What is Heat Transfer Technology?

1.Transfer Printing Definition

Transfer printing in the textile industry usually means the sublimation of thermally stable dyes from a colored design on paper at high temperature followed by absorption of the dye

vapors by synthetic fibers in the fabric. The paper presses against the fabric and dye transfer occurs without any distortion of the pattern.

2.Which Fabrics can be Printed With Heat Transfer?

• The fabric usually has a high proportion of hydrophobic fibers such as polyester since the vaporized dyes are not strongly absorbed by natural fibers. 
• Cotton/ polyester fabrics with up to 50% cotton can be transfer printed provided a resin finish has been applied. The vaporized dyes absorb into the polyester fibers and into the resin finish in the cotton. 
• With melamine-formaldehyde pre-condensates, curing of the resin and vapor transfer printing can be combined into one operation.
• The fabric must be dimensionally stable up to a temperature of 220 °C during the transfer period to ensure good pattern definition. 
• Heat setting or relaxation by scouring prior to printing is therefore essential. The process also eliminates spinning and knitting oils.

3.How Transfer Printing Actually Works?

• Even though the paper is in contact with the fabric during printing, there is a small air gap between them because of the uneven surface of the fabric. The dye vaporizes when the back of the paper heats up and the vapor passes across this air gap. 
• For vapor phase dyeing, the partition coefficients are much higher than for aqueous systems and the dye rapidly adsorbs into the polyester fibers and builds up. 
• There is an initial temperature gradient across the air gap but the fiber surface soon heats up and the dye can then diffuse into the fibers. In most respects, the printing mechanism is analogous to Thermosol dyeing in which disperse dyes are vaporized from cotton and absorbed by polyester fibers.