Direct thermal printing requires the print head elements be in direct contact with the label material as it is pulled across the print head. Conversely, thermal transfer printing has thermal ribbon acting as a “buffer” between the print head elements and the label material. Many thermal ribbons are designed with a back-coating that serves to increase print head life by reducing static and friction. This benefit is not possible when direct thermal printing due to the lack of ribbon. Instead, the label material is in direct and constant contact with the print head, resulting in increased wear when compared to thermal transfer printing.
In direct thermal applications, dust and debris that may become present on labels are in direct contact with the print head. As these foreign materials are pulled across the print head, they may burn onto the elements or physically damage the elements resulting in poor print quality and/or premature print head failure. The same foreign material can exist in thermal transfer printing applications, but the debris would be between the label and the ribbon (i.e. not in contact with the print head elements) reducing the potential for damage.
Print head life in direct thermal printing applications is significantly reduced when compared to thermal transfer printing applications. Generally speaking, a company should anticipate direct thermal print heads providing an expected lifetime of 25% – 50% of a thermal transfer print head. As an example, if a company is printing 10 million, six inch long labels per period with an expected thermal transfer print head life of 4 million inches, they would expect to replace the print head 15 times. If the same application were direct thermal, they would expect to replace the print head 30 – 60 times. Depending upon throughput volumes, the cost differential may be significant and has to be considered in any evaluation.