Optical information-recording medium and optical...

Details Optical information-recording medium and optical... Optical information-recording medium and optical...

2002-02-20

2004-03-30

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064800, C430S270140

Reexamination Certificate

active

06713147

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical information-recording medium and an optical information-recording method. Particularly, the invention relates to an optical information-recording medium of recordable type that comprises a recording layer containing an oxonol dye and is capable of recording and reproducing information with laser irradiation, and to a method of optical recording information using the optical information-recording medium.
BACKGROUND OF THE INVENTION
Conventionally, information-recording media (optical disc) capable of recording just once with laser light are well known. Such information-recording media are also called recordable CD (CD-R), which have an advantage that they can rapidly produce few numbers of CD's at a reasonable cost compared with the conventional manufacturing method for CD. Owing to this advantage, the market demand for CD-R is increasing along with the prevalence of the personal computer. As for a typical structure of the information-recording medium of CD-R type, on a transparent disk as the substrate, a recording layer comprising an organic dye, a reflection layer comprising a metal such as gold or silver, and a resinous protective layer are superimposed in this order. Information is recorded on such an optical disk by directing a near-infrared laser beam (usually having a wavelength around 780 nm) on the disk to cause a local deformation of the recording layer by the generated heat. On the other hand, the read-out (reproduction) of the information is performed by irradiating the laser light having the same wavelength as that used for recording whereby the difference in reflectance between the deformed (recorded) region and the non-deformed (unrecorded) region is detected.
In recent years, information recording media of higher recording densities are demanded. To raise recording density, it is effective to reduce the beam diameter of the irradiated laser. Since the beam diameter of a laser light can be made smaller for a shorter wavelength, it is theoretically deduced that the use of a shorter wavelength laser is advantageous for a higher recording density. Hence, optical disks that are recorded and read-out with lasers of shorter wavelengths than 780 nm that has been conventionally adopted are now being developed. For example, an optical disk called recordable digital versatile disk (DVD-R) has been proposed, in which a pre-groove with a track pitch of 0.7 to 0.8 am narrower than that for CD-R (1.6 &mgr;m) is formed on a transparent disk substrate of 120 mm or 80 mm diameter. The DVD-R comprises a unit disk comprising the substrate having thereon a recording layer containing a dye, and usually a reflection layer and a protective layer provided on the recording layer. The DVD-R is produced by laminating two unit disks with each other, or one unit disk with a transparent protective disk of substantially the same dimensions as those of the unit disk, using an adhesive with the respective recording layer(s) inside relative to the respective substrate(s). For the DVD-R, information recording and read-out are carried out with use of a visible laser light (usually of a wavelength between 600 and 700 nm). Accordingly, it is said that the DVD-R type optical disk can achieve a higher recording density than the CD-R type optical disk.
The information-recording medium of the DVD-R type, which can store information several times larger than the conventional CD-R, is desired to have not only a high recording sensitivity, but also a low error rate for a high-speed recording, particularly, from the standpoint of the need to rapidly treat a large amount of information. Further, recording layers that can maintain a consistent and stable performance under the actions of heat and light over an extended period are demanded since the conventional dye-based recording layers are not sufficiently stable against heat and light over a long period.
Japanese Patent Laid-Open No. 209995/1988 discloses a CD-R type information-recording medium comprising a recording layer containing an oxonol dye provided on a substrate. It is disclosed therein that stable recording and read-out characteristics over a long period can be attained by the use of the compound. In this publication, an oxonol dye compound having ammonium introduced in its molecule in the form of a salt is disclosed.
The present inventors applied the oxonol dye set forth in the above-noted publication to the DVD-R type recording medium and investigated the characteristics thereof. The investigation results indicated that the recording and reproduction characteristics of the recording medium having the oxonol dye-based recording layer are not satisfactory since the reflectance and the degree of modulation are low. Moreover, the medium exhibited an insufficient light-fastness, often causing regeneration failure when exposed to light such as sunlight for a long period. On the other hand, Japanese Patent Laid-Open 138998/1999 discloses an optical information-recording medium having a recording layer comprising an oxonol dye which is salt-bonded with a diimmonium acting as a singlet oxygen quencher. It is disclosed therein that the medium can keep stable recording and read-out characteristics even under a prolonged exposure to sunlight. However, it was found that the optical information-recording medium having a recording layer which is composed of solely the oxonol dye tends to cause read-out failure under storage conditions of high temperature and high humidity and hence has an insufficient resistance against moisture and heat.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an information-recording medium which is suitably used for information recording and regeneration with use of a visible laser, and which has high recording characteristics and such a high stability that can adequately maintain the recording characteristics over a long period of time (particularly, even under high temperature and high humidity conditions).
Another object of the invention is to provide an information recording method using the information-recording medium.
Other objects and effects of the invention will become apparent from the following description.
The above-described objects of the invention have been achieved by providing an information-recording medium comprising a substrate having thereon a recording layer capable of recording information with laser light, said recording layer containing: at least one compound selected from the group consisting of compounds represented by the following general formulae (I-1), (I-2), (I-3) and (I-4); and an organic dye other than said compounds:
wherein A
1
, A
2
, B
1
and B
2
each independently represents a substituent; Y
1
and Z
1
each independently represents an atomic group necessary to form a carbocyclic or heterocyclic ring; E and G each independently represents an atomic group necessary to complete a conjugated double bond chain; X
1
represents ═O, ═NR or ═C(CN)
2
; X
2
represents —O, —NR or —C(CN)
2
(wherein R represents a substituent); L
1
, L
2
, L
3
, L
4
and L each independently represents a methine group which may be substituted; m and n each independently represents 0, 1 or 2; x and y each independently represents 0 or 1; and K represents an integer needed to neutralize the charge of the counter cation; R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
each independently represents a hydrogen atom or a substituent (wherein each pair of R
1
and R
2
, R
3
and R
4
, R
5
and R
6
, and R
7
and R
8
may combine with each other to form a heterocyclic ring together with the nitrogen atom); R
9
, R
10
, R
11
, R
12
and R
13
each independently represents a substituent; p represents 1 or 2; and q and r each independently represents an integer of 0 to 4.
The information-recording medium of the invention has a feature that the recording layer, which is provided on the substrate and which is capable of recording information by the exposure to laser light, contains at least one compound represe

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