The pad printing works on the principle of gravure printing. This means that the printing plane is embossed and the printing areas are below the non-printing area surface level. It s also an indirect printing method. This means that the printing plate never comes in contact with the substrate. The ink is transferred using a pad made of silicone rubber.
Pad printing was originally invented as a technique intended for printing on dials of wrist watches. This technique experienced a huge development as late as in the 1960s. Since then this technique, employed solely in the clock and watch industry, appeared as an ideal solution for printing on the most difficult substrates. When the silicone pad was invented and the printing machines were improved, this technique experienced a real boom.
Pad printing is basically a gravure printing modified as an indirect printing method. The beginning of the printing process is the same as the gravure printing. There is an embossed printing forme (cliché) that is coated with the ink using a floodbar. Then the cliché is wiped using a blade, the excessive ink is removed from its surface and the ink remains only on the printing (embossed) areas. The printing forme is not pressed directly on the substrate but on the pad. The pad is pressed to the cliché and the ink is transferred from it to the pad. The pad transfers the printed pattern to the substrate. While the pad roller prints the pattern on the substrate the cliché is again filled with ink and the process starts again.
A special ink is necessary for this process. It should dry unevenly and its surface must always remain slightly sticky. It enables transferring the pattern from the pad plate to the substrate.
The pads are nowadays made of the silicon rubber by adding silicone oil and other fillers. The content of silicon oil in the pad determines the hardness of the pad. There are several hardness levels. In general, the more uneven substrate surface, the softer and thus more adaptable pad is required. Except of various hardness levels, also different shapes are available. Also here the requirements are based on the shape of the substrate.
Thanks to transfer of the pattern via the pad that is enormously flexible it is possible to print on substrates of virtually any shape or surface. This feature enables using this method to print on small and/or uneven areas. It is applied in promotion and advertising (printing on pencils, lighters, beer openers, supermarket cart tokens or gift items), in pharmaceutical industry (printing on pellets, syrettes, infusion sets, etc.). This method is also used for printing on toys, cosmetics or selected food packages. The pad printing is used for industry printing (lighting bodies, car accessories, consumer electronics, buttons and covers of mobile phones). Tampography can be simply applied in the cases when the other printing techniques fail.