Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2000-03-20
2002-01-15
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S064400, C428S402000, C430S270110
Reexamination Certificate
active
06338889
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical information recording medium such as a compact disc (namely, CD), a digital video disc (namely, DVD), a recordable compact disc (namely, CD-R) or a recordable digital video disc (namely, DVD-R). In particular, the invention relates to an optical information recording medium having an ink-printable layer on its surface, on which letters and a graphic image can be printed.
BACKGROUND OF THE INVENTION
An optical information recording medium on which information can be only once recorded by means of a laser beam (i.e., an optical disc of write-once type) is known as a recordable compact disc (CD-R), and is widely used in practice. The optical disc of CD-R type generally has a multi-layered structure typically comprising a disc-shaped transparent substrate (support), a recording layer comprising an organic dye (often referred to as “recording dye layer”), a light-reflecting layer comprising a metal (hereinafter, often referred to as “metallic light-reflecting layer”, or simply “reflecting layer”), and optionally a protective layer made of resin overlaid in order.
A demand for large recording capacity has recently increased, but an optical disc of CD-R type does not have satisfactorily large information-recording capacity. Therefore, an optical disc having satisfactorily large information-recording capacity has been studied and proposed. For example, a recordable DVD (i.e., recordable digital video disc, DVD-R), in which information can be recorded on and read out from by means of a laser beam having a shorter wavelength than that for CD-R, has been developed. The optical disc of DVD-R type is formed by laminating two composites having a layered structure. Each of the layered composites comprises a transparent disc substrate provided with a guide groove (i.e., pregroove) for tracking of the laser beam, a recording layer comprising an organic dye, a light-reflecting layer, and a protective layer arranged in order. The layered composites are combined with an adhesive so that the recording layers would be placed inside. Otherwise, the optical disc of DVD-R type is formed by combining a protective disc plate and the layered composites comprising a substrate, a recording layer, a light-reflecting layer, and a protective layer arranged in order.
For writing (i.e., recording) and reading (i.e., reproducing) the information, a CD-R is irradiated with a laser beam having a wavelength in the range of 770 to 790, typically approx. 780 nm, while a DVD-R is irradiated with a laser beam of visible wavelength region (generally having a wavelength of 600 to 700 nm). By the irradiation of the laser beam, irradiated area of the recording dye layer is locally heated to change its physical or chemical characteristics, and therefore pits are formed in the irradiated area of the recording layer. Since the optical characteristics of the formed pits are different from those of the area having been not irradiated, the digital information is recorded. The recorded information can be read by a reproducing procedure generally 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 their periphery.
Most of optical information recording discs such as CD-R and DVD-R have on one side a surface on which letters and a graphic image are printed, so that the contents or recorded information can be easily read. For the printing, an ink-jet printer is most generally employed, because it can give a color image using an aqueous color ink by means of a relatively simple printer mechanism.
Japanese Patent Provisional Publication No. 11-162438 describes an optical information recording medium of CD-R type which has a hydrophilic surface layer comprising a resin layer derived from an acrylate monomer and a protein powder. The hydrophilic surface layer serves to receive thereon an aqueous ink for printing letters and a graphic image. The protein powder is stated to serve for fixing the aqueous ink on the surface layer and further to increase whiteness of the disc surface.
In the CD-R recording disc typically, metallic glitter of the metallic light-reflecting layer comprising gold, silver, or the like, is observed through the generally transparent surface layer, and therefore it sometimes becomes difficult to read letters or a graphic image printed on the transparent surface layer under the glittering background. The above-mentioned patent provisional publication proposes that a white pigment-containing layer be placed between the metallic light-reflecting layer and the ink-printable layer. A representative example of the white pigment is titanium dioxide.
Japanese Utility Model publication No. 3021164 indicates that a light-shielding layer is provided between the metallic light-reflecting layer and the hydrophilic layer for ink-printing. In more detail, under a hydrophilic resin layer comprising a ultraviolet curing resinous composition, a polyvinyl pyrrolidone fine powder and a silica fine powder is provided a light-shielding layer comprising a ultraviolet curing resin composition and a white pigment.
A compact disc (i.e., CD) or a digital vide disc (i.e., DVD) comprising a transparent substrate disc, a recording layer (i.e., recording surface) on which information is already recorded, and a metallic light-reflecting layer also has a surface on which letters and a graphic image indicating the content of the disc is printed. Generally, the letters and a graphic image are printed already on the surface by screen printing. However, it may be convenient to further print additional information on the already printed surface of CD or DVD.
The present inventors have made studies on the ink-printable surface layer of an optical information recording medium and noted that the known hydrophilic surface layer is apt to show blur of an ink phase around the printed letters and image when the ink is printed thereon and kept for a long time under atmospheric conditions.
Accordingly, it is an object of the present inventors to provide an optical information recording medium such as CD-R, DVD-R, CD or DVD which have a surface layer on which an ink, particularly an aqueous ink composition, is clearly printed, and the clearly printed ink image is kept with almost no blur under atmospheric conditions for a long storage period.
SUMMARY OF THE INVENTION
It has been now discovered by the inventors that the troublesome blur of the printed ink observed on the ink-printable layer after a long term storage under atmospheric conditions is effectively prevented by utilizing a zinc sulfide fine powder as a white pigment for the incorporation into the light-shielding layer. Further, the use of a zinc sulfide fine powder as the white pigment in the light-shielding layer is effective to ensure to form a clear printed image on the uppermost ink-printable surface layer.
Accordingly, the present invention resides in an optical information recording medium comprising a transparent substrate, an information recording layer, a metallic light-reflecting layer, a light-shielding layer, and an ink-printable layer, in order, wherein the light-shielding layer comprises a binder polymer and zinc sulfide particles.
In the optical information recording medium of the invention, the zinc sulfide particles preferably have a mean particle size of 0.05 to 5 &mgr;m, particularly 0.1 to 1.0 &mgr;m. The binder polymer in the light-shielding layer preferably is a cured ultraviolet light-curing resin.
The light-shielding layer preferably has a thickness of 8.0 to 11.5 &mgr;m, particularly 8.0 to 10.0 &mgr;m, more preferably 8.0 to 9.5 &mgr;m, and the binder polymer and the zinc sulfide particles are present in the light-shielding layer in a ratio of 10:90 to 50:50.
DETAILED DESCRIPTION OF THE INVENTION
The optical information recording medium of the invention comprises a transparent substrate, an information recording layer, a metallic light-reflecting layer, a light-
Miura Toshihiko
Shibata Michihiro
Suda Takashi
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