Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2003-03-07
2004-10-26
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S064800, C430S270140
Reexamination Certificate
active
06808782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording medium, and more specifically to an optical information recording medium writable only once by heat mode.
2. Description of the Related Art
An optical information recording medium (optical disc) on which information can be written only once by irradiation with laser beam is widely known. Such an optical disc is called a writable CD (so called CD-R), and typically comprises a transparent disc substrate having successively disposed thereon a recording layer including an organic dye, a light-reflective layer including a metal such as gold, and a protective layer (cover layer) made of a resin. Information is recorded on such a CD-R by irradiating the CD-R with a near-infrared laser beam (usually laser beam having a wavelength of around 780 nm). Specifically, a portion of the recording layer that is irradiated absorbs light, whereby the temperature rises at the irradiated portion. The rise in temperature produces a physical or chemical change (e.g., formation of pits) to alter the optical properties of the irradiated portion, whereby information is recorded. The information thus recorded on the CD-R is ordinarily reproduced by irradiating the CD-R with laser beam having the same wavelength as that of the laser beam used to record the information and detecting a difference in reflectance between regions of the recording layer whose optical properties have been changed (recorded portions) and regions of the recording layer whose optical properties have not been changed (unrecorded portions).
In recent years, there has been a demand for optical information recording media having higher density, and writable digital versatile discs (DVD-Rs) have been proposed in response to that demand (
Nikkei New Media
, extra issue entitled “DVD”, 1995). A DVD-R typically comprises two transparent disc substrates that each have successively disposed thereon a recording layer containing an organic dye, a light-reflective layer, and a protective layer, with the discs being adhered so that the recording layers face inward or so that protective substrates having the same disc shape as these discs are disposed on outer sides of the adhered discs. Moreover, the transparent disc substrate includes a guide groove (pre-groove) used for tracking a laser irradiated onto the CD-R, with the groove having a narrow track pitch (0.74 to 0.8 &mgr;m) that is equal to or less than half of that in a CD-R. Information is recorded and reproduced (played back) by irradiating the DVD-R with laser beam in a visible region (usually laser beam having a wavelength region ranging from 630 to 680 nm), whereby information can be recorded at a higher density than on a CD-R.
Recently, high-vision television and networks such as the Internet have rapidly become more widespread. In addition, the start of HDTV (High Definition Television) broadcasting is near at hand. As a result, large-capacity optical recording media capable of recording visual information easily and inexpensively are in demand. While DVD-Rs currently play a significant role as large-capacity recording media, the demand for media having greater recording capacity and higher density continues to escalate, and development of recording media that can cope with this demand is also needed. For this reason, development of recording media having ever greater storage capacity with which high-density recording can be effected with short-wave light continues to advance.
Methods for recording information on and reproducing information from an optical information recording medium including a recording layer containing an organic dye, by irradiating the medium, from a side of the medium disposed with the recording layer towards a side of the medium disposed with a light-reflecting layer, with laser beam having a wavelength of 530 nm or less, are disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 4-74690, 7-304256, 7-304257, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513, 2000-113504, 2000-149320, 2000-158818 and 2000-228028. In these methods, information is recorded on and reproduced from an optical disc having a recording layer containing a porphyrin compound, an azo-based dye, a metal azo-based dye, a quinophthalone-based dye, a trimethine cyanine dye, a dicyanobiphenyl-skeleton dye, a coumarin dye, a naphthalocyanine compound or the like, by irradiating the optical disc with a blue laser (having a wavelength of 430 nm or 488 nm) or a blue-green laser (having a wavelength of 515).
However, the present inventors have found that practically employable sensitivity cannot be obtained with the optical discs disclosed in the above publications when information is recorded thereon by irradiating the optical discs with a short-wave length laser beam having a wavelength of 450 nm or less, and that sufficient levels cannot be achieved with respect to other recording characteristics such as reflectance and modulation. In particular, it was confirmed that recording characteristics of the optical discs disclosed in the above publications decreased when the discs were irradiated with laser beam having a wavelength of 450 nm or less.
Currently, studies are being undertaken to improve the reflectance of the optical discs described in the above-listed publications by using silver (Ag) in the light-reflective layer. However, use of Ag in the light-reflective layer involves increased costs, and hence a significant problem arises if such optical discs are mass produced. Further, the light-reflective layer including Ag poses a problem of a lowered resistance to corrosion depending on the conditions for forming the layer.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide an optical information recording medium that exhibits excellent recording characteristics and achieves cost-reduced production by including aluminum or an aluminum alloy in a light-reflective layer.
The object is attained by the invention described below.
The invention provides an optical information recording medium comprising a substrate including a groove that has a track pitch of 200 to 400 nm and a depth of 10 to 150 nm, the substrate having successively disposed thereon a light-reflective layer, a recording layer and a cover layer, wherein information is recordable and reproducible by irradiating a laser beam having a wavelength of 500 nm or less from a side of the medium disposed with the cover layer, and the light-reflective layer contains aluminum or an aluminum alloy.
In the optical information recording medium according to the invention, the light-reflective layer preferably has a thickness of 20 to 200 nm and is formed at a layer-forming rate of 6 to 95 nm/s.
DESCRIPTION OF THE INVENTION
An optical information recording medium of the present invention comprises a substrate including a groove that has a track pitch of 200 to 400 nm and a depth of 10 to 150 nm, the substrate having successively disposed thereon a light-reflective layer, a recording layer and a cover layer, wherein information is recordable and reproducible by irradiating a laser beam having a wavelength of 500 nm or less from a side of the medium disposed with the cover layer, and the light-reflective layer contains aluminum or an aluminum alloy.
The optical information recording medium of the invention will be described below in more detail.
Light-reflective Layer
The light-reflective layer is disposed in order to improve the reflectance when information is reproduced. In the invention, it is necessary that the light-reflective layer contains aluminum or an aluminum alloy which is less expensive as compared with silver (Ag) or gold (Au). The light-reflective layer that contains aluminum or an aluminum alloy has a reflectance with respect to a laser beam of preferably 70% or more, more preferably 75% or more, and particularly preferably 80% or more.
Examples of the aluminum and the aluminum alloy used in the light-refl
Ishida Toshio
Usami Yoshihisa
Fuji Photo Film Co. , Ltd.
Mulvaney Elizabeth
Sughrue & Mion, PLLC
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