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.
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.
How does this work in the context of dye-sublimation printing? As you well know, an ink comprises two basic elements: a colorant, which is a pigment or a dye, and a vehicle, which is a liquid that is used to transport the colorant to the substrate. It’s common to think of dyes as liquids and pigments as solids, but actually both are solids, and the real difference between them is solubility (among many other things). Generally speaking, dyes and dyestuffs are soluble in water and other solvents, while pigments are not.
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 paper. The sublimation 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 transfer 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.
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