The authors discuss right and wrong ways to clean screens on press.
Another ink-management problem involves using an improper floodstroke. An incorrectly set floodstroke on an automatic press or inadequate floodstroke on a manual press will result in irregular ink distribution, leading to under-filled mesh openings that dry out quickly.
A final cause of drying is an incorrectly set or worn squeegee. Fine-detail images printed with a high mesh count require a squeegee with a sharp edge set at an angle of approximately 75°; from horizontal. As the squeegee wears or distorts through normal use and solvent absorption, image definition will deteriorate around the edges, indicating that ink may not be properly flowing through the mesh. If the problem is allowed to continue, ink may dry in the mesh. To prevent these problems, flip the squeegee periodically to extend edge life, or replace it completely before image deterioration begins.
The next mesh-saving procedure involves controlling dirt--either in the ink or on the substrate. Substrates can become dirty due to static electricity that attracts airborne contaminants or from poor storage conditions. But you can avoid this problem with good housekeeping and process control. Additionally, tools such as static-elimination and substrate-cleaning systems can prevent dust and dirt on substrates from getting onto the mesh, were it can contaminate the ink and clog stencil openings.
But how do you remove contamination from a stencil if it does occur? If you're printing with a flatbed graphics press, stop the machine after the print stroke. Next, feed in a sheet of absorbent paper, and make sure that the screen's off-contact height is correctly set so that the screen makes contact with the absorbent material during cleaning.
With the screen in its printing position, wash the squeegee side (top) of the stencil with a non-abrasive cloth or tissue that you have wetted with the appropriate screen-washing product. Gently wipe the surface. This will flush contaminants through the mesh onto the absorbent material below. If necessary, repeat the procedure with another absorbent sheet. Some dirt particles on the top surface may be too big to wash through the mesh, but they will lift off with the cleaning cloth instead. When you are satisfied that the contaminants are removed, dry the stencil with a hair dryer set to "cool."
Did you enjoy this article? Click here to subscribe to the magazine.