Whilst anilox substrate corrosion was once a regular problem faced by many flexographic printers, several improvements in the manufacturing processes, better awareness of maintenance procedures, and improved technology regarding cleaning solutions and machinery have all led to a marked reduction in this problem.
Although the problem of base metal corrosion, which leads to blistering of the ceramic coating has greatly reduced, we still see an excessive number of anilox rollers requiring a complete refurbishment due to corrosion.
Substrate corrosion on anilox rollers can have catastrophic consequences on your business through poor print quality, disrupted schedules, and print rejects. Regular inspection of your anilox rollers can avoid significant damage and related costs.
So, what is ‘base metal corrosion’, and how can it be identified?
In simple terms the blisters form when the ceramic coating loses adhesion to the steel base of the roller. These raised areas are often too small to see upon initial inspection but can be identified by feeling the surface of the anilox roller for small, raised areas.
The problem also shows itself by causing ‘flying saucer’ shaped patterns in the print, usually more apparent on block solid areas where they initially appear as 1 or 2 random patches but can quickly start to appear across the full surface of the anilox roller.
The raised areas will then start to damage doctor blades or rubber rollers leading to lines appearing through the print. If left untreated the anilox coating can break away entering the ink system. Once trapped between doctor blades or rubber rollers these particles will cause further damage, scoring the anilox roller surfaces.
Print Tech Solutions have carried out extensive research on the problem, including laboratory testing of products, analysing manufacturing techniques, through to detailed inspections of affected anilox rollers. This has given us a much better understanding of what causes the damage.
What causes ‘base metal corrosion’?
Base metal corrosion problem can be caused by several factors, starting from the manufacturing processes and base metal material selection all the way through to treatment of the anilox rollers, and the products and processes used to clean them.
Base Material Quality
If we start with the material selection it is essential that the standard of steel used to manufacture the anilox roller body is premium quality. Impurities and inclusions within the steel can start to corrode after the anilox is complete, thus undermining the integrity of the bond between the anilox roller base and the coating. Cheaper steel can provide significant cost savings on new anilox manufacture, but really it is false economy.
We have seen an increasing number of anilox rollers that have been manufactured using poor-quality steels. When the coating is diamond ground in small increments a picture starts to form highlighting where the problem stems from, and where poor-quality steels have been used this can be seen in the form of small corrosion pits or holes.
To help explain the problem we can draw parallels with laying a new road surface. Placing tarmac on a poorly prepared road surface, will after a short period, result in the road deteriorating. We’ve all experienced cracks in roads which leads to potholes forming. The only way to prevent this from occurring is to ensure the surface underneath is properly prepared initially.
Another major factor in ensuring anilox longevity is the manufacturing process. Small details can make a significant difference to anilox life expectancy, for example roller bases should be prepared for plasma spraying immediately before the process, otherwise oxidation and potential contamination could affect the integrity of the base.
This important practice can be overlooked unless a regimented ‘just in time’ production schedule is adhered to.
Another key element of anilox coating is the use of Nickel Oxide as a ‘bond coat’ prior to applying the chromium oxide ceramic outer coating. Not all manufacturers include this process on every roller, but despite the additional time and cost involved this process is proven to increase the bond and adds an additional level of protection to the anilox roller steel base.
Sealing the Coating
One other key component to avoid base metal corrosion is the application of sealant. Again, this process is not adopted by all suppliers, but the extra time and cost involved is well spent. Despite significant improvements in plasma spraying technology and no matter how good the plasma coating is, there will always be a small level of porosity that must be sealed to avoid any ingress of water, inks, cleaning products etc.
Ongoing Care of Your Investment
Anilox rollers are a core element to your flexographic print. Having made a significant investment in purchasing the right anilox rollers for your print, it is essential that you carry out a few simple steps to avoid unnecessary and avoidable damage:
- Inadequate storage – Always store anilox rollers in wooden storage boxes, in a dry location. Damp warehouses provide the ideal environment for corrosion to begin on the journal ends of your anilox base.
- Impact damage to your anilox roller can chip away the ceramic and bond coat layers, exposing the steel anilox base to oxidisation. It is important to always handle anilox rollers with care during installation and avoid any impact damage throughout their life cycle.
- Only use approved cleaning methods and products to clean your anilox rollers. Exposure to unsuitable cleaning products can lead to blistering that only appears months, or even years after exposure. Unapproved cleaning methods can also lead to ‘micro-fractures’ of the ceramic coating leading to exposure of the base metal.
Following these guidelines and tips will help you protect your precious anilox rollers and assist with their optimum performance and pro-long their lifespan.
If you need help with your anilox roller and flexographic print care and maintenance, Contact our team now.
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