Dye Sublimation

Technology

Dye sublimation ("dye sub") printers first became commercially available during the 1980’s. By the 1990’s, however, dye sublimation printers had been reduced enough in size to make 4x6 print devices commonly sold today. Dye sublimation printers (technically referred to as dye diffusion thermal transfer printing) use heat to transfer cyan, magenta, and yellow dyes from a plastic donor ribbon to the paper via a thermal printing head. The temperature of the printing head can be varied up to 256 levels to control the total amount of colorant transferred. This means that any spot on the print can be very light, mid-tone, very dark or any level in between. This differs from inkjet and electrophotographic which can only apply one level of colorant and must use halftone patterns to create the illusion of tonality. Dye sublimation also differs from inkjet and electrophotographic in that it is only used to print photographs and never documents. After the last color is printed the printer then applies a clear overcoat. This overcoat protects the dyes from atmospheric pollution, moisture, or water damage.

The thermal head heats the dyes on the donor ribbon causing them to diffuse into the paper’s receiver layer. A clear plastic sheet is applied over the dyes to protect them from moisture and airborne pollutants. The movement of dye from the carrier ribbon to the paper is shown above.

Image Structure

Dye sublimation images are made up of millions of tiny squares. Each square can be made to a different tone ranging from white all the way to black. Because the dyes can be printed at different densities, they do not need white spaces between the squares like inkjet and electrophotographic images do. They are, thus, continuous tone images as opposed to half tone images.

The photo below is a micrograph showing a dye sublimation print’s image forming squares. Notice the lack of white spaces between the image elements. Also, soft lines across the image surface betray the heater array used to diffuse the dye from the carrier ribbon to the paper.

Close up of a dye sublimation print

Colorants and Paper

All dye sublimation printers use cyan, magenta, and yellow dyes to create the image. The only papers available for any given printer model are the ones produced by that printer’s manufacturer. The papers are made using the same base that is used for traditional color photos so that they look and feel like “real” photographs. These papers are called RC papers (resin-coated) because they have a thin layer of polyethylene on each side. This gives the back of the print a plastic feel. In most cases only glossy papers are available for dye sublimation printers although newer dye sub printers at retail can vary the overcoat to produce a more matte surface appearance, called laminate modulation technology. The diagram below shows the layers that make up the dye sub print.