Optical information recording medium

Details Optical information recording medium Optical information recording medium

1998-07-31

2001-07-10

Angebranndt, Martin (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

Reexamination Certificate

active

06258509

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical information recording medium of heat mode type on which information can be recorded and reproduced by means of a laser beam.
BACKGROUND OF THE INVENTION
An information recording medium on which information can be only once recorded by means of a laser beam is known as a recordable compact disc (i.e., CD-R), and has been getting widely used because it can be produced on a relatively small scale and at low cost, as compared with a conventional compact disc (i.e., CD).
The optical disc of CD-R type generally has a multi-layer structure typically comprising a disc-shaped transparent substrate (support), a recording layer comprising an organic dye, a light-reflecting layer comprising a metal, and a protective layer made of resin overlaid in this order. The information can be recorded by irradiating the disc with a laser beam of near infrared region (usually 780 nm). By the irradiation of the laser beam, irradiated area of the recording layer is locally heated to change its physical or chemical characteristics, and thus pits are formed in the recording layer. Since the optical characteristics of the formed pits are different from those of the area having been not irradiated, the information is optically recorded. The recorded information can be read by a reproducing procedure comprising the steps of irradiating the recording layer with a laser beam having the same wavelength as that employed in the recording procedure, and detecting the light-reflection difference between the pits and the area having been not irradiated.
In order to reproduce the recorded information by means of a commercially available CD player, the CD-R is required to reflect the laser beam of near infrared region at a reflectance of more than 70%. Therefore, the light-reflecting layer is preferably provided on the recording dye layer. The light-reflecting layer is generally made of Au (gold), because it gives a high reflectance and a high corrosion resistance. However, the light-reflecting layer made of gold has certain disadvantageous features in that gold is expensive and further that the protective layer provided on the light-reflecting layer of Au (gold) exhibits golden gloss which makes printed letters or figures on the protective layer unclear.
The light-reflecting layer can be made of metal other than gold. Japanese Patent Provisional Publications No. H3-286432 and No. H4-49539 disclose an optical information recording medium having a light-reflecting layer made of Ag (silver), Cu (copper) or alloys essentially consisting of them. According to Japanese Patent Provisional Publication No. H3-286432, the light-reflecting layer of Ag (silver) or Cu (copper) has a reflectance higher than that of the layer of Au.
As the dye compound contained in the recording layer, a cyanine dye having a benzoindolenine structure (in which a benzene ring is condensed with an indolenine skeleton) is stated to be advantageously used (Japanese Patent Provisional Publication No. H4-175188), and further the cyanine dye having ClO
4
−
ion is particularly preferred to use.
However, the present inventors have found that the cyanine dye having ClO
4
−
ion in the recording dye layer is liable to lower the reflectance of the light-reflecting layer of Ag or Ag-containing alloy.
Accordingly, it is an object of the present invention to provide an optical information recording medium having a high light-reflectance. Particularly, the object of the invention is to provide an optical information recording medium having a high light-reflectance in the case that the light-reflecting layer is made of Ag or Ag-containing alloy.
SUMMARY OF THE INVENTION
It has been not known why the reflectance is lowered in the case of using a cyanine dye having ClO
4
−
ion. The study of the inventors has revealed that ClO
4
−
and Ag react to form Ag compound at the interfacial zone between the recording dye layer and the light-reflecting layer because Ag is more active and unstable than Au.
The inventors have further studied to provide a CD-R having a high reflectance in the case that the light-reflecting layer is made of Ag or Ag-containing alloy, and found that a dye having an organic counter ion (for example, a cyanine dye having an organic counter ion) ensures a high reflectance of the light-reflecting layer.
The present invention resides in an optical information recording medium of heat mode type comprising a substrate, a recording dye layer on which information can be recorded by irradiation with a laser beam, and a light-reflecting layer overlaid in order, wherein the recording dye layer comprises a dye having an organic counter ion, and the light-reflecting layer is made of inorganic material comprising Ag.
The preferred embodiments of the invention are as follows.
(1) The light-reflecting layer comprises Ag or an alloy of Ag with at least one element selected from the group consisting of Pt, Cu, Au and Al.
(2) The dye having an organic counter ion contained in the recording dye layer is a cyanine dye.
(3) The recording dye layer contains a cyanine dye represented by the following formula (I):
[DYE
+
]
n
X
n−
  (I)
in which DYE
+
represents a monovalent cyanine dye cation, n represents an integer not less than 2, and X
n−
represents an organic n-valent anion.
(4) In the above (3), the cyanine dye is represented by the following formula (II):
in which each of Za and Zb independently represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring; each of R
1
and R
2
independently represents an alkyl group or an aryl group; each of L
1
, L
2
, L
3
, L
4
and L
5
independently represents a methine group which may have a substituent group, and in the case that at least one of L
1
to L
5
has a substituent group, two of L
1
to L
5
may be combined to form a ring; j is 0, 1 or 2; k is 0 or 1; X
n−
represents an organic n-valent anion and n is an integer of not less than 2.
(5) In the above (3), the cyanine dye is represented by the following formula (IIA):
in which each of Z
1
and Z
2
independently represents an atomic group necessary for forming an indolenine nucleus or a benzoindolenine nucleus; each of R
1
and R
2
independently represents an alkyl group or an aryl group; each of R
3
, R
4
, R
5
and R
6
independently represents an alkyl group; each of L
1
, L
2
, L
3
, L
4
and L
5
independently represents a methine group which may have a substituent group, and in the case that at least one of L
1
to L
5
has a substituent group, two of them may be combined to form a ring; j is 0, 1 or 2; k is 0 or 1; X
n−
represents an organic n-valent anion and n is an integer of not less than 2.
DETAILED DESCRIPTION OF THE INVENTION
In the optical information recording medium of the invention, the recording dye layer provided on the sub-strate comprises a dye having an organic counter ion, and the light-reflecting layer provided on the recording dye layer is made of inorganic materials comprising Ag.
The dye employed for the invention is not restricted, provided that it has an organic counter ion, but cyanine dyes and oxonol dyes are preferred. Particularly preferred is a cyanine dye having an organic counter ion because it can be easily prepared.
First, the detailed description about the cyanine dye is given below.
The cyanine dye employed for the invention is preferably a compound having the following formula (I):
[DYE
+
]
n
X
n−
  (I)
In the formula, DYE
+
represents monovalent cyanine dye cation having no anionic substituent. X
n−
represents an organic n-valent anion, and n represents an integer not less than 2 (namely, X
n−
represents an organic anion having the valence of not less than 2).
Examples of the polyvalent organic anions represented by X
n−
include carboxylate ions (e.g., succinate ion, maleate ion, fumarate ion, and terephthalate ion), aromatic disulfonate ions (e.g., benzene-1,3-disulfonate ion, 3

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