Summary

Thermal printing technology has stood the test of time. Since 1972, its use has become widespread and it's typically the technology of choice when printing labels.  There are two methods for thermal label printing and most printers support both methods:

1. Direct Thermal
2. Thermal Transfer

When deciding which method is best, your decision should be based on which method best fits your unique labeling situation.

Direct Thermal

The print head applies heat to the label directly. When the printer, using a material sensitive to heat, exposes the label to the heat from the print head, the part of the label exposed turns dark. As the label runs under the print head, the dark markings from the heat form the label image. Thus, direct thermal printing requires specially formulated labels to work properly.

Direct thermal is known as a lower maintenance and cost-effective way to print thermal labels.  Sensitivity to ambient heat, however, means the label stock will degrade (i.e. start to darken) over time.  Think of old fax paper or the parking permit ticket often given by pay parking kiosks.  Thus, direct thermal is typically used in an environment where the label clarity and quality do not need to persist for extended periods of time.  Examples include:

• Labels at grocery store meat departments (the meat has long since gone bad by the time the label quality diminishes)
• FedEx and UPS shipping labels (if the package has not arrived by the time the label starts to degrade, there are big problems)
• Pallet and case labels on prepackaged food (the food will hit the expiry date long before the label degrades)

Thermal Transfer

The print head applies heat to a ribbon sandwiched between the label and print heat.  In this method of thermal printing, the print heat ‘burns’ the ribbon material on to the top of the label. The thermal print advances the ribbon at the same time as the label allowing the printer to continually transfer the ribbon ink to the label as it travels under the print head.

Thermal transfer is widely used in many industries for many purposes. It is still considered a superior printing method over newer printing technologies such as laser printing and inkjet printing in many situations. The main advantage of thermal transfer is the flexibility and adaptability to print durable permanent labels on wide variety of different label materials.  Materials used with thermal printing include paper, plastic, metal foil, fabric, polyester, Tyvek, rubber based compounds, and many others.  Commonly used thermal transfer label examples include:

• Durable product labeling (e.g. electronics, medical devices, etc.)
• Product certification labels (identifies the product meets certain standards)
• Asset tracking (often barcoding assets)
• Labeling for harsh environments (outdoors, wash-down in chemical or healthcare, etc.)

Conclusion

For many industrial labeling applications, thermal printing is the technology of choice.  Choosing the best type of thermal printing method (direct or transfer) is extremely important to make sure you get the results you require.  Consider the advantages and disadvantages of each type, while working with a knowledgeable labeling system integrator, to ensure you build a highly effective and efficient labeling system.

Other Related Articles

• Wikipedia article on thermal printing