Pad Printing is an indirect printing system through which you can print any kind of objects, curved or wrinkled, with very high definition. The system is specially designed to print on the deformatios of the piece.
Method - The method is to put ink on a hollow done in a steel sheet (cliché) that then is superficially swept by a steel strip really slim (Racla), leaving ink only in the engraved hollow. A piece made of rubber (pad) goes down on the cliché taking the ink left in the engraved hollow, and then it puts it on the piece to print. The cycle is short, and the ink gets dry in seconds after being printed. Nowadays, despite the system remains generally the same, tha Racla system has been replaced by the cup that has the same fuction, but works with the ink in a sealed container.
"CUP" Sealed Inkwell - These equipments are equiped with an aluminum cup and a ceramic ring that make up the inkwell, a chiché back that works as a lean bracket of the engraved under relief sheet, with the graphic to print. This equipments can print without tonal variations, because the ink doesn't change its quality when the evaporation is supressed, avoiding the add of diluents and this way, the change in the mixture dilution. Something else to take into account is that, as the daily cleaning is avoided, the productivity can be increased because you take advantage of the time you lose with the machines with open inkwell. As it is a simple system, the cliché and colour change can be done in less than a minute without washing any implement.
The Pad - The pad is manufactured in many ways depending on the product you need to print. It has 200 or 300 different varieties, although the used in the 80 % of the cases aren't more than 100 models. As the printing system needs a mean of transport between the cliché and the piece (the pad) it is called indirect, the same way as the offset (system used for paper printing). The durability of the pads is high allowing us to use the same pad for different products. Its care is limited to keep them in a closed place without any contact with the printing surface. In case you keep them for a lon period of time, it is not recommendable to pack them, just keep them in a clean and dry place. When you want to use them again, you should clean them with Thinner. Do never use Acetone for this process because the pad is left useless.
The Cliché - To manufacture a cliché, you first need the original art armed in Professional Vectorial Drawing. Then, with the design file, you have to go to a Phtomechanics Services House to get a transparent positive movie with the art to engrave in the cliché with the emulsion below with more than 3,6 log opacity (Same movie required to engrave printing sheets in the graphic industry). In a steel sheet with superficial emulsion sensitive to the light altogether with the movie in a vacuum plaque that ensures the quality of the exposition, inside a machine called UV Exposure Unit, that sends out UV light, you do the heating process. The UV light fixes the emulsion where the movie is transparent, it means where it wasn't hit by the light. Once it was heated, the cliché developing is done (as the process of photographic developing) leaving only uncovered the surface of the steel you need to remove. Etching it with an acid. To have a parameter of how thin a stroke of an engraving can be, we can compare it with a laser printer which only has 90 lines per inch against 200 LPI that Pad Printing allows.
That is why Pad Printing can print finely little graphics, thin strokes, or grey spectrum, that combined in different steps of colour printings, can print photochromy, or as it is better known, colour photography.
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