Rollers in the deep: cleaning beneath the surface

02 Dec 2015
Topics: anilox

Anilox cleaning system from Flexo Wash

 

If you want an anilox roller to perform at its best then it needs to be cleaned properly. Michal Lodej looks at the options printers have when it comes to keeping the cells open.

The key to high quality flexo print is consistency throughout the print run, and to lay a consistent quantity of ink onto a substrate requires a clean anilox roller. Looking at the surface of a roller at a microscopic level can reveal that its cells are clogged with dried ink fragments invisible to the naked eye.

These dried ink spots can seriously alter the overall performance of a roller by reducing the volume of ink that it can hold. Trying to match colour without an accurate ink placement is near impossible; only an adequate cleaning process can prevent this from happening. There are different ways by which a printer can keep an anilox clean, however, the cell structure engraved on the surface and type of ink used should be taken into account.

Can't touch this

Some anilox cleaning specialists advocate a contactless cleaning system to prevent any damage to the delicate surface of the rollers.

Anilox cleaning specialist, Alphasonics, has a combination of cleaning techniques such as Dual Frequency Alphasound, Enhanced Super Sweep and Active Cavitation, which it says delivers five tangible benefits. These comprise no over pigmentation of inks, faster and more consistent makeready, reduced waste, higher and consistent print quality, and accurate anilox inventory management.

Meeting these conditions means printers can achieve correct pigmentation simply and effectively, have runs that are not wasted due to poor production quality and can accurately plot, measure and forecast the lifetime of an anilox.

New kid on the block, FlexoMaid, showed its contactless cleaning solution for the first time at Labelexpo Europe. The company says it can work with all types of anilox cell structures. It uses a detergent and rinsing system that is effective in breaking down the molecular links in the ink solution to help remove it from the cells while keeping water usage down. The company emphasises that new cell geometry can make it harder to clean anilox rollers than it used to be.

It is key to apply the right amount of detergent, so once the roller is placed inside the cleaning unit, the exact surface area of the roller is calculated automatically, which determines how much detergent is required. After the detergent has been applied to the roller a rinsing solution is used to wash off the residue.

The FlexoMaid unit uses a high powered air jet stream to push the ink out of the cells onto a material strip, which collects the residue, a method that creates no liquid waste. Cleaning times will vary, depending on the size of the anilox, but as a guideline it takes approximately 12 minutes to clean a 30 cm roller. 

The washer has three types of wash cycles and is suitable for all types of ink. Ten litres of detergent can make anything from 250 passes to 800 passes depending on the size of the anilox rollers.

Smaller cells

As cell sizes get smaller, the need for higher quality cleaning grows. The deeper cells can exacerbate plugging issues, which causes inadequate ink distribution, poor colour density, difficulties in getting the right colour, and a waste of time, ink and substrate. Smaller cells mean a more delicate cell structure, and these are more susceptible to damage caused by improper handling, doctor blade scoring and poor cleaning methods.

The majority of inks and coatings are formulated to resist moisture, chemicals, rubbing and scuffing. The longer an ink or coating is left to dry in the cells, the more difficult the cleaning process becomes. Also, plugged, dirty rollers create surface tension, which prevents cells from accepting and releasing the correct ink volume.

Flexo Wash says that keeping a proactive approach to anilox maintenance is imperative to becoming more competitive. Printers should do this by cleaning the rollers after each job, keeping to a regular maintenance schedule, clean the rollers immediately after removal from the press, and do this from day one.

Due to today's fine line printing, it is essential to find a safe, gentle and automatic cleaning method that will not cause wear and tear to the delicate anilox rollers.

The Flexo Wash FW Anilox Cleaning System incorporates a 'plug-n-play' system. Users insert the anilox, close the lid and push the start button. The entire cleaning process begins with a liquid spray, then rinses with high-pressure water and finishes with air drying.

Harper corp

Harper Corporation offers a wide range of liquid cleaners.

This systematic cleaning process is safe and harmless to the anilox rollers, employees and the environment as the cleaning solution is filtered for re-use again and again. To maintain results users need change the filter monthly and clean the liquid tank every six months.

Expert opinion

Troika Systems, inspection system manufacturer, has a mantra of 'right first time'. Phil Hall, managing director, said, 'At the majority of printers we see good cleaning processes. Some have cleaning equipment and others are simply hand cleaned, but often we see blind belief in what has been stated by the supplier and little or no interpretation of the cleaning achieved which has led to costly time and product waste on press.

'The majority of machine cleaning systems if used as per the manufacturers' specifications, with the chemicals they recommend work well, however, we have seen that the duration of the cleaning cycles can be rather optimistic in some units and may need extending for thorough cleaning of the anilox. Using lower cost chemical, to save a few cents, has frequently proven to be a poor investment - you get what you pay for.

'There is also a belief ultrasonic units crack and damage aniloxes; we have seen no evidence of this in the past 10 years on the multi frequency, multi sweep units. This out of date information may be legacy from earlier types of ultrasonic cleaners which is before the AniCAM was invented.

'Hand cleaning is certainly a much less efficient method of cleaning than machine cleaning, and is where we have seen the greatest variation in cleaning quality. Often because users either have not been trained to use the products properly or simply take short cuts which makes the products ineffective.'

