Components of Thermal Transfer Foils
Composition of Thermal Transfer Ribbons
A thermotransfer ribbon consists of three parts: Back coating, lacquer coating and carrier foil. The back coating has three functions: to protect foil from burning through, to diminish electrostatic charging and to improve foil slippage. Good back coating is slightly rough so that residue from the printing process does not settle on the ribbon. The lacquer coating consists of wax, synthetic resin, color pigments and additives in various proportions. The type of lacquer coating defines the properties of the thermal transfer ribbon. The carrier foil normally consists of a very thin PET layer.
Components in Detail
The thermal transfer ribbon is on a rotating cylinder from which it gradually unwinds. After the coated ribbon passes the print head, the thermal-transfer foil is automatically wound up with an engine cylinder. This facilitates handling and disposal of thermal transfer ribbons.
The Counter-Pressure Roll
This rotating rubber roller is located under the print head where the coated thermal-transfer foil and labels meet. It ensures that the precise pressure is applied to the color ribbon for the print head to transfer ink onto the label at ideal temperature. Substrate feed (e.g. labels) also relies on the counter-pressure roller.
The Foil Detector
Printing without ink ribbons is impossible. The foil detector checks whether a thermal-transfer ink ribbon has been inserted.
The Print Head
This is the heart of a thermal transfer printer and consists of 300 to 600 heating elements per inch (dpi). During the printing process the label material and ink ribbon synchronously advance between the print head and counter-pressure roller. Meanwhile, individual heating elements in the print head heat the ink on the ink ribbon above its melting point, transferring the color layer of the thermal transfer foil directly onto the label material and continuing until printing is complete.
In the schematic diagram, small black squares represent the heating elements in the print head, and switch symbols represent software switching the heating elements on and off.