The ink roller train consists of an ink fountain with ink keys, an ink distribution blade and roller, a ductor roller and alternating hard and soft distribution rollers. Proper ink distribution begins at the ink fountain. If the blade is nicked, the roller surface scored or pitted, or the fountain ends clogged, the ink distribution will be inconsistent and uncontrollable. The ink keys must be routinely cleaned to keep these parts moving smoothly.
The metered ink from the ink fountain passes between the alternating hard and soft rollers. This ink film is milled, split and delivered all the way to the form rollers, then to the printing plate. If the press is to print with the expected quality, the soft rubber rollers must maintain their correct shape and durometer (or softness).
- Proper roller durometer is critical to the performance of the ink roller train. Hard rollers require more pressure to attain the proper “stripe” or contact with the next roller surface.
- When more roller pressure is required to get the proper “stripe,” friction and heat will build up and further damage the roller’s ability to split and deliver the ink film.
- Hard rollers transfer less ink than soft rollers, and ink feed must be increased to achieve proper density. Increased ink feed results in increased water feed.
- Changes in the shape of a roller cause the “stripe” to become uneven and the ink will not transfer evenly across the press. This shows up on the printed sheet as an inability to achieve proper ink density from side to side.
- Rollers change shape as they age. Swelling on the ends of the roller usually indicates that the center of the roller has collapsed due to the leaching of plasticizers. Plasticizers are an ingredient in the rubber compound that gives the roller its softness and shape. Exposing rollers to harsh solvents and deglazes depletes the amount of plasticizers in the rubber and the rollers can harden or collapse.