Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-04-03
2003-05-20
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064800, C430S270140, C430S270200
Reexamination Certificate
active
06565939
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat mode type optical information-recording medium which can record and replay information using a laser beam, and a method for recording information. In particular, the present invention relates to a heat mode type optical information-recording medium such as an optical disk-recordable (CD-R) or a digital video disk-recordable (DVD-R), which is suitable for recording information using a near infrared laser beam or a visible laser beam.
BACKGROUND OF THE INVENTION
Optical information-recording media (e.g., optical disks) which can record information only once with laser beams, have hitherto been known. These optical information-recording media are called CD-recordable (so-called CD-R), and have the typical structure that a transparent disk-shaped substrate is laminated with a recording layer comprising an organic dye, a light reflective layer comprising a metal such as gold, and a resin protective layer in this order. Information is recorded on this laminated product by irradiating a near infrared laser beam (usually, a laser beam having a wavelength of about 780 nm) to locally deform the recording layer by heat generation. On the other hand, reading (replay) of the information is usually carried out by irradiating a laser beam having the same wavelength as the laser beam for recording to detect the difference in reflectance between a deformed site (recorded area) of the recording layer by heat generation and a non-deformed site (non-recorded area).
With the recent spread of personal computers, optical information-recording media higher in recording density have been desired. For increasing the recording density, it is effective to decrease the diameter of a laser beam irradiated. Further, it has been theoretically known that a laser beam having a shorter wavelength is effective for an increase in density, because the diameter of the laser beam can be decreased. Accordingly, optical disks for carrying out recording and replay using laser beams having wavelengths shorter than 780 nm, which is a wavelength of the laser beam having hitherto been used, have been developed. For example, optical disks called DVD-recordable (so-called DVD-R) have been proposed. This optical disk is produced so as to provide the structure that two disks each comprising a transparent disk-shaped substrate having a diameter of 120 mm on which pregrooves are formed at a track pitch of 0.8 &mgr;m which is narrower than 1.6 &mgr;m in the CD-R medium and having provided thereon a recording layer comprising a dye and usually further a light reflective layer and a protective layer on the recording layer, or the disk and a disk-shaped protective substrate having the same shape as said disk, are adhered to each other with an adhesive, facing the recording layer inside. In the DVD-R media, recording and replay are carried out by irradiation of a visible laser beam (usually, a laser beam having a wavelength ranging from 630 nm to 680 nm), and higher density recording than that of the CD-R media is possible.
In the design of the above-mentioned DVD-Rs, the absorption maximum wavelength of dyes used in the dye recording layers is required to be decreased to the wavelength of a laser beam used for recording and replay, because it is shorter than that of the laser beam used in the CD-R media. However, the absorption maximum wavelength of dyes is known to be generally increased as the spread of a &pgr; electron system contributing to the optical absorption thereof increases. In particular, for cyanine dyes which have previously been utilized in many optical disks, the longer length of conjugated methine chains results in the longer wavelength. That is to say, for decreasing the absorption maximum wavelength of dyes, it is effective to decrease the length of conjugated methine chains. However, the shorter length of conjugated methine chains results in the lower coefficient of absorption, so that a reduction in recording sensitivity (a reduction in the degree of modulation) is inevitably liable to occur. It is therefore difficult to obtain a performance satisfactory as the dyes for DVD-R only by decreasing the length of conjugated methine chains of the conventional dyes for CD-R media to decrease the absorption maximum wavelength thereof.
On the other hand, in the CD-R media, the reflectance at 780 nm is required to be as high as readable with commercial CD players. For increasing the amount of light reflected by the light reflective metal layers provided on the dye recording layers, the optical absorptance due to the dyes is preferably low. It is therefore considered that the absorption maximum wavelength of the dyes is preferably low. However, the use of dyes having an absorption maximum wavelength on the short wavelength side raises the problem that changes in reflectance between recorded areas and non-recorded areas at 780 nm become small, which causes the difficulty of detecting the difference therebetween. Accordingly, in the conventional CD-R media, dyes having a high reflectance and giving a high recording sensitivity are selectively used. For example, as such dyes, cyanine dyes having benzoindolenine skeletons described in JP-A-64-40382 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) are preferably used. However, the conventional cyanine dyes do not necessarily satisfy both the reflectance and the recording sensitivity, and further improvement has been desired.
JP-A-4-175188 proposes cyanine dyes suitable for CD-R media having a high reflectance and also giving significant improving effects in recording and replay performances such as the sensitivity and C/N value. These cyanine dyes are described to be able to have monovalent to trivalent anions. However, as specific examples, cyanine dyes are only disclosed in which monovalent anions are combined, and for divalent or trivalent anions, there is no description of how to combine the cyanine dyes.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a heat mode type optical information-recording medium having a high recording sensitivity in recording information using a laser beam.
Another object of the present invention is to provide a heat mode type optical information-recording medium in which a high recording sensitivity is obtained even when a visible laser bean (for example, a red laser beam having a wavelength of 630 nm to 680 nm).
A still other object of the present invention is to provide a method for recording information, and particularly, to provide a method for recording information in which a high recording sensitivity is obtained even when a visible laser beam (for example, a red laser beam having a wavelength of 630 nm to 680 nm).
A yet further object of the present invention is to provide a heat mode type optical information-recording medium which can attain a high recording sensitivity at a high reflectance.
Other objects and effects of the present invention will become apparent from the following description.
As a result of the extensive studies, the present inventors found that optical information-recording media having a high recording sensitivity and showing a high reflectance, compared with the conventional ones, can be produced by using cyanine dye compounds in which multivalent cations are combined with cyanine dye components whose valence is adjusted to the same as that of the cations. In particular, it was found that cyanine dye compounds obtained by combining multivalent anions with cyanine dye components having relatively short conjugated methine chains can be advantageously used in DVD-R type optical information-recording media in which information is recorded using a laser beam having a short wavelength.
That is, the above-described objectives of the present invention have been achieved by providing the following optical information-recording media 1) to 8) and information-recording method 9).
1) A heat mode optical information-recording medium comprising a substrate having thereon a recording layer on which
Inagaki Yoshio
Saito Naoki
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