Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-12-28
2001-06-05
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S064400, C428S064800, C428S457000, C428S913000, C430S270160, C430S495100, C430S945000, C369S283000, C369S288000
Reexamination Certificate
active
06242068
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical media and, more particularly, to the reflecting layer typically found on recordable optical media.
BACKGROUND OF THE INVENTION
Recordable optical media such as recordable compact discs (CD-R) and recordable digital versatile disks (DVD-R), that is data disks upon which information can be written after the manufacture thereof, are known. The media is usually in the form of disks but can be in other forms such as optical tape or optical data cards. Recordable optical media typically has a transparent substrate, a dye containing recording layer is disposed on top of the substrate, a reflective layer is formed on top of the dye layer, and a protective layer is formed on top of the reflective layer. The transparent substrate typically has a groove on its surface. Embossing or injection molding can form the groove.
Typical dye layers are described in commonly-assigned U.S. Pat. No. 5,922,504 which describes the use of cyanine and formazan dye mixtures in CD-R media, U.S. Pat. No. 5,646,273 which describes the use of pthalocyanene dye in CD-R media, and U.S. Pat. No. 5,492,744 describes the use of benzoylferrocene as a beneficial additive to pthalocyanene dye in CD-R media.
Typical recordable optical media use a thin layer of gold as the reflective layer. (CD-ROM or “stamped” CDs often have an aluminum reflective layer. However, since a recordable CD requires that the light pass through the dye containing recording layer during writing and reading, a higher reflective material, such as gold, is needed for a recordable CD.) The gold reflective layer exhibits both high stability and high reflectivity. However, gold is expensive and has recently been replaced by silver by a number of CD-R manufacturers. Silver, in addition to being much less expensive, also has a slightly higher reflectivity at the wavelength of light used by CD readers and writers. However, silver is also known to be more reactive than gold. We have found that in accelerated keeping tests, recordable CDs with silver reflective layers often display less than desired stability. Trade journals have indicated that many customers have concerns over the expected lifetime of recordable optical disks with silver reflective layers. A benchmark test of the stability of optical media is the length of time which media with data recorded on them can survive in a high temperature and humidity environment. A condition frequently selected by testers is 80° C. and 85% relative humidity (RH). Typically, media fabricated with 100% silver as the reflective layer will work well initially but will fail this incubation condition in a time much less than media with a gold reflective layer.
Commonly assigned U.S. Pat. No. 5,948,849 and commonly-assigned European Patent 0594516 discuss the use of silver-palladium, and silver-palladium-copper reflective layers in recordable compact disc media.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical medium such as CD-R or DVD-R, with a reflective layer that would have the reduced price of silver, the high reflectivity of both silver and gold, and a stability much greater than is provided by a pure silver reflective layer.
The present invention provides a dye based recordable optical medium such as CD-R or DVD-R with an improved reflective layer which has a reflectivity comparable to gold or silver, a cost substantially less than gold, and a stability substantially greater than pure silver.
This object is achieved by a recordable optical medium comprising:
(a) a transparent substrate;
(b) a dye recording layer on the transparent substrate;
(c) a reflective layer provided on the dye layer wherein the reflective layer comprises a mixture of silver and palladium in such proportions that the palladium comprises between 0.25 and 2.5 atomic percent of the mixture; and
(d) a protective layer formed over the reflective layer.
The combination of certain dye recording layers with particular reflective layers provide the desired cost savings and stability. It was found, quite unexpectedly, that the preferred range of Pd in Ag is limited to a narrow region of 0.25% to 2.5%. This has been discovered when considering the incubational stability of the metric of block error rate in the read back of compact disc data, rather than just the incubational stability of the reflectivity of the media.
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John L. Vossen et al., Thin Film Process, Academic Press Inc. p. 514, 1978.
Eastman Kodak Company
Evans Elizabeth
Owens Raymond L.
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