The effect of exposure to inks and solvents on squeegee performance

The effect of exposure to inks and solvents on squeegee performance The squeegee in screen printing forces ink into the screen and the screen into contact with the substrate. The squeegee, which is manufactured from polyurethane, has a major influence on screen printing quality. This paper summarises an experimental programme into the durability of squeegees when exposed to inks and solvents. The softer the squeegee the more it was affected by exposure to any ink or solvent with the increases in mass of up to 14%, increases in volume of up to 12%, and reductions in elastic modulus of up to 80%. The low boiling point cleaner and solvent ink had the greatest effect of all the liquids tested, Distortion of the samples during solvent absorption caused small errors in the measurement of the volume and elastic modulus of the samples. The measurement in the increase in mass of the sample provided the most reliable method for estimating any ink/squeegee compatibility problems. Relaxation in the air returned the squeegee to its original mass. No clear relationship could be established between the surface roughness of the sample and the change in squeegee properties. Exposure to ultraviolet (UV) ink increased the mass of the sample with time. Unlike exposure to solvent-based inks, the effect of UV exposure was cumulative with relaxation between exposures doing little to reduce the mass of the squeegee. Relaxation of the squeegee over a two-week period of time under room temperature conditions did little to reduce the mass back to its original level. A printing experiment with an 'inked' and new squeegee showed that a two-hour exposure caused a hard squeegee to act like a medium and resulted in a 0.05 increase in printed density. Finite element modelling of a. compound' squeegee showed that the change in modulus had a significant effect on the deformation of the squeegee tip.