Thermal Transfer Labels Guide

We have all seen thermal transfer labels. They are everywhere and on nearly every product we purchase. The most common form of thermal transfer labels are UPC or bar code labels. They are a series of vertical lines or bars of different widths, representing digits zero through nine, which can be read by a laser scanner. Bar code labels and all thermal transfer labels are created by thermal transfer printing.

The thermal transfer process is one of the most popular methods for producing quality, free format, and on-demand printed images. The many advantages of this process include low equipment and maintenance costs, and high quality images. During the 1960′s the development of the thermal transfer ribbon printer began, becoming more intensified by the late 1970′s and by the early 1980′s huge volumes of thermal transfer printers were on the market. Today the technology has continued to advance with the development and refinements of such items as ribbon films, ink coatings, receiver media, and printer mechanism designs.

The Advantages and Disadvantages

Thermal transfer printing and thermal transfer labels have several advantages, making their technology extremely attractive for bar code printing. Some of their advantages include flexible format, graphic capability, high quality printing, required very little maintenance, and high density bar code capability including the ability for infrared scanning.

However, though thee advantages are revolutionary, thermal transfer printing and thermal transfer labels do have several drawbacks including the fact that thermal printer heads requiring frequent replacing. Another draw back is the print speed is very limited. This is because of the time required to heat the print head to transfer ink from the ribbon onto the media, and then the time required to cool the print head for the next print cycle. New thermal transfer labels have a maximum speed for printing about six to eight inches per second, however the most common is two to three inches per second. The speed of thermal transfer printing is constantly being improved, with faster output rates expected in the near future.

Smudging is another draw back with thermal transfer images, especially if they are rubbed or scratched with a hard object. The reason for this is because of the type of ink used has a low viscosity when heated so that the ink can be transferred onto the receiving media. The ink used is rather soft at room temperature, very much like wax crayons, once heated, the ink can be smeared. With the use of resin melt agents, it was possible to create thermal transfer ribbons, which produced a smear free image, however, these inks require a higher transfer temperature, which reduces the life of the thermal print head, thus require it to have to be replaced frequently. Having a proper match between both the thermal ink and the thermal transfer labels, or receiving media, improves smudge resistance.

Thermal transfer print bar codes are sufficient for non-contact scanning applications. However, just like any other printed image, if handled roughly or is scanned frequently the image life is decreased. Therefore, to protect the bar code or image when subjected to abuse or a harsh environment, a protective overlaminate should be used.

Hotter print head temperatures will increase the amount of ink to the thermal transfer label, creating larger, darker bar code bars, whereas lower temperature print heads will produce thin bar code bars, which will have gaps and voids that are caused by inconsistencies on the thermal transfer label surface. To avoid this, care should be given when adjusting the heat settings according to the label manufacture to guarantee the production of the correct bar code widths. When printing bar codes, it is important to periodically verify the print quality, no matter what printing technology is being used to ensure conformance to the correct bar code specifications.