Stock material or miscellaneous articles – Article having latent image or transformation
Reexamination Certificate
1999-03-26
2003-09-02
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Article having latent image or transformation
C106S031130, C427S256000, C427S258000, C428S195100, C428S201000, C428S204000, C428S913000, C503S200000, C503S226000
Reexamination Certificate
active
06613403
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to inks with near infrared fluorescent (NIRF) compounds which provide coatings and markings invisible to the human eye that can be used as security features to thwart counterfeiting. More particularly, the invention relates to inks which provide coatings, markings and images containing NIRF compounds with improved light stability to extend their useful life.
BACKGROUND OF THE INVENTION
The use of near infrared fluorescent (NIRF) compounds in inks is well known. Representative disclosures in this field are as follows:
U.S. Pat. No. 5,292,855 (Mar. 8, 1994), U.S. Pat. No. 5,423,432 (Jun. 13, 1995) and U.S. Pat. No. 5,336,714 (Aug. 9, 1994), all issued to Krutak et al., describe polyester-based and polyester-amide based coatings and ink compositions with near infrared fluorescent (NIRF) compounds which are used for marking articles for identification/authentication purposes.
U.S. Pat. No. 5,461,136 (Oct. 24, 1995), U.S. Pat. No. 5,397,819 (Mar. 14, 1995), and U.S. Pat. No. 5,703,229 (Dec. 30, 1997), also issued to Krutak et al., also disclose tagging thermoplastic containers and materials with near infrared fluorescent compounds.
International application WO 97/32733, published Sep. 12, 1997, discloses the use of near infrared fluorescent compounds as a security ink in thermal transfer printing wherein an image is formed by thermally transferring ink from a ribbon to paper.
U.S. Pat. Nos. 5,614,008 and 5,665,151, issued to Escano et al., disclose inks containing NIRF compounds.
Kaule et al., U.S. Pat. Nos. 4,452,843 and 4,598,205, disclose rare earth metal luminophores which absorb in the visible region and optionally the near-infrared region and can be excited in substantial portions of the visible or near IR-region.
Yoshinaga et al., U.S. Pat. No. 5,503,904, disclose recorded media with an invisible identification mark composed of regions of high reflectance and low reflectance in the same near infrared region.
NIRF (Near Infrared Fluorescence) compounds are desirable for use in security printing and invisible identification applications because they are not easily identified by human vision under the black light, broad spectrum light and infrared light. The images or marks of NIRFs are virtually free from interference deriving from background near infrared fluorescence or absorption because such materials are very rarely encountered in paper or other print receiving materials. However, like most dyes, the NIRF compounds intrinsically have very poor light stability and this greatly limits the applications of NIRF technology.
By nature, NIRF compounds are vulnerable to oxidation in the presence of oxygen, and gradually lose their near infrared fluorescence properties. The oxidation process is greatly accelerated when the NIRF compounds are exposed to U.V. light. This makes the NIRF inks and coatings unsuitable for use even in the normal office lighting conditions with practical amount of inks or coating applied.
Based on the mechanism of oxidation, there are two key elements in this process; one is oxygen and the other is U.V. light. If both or either one of them could be blocked or inhibited, the useful life of NIRF compounds would be remarkably improved. Based on this theory, Eastman Chemical Company captured the NIRF dyes with glassy type of polymers to shield NIRF dyes from oxygen, and then grind them to small particles for use. This approach does improve the light stability of NIRFs from days up to two months in the normal office lighting conditions.
SUMMARY OF THE INVENTION
It is a general object of the present invention to prolong the useful life of NIRF compounds used in print media to provide security features, sense marks and data images which are invisible to the human eye.
A specific object of the present invention to provide a printing ink comprising a NIRF compound and a U.V. absorbing pigment or compound which does not interfere with the emission of radiation at wavelengths in the range of from 650 nm to 2,500 nm by the NIRF compound.
Another specific object of the present invention to provide a printing ink comprising a NIRF compound and a U.V. absorbing pigment such as titanium dioxide, and zinc oxide.
An additional object of the present invention to provide a printing system comprising a printing ink containing a NIRF compound and a coating formulation containing U.V. absorbing pigment such as titanium dioxide and zinc oxide.
A further object of the present invention to provide a substrate such as a print medium with a near infrared radiation scannable coating, sense mark or data image positioned thereon that either contains a U.V. absorbing pigment or compound or is over coated with a layer which comprises a U.V. absorbing pigment or compound.
Yet a further object of the present invention to provide a thermal paper with a near infrared radiation scannable coating, sense mark or data image positioned thereon that either contains a U.V. absorbing pigment or is over coated with a layer which comprises a U.V. absorbing pigment.
Yet a further object of the present invention to provide a thermal transfer ribbon capable of applying a near infrared radiation scannable coating, sense mark, or data image onto a suitable receiving medium that either contains a U.V. absorbing pigment or contains a U.V. absorbing pigment in a protective second layer.
Still yet another object of the present invention to provide printing methods for preparing printed images with a near infrared fluorescent (NIRF) scannable coating, sense mark or data image that is protected by a U.V. absorbing compound or pigment.
The above objects are achieved through the printing inks, printing systems, print media and printing methods of this invention.
The printing inks comprise at least one resinous binder, at least one near infrared fluorescent (NIRF) compound which fluoresces photons at wavelengths in the range of 650 nm to 2500 nm and optionally a solvent or aqueuous based solvent. The amount of NIRF compound in the ink is sufficient to form coatings, marks and images which can be sensed by a photon detector operating in the near infrared region of 650 nm to 2500 nm. The printing inks further comprise a U.V. absorbing pigment or compound which does not attenuate the emission of radiation at wavelengths in the range of from 650 nm to 2,500 nm by the coatings, marks and images formed containing the NIRF compound.
Preferably, the U.V. absorber is a pigment selected from the group consisting of titanium dioxide, zinc oxide and combinations thereof and is preferably present in an amount sufficient to form coatings, marks and images containing NIRF compounds with enhanced light-fastness. In preferred embodiments, the NIRF compound is shielded from ambient air so as not to react with the oxygen therein.
In another aspect of the present invention, there is provided a printing system which comprises a printing ink and a coating composition. The printing ink comprises at least one solvent or aqueous based solvent, at least one resinous binder and at least one near infrared fluorescent (NIRF) compound as described above in an amount as prescribed above. The coating formulation comprises a U.V. absorbing pigment selected from the group consisting of titanium dioxide, zinc oxide and combinations thereof in an amount sufficient to form an overcoat on coatings, marks and images containing NIRF compounds which enhances the light-fastness of said NIRF compounds.
In a further aspect of this invention, there is provided a substrate, preferably a print medium such as thermal paper, with at least one near infrared radiation scannable coating, sense mark or data image positioned thereon. The near infrared radiation scannable coating, sense mark or data image comprises at least one near infrared-fluorescent (NIRF) compound as described above and a polymer binder resin which limits contact of the NIRF compound with air. The near infrared radiation scannable coating, sense mark or data image either: a) additionally comprises a U.V. absorbing pigment or compound, b)is over
Dashiell David M.
Lewis Maurice W.
Tan Yaoping
Hess Bruce H.
Millen White Zelano & Branigan P.C.
NCR Corporation
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