The image made by a Thermal Transfer Printer appears when a substrate and ink ribbon contact a heated print-head. The heat from the print-head melts the ink on the ribbon and releases (transfers) the ink directly onto the substrate. The printer uses a Thermal Transfer Ribbon, often abbreviated to TTR.
Thermal Transfer is mostly used for printing variable information. This particularly concerns information for identification, such as barcodes, batch codes and expiry dates. Thermal Transfer is the preferred method when a durable print is needed, for example against heat, chemicals and abrasion. In addition, Thermal Transfer works well in making highly durable non-variable information, such as warning signs.
Printing with Thermal Transfer Ribbons is a proven technique to deliver durable variable codes, such as barcodes, that always read or scan. It produces dense, high-resolution images in colour or black-and-white. Additionally, it can be used on a wide variety of substrates. Images made with Thermal Transfer Ribbons are highly resistant to chemicals and extremely durable. The printers work at high speeds and require little maintenance.
The ink used in the Thermal Transfer process can be made with wax, resin, or wax/resin. As a result, the different types of ribbons have a different print sensitivity. This means they transfer ink at different temperatures of the printhead. The requirements of the application determine which ink is needed.
Two types of printers are used: flat-head and near-edge.
In a Wax Thermal Transfer Ribbon, the pigments of the ink are captured in wax. The wax is quite soft and therefore transfers at relatively low temperatures. It also fills up unevenness in the surface of the printed material/substrate. Therefore, wax ribbons are the standard for printing on (un)coated paper and other materials with a rougher surface. Due to the ability to fill up uneven surfaces, these ribbons deliver a high optical density print for scannable barcodes and other variable information.
In a Wax/resin Thermal Transfer Ribbon, the ink is captured in a mix of soft wax and hard resin. Wax/resin ribbons make prints that are more resistant to scratching, rubbing and chemicals. These ribbons need a higher temperature for the ink to be transferred onto the substrate. Wax/Resin Thermal Transfer Ribbons are suitable for both print & apply and in-line flexible packaging applications. For in-line printing at high speed, wax/resin ribbons are the obvious choice.
In a Resin Thermal Transfer Ribbon, the ink is captured in resin. Resins are hard and provide the highest possible resistance against severe abrasion, harsh chemicals or other severe circumstances. Resin ribbons require a higher transfer temperature setting of the printer over wax or wax/resin ribbons. Typical applications where resins are used are labelling of chemicals, marking of laboratory samples and challenging circumstances in, for example. the automotive and electronic industry.
Flat-head printers have a traditional printhead that can generally provide image resolutions between 200 and 600 dots per inch (DPI), in some cases, this can go up to 1200 DPI. Their ribbons are married with labels for a small distance to the peel point after passing the heating element. These models will generally print at speeds up to 12 inches per second (IPS). Some printers are able to print up to 20 IPS when the right ribbon is selected.
In contrast, near-edge printers with their floating printheads will run more than twice as fast. Speeds over 26 IPS are the norm where 55 IPS is also reached by certain printer-ribbon combinations. Ribbons for near-edge printers are married with labels only for an instant prior to the peel point, requiring a special formulation engineered for quick release of ink from the base PET film. A floating printhead means not having to make adjustments for various media thicknesses. In addition, the image resolution for these printers is lower at between 200 to 300 DPI.
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