Digital Plates C. Holland

Transcript

√p9-10 Kodak:•7-8 Simon XML feature 29/9/08 17:56 Page 1 OCTOBER 2008 9 Production Journal DIGITAL PLATES To process or not to process One of the main topics at this year’s IfraExpo in Amsterdam is expected to be the so-called ‘chemistryfree’ or even ‘processless’ newspaper plates. But what does this actually mean? CARYL HOLLAND visits Kodak’s r&d facilities in Windsor, Colorado, to find out VIRTUALLY ever since computer-to-plate (ctp) technology was introduced, the holy grail has been to develop a processless digital plate. This is not surprising really since who doesn’t want to eliminate plate processing? Not only does it mean a reduced need for people and hence lower labour costs but it also eliminates a number of the variables in the production process. Then, there is the cost of plate processing consumables, plus the cleaning and maintenance of the processor. If to this is added the environmental factors, it all adds up to some significant benefits. To understand what has to be done to achieve a processless plate, it is necessary to go back to basic principles. What better place to do this than at Kodak’s research and development facilities at its plate manufacturing plant in Windsor, Colorado. For one thing, Kodak is somewhat unique in that it not only designs and manufactures platesetters, plates and digital workflows for the newspaper market but it also uses both thermal and violet laser technology. In addition, the core competency of the r&d labs at Windsor is what it calls ‘non-process’ digital plate technology. As is explained by Chris McCullough, head of the in a quarter of a second and research and development could be required to occur up group at the Windsor plant, to one million plus times in although offset litho printing is succession. taken for granted, technically it As McCullough points out: is an amazing achievement. For “When you think of what the instance, an image measuring, ink, the fount and the plate are say, 40 x 28 inches is formed by doing, it is a stunning tribute to splitting a film of ink four the robustness of litho”. microns thick, not once but Put like this, it is also obvitwice - from plate to blanket ous that the plate’s job is not and then blanket to paper. an easy one. Nor is plate manuThe ink is emulsified in an facturing and, as McCullough aqueous solution to a depth of admits, it is even harder maka few molecules and, with an ing digital printing plates. As is image of this size, is carried by explained by Mike Rundle, 19,250,000 halftone dots averprogram manager, Kodak aging in size from ten to 60 Graphic Communications microns. The final ink film Group: “With analogue plates, over the whole 1,120 square the energy is applied to the inches of the image has to be plate using either a step and held to a thickness of about one repeat machine or a vacuum micron with a tolerance of +/printing down frame and the one tenth of a micron, while energy is literally applied by the positional accuracy has to the bucketful. This creates a be held to within around 40 greater reaction, enabling an microns. And if this is not bad enormous amount of latitude in enough, all this has to happen the coating. ● Chris McCullough and Jeffrey Collins, research scientist, discusses the printed result ● Jack Knadjian, vicepresident for newspapers at Kodak GCG “With digital plates, be they violet or thermal, you are putting energy on the plate with the equivalent of an eye dropper. So the reactivity needed in the coating and the consistency of that reactivity are exponentially different than for analogue plates”. And there are additional challenges due to the automation of the modern computerto-plate (ctp) systems. For instance, if the plates are not cut square every time, an automatic platesetter will not be able to load them. Also, if the interleaving is not right, you won’t be able to de-interleaf. There are also enormous challenges on the coating side as is pointed out by McCullough: “A printing plate is a product full of conflicting requirements. For example, there is the hydrophilic/ oleophilic balance – the aluminium substrate needs to ● Mike Rundle, program manager at Kodak GCG checks the sheet carry water on press so it needs to be hydrophilic but the coating needs to accept ink on press so it needs to be oleophilic. “However, the coatings are organic formulations which require organic solvents and have to coat the hydrophilic substrate. In addition, portions of the oleophilic resin needs to be dissolved in an aqueous solution which is hydrophilic, while the remaining oleophilic resin has to stick to the hydrophilic substrate for many impressions on press. “The compromise needed to do all that is phenomenal. It is amazing that it works at all and yet thousands of people use it every day without giving it another thought! “Admittedly, non-litho coatings such as paint are made all the time but they tend to be cured straight after being applied as when painting cars. We have to put a coating down which will arrive at the customer in exactly the right condition, will react when the customer wants and in exactly the right place. Customers also