Roller Scumming

  The Problem:

The metering (chrome) roller is "scumming" or building up with ink. As a result, fountain solution is not being transferred adequately to the plate.

  The Possible Causes:

What's happening here is that the ink is emulsifying into the water instead of the water emulsifying with the ink. As a result the ink is working its way into the water system from the form cover to the chrome oscillator. Factors that can cause this problem include the type of  fountain solution, the source of the water used in the fountain mix, the type of  ink, and the paper being printed. Sometimes the operator may be running the job with too much ink.

Additionally, the culprit is often the metering roller itself. If the surface of the chrome roller becomes "sensitized" by grease or oil it will begin to attract ink.

  Suggested Solutions:

• Clean and desensitize the chrome roller: Degrease the chrome roller with an appropriate metal cleaner and rinse with water. Then coat the roller with a 50/50 solution of water and Gum Arabic and buff dry.
• Check the pH level: The optimum pH level is 5.0 to 5.5.