Putting in place effective anilox cleaning procedures, adapted to the needs of the facility, should be a priority for . If done right, they will translate into longer anilox lifetimes and better ink transfer, which improves the stability and repeatability of printing. It is a crucial component of pre-press and should be a key part of an advanced quality control system.
It is worth answering these questions: Why pay several thousand euros for new anilox rollers? How much production time and materials are wasted because of inadequate set-up? Why compromise the business reputation and printing quality?
To help printing houses take informed decisions about anilox cleaning, we analyzed the advantages and disadvantages of commonly used methods.
Chemical cleaning – manual
How it works: There are usually two types of chemical anilox cleaning: daily cleaning after each new set-up and deep, acid-based cleaning every 1-3 months. On a daily basis, anilox rollers are washed with ink-specific solvents after each retooling. Every 1-3 months aggressive chemicals are used for deep cleaning with a noble steel brush applying the agent on the roller and letting it react, penetrate the ceramic surface and clean.
Advantages: No tools necessary. Quick cleaning process.
Disadvantages: The use of chemicals on some anilox rollers containing light metal or rubber elements and bodies can lead to surface damage. The process is manual and so not fully repeatable and precise. Manual washing with chemical agents may have a negative impact on operator health, the environment and chemical waste generation that needs to be neutralized. It is necessary for operators to use proper safety clothes and equipment (goggles and protective gloves).
Chemical machine cleaning
How it works: The anilox roller is first treated with ink-specific solvents and then blasted with heated chemical agents (usually alkaline wash). Solvents are used to quickly separate the binding agent from ink. Alkaline cleaning agents (e.g. caustic soda) are used to dissolve the remaining mixture, which takes more time.
Advantages: With a good selection of solvents relative to ink, chemical anilox cleaning can be very effective. It is a fast-paced process that takes place within a sealed machine. There are environmentally-friendly solutions (e.g. water-based) that make it less troublesome for operators and the environment.
Disadvantages: The use of chemicals on some anilox rollers can lead to corrosion of metal parts and blister problems under ceramic microcells that may affect the physical properties of the roller, interaction with doctor blades and ink transfer. Stains on the anilox surface are likely. There are also many worker safety and environmental concerns connected with the chemical method.
How it works: The anilox roller is dry cleaned by blasting powdered agent such as sodium bicarbonate (NaHCO3) from a nozzle at relatively low pressure. Tiny particles of NaHCO3 granulate penetrate inside the microcells brushing off dried ink and other types of contamination. Powder residues can be removed with water. The cleaning cycle takes about 40-60 minutes!
Advantages: The process is worker and environment-friendly. Sodium bicarbonate waste needs no special treatment. The system is easy to operate and takes little space
Disadvantages: Small amounts of cleaning granulate residue may remain in cells even after water washing. Blasting may leave white traces on the anilox roller. Individual grains of sand may be bigger than the area of anilox cells, which makes cleaning anilox rolls with a screen ruling larger than 800lpi more difficult.
Ultrasonic cleaning systems
How it works: A combination of ultrasound waves and a cleaning agent is used to thoroughly wash the roller. The anilox rotates in the heated chemical agent solution (e.g. caustic soda). Ultrasound waves activate a cavitation process, forming gas bubbles whose implosion on contact with the anilox surface releases pressure and temperature that help dissolve and destroy contamination in anilox cells. The process takes approx. 20-30 minutes.
Advantages: Ultrasonic cleaning is very effective with all types of ink used in flexography. It is also easy to install and operate. The process is fully automated. It is easy to filter the cleaning agent so it can be reused for an extended period of time, which is very economical. The system has low water consumption. Investment costs are relatively low and the washing machines can be easily adapted to suit the individual needs of the printing company. Ultrasonic washer specification contains the number of units in the machine, working unit length and internal and external diameter. The machine can be fitted with single or double frequency and rinsing functions.
Disadvantages: With mechanically damaged anilox cleaning agents may penetrate to metal parts causing corrosion or blisters. The roller must cool down to room temperature before re-installation.
Anilox cleaning with laser
How it works: The anilox roller absorbs the energy of the laser beam, which has a high-intensity impact on its ceramic surface. It leads to the so-called cold evaporation of all types of contamination from the roller. Suction unit for removing ink resides and other contaminations are required. The process takes about 45 minutes to complete.
Advantages: It is a dry and gentle method that uses no chemicals. If correctly set (laser focus, power relative to ink type, rotational speed), the results are very good. It is suitable for inline cleaning. The anilox surface is not heated so the risk of damage during cleaning is smaller and the roller can be sent to production right after cleaning.
Disadvantages: Effective and damage-free cleaning with laser is only possible with the right settings regarding, for example, anilox rotational speed, laser beam scan width or feed speed. This requires knowledge and experience. Poor set-up can cause permanent damage such as cracks in the ceramic surface. The operator must wear protective goggles. Investment costs can be very high, which is why this cleaning method is usually offered as an outside service by specialized providers.
The decision to choose an anilox cleaning technology needs to be taken in relation to the needs of a particular production process. The key element should be an honest analysis of the advantages and disadvantages of particular cleaning methods relative to the production profile and inventory of anilox rollers. Taking into account the speed, efficiency, investment costs, and the environmental impact, the Ultrasonic Anilox Roll Cleaning system seems to be the most favorable choice.
Before making the investment it is important to be able to test the method under production conditions, verify its impact on the condition and wear of anilox as well as check the efficiency of a chosen cleaning method through volumetric measurement (cm3/m2 / BCM) after washing anilox with different screen rulings.