December 2018 - After seven years of research and development, Globus has achieved the ability to digitally print images on an individual sheet or they can be integrated into a continuous coil coating line. The technology allows the user to print any digital picture—a photograph, computer designed image or a combination of both—using Raster Image Processing (RIP) software, on a continuously running pre-painted strip.

“This is a totally different process and setup compared to the multi-pass scanner -type printing [currently available],” according to Bob Lukacs, president of Double Globus, the U.S. subsidiary to Torino, Italy-based Globus S.r.l. The digital printing process, Coilor, is named after Coilor S.r.l., the new company Globus founded to further develop, market and supply the new digital printing line.

During the multi-pass system process on sheets, printing heads print while traveling across the strip of metal coil. The RIP single-pass system includes four color bars: cyan, magenta, yellow, and black—each equipped with multiple printing heads. The strip travels beneath stationary color bars. Each head covers approximately 2.55 inches of strip width for each color. That means for a 40-inch strip width with four-color printing, 64 heads would be needed. Each printing head has 1,000 jetting nozzles, which requires the printing process to individually control 64,000 jetting nozzles, explains Lukacs.

Raster Image Processing (RIP) software allows users to print any digital picture on a continuously running pre-painted strip.

Digital printing offers unlimited patterns and colors, including a much longer pattern of up to 33 feet long, whereas the previous method of multi-pass scanner printing and rotogravure processes are limited as to the number of colors and the length of patterns—in some cases limited to a mere 40 inches long, according to Luigi Bagnasco, president of Globus. “Once a pattern is programmed into the system, it can easily and quickly be repeated,” he says. “A different pattern can be printed immediately after one pattern is completed, without stopping the line to make changes.”

Crystal clear

Engineers overcame design challenges during the development of the single-pass system. “One [challenge] was the software required to manage the high number of printing heads and the related jetting nozzles—there are approximately 1,000 nozzles per head, or 64,000 nozzles for each meter of printing width total,” explains Bagnasco. “The second [challenge] was designing the mechanical system to manage the strip alignment as it travels under the printing machine. The maximum allowed side movement is 0.00137-inch.”

The design complete, users need only a week to learn how to use the printing machine. “For the remaining painting process, such as clear coating and curing, it depends on the operator’s previous experience,” Bagnasco adds.

Replacing printing heads is a simple process. “The new head initially has a mechanical alignment and afterwards an electronic alignment is done by the machine,” Bagnasco says. “The total time [to switch heads] is less than an hour. On average, printing heads last for two years.”

Four conditions

Instead of methods like hot lamination, where users need to wait for film to be printed and shipped, RIP software single pass system creates detailed results as intricate as a photograph and “once the pattern is programmed into the digital printing system, you can print any time,” Bagnasco says.

In order to print, the process requires four conditions:

• Printing inks are UV type;

• Strip painted surface must have a high surface tension (30 dynes or more);

• Printed images must be protected by a clear coat (a solvent base is used);

• Strip maximum wavelength must be as low as possible and cannot exceed 0.02 inches (5 mm).

Digitally printed images are 400 dpi resolution and offer unlimited patterns and colors, including a much longer pattern of up to 33 feet long compared to 40 inches using older methods.

Currently stationed in Italy, the Coilor digital printing line can print on pre-painted aluminum, steel or galvanized steel. The maximum width of the line in Italy is 28 inches (710 mm) and has a maximum speed of 200 fpm (60 mpm) and prints at a resolution of 400 dpi.

“To maintain the desired 400 dpi resolution on wider and faster lines, additional printing heads would be required,” according to Lukacs. The printing heads are located above the strip while four ink tanks lie beneath the strip and are easy to refill while digital printing is in operation. Coilor is now producing printed panels for garage doors.

A basic line is laid out with the coil payoff section, followed by the digital printing with UV drying and the rewind section. The coil is then sent to the paint line to apply the UV clear coat. Clear coat section and accumulators can be included in the line or added later. Another configuration would be to integrate digital printing into an existing line or a standalone new paint line.

Today, the clear coat is a solvent base and the maximum speed is 200 fpm. But Coilor plans to test a water-base clear coat and conduct tests to increase the maximum speed to 300 fpm while maintaining the 400 dpi image resolution. Coilor is working with several customers and plans to install the first production line in 2019. MM