Ink Viscosity and Seasonal Adjustments

Pad printing is a thin film process. It starts with an etch depth in the cliché of approx. 25-75 microns and only a fraction of that ink film is picked up by the pad. Of the wet ink, 50% is a solvent that evaporates leaving only a 5 micron dry ink deposit. You can easily see why such a thin ink film is so susceptible to changing temperatures, humidity levels, static charges and even variations in airflow. Listed below are the ways you can control the ink viscosity and seasonal adjustments.

Control the rate that solvents evaporate from the ink
• Solvents evaporate too slowly
– The surface of the ink may not be tacky enough to pick up or release images from the pad
• Solvents evaporate too quickly
– Ink might not pick up from the cliché because it has dried in the etched portion of the plate, or dried on the pad in transit to it’s destination.

Same for the pad
• Solvents evaporate too slowly
– Only some of the ink will release from the pad to the substrate
• Solvents evaporate too quickly
– Ink dries and stays on pad.

Tips
• Warm environments: Add solvents every 20 – 30 minutes. Always add a measured amount, use a viscospatula and don’t guess!
• Control temperatures: Keep printer out of the sun, away from drafty entrances, exits, dryers.
Keep the temperature of the substrate to room temperature.
Don’t let printed part drop below 59°F until fully cured – 4 days or longer.
• Good housekeeping: Dust and vacuum floors instead of sweeping. Avoid cardboard boxes in production area. Wipe down all surfaces using a damp cloth.
Static electricity feathers the print. Slow the down stroke and pickup.
• Too hot: Solvents in the ink will evaporate very quickly. Solvents are attracted to water vapor molecules in the air.
– Speed up the forward travel of the pad stroke.
– Thinner / retarder mix (75% Thinner to 25% Retarder)
• Too cold: Solvents won’t evaporate quickly enough. Ink won’t be tacky enough between pickup and and lay down to transfer completely to the substrate.
– Slow down the forward travel of the pad stroke
– Select a faster drying thinner
– Use a hair dryer pointed at the pad as it travels forward after ink pickup to speed up the evaporation of the solvent
– Raise ambient temperature.