.

FIG. 10 is a cross-sectional view of essential parts showing an example of an optical disc to which the present invention is applied.

FIG. 11 is a diagram showing an example of measurement results of the relationship between the thickness of the ultraviolet curable resin layer and the amount of warpage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical head 11 Disk substrate 12 Si-N layer 13 MO layer 14 Si-N layer 15 Al layer 16 UV curable resin layer

Claims (2)

[Claims] 1. A maximum change in the warp at the outermost circumference of the disk when the relative humidity changes by 20% under an environment of a relative humidity of 3 to 85% and a temperature of 5 to 55 ° C., using a synthetic resin substrate as the disk substrate. Is A [mrad], a warp is given in advance so that the warp amount becomes −A / 2 ± 0.5 [mrad] when left for 3 days in an environment with relative humidity of 50% and temperature of 23 ° C. An optical disc characterized by being recorded. 2. The optical disk according to claim 1, wherein an ultraviolet curable resin layer is formed on the surface by coating, and the amount of warp applied in advance is controlled by the thickness of the ultraviolet curable resin layer. .