Editor’s Note: The information on this page is intended to give you a brief overview of solid ink printing. Instead of going into great detail, this page provides just the basic concepts. It is based on a more comprehensive and technically detailed essay. At the bottom of this page, you’ll find information on where to find the complete text.

Color Solid Ink Printing
C. Wayne Jaeger, Ph.D., Xerox Corporation

How does a solid ink printer work?

Normally ink is thought of as a liquid. However, there is a printing technology that utilizes solid ink, also called phase change ink or hot melt ink.

The concept of solid ink is that it is solid at normal ambient temperatures but in the printing device, the ink is melted, converting it into a liquid that can be applied much as any other liquid ink is handled. The real advantage of solid ink over aqueous ink is that the molten ink does not have to dry.

Instead, the ink freezes (solidifies) almost instantaneously on the cool printing surface. In addition, solid ink does not wick into the paper as liquid inks do. It remains bound to the surface of the paper, resulting in more vivid colors and producing an enhanced color range.

The heart of the printer is an anodized aluminum cylindrical drum. The uniformly heated (135 °C / 275 °F) printhead sprays microscopic drops of molten ink onto the rotating print drum very precisely. The print drum is maintained at an intermediate temperature (65 °C / 150 °F). The ink droplets striking the oiled print drum change almost instantly from a molten liquid to a malleable semisolid.

Figure 1. Solid ink printer with offset printing. Molten color ink is sprayed onto the drum by an ink-jet printhead.

The paper to be printed passes through a preheater into a pressure nip formed by a pressure roller and the print drum. Under heat and pressure the image transfers from the drum onto the paper in a single pass. By the time the paper exits the printer the ink has fully set and the print is immediately ready for use.

Figure 2. Solid ink printer with offset printing path. Semi-solid color ink transfers from the drum onto a heated sheet of paper.

The prints are completely water-fast. Because the inks are not liquid when they come in contact with the paper, the ink fuses to the paper rather than soaking into it, giving vivid colors on a wide range of papers.

Figure 3. Cut-away view of a solid ink printer

Because of solid ink's good image quality, photographers are now using it to generate proof sets for school pictures. Many schools are using the printer because it can print on just about any paper. The printed image is unaffected by humidity or temperature and is consistent week after week and month after month through many years of use.

© Copyright 2009 Society for Imaging Sciences and Technology. All Rights Reserved.
Reprinted with permission of IS&T: The Society for Imaging Science and Technology and C. Wayne Jaeger.

Note: This is an edited (shortened) version of the original essay. The original full-length essay is located at the following URL:
http://www.imaging.org/ist/resources/tutorials/solid_ink.cfm