Non-Sticking Ink... ..CSMA Investigates

The Problem

An ink manufacturer recently commissioned CSMA to resolve a product defence claim. A batch of ink was being blamed for poor ink adhesion properties on a shampoo bottle.

The Strategy

Batches of unprinted shampoo bottles were obtained over a certain time period. X-Ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToFSIMS) were conducted on sample surfaces from the bottles to ascertain differences, if any, in surface chemistry. Where printability/paintability is an issue a single atomic or molecular layer of material at the surface is more than enough to change the interaction between substrate and ink/paint.

The Results

ToFSIMS provides detailed molecular information. Both samples of good and bad bottles were qualitatively similar. Levels of anti-oxidants and anti-statics were consistent for all samples. Interestingly, high levels of anti-statics (ethoxylated dodecylamines) were a major suspect. ToFSIMS did, however, indicate a generally higher level of oxidation/oxygen containing functionality for the good sample.
XPS provides quantified elemental and oxidation state information. The XPS results showed a dramatic 6 times greater level of surface oxygen for the good sample. Additionally there was 2 to 3 times higher levels of oxygenated carbon functionality for the good sample (C-O-C; C-OH; C=O; O-C-O).

Conclusion

The poor ink adhesion is due to the surface chemistry of the bottle substrate. Poor ink adhesion is related to low levels of surface oxidation which in turn are likely to be due to lower levels of corona treatment, flame treatment or surface chemical processing.