Thermal transfer printing
Thermal transfer printing is a digital printing process in which material is applied to paper (or some other material) by melting a coating of ribbon so that it stays glued to the material on which the print is applied. It contrasts with direct thermal printing where no ribbon is present in the process. It was invented by SATO corporation around the late 1940s.
Color thermal printers
Thermal printing technology can be used to produce color images by adhering a wax-based ink onto paper. As the paper and ribbon travel in unison beneath the thermal print head, the wax-based ink from the transfer ribbon melts onto the paper. When cooled, the wax is permanently adhered to the paper. This type of thermal printer uses a like-sized panel of ribbon for each page to be printed, regardless of the contents of the page. Monochrome printers have a black panel for each page to be printed, while color printers have either three (CMY) or four (CMYK) colored panels for each page. Unlike dye-sublimation printers, these printers cannot vary the dot intensity, which means that images must be dithered. Although acceptable in quality, the printouts from these printers cannot compare with modern inkjet printers and color laser printers. Currently, this type of printer is rarely used for full-page printing, and is now employed for industrial label printing due to its waterfastness and speed. These printers are considered highly reliable due to their small number of moving parts. Printouts from color thermal printers using wax are sensitive to abrasion, as the wax ink can be scraped, rubbed off, or smeared. However, wax-resin compounds and full resins can be used on materials such as polypropylene or polyester in order to increase durability.
Tektronix/Xerox solid-ink printers
So-called "solid ink" or "phaser" printers were developed by Tektronix and later by Xerox (who acquired Tektronix's printer division). Printers like the Xerox Phaser 8400 uses 1 in³ rectangular solid-state ink blocks (similar in consistency to candle wax) which are loaded into a system similar to a stapler magazine in the top of the printer. The ink blocks are melted and the ink is transferred onto a rotating, oil coated print drum using a piezo inkjet head. The paper then passes over the print drum, at which time the image is transferred, or transfixed, to the page. This system is similar to water-based inkjets, provided that the ink has low viscosity at the jetting temperature (140°C). Printout properties are similar to those mentioned above, although these printers can be configured to produce extremely high-quality results and are far more economical, as they only use the ink needed for the printout, rather than an entire ribbon panel. Costs of upkeep and ink are comparable to color laser printers, while 'standby' power usage can be very high, about 200W.
ALPS MicroDry printers
MicroDry is a computer printing system developed by the ALPS corporation of Japan. It is a wax/resin-transfer system using individual colored thermal ribbon cartridges, and can print in process color using cyan, magenta, yellow, and black cartridges, as well as such spot-color cartridges as white, metallic silver, and metallic gold, on a wide variety of paper and transparency stock. Certain MicroDry printers can also operate in dye sublimation mode, using special cartridges and paper.
Usage of TT printers in industry includes:
- barcode labels (as labels printed with thermal printer tend not to last long), or for marking clothing labels (shirt size etc.)
- Printing plastic labels for chemical containers (because the cheaper types of plastic would melt in a laser printer)
Barcode printers typically come in fixed sizes of 4 inches, 6 inches or 8 inches wide. Although a number of manufacturers have made differing sizes in the past, most have now standardised on these sizes. The main application for these printers is to produce barcode labels for product and shipping identification.