Thermal Papers in Kiosks
A key feature of modern kiosk systems is that they have to be in operation round the clock without supervision. They have to be available for use 24 hours a day, operate with absolute reliability and require little or no maintenance. And as a rule they have to print out variable information. Thermal printers offer a high quality solution to these demands, which is why more and more systems manufacturers are opting for thermal imaging technology.
By Thomas Wirtz, Business Unit Manager, Kanzan
The choice of paper is crucial
Generally, both topcoated and non-topcoated papers can be used in kiosk systems. However, topcoated papers produce thermal prints with considerably greater image stability than non-topcoated papers. So topcoated papers offer a reliable way of avoiding the traditional problem of ‘image fading’.
Thermal heads are sensitive
The thermal head is the most sensitive and fragile element in the whole system of a thermal printer. Paper which is unsuitable or of inferior quality, even when it has not been pre-printed, can destroy the thermal head and so put the thermal printer out of operation.
The chemical components of the thermal paper may lead to deposits forming on the thermal head. Mostly it is the so-called sublimation effect which plays a main role here. Due to the effect of the thermal energy (heat), the thermal coat melts for a fraction of a second at the thermal head. However, if the chemicals used in the thermal coat are too abrasive or have too high a concentration of ions, this may result in the thermal head being soiled or damaged. This considerably impairs the heat transfer and thus the quality of the thermal image.
Figure 3 shows a thermal head soiled through use of unprinted, inferior quality thermal paper. As a result, this thermal head will need replacing after only a short time in operation.
In comparison, Figure 4 shows a thermal head which has been run for a longer period of time using Kanzan thermal paper. The deposits are so minimal that the thermal head, thanks to its self-cleaning function, can protect itself against damage.
Basically, topcoated thermal papers considerably increase the service life of thermal heads. This is partly due to the greater smoothness of the paper and the resulting reduction in mechanical friction. In addition, there is no sublimation effect as described above, since a perfectly functioning topcoat does not melt at the thermal head. The heat transfer affects only the thermal coat below the topcoat, thus generating the thermal image.
Further processing requires expert knowledge
Another possible reason for the breakdown of a thermal printer might lie in inadequate further processing of the thermal paper, especially with respect to pre-printing. Here, pre-printing means the application of inks to the front or reverse side of the thermal paper. When pre-printing thermal papers, it is essential to make sure that only suitable inks are used. Moreover, these inks must also be applied correctly.
The temperature at a thermal head may easily reach up to 250°C during the thermal imaging process. So the inks applied during pre-printing must be appropriately temperature-resistant and must not smear when heated.
If the inks are not suitable and/or were not correctly cured, the ink may smear off at the thermal head, which will inevitably lead to soiling and deposits after a very short time, and these will result in the thermal head breaking down. This phenomenon is well illustrated in Figure 5b.
The heat transfer in the figure on the right is strongly impaired by the smeared-off ink. The heat can no longer escape. At first this results in athermal image which is grimy, blurred and no longer sufficiently blackened. Very soon, a thermal head like this will have been completely destroyed, since the resistors in the thermal head will burn out.
Whether non-topcoated or topcoated thermal papers, whether printed or non-printed, correct processing of thermal papers is a key factor in ensuring a long service life of the thermal head and in securing the smooth operation of the kiosk system. This guarantees an essential performance feature of such systems, namely their operability round the clock without supervision, and thus their availability for the customer 24 hours a day.
After years of intensive market testing in collaboration with specialists from printing houses and ink manufacturers, Kanzan has developed extremely good know-how on this subject and has compiled a comprehensive list of tested systems and their operational conditions call for a wide range of different thermal papers, which can be found in Kanzan’s product portfolio. It is thanks to Kanzan’s commitment to quality that direct thermal imaging, as long as the right materials are used, has developed into an extremely reliable technology for kiosk systems.