Gravure printing of the future – sustainable, premium quality print
von Ansgar Wessendorf,
The HelioGreen Process is a three-pronged strategy developed by the Heliograph Holding group that offers a radically different way of producing the gravure forme and that therefore fundamentally changes the entire gravure printing process. Helio Pearl, a three-step process for the production of gravure cylinders, is a key part of this strategy. Flexo+Tief-Druck talked to Christoph Gschoßmann, Managing Director of Kaspar Walter (part of the Heliograph Holding group), about this innovation and gravure printing’s future prospects.
Mr Gschoßmann, why have you chosen to unveil your new gravure cylinder production developments now? Christoph Gschoßmann: As you know, chromium trioxide, which is also known as heaxavalent chrome, is a major electrolyte for the chrome plating of gravure cylinders. As an electrolyte it is toxic but as metallic chrome it is not poisonous. The European Chemicals Agency (ECHA) lists chromium trioxide in REACH Annex 14, and the default position is therefore that its use is prohibited unless an authorization has been granted. Currently, gravure printing is covered by a so-called upstream authorization issued to the CTAC consortium. However, although the authorization has been applied for, the EU Commission has not yet reached a final decision. Until this final decision, the highest safety standards should always be adop-ted when using chromium trioxide, since this is the first application since the directive came into force. We are working on the basis that any authorization that is granted for hexavalent chrome will allow its use until at least September 2024. For the time after we anticipate the current approval will end, we are currently applying for a further authorization that is specifically tailored to gravure printing and embossing. At the same time, we are working hard on industrial alternatives and are making good progress on these. This is what has driven us to present our vision for the gravure printing of the future now. Gravure is a sustainable and top quality prin-ting process and we are seeking to give it fresh impetus and new prospects with our initiatives and new products.
In practical terms, what does this mean for gravure printing and gravure cylinder making? Gschoßmann: The climate and sustainability debate means that such applications for authorizations are now evaluated and considered rather differently by the ECHA and the EU. In the past, socio-economic studies were undertaken and evaluated, and the question of alternatives only played a subsidiary role as a side issue. Today, it is a requirement to present a detailed substitution plan along with the application, and failure to do so will mean refusal of the authorization application. Conversely, anyone who can convincingly show that they are working on genuine substitution solutions and can already point to initial field trials is highly likely to be given more time for research into and development of the alternative solutions by the authorities in question. This is now the norm. It is not just important that hexavalent chrome is eventually substituted but that companies are given enough time to evaluate and imple-ment commercially suitable alternative products.
So, you would like to secure the longest possible timespan for the use of hexavalent chrome in order to get your alternative solutions ready for the market within this period. What approach and strategy are you adopting for this? Gschoßmann: We are certain that we can make gravure forme production better, faster and more sustainable. Heliograph Holding is pursuing a three-pronged strategy for this involving the ChromeXtend, HelioChrome Neo and Helio Pearl projects that together comprise the HelioGreen Process. We have taken the initiative with ChromeXtend and are applying on behalf of the European gravure industry to the European Commission for longterm approval for the hex-avalent chrome process beyond 2024.
The aim of our application is to ensure that customers are not exposed to a commercial risk should they very sensibly want to continue to use gravure printing after the end of the current authorization period. Long-term approval also allows a commercially viable substitution to be implemented, with customers successfully integrating our new products into their processes once they are fit for market.
From our many years of experi-ence in gravure printing we know that safety standards in gravure cylinder production are much higher than in the rest of the electroplating industry. This means that gravure printing cannot derive sufficient further benefit from broadly based industry consortia such as the CTAC. We are, however, relying on the support of the gravure printing industry and the cylinder makers in particular for a successful applica-tion. We started work on compiling the approval submission in mid February with a large-scale survey designed to quantify the socio-economic consequences of a possible ban on hexavalent chrome.
The European Rotogravure Association (ERA) is supporting the Heliograph Holding application. With HelioChrome NEO we are taking things one step further. Kaspar Walter is developing an alternative electroplating process based on trivalent chrome that is designed to replace hexavalent chrome-based plating. This process is fit for the future, not governed by regulations and exhibits low toxicity. It can be seamlessly integrated into today’s gravure cylinder production process. Helio Pearl is a new polymer based gravure cylinder production process that does involve electroplating. In future, it could supersede traditional cylinder production.
What is the timescale for your three-pronged HelioGreen Process strategy? Gschoßmann: First of all there is our application for ChromeXtend approval, which we would like to submit in the second half of the year. In our experience it then takes around two years to be considered by the European authorities, mean-ing that we might expect a decision on a seven to twelve year approval for hexavalent chrome in the gravure printing industry by early 2023. Meanwhile, we want to present HelioChrome Neo to the market and have further discussions about some initial beta sites. Of the three, Helio Pearl is the project that is still at a comparatively early stage in its development and it is still several years away from being ready for the market. The substitution of hexavalent by trivalent chrome is being followed very closely by the entire electroplating industry.
