Offset uses a more complex system for transferring ink to the substrate: a long ink train made up of many rollers. The plates in offset are positives of the desired images instead of negatives as in flexo. With offset, the roller containing the plate transfers the ink to the blanket, a roller with a rubber layer. The image is a negative on the blanket. Then the blanket transfers the ink to the substrate as a positive, producing the desired image.
|Codimag's VIVA 340, an offset machine, was on display at Labelexpo Americas in September.|
Josep M. Soler, corporate strategy managing director for Rotatek, a press manufacturer in Barcelona, Spain, points out other differences. He says the maximum resolution from flexo is 170 to 180 dpi, while offset can print between 200 and 350 dpi. When it comes to prepress, Soler says, "Offset is much simpler and less costly than flexo."
Jes Hilfling, managing director at Etipol, a press manufacturer in Taastrup, Denmark, says, "It is imperative that a UV dryer be used in offset printing. In flexo printing either hot air or UV drying can be used."
|Gallus' RCS 330 offset press|
Ink flow is another area in which flexo and offset differ. Hilfling explains, "The ink flow in flexo printing is controlled by the ink volume of the anilox roller. This factor is chosen according to the paper surface and image to be printed. In offset printing the ink flow is controlled by screws [also known as keys] in the ink fountain." The keys adjust the amount of ink that is allowed into the ink train for use on the substrate.
Hilfling also points out some similarities between flexo and offset. He says, "The makeready time is the same for flexo and offset if a lock system is used for the offset plate and a mounting device with a camera is used for the flexo plate." He also says the printing speed is high for both techniques, at about 100 to 200 meters per minute. Soler agrees that the speeds are similar between flexo and offset, saying both can run at up to 1,000 feet per minute.
Advantages of offset
The advantage mentioned most often for using offset is better print quality. Soler explains that offset has "more dots per inch and more uniformity of optical density compared to flexo."
Paul Mattle, marketing manager for Gallus, a press manufacturer based in St. Gallen, Switzerland, says, "Print quality for flexo printing screen resolution is generally seen from 3 percent to 98 percent, while offset does much better from 0 percent to 100 percent."
Gerben van Wijk, public relations manager for Drent Goebel, a company that specializes in web offset printing presses in Montreal, QC, Canada, says, "Offset has a big advantage in start-up costs of new jobs; the cost of an offset plate is dramatically lower than that of flexo plates or gravure cylinders. Also the production time of an offset plate, with an average of 10 minutes, is significantly shorter than flexo. This means that you can start producing new jobs very quickly."
Ease of use is another benefit. Jakob Landberg, sales and marketing director at Nilpeter, a narrow web press manufacturer in Slagelse, Denmark, explains, "I normally say even a sloppy printer can print fine quality in offset — but you have to be 100 percent on your toes to do so in flexo and UV flexo." He also says offset's consistency is high, which is good for repeat jobs and longer runs.
|An offset machine from Nilpeter's MO line|
Jon Guy, president of Gallus Inc., the US arm of the Swiss company, agrees that consistency is an important quality of offset. "Offset's greatest advantage is that it is the only truly standardized printing process worldwide. While chemistry will always be a factor, it is like a baking recipe which can be followed precisely for consistent results," he says.
Pierre Panel, export sales for Codimag, a press manufacturer in Cedex, France, sees being able to print with fewer colors as an advantage. He explains, "Flexo requires separation into many spot colors. In offset you can print on the same plate a 10 percent black screen and a dark black text. That means that an eight-color flexo press can be a five- or six-color offset press. Setup times are also reduced. Instead of changing eight colors, you just switch one or two special colors."
No process is perfect and offset printing is no exception. According to van Wijk, "The challenge is in how well your printer can master the press. The process is different from flexo and needs some getting used to. There is a certain learning curve, but with good training there should not be any problems."
Soler says, "The challenge is to use offset technology in flexible non-absorbent substrates like plastics, poleolephines or self-adhesives substrates."
Christoph Schoenenberger, head of operational process technology at Gallus, says, "Several challenges we find with offset are the high skills required for the printer, higher investment due to the machine design, higher waste, and a longer makeready than flexo presses."
Hilfling says, "The disadvantage of rotary offset is that the printing size is fixed. Cassettes with printing cylinders corresponding to other printing lengths are available as an option but they are relatively expensive."
Another way to deal with the problem is to use semi-rotary technology, also known as intermittent feed. In offset presses that use semi-rotary technology, the substrate is not in constant forward motion. Instead, it is intermittently moved backward for printing on blank sections to eliminate waste. Panel provides an example with Codimag's VIVA 340, which uses 14" cylinders. To print a 10" image, the web moves forward 10 inches. Since there are four inches left on the cylinder, the web moves backward, repositioning itself right after the printed 10" image. This action is repeated throughout the job.
