JPH10269626A - Phase transistion type optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the phase transition type optical disk in which the progress of corrosion under an accelerated environment and the secular change in the amount of warpage are reduced and the reliability is improved. SOLUTION: A dielectric layer 304a, a phase transition type recording layer 304b, a dielectric layer 304c and a reflection layer 304d are formed on a circular shaped plastic transparent substrate 301 having a diameter of more than 120 mm. Then, a transparent resin protective film 302 is formed on the layer 304d. The film 302 is formed by coating ultraviolet curing liquid resin over the layer 304d. If the glass transition temperature is more than 95 deg.C and less than 120 deg.C, the thickness of the film 302 is set to more than 4 μm and less than 6 μm. If the temperature is more than 120 deg.C, the thickness is set more than 4 μm and less than 8 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to a highly reliable optical disk suitable for data recording / reproduction in a computer.

[0002]

2. Description of the Related Art A typical medium currently used as an optical disk is a CD or CD-ROM made of a transparent resin such as polycarbonate and having a thickness of 1.2 mm and a transparent substrate having a diameter of 120 mm as a component. , CD-R, P
Group D. Usually, a protective film is formed on the information recording layer or the reflective layer of these optical discs in order to prevent the reflective film or the recording film from being damaged by contact.

[0003] This protective film also serves to prevent scratches due to contact and also to prevent corrosion due to oxygen and moisture. Tests are made on the likelihood of corrosion in an accelerated environment. However, when the thickness of the protective film is small, defects such as pinholes are likely to occur in the recording layer or the reflective layer. As a method for solving this problem, as disclosed in Japanese Patent Application Laid-Open No. 2-292754, a structure in which two optical disks are adhered with a hot melt resin or the like to cover the protective film, or a method disclosed in Japanese Patent Application Laid-Open No. 5-292754. As disclosed in Japanese Patent No. 159364, a configuration has been proposed in which the thickness of the protective film is increased to 10 μm or more.

However, in the case of a configuration in which two optical disks are bonded, there is no problem if the adhesive force is sufficient, but in the case of a single-layer optical disk that does not adhere, or in the case where the adhesive force is weak, an acceleration test is performed. If this is done, a phenomenon occurs in which the optical disk is warped in a direction in which the recording film side is concave.

The amount of warpage of the deformation increases as the thickness of the protective film increases, and increases as the optical disk has a larger substrate outer diameter and a smaller substrate thickness. Therefore, a diameter of 3.5 inches (about 8
In the case of an optical disc having a thickness of 8.9 mm) and a thickness of 1.2 mm, it is possible to increase the thickness of the protective film.
In the case of an optical disk having a CD size of 20 mm or an optical disk having a substrate thickness of 0.8 mm or less, a means for further reducing the change in the amount of warpage due to an acceleration test of the optical disk has been desired.

As means for solving this problem, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No.-295470 discloses that the change in the amount of warpage due to an acceleration test in an environment of 55 ° C. and 95% RH can be suppressed by setting the product of the thickness of the protective film and the Young's modulus to a certain value or less. That is, it is considered that this suggests that the use of a resin having a low Young's modulus can reduce the amount of warpage when it is desired to increase the film thickness.

[0007]

However, in a recording type optical disk which requires higher reliability, 80 to
Although it is required to suppress warpage and corrosion generated under an accelerated test at a higher temperature such as 90 ° C., the above publication does not suggest warpage under such severe acceleration conditions. Further, the above publication describes a read-only optical disk in which irregularities formed directly on the substrate become signal pits. However, in the case of a phase-change optical disk,
In an initialization step of crystallizing the entire surface before shipping, stress is generated on the substrate.

This stress is caused by a change in the arrangement of atoms due to initialization. A read-only optical disk that does not require initialization itself, and a change in arrangement of atoms occurs even when a magnetic change occurs due to initialization. This does not occur in the case of a magneto-optical disk that does not.

According to the study of the present inventors, the stress caused by this initialization step is hardly released under the acceleration condition of 60 ° C. or less, and the change in the amount of warpage due to the acceleration is as small as 1 milliradian or less. Under the above acceleration conditions, in the phase change type optical disk, since the stress due to this initialization is relaxed,
It has been found that there is a problem that the amount of warpage is large as compared with the read-only type and the magneto-optical type.

