JPH08203120A - Optical disk - Google Patents

Abstract

PURPOSE: To obtain a highly reliable optical disk by forming a protective layer of the optical disk in such a manner that the thermal conductivity in the layer is decreased from the inner side toward the outer side. CONSTITUTION: This optical disk consists of a recording part 2 comprising a first dielectric film, recording magnetic film, second dielectric film and reflecting film formed in this order on one principal plane of a transparent substrate 1, and a protective layer 3 to cover the recording part 2. The protective layer 3 is formed in such a manner that the thermal conductivity is decreased from 0.03J/s.cm. deg.C) on the inner circumference side to 0.002J/(s.cm. deg.C) on the outer circumference side. The optical disk is produced by using a 1.2 mm-thick polycarbonate substrate 1 as the transparent substrate 1, then forming a 100nm-thick Si3 N4 film as the first dielectric film, 20nm-thick TbFeCo film as the recording magnetic film, 30nm-thick Si3 N4 film as the second dielectric film, and 50nm-thick Al film as the reflecting film each by sputtering to form the recording part 2, and then forming a protective layer 3 by using a spin coating machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention utilizes the magneto-optical effect or the crystal-amorphous phase transition phenomenon to record and record information signals.
The present invention relates to an optical disc for reproduction, and more particularly, to an optical disc capable of ensuring a wide recording power margin for good recording.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of information processed by computers and the like, the storage medium used as an external memory is also required to have an increased storage capacity. Also,
It is also required to improve the capacity of the central processing unit (CPU) of the computer and to cope with diversification of applications. Therefore, it is effective to use an optical disk, which is capable of extremely high density recording and excellent in portability, as a storage medium for a large capacity external memory. In particular, the use of a rewritable optical disk utilizing the magneto-optical effect or the crystal-amorphous phase transition phenomenon is very promising.

Under such circumstances, the demand for higher recording density of optical discs is increasing more and more, and in order to improve the recording density, the wavelength of laser light is shortened and the so-called mark edge recording system is adopted. It is being appreciated.

[0004]

By the way, in an optical disk used as an external memory of a computer, there is a difference in drive, presence or absence of dust attached to a lens,
It is necessary to be able to perform excellent recording in a wide range of recording power so that the recording / reproducing characteristics are not affected by the difference in environmental temperature.

However, in an optical disc whose recording density is increased by shortening the wavelength of laser light and adopting a mark edge recording system, the recording power that enables good recording due to a decrease in C / N and intersymbol interference. Margin will be reduced. In addition, when recording is performed while rotating the optical disc at a constant angular velocity, since the linear velocity varies in the radial direction of the optical disc, the recording sensitivity deteriorates toward the outer peripheral side where the linear velocity is faster. The margin of the recording power that enables good recording in any of these places becomes very narrow.

Therefore, the present invention has been proposed in view of the above circumstances, and provides an optical disc with a small recording sensitivity difference between the inner circumference side and the outer circumference side and a large margin of recording power that enables good recording. The purpose is to do.

[0007]

An optical disk according to the present invention has been proposed in order to achieve the above-mentioned object, and comprises at least a recording layer and a protective layer formed on a transparent substrate. The thermal conductivity of the protective layer is reduced from the inner peripheral side toward the outer peripheral side.

That is, according to the present invention, the difference in recording sensitivity between the inner circumference side and the outer circumference side, which has occurred in the optical disc in which the writing / reading of the information signal to / from the recording layer is performed during the rotation at a constant angular velocity, is eliminated. The thermal conductivity is changed in the radial direction so as to be substantially matched.

If the difference in thermal conductivity between the inner and outer circumferences is small, the effect of equalizing the difference in recording sensitivity is small. On the contrary, if it is too large, the recording sensitivity on the inner circumference side becomes relatively small. The recording sensitivity is deteriorated as compared with the recording sensitivity on the outer peripheral side, and the recording sensitivity becomes rather uneven.

By the way, the recording layer may be composed of a material layer having a magneto-optical effect, or may be composed of a material layer which undergoes a phase transition between crystal and amorphous when irradiated with a laser beam.