Getting hands on

FlexoConcepts advises that cleaning should be done on a daily, weekly and monthly basis, using different methods. They say that applying a liquid cleaning agent by hand and wiping down the roller with a rag on a daily basis is the simplest and most effective way to keep an ink or coating from drying and building up in the cells. As a basic rule of thumb, the best time to clean the anilox is as soon as it is removed from the press.

The company suggests that manually scrubbing the roller once or twice per week with a brush and a paste or cream chemical cleaner will mechanically loosen and remove any ink or coating residue that remains in cells despite daily cleaning. The cleaner is applied to the roller, vigorously scrubbed with an anilox brush and flushed with water while it stays on the press. It is important to remember that stainless steel brushes are suitable only for ceramic anilox surfaces and brass bristles should be used for chrome surfaces to prevent damage to the engraving.

Over time a residual amount of ink or coating material is left behind in the cells and the anilox requires a deep cleaning on the press to remove these tough deposits. Types of deep cleaning vary in effectiveness, risk of damage to the roller and water and chemical consumption.

Recyl Graphics reminds us that there is no clear consensus, nor a best method to clean anilox rollers. The cell structure, the type of ink/coating, the application and most importantly, the expectations of the printing and finishing professionals make it tough for one method to stand above the rest. 

Arnold Cosme, global OEM relationship manager, Recyl, said, 'Printers generally ask me - which is the best method to clean an anilox and after having spent two decades in the industry, I still call it a trick question. Many new players in the industry, on the other hand believe in saying, 'This is the best method for everyone because I specialise in it'.'

A word with the makers

On the manufacturers front, Anilox Laser Technology focuses on the geometry of and sizes of a cell and offer tailor made awareness sessions looking further into these aspects. The company says it is imperative the print teams and pre-press crews have a good awareness of the anilox and how to care for and handle them. It likens not knowing the specification or condition of the anilox roller to driving a car without a dashboard.

Harper Corporation says that a proper cleaning brush is a .003 inch stainless steel bristle brush or the Poulsonator Brush with two stainless steel brushes which should be used with an effective industry proven cleaner or detergent as well. In addition to the cleaning tools, you will also need a handheld microscope with 400X magnification to view the anilox roller's condition, however, there are other more sophisticated tools needed that will help with getting the proper analysis at a glance. Other more expensive scopes are available and should be considered if printers have a large inventory of rollers. The AniCAM and the MicroDynamics 3DQC are more sophisticated instruments that can measure line screen and calculate volume.

Knowing what to look for is the key to visual inspection. There are also more sophisticated tools for visualising line screen and even calculating volume. If a quick check is required, an Echochek can be provided by the anilox supplier. This is an impression tape that takes a visual picture of the anilox and also yields the volume of the roller at that time. 

Zach Root, technical sales engineer, Pamarco, commented, 'Major sources of help for these problems can be found in the recent advancements within the anilox roller industry. These advancements have given rise to innovative cell geometry and a greater consistency of engravings. It is critical to continuously educate and be educated on the rapidly evolving technologies and growth of the flexo industry.

'Investing valuable time to properly train employees, and undertaking collaborative technology implementations with key suppliers will translate to the bottom line. Sometimes the way to get a message across or receive a higher plane of focus is by bringing in someone with a fresh outlook. The press operators are the most knowledgeable about their individual revenue generators, so empowering them with the tools and knowledge they need will create a greater sense of ownership and openness to change.' 

Apex International recommends that anilox care should involve much more than just keeping them clean. The company advises its customers that they need to be aware from day one and should inspect any new anilox that enters the facility immediately. 'One of the biggest mistakes a printer can make is simply adding an uninspected anilox to inventory, particularly if it arrived in a damaged crate.' said Doug Jones, vice president of marketing. 'By identifying issues early, anilox companies are often able to help correct the issue before it disrupts print production.'

Anilox rollers are not 'set and forget' components, and the company advises that once the anilox is installed, it should never run dry with the ink chamber against the roller as doing so can cause excessive doctor blade wear and potentially score the anilox.

Keeping the roller running while ink is in the chamber will help prevent standing ink from drying in the cells. The company adds that if plugging does occur printers should follow a proper cleaning schedule that includes chemical cleaners with a pH between 6.5 and 10.5. Chlorine, ammonia or any cleaning solution that is 100% acidic should never be used as these will corrode the anilox. Finally, the anilox should be stored either covered on a rack (to prevent contaminants such as dust from entering cells) or in its original crate, taking care that the surface is 100% clean and dry prior to storage.

A closer look

If the anilox has not been properly cleaned it is usual to see that the cells have retained ink, as well as seeing the volume is lower than usual.

Mr Hall commented, 'Once printers have learnt to interpret the 3D images from the AniCAM, many have modified their cleaning processes. Sometimes for more regular cleaning and in some cases to reduce their cleaning regime, but in all cases where they have chosen to optimise their cleaning processes they have seen improved press set up times and reduced ink waste by reducing the need make ink adjustment to achieve the correct density.'

A regular cleaning regime is important for printers who want to achieve the best possible results on a consistent basis, but what may be more important than cleaning regularly is a deeper understanding of the roller itself. Understanding which cell structure the roller has along with what type of ink was used with it should lead to an informed and structured cleaning programme.

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