In the case of a phase change type optical disk, it is not preferable to change the initialization conditions in consideration of the amount of warpage after acceleration, since the initialization conditions greatly affect the recording / reproducing characteristics. According to this, it was also found that the higher the power density input for initialization, the larger the amount of warpage generated under acceleration conditions.

The present invention has been devised in view of this situation. In particular, in a phase change optical disk on which it is assumed that an initialization step is performed, a phase change optical disk at a temperature of 80.degree. It is an object of the present invention to provide an optical disk in which both the amount of change in the amount of warpage and the degree of occurrence of corrosion are small even by a severe acceleration test.

[0012]

As a result of repeated studies by the present inventors to achieve the above object, the degree of corrosion after the accelerated test is generally determined by the thickness of the protective film formed of an ultraviolet-curable resin. It is found that the amount of warpage in the accelerated test depends not only on the thickness of the protective film but also on the heat resistance of the resin, while the difference greatly depends on the characteristics of the resin. From this knowledge, the inventors have found a configuration that can effectively reduce the change in the amount of warpage while reducing the occurrence of corrosion due to the accelerated test, and have completed the present invention.

That is, according to the first aspect of the present invention, a phase change between a crystalline state and an amorphous state is reversibly formed as a thin film layer on a disc-shaped plastic transparent substrate having a diameter of 120 mm or more. A phase-change optical disc in which a transparent resin protective film is formed by applying at least a recording layer made of a material to be formed, and applying and curing an ultraviolet-curable liquid resin on the thin-film layer. ,
The protective film has a glass transition temperature of 95 ° C. or more and less than 120 ° C. and a thickness of 4 μm or more and 6 μm or less.

The invention according to claim 2 has a diameter of 120 mm.
On the disc-shaped transparent plastic substrate described above, at least a recording layer made of a material whose phase change between a crystalline state and an amorphous state is reversibly performed as a thin film layer, and the thin film layer In a phase-change optical disc in which a transparent resin protective film is formed by applying and curing an ultraviolet-curable liquid resin on the protective film, the protective film has a glass transition temperature of 120 ° C. or higher, 4μ thick
Provided is a phase change type optical disk characterized by having a length of not less than m and not more than 8 μm.

Examples of the material for the transparent substrate include resins for heat-resistant optical materials such as polycarbonate resin, polymethyl methacrylate resin and amorphous polyolefin resin, and polycarbonate resin is most preferable from the viewpoint of heat resistance and cost. . The transparent substrate can be formed by an injection molding method, an injection compression molding method, a 2P method, or the like.

The recording layer formed on the transparent substrate is GeS
Any phase change type recording layer such as a bTe alloy can be used. The reflective layer can be made of an Al alloy or the like. These can be formed by a sputtering method, a CVD method, an evaporation method, or the like.

The protective film is formed by applying and curing an ultraviolet curable liquid resin on the thin film layer.
As an application method, there is a spin coating method as shown in FIGS.

First, as shown in FIG. 2, an excessive amount of liquid resin 102a with respect to a target film thickness is dripped from the inner periphery using a nozzle 103 onto a substrate 101 rotating at a low speed. After the resin is applied to the shape 102b, FIG.
As shown in (1), the resin 102c is rotated at a high speed for a certain time to shake off the excess resin 102c from the outer periphery. According to this method, the coating thickness is determined by physical properties such as the viscosity, surface tension and specific gravity of the resin and the coating conditions such as the number of rotations and the rotation time at the time of shaking, so that the coating thickness is controlled by selecting these conditions. can do.

As a method of measuring the thickness of the protective film, a method of mechanically measuring the thickness before and after coating to obtain a difference, a method of providing a portion not coated by a mask and measuring the step mechanically. However, it is preferable to employ an optical interferometry which has advantages of non-contact and high measurement accuracy. Since the outermost peripheral portion is partially thickened due to surface tension, the presence of burrs, and the like, the coating thickness is determined based on the thickness of the portion excluding the outermost portion.

A substrate on which a protective film made of an ultraviolet curable resin is formed is set on a spectroscope, and the wavelength is changed from 800 nm to 400 nm.
The reflectance is measured while scanning in the range of nm. As schematically shown in FIGS. 4 and 5, light 2 reflected on the surface of the protective film
Due to the interference of the light 203b reflected at the interface between the substrate 03a and the substrate surface or the recording layer or the reflection layer, the reflectance shows the repetition of the maximum P1, P2 and the minimum B1, B2 depending on the wavelength.

