Screening: Two voices from web printing

For rotary printing, with the use of non-traditional screen technology, the problem of ink stacking often occurs. Mr. John Lind, the director of PIA / GATF's laboratory, reminded us: "Successful use of new screening technology also depends on supporting facilities such as ink, paper, rubber liner, and arrangement of printing rollers. It often happens in high-gloss areas-there is a lot of fountain solution adhering to these places. If you do not stop the cleaning frequently, it will damage the blanket. "

In Stuttgart, Germany, there was a seminar initiated by M-Real Paper. Nine rotary printing companies came together to discuss various problems in random screen printing. The meeting reached an amazing conclusion: all members refused to use random screening technology.

These printing companies complain most about problems such as dot expansion, compensation curves, and various complicated adjustments in the printing process. They think that the use of FM screening will make the ink film thinner, which will result in more serious stains on the blanket, which means that frequent shutdowns to clean the blanket.

In order to get a full reproduction effect in dark areas, it will often cause serious ink accumulation on the blanket. Printing operators usually do not pay attention to this problem, because this is not obvious on the printed sheet. Therefore, the ink will form an ink skin on the blanket, and when the blanket is cleaned, a tiny crack has been left. Soon the cracks in the blanket will become larger until the blanket is replaced.

These problems are sometimes reflected in ink manufacturers. Don Sierzega, the production manager of Taiyang Chemical Company, received feedback from many customers. He believes that: “The problem of ink stacking is on the one hand because the dots are too small, and on the other hand, the random screening process itself uses a very thin ink film. There is also less plate fluid. As a result, the printer has no more room or choice to adjust on the press. "

Sierzega suggested that when encountering such problems, either replace the ink or reduce the fountain solution concentration, so that the operator can use more fountain solution to reduce the occurrence of ink stacking problems.

Mr. Andrew Matthews, Flint Ink's thermosetting ink production technology director, also received similar technical consultations. He said: "We don't have special production of ink for random screen printing, but we know what kind of ink is suitable for what is not suitable, hard ink is not suitable for random screen printing, because the random screen printing plate is inked It is so thin that water flushing will occur, resulting in imbalance of water and ink. Ink with good applicability has strong water repellency. "

When switching from amplitude modulation screening technology to frequency modulation screening, some companies have to create different dot gain compensation curves and use inks with different viscosity values.

Gary Samuels, a shareholder of Pictorial Offset Offset Printing Company, told us: “Our printers prefer to use FM screening in sheetfed printing rather than web printing. Sheetfed printing has short preparation time and little color change. The registration accuracy is easy to guarantee and it is difficult to see the visible white dot pattern. For single-sheet printing, especially for the face of people, we can print a smooth skin tone effect with fine tone, high light and dark tone transition. This is not an easy task for web printing. Our staff do not like FM screening. Because there will be ink stacking failures on the web printing machine. "

The use of FM screening will also reduce the life of the printing plate. Samuels explained: “Using Creo ’s Staccato technology on a rotary press reduces the durability of the printing plates, which increases our printing plate usage. We found that as far as the current technical level is concerned, FM screening technology It is suitable for rotary printing of high screen line printing. If the number of screen lines is higher than 200 lpi, there will be problems. "

But at Grandville Printing, the situation is different. The company has used Creo's Staccato screen technology for a year. Estes told us that the use of this technology is very smooth. He said: "We have some old rotary printing equipment, these equipment also produced us with fine details and bright prints, we print some furniture leaflets, for our customers, the bright colors of the prints are clean and tidy. Important. We will not have any problems about moiré here, and the registration effect can also be guaranteed, which is very important for wide web printing. "

Suffoletto, a researcher at RIT School, believes that the best reason for new technologies to be accepted is ease of use. Printing companies want plug-and-play to be so convenient. They do n’t want any expensive and time-consuming improvements, research, and testing. They really do not want to change the existing raw materials or supply channels. Therefore, when the manufacturer says that the fountain solution, blanket or ink must be replaced, they want to block their ears. "

Classic Color, located in Broadview, IL, uses Fuji ’s Co-Res screening technology. Mr. Jeff Hernandez, the company ’s deputy general manager, summed up a secret-keep it simple, he said: "I think random screening has it There is value in it, but what I need is the advantage that allows me to keep 95% of the time without downtime, compete with random screening and not have to make too many changes. If you want to use random screening technology, Would mess up his prepress and printing department. "

Kodak / Creo's Pritchard believes that the use of FM screening technology does not require additional process control, he said: "If printing companies use conventional process control methods, the printing press is also in normal working condition, then they Random screening technology can be used. Many of our customers directly apply the new screening technology without making any changes. If you go through the yellow pages, you will see that 80% of North American factories use random screening. Printed, the same is true of most poster flyers of Wal-Mart and Home Depot. When printing this type of printing, the printing machine requires very little control of the printing process. Any sheet-fed printing plant wants to Completing a good job is more costly than a company using FM screening technology in process control. I do n’t think FM screening is a difficult task. "

Gary Samuels of Pictorial said: "Printers cannot change colors during the printing process, and you may have a 40-60% chance of changing colors compared to traditional screening. Using random screening technology on printing machines, We can increase the ink density to 20% without seeing any changes. "

Troy Mone, the pre-press manager of Merit Printing, also said: "We have conducted some printing tests and found that the use of linear random screening technology is not easy to grasp the dots. On the contrary, a hybrid screening technology that combines AM and FM screening And Screen's Spekta screen technology can show extraordinary results. "

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