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
2000-02-07
2004-04-27
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
C430S270190, C430S270200, C430S945000, C369S288000, C428S064800
Reexamination Certificate
active
06727041
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical recording medium and in particular, to an optical recording medium of a writable type using an organic pigment as a recording material.
BACKGROUND OF THE INVENTION
With the advent of information-oriented society, a request for a large-capacity memory for recording a great amount of information such as image, voice, and data is becoming stronger and stronger.
In order to answer such a request, a disc-shaped optical recording medium has a large recording capacity and a high reliability as recording and reproduction are carried out in a non-contact state. Besides, such a disc-shaped optical disc has various other merits that it can easily be carried and produced at reasonable costs in a mass production, and has been widely spread up to now.
As a recording material of an optical recording medium, the have been proposed various materials: rare earth-transition metal amorphous alloy thin film such as Tb—Fe—Co, a phase change material such as Ge—Se—Te, an organic pigment material such as cyanine pigment. Among these materials, the organic pigment is used in a writable optical recording medium on which a user can write in once. This material has no problem of corrosion and is low in toxicity, which is a merit that only a small environmental load is caused.
As a specific configuration example of an optical recording medium using such an organic pigment, there can be exemplified the following.
Firstly, there can be exemplified an air sandwich configuration consisting of two light transmitting substrates each having a recording layer containing an organic pigment and bonded so as to oppose the recording layers to each other and to form an air layer between the substrates. This air sandwich type optical recording medium is available in market for data recording.
After this, the Proceeding of SPIE, vol. 1078, page 1078 discloses a configuration having a recording layer containing an organic pigment, an optical reflection layer, and a protection layer successively formed on an light transmitting substrate, i.e., a normal compact disc configuration having a recording layer containing an organic pigment. As this optical recording medium has a high reflection ratio of 70% or above in a wavelength band of 780 nm used in a compact disc, after recording it is possible to obtain a signal characteristic compatible with a compact disc on market. This optical recording medium is used for music recording, video recording, and a personal computer data recording and now is forming a large market.
Moreover, in the field of optical recording, besides such a recording material and medium configuration, study has been made on the optical system for recording.
That is, in the optical recording medium, a laser beam is used for recording and reproduction.
In recording, a laser beam is focused on a recording layer and within the laser spot, an optical change is generated in the recording layer so as to form a pit. Moreover, in reproduction, a laser beam is focused on the pit so as to detect a difference between the reflection ratios of the pit and a portion not having the pit. The recording density on such an optical recording medium is determined by a laser beam spot diameter. As this spot diameter is reduced, it is possible to record with a higher density.
On the other hand, the laser beam spot diameter is proportional to the L/NA of the optical recording/reproduction optical system (wherein NA is a numerical aperture of the objective lens and L is the wavelength of the laser beam). Consequently, the recording density of the optical recording medium is determined by the numerical aperture NA of the objective lens used in this optical system and the wavelength L of the laser source. As the NA increases and the L decreases, the recording density can be increased.
For this, recently, a study has been made so as to reduce the wavelength of the semiconductor laser as a laser source. For example, as reported in “O plus E”, vol 199, page 71 (1996), there is a trial to apply a semiconductor laser having a wavelength band of 630 nm to 650 nm for optical recording.
However, when reducing the wavelength of the laser beam for recording and reproduction, it is necessary to select a recording material matched with the wavelength band. An organic pigment is selected because of having a sufficient optical absorption and reflection ratio in the wavelength band of the laser beam for recording and reproduction.
For this purpose, for example, organic pigments to be used for 630 nm to 650 nm are disclosed in Japanese Patent Laid-Open 6-40161, Japanese Patent Laid-Open 6-40162, Japanese Patent Laid-Open 6-199045, and Japanese Patent Laid-Open 7-186530.
However, these organic pigments do not have a sufficient optical absorption or reflection ratio in the range from 630 nm to 650 nm and have a problem in the recording sensitivity and the signal modulation degree.
SUMMARY OF THE INVENTION
It is therefore object of the present invention to provide an optical recording medium showing a high reflection ratio and an appropriate optical absorption in the short wavelength range of 630 nm to 650 nm and enabling a preferable recording and reproduction characteristic.
In order to achieve the aforementioned object, the inventor studied and found that a polymethine pigment having 1 to 4 carbons in the methine main chain and an atomic groups including a predetermined aromatic ring at both ends enables a high reflection ratio and an appropriate optical absorption in a wavelength band from 630 nm to 650 nm.
The optical recording medium according to the present invention has been proposed according to the aforementioned finding and includes a recording layer and reflection layer formed on a light transmitting substrate, the recording layer formed as (1) a pigment layer containing at least one of a pigment compound a, pigment compound b, and pigment compound c; (2) an organic pigment layer containing at least two of the pigment compound a, the pigment compound b, and the pigment compound c; (3) an organic pigment layer containing at least one of the pigment compound a, the pigment compound b, and the pigment compound c in combination with at least one of a pigment compound d, a pigment compound e, and a pigment compound f; (4) an organic pigment layer containing at least one of the pigment compound a, the pigment compound b, and the pigment compound c in combination with a pigment compound g, a pigment compound h, a pigment compound i, and a pigment compound j; (5) an organic pigment layer containing at least one of the pigment compound a, the pigment compound b, and the pigment compound c in combination with at least one of the pigment compound d, the pigment compound e, and the pigment compound f in combination with at least one of the pigment compound d, the pigment compound e, and the pigment compound f; (6) an organic pigment layer containing at least two of the pigment compound d, the pigment compound e, and the pigment compound f; or (7) an organic pigment layer containing at least one of the pigment compound d, the pigment compound e, and the pigment compound f, and pigment compound j in combination with at least one of the pigment compound d, the pigment compound e, and the pigment compound f.
These organic pigment layers enable a high absorption degree and a reflection ratio in the wavelength band from 630 nm to 650 nm and show a small wavelength dependency in this range. Consequently, the optical recording medium having a recording layer made from these organic pigments enables to obtain a high recording sensitivity and a signal modulation degree in the wavelength band of 630 nm to 650 nm.
(wherein X— represents Br—, I—, ClO
4
—, BF
4
—, PF
6
—, and SbF
6
—. Moreover, A
1
is an atomic group expressed by Chemical Formulae 136 to 138, and B
1
is an atomic group expressed by Chemical Formula 139.)
(In Chemical Formulae 136 to 139, R
1
represents an alkyl group, alkoxy group, and aryl group. When a molecule contains a plurality of R
1
, the R
1
may be either identical substitu
Oyamada Mitsuaki
Tamura Shinichiro
Angebranndt Martin
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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