want the coating to be as reactive as possible so that it images faster. “However, the more reactive it is, the more unstable it becomes. So another compromise is that the faster the plate, the more careful you have to be with the shelf life. All these compromises have to be balanced which is why it is so challenging”. Despite this, since it was first introduced back in the early 1990s, digital plate technology has improved significantly. As is explained by Jack Knadjian, vice-president of the newspaper market segment at Kodak’s Graphic Communications Group: “Today, most of the popular plates in the world of newspapers, whether thermal or violet, have at least two layers. The actual underlying technology in terms of their chemical make-up and structure is simi- lar whoever is the manufacturer. The difference is in the sensitiser. “The plate consists of a substrate (the electrochemically grained and anodised aluminium), the photosensitive image forming layer (photopolymer components with sensitiser), which is called the base coat, and the water soluble polyvinyl alcohol (PVA) oxygen barrier top-coat. With newspaper plates, the base coat is soft to enable additional reactivity in the plate so as to meet newspaper productivity demands. “As well as helping to protect the soft base layer, one of the most important things that the top-coat does is to keep oxygen from getting to the base coat where the reaction takes place. If this happens, it stops the reaction so no image or only a weak image is formed”. Knadjian continues: “All plates whether they are photopolymer violet or photopolymer thermal go through the same multi-step processes. First, there is the exposure where the laser causes the sensitiser to release the “free radicals” which start polymerisation or the cross linking of the monomers. At this stage, a weak temporary latent image is formed, not yet strong enough to survive the printing press. “To strengthen the image, the plate is put into the preheat section of the processor. This energsies the molecules and allows the monomers to cross-link further continuing the reaction started by the laser. The aim is to create as long a chain and as many chains as possible since that is what is going to give the coating hardness and consequently a long life on press. “The next step is the prewash, which removes the water-soluble PVA top-coating and exposes the photopolymer image layer. The plate is then put in the dip tank to remove the unexposed and therefore soluble coating. The developer in the tank, which these days, is an alkaline solution of around pH 11, loosens the unexposed photopolymer and brushes remove it. “The photopolymer particles remain in the developer which consequently needs replacing at some point. It also needs replenishing. “We then rinse off the plate to remove any developer solution remaining, and the gum section applies a protective layer which is subsequently dried. This completes the six stages in a typical photopolymer processor and is what we call the wet process”. Knadjian then turns to the so-called ‘chemistry-free’ violet technology which, he believes, should be described more accurately as combined developing and gumming. “With this, there is still the laser exposure to create the latent image and the pre-heat process to continue the crosslinking reaction to create a hardened image. There is, however, no pre-rinse and so the plate is put straight into the single bath dip tank with brushes. “This contains what I would describe as a “specially conditioned” gum solution since it does not just consist of gum. However, it does have a lower pH than the developer used in the wet process. “This solution removes the PVA protective top-coat layer, loosens and removes the coating which has not been exposed and applies the preserving gum: as the gum is already in the solution, post rinsing is unnecessary. The plate is then dried. “Since both the PVA and the photopolymer particles are now suspended in the gum solution, it has to be replaced from time to time. The tank also has to be cleaned in the same way as with the wet process. In other words, with the violet “chemistry free” process, the only Continued on page 10 ➤ √p9-10 Kodak:•7-8 Simon XML feature 29/9/08 17:57 Page 2 10 OCTOBER 2008 Production Journal DIGITAL PLATES ➤ Continued from page 9 things which are removed from the process are the prewash and the post-rinse. “This makes the process more environmentally friendly because it uses less water and there is a lower pH value but the soiled gum solution still needs to be disposed. You also still have to maintain and clean the unit – as there is no prewash process, the solution is loaded with PVA as well as polymer which can cause biological growth”. Knadjian also questions whether the chemistry-free violet process is more stable as is also often claimed. “Two rinse sections have been removed from the processor but rinsing does not cause instability. This is caused by variations in the Gausian laser, and the pre-heat and developing processes, all of which are still used.’ Future prospects Admittedly, Knadjian and indeed, Kodak generally, does have somewhat of an axe to grind. For one thing, it does not manufacture a violet ‘chemistry-free’ plate, although it does offer the VioletNews ctp system including a violet plate for the lower end of the newspaper market where capital investment is an issue and higher productivity is required than is available with its manual loading thermal Trendsetter News SA platesetter. Secondly, and more pertinently, Kodak’s main focus is on thermal technology where it has a USP in the newspaper market. Indeed, more impressive are the arguments in terms of the future potential for thermal technology. “We have always had the ability to produce the thermal equivalent of the violet chemistry-free plate,” says Knadjian. Indeed, this technology which Kodak is calling ‘simple process’ was demonstrated in the labs at Windsor during our visit. The additional bonus of this technology is that it eliminates the need for pre-heat which is still required for the violet chemistry-free plates. As Knadjian explains: “With the simple process, because the thermal laser can deliver such high amounts of energy, it can cause the sensitiser to release enough “free radicals” to complete the polymerisation of the monomers and so form a press-ready image. There is therefore no need to pre-heat and so we can go straight from exposure into a simple one bath processor where a mild wash-out fluid with an almost neutral pH removes the PVA top-coat and the unexposed polymers. The plate is then gummed and dried, and is ready for printing. So, with such a technology, we are down to two processing steps, develop and gum. “However, we made a conscious decision to skip this intermediate development stage and go straight for a “non-process” newspaper plate. In other words, a plate which does not require a separate processor and is “developed” within a few revolutions of the press”. Indeed, Kodak’s PF-N plate, which is an extension of its ThermalDirect commercial plate, is already being used at some 15 newspapers in the United States. “The way it works is that the fount solution softens the photopolymer which allows it to be removed by the ink,” explains Knadjian. “The ink is almost like a glue taking the unexposed coating and depositing it on to the paper”. McCullough adds: “If you look at current thermal technology, there are materials in the developer which swell the matrix. You then have brushes in the processor to help take it away. With the develop-onpress plate, we are sort of using the fount as the swelling agent and then the tackiness and pressure of the ink and the dampener to remove the physical components on to the first copies put through the machine”. Both McCullough and Knadjian believe that such a system would be practically impossible to achieve with violet technology. As McCullough points out: ● Thermal computer-to-plate systems have made significant progress. Kodak’s Generation News platesetter is now one of the fastest on the market, whether violet or thermal. This has been achieved by reducing the ‘dead’ time in the operation such as plate loading, mounting and unloading, as well as by shrinking the size of the drum “There are real big barriers against having a violet develop-on-press plate. For one thing, thermal technology allows us to operate in a white light environment whereas, due to the small amount of energy available from violet diodes, the violet chemistry has to be very reactive. To stop it fogging, it needs yellow lighting which makes it difficult to mount the unprocessed plates on press”. McCullough also points to the need for pre-heating. He admits that violet diodes are becoming more powerful and so might be able to overcome this. However, since the exposure energy in a thermal laser is already over 1,000 times more than the current violet diodes, he doubts very much that they will ever reach parity, at least not at an acceptable price due to insufficient market demand to make mass production viable. Mind you, as Knadjian admits, the existing PF-N develop-on-press newspaper plate is not for everyone. It is currently being aimed at the low end of the market where the annual plate consumption is some 10,000 square metres. One reason for this is that currently the plate is not fast enough for mainstream use by newspapers although Knadjian cannot see why this will always be the case. McCullough agrees. “The challenge is productivity and is the reason why we have targeted the smaller newspaper market. Currently, for a double-truck plate for, say, a Goss Community press, it is around 27 panorama plates an hour”. Another current possible drawback is the relatively light image created. This is said to be readable by some machines such as optical punch benders but not at the moment by densitometers. The reason for this is to eliminate press contamination as Rundle explains: “Develop-on-press technology is not new. However, those early plates did contaminate the press. There were two reasons for it. One was the colour agent which you had to put in the coating to make the image highly visible. It was the same colour agent as used in the standard processor but when it was removed on press it contaminated the light coloured inks. We have solved this problem by