A dye-sublimation printer (or dye-sub printer) is a computer printer which employs a printing process that uses heat to transfer dye onto a medium such as a plastic card, paper, or fabric. The sublimation name is applied because the dye transitions between the solid and gas states without going through a liquid stage. Many consumer and professional dye-sublimation printers are designed and used for producing photographic prints.
Most dye-sublimation printers use CMYO (cyan, magenta, yellow and overcoating) colors, which differs from the more recognized CMYK colors in that the black dye is eliminated in favour of a clear overcoating. This overcoating (which has numerous names depending on the manufacturer) is also stored on the ribbon and is effectively a thin laminate which protects the print from discoloration from UV light and the air, while also rendering the print water-resistant.
The most common process lays one color at a time, the dye being stored on a cellophane ribbon that has each color on a separate panel. Each colored panel is the size of the medium that is being printed on; for example, a 6" by 4" dye sub printer would have four 6" by 4" panels.
During the printing cycle, the printer rollers will move the medium and one of the colored panels together under a thermal printing head, which is usually the same width as the shorter dimension of the print medium. Tiny heating elements on the head change temperature rapidly, laying different amounts of dye depending on the amount of heat applied. After being heated into a gas, the dye diffuses onto the printing medium and solidifies.
After the printer finishes covering the medium in one color, it winds the ribbon on to the next color panel and partially ejects the medium from the printer to prepare for the next cycle. The entire process is repeated four times in total: the first three lay the colors onto the medium to form a complete image, while the last one lays the laminate over top. This layer protects the dye from resublimating when handled or exposed to warm conditions.
Comparison with inkjet printers
Traditionally, the advantage of dye-sublimation printing has been the fact that it is a continuous-tone technology, where each dot can be any color. In contrast, inkjet printers can vary the location and size of ink droplets, a process called dithering, but each drop of ink is limited to the colors of the inks installed. Consequently, a dye-sublimation printer produces true continuous tones appearing much like a chemical photograph. An inkjet print is composed of droplets of ink layered and scattered to simulate continuous tones, but under magnification the individual droplets can be seen. In the early days of inkjet printing, the large droplets and low resolution made inkjet prints significantly inferior to dye-sublimation, but today's inkjets produce extremely high quality prints using microscopic droplets and supplementary ink colors, producing superior color fidelity to dye-sublimation.
Dye sublimation offers some advantages over inkjet printing. For one, the prints are dry and ready to handle as soon as they exit the printer. Since the thermal head doesn't have to sweep back and forth over the print media, there are fewer moving parts that can break down. As the dye never enters a liquid phase, the whole printing cycle is extremely clean; there are no liquid inks to clean up. These factors make dye-sublimation generally a more reliable technology over inkjet printing.
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