In order to manufacture the above optical disk,
When at least the recording layer is formed on the transparent substrate, the protective layer coating material is supplied onto the recording layer, and the protective layer coating material is applied to the entire surface of the recording layer by spin coating to form the protective layer. The paint having high thermal conductivity may be supplied to the inner peripheral side of the layer, and the paint having low thermal conductivity may be supplied to the outer peripheral side of the recording layer.

The protective layer coating composition is preferably composed mainly of an oligomer which is cured by irradiation with ultraviolet rays. Specifically, a composition obtained by adding a reactive diluent or a photopolymerization initiator to an oligomer such as urethane acrylate, polyester acrylate, or epoxy acrylate, a cationic photopolymerization epoxy, or a resin obtained by adding a cationic polymerization catalyst to an epoxy resin is used. Can be used.

The thermal conductivity of the protective layer coating material may be adjusted by adding fine particles of metal or ceramic to the oligomer. Ag, Ni, Al, C, etc. can be used as the metal fine particles, and Al ₂ O ₃ , TiO ₂ , Fe as the ceramic fine particles.
₂ O ₃ , Fe ₃ O ₄ , In ₂ O ₃ , ZnO, AlN, S
iO ₂ or the like can be used. The diameter of these fine particles is preferably 0.1 to 1 μm, and the addition amount is preferably 1 to 50% by weight.

[0014]

In the optical disc having the recording layer and the protective layer on which the recording is performed by the heat generated by the irradiation of the laser beam on the substrate, the thermal conductivity of the protective layer is decreased from the inner peripheral side to the outer peripheral side. By changing it in the radial direction, it is possible to reduce the difference in recording sensitivity in the radial direction.
As a result, the range of recording power at which good recording is possible on the inner circumference side of the optical disc and the range of recording power at which good recording is possible on the outer circumference side substantially match,
It is possible to expand the range of recording power that enables good recording at any position in the radial direction, that is, the total power margin.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of optical disks to which the present invention is applied will be described below with reference to the drawings.

Example 1 In this example, the thermal conductivity of the protective layer was varied in the radial direction with respect to an optical disk capable of rewriting information using the magneto-optical effect.

As shown in a part of the cross section of FIG. 1, this optical disk has a first dielectric film, a recording magnetic film, and a first dielectric film on a main surface of a transparent substrate 1 having a diameter of 89 mm (3.5 inches). The recording layer 2 is formed by depositing a second dielectric film and a reflective film in this order, and a protective layer 3 covering the recording layer 2. The protective layer 3 is from 0.03 J / (s · cm · ° C) to 0.000 from the inner circumference side to the outer circumference side of the optical disc.
The thermal conductivity is reduced to 2 J / (s · cm · ° C). It should be noted that this optical disc is for recording while rotating at 3000 rpm.

To manufacture such an optical disc, a polycarbonate substrate having a diameter of 89 mm (3.5 inches) and a thickness of 1.2 mm is prepared as the transparent substrate 1, and first, a film thickness is formed as the first dielectric film. the Si ₃ N ₄ film of 100 nm, TbFeCo film with a thickness of 20nm as a recording magnetic film, the Si ₃ N ₄ film having a film thickness of 30nm as a second dielectric film, by respectively sputtering film thickness 50nm of Al film as a reflective film The film was formed to form the recording unit 2.

After that, in order to form the protective layer 3 so as to cover the recording portion 2, the spin coater shown in FIG. 2 was used. This spin coater is a disk 1
0 (a transparent substrate 1 on which the recording unit 2 is formed) on which a mounting table 4 is mounted, a central shaft 5 of the mounting table 4 is connected to rotate a motor (not shown), and the mounting table 4 is mounted on the mounting table 4. It is composed of a first nozzle 6 for supplying paint to the inner peripheral side of the mounted disk 10 and a second nozzle 7 for supplying paint to the outer peripheral side of the disk 10.

