Optical information recording medium

Details Optical information recording medium Optical information recording medium

2000-09-08

2002-04-30

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064800, C430S270180

Reexamination Certificate

active

06379768

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical information recording medium on which information can be recorded by means of a laser beam and the recorded information can be reproduced by means of a laser beam. Particularly, the invention relates to an optical information recording medium of heat-mode type on which information can be recorded utilizing a laser beam of a short wavelength such as 550 nm or shorter.
BACKGROUND OF THE INVENTION
An optical information recording medium (namely, optical disc) on which information can be only once recorded by means of a laser beam is known as a recordable compact disc (CD-R). The optical disc comprises a transparent substrate on which an recording organic dye layer, a light-reflecting layer (made of metal such as gold), and a protective resin layer are placed in order. The information is recorded on the CD-R by applying a laser beam of a near infrared region (generally, a laser beam having a wavelength in the vicinity of 780 nm). The recording layer of CD-R absorbs energy of the laser beam on the applied area, and the temperature of the recording layer on the area rises to bring about change of physical or chemical property in the layer (for instance, production of pit). The laser beam-applied area in the recording layer is thus changed in its optical property, whereby the information is recorded on CD-R.
The read-out (i.e., reproduction) of the recorded information is generally performed by applying on the CD-R a laser-beam having the same wavelength. The recorded information is detected by comparing difference of reflectance between the information-recorded area and its surrounding area.
Recently, an optical information recording medium having increased recording capacity is desired, and a recordable digital video disc (DVD-R) is developed. The developed DVD-R comprises a transparent substrate disc having such a narrow pre-groove (approximately in the range of 0.74 to 0.8 &mgr;m, which is less than a half of the pre-groove of CD-R), a recording dye layer, a light-reflecting layer, and a protective layer. On the protective layer or in place of the protective layer, another transparent substrate having the same size is fixed using an adhesive. Otherwise, a pair of the composite structure composed of the transparent substrate disc, recording dye layer, and light-reflecting layer are combined by an adhesive under the condition that the substrate discs are placed on the outermost side. On the DVD-R is recorded information by applying a laser beam in the visible region (generally, 630 to 680 nm). On the DVD-R, it is capable to record the information at a density higher than on the CD-R.
At present, a network which can transmit an image information such as Internet is widely utilized. Moreover, a high-vision television system and a high definition television (HDTV) system are developed. In any systems, a recording medium which can store a large amount of information is required. Although DVD-R has a an enough recording capacity at the present time, its recording capacity appears to be not sufficient, in view of the forthcoming requirement for increased recording capacity. From the above-mentioned viewpoint, an optical information disc showing increased recording capacity using a laser beam of further shorter wavelength is now under study.
Typical study is focused on the use of a laser beam of 550 nm or shorter to record information on a recording dye layer on a transparent disc. A variety of dyes, such as porphyrin compounds, azo dyes, metal azo dyes, quinophthalone dyes, trimethinecyanine dyes, dicyanovinylphenyl dyes, and coumarin compounds are studied and reported in Japanese Patent Provisional Publications No.8-1271705, No.11-53758, No.11-334204, No.11-334205, No.11-334206, No.11-334207, No.2000-43423, No.2000-108513, and No.2000-149320. As for the laser beam for recording and reproducing procedure, a laser beam of blue light (wavelength: 430 nm or 488 nm) or a laser beam of blue-green light (wavelength: 515 nm) is reported.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical recording medium which shows enough recording properties such as a high density recording capacity, a high sensitivity and a high modulation when a laser beam of light having a shorter wavelength such as 550 nm or shorter, particularly a laser beam of light having a wavelength of 450 nm or shorter is employed in the information recording and reproducing procedures.
As a result of studies performed by the inventors, it is discovered that specific dye compounds, namely, aminobutadiene dyes, are favorably employed because the aminobutadiene dyes show a high sensitivity to a laser beam of light having a shorter wavelength such as 550 nm or shorter, particularly, 450 nm or shorter, and further show a high light reflection and a high modulation.
Accordingly, the present invention resides in an optical information recording medium comprising a substrate and a recording layer provided thereon on which information is recorded by irradiation with a laser beam, wherein the recording layer comprises a dye compound having the following formula (I):
R
1
R
2
C═L
1
—L
2
═L
3
—NR
3
R
4
  (I)
in which each of R
1
and R
2
independently represents an electron-attracting group having a Hammett's substituent constant &sgr;
p
in the range of 0.2 to 0.9; each of L
1
, L
2
, and L
3
independently represents a methine group which can have a substituent under such condition that two or three of L
1
, L
2
, and L
3
can form a ring structure together with the substituent; and each of R
3
and R
4
independently represents a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, or a heterocyclic group, provided that each set of R
1
and R
2
, R
2
and a substituent of L
1
, R
2
and a substituent of L
2
, R
2
and a substituent of L
3
, a substituent of L
1
and R
3
, a substituent of L
2
and R
3
, a substituent of L
3
and R
3
, and R
3
and R
4
can be connected to each other to form a ring structure.
When a set of R
1
and R
2
, R
2
and a substituent of L
1
, R
2
and a substituent of L
2
, R
2
and a substituent of L
3
in the formula (I) is connected to each other to form a ring structure, the Hamett's substituent constant &sgr;
p
corresponds to that of a substituent group which is formed by cutting the ring at the end of the substituent (corresponding to the furthermost position (i.e., top position) of the substituent and then putting a hydrogen atom to the end position.
The determination of Hamett's substituent constant &sgr;
p
is further explained by referring to the following examples.
(1) The case where R
1
and R
2
are connected to each other to form a ring structure (its representative compounds are the after-illustrated compounds I-5, I-6, I-7, I-12, I-13, I-15, I-20, I-21, I-22, and I-23)
The substituent constant &sgr;
p
of R
1
is equivalent to a of H—R
2
—R
1
— group, and the substituent constant &sgr;
p
of R
2
is equivalent to &sgr;
p
of H—R
1
—R
2
— group. In this case, therefore, the substituent constant &sgr;
p
of R
1
may differ from the substituent constant &sgr;
p
of R
2
, since the end portion of each of R
1
and R
2
differs from each other.
(2) The case where. R
2
and a substituent of L
2
are connected to each other to form a ring structure (its representative compounds are the after-illustrated compounds I-16 and I-18)
The substituent constant &sgr;
p
of R
2
is equivalent to &sgr;
p
of —R
2
—H group which is formed by cutting R
2
at the end position at which R
2
is connected to L
2
, and then putting a hydrogen atom to the end position
The present invention further resides in a method of recording information on the optical information recording disc of the invention 1 by means of a laser beam having a wavelength of 550 nm or shorter, particularly a laser beam having a wavelength of 450 nm or shorter.
In the formula (I), it is preferred that each of R
1
and R
2
independently is a cyano group, a nitro group, an acyl group, an alkoxycarbonyl group, an

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