What is Direct Thermal Barcode Printing?

By Tim Walker

The first concept we are going to look at is the difference between the two primary printing methods: Direct Thermal and Thermal Transfer. Both technologies have their advantages and disadvantages. Which one you chose is dictated by your needs. The good news is most barcode label printers, outside of the small desktops, have the ability to utilize both technologies.

Direct Thermal

• Uses special heat sensitive media
• Does not use a ribbon (advantage) but does not stand up to heat or light (disadvantage)
• Used for temporary labeling applications like shipping labels
• The chemical process that creates the image will fade over time

Direct Thermal Basics

Direct Thermal (also known as Thermal Direct) works by directly heating a heat sensitive label. The printhead comes in direct contact with the media. For this method you have to use a special heat sensitive media. These Direct Thermal labels have a layer of heat sensitive dye which is clear until heated. Where the printhead heats up an image is formed on the label. Direct Thermal has the advantage of not using a ribbon. There is no down time replacing the ribbon when empty, and no extra expense of purchasing ribbons. The disadvantage is Direct Thermal labels use a chemical process to print. These chemicals will break down over time, causing the print to fade and the label to yellow. How long this takes can depend on a number of variables including light and heat levels.

The lack of a ribbon also causes the second disadvantage. The ribbon used in Thermal Transfer printing has a special coating on the back that helps protect the printhead. Compared to this coating the label itself is like sandpaper. It will wear the printhead down over time. Some of the extra cost of using ribbons can be offset by a longer printhead lifespan. However, this is really only a factor in high volume printing applications. In most low volume applications the life of the printhead even using Direct Thermal, is as long as the life of the printer.

Where you see Direct Thermal Labels

The limited life span of Direct Thermal labels means they are best used for labels that have a temporary life span. Direct Thermal is most often seen in applications like shipping labels. Labels that while important are disposable. Once the product reaches its destination it is no longer needed. Receipt printing, traffic tickets, pharmacy labels, packing list, patient and retail price tags are also examples of common applications in which Direct Thermal is often used.

Advantages of Direct Thermal

• No ribbon to deal with
• Fewer internal parts
• Great solution for short life span labels

Direct Thermal printing has advantages over Thermal Transfer printing – the main advantage is that it does not require a ribbon. This reduces downtime changing ribbons, reduces cost since no ribbons are to be purchased, and media mismatch issues (label smears/flake off) do not happen. Another advantage of not having a ribbon is that the ribbon mechanism that keeps the ribbon taut and wrinkle free is not needed so you should see a decreased cost in the printer and have the benefit of less internal moving parts to break or jam during use. Direct Thermal labels are a perfect solution for temporary labeling needs that do not require exposure to extreme environments and ideal for shipping or work in process tickets.

Disadvantages of Direct Thermal

• Direct Thermal paper will deteriorate over time
• Direct Thermal paper can deteriorate in adverse environments
• Printhead wear

Direct Thermal printing has disadvantages as well. Since the labels are not archival quality due to the nature of the media composition, they will yellow/fade over time as the paper breaks down. Direct Thermal labels will deteriorate when exposed to extreme temperatures as seen in a non-temperature controlled warehouse. Direct Thermal labels also offer no printhead protection – the media (in comparison to a ribbon) is abrasive as it passes the printhead. In time this abrasion can cause printhead pixel failure which would reduce print quality and possibly require a printhead or printer replacement.