The reflection angle θ and the difference 2ndsin θ between the optical distances determined by the thickness d of the protective film and the refractive index n are obtained from the following formulas (1) and (2) from the maximum and minimum intervals of the reflectance. Since the calculation can be performed, if the refractive index n of the protective film is known, the film thickness d can be obtained. As long as a normal ultraviolet curable resin containing no fluorine or bromine is used, even if the refractive index is assumed to be 1.5, there is no large error in the calculated value of the film thickness. Refractive index is all 1.5
It was determined assuming that:

2ndsin θ = N · P1 ‥‥ (1) 2ndsin θ = (N − ／) B1 ‥‥ (2) The amount of warpage was measured by using a commercially available optical disk mechanical property inspection machine. It is measured by obtaining the inclination in the radial direction (the angle θ1 in FIG. 6). The angle θ1 is obtained by measuring the displacement A of the two points 18 and 19 along the radial direction of the optical disc 10 in the direction parallel to the reference plane, and using this displacement A and the radial distance D between the two points. , Can be approximately obtained from the following equation (3).

Θ ¹ = tan ⁻¹ (A / D) ‥‥ (3) In the case of an optical disk having a diameter of 120 mm, a position having a radius of 53 mm as the radially inner point 18 and a position of 58 mm as the outer point 19 are used. The position is set, the displacement A from each reference plane is measured, and the difference and the distance D between the two are measured.
(= 5 mm).

Since the value of the amount of warpage changes due to moisture absorption of the optical disk, the measurement environment is measured in an environment where the temperature is between 22 ° C. and 24 ° C. and the humidity is between 45% and 55%. It is necessary for the reproducibility of the measurement to keep the optical disk to be measured at least four days before the measurement in the environment.

In addition, since this measuring method needs to be focused by a mechanical property inspection device, the warpage is large.
If focus is not achieved due to a low reflectivity or the like, another measurement method using a value obtained by this measurement method and calibration may be employed. As an example, there is a method in which light emitted from a point light source is reflected on an optical disk to be measured, projected on a screen, and the projected diameter is measured to measure the amount of warpage.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to specific examples. Example 1 A transparent substrate made of polycarbonate having an outer diameter of 120 mm and a thickness of 1.2 mm was produced by an injection molding method. After annealing at 90 ° C for 2 hours to remove molding distortion, UV curable resin S manufactured by Dainippon Ink and Chemicals, Inc.
D-1700, SD-101, SD-301, SD-3
Using No. 18, a protective film having a thickness of 5 μm was formed by a spin coating method, and irradiated with light of 700 mJ / cm ² by a high-pressure mercury lamp to be cured to prepare a sample having only the transparent substrate and the protective film.

The amount of warpage generated by the accelerated test was 80 ° C.
Table 1 shows the results of a test under an accelerated environment of 0% RH for 150 hours.
Shown in

[0028]

[Table 1]

From these results, in an environment accelerated at 80 ° C., the magnitude of the warpage generated cannot be determined at a Young's modulus of 30 ° C. close to room temperature, and SD-17 having a low glass transition temperature of 80 ° C.
It can be seen that the curvature of 00 is large. (Example 2) As schematically shown in the sectional view of FIG. 1, a polycarbonate transparent substrate 301 having an outer diameter of 120 mm and a thickness of 1.2 mm was prepared by injection molding.

Subsequently, using a UV-curable resin UR-4511 manufactured by Mitsubishi Rayon Co., Ltd., a coating film 30 is formed on the opposite side of the recording film forming surface of the substrate 301 by a spin coating method.
3 was formed and cured by irradiating light of 1000 mJ / cm ² with a high-pressure mercury lamp. Subsequently, the dielectric layer 304a made of ZnS-SiO ₂ and the recording layer 30 made of GeSbTe
4b, a ZnS-SiO ₂ formed of a dielectric layer 304c, and a thin layer of 4-layer of the reflective layer 304d made of AlCr were formed by sputtering.

Next, ultraviolet-curable resins SD-101, SD-301 and SD-301 manufactured by Dainippon Ink and Chemicals, Inc.
318 and the protective film 30 by a spin coating method.
2 was formed and cured by irradiating light of 500 mJ / cm ² with a high-pressure mercury lamp. By irradiating the thus obtained phase change optical disk with laser light,
An initialization process for crystallizing the eSbTe recording layer from amorphous was performed, and the following accelerated test was performed on the initialized optical disk.

