Pad Printing Process

Pad printing is a fairly simple print process used for printing onto three dimensional objects that the other printing processes cannot accommodate for. The key elements to the pad printing process are the pad, the cliché, and the ink. Together, these three elements allow more flexibility in the types of products that can be printed using this process than any other printing process.

The basic steps in pad printing are as follows:

The cliché step - the image on the cliché is inked via thedoktor blade system or inkcup while the pad travels to the image.

The transfer step - the pad picks up the inked image from the cliché and travels to the substrate.

The print step - the pad makes contact with the substrate using just the right amount of pressure to deliver the image.

Pad Printing using a inkcup:

and for a pad printing machine that uses a doctor blade :

The Cliché

The desired image to print is etched into a plate called a cliché. The cliché is usually made of a polymer coating on a metal backing or of hardened steel. Once placed on the printer, the cliché is inked by either an open inkwell system or by a closed inkcup sliding across the image.

When choosing which type of cliché to use costs are the main concideration as it relates to the size of the Pad printing job for which the cliché is being chosen

Any print job that exceeds 10,000 cycles will usually consume at least one or more polymer cliches and if you cannot make your own clichés in house, you are probably better off with a thin steel or thick steel cliché to prevent interruption of the print job.

The Ink

Pad-printing inks come in a variety of series, which are specific to the type of stock being printed on. Different materials react differently to the various elements in inks. For example, the ink used for printing on certain plastics may not adhere to glass or aluminum. There are medical grade inks for use in the medical industry, as well as edible inks which can be pad printed onto sweets or other food products.

Pad-printing inks are similar to screen-printing inks. However pad-printing inks are designed to rapidly evaporation during the printing process. Also, pad-printing inks don't have the advantage of being applied in very thick films like screen-printing inks.

The Pad

Once the cliché is inked, the silicon pad then picks up the image and transfers it to the product or stock. The pads are made of a silicon material, which can vary hardness. The pad allows the inks to temporarily stick to the pad, yet fully release from the pad when it comes into contact with the product to be printed. The “durometer” of the pad dictates how the image molds to the product. For example to print an image on to a 3d spherical product a harder pad will get more of the image onto the surface. A larger image to be placed on a flat surface would normally require a fair amount of down pressure to print the entire image with a hard pad.

Advantages of Pad Printing:

A Variety of materials and objects, including glass, ceramic, and metal can be printed onto with suitable inks. Pad printing allows you to print fine details, the resolution is far better than that of screen printing in fact up to 120 lines / Cm (300 lines per inch). Pad offers easy handling and little maintenance, compared to other printing processes pad printing is easy to learn, as it requires very little technical input. Pad printing uses short preparation times as the plates and inks can be exchanged within a few minutes and also has low set up cost as plates can be produced in-house rather through a separate company which would increase the costs. Also linking with costs are that pad has a low drying cost as in the most simple case, air drying at room temperature is sufficient.

Limitations of Pad Printing:

Pad printing has limitations on the size of the motive as motives sizes are limited by plate, pad and efficiency of the pad-printing machine. The diameters of the largest efficiently printed motives are currently around 30 cm. The pad process uses plates up to a depth of approx. 20-25cm.

Printing speed has to be the biggest disadvantage of Pad printing in comparison with the other Rotary and Digital methods as even flat paper stocks can be printed a lot faster with other printing processes.