A Closer Look at Digital Dye-Sublimation Printing

It is possible that some of us recall the 1980s, when dye-sublimation printers first became available for purchase. In the 1990s, they gained considerable popularity for color proofing, and tiny dye-sub photoprinters were marketed as add-ons for the initial digital camera models. Although it was believed at the time that the dye would sublimate, these printers were not actually dye-sublimation printers. In hindsight, the term dye-diffusion printer would have been more appropriate for them. The dyes do sublimate in modern printers used, among other things, for textile printing.

A key perhaps to understanding dye sublimation is understanding what sublimation is. As you probably recall from high school chemistry or physics, sublimation is the physical process whereby a substance transitions from the solid phase directly to the gas phase without first passing through the liquid phase. The emblematic example of sublimation in action is dry ice, which is frozen carbon dioxide which immediately become a gas at room temperature. Sublimation takes place because of heat, because of pressure, or both.

(By the way, sublimation in this context is distinct from the psychological concept of sublimation, which Freud defined as “the process of deflecting sexual instincts into acts of higher social valuation.” As far as I know, this type of sublimation has yet to be applied to a printing technology, although I bet it would liven up press conferences.)

The opposite of sublimation is called deposition, the process by which a gas transitions directly into a solid without first becoming a liquid. Examples of this are snowflakes and frost, which is the result of water vapor (a gas) becoming a solid without first condensing into liquid water.

In the context of dye-sublimation printing, how does this operate? As you are well aware, an ink is made up of two primary components: a vehicle, which is a liquid that is used to transfer the colorant to the substrate, and a colorant, which is a pigment or dye. Although it's usual to think of pigments and dyes as liquids and solids, respectively, the truth is that both are solids, with solubility being one of their numerous differences. Pigments are generally insoluble in water and other solvents, although dyes and dyestuffs are soluble.

So, in traditional (if we can use that term at this stage) dye-sublimation printing, the ink consists of solid dye particles in a liquid suspension, usually water-based. The dye-sublimation printer transfers the ink to a transfer medium, usually sublimation paper. The sublimation transfer paper has a special coating that will not only accept this ink, but also facilitate its release in the next step of the process. It should also be noted that the image is printed in reverse on the dye sublimation paper.

The next step, variously called fixation or outgassing, involves a heat press, which can either be rotary or flatbed. Usually the term heat press refers to flatbed devices used for the fabric equivalent of sheets, while the term calender is used to refer to a fixation unit used with rolls.

In the heat press, the printed transfer paper is brought into contact with the fabric that is to be imaged. If you are planning to print on a stretchy material, you may get better results by using a tacky transfer paper that will adhere slightly to the fabric so that it won’t shift during fixing and cause blurring, ghosting, or other imaging imperfections.

Here’s the sublime part. Under the heat (around 375° to 410°F, depending on the fabric) and pressure of the heat press or calendering unit, the solid dye on the printed transfer paper is converted to a gas and penetrates (gasses or outgasses) into the fabric. The dye then resolidifies on the fibers of the fabric which makes the colors quite durable, wash-resistant, and colorfast.

The greatest results will be obtained using 100% (or at least most of the time) polyester materials when using this procedure. Why not use organic materials like cotton? The polyester, which is essentially a plastic, is slightly melted by the same heat that sublimates the color. (It is not good for cotton or other natural fibers to be subjected to the heat of a heat press; they will burn instead of melting.) By "melting," I don't mean that the cloth becomes a sticky mess; rather, I mean that it merely melts just enough to cause minute gaps in the polyester threads, which the gaseous color subsequently fills in. The dye and the fibers resolidify and fuse together when the heat is removed. This explains the remarkable colorfastness and durability of dye-sub printing.