METHOD OF DETECTING FLUORESCENT IMAGE IN ARTICLES
A fluorescent colored image can be detected in an image on an article. This fluorescent colored image is obtained from applying an aqueous colored pigment-based ink that is capable of fluorescence, onto a suitable non-UV fluorescent substrate. This aqueous colored pigment-based ink has 1-7 weight % of a pigment colorant; and 0.1-2 weight % of a non-polymeric fluorophore that when excited by fluorescence-exciting radiation having a peak of at least 200 nm and up to and including 400 nm, exhibits an emission peak of at least 400 nm and up to and including 750 nm. This aqueous colored pigment-based ink that is capable of fluorescence can be applied using inkjet printing, onto non-UV fluorescent substrates to provide images that can be detected when excited as noted above, which images can be provided on articles such as security documents, currency, and lottery tickets.
1 . A method of detecting a fluorescent image, comprising:
irradiating a colored latent fluorescent image disposed on a non-UV fluorescing substrate, the colored latent fluorescent image having an emission peak of at least 400 nm and up to and including 750 nm, on an outer surface of a non-UV fluorescing substrate, with fluorescence-exciting radiation having a peak of at least 200 nm and up to and including 400 nm,
wherein the colored latent fluorescent image comprises:
a pigment colorant; and
a non-polymeric fluorophore that when excited by fluorescence-exciting radiation having a peak of at least 200 nm and up to and including 400 nm, exhibits an emission peak of at least 400 nm and up to and including 750 nm, wherein the weight ratio of the pigment colorant to the non-polymeric fluorophore in the fluorescent image is from 70:1 to 0.5:1.
2 . The method of claim 1 , wherein the non-UV fluorescing substrate is an article to be used as a security document, currency, or lottery ticket.
3 . The method of claim 1 , wherein the colored latent fluorescent image is a black latent fluorescent image, and the pigment colorant is a black pigment.
4 . The method of claim 1 , wherein the pigment colorant is a black pigment, and the colored latent fluorescent image exhibits a CIE L* value of 50 or less, an a* value of −20 to and including +20, and a CIE b* value of at least −15 to and including +20 when observed under illumination that excludes fluorescence-exciting wavelengths.
5 . The method of claim 1 , wherein the pigment colorant is an anionically-stabilized pigment.
6 . The method of claim 1 , wherein the non-polymeric fluorophore is colorless.
7 . The method of claim 1 , wherein the non-polymeric fluorophore is a diamino stilbene compound comprising multiple sulfonate groups.
8 . The method of claim 1 , wherein the fluorescent image further contains one or more water-soluble black dyes.