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Tips for Direct Projection

(August 2003) posted on Fri Aug 08, 2003

Learn about the intricacies of direct-projection exposure systems, how to keep your mesh from deteriorating, and the secrets of pad printing on inflatable objects.

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By Carol Swift, Peter Kiddell

Following closely on the heels of this development, new thinner gauge capillary films have been introduced that provide a genuine 2-micron stencil thickness with a very good Rz value. They are capable of controlling ink deposit to the point where you can get results with conventional UV inks that are comparable to those you get with water-based UV. Trials with such films have led to printed tonal ranges of 5-95% at 150 lines/in. Some tests even suggest that users can obtain 175 lines/in. with a similar tonal range.


Another, more established development in the CD industry is the use of precoated mesh. This has been an important step forward in a market where a high volume of screens are needed per day and stencils are seldom reclaimed--mesh is simply cut from the frame and discarded once the stencil is no longer needed. Precoated mesh offers a consistency in emulsion coating that can only be achieved by high-end coating equipment. It also can save money when all of the capital, labor, and space costs of setting up screen-coating facilities in house are taken into account. Although precoated mesh is a very useful product, its use will likely be limited to niche markets.


These recent advancements clearly show that screen printing is far from dead. In fact, competing analog and digital processes continue to spur new developments in screen-printing technology. The prophets of doom were somewhat premature.


Pad printing on inflatable balls


Visit gift and souvenir shops on your next vacation, and you'll likely see a wide assortment of inflated balls printed with multicolor cartoon characters and logos across their surfaces. Looking at these toys, you may think, "How do they do that?" The answer is pad printing.


If you look closely at the "equator" of such a ball, you will see that the print is actually made up of two individual images. Each hemisphere is printed separately, but on the same machine. It's done on a specialized multicolor pad-printing press that prints the balls while they are inflated. While there are many novel features to this press, the most important are the printing pads.


Normally, pads are made of solid, molded silicone rubber. The pads for this application also are made from silicone rubber, but they are hollow. Large air reservoirs mounted above the press pressurize the pad before ink pickup, then depressurize it during the print stroke. This variation in internal pressure enables the pad to pick up ink from the cliche, yet conform to the inflated ball surface during printing. Watching these presses in action is very impressive, as they can print up to 600 balls/hr with a four-color image covering 360° of surface. More print stations can also be added, allowing six to eight colors to be printed.




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