Case Studies:

Cleaning Anilox Rollers Off Press: A Case Study

Case Study Summary:

Maintaining the integrity of Anilox print rollers, is an essential process in flexographic printing, and keeping them clean and free from damage is a priority.

Suggested cleaning methods for the rollers, are plentiful, and the best method is a hotly debated topic. None so far has been proven to be without its flaws.

Partswash have now designed a new water based spray wash system, specifically for cleaning Anilox rollers, which they believe could provide the answers that the printing industry have been looking for.

Background:

Anilox rollers consist of a fine ceramic coating, which is etched with millions of cells. These cells are used to carry the exact quantity of ink to the printing plate, ensuring that accurate and consistent colour density is achieved.

The anilox rollers, simply cannot be damaged or scratched, nor can they have plugged cells. Any reduction in the quality of the anilox roller will reduce ink quantities and subsequently compromise graphic quality. Similarly if rollers are not thoroughly cleaned, cross contamination can occur and inconsistent colour matching can occur.

Anilox rollers need to be taken off the press and thoroughly cleaned at regular intervals, as part of ongoing maintenance.

The best cleaning method for this process, is a much debated topic, and when examining the current cleaning methods, it can be seen that as yet, not one provides a complete solution.

The current recognised cleaning methods for anilox rollers

Solvent Cleaning

If cleaning results were the only consideration, then a solvent process could be more than satisfactory.

One of the most effective solvent cleaning method involves immersing the rollers in cleaning tanks, which contain highly aggressive solvents. The solvent solution is circulated to promote a cleaning action, resulting in the solution literally burning off all traces of the ink.

The cleaning results are good. However using solvents is a notoriously hazardous and complicated process, governed by lengthy health and safety directives, and detailed environmental legislation.

In order to carry out responsible solvent cleaning, operator safety must be given the highest priority, environmental issues must be complied with, complicated effluent disposal processes and documentation must be completed, and preventative action must be taken to guard against never ending risks such as toxicity, flammability and possible leakages.

In addition, the ceramic coating on the rollers is porous, which means that the solvent solution can seep through the roller onto the Anilox base. Regular exposure to aggressive solvents has the potential to cause corrosion of the base (especially if made of aluminium), and this can severely shorten the expected life span of the roller.

Putting it in perspective, the whole process is costly, hazardous, and subject to risk. The question remains therefore, if any benefits of solvent cleaning can now ever really outweigh the hassle.

Ultrasonic Cleaning

Ultrasonic Cleaning systems are another established cleaning method for Anilox Rollers.

The rollers are again submerged, this time in Ultrasonic Cleaning tanks, which contain transducers. The transducers (when placed in liquid), produce an ultrasonic frequency wave, which in turn causes the production of millions of microscopic bubbles. The pressure of the ultrasonic frequency causes the bubbles to implode, and this action coupled with the size of the bubbles means that they are able to get inside the anilox roller cells and effectively dislodge and clean out all ink traces, and any other unwanted residues.

The problem with ultrasonic cleaning however, is that wave frequency distribution levels in an ultrasonic tank can be inconsistent, and any instability like this can cause damage to the fine ceramic coating wall of the roller. 

The ultrasonic cleaning method only works if frequency distribution stability is guaranteed. If not, then the whole process becomes a fine balance between achieving a satisfactory clean, and potentially destroying the roller altogether.

Sodium Bicarbonate Process

A traditional method for Anilox roller cleaning, is via the Sodium Bicarbonate process.

Based around the concept of refracture, a combination of air pressure and a specially developed sodium bicarbonate medium is blasted at the roller assembly. The sodium bicarbonate crystals, break into smaller crystals upon impact, and these smaller crystals are able to get right inside the roller cells and break up the dried ink.

Whilst this method has its advantages, and is environmentally friendly, it is still potentially flawed.

There is some concern that the powder residue being blasted at the very thin roller cell walls, could break down the walls, leading to cross contamination and ink transfer inconsistencies. It has also been noted that this method does not always work on very tough inks or varnishes

Laser Cleaning

Laser cleaning of anilox rollers has been put forward recently as an alternative to the  other methods. This involves a laser beam being finely tuned onto the roller cells, and burning off dried inks.

Whilst this causes no damage to the cell structure, and can remove tough inks and varnishes, it is a very costly process, and is therefore not practical as an option for regular maintenance procedures.

A new method:

Water-based Spray Washing

A new method for cleaning Anilox rollers has been developed by degreasing and cleaning equipment specialists Partswash Ltd.

The aim has been to produce a system, which would include all the benefits of the previous cleaning methods yet none of the hazards.

The results has been a cleaning method which produces an exceptional deep clean, has low environmental risk, causes no damage to the rollers, and is both inexpensive and easy to use.

The cleaning method itself is essentially based around a simple aqueous based top loading spray wash system.

The anilox rollers are placed inside the top loading spray wash machine, and locked onto soft faced powered rolls. The powered rolls are carefully positioned under spray bars, which contain high pressure jets. During the wash cycle the high pressure jets spray a specifically developed water based wash solution onto the surface of the Anilox rollers.  At the same time the rollers are slowly rotated (approx 10rpm) via the powered rolls for the duration of the wash cycle, ensuring the full surface area of the roller is reached by the spray pattern, and that ink residuals are being continually drained away.

This wash process is then followed by a clean mains water rinse, which removes any remaining traces of the wash solution.

Upto eight Anilox rollers can be washed at any one time, and due to the temperature inside the wash tank, rollers generally come out dry. A special rust inhibitor has been added into the wash solution, which prevents any risk of flash rusting.

Being a water based process, there are minimal environmental issues to address. The spray wash technology provides a rigorous clean, yet causes no damage to roller surface, the cell walls, or the anilox base. The cleaning results achieved are consistent and thorough, wash cycle time is relatively quick, and Operator usage is simple.

In addition the machines are not costly to run, and are units are available to be either bought or rented.

Proven success

Printing firm Skanem were the first to take notice of the new machine, and a Partswash Anilox Spray Wash Cleaner, has been based at their site in Durham, with considerable success. Now Skanem’s other sites, are also showing an interest, and Skanem Cardiff have also just signed a new contract with Partswash.