Cleaning systems available in the market

Anilox cleaning is a must to keep engraving characteristics, ink release and performances unaltered in time.

Still, the cleaning product and equipments utilized might severely damage the anilox performances and life.

When chemical products are used the chemical action must be combined with the manual action by means of special brushes with fine bristles. This operation must be carried out while the roller is rotating and the mechanical action must be as homogeneous as possible. Once manual cleaning is over, the roller must be washed immediately to remove the caustic agent and the product wastes.

Never wrap up the roller in plastic film after applying the chemical product since the chemical aggression would be too strong and would compromise the integrity of the roller.

Simec recommends this cleaning method only in emergency situations and anyway only after reading the above instructions and adopting all protective measures for the operators.

This is the most common cleaning method and is usually carried out off-line and by means of specific equipments using caustic solutions to dissolve the ink residues in the cells. Various equipments are available in the market and either work by partial immersion of the rollers into the cleaning solution or are equipped with special spray nozzles.

In both cases, the chemical agent gives rise to a chemical reaction to dissolve the ink deposits. At the end of the cycle, the roller is washed with water to stop the chemical reaction and to remove the cleaning product and the ink wastes.

In order to trigger the chemical reaction,  the solution is quite often heated up to 40÷60 °C. This is acceptable for steel-base cylinders but it is not good for sleeves and aluminum light rollers because their structure might get damaged.

If the temperature of the solution goes above 55÷60 °C and if the solution utilized is particularly aggressive, at the end of the cycle there might remain some aloes on the roller due to the change of surface tension of the ceramic layer. 

In conclusion, we can say that chemical cleaning is effective for screens up to 500 lines/cm but it is suitable only for conventional steel-base rollers. On the other hand, these systems might damage the structure of the sleeves.

Cleaning by baking soda has many advantages in terms of efficiency of the system, ease of use and low environmental impact. Still, some notes on the different types of equipments are necessary and are listed below:

Cleaning systems by water under pressure

For this type of equipments, the grains of baking soda are transferred by means of water under pressure and mixing of the grains occurs directly in the spray nozzle.

For the proper functioning of the system, the baking soda granulometry must be rather high in order to ease the transfer to the anilox but in this case the risk is that the cell bridges might get damaged, in particular with screens over 100 lines/cm. Other important issue is that part of the powder transferred is not sprayed uniformly and cleaning might result not homogeneous.

Pressure dry cleaning systems

This type of cleaning machines exploits the principle of industrial sand blasters. Presently, these systems are mostly used by the companies that offer an on-site anilox cleaning service at the customer’s especially in the field of corrugated because this kind of cleaning machines can be easily installed in-line and exploit the press motorization.

Specific closed cleaning machines for the off-line cleaning of the anilox are also available in the market but hardly ever these machines allow baking soda recovery and this is why powder consumption is significant, especially when big rollers are cleaned.

Very often, and in particular when this service is proposed by external companies, cell damages are reported and the causes are mainly: excessive pressure during cleaning operations and use of baking soda with big grains. Usually these plants operate with powders grains of 100 micron diameter and when the grains touch the cell bridges, they compromise the cell integrity.
 

Dry low-pressure systems

This system was developed by Simec back in 2000. Thanks to the reduction of pressure and to a particular Venturi system, our equipment can guarantee the cleaning of anilox with screens up to 500 lines without damaging the anilox surface.

For technical features, visit the Profil section in our website.
 

These cleaning systems transform liquid carbon dioxide into dry ice micro-grains which are then sprayed onto the cylinders at high pressure.

This technology is quite effective and environmental friendly but recommended especially for encrusted surfaces. Anilox cylinders should not be treated with this system since deposits can be eliminated only up to 100 lines/cm and the impact of the grains (sizes above 100 microns) with the anilox surface might damage the cell bridges which would result in a non-homogeneous transfer of material to the support.

Simec does not recommend this cleaning method for screens above 100 lines/cm and above all not for anilox sleeves.

Ultra-sound cleaning is probably the most common in particular in the Label Industry and is effective for the cleaning of anilox at high screens.

The performances of the different equipments may vary in consideration of the following elements:

•    Type of equipment utilized
•    Size of the rollers to process
•    Type of engraving
•    Material utilized for removing the deposits and PH of the solution
•    Percentage of the roller surface immersed into the solution
•    Treatment time
•    Energy and intensity of the sound waves
•    Temperature of the solution

Errors in the set-up of the equipment may result in damages to the anilox surface and this is true especially for light rollers with aluminum body and sleeves.

Still, it remains the most suited system for cleaning label rollers since the dimensions of both cleaning machine and rollers are rather small.
 

Several laser cleaning systems are now available in the market. These systems are quite expensive if compared to other systems and need utmost care in use and frequent maintenance operations.

The tests carried out by Simec proved that the system is indeed successful for the removal of such materials as inks, resins and adhesives but the prolonged use gives rise to several problems.

The tests were carried out by monitoring different rollers over a certain period and, after a series of approx. 20 cleaning cycles, the rollers appeared as shown in the picture.

Also, we noticed that as the number of cleaning cycles increased, the period in which the roller could be used became shorter, the print quality became poorer and the roller had to be refurbished after approx. 30 cleaning cycles.

Therefore, Simec suggests this cleaning method only when the anilox is used to transfer resins or interlacing agents since other cleaning methods would not be successful.