Troubleshooting the pad-printing process requires the identification and control of associated variables. The tips presented here will help you avoid some of the persistent problems you encounter on press.
By Julian Joffe
The ink and substrate must be compatible and adhesion should be suitable for the product under print. Often an ink with hardener is used when adhesion requirements are not that high. Inks that have hardeners added may be tossed out and replaced once or more per shift, therefore unnecessary wasting hardener (catalyst). This can waste money. The reverse is true as well. Do not get a job rejected because you used a single-component ink on a glass substrate that commonly requires an ink with hardener added.
Ink/thinner ratios should be ad-justed to match ambient environmental conditions. Many pad printing inks come with standard recipes on the label: add 25% thinner, etc. Proper ink mixing is key to successful pad printing. Following simple documented recipes can really save time.
Thinners flash (evaporate) more quickly in warm humid climates and slower in cool dry conditions. It is better to mix ink to a specific viscosity. This requires seasonal adjustments in thinner/retarder content, but results in a consistent ink mixture (and consistent printing results) throughout the year. If you were to follow the standard recipe on the ink container, ink could dry up prematurely on a hot day and remain too wet to transfer properly on a cold day. Documenting mixes that achieve the best results under specific conditions saves time spent searching for the ideal mixture–especially if you have found it once before. Moving pad printers into the climate-controlled area will be a money saver in the long run.
There are many tools available to mix and maintain a specific viscosity, from an inexpensive hand tool used as a gauge during mixing to an in-inkcup sensor that can measure and control viscosity automatically.
Choose between fast, medium, and slow-drying thinners (also referred to as retarders). Combine them as needed, especially in multicolor prints on a shut-tle conveyor where final colors tend to dry out before the transfer is complete. We often use a fast-drying thinner for the first print stations and a slower-drying thinner for the latter. This is not a concern with elliptical racetrack or over/under conveyor styles, where fresh ink is brought to the pad with each cycle advance.
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