Cyanine dye based high saturation sympathetic ink having time delayed disappearance

DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of my invention are incorporated in an ink utilizing indicator dyes which become colorless at higher acid levels.
In the course of my associates at Burroughs investigation, they and I discarded the use of fluorescent ink formulations as those utilizing General Electric's organic phosphors, Catalogue No.
118-15-1 (blue) and No.
118-15-2 (yellow) because it is difficult to obtain sufficient phosphor loadings in the inks in order to obtain crisp visibility utilizing ultraviolet (black) light in a commercial surroundings as in daylight or under office lighting conditions.
In addition, in order to avoid confusion in the future, the marks cannot be "permanent" as is the case of fluorescent colors and most dye formulations.
I have discovered that the desired "disappearing inks" can be obtained from a mixed acid based system which maintains color in solution and yet which upon exposure to air does not disappear rapidly but over a predetermined extended period of time.
In order to obtain the sufficient high saturation so as to obtain the required contrast in daylight and under office lighting conditions when the ink is applied to ordinary documents such as checks, I have found that the most useful formulations suitable for use are those given in the examples below.
The formulations resulting from my investigation are readily visible and disappear slowly when exposed on paper to air.
The ink meets a 70% visibility test two minutes after printing; is 50% visibile after five minutes, but has almost completely disappeared (less than 20% visible) after eight hours from printing, after exposure to air.
It can be stored for a period exceeding six months in a polyethylene container with plastic screw-on top.
The ink is of high contrast with a background ranging from white through the pastels used for checks.
It will be understood that in the examples all percentages given are percentages by weight, if liquid, weight wet.
The variances which are acceptable from the percentages by weight given are