In most cases the failure of an ink to adequately cure can be traced to the ink formulation – but this formulation can be affected by the printing process itself. The Bureau of Engraving and Printing (BEP) employs a number of different types of printing equipment to produce banknotes. Indirect materials, which do not contact banknotes during the printing process, are critical to the proper function of the printing equipment e.g. the ink train rollers in a production press. In the course of commissioning a new printing press, the BEP discovered the adverse impact roller formulation could have on ink curing. During pre-production trials, routine quality testing and root cause analysis identified that roller formulation has an effect on the curing of the green letterpress ink used to print Treasury seals and serial numbers.<br/><br/>Time of Flight Mass Spectroscopy measurements using Desorption Atmospheric Pressure Chemical Ionization sample introduction (DAPCI-TOF) were performed on the pure ink and ink exposed to a new roller. Results showed phthalates present as plasticizers in the rollers, were transferred to the ink from new rollers. In contrast, the phthalate content of aged rollers was about 50% less than new rollers and ink exposed to these rollers passed quality testing. Fourier Transform Infrared – Attenuated Total Reflection spectroscopy (FTIR-ATR) analysis confirmed that exposure to newly coated rollers resulted in curing retardation.<br/><br/>When a similar issue developed with offset inks, the BEP focused on roller formulation. A combination of DAPCI-TOF and solvent extractions performed on the rollers analyzed using Gas Chromatography - Mass Spectrometry (GC-MS) revealed that phosphate-based plasticizers were the most likely root cause. When ink was exposed to rollers containing these phosphate-based plasticizers, they exhibited slower curing and smudged when run through subsequent printing operations. This further underlies the importance of understanding the composition of indirect materials and treating the entire printing process as a system of interconnected parts.

Identification of leachable plasticizers by mass spectrometry: Deciphering press roller influence on ink curing

254th National Meeting (2017)

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