The degree of occurrence of corrosion is as follows: 110 ° C. 90
FIG. 7 shows the results of a test conducted under an accelerated environment of 67% RH. Corrosion was quantified by counting the number of pinholes having a size of 10 μm or more with an optical microscope per fixed area. From this figure, it can be seen that the thickness is preferably 4 μm or more, and more preferably 6 μm or more, regardless of the resin type.

The amount of warpage is as follows: 90 ° C., 80% R
Table 2 shows the results of a test performed under an accelerated environment of H900 hours.

[0034]

[Table 2]

From this result, it can be seen that even with the same thickness, the warpage of SD-101 having a low glass transition temperature of 95 ° C. is large. The allowable amount of warpage is 7 milliradians (mrad)
Therefore, SD-10 having a glass transition temperature of 95 ° C.
In the case of 1, it can be seen that 6 μm is the upper limit of the thickness. In contrast, SD-3 having a glass transition temperature of 120 ° C.
In the case of 01, when the thickness is 6 μm, the amount of warpage is smaller at 5 milliradians, and it is presumed that when the thickness is 8 μm, the amount of warpage is 7 milliradians.

Therefore, when a substrate having an outer diameter of 120 mm or more is used, the resin of the protective film is coated with a resin having a thickness of 4 to 6 when the glass transition temperature after curing is 95 ° C. or more and less than 120 ° C.
When the temperature is 120 ° C. or more, by forming the layer with a thickness of 4 to 8 μm, the amount of warpage in an environment of 90 ° C. and 80% RH acceleration can be suppressed to 7 milliradians or less, which is the allowable amount of warpage. I understand.

[0037]

As described above, the phase change type optical disk of the present invention has a small amount of warpage and hardly corrodes even in a severe acceleration test at a temperature of 80 ° C. or more performed after the initialization step. . That is, according to the present invention, a highly reliable optical disk suitable for data recording / reproduction in a computer can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a structure of a phase change recording type optical disc corresponding to one embodiment of the present invention.

FIG. 2 is a schematic view showing the principle of application of an ultraviolet curable resin by a spin coating method.

FIG. 3 is a schematic view showing the principle of applying an ultraviolet curable resin by a spin coating method.

FIG. 4 is a schematic diagram showing the principle of measuring a film thickness by an interference method.

FIG. 5 is a schematic diagram showing the principle of measuring a film thickness by an interference method.

FIG. 6 is an explanatory diagram for explaining an amount of warpage of a substrate.

FIG. 7 is a graph showing a relationship between the thickness of a protective film and the number of corrosions generated in an accelerated environment.

[Explanation of symbols]

101 Transparent substrate or substrate on which a recording layer or a reflective layer is formed 102a UV curable resin dropped 102b UV curable resin applied to the inner circumference at low speed 102c UV curable resin shaken off from the outer circumference at high speed rotation 103 UV curable resin Supply nozzle 201 Protective film 202 Substrate on which recording layer or reflective layer is formed 203a Light reflected on the surface of protective film 203b Light reflected on the boundary surface of protective film 301 Transparent substrate 302 Protective film 303 On the opposite side of the recording layer of substrate Surface protective film 304a Dielectric layer 304b Recording layer 304c Dielectric layer 304d Reflective layer

Claims (2)

[Claims] 1. A recording layer made of a material whose phase change between a crystalline state and an amorphous state is reversibly performed as a thin film layer on a disc-shaped transparent plastic substrate having a diameter of 120 mm or more. A phase-change optical disc in which a transparent resin protective film is formed by applying and curing an ultraviolet-curable liquid resin on the thin film layer, wherein the protective film has a glass transition A phase-change type optical disk having a temperature of 95 ° C. or more and less than 120 ° C. and a thickness of 4 μm or more and 6 μm or less. 2. A recording layer made of a material whose phase change between a crystalline state and an amorphous state is reversibly formed as a thin film layer on a disc-shaped plastic transparent substrate having a diameter of 120 mm or more. A phase-change optical disc in which a transparent resin protective film is formed by applying and curing an ultraviolet-curable liquid resin on the thin film layer, wherein the protective film has a glass transition The temperature is 120 ° C. or higher,
A phase-change optical disk having a thickness of 4 μm or more and 8 μm or less.