Optical information storage medium

Details Optical information storage medium Optical information storage medium

2001-08-17

2003-04-01

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064800, C430S270140

Reexamination Certificate

active

06541092

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information storage medium and more specifically relates to an optical information storage medium having a small jitter value and a high sensitivity.
2. Description of the Related Art
Heretofore, an additionally recordable, optical information storage medium (optical disk) that enables recording one time only known as a CD-R has been widely known. A typical construction of a CD-R type optical information storage medium comprises a transparent discoid substrate having thereon a dye recording layer made of an organic dye, a light-reflective layer made of a metal such as gold, and a protective layer made of a resin, in the order listed. Recording of information on this optical disk is performed by the irradiation of the optical disk with a laser in a near-infrared region (usually a laser having a wavelength of about 780 nm). The irradiated portion of the dye recording layer absorbs light and the temperature rises locally. The rise in the temperature causes a change of a physical or chemical property in the irradiated portion (such as pit formation) and thus brings about a change in optical properties at the irradiated portion. As a result, information is stored. When the information is reproduced, generally the optical disk is irradiated with a laser having the same wavelength as that of the laser for recording so as to detect a reflectivity difference between the portion whose optical properties have changed (recorded portion) and a portion whose optical properties have not changed (unrecorded portion) in the dye recording layer.
Recently, as a medium that enables information storage at a higher density than CD-R, DVD-R, which is an additionally recordable optical disk, has been proposed (for example, in “Nikkei New Media”, extra issue entitled “DVD”, 1995) and put to practical use, thus establishing a reputation as a large-capacity information storage medium. Generally, a DVD-R is made of two disks, each of which comprises a transparent discoid substrate having thereon a dye recording layer containing an organic dye, a light-reflective layer, and a protective layer, laminated in the order listed, and these disks are adhered to each other such that the dye recording layers face inward. Alternatively, the DVD-R is made of a disk having the above-described construction and a discoid protective substrate in the same shape, wherein the disk and the discoid protective substrate are adhered to each other such that the dye recording layer faces inward. On the transparent discoid substrate, guide grooves (pregrooves) designed for tracking of a laser at a time of recording by laser irradiation are formed with a narrow track pitch (0.74 to 0.8 &mgr;m) which is less than half that for a CD-R. In the DVD-R, recording and reproduction of information are performed by irradiating the optical disk with a laser in the visible region (usually a laser in a wavelength region ranging from 630 to 680 nm). Accordingly, since the recording is performed by light having a wavelength shorter than that for CD-R, information storage at a higher density is possible in the DVD-R.
In DVD-R, the recording light has a shorter wavelength and therefore a beam spot is smaller than for CD-R. Because of this, DVD-R had a problem that the pit size to be formed in the dye recording layer was smaller and jitter became larger. Jitter means scattering of pit signals and blank signals, which are obtained from pits and blanks between the pits which are respectively formed on the substrate according to information signals when information is recorded. In other words, jitter means scattering of pit shapes. Generally, as recording sensitivity of the dye contained in the dye recording layer is raised, the jitter value tends to become larger. Therefore, it was difficult to obtain an optical information storage medium having a small jitter value and a high recording sensitivity.
SUMMARY OF THE INVENTION
In view of the problems associated with the prior art, the present invention was made. It is accordingly an object of the present invention to provide an optical information storage medium having a small jitter value and a high recording sensitivity.
The present inventors have established the present invention based on the discovery that jitter value is remarkably improved and recording sensitivity of a dye recording layer is maintained at a high value if two kinds of dyes, each of which fulfills predetermined requirements, are used in a mixture.
According to a first aspect, the optical information storage medium of the present invention includes: a transparent pregrooved substrate; a dye recording layer provided on the substrate, at which information can be recorded by irradiation with a laser; and a light-reflective layer provided on the dye recording layer, which is made of a metal, wherein the dye recording layer comprises a dye A, which has a maximum absorption wavelength in a range from 400 to 700 nm, and a dye B, which has a maximum absorption wavelength 3 to 50 nm longer than the maximum absorption wavelength of the dye A, and a sensitivity ratio Q of the dye A to the dye B, which is represented by the following equation, is from 0.20 to 0.55:
Q
=(
PA−PB
)
/PA
where PA represents an optimum recording power for the dye A and PB represents an optimum recording power for the dye B.
In general, the use of a dye having a high recording sensitivity in the dye recording layer tends to raise the jitter value. The incorporation of the dye A and the dye B, whose recording sensitivity is higher than that of the dye A, in the dye recording layer improves the recording sensitivity relative to the case where the dye A is used singly. If the dye A and the dye B are used in a combination such that the difference between the recording sensitivities of the two dyes is controlled to within a predetermined range, the dye A has the maximum absorption wavelength in the 400 to 700 nm range and the dye B has the maximum absorption wavelength 3 to 50 nm longer than that of the dye A, the jitter value is remarkably improved in comparison with the case where one of the two dyes is used singly.
In the optical information storage medium, preferably, the dye A and the dye B to be used in the dye recording layer are each an oxonol-based dye and particularly preferably an oxonol-based dye represented by the following general formula (1):
In the formula, X
1
and X
2
are each a carbocycle or a heterocycle; R
1
represents a hydrogen atom, an alkyl group, an aralkyl group, an alkoxy group, an aryl group, an aryloxy group, a heterocyclic group, a halogen atom, a carboxyl group, an alkoxycarbonyl group, a cyano group, an acyl group, a carbamoyl group, an amino group, a substituted amino group, a sulfo group, a hydroxyl group, a nitro group, a sulfonamide group, a ureido group, a sulfonyl group, a sulfinyl group, or a sulfamoyl group; and R
2
and R
3
each independently represents an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, or a heterocyclic group.
A mixing ratio by weight between the dye A and the dye B is preferably A:B=from 100:20 to 100:100. The dye recording layer preferably contains a browning inhibitor and it is preferable that the browning inhibitor has a maximum absorption wavelength at a wavelength longer than the recording wavelength.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Details of the embodiments of the optical information storage medium of the present invention are given below.
The optical information storage medium of the present invention has a dye recording layer in which information can be recorded by irradiation with a laser, and the dye recording layer contains a dye A, which has a maximum absorption wavelength in a 400 to 700 nm range, and a dye B, which has a maximum absorption wavelength 3 to 50 nm longer than the dye A. A sensitivity ratio Q, which is represented by the following equation, between the dye A and the dye B is 0.20 to 0.55:
Q
=(
PA−PB
)
/PA
where

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