What is direct thermal printing?
Direct thermal printing is a digital printing process that forms an image by heating thermochromic, heat-sensitive paper or label media. Electrically heated printhead elements apply heat to the media, causing the coating to change colour, commonly to black. Unlike thermal transfer printing, this method forms the image directly in the media rather than using a heat-sensitive ribbon.
At a glance:
- A thermal printer typically includes a thermal head, a platen that moves the paper, and a spring that holds the paper and printhead together.
- In conventional direct thermal printing, heating elements physically contact and slide against the thermal marking paper. Contactless direct thermal printing has also been explored as an alternative.
- Applications include bills and receipts, point-of-sale systems, and print-on-demand labels for shipping and products.
- Most thermal printers are monochrome, although some two-colour designs use different heat levels for black and an additional colour.
How does direct thermal printing work?
The process follows a heat-to-image sequence. In a conventional printer arrangement, electrically heated elements in the thermal head contact the media. At the same time, a platen moves the paper, and a spring holds the printhead and paper together.
Thermochromic image formation
Electrically heated elements in the printhead apply heat to thermochromic, heat-sensitive paper or label media. The coating changes colour in these heated areas, commonly turning black to form the image directly in the media. This action is a thermo-chemical reaction in special thermal marking paper, with the thermal printhead acting as the central printing component.
Thermal printer components and media contact
A typical thermal printer includes a thermal head, a platen, and a spring. The platen moves the paper, while the spring holds the paper and printhead together.
Conventional direct thermal printing relies on physical contact and sliding between the heating elements and the thermal marking paper. Contactless direct thermal printing has also been explored as an alternative.
Applications and colour output
Thermal-printing applications include bills and receipts, point-of-sale systems, and print-on-demand labels for shipping and products. Industrial label printers produce labels for these applications.
A label applicator performs the separate application function when a pre-printed label needs to be placed automatically. Most thermal printers are monochrome. Some two-colour designs use different heat levels to print black alongside an additional colour.
Direct thermal printing compared with thermal transfer printing
The two methods use similar thermal printheads, but their consumable arrangements differ. The comparison below focuses on the medium receiving heat and the material used during printing.
Image-forming medium
The direct process activates a thermochromic coating on heat-sensitive paper or media, with heat creating the image in that coating.
Thermal transfer printing heats a ribbon, transferring material from the ribbon onto a substrate. This transferred material then forms the printed image on that substrate.
TTO printers are used for thermal-transfer printing on packaging films, which is a separate application from direct thermal label printing.
Consumable arrangement
With direct thermal printing, the image forms directly in heat-sensitive media. The coating changes colour when heated.
Thermal transfer printing requires a heat-sensitive ribbon. During printing, material from the ribbon adheres to the substrate to create the image there.
Media and label-system boundaries
The process depends on the media itself to receive and form the image. At a system level, printing and label application are separate functions. Print-and-apply combines them when automated application is required.
Within integrated equipment, print engines can provide the printing module used as part of a wider print-and-apply system.
Heat-sensitive paper and label media
The image-forming medium is thermochromic and heat-sensitive. It may take the form of paper or labels, with the coating changing colour where the thermal printhead applies heat. The process uses labelling consumables as the image-forming media.
This direct image formation separates the process from ribbon-based printing. Media selection therefore focuses on the heat-sensitive material receiving the image, rather than a ribbon transferring material onto a separate substrate.
Printing and label application
A label printer prints labels for later use or integration, while label application sits outside the printer’s function.
Print-and-apply describes a combined system that brings variable-data label printing together with automated label application. The term direct thermal printing describes how the image is formed, while print-and-apply describes the wider combined printing and application function.
Barcode reading, code verification, vision inspection, RFID and traceability remain separate functions from printing. Printing a label alone does not establish that any of these activities take place.
When you need direct thermal printing: This method suits a requirement for an image to form directly in thermochromic, heat-sensitive media, such as a shipping or product label. Specify a separate application stage when the line must place that label automatically.
ALS Identify industrial label printers for direct thermal printing
For direct thermal printing requirements, ALS Identify supplies and configures industrial label printers for labels used later or integrated into a wider labelling system.
Contact ALS Identify to discuss the required printing setup.