reducing the amount of colour agent. “The other reason for press failure was that the coatings which were applied to the alu- minium were thicker so we were having to remove huge amounts of coating. We needed to reduce the amount of coating but that reduces the run lengths of the plate. So we had to design more wear into the molecules left on the plate to compensate for this”. McCullough adds: “We are very sensitive to contamination on press because we have technologies which we discarded which did it. However, this is not the case with this technology plate as proven by the 500 or so commercial sites we have using ThermalDirect and around 15 newspaper sites using the PF-N version”. So do special inks have to be used or what happens if the ink manufacturer changes the ink ingredients? “We do not require special inks on the press and we have not seen any ink problems,” replies McCullough. “The only problem we have seen is if you have an aggressive blanket wash. That can sometimes have an effect but that’s no different to any other plate. “It is the tack of the ink, not so much the ink’s ingredients, and the shear force. We cannot give you a tack value range which works with our plate but what we can tell you is that we have never had any problems with any customer nor have we had any press contamination problems. “The advantage newspapers have compared to a sheet-fed press is that their roll-up is higher which means that they are actually dispersing the polymer further than with a standard sheet-fed press.’ Indeed, there has been some surprise at the progress already made in the newspaper market. As Rundle reports: “Initially, we took ThermalDirect to a couple of heatset web sites and, to our surprise, we saw the same sort of run lengths that we were getting on sheetfed presses, that is 100,000+, while at one unique site on a Sunday press the plate went to 600,000. We thought that if it can do that on a heatset press then maybe a variant of it will work on a cold-set newspaper press. So we took PF-N to a handful of small to mid-sized community newspapers in North America to test it and it worked. “What really surprised us is that it also worked with dilitho and didn’t take the image right off. So we decided to commercialise a newspaper version. “The longest runs currently being undertaken are around 100,000 but that is all that these smaller newspapers need. If you have good press conditions on a coldset web, I think that the plate might make 300,000”. McCullough adds: “We have some customers who say one of the advantages of not having a processor, apart from the cost, is the fact that the time to make a press ready plate is quicker, since there is no processing time. In fact, we have some sites which are using the PF-N plate as a back-up to ThermalNews Gold. So, when there is a problem with an edition, they can quickly put a new PF-N plate on the press and the pressroom does not use it any differently from the other plate. They use the same ink settings, water balance, etc, and the make-ready time is very comparable. In some cases, it has been slightly better but overall it has been equal so if they had 100 makeready copies with the existing plate, it is the same for the PF-N”. McCullough concludes: “We do not say that the current PF-N plate is for everyone. However, as we have developed the technology for commercial use, we will also continue to develop the technology for newspapers. If you genuinely want to take out all of your processing costs, this is the way to do it and we will help you. Thermal technology, irrespective of the manufacturer, is the only one that can completely eliminate the processor”. So are we really on the road of achieving the holy grail of having a processless newspaper plate? Well, it seems it all comes down to terminology. It is technically impossible for a plate to be processless since whatever the technology a process is required to remove the unexposed coating. On the other hand, we are pretty close with a develop-on-press plate since it is a non-processor plate but it is not completely processless. PJ US moves to developon-press plates ● The core competency of the r&d labs at Windsor which employ 37 people is ‘non-process’ technology. Other Kodak CGG labs are in Germany, Israel and Japan, each having its own core technology competencies MOUNT Vernon News, as part of its move to ctp, is to install a Kodak Trendsetter News 50 platesetter on which it will image Kodak’s PF-N develop-on-press plates. In addition to printing the 9,300 copies of the daily newspaper, it also prints a 27,000 circulation weekly shopper and various commercial jobs. “Saving money ultimately was the main reason we selected the Kodak PF-N non-process plates but we also needed to save time. The Kodak plates will eliminate steps in our process and improve our pre-press operation,” explains Liz Lutwick, assistant publisher at the newspaper. “The Kodak non-process plates have performed extremely well in the tests we've run and the Kodak sales team has been great to work with as we have moved through this process”. Other American newspapers using the plate include the Osteen Publishing Company in Sumter.