For awhile now have been printing large format posters for KCTS, Seattle’s public television station. The posters serve as promotional collateral for KCTS programing. They are displayed in custom made outdoor poster boxes just outside the KCTS facility. The posters, 40” x 70” in size, were printed on vinyl and lit from the front interior of the frame.
Recently KCTS retrofitted their poster boxes with LED backlighting. To take advantage of the backlighting effect, the new posters would now need to be printed on special backlit 9 mil film stock. The problem is that 9 mil stock is only about .23 millimeters thick, which was not thick enough for for the clips inside the retrofitted boxes to secure the poster in place. Also, the new LED backlighting was so strong that it washed out the rich, deep tones in the blacks.
Being their go-to print service provider, KCTS came to us with this unique printing problem. The challenge was to thicken the poster without compromising the quality of the desired backlighting effect. The overall contrast of the print needed to be strong while the details stayed sharp.
To properly prepare the image for the backlit effect we used a special technique developed by our prepress department. It involved separating out the image’s color channels from the black channel and setting the black channel to print white ink. Once the digital file was ready to go, the prints required three passes on our Vutek press. The first pass printed the black channel with white ink. The second pass was the black channel with black ink. And the third pass was the full colored image.
This combination of using white ink and multi-layer printing allowed just the right amount of light to pass through the posters. The details in the blacks remained crisp and clear.
An extra layer of silk laminate needed to be added to the print to thicken it up. There were three options to consider — laminate on both sides of the print, laminate on just the front, or laminate on just the back. Smaller scale test samples of each scenario were printed on the Indigo press, brought to the client and viewed on portable backlit tables. Under the view of their critical eye it was determined that silk laminate on the front of the prints yielded the best results.
The final 40” X 70” backlit posters were printed on our large format digital Vutek press. They turned out beautiful with stunning contrast and sharp detail. The client was more than happy with the results.
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