Solvents and press cleaning solutions are essential for cleaning after a print run. Many solvents used 50 or 100 years ago, such as kerosene and petrol, are no longer appropriate choices for a modern pressroom.
There is often a trade-off between cleaning performance and health concerns. Solvents that clean particularly well may present greater risks, while safer alternatives do not always work as quickly or effectively.
Printing involves a mixture of chemicals, including hydrocarbons, solvent naphthas, oils, defoamers and corrosion inhibitors. Different cleaning formulations are therefore used for different pressroom tasks.
Cleaning solutions for heatset offset
Heatset operations require particular care in selecting cleaning solutions because inks pass through a continuous-flow dryer at temperatures above their solvents’ evaporation points. The article describes solvent evaporation levels of up to 85%. Air entering the dryer mixes with the vapour, so extraction is needed to control the risk of an explosive atmosphere.
The amount of cleaning solution used and its maximum delivery rate during blanket washing must match the extraction capacity of the dryer’s ventilation system.
Cleaning rollers and blankets
Ink rollers and ink fountains are cleaned with undiluted cleaning solution where the task is to dissolve ink. A blanket-cleaning paste is also useful for a fast, effective clean, particularly when changing from dark inks to lighter colours. A cylinder-cleaning paste can remove residual contamination from dirty metal surfaces and help protect the rollers.
Over time, paper and ink components form deposits on rollers and can cause substantial printing problems. Calcium carbonate in particular can affect emulsification and ink transfer.
Safety considerations
An “all natural” label does not establish that a solvent is safe. Refined citrus-oil solvents can be flammable and hazardous, as can turpentine or petrol. Natural origin and safety are separate considerations.
“Odourless” solvents also require care. They may be more pleasant to work around than strongly scented cleaners, but the absence of a smell can make exposure to vapour easier to overlook.
Wear gloves appropriate to the selected solvent. The source discusses nitrile gloves, available in reusable and disposable versions, rather than assuming that latex offers suitable protection. Consult the manufacturer’s safety data sheet (SDS, formerly MSDS) for the required protective equipment, precautions, hazards and flammability information. Keep a copy available in the pressroom.
Regular cleaning and maintenance
Routine press cleaning and maintenance are important for trouble-free operation and satisfactory print results. Cleaning solutions remove ink particles; water-miscible cleaners can also remove water-soluble deposits such as paper components. Automatic brush and blanket washing units are standard cleaning equipment, although their operation also involves time, cost and cleaning-solution consumption.