Read on to find out more about the latest technologies available for this screen-printing specialty.
By Harald Gavin
The maximum number of colors that can be printed in one machine pass is usually six to eight, which gives more options in the design of a decoration. Tight control of the item position in the machine makes it possible to keep color-to-color registration accurate to within ±0.004 in., depending on the manufacturing tolerances of the part.
Manufacturing tolerances for glass containers and bottles are usually such that color-registration accuracy is within 0.008 in. Cylindrical glass bottles and jars can have uneven surfaces, relatively high tolerances in diameter, and a cross-section that can deviate slightly from a perfect circle. Presses equipped with a squeegee-pressure-control system with balanced squeegees can offset the negative effect that these manufacturing tolerances can have on print quality. Such systems maintain constant squeegee pressure during printing around the circumference, even when an item shape or an uneven surface could cause a change in squeegee pressure. These systems also simplify the setting of equal squeegee pressure in all printing stations, and the balanced squeegees extend the operating life of screens.
Modern inks and modern screen-printing machines ensure a uniform ink deposit. Ink formulation allows the ink to flow through the mesh and then even out quickly once the mesh has lifted from the substrate. Vibrations from the press that could affect print quality are prevented through sturdy machine construction and design features such as a sinusoidal screen-carriage acceleration and deceleration, which provides smooth reversal of movement direction. Some systems are even able to print wraparound images with a virtually invisible overprint using UV inks. Such machines use a special UV-curing system that surface cures the leading edge of an image so that it can be overprinted with the trailing edge.
New, high-speed presses for printing with UV inks require curing systems with high UV output power and high UV light intensity focused on the UV-curable ink. At a production speed of 90 cycles per minute, the drying period is reduced to approximately six milliseconds. UV output power of up to 1250 W/in. is required to ensure thorough curing of each layer of UV ink at maximum production speed.
These power requirements would stress a UV lamp and reduce its operating life, but it's possible to provide high output power only during the curing period and reduce the output power of lamps during the part transport period—when the machine is stationary, the UV lamps are switched to stand-by mode to reduce power consumption.
Focusing on quality printing
Modern container-decorating equipment can ensure the competitiveness of the screen-printing process. Advances in the mechanical and electronic capabilities of these systems enable screen printers to directly print images of superior quality onto a wide range of materials, including those designed with challenging surfaces and shapes. These enhancements also allow screen shops to focus their attention where it belongs—on printing.
About the author
Harald Gavin earned a BSc in electronics and mathematics from the University of Hamburg, Germany and an MSc in control engineering from the Cranfield Institute of Technology, England. He has worked in web-offset printing, control-system design, contract engineering, and software. Gavin founded Path 2 Print Ltd. in 2000 as a marketing company for ISIMAT screen-printing machines in the UK and Ireland.
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