How can sublimation ink work on polyester fiber?

Sublimation printing accounts for around 6% of textile printing in the world. It is mainly applied to Polyester fabrics and uses disperse inks. These inks have the ability to move from a solid to a gas directly. The inks are printed on lightweight paper which acts as a carrier.

Sublimation - as related to chemistry, is defined as "To cause (a solid or gas) to change state without becoming liquid". For example, dry ice changes to gas without ever becoming liquid. The sublimation process imprints images into polyester, or polyester coated objects by applying dyes that turn from a solid to gas when heated. When the sublimation dye is placed next to polyester and heated, at approximately 325 degrees the polyester molecules open. The sublimation dye, which at this time is a gas, will then be able to penetrate the surface of the polyester. After the heat is removed, the polyester molecules will close and permanently trap the sublimation dyes, thus the image, into the polyester substrate.

Polyester fibres are chains of molecules. Imagine that a single fibre is a made up of lots of strands of beads. At everyday ambient temperatures the beads are very tightly packed together yet pliable.

• Polyester softens as it is heated and imagine that the tight strands of beads begin to move apart at temperatures between 175 – 220 C.

The Disperse inks, printed on the sublimation paper, at these temperatures move from a solid to a gas. They will happily move into the spaces in the open molecular chain.

• Colour is trapped inside when the fibres cool down.

The fabric and paper are put in a machine at temperatures around 205C for 25 seconds. When the paper is peeled back from the fabric, exiting the machine, the design has been transferred onto the fabric.
The print moves from the paper to the fabric without water but by the regulated application of heat and dwell time.