This invention developed an aqueous ink jet ink that contains an effective amount of an azomethine dye having at least one water solubilizing functional group covalently attached to it, overcoming the problem of finding stable, lightfast dye-based ink suitable for use in an aqueous-based ink jet system.
The water solubilizing functional group can either be directly attached to the azomethine dye and/or can be attached to the azomethine dye through an electrophilic coupling groups. If an organic spacer group is used to separate the water solubilizing functional group from azomethine dye or the electrophilic coupling moiety, then straight and branched chained alkyl groups having from about 1 to 10 carbon atoms is preferred.
The preferred azomethine dyes can be pyrazolone azomethines, pyrazolotriazole azomethines, and combinations thereof. Additionally, an effective amount of a dye-based colorant can be added with and an essentially water soluble spiroindane additive for improving light fastness and stability of the dye-based colorant.
Background of Invention
In order for ink jet prints to effectively compete with silver halide photography, one important improvement that must occur is that ink jet inks must improve their ability to remain stable to light exposure for longer periods of time. In the photographic industry, technologies have been developed which have been reported to last much longer than the typical 14-18 years, and even up to 60 years. Such long lasting ink stability has been attributed to specific, very stable dyes. Even though these dyes are very stable under prolonged light exposure, they are not water-soluble and contain long chain organic groups necessary for anchoring dyes in photographic media. Such structures are not useable in aqueous-based ink jet systems.