Anilox sleeve and roller from Harper Corporation
It is essential for all flexo printers that the anilox gives the correct ink density from the first print and stays consistent throughout the whole run regardless of which cell structure or shape is used, and the anilox manufacturers are going to great lengths to achieve this. By Michal Lodej.
In recent years the flexo print process has enjoyed a period of persistent growth thanks to new advancements in ink, anilox and plate technology, as well as printing presses. These improvements have elevated flexo reproduction capabilities far beyond what has traditionally been possible and put flexo on a similar level to offset and gravure printing techniques.
Printers and converters today are under pressure to achieve consistency and repeatability, with everything from ink viscosity, dot gain and density, to feeds, speeds and waste being measured and analysed, and the ink transfer from the anilox is scrutinised now more than ever.
Making the anilox
Harper Corporation uses new technology, equipment and software developments to scientifically measure its processes to maintain consistency. The company uses thermal spray plasma systems in the ceramic coatings process, Echoplasma. The coating of the anilox is the foundation that ensures all subsequent processes stay consistent. The hardness of Harper’s ceramic coating averages 1200 Vickers (the unit hardness is measured in) with a coating range of between 1100 to 1300 Vickers, providing a durable ceramic coating that is not too hard or too soft. A harder surface becomes more brittle which can lead to damage and a softer coating can cause pre-mature wear.
As part of the finishing process, every anilox surface is measured using a non-contact surface finish instrument and the Roughness Average (RA) is recorded. RA measuring gauges are used to measure roughness after polishing and before the surface is engraved. The lower the RA number, the smoother the component. Every anilox roller manufactured by Harper, regardless of specification, must have a RA of 3.0 or lower before being engraved.
Harper uses a 500 Watt fibre optic engraver, which is the company’s standard offering for cell profiles that are more defined with tops and cell walls which are more crisp and smooth. The company uses interferometry to measure its anilox volumes and to check that the rollers are made uniformly. Every anilox engraved is set up in the laser using 3D quality control measurement verification prior to engraving, and checked across the anilox surface after engraving. The 3DQC interferometry ensures a consistent cell volume across the face of the roller. This allows printers to provide their customer more consistent print quality.
Apex International, which recently changed its name from Apex Group of Companies, uses laser technology on its range of conventional anilox rollers and its GTT slalom cell structure anilox rollers.
The base of the anilox is a steel roll, which then has a ceramic, titanium and water mix sprayed over it. This is then fused to the base using a flame. Once the ceramic is built up, it needs to be smoothed down. Smoothness is the most important aspect of any anilox roller, but when using a material as hard as ceramic there is only one substance that is physically able to do this, namely diamond.
The GTT metering rollers feature laser-cut slalom structured channels as opposed to the tradition hexagonal cells. According to the company this type of engraving is smoother as the laser is working as a constant beam rather than through quick short bursts used to create the hexagonal cells. It can also make shallower cells, which again helps the ink transfer to the plate.
Lifespan analysis
Sandon Global has invested heavily in research and development to ensure that print quality and efficiency is optimised for its customers. This is highlighted by recent developments in anilox sleeve manufacture. The company has been able to re-design and test onsite the construction of its component parts. These developments are anticipated to extend the lifespan of anilox sleeves in terms of overall concentricity and a more resistant nature to abrasive mechanical cleaning systems.
At the beginning of this year, Sandon installed a sixth laser in its laser laboratory, which comes complete with anti-vibratory isolated flooring to maintain engraving consistency. The laser, supplied by RHO, will help increase the parameters of laser engraving the company can achieve. Sandon is currently developing two new engraving styles, HVP+ and xPro, which it said will improve efficiency and longevity of cell structures. The new engraving formats will compliment the company’s current suite of engraving products, such as iPro, HVP, HOW and HOC.
Much of the company’s focus is on statistical quality control. This includes the implementation of a metallurgical laboratory to continually improve and maintain the standard set for its chromium oxide (ceramic) coating. It has the facility to carry out tab sample analysis in house, which is a critical aspect of its measurement and control programme.
Furthermore, Sandon is working in partnership with one of its clients to analyse the lifespan of its engravings in terms of volume and cell degradation. This data will enable accurate prediction of engraving life expectancy. The advantage is that the customer will be able to take pre-emptive steps to replace an anilox prior to it causing downtime on press due to low densities and thus increasing overall press efficiency.
Inspecting print
New advancements
Cheshire Anilox Technology recently developed MaxFlo XT engraving, which it said is a major step forward in ink transfer efficiency, enabling flexo printers to achieve up to 10% increase in colour densities.
This channel engraving pattern has a continuous spiral structure made possible with the screening software in its new ALE laser. This software allows the company to expertly control the internal dimensions of the continuous spiral channel, widening it to provide a higher ink carrying capacity and improve its release characteristics.
According to the company this new innovative engraving dramatically improves ink transfer by as much as 15%. Its continuous cell structure has 50% less land area than 60° or elongated 75° hexagonal engravings because there are fewer cell walls. This offers a more efficient and finer ink distribution to the plate. Consequently MaxFlo XT promises to deliver high ink densities with the absence of voids improving ink transfer.
Customers are reporting an average increase in colour densities of up to 10% compared to conventional engravings. Uniformity of coverage, reduction of pin holing and smooth and cleaner vignettes perfectly fading out to zero, are other reported benefits of the MaxFlo XT engraving.
