Luminescent sheet for stamp and a method for the production thereof

A method for the production of a luminescent sheet for stamps said sheet capable of being printed with a printing ink by gravure printing and to provide individual stamps which can be distinguished in a mail distinguishing system when said stamps are used on mail, said luminescent sheet comprising a substrate and a luminescent coating layer formed on the surface of said substrate, said method comprising

• (i) subjecting an aqueous dispersion (A) containing particles (a) of an inorganic fluorescent pigment having a mean specific surface area of Sw.sub.2 to wet-grinding using a wet-grinding machine, whereby said particles (a) of said aqueous dispersion (A) are finely ground to a mean specific surface area of Sw.sub.1, thereby obtaining an aqueous dispersion (B) containing fine particles (b) of said inorganic fluorescent pigment having a mean specific surface area Sw.sub.1, the said particles (b) satisfying the equation 2.0.gtoreq.Sw.sub.1 /Sw.sub.2 .gtoreq.1.05,
• (ii) incorporating said aqueous dispersion (B) in an amount sufficient to provide an abrasion resistance of less than 1000 .mu.g to the resulting luminescent coating layer into a coating composition (C) containing at least one pigment other than said fluorescent pigment to obtain a coating composition for the formation of said luminescent coating layer,
• (iii) applying said coating composition obtained in step (ii) onto the surface of a substrate to form a liquid coating thereon, and
• (iv) drying said liquid coating formed on said substrate.