The stages of dye migration in transfer printing are :
- Sublimation of the dyestuff on the paper
- Diffusion ink layer into the gap between paper and fiber.
- Adsorption at thee fiber surface
- Diffusion of the dye from the surface to the fabric
Prior to heating the dye is contained in the ink layer. When the paper is heated on the reverse side dye sublimes into the gap and transfers by diffusion down a concentration gradient to the fiber surface. Initially there is also a temperature gradient across the gap, which may lead to dye condensing on the fiber surface, but after a brief daily a uniform steady state system will be stabilized. The length of this delay will depend on the size of the gap as well as on the thermal properties of the paper and the fiber. At this steady state temperature, dye will diffuse from fiber surface to inwards down a second concertration gradient within the fibre.
For a rapdi-diffusion, the tansfer temperature needs to be such that segmental motion in the polymer is rapid. Provede the flux of dye vapour from the paper, adsorption and diffusion will proceed until a thermodynamic equilibrium is established between the tree phases “F” “G” and “I”
In practical systemthe sistinguish of dye will be strongly in favor of the fiber phase a little dye will be retained by the paper phase, due to the small affinity of dye for paper surface and ink binder as well as degree of back diffusion into the paper during transfer.