One drawback to semi-rotary technology is decreased speed. Panel says, "With the intermittent motion, press speed is limited compared to rotary presses. Our maximum speed is 150 feet per minute." He adds, however, "This technology is well suited to short and medium runs, as job change is much more flexible than on a rotary press. And when you have to print 10 jobs of 20,000 labels each, speed is not the important factor; job change is much more fundamental."
A third possible solution to the fixed printing size is using sleeves. Drent Goebel's van Wijk explains, "For 10 years, rotary offset wasn't so attractive for flexible packaging and label converters since you had to exchange a complete cassette (which was heavy and very expensive) to change a repeat length. With the introduction of the VSOP press you only have to exchange two lightweight sleeves to change a repeat length. This makes offset much more interesting for flexible packaging and label converters, which need many repeat lengths for their
|Rotatek's specialized COMBI flexo/offset machine, printing self-adhesive labels|
Pancoast has a different perspective on challenges. He says, "Some of the challenges to offset printing may be mostly in the increased expectation of perfection. Customers expect better jobs, so a better job is required. More time is spent setting up to ensure that quality is achieved."
Wet vs. waterless
There are two kinds of offset printing: wet and waterless. For wet offset, water is transferred to the plate via dampening rollers. The ink will not be picked up where the water is on the plate. With waterless offset, water is not part of the process. Instead, the plate is configured differently. Pancoast, of Label One Connect, says, "The plate is still aluminum, but it has layers of silicone and a layer of another material. The areas exposed to the silicone are what show the ink." With this configuration, printers don't get impressions like standard offset plates so there is no dot gain. Although he adds, "Plate life is somewhat short because it's a fragile sandwich."
Hilfling says, "The material waste when starting up a new job in wet offset is many times higher as the balance between water and ink is to be found corresponding to the correct production speed. The material waste amounts for waterless offset and flexo are almost identical."
Kyle Knight, operations manager at the Shelton, CT, USA facility of CCL Label, a converting company with headquarters in Farmington, MA, USA, says, "Waterless offset is similar to letterpress. Maintaining temperature and humidity is critical in waterless printing."
Cost of offset
Comparing the costs of offset and flexo involve several factors. An offset press is usually more expensive than a flexo machine. Mattle says, "Offset machine equipment is generally a higher investment in the range of 30 to 40 percent over a comparable flexo unit. This is primarily due to a more complex design of a quality inking and dampening unit."
Although the offset press costs more than its flexo counterpart, the materials used can be cheaper. Federico d'Annunzio, managing director at GIDUE, Turate, Italy, says, "The consuming material for offset costs less if compared with those used in flexo. A set of flexo plates costs even 10 times more in comparison with the same set in offset. In addition to this, while the cost of flexo plates raises exponentially with the approaching of excellence, the cost of offset plates remains the same for any kind of quality."
According to van Wijk, of Drent Goebel, solvent costs can be dramatically decreased with offset. He explains, "Together with customers we've calculated that a flexo printer going to offset can save up to $1 million on his solvent usage and storage. The offset press is more expensive but the cost per square meter production is significantly lower." In Europe, van Wijk says, it is not unusual for flexo companies to use primarily solvent based inks, so switching to offset is financially advantageous.
Landberg from Nilpeter says, "An offset plate costs approximately $6 and a flexo polymer plate costs approximately $60." He believes, however, that cost advantages exist for both offset and flexo, depending on the printing job. He says, "Plate costs are higher in flexo, but investment is lower. Therefore the running costs in offset are lower than in flexo, but the waste is higher in offset. For runs over 2,000 meters the offset costs are lower than flexo. For very short runs the balance is in favor of flexo."
|GIDUE's Xpannd offset/flexo press|
Training press operators to use an offset press is another factor converters need to keep in mind. "The challenge is in how well your printer can master the press. The process is different from flexo and needs some getting used to," says van Wijk. "We normally train the printers of a new customer for two weeks in our plant and help them with their machine for about a week. After that they have the knowledge to start production."
Landberg says, "We normally offer one week of intense training and that starts clients off fine. However, all of our offset clients are combining offset with a vast number of other processes — flexo, screen, gravure, embossing, laminating, glue-side-printing, diecutting, sheeting, stacking — so the trick is to master all these processes, not just flexo or offset."
Pancoast believes training takes longer than a few weeks. He says, "We have guys that catch on pretty quick, but I think an average time is three months to a year to get an operator really proficient at running an offset press." He adds, however, "We have some mitigating circumstances. We do a lot of foil stamping and embossing, a lot more so than a flexo operator would see."
