To obtain an ink composition with high storage stability capable of affording printed matter which is colorless under ordinary visible light but radiates red when irradiated with ultraviolet rays, by including an arylsulfonic acid and a tertiary amine.
This ink composition contains a fluorescent compound of formula I [A is a group of formula II (R5 and R6 are each H, a halogen, alkyl or the like) or the like; R1 to R4 are each H, an alkyl or aralkyl], an arylsulfonic acid (e.g. benzenesulfonic acid) and a tertiary amine (e.g. triethylamine); wherein it is preferable that this composition also contains, as binder resin, at least one kind selected from polyvinylpyrrolidone, ethyl cellulose and polyvinyl butyral, and ethanol account for ≥70 wt.% of the whole composition.
NAKATSUKA MASAKATSU
TAKUMA HIROSUKE