‘Improved results are immediately visible in the print as increased densities provide higher image contrast and greater colour vibrancy,’ explained sales director, Sonia Arcos. ‘Once our customers try this new engraving they never revert back to the old styled cell engraving.’
Anilox Laser Technology (ALT) has seen steady growth due to the development of its existing cell geometry and the success of its new Nano cell technology. The company recently attended a print demonstration at the Swedish flexo association (Sweflex) conference held at Broby Grafiska College in Sunne, Sweden, demonstrating the advantages of nano technology. The feedback from this event was very positive and the company was able to demonstrate high ink volume transfer with minimal waste in high definition flexo printing.
The demonstration used 470 l/cm on the anilox rollers and 80 l/cm on the plates and visitors could see the benefits of using the increased line count on the anilox and increased screen count on the plate. The resulting ink transfer was accurate and consistent as the company was able to ensure the depth to opening relationship was well within the desired tolerance band.
Now operating two fibre optic laser machines, ALT intends to push on with further planned investment later this year in a third large format machine to complement its existing equipment.
Tighter tolerances
Higher ink transfer efficiency from anilox to plate allows printing with low pressure ensuring consistent quality in every run from start to finish which is critical when adopting fixed palette or high definition flexographic techniques.
Colour tolerances for high-end process printing and expanded gamut printing continues to demand tighter tolerances. Harper’s XLT 60° hexagonal engraving delivers consistency and repeatability with a tight window of colour tolerances. According to the company, the structural integrity of the hexagonal shape and the stringent control of the manufacturing process enable these engravings to meet the demand of these tighter colour tolerances.
In addition to the XLT 60° Hex cells, there are also other engraving options available from Harper, such as the XLT 30° channel engraving, which works well for UV inks, whites, varnishes and adhesives. For specialty inks, a variety of channel engravings are available; XTR 60°, XTR 89° or the 45° Tri-helical engraving. These engravings work great for solids, heavy laydowns and specialty inks such as metallic, glitter, fluorescents and tactile inks.
Different applications
Pamarco treats the application of anilox for flexible packaging markets differently, understanding that with the use of non-absorbent film substrates, anilox cell volume frequently takes a secondary position to the primary goal of accurate control and placement of dots. The high ink transfer from the company’s EFlo cells can be particularly useful when trying to print difficult, highly pigment whites or combinations of full and half tone images. However maintaining optimum control of inks by the use of multi-hit high volume fine screen ThermaFlo (60°) cells can keep dot gains to a minimum. At the same time, Pamarco has resisted the trend to move towards ultra-fine (in excess of 1200 l/in) screens for HD process printing, in favour of the theory that a good selection of anilox screen count and cell volume, combined with machine polishing of the cells, provides the best possible solution for precise, long lasting high graphic flexible packaging printing.
Having invested in YAG lasers, Pamarco can create all varieties of cell profiles from standard 60° ThermaFlo cells, through to innovative 75° extended EFlo and the EFlo UV.
The company has conducted banded roller trials of the application of EFlo that has enabled this cell technology to be applied successfully into various printing markets, such as corrugated paper, flexible packaging and labels.
In the corrugated paperboard market, this application work has led to the standardisation of anilox cell specifications for different types of paper boards. Irrespective of the graphic demands of the print, in corrugated printing, the absorbency and surface deviations of the substrate, dictate the amount of ink required. In conjunction with its major clients, Pamarco has established EFlo and ThermaFlo anilox specifications for the four major categories of paper. This approach of establishing a target cell volume for each paper, for example 11 cm3/m2 for Kraft paper and 4.5 cm3/m2 for coated papers, means that printers can still be flexible and select conventional 60° cells or extended 75° cells with a range of screen specifications, but still be sure they can achieve excellent board coverage and ensure inks are dry on substrates.
(L-R) EFlo 75°, ThermaFlo 60° and UVFlo 45° engravings from Parmarco
For UV inks
Not all inks are the same and if some printers opt for UV curable inks, which tend to be of a higher viscosity, then they need an anilox to suit. The MaxFlo XT from Cheshire Anilox Technology is one such product that when used with UV inks helps to eradicate the common problem of spitting. The continuous engraving improves the ink flow within the anilox eliminating the build-up of ink behind the doctor blade, which forces it to lift and cause the ink to spray or spit.
These inks require the anilox to allow a flow of ink between cells, effectively passing under the doctor blade and another suitable product is Pamarco’s UVFlo and EFlo UV, which can both give precise and controlled transfer of inks onto high graphic printing plates, whilst maintaining a smooth flow of ink past the doctor blade, eliminating any risk of ink spitting at high press speeds.
Anilox care
The stress caused by common printing problems is often time consuming and expensive. In many respects, searching for the underlying cause can feel like searching for a needle in a haystack.
However, help is on hand from Apex International which has established the Anilox Assessment & Analysis Program, a free service aimed at eliminating costly and avoidable printing challenges. The company will provide free, on-site process reviews conducted by trained anilox solution specialists and present customised technical advice and troubleshooting options.
‘As the world leader in anilox related technical innovation, Apex is in a unique position to help printers better understand the root causes of some of their most common challenges. Our AAA programme is designed to provide free resources aimed at diagnosing problems related to spitting and bouncing while also offering recommendations to increase press speed, ultimately helping our customers make more money,’ stated Doug Jones, vice president of global marketing. ‘And although the programme is intended to improve the Apex experience for our customers, this service is available to anyone looking for solutions to these issues.’