The second nozzle 7 supplies the coating material (A) made of an acrylic oligomer which is cured by ultraviolet rays, and the first nozzle 6 contains 5% by weight of a filler made of Ag in the oligomer. The coating material (B) is supplied. Here, the coating material (A) has a thermal conductivity of 0.002 J / (s · cm · ° C) after ultraviolet curing, and the coating material (B) has a thermal conductivity of 0. 03
J / (s · cm · ° C).

In order to actually form the protective layer 3, first, the disk 10 is placed on the mounting table 4 of the above spin coater and the recording section 2 is formed.
With the disk facing upward, and the disk 10 at 60 rp
2 g of paint (B) and paint (A) from the first nozzle 6 and the second nozzle 7 respectively while rotating at m.
/ Sec was supplied for 1.0 second.

Then, by rotating the disk 10 at 4000 rpm, the paint (B) and the paint (A)
Was applied to the entire surface of the recording portion 2, the rotation of the disk 10 was stopped, and ultraviolet rays were irradiated. As a result, the coating material (B) and the coating material (A) were cured and the protective layer 3 was formed.

In the optical disk thus formed, the thermal conductivity of the protective layer 3 is 0.002 at the outermost side.
The value gradually increased from J / (s · cm · ° C) toward the inner peripheral side, and changed to 0.03 J / (s · cm · ° C) at the innermost peripheral side. This is because the coating material (B) and the coating material (A) existed independently in the areas facing the first nozzle 6 and the second nozzle 7, respectively, but the coating material (B) and the coating material (A) existed in the central portion. This is because (A) was mixed with a predetermined concentration gradient.

By the way, the thermal conductivity of the protective layer 3 in the optical disk of this embodiment is set based on the following experimental results.

First, an optical disc is prepared in which the protective layer 3 having a thermal conductivity of 0.002 J / (s · cm · ° C.) is formed on the entire surface of the recording portion 2 having the above-mentioned structure, and the optical disc is set to 3000 rpm. Then, the relationship between the linear velocity and the recording sensitivity was obtained by simulation. As a result, as shown in FIG. 3, it was found that the recording sensitivity was directly proportional to the square root of the linear velocity.

Next, from 0.002 J / (s · cm · ° C.) to 0.13 J / on the entire surface of the recording unit 2 having the above-mentioned structure.
Optical discs having protective layers 3 having various thermal conductivities up to (s · cm · ° C.) are prepared, and each optical disc is rotated at 3000 rpm to obtain the innermost peripheral side (linear velocity 9.
The recording sensitivity at a position of 26 m / sec) was measured. Then, when the relationship between the thermal conductivity and the recording sensitivity was obtained,
As shown in, the recording sensitivity was found to be directly proportional to the square root of the thermal conductivity.

From these results, in an optical disc in which the recording sensitivity decreases toward the outer circumference side, in order to make the recording sensitivity on the inner circumference side and the outer circumference side coincide with each other, the thermal conductivity of the protective layer 3 on the inner circumference side is set to the outer circumference side. It turns out that it should be higher than. Then, specifically, the thermal conductivity on the outer peripheral side is 0.002 J.
When fixed at / (s · cm · ° C), in order to have recording sensitivity equal to the recording sensitivity on the outer peripheral side under this condition on the inner peripheral side (position at which the linear velocity is 9.26 m / sec), What value should be set for the thermal conductivity on the side was calculated. Fig. 5 shows that the thermal conductivity is 0.002 J / (s ・
(cm.degree. C.) The relationship between the linear velocity on the outer peripheral side fixed at (cm.degree. C.) and the thermal conductivity on the inner peripheral side that can achieve a recording sensitivity equal to the recording sensitivity on the outer peripheral side. When a 3.5-inch optical disc is rotated at 3000 rpm, the thermal conductivity on the outer peripheral side (linear velocity 13.3 m / sec) is fixed to 0.002 J / (s · cm · ° C). , The thermal conductivity on the inner peripheral side is 0.04 J / (s · cm ·
It is understood that the recording sensitivities on the inner circumference side and the outer circumference side become equal when the temperature is set to ° C.

However, if the recording sensitivity on the inner circumference side is made equal to the recording sensitivity on the outer circumference side, the recording sensitivity on the inner circumference side is deteriorated. Therefore, in the present embodiment, the thermal conductivity of 0. The thermal conductivity on the inner peripheral side was set to 0.03 J / (s · cm · ° C) with respect to 002 J / (s · cm · ° C).

