Fading of carbonless copying paper

Abstract

The reactions of crystal violet lactone (CVL) (1) and carbazolyl blue (S-RB) (2) were studied on the acid activated clay Fulacolor.
The colourless leuco dye CVL (1) undergoes lactone cleavage, when adsorbed on Fulacolor, to give a blue zwitterion. CVL (1) was also shown to adsorb as the unchanged lactone which could be photochemically ring opened. The zwitterion could be displaced readily by water vapour. When a high surface acidity was kept, the zwitterion was more resistant to displacement, the humidity and any exchanged cations being important factors. Prolonged exposure to light causes fading of the zwitterion, the products from which are mainly demethylated species.
It was shos.jn that the fading mechanism involves singlet oxygen production, by the dyestuff itself, which subsequently attacks the dye.
Singlet oxygen quenchers retarded the fading process. The slow developing dye S-RB (2) was found to have a rate constant for photo-oxidation (at 30 ° C) of approximately twice that of benzoyl leuco methylene blue (BU€) (4), a previously commonly used dye.
Addition of the Lewis acid aluminium chloride, - greatly enhanced the rate of production of the dye from S-RB (2),f whereas the weaker Lewis acid boron trifluoride, did in fact retard the dye development. A coordination complex with a different ,tmax for 1absorptionwas detected with boron trifluoride and S-RB (2). The oxIdation of S-RB (2) on Fulacolor was shown to occur at two distinct sites: iron atoms in the aluininosilicate lattice and at aluminium Lewis acid lattice edge sites.
A method was devised for promoting the migration of Fe 3 cations back into the damaged octahedral layer of the acid activated montmorillonite Fulacolor, and thus of increasing the rate of S-RB (2) dye development.