Screening: Two Voices from Web Printing

For rotary printing, with the use of non-traditional screening techniques, the problem of stacking ink often arises. Mr. John Lind, research director of PIA/GATF, reminded us: “Successful use of the new screening technology will depend on suitable ink, paper, rubber lining, and arrangement of printing rollers. It often happens in high light areas where many fountain solutions are adhered. If you do not wash down often, the blanket can be damaged.

In Stuttgart, Germany, a workshop initiated by M-Real Paper was held. Nine rotary printer manufacturers came together to discuss various problems in random screen printing. The meeting came to a surprising conclusion: All members refused to use random screening technology.

Most of these printers complained about issues such as dot gains, compensation curves, and complex adjustments in the printing process. They believe that the use of FM screening will make the ink film thinner, which will lead to more serious blankets dirty, which means that frequent cleaning down the blanket cleaning.

In order to be able to achieve a full reproduction effect in the dark tone area, a serious ink accumulation on the blanket is often caused. Printing operators usually do not pay attention to this problem, because this is not obvious on the printed sheets. As a result, the ink will form ink on the blanket, leaving tiny cracks when cleaning the blanket. Soon the crack on the blanket will grow until the blanket is replaced.

These problems are also sometimes reflected in ink manufacturers. Don Sierzega, the production manager of Sun Chemicals, received a response from many customers. He believes: “The problem of stacking ink is due to the tiny dots. On the other hand, the ink film used by the random screening process itself is very thin. There is also less fluid, which results in the printer not having more room or choice on the press.”

Sierzega suggested that when such problems are encountered, either the ink or the fountain solution concentration should be replaced, so that the operator can use more fountain solution to reduce the problem of stacking problems.

Mr. Andrew Matthews, head of thermosetting ink production technology at Flint Ink, also received similar technical advice. He said: "We did not specialize in the production of inks 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 ink It is so thin that water rushes out of the ink, causing the ink and ink to become unbalanced. The ink with good applicability has a strong water repellency."

When moving from AM screening technology to FM screening, some companies have to create different dot gain compensation curves and use inks with different viscosity values.

Gary Samuels, a shareholder of the Pictorial Offset offset printing company, told us: “Compared to web printing, our printers prefer to use FM screening for sheetfed printing. Sheet-fed printing has short print job setup time and small color shifts. The registration accuracy is easy to guarantee and it is difficult to see the visible white dot pattern.For sheetfed printing, especially for the printing of human faces, we can print out smooth and smooth transitional skin tone effects. In the case of web printing, this is not an easy task. Our staff does not like FM screening due to stack failures on the web press."

Using FM screening will also reduce the life of the printing plate. Samuels explained: “The use of Creo's Staccato technology on rotary presses has reduced the printing rate of printing plates, which has increased our printing plate usage. We found that FM screening technology is not available at the current state of the art. It is suitable for printing and printing of high-speed lines. If the number of lines is higher than 200 lpi, problems will occur."

But at Grandville Printing, the situation was different. The company used Creo's Staccato screening technology for a year. Estes told us that using this technology is going well. He said: “We have some relatively old rotary printing equipment. These equipment also produced fine details and vivid prints for us. We printed some furniture leaflets. For our customers, the printed materials are bright and the screen is clean and tidy. It is important that we don't have any problems with moiré here, and that the effect of registration can be guaranteed, which is very important for wide web printing."

Suffoletto, a researcher at RIT School, believes that the best reason why new technologies make people accept is that they are easy to use. Printing companies want plug-and-play convenience so they don't want to invest in expensive, time-consuming improvements, research, and testing. They also do not want to change the existing raw materials or supply channels. Therefore, when manufacturers say they must replace the fountain solution, blanket or ink, they want to block their ears. ”

The Classic Color Company in Broadview, IL is using Fuji's Co-Res screening technology. Mr. Jeff Hernandez, the company's vice president, summed up a secret - keep it simple, he said: "I think random screening has it. The value that exists, but what I need is for me to be able to keep 95% of the time without downtime, be able to compete with random screening, and be able to have the advantage of not having to change too much. If you want to use random screening techniques, It will confuse its prepress and printing departments."

Kodak/Crio'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 and the printing presses are in normal working condition, then they will Random screening technology can be used, and many of our customers directly apply new screening techniques without any changes. If you go through the yellow pages, you will see that 80% of North American factories use random screening. This is also true of most of the print flyers printed by Wal-Mart and Home Depot Home Sales, which require very little control over the printing process. Any sheetfed printer wants to Completing a good job is a lot more costly than a company using FM screening technology. I think it is not a difficult task to use FM screening."

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

Troy Mone, a prepress manager at Merit Printing, also said: “We conducted some printing tests and found that it was not easy to use a linear random screening technique to control the dots. Instead, we used hybrid screening techniques that combined AM and FM screening. And Screen's Spekta screening technology can show extraordinary results."

Source: China Light Industry Information Network