Thermal transfer

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In printing, a thermal transfer is the transfer of a design or text onto paper by the melting of wax within the print-heads of a specialized printer. Thermal transfer is preferred over direct thermal printing on surfaces that are heat sensitive or when higher durability of printed matter (especially against heat) is desired.

Thermal Transfer is a popular print process particularly used for the printing of identification labels. It is the most widely used printing process in the world for the printing of high quality barcodes. The thermal transfer print process utilises three main components: a non-movable print head, a carbon ribbon (the ink) and a substrate to be printed, which would typically be paper, synthetics, card or textile materials. These three components effectively form a sandwich with the ribbon in the middle. A thermally compliant print head, in combination with the electrical properties of the ribbon and the correct rheological properties of the ribbon ink are all essential in producing a high quality printed image.

Print heads are available in 203 dpi, 300 dpi and 600 dpi resolution options. Each dot is addressed independently and when a dot is electronically addressed it immediately heats up to a pre-set, (adjustable) temperature. The heated element immediately melts the wax or resin based ink on the side of the ribbon film facing the substrate and this process, in combination with the constant pressure being applied by the print head locking mechanism immediately transfers it onto the substrate. When a dot ‘turns off’ that element of the print head immediately cools down and that part of the ribbon thereby stops melting/printing. As the substrate comes out of the printer it is completely dry and can be used immediately.

Carbon ribbons are on rolls and are fitted onto a spindle or reel holder within the printer. The used ribbon is rewound by a take-up spindle forming a roll of ‘used’ ribbon. It is termed a ‘one-trip’ ribbon because once it has been rewound the used roll is discarded and replaced with a new one. If one were to hold a strip of used carbon ribbon up to the light one would see an exact negative of the images that have been printed. The main benefit of using a one-trip thermal transfer ribbon is that providing the correct settings are applied prior to printing, an 100% density of printed image is guaranteed; compare this with a pre-inked ribbon on a dot matrix impact printer ribbon which gradually fades with usage.

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