Application of microscopic techniques to pigment manufacture and performance in fluid inks

Abstract

A number of physicochemical techniques including transmission electron microscopy, optical microscopy, densitometry, X-ray diffraction and surface area determinations were used in the study of organic pigment yellows in correlation with their performance characteristics in fluid inks. The pigment chosen for this study was Diarylide Yellow, CI Pigment Yellow 14, which is widely used in nitrocellulose-polyamide alcohol flexographic inks. Transmission electron microscopy was employed to obtain the particle size and shape of several preparations of the pigment (particle size distributions and average particle diameters). Crystallite size and average particle diameters were determined by X-ray diffraction line broadening and surface area techniques, respectively. Optical microscopy and densitometry were utilized to study properties of the flexographic ink films such as transparency and strength. The results show the significant effect on particle size caused by process variables in pigment manufacture such as drying conditions and use of additives such as solvents and surfactants. Variations in particle size are in turn related to differences in strength and transparency exhibited by the corresponding ink films.