A problem of information, not of care
Rollers are called the heart of the printing press and then given minimal attention. Their care correlates directly with the results they produce.
Any misuse or abuse that rollers receive is not so much the result of deliberate carelessness as a lack of information.
Pressmen should check their rollers every day to watch for and prevent accumulated ink and glaze.
Immediate cleaning prevents cracking, pitting and deterioration. Glazed rollers routinely mislead pressmen into suspecting the water solution or the ink, and hours are lost chasing the wrong variable.
The chemistry, and the two-step procedure
Printers work with both water-soluble and solvent-soluble mineral materials, and removing the materials that cause glaze requires an approach that addresses both. Hence the two-step procedure: step one is formulated to break down the ink and make it water-miscible; step two flushes the suspended solution away while removing lint and gum.
The basic procedure
- Wash with a quality two-step solution — the first step dissolves water, grease and contaminants and makes them water-miscible; the second flushes the glaze-causing materials out
- Wash metal rollers with a chrome roller cleaner and desensitiser, or equivalent
- Where glaze persists, wash with a strong proprietary glaze remover
- If that is still ineffective, return the rollers to the factory for reconditioning or recovering
Chemical safety
Some pressroom products harm rollers and blankets. A prudent pressman tests a solution's harshness by soaking a piece of blanket or roller covering overnight and checking for swelling before it goes anywhere near the press. Avoid ketones, acetates and chlorinated hydrocarbons.
What automatic wash-up devices miss
Mechanical devices accomplish reasonable cleaning within their limits — and the limit is the face length.
Most offset presses have automatic washup devices that do not clean beyond the face length of the roller.
- Heavy accumulation beyond the face length eventually flakes off into the press and causes hickies
- Hand-clean the shoulder areas weekly, using a long-handled brush where they are inaccessible
- Examine the wash-up blade monthly for cleanliness, alignment and wear, and replace it when worn
Thin films, and how glaze builds
Some solutions leave a thin ink film behind after wash-up. Eventually the rubber surface fills with dried ink, becomes hard and glazed, and stops accepting and distributing ink properly. At that point hand-washing with a stronger proprietary solution is the next step; if glazing persists, the rollers come off for factory reconditioning.
Composition rollers
Clean composition rollers with the recommended wash after use. After the end-of-day wash-up, apply oil to the ink plate and run the press briefly — the rollers pick up an oil film that prevents ink drying if any wash-up residue remains.
Ink roller stripping
Occasionally an area of a roller refuses ink. This is called stripping. It is usually steel rollers that strip, though rubber rollers occasionally show it too. There are two main causes: a dried ink film on the roller, and desensitisation of the steel roller.
Dried ink films left after wash-up eventually harden the roller surface into a glaze that prevents proper ink acceptance — pressmen usually call this oxidation. Once the glaze has built, removing it is mandatory, not optional.
Additional practice
- Wash rollers before any extended shutdown period
- Give special attention to the roller ends beyond the form, ensuring complete ink removal
- Wash metal vibrator rollers on offset presses approximately every 30 days with the appropriate cleaner
- Urethane rollers need careful, complete cleaning after every daily run — dried films obscure their natural tack and destroy print sharpness
- Consult the manufacturer on appropriate wash solutions rather than inheriting whatever is on the shelf