Knight agrees that training takes months. "Flexo and offset are two different animals. You should give an operator at least six months to train on offset," he says.
The press operator's mindset may need to change. Pascal Duchêne, managing director at Codimag, explains, "The main shift with offset is that the operator can adjust the color on the press and does not just mount an anilox. Therefore the printer needs to accept this responsibility."
Press manufacturers have taken a recent interest in offset. There may be several reasons why this is the case. "In a world oriented to the digitalization of the information flow, the tendency will be more and more to invest in an offset machine," says d'Annunzio. "Digital and offset share the same workflow; the same data can be used for a digital or an offset machine. These two technologies share the same environment of prepress file management, which enables them to obtain the same print quality, sharing the same standard."
According to van Wijk, market pressure may be a driving factor in the pursuit of offset. "Press manufacturers' customers are demanding higher quality and more flexibility. If you want to be successful in this market, you have to stand out and think outside your own little box," says van Wijk. He believes offset is a way to solve this problem.
Landberg agrees. "There is a clear end user drive in this direction led by the global brand owners. Nilpeter was alone when in 1994 we introduced offset in the label industry, but more suppliers have opened their eyes for the top segment niche," he says.
Panel of Codimag believes the decision can also be on the part of converters. He says press manufacturers are interested in offset "because label printers are finding limitations to flexo or finding the cost too high to reach the required quality."
Pressure sensitive applications
Since offset's quality is higher than flexo's, Pancoast says the most common pressure sensitive applications that use offset are for industries that rely on packaging at the store level. An example he gives is the wine industry. He explains, "There's a lot of different wine available. The package is what sells, so they're very image conscious. A label can make an enormous difference in sales."
Gallus' Mattle agrees. "We find brand owner products for health and beauty care and wine labels are in high demand. They see an opportunity to differentiate their products on the shelves with offset," he says. "Many of these labels have graphic design elements that favor the higher line screens and lower dot gain of offset."
Another application where converters use offset, according to d'Annunzio, are for those that require a wide range of substrates. He cites high quality oil and wine labels as examples.
In addition to wine labels, Landberg says health and beauty products, cosmetics and some pharmaceuticals commonly use offset printing. In the case of pharmaceuticals, rather than standing out on the shelf for consumers, it is more of a quality issue for the package's wording, which needs to be correct and easily read.
Prevalence of use
Flexo dominates the pressure sensitive label markets, particularly in North America (and of late in Europe, where it has overtaken letterpress), but some see offset growing. Drent Goebel's van Wijk says, "Worldwide we now have 20 to 25 customers using this application and we certainly believe this number will grow, especially since offset is getting more and more accepted in this market."
Rotatek's Soler says, "Today many converters are already using offset for pressure sensitive labels. Every year there is a minimum of 30 to 40 offset and combined machines with flexo and rotogravure sold for that purpose. The number will grow."
Landberg, from Nilpeter, also believes offset is becoming more common. "The demand for high quality and value adding is growing. It's driven by global brands, but is spreading to second tiers. Self-adhesive labels is growing fast in the wine sector and the demand for innovative, flashy labels follows this," he says.
GIDUE's d'Annunzio explains his company's views on offset's growth: "We see further growth of offset in global converters, but also the introduction of offset in middle companies who can have access to a viable technology, both in terms of friendliness of technology and also in terms of economic convenience. We believe the number of converters using offset will increase in the future because this technology gives the possibility to grow in the market accepting practically any job, including the most difficult ones, and will involve a change in the vision and commercial approach with the customers."
Label One Connect's Pancoast isn't as optimistic. He estimates that under 20 converters use offset in the US. "I'm not sure if the number will grow. I would have said yes a few years ago," he says. "The flexographic industry is a very loyal group that worked very hard at perfecting flexo printing. I think an offset press runs too slowly for them. At the end of the day, that's probably what keeps them running flexo as opposed to making the switch."
Knight believes that only a small percentage of converters are using offset presses. As for the future, he says, "In some areas of the industry it will grow but cost of equipment will keep it away from the smaller companies."
Jon Guy, of Gallus, believes offset and flexo can coexist in the marketplace. On a Gallus offset press, he says, it is possible to use different techniques, such as offset, gravure and line screen, in all print station areas to maximize options for customers. He says the goal is to give more information to graphic designers so they know what is available and possible with various printing techniques.
"We think offset has a place, a very useful place," Guy says. "When you have a press that's capable of doing flexo or other processes, it becomes a question for the graphic designer to come up with the best result. Offset is another weapon in the arsenal."