Comparative Example 1 For comparison, an optical disk was produced in which the thermal conductivity of the protective layer 3 was equal in the radial direction.

Specifically, first, the disk 10 was manufactured in the same manner as in Example 1 up to the step of forming the recording portion 2 on the transparent substrate 1. Then, the disk 10 is mounted on the mounting table 4 of the spin coater described above, and the first nozzle 6
The protective layer 3 was formed in the same manner as in Example 1 except that the coating material (A) was supplied from both of the second nozzle 7 and the second nozzle 7.

In the optical disc thus formed, the thermal conductivity of the protective layer 3 was 0.002 J / (s · cm · ° C) over the entire surface from the outer peripheral side to the inner peripheral side.

Comparative Example 2 Here, the protective layer 3 was formed in the same manner as in Comparative Example 1 except that the coating material (B) was supplied from both the first nozzle 6 and the second nozzle 7.

In the optical disk thus formed, the thermal conductivity of the protective layer 3 was 0.03 J / (s · cm · ° C) over the entire surface from the outer peripheral side to the inner peripheral side.

Evaluation of Characteristics Below, the margin of the recording sensitivity and the recording power of each optical disk having the above-mentioned structure is examined.

Specifically, first, each optical disc is rotated at a constant angular velocity, and the inner peripheral side with a linear velocity of 9.26 m / s and the outer peripheral side with a linear velocity of 13.3 m / s differ in the radial direction. Recording sensitivity was measured at two points. The recording conditions are as follows: wavelength of laser light: 680 nm, lens numerical aperture N
A: 0.55, clock: inner circumference side 28.2 MHz, outer circumference side 39.9 MHz, recording signal: (1,7) RLL random signal. The measurement results are shown in FIG. 6 as the relationship between the linear velocity and the recording sensitivity.

From FIG. 6, in the optical discs of Comparative Examples 1 and 2 in which the thermal conductivity of the protective layer 3 is uniform over the entire surface,
It can be seen that the recording sensitivity deteriorates as the linear velocity increases, that is, the recording sensitivity deteriorates toward the outer peripheral side. Further, when comparing Comparative Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 in which the thermal conductivity of the protective layer 3 is high is inferior in recording sensitivity. On the other hand, in the optical disc of Example 1, on the inner peripheral side, Comparative Example 2
Recording sensitivity is suppressed by having the same thermal conductivity as that of the optical disk of No. 1, and the recording sensitivity is improved at the outer peripheral side by having the same thermal conductivity as that of the optical disk of Comparative Example 1, resulting in the inner peripheral side. It can be seen that the difference in recording sensitivity between the outer peripheral side and the outer peripheral side is reduced.

Next, with respect to the optical discs of Example 1 and Comparative Example 1, the relationship between the recording power and the bit error rate was measured on the inner circumference side and the outer circumference side, respectively. The measurement results for the optical disc of Example 1 are shown in FIG. 7, and the measurement results for the optical disc of Comparative Example 1 are shown in FIG. In addition, in FIG. 7 and FIG. 8, the measurement results on the inner circumference side are shown by a plot of ○,
The measurement result on the outer peripheral side is shown by a plot of Δ. Further, the same drawing also shows the margin of the recording power at which the bit error rate becomes 10 ⁻⁵ or less.

Comparing FIG. 7 and FIG. 8, a recording power margin (indicated by A or a in the drawing) that enables good recording on the inner circumference side and recording that enables good recording on the outer circumference side. Although there is almost no difference in the size of the power margin (indicated by B or b in the figure) itself, the recording power of the recording power that enables good recording at both the inner and outer circumference sides. It can be seen that the size of the margin (indicated by C or c in the figure) is larger in the optical disc of Example 1 shown in FIG.