What are the particular challenges for such a new process in gravure printing? Gschoßmann: The hard chrome layer of the printing cylinder is subjected to considerable mechanical stress by the doctor blade and abrasive substrates during gravure prin-ting, and so the wear, friction and lubrication of the chrome layer needs to be precisely tailored to these requirements. The trivalent chrome processes that are becoming commercially available in other industries do not satisfy these requirements. An additional nickel layer is also required for corrosion protection and this entails further health and therefore regulatory risks. Development work on Helio Chrome Neo is well advanced and the first pilot system is already being alpha tested at a well-known customer. Together, we are jointly conducting intensive trials with a view to further optimizing the process parameters and the first commercial orders have already been successfully printed by trivalent chrome cylinders. Our aim is to deliver the surface properties with HelioChrome NEO that one is accustomed to with hexavalent chrome. Ultimately, the customer should not notice any difference between prints from a trivalent or a hexavalent chrome cylinder. In the past there have been repeated attempts to replace copper and chrome with plastics or polymers in gravure cylinder production.
What reasons are there to think that this time round it will be different with Helio Pearl? Gschoßmann: We have been conducting numerous extensive tests since 2016 as part of the development of the Helio-Pearl process. It rapidly became clear that con-ventional polymers were not able to fulfil the demanding requirements placed on materials during gravure printing. Working closely with a well-known research institute we have therefore developed a new formulation for a hybrid polymer that possesses the required properties and that is easy to work. On top of this, major advances have now been made in imaging technology. Previously, the use of plastics primarily foundered on two conflicting requirements that are nevertheless crucial if a gravure forme it to be fit for purpose.
On the one hand, the material must guarantee a relatively long life for the gravure cylinder during the printing of long runs. This requires a high degree of hardness or wear resistance to the doctor blade and abrasive inks. On the other hand, the material must be soft enough (i.e. less wear resistant) so that the stylus can penetrate the layer during electromechanical engraving without it breaking or suffering extreme wear. Until a couple of years ago it was not possible to satisfactorily reconcile this conflict. The rapid development of laser technology opens up new prospects for the imaging and structuring of very different materials. New or improved laser sources have now become available for industrial use. Not only do they offer better quality engraving, they have also become faster, more productive and more cost effective. Even five years ago we were only able to laser our polymer material under laboratory conditions and on a small scale.
Today’s laser sources are capable of directly imaging hard and wearresistant materials. This in turn means that the material is less crucial for high quality laser engraving than it is for the electromechanical engraving of the copper layer of a gravure cylinder. Over the decades, the mechanical and engraving properties of the copper have been optimized for engraving by a stylus.
Laser technology has a number of other advantages over electromechanical engraving: screen ruling, cell volume and cell geometry can be freely configured independently of each other. With a laser it is, for example, possible to engrave cells with both a fine ruling and a high cell volume. These capabilities are currently opening many doors for us that will allow gravure formes to be developed further and to secure the future of gravure printing. However, there is still some time to go before every substrate, every doctor blade and every ink system has been thoroughly tested with our polymer-based Helio Pearl gravure cylinder.
What is the goal of your Helio Pearl gravure cylinder development project? Gschoßmann: The goal of our project was the development of an information carrier for printing small batches of packaging in the form of a short run gravure cylinder with a mechanically stable polymer surface that could be engraved by laser and that would last for a total run length of 100,000 metres. Market research carried out by us found that the average run length today for a gravure cylinder in packaging printing is around 30,000 metres and that it is reused an average of three times. Pretty much every printer that we spoke to confirmed that these figures reflected day-to-day reality in a packaging printer.
What requirements must this polymer material fulfil? Gschoßmann: Before embarking on this substantial project we defined a series of requirements and properties that a polymer-based engraving surface must fulfil., and for this we were able to draw on our existing comprehensive gravure cylinder production know-how. A fundamental requirement is that the material layer must be resistant to solvents. During the printing process the polymer should not swell on contact with solvent-based inks and coatings. For stable and reproducible laser engraving the polymer layer needs to be as homogeneous as copper and chrome, whose surfaces are extremely homogeneous as a result of their electrolytic deposition. Furthermore, the polymer must exhibit outstanding coating and bonding properties. We have successfully used steel, aluminium and copper as the base on which to apply the polymer without requiring an intermediate layer to anchor the polymer. Here it was very important to us that gravure printers should be able to use their existing printing cylinders in this new gravure cylinder production process. This is because a gravure printing plant will house thousands of metal printing cylinders that can be repeatedly re-coated and imaged. Being able to use the existing stock of cylinders makes both environmental and economic sense. However, new carrier materials or cylinder concepts are also conceivable.
