Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-03-20
2003-01-14
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S275100, C369S284000
Reexamination Certificate
active
06507547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a medium for recording optical information and to a method for recording optical information, and more particularly relates to a writable medium for recording optical information provided at least with a light-absorbing layer and a light-reflecting layer on a translucent substrate, and to a method for recording optical information.
2. Description of the Related Art
In conventional media (so-called “CD-Rs”) for recording optical information that have writable structures, it is important not only to provide recorded disks with adequate playback characteristics, but also to achieve the needed recording sensitivity (that is, the low recording power that allows optimum recording to be performed) in order to be able to adequately deal with high-speed recording.
To reduce the recording power of a conventional medium for recording optical information, it has been suggested to enhance the recording sensitivity thereof by increasing the degree to which the light-absorbing layer absorbs light (that is, by increasing the light attenuation coefficient) or to increase the thickness of the light-absorbing layer and hence to enhance the overall light absorption of the dye film.
There are, however, limits as to how much recording sensitivity can be raised by the aforementioned techniques.
Specifically, a maximum reflectivity Rtop of 65% R or higher is needed in order to achieve the level of the Orange Book, which is a CD-R standard, but increasing the amount of light absorbed by the dye film above a certain level brings about reduced reflectivity and makes it impossible to satisfy the requirements of the Orange Book in terms of reflectivity.
In other words, achieving higher recording sensitivity with the aid of a conventional technique is disadvantageous because the result is often proportional to the light attenuation coefficient of the dye, so the light attenuation coefficient of the dye material in the a a laser beam wavelength region should be increased in order to ensure higher recording sensitivity, which is incompatible with maintaining adequate reflectivity. Because the light attenuation coefficient is proportional to the absorption of light (absorbance) in the dye material, increasing the light attenuation coefficient reduces reflectivity and increases the proportion of luminous energy absorbed by the dye film.
Consequently, with conventional techniques based on the light attenuation coefficient alone, it is difficult to provide the desired recording sensitivity while maintaining reflectivity on a par with the CD-R standard, particularly in light of the fact that keeping both recording sensitivity and reflectivity at a level suitable for high-speed recording is an indispensable condition.
SUMMARY OF THE INVENTION
An object of the present invention, which was perfected in view of the above-described shortcomings, is to provide a medium and a method for recording optical information that allow a prescribed recording sensitivity to be maintained together with the desired reflectivity and other playback characteristics, particularly under conditions of high-speed recording.
Another object of the present invention is to provide a medium and a method for recording optical information that allow recording sensitivity to be improved by adopting an approach in which a material prone to increased absorption of a a laser beam under high-temperature recording conditions is selected as the dye material used for CD-R.
Yet another object of the present invention is to provide a medium and a method for recording optical information that allow recording sensitivity to be increased using the temperature dependence of the recording sensitivity of the light-absorbing layer instead of the light attenuation coefficient thereof while maintaining playback characteristics at the same level as in the past.
Specifically, it was discovered in relation to the present invention that the absorbance or recording sensitivity of the dye material films used in CD-R disks (or in media (so-called DVD-R disks) for recording optical information that have writable structures in which shorter-wavelength a a laser beam is used) is dependent on temperature. Specifically, it was found that the absorption spectrum of a dye material varies at high temperatures and that recording sensitivity can be improved by selecting a material in which absorption of light is apt to increase at a high temperature. The first invention resides in a medium for recording optical information comprising a translucent pregrooved substrate; a light-absorbing layer that is formed on the substrate and that contains a light-absorbing substance composed of a dye for absorbing recording light based on a a laser beam; and a light-reflecting layer that is formed on the light-absorbing layer and is designed to reflect a a laser beam, wherein information is recorded by irradiating the light-absorbing layer with recording light, the aforementioned medium for recording optical information being characterized by satisfying a relation A
2
/A
1
≧1.30, where A
1
(Abs) is an absorbance of the light-absorbing layer at a wavelength of recording light under room-temperature conditions, T (°C.) is a pyrolysis temperature of the light-absorbing layer, and A
2
(Abs) is an absorbance at a wavelength of said recording light under T−50 (°C.) conditions.
The second invention resides in a method for recording optical information on a medium for recording optical information comprising a translucent pregrooved substrate; a light-absorbing layer that is formed on the substrate and that contains a light-absorbing substance composed of a dye for absorbing recording light based on a laser beam; and a light-reflecting layer that is formed on the light-absorbing layer and is designed to reflect a laser beam, wherein information is recorded on the medium for recording optical information by irradiating the light-absorbing layer with recording light; the method for recording optical information involving directing recording light to the light-absorbing layer satisfying a relation A
2
/A
1
≧1.30, where A
1
(Abs) is an absorbance of the light-absorbing layer at a wavelength of recording light under room-temperature conditions, T (°C.) is a pyrolysis temperature of the light-absorbing layer, and A
2
(Abs) is an absorbance at a wavelength of recording light under T−50(°C.) conditions.
It is possible to satisfy a relation N≧2.0×10
−4
, where N (Abs/°C.) is a rate at which an absorbance of the light-absorbing layer varies at a wavelength of recording light under temperature conditions ranging from room temperature to the pyrolysis temperature.
It is also possible to satisfy relations 40≦dav≦100 and 0.15≦A
1
≦0.25, where dav (nm) is the mean thickness of the light-absorbing layer.
A more-detailed description will now be given.
FIG. 1
is an enlarged cross section of an example of the medium
1
for recording optical information in accordance with the present invention. The medium
1
for recording optical information comprises a translucent substrate
2
, a light-absorbing layer
3
(recording layer) formed on the substrate
2
, a light-reflecting layer
4
formed on the light-absorbing layer
3
, and a protective layer
5
formed on the light-reflecting layer
4
.
The substrate
2
is provided with a spiral pregroove
6
. Portions other than the pregroove
6
, that is, lands
7
, are disposed on the right and left of the pregroove
6
.
The substrate
2
and light-absorbing layer
3
are in contact with each other along a first layer boundary
8
. The light-absorbing layer
3
and light-reflecting layer
4
are in contact with each other along a second layer boundary
9
. The light-reflecting layer
4
and protective layer
5
are in contact with each other along a third layer boundary
10
.
It can be seen in the drawing that when the medium
1
for recording optical information is irradiated with recording light (recording a laser beam) L
1
, heat is evolved
Hamada Emiko
Shibuya Kazuyuki
Takagishi Yoshikazu
Yoshizawa Takanori
Taiyo Yuden Co. Ltd.
Tran Thang V.
Vuong Bach Q
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