Duroweave Trouble Shooting
Linting or Fiber Separation
The cover is shedding excessive fibers or "linting" which is affecting the print quality. The fibers are building-up on the ink rollers and/or the plate.
The Possible Causes:
Several factors can cause fiber separation. One general statement that can be made is that cotton covers are much more prone to this problem than synthetic covers. The reason is that cotton yarn is not a continuous fiber but rather it is made up of multiple lengths of yarn called "staples". These short pieces are intertwined or spun into a length of yarn. (A comparative example of this type of construction would be hemp rope).
Dampening covers made from synthetic yarn, most commonly rayon, are less prone to breakdown and the resulting linting. Man-made fibers are continuous in their construction so there are no individual lengths of yarn to become separated. A comparative example of this type of construction would be fishing line.) By the way, Novatech uses only synthetic yarns in all of its products.
Even given this distinction in yarn type, both types of covers, however, can suffer from fiber separation. The most common causes are excessive water form roller-to-plate pressure and/or high ink tack. (The form roller cover is almost always the culprit as the ductor cover does not make contact the plate nor does it undergo as much contact abrasion). Another cause can be too aggressive cleaning.
- Reduce the form roller-to-plate pressure: Excessive contact pressure to the plate can cause a variety of problems, fiber separation among them. Set the roller pressure as light as you can without affecting moisture transfer. A suggested method for setting the pressure is available for your review.
- Reduce the ink tack: Add a tack or ink reducer to the ink. This will minimize the inks' tendency to strip the fibers off the cover.
- Try less aggressive cleaning techniques: If you are cleaning the covers by scrubbing with a brush or squeegeeing the covers dry with a sharp instrument (an ink knife blade is a favorite among press operators) try a less aggressive method. Hot water under pressure will do a more efficient job of cleaning as well as minimizing abrasion.
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.
- 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.