Due to the ever-growing number of bank cards and the worldwide replacement of magnetic strips with modern EMV (electromagnetic compatibility) based security technologies, there is a high demand in the field of bank card personalization. After continuous further development of the first printing processes, thermal transfer and embossing technology, DoD printing is increasingly being used to achieve better results with significant cost savings. The world's two largest credit card companies, Mastercard and Visa, have now approved this technology for all their products.
The processes for bank card personalization at a glance:
Embossing technology
The first process that was used to personalize plastic cards and is still mainly used for credit cards today is embossing technology. In this process, a heated, metallic embossing die is pressed into the back of the plastic card with great force. On the front of the card, a negative of the printing form presses a monochrome ink ribbon onto the stamped areas and transfers the ink. For credit cards, silver or gold foil is often used instead of ink. This creates an aesthetically pleasing and very durable personalization.
When bank cards were still recorded mechanically, embossing was used to carry out transactions. For this purpose, the embossed number was printed on a receipt together with the amount to be paid using an imprinter, better known as a "Ritsch-Ratsch device". This receipt had to be taken to the bank by the customer, only then was the transaction carried out. With the advent of electronic payment methods, the embossing process increasingly lost this technical significance, as electronic payment processes are significantly faster and creditworthiness can be checked directly during the payment process.
Thermal transfer
Thermal transfer printing is a widely used process for personalizing chip cards and generally for printing on 3-dimensional objects. A special color foil is used for imaging. This is placed between the substrate and a thermal print button. The thermal print button contains a large number of controlled heating elements, which heat the foil at certain points and thus release the ink from it. To print multi-colored images, several print heads can be used (single-pass system) or different colors can be periodically applied to the ribbon (multi-pass system). This means that 4 individual color transfer processes are required for a four-color image. Resolutions of up to 600 dpi are possible with thermal transfer systems, which are also frequently used for printing photographs.
Ink Jet
The inkjet process is one of the most commonly used technologies in digital printing systems and is also used in commercially available inkjet printers. It is a computer-to-print (CtP) technology, whereby the data to be printed is processed by the computer and transferred to a printing unit that does not require an additional stencil or other aids. Imaging is carried out by spraying the ink directly using controlled nozzles. This means that the information to be printed can be transferred to the image carrier in the shortest possible way and with a minimum of functional units.
There are two different ways of implementing inkjet printing. One is continuous ink jet technology, whereby small drops of a continuous stream of ink leaving the nozzle are directed onto the paper depending on the image. The second is drop-on-demand technology, whereby drops of ink only leave the nozzle when they are needed in the image. The second variant is much more important both in the personalization of chip cards and in domestic inkjet printers.
Process of Drop on Demand
Thermal Ink Jet
The Thermal Ink Jet process is based on heating the ink and the resulting pressure differences. A heating element is installed in the nozzle, which heats the ink to boiling point. This causes some of the ink to change into the gaseous phase, generating high pressure and "shooting" the ink out of the nozzle onto the material to be printed. If the temperature drops, the bubble condenses, resulting in a lower pressure in the nozzle than in the connected ink container and ink is sucked into the nozzle.
With thermal ink jet technology, drop volumes of approx. 23 pl are achieved, making resolutions of 600 dpi possible. With the standard size of chip cards in ID-1 format, this corresponds to a resolution of around 2000 * 1250 pixels. This enables many design options and depth of field for printed photographs or other images. The drop frequencies are in the range between 5 and 8 kHz, which enables a single chip card to be printed with the minimum number of 4 nozzles (black, cyan, magenta and yellow) in around 125 seconds. In modern inkjet systems, arrays with several thousand nozzles are sometimes possible, which shortens the production time proportionally.
Piezo Ink Jet
The Piezo Ink Jet process works in a similar way, but the ink is not ejected as a result of thermal heating but by mechanical displacement. Piezo ceramics are used to generate the necessary pressure differences. These are materials that spontaneously change their shape or volume below the Curie temperature (150 °C - 200 °C) as a result of electromagnetic forces. Applying a voltage to the ceramic causes it to deform, as in piezo tweeters. However, the effect also works in reverse, for example in electric lighters or record players, where the voltage is generated by deformation.
The so-called bend mode is used for the printing technology. Here, the ceramic forms the back wall or ceiling of the nozzle chamber. A voltage is applied to the piezo ceramic, which bends as a result and changes the volume of the ink chamber. The drop is formed and new ink is drawn into the chamber when the piezo ceramic is released. In shear mode, the piezo ceramic is controlled differently so that the crystals generate gravity. The crystals, which are fixed to the top of the nozzle chamber, create trapezoidal deformations. These generate the necessary pressure to form a droplet.
With Piezo Ink Jet technology, significantly higher drop frequencies of up to 125 kHz are possible. Other advantages are that the ink does not have to be heat-resistant and pigmented inks can also be used. One disadvantage is the production costs, as piezo ceramics have a significantly higher base price than a simple heating resistor.
Conclusion
Embossing is now an outdated process that has not evolved much and is used almost exclusively on credit cards. Embossed plastic cards are intended to convey a higher value to the customer. However, holograms and high-resolution printed microprinting or guilloches are used as security features. The characters per line and fonts are still very limited, which means that embossing can be easily imitated. Embossing therefore serves more as a visual enhancement than as a security feature. While embossed credit cards have no longer been issued in the USA since 2008, embossed prepaid credit cards are currently in demand in Germany, as they give the impression of a "real" credit card and are intended to suggest a high credit rating, which is not necessarily true.
The advantages of embossing are the almost unlimited durability and the mechanical readability of the embossed digits. Embossing is problematic when using contactless RFID cards, as the antenna could be damaged in the area of the embossing, which is why particular attention must be paid to its geometry.
Inkjet printing is a successful alternative to previously used personalization processes for chip cards. Modern security features mentioned above can be printed without any problems.
Operating costs can be significantly reduced in comparison to the frequently used thermal transfer printing, in some cases by more than 90 %. Thanks to special UV ink, chip cards produced using the inkjet process are significantly more abrasion-resistant and therefore more durable. The personalization process can be carried out up to three times faster and, thanks to non-contact printing, is virtually wear-free and can therefore be repeated as often as necessary. As inkjet is a CtP technology, it is very easy to make adjustments to the design, data, font or similar, which makes personalization very flexible.
In principle, there are many advantages over older technologies, and inkjet printing looks set to become the most widely used method for personalizing bank cards in the near future. With the continuous development of three-dimensional inkjet printing, new, mechanically detectable security features are sure to emerge.
