The basics of Pad Printing
The basic pad printing process is a relatively simple. It is especially suited for printing on irregular shaped objects but can be used to print on to flat surfaces as well.
The main parts to the pad printing process are the cliché, the pad and the ink. These three parts allows for more flexibility in the types of products which can be printed on using this process, when compared with any other printing processes.
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The basic steps as illustrated below are as follows:
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The inking stage: the image on the cliché is inked by the ink cup while the silicone transfer pad is travelling to the image. |
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The transfer step: the silicone transfer pad picks up the inked image from the cliché and travels to the product. |
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The print step: the silicone transfer pad makes contact with the product and using pressure transfers the image onto the product. |
The required image that has to be printed is etched into a plate called a cliché. The cliché is usually made of either a polymer plate or of hardened steel. Once placed on the printer, the cliché is inked by either an open inkwell doctor blade system or by a closed cup sliding across the image. For medium to long production runs the etched metal cliché is recommended and for short to medium runs a photopolymer cliché is suggested.
Pad printing inks are similar to silk screen printing ink and so should be easily available anywhere in the world. The pad printing inks are available in any colour you can think of and are available in various grades with varying characteristics. Material specific inks are made to print onto on the huge range of materials available. Food grade edible inks, medical grade inks, inks designed to print onto plastics, glass, soft metals (e.g. Aluminium), hard metals (stainless steel) etc. Some inks will bond onto certain materials only and not on others. The final appearance and adhesion quality of the ink is dependant on factors such as the viscosity and evaporation characteristics of the ink. By the addition of a compatible hardener the ink will bond on permanently on to ceramics or metals.
Once the cliché is inked, the tampon pad then picks up the image and transfers it to the product. The pads are made of silicon which varies in hardness (durometer). The properties of the silicon allow the ink to temporarily adhere to the pad and completely release from the tampon pad when the pad comes into contact with the product to be printed on to. The hardness of the pad determines how the adhered image moulds to the product. To avoid the use of unnecessary pressure you would normally use a soft pad to print on to flat or nearly flat product and a hard pad for printing onto textured round but firm products. Usually using a medium hardness pad is a happy medium between the harnesses.
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