Foaming in water-based flexo ink
Water-based flexo inks contain surfactants that can generate foam. A limited amount is normal, but excessive foaming can affect print quality. Pumping and circulating the ink during printing can introduce bubbles. Excessive foam means the anilox roller transfers bubbles to the plate instead of a consistent ink film, causing pinholes in the print. Ink manufacturers include a controlled amount of defoamer in the formulation; printers can also add an appropriate defoamer during a run when required.
Cleaning the press and anilox roller
In a flexographic press, the anilox roller transfers ink to the plate. If it is not cleaned after printing, ink components can leave deposits in its cells. Fresh deposits can be removed with water and a plastic-bristle brush. Once the deposits have dried, a stronger alkaline anilox cleaner may be needed.
Ink drying on the plate
Water is used to bring this type of ink to the required viscosity. Moisture in the paper and its interaction with the ink components can lead to deposits between the raised areas of the plate. These deposits become thicker as the run continues, interfere with ink transfer and reduce print quality. Wherever possible, use treated water whose pH can be controlled.
Low resistance to moisture
Some printed packaging, such as ice-cream cartons, is stored in an industrial cold room after the product has been packed. When cartons are taken out for distribution, the change in temperature can cause condensation on their surfaces. This moisture may transfer ink to staff members’ hands or clothing. The extent depends on the ink type. To reduce transfer, ask the water-based flexo ink manufacturer for a formulation suited to the packaging’s storage conditions.
Poor transfer from the ink reservoir to the plate
Poor ink transfer is often caused by viscosity that is too high for the anilox roller, or by dried ink blocking its cells. If dilution is unsuitable for the application, ask the manufacturer to supply ink at the correct viscosity. Otherwise, add the amount of water needed to achieve the required viscosity. Clean the anilox with water and a plastic-bristle brush; use an appropriate anilox cleaner if a substantial layer of dried ink has built up inside the cells.