How did you go about searching for the right polymer? Gschoßmann: In order to evaluate wear resistance we set up a test bench to study wear, friction and lubrication in the Kaspar Walter facility in Munich. We then tested the polymer coatings being considered in combination with every possible type of doctor blade and ink. Materials that had previously satisfied every criteria but whose surfaces were, for example, sensitive to scratching, rapid abrasion or prone to slight scumming were removed from the “pool of favourites”. This allowed us to narrow down the candidates to the polymer that was the ideal material for the production of gravure cylinders.
Does the polymer material match the hardness of chrome? Gschoßmann: No. The polymer material is not as hard as chrome. Nowadays, the hardness of copper measured in Vickers is used as an indicator in electromechanical engraving of how it will behave when cut by a diamond stylus. The hardness also allows certain conclusions to be drawn about the wear resistance of the chrome during print production. Essentially, in such a system, the chrome is harder than the doctor blade. In the course of our numerous and extensive test runs we have found that the wear resistance is good, although its hardness is lower than chrome. For Helio Pearl therefore we need to re-evaluate the way the doctor blade, surface and substrate interact in terms of wear and friction.
What stages does a Helio Pearl gravure cylinder need to pass through during its production? Gschoßmann: The production of a Helio Pearl laser engravable polymer monolayer gravure cylinder is a patented process that involves just three steps. In the first, the pre-polymer is applied to any desired gravure cylinder in the coating unit. Next, the polymer layer is cured and then finished in the grinding and polishing machine. Grinding the cylinder’s surface ensures that its geometry and circumference are precisely right. It is also given a defined surface roughness of between 0.5 and 1.0 Rz that depends upon the substrate.
The final step is the imaging of the finished polymer cylinder using a high resolution laser. Subsequent finishing is no longer necessary, which has the attendant advantage that the direct laser engraving of a Helio Pearl gravure cylinder can be left to the last possible moment or immediately prior to print production. As a result, not only does the Helio Pearl process significantly shorten production timescales for gravure formes it also makes the entire gravure printing process faster, more efficient and more flexible. After printing, the cylinder is prepared for recoating by removing the old polymer layer and polishing the surface, at which point it is ready to be reused.
What has been the practical experience with the new gravure cylinder so far? Gschoßmann: Several intensive print trials of gravure cylinders coated with Helio Pearl have been carried out under production conditions and at a speed of 400 m/min in the technology centre of a large press manufacturer. For example, a cylinder set was used to print a 100,000 metre run of a test chart on white BOPP film. Standard doctor blades and standard solvent-based inks were used for the printing and we were extremely satisfied with the printed results. There was no scumming during the production run and – much even to our astonishment – ink transfer by the laser engraved polymer layer surpassed that of chrome. In the near future we will move forward to carrying out follow-on print trials with different motifs, parameters and substrates.
Is it necessary to use an ESA to achieve good printing behaviour? Gschoßmann: Electrostatic Assist (ESA) systems such as have become the norm on modern gravure presses to improve the emptying of ink from the cells were not necessary with Helio Pearl cylinders because of their good printing behaviour. Whether it will ultimately be necessary to use ESA systems with other substrates, such as different types of film or paper, would need to be evaluated through further trials.
What is the dissipation behaviour of the polymer cylinder like? Gschoßmann: The Helio Pearl cylinder dissipates electrostatic charge. As an expert opinion drawn up by an independent expert on printing processes and presses has confirmed, no electrostatic charge builds up on its polymer surface.
Helio Pearl – three step gravure forme production Helio Pearl is a development by Kaspar Walter. The three step process for the production of gravure formes includes not just the generation of a laser engravable polymer layer exhibiting wear and friction behaviour that is suitable for gravure printing but also the patented overall process for coating, surface finishing and imaging. The materials used are non-toxic, generate no pollution through waste water or air, and are therefore not subject to any future approval process.Helio Pearl is a single layer process involving three steps:
Step 1: Coating of any desired gravure cylinder with the Helio Pearl polymer layer instead of a copper and chrome layer
Step 2: Surface grinding
Step 3: Direct engraving with a high resolution laser
The eight to twelve steps that are currently required for gravure cylinder production are reduced to just three, with imaging being the final step, so that the time to printing can be minimized. Numerous trials over a period of years have led up to the current position and from 2016 onwards these have been brought together in the development centre in Munich set up for this purpose, over 400 blank cylinders have been coated in this facility by a specially developed machine and the best selected from over 200 combinations of materials.
Who is Kaspar Walter? Kaspar Walter is based in a modern 10,000 square metre production and office facility in Krailling just outside Munich, where its 70 or so employees design and produce state of the art electroplating systems for gravure cylinder production. Kaspar Walter also develops process technologies as well as system integration solutions that are tailored to customer requirements. High performance measurement technology completes the company’s portfolio. It is, in short, the Heliograph Group’s centre of expertise for automation, electroplating and process development.