Thus, as in the optical disc of Example 1, the recording sensitivity is made uniform in the radial direction, and the margin of the recording power is increased so that good recording can be performed at any position in the radial direction. I found that

Although an example of the optical disk according to the present invention has been described above, the present invention is not limited to this. For example, in the spin coater shown in FIG. 2, the first nozzle 6 and the second nozzle 6 are provided. A third nozzle may be provided between the nozzles 7 to supply the paint having a thermal conductivity intermediate between those of the paint (A) and the paint (B).

Also in an optical disc for recording / reproducing information by utilizing the crystal-amorphous phase transition phenomenon, if the thermal conductivity of the protective layer is equal in the radial direction, as shown in FIG. The higher the linear velocity, the lower the recording sensitivity. Therefore, for example, a ZnS—SiO ₂ film having a film thickness of 200 nm and a GeS film having a film thickness of 30 nm are formed on a polycarbonate substrate.
bTe film, 30 nm a film thickness ZnS-SiO ₂ film, 20
The present invention can also be applied to an optical disk in which an Al film having a film thickness of 0 nm is laminated in this order.

In addition, the structure, constituent material, size, etc. of the optical disk can be appropriately modified and changed without departing from the gist of the present invention.

[0043]

As is apparent from the above description, when the present invention is applied, it is possible to increase the margin of the recording power that enables good recording at any radial position. For this reason, it is possible to provide a highly reliable optical disk in which the recording characteristics are not affected by various changes in the usage environment, which also contributes to the increase in the recording density of the optical disk.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a main part of a configuration example of an optical disc.

FIG. 2 is a schematic diagram showing a spin coater for applying a protective layer coating material.

FIG. 3 is a characteristic diagram showing the relationship between the linear velocity of an optical disc and the recording sensitivity.

FIG. 4 is a characteristic diagram showing the recording sensitivity on the inner circumference side of optical disks in which the thermal conductivity of the protective layer is different, and showing the result as the relationship between the square root of the thermal conductivity and the recording sensitivity.

FIG. 5 is a linear velocity on the outer peripheral side where the thermal conductivity is fixed to 0.002 J / (s · cm · ° C.) and an inner peripheral side where the recording sensitivity equal to the recording sensitivity on the outer peripheral side can be obtained. It is a characteristic view showing the relationship with the thermal conductivity of.

FIG. 6 is a characteristic diagram showing the results of measuring recording sensitivities on the inner circumference side and the outer circumference side of the present invention and the conventional optical disk as a relationship between the linear velocity and the recording sensitivity.

FIG. 7 is a characteristic diagram showing the relationship between the recording power and the bit error rate measured on the inner circumference side and the outer circumference side, respectively, in order to show the margin of the recording power that enables good recording in the optical disc of the present invention. is there.

FIG. 8 is a characteristic diagram showing the relationship between the recording power and the bit error rate measured on the inner circumference side and the outer circumference side, respectively, in order to show the margin of the recording power that enables good recording in the conventional optical disc. .

FIG. 9 is a graph showing the relationship between the linear velocity and the recording sensitivity obtained by measuring the recording sensitivities at different radial positions on a phase-transition type optical disc having a protective layer having the same thermal conductivity over the entire surface. It is a characteristic view to show.

[Explanation of symbols]

 1 transparent substrate 2 recording part 3 protective layer 4 mounting table 5 central axis 6 first nozzle 7 second nozzle 10 disk

Claims (6)

[Claims] 1. An optical disc having at least a recording layer and a protective layer formed on a transparent substrate, wherein the thermal conductivity of the protective layer decreases from the inner peripheral side toward the outer peripheral side. Optical disc. 2. The optical disc according to claim 1, wherein writing / reading of an information signal to / from the recording layer is performed during rotation at a constant angular velocity. 3. The thermal conductivity of the protective layer is changed so that the recording sensitivity on the inner circumference side and the recording sensitivity on the outer circumference side are substantially matched with each other. Optical disc. 4. The optical disc according to claim 1, wherein the protective layer is mainly composed of an ultraviolet curable resin. 5. The recording layer is formed of a material layer having a magneto-optical effect.
The optical disc according to any one of 1. 6. The recording layer according to claim 1, wherein the recording layer is made of a material layer that undergoes a phase transition between crystal and amorphous by irradiation with laser light. optical disk.