Solid ink (also known as hot melt ink or phase change ink) is a type of ink used in printing that is solid at room temperature and must be melted prior to use, unlike conventional liquid inks or toner powders. It is a waxy, resin-based polymer that is applied to a substrate in a molten state and then solidifies ("freezes") almost instantly upon contact with the cooler surface of the paper.
Design and Mechanism
Solid ink technology utilizes solid ink sticks, crayons, pearls, or granular solid material. In a solid ink printer, the solid ink is loaded into the printer, melted by a heating element, and then jetted onto a drum or directly onto paper using a heated printhead. The printhead uses piezoelectric devices to eject droplets of molten ink. Once the ink contacts the cooler paper, it solidifies immediately, producing a glossy, durable print.
History
Solid ink technology traces its origins to 1962 at Teletype Corporation under "Project 176." The first solid ink product was introduced with the Teletype Inktronic Terminal in 1966, which used wax-based ink in a continuous inkjet system. A patent for hot-melt wax ink was issued in 1972 (US3653932).
In 1984, Robert Howard founded Howtek, Inc., which developed the Pixelmaster printer using "hot melt" thermoplastic ink jetted by piezoelectric crystals. Dataproducts Corporation released the SI-480 monochrome solid ink printer in 1988 and the Jolt color solid ink printer in 1991. Tektronix introduced the PhaserJet PXi in June 1991, followed by a series of solid ink printers throughout the 1990s.
Xerox acquired Tektronix's Color Printing and Imaging Division in 2000 and continued producing solid ink printers under the Phaser and ColorQube product lines. Around the first half of 2016, Xerox discontinued selling solid ink printers.
Advantages
- Print quality: Produces precise, vibrant colors with a glossy finish. Performs well on low-quality paper stock.
- Media versatility: Can print on many types and thicknesses of media with less sensitivity to media type changes than color laser printers.
- Reduced waste: Solid ink blocks generate less waste than inkjet or laser printer cartridges, as there is no empty cartridge to dispose of—only minimal packaging.
- Intermittent use: Well-suited for environments with long periods of downtime, as solidified ink inside the delivery pathways does not dry out and helps protect internal components from oxygen and moisture.
- Safety: Solid ink blocks can be made non-toxic and safe to handle. In the 1990s, the president of Tektronix publicly ate a piece of solid ink derived from food-grade processed vegetable oils to demonstrate its safety.
Disadvantages
- Warm-up time: When cold, the printer may take several tens of minutes to produce the first page while the ink melts.
- Power consumption: The printer must keep ink heated near its melting point during use, consuming approximately 50 watts in sleep mode.
- Clogging: Solid contaminants can clog printhead nozzles, and replacing a damaged printhead can be costly.
- Immobility: The printer cannot be moved while containing melted ink without risk of damage. A special cool-down cycle is required before transport.
- Speed: Generally slower than inkjet or laser printers due to the melting process.
- Lamination difficulty: The wax-based ink can melt and smear under standard laminator temperatures.
- Discontinuation: Xerox discontinued solid ink printers around 2016, making the technology largely obsolete in the mainstream market.
Applications
Solid ink technology was used most often in graphics and large-format printing environments where color vividness and cost efficiency were important. It was also influential in the development of early 3D printing technologies, as the same thermoplastic inkjet mechanisms were adapted for additive manufacturing by companies such as Sanders Prototype, Inc. (later Solidscape, Inc.) and Ballistic Particle Manufacturing (BPM).
