Printing press rollers require extra caution when cleaning. There are two basic ways when it comes cleaning the roller: On Press or Off press. On press cleaning may be more economical and is suitable for some situations. On the other hand off press ultrasonic cleaning achieves more effective cleaning when compared to other cleaning systems.
Gravure, flexographic and offset printing presses utilize chrome and ceramic rollers that are laser engraved. Anilox rollers are used in flexographic printing for metering ink. Graphic printers are automatically set to several acceptable color standards. Each roller has cells etched onto it that carry a specified amount of ink to the printing plate.
To get a neat, smudge-free and perfect end-product from the printing process, care must be taken to ensure that the cells are extremely clean. Dust, dirt and grime may accumulate on these cells that reduce the required amount of ink needed for accurate printing. A deviation from the tolerable color calibration can cause extensive loss if the prints cannot be used. This is because this kind of printing use sophisticated machinery and colored inks that are very expensive.
Ultrasonic cleaning involves immersing the object to be cleaned in a liquid bath where ultrasound vibrations occur. These vibrations create localized, microscopic vacuum-filled bubbles that quickly expand and then implode liberating a high stream of energy. This energy is responsible for dislodging dirt and other contaminants from the surface of the object.
A primary concern for printing press rollers is the damage that an ultrasonic cleaner may cause to the thin cell walls of the roller. Roller cells can be damage-free by increasing the operational frequency of the ultrasonic cleaner. Usually, ultrasonic cleaners operate at 25-40 KHz. The cleaning action is more of a vigorous scrub at this frequency range, that can dislodge stubborn grime and dirt that are virtually bonded to the surface. The ultrasound cleaning action should be more ‘gentle’ for effective cleaning of the roller cells. This is achieved by setting the operating frequency to 80KHz or above. At these frequency ranges, the ultrasonic action is much gentler but just as efficient.
The usual problem with single frequency ultrasonic cleaners is the creation of hot zones and dead zones within the cleaning liquid. This is due to the collision of an ultrasonic wave returning from the top of the liquid, with that of the next wave. Depending on the intensity of collision, hot spots may develop from ultrasonic cleaning action that could be damaging to the printing press roller. To resolve this, printing press rollers should be cleaned in variable sweep frequency ultrasonic cleaners. This feature ensures that the ultrasonic wave propagation is the same throughout the liquid medium ensuring a more consistent cleaning action at all points within the ultrasonic cleaning tank.
Ultrasonic cleaners can be used for both fine and coarse screen rollers. It is a low-maintenance, low labor-intensive system. What’s more, the cleaning solution can be changed in just once in fifteen to twenty days as compared to other cleaning systems.