By Anne Locascio -- Graphic Arts Online, May 1, 2009.
In a market dominated by flexo printing, Visstun Industries in Las Vegas is using lithographic printing to create high quality graphics for promotional drink cups. How do they do it without flattening the cups?
The trick is the order in which the printing is done. With flexo, cups are printed after the plastic cup has already thermoformed or injection molded. Flexo, which uses rubber or plastic relief plates, requires that artwork be created with compensation for distortion. That’s because the rubber image stretches as it curves around the cylinder. Flexo historically has limited resolution quality, though new advances in high resolution digital flexo platemaking (such as 10-micron spot Kodak Flexcel) are arriving. With flexo, there have been limits to the amount of sports team photography that can be shown—faces might look funny, or long-view photos won’t reproduce with clarity.
Visstun sidesteps these issues by doing the printing on an offset press, at the beginning of the process, before the cups are even formed. Using fan-shaped templates—the format of unformed cups—designers create and submit artwork to Visstun intended to be printed flat. This eliminates the need for the calculations to project distortion on a rounded surface. Visstun also provides stock art and designs for customers.
Proprietary software is utilized for workflow and files are sent direct-to-plate using Screen 8800 platesetters and Fuji plates. Files are imaged at 300 dpi.
The fan-shaped blanks are printed two- to eight-up on Barrier Plus polypropylene plastic, converted on PMC-1250P machines from Paper Machinery Corp., Milwaukee, and run on any of Visstun’s offset presses: two, 6-color Heidelberg Speedmaster CD74 UV or a 20´´ KBA Genius. They typically use UV ink to create the chemistry necessary for ink to adhere to the plastic’s fine, smooth surface. The original sheet size, 23 x 29´´, is cut down based on the quantities required by customers. Substrates are either frosted or white.
Conversion to drinkability
Once run through the presses, each blank is diecut using standard die-shapes for any one of four cup sizes ranging from 12 oz. to 32 oz. Using specially engineered cup machinery, the blanks are picked up from the conveyor belt by suction and moved along to be formed into the cup shape with the side seam heat-sealed. A bottom is next placed onto each cylinder and heat-sealed into place. The final step of the process is to heat the rim and roll it to form a lip. The cup converters can make up to 165 per minute. The finished cups can then be sleeve-packaged into customer-specified quantities. Visstun requires a 250 minimum to order, and orders come in as high as the millions.
The finished product is one that is recyclable and reusable—and they are dishwasher-safe. Printing on plastic provides greater brightness than printing on paper as the ink remains on the surface of the substrate. A UV coating is applied for further durability. While the cost of the Barrier Plus substrate is more than pre-formed cups, the quality is better and creates a more durable product, says Visstun.
from the GraphicArtsOnline