Over time soft ink rollers become sensitized from chemical and physical contaminations of the printing process.
Soft roller pores collect contaminates such as ink pigment, dye, clays, calcium carbonates and other paper bi-products which creates a ‘barrier’ to ink, causing rollers to reject ink once water is introduced into the inking system.
Roller surface sensitization is a gradual process that developes over time to where it negatively effects the inking system’s ability to supply adequate ink supply to the plate.
Sensitized rollers is more of a problem with presses with ‘intregrated’ dampeners that carry more/excess wetting solution within inker.
The most vexing symptom of having sensitized rollers is having to ‘over-ink’ the plate in order to hold color.
This condition evenutally leads to the development of tone bands accross plate that appear to be caused by excess pressure or worn ink oscillator roll/cylinder gears.
I know of Printers who have re-geared presses at recommendations of Field Engineers hoping to solve this problem.
The solution is simple. First you must recognize the problem and its cause. Then institute a procedure of proper preventive roller maintenance.
A good water misiable roller wash is ‘necessary’ to cut through paper a bi-product roller glaze. Pure petroleum solvents alone won’t do, you ‘need’ the strong detergent properties of a good water misiable roller wash to cut/disolve paper bi-products.
A weekly application of Varn Revitol helps to cut the deep contamination cuased by dyes that actually become absorbed in soft roller surfacces. At first use you will emmediately notice a blue/purple color leaching out of your soft rolls which is the blue paste tone that makes carbon black look blacker.
Follow up each application of revitol with a water misiable wash deluted with water until the revitol does not change color. Then as a final wash, follow up last application of water misiable wash with a neutralizing rinse of 15% white kitchen vinegar and water to make roller surfaces more ink receptive.