Pressure sensitive transfer sheet

Claim 1

A transfer sheet, for use in a pressure-sensitive copying system, comprising a support material having on one surface thereof a coating composition containing at least one colourless colour former, wherein said colourless colour former comprises a single organic compound having the structural formula: ##EQU3## wherein Y represents a phenylene or naphthylene or substituted phenylene or naphthylene radical, Z represents a 1,2-phenylene or substituted 1,2-phenylene radical, W represents oxygen or a group of the formula -NR 6 - wherein R 6 is selected from the group consisting of hydrogen, lower alkyl, aryl, substituted lower alkyl, and substituted aryl radicals, A and B each independently represents a 1,4-phenylene residue, R 1 , R 2 , R 3 and R 4 , each is selected from the group consisting of lower alkyl, substituted lower alkyl, aralkyl, substituted aralkyl, cycloalkyl and substituted cycloalkyl radical or forms part of a divalent organic chain which together with the attached nitrogen atom constitutes a heterocyclic ring, R 7 and R 8 each independently represents a lower alkyl or substituted lower alkyl radical, and the -NH- group is either attached to Y or is attached as one substituent or the sole substituent of R 6 when said R 6 is a substituted aryl radical, said organic compound thus containing within the same molecule at least two potential chromophoric systems, each of said potential chromophoric systems being capable of being activated substantially immediately when the compound is brought into contact with one or more acidic activating substances.