What is "Pad Printing"?

Pad printing is a means of applying a pattern of ink on almost any surface. Conventional printing is designed to apply ink to a thin, flat material, such as paper. It's not suited for a solid object—say, a boxcar.

Pad printing begins with a thick steel plate into the surface of which an image or artwork is etched, either by a photo-chemical process or using a laser. Ink is spread across the printing plate, and the excess is removed, usually with a sharp steel "squeegee" under high pressure. Then a very soft block of silicon—the "pad"—is pressed onto the plate, and the ink is transferred to the pad.

A mechanism moves the pad over the object being printed, and lowers the pad precisely onto the surface. In this way, the ink is transferred to the object. The mechanism does this with great precision so that it lands in the same place on every object, thus multiple colors can be applied with perfect registration. Different sizes and shapes of pad are used so that the image can be applied to curved or irregular surfaces, such as a tank car or ribbed hopper.

Pad printing produces the highest quality of lettering for models, since it has no carrier film like decals, and it's positioned with great accuracy. It is costly, however, because the equipment is expensive, especially the printing plates. Also, for multi-color designs, the object must be pad-printed for each color individually; some pale ink colors, such as white, may need to be applied more than once.

There are many levels to the technology. On the high end, computers are used to run the printers for hands-free automation, high speed and super precision. At the other end of the spectrum, all-manual pad printers are available for DIY shops doing short runs; a small printer can be had for about a thousand dollars. What they all share, however, is the cost of making the steel plates.

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