Thermal printers are designed to print very high quality labels with or without bar codes. There are two general types of thermal printers, "Direct Thermal" and "Thermal Transfer". Each type utilizes a computer-controlled print head that contains many hundreds, or even thousands, of tiny electric heating elements (called dots) that can be heated and cooled very rapidly. Like Conventional FAX machines, direct thermal printers image the paper directly, using no ribbon, while thermal transfer printers use a temperature sensitive inked ribbon that transfers ink to the paper or synthetic label material when heated. Both types can print bar codes with "X" dimensions as small as 3 mils. Thermal printers are capable of producing very high quality labels and can be used to print as few as one label at a time or very large batches of labels. Additionally, since thermal printers directly image onto the label material, no "fusing" process is required and a very large variety of label material can be used.

Direct Thermal Printing
Direct thermal printers create high quality images on temperature sensitive label media without using a ribbon. FAX machines work in a similar fashion but direct thermal printers use a much higher quality of label material. The imaging process is called "dye melt reaction". An image is formed by selectively getting a special type of "dye" (coloring agent) to mix with a special type of "developer" (a material that when mixed with the dye, creates a permanent coloring to occur). A thin coating of a colorless "leuco dye" and an "acidic developer" resides on the label surface. The thermal print head selectively applies thermal heat energy to the label surface, melting the "leuco dye" and the "acidic developer" together. A chemical reaction occurs between the dye and developer forming the contrasting color visible image, typically black. The process is depicted by the diagram below:

What is Thermal Transfer Printing?
Thermal transfer printers create a very high quality bar code label, very quickly and in small or large quantities. Unlike direct thermal printers, thermal transfer printers use a specially formulated inking ribbon and can print on a very large variety of paper and synthetic materials, satisfying a wide variety of labeling applications. The imaging process is technically known as "resistive heating element material transfer", in which a thermal print head is used as a thermal energy source to selectively cause the transfer of a colored inking material from a carrier surface onto the label material. The combination of the colored inking material and the carrier is known as the "thermal transfer ribbon". The tiny resistive heating elements within the thermal print head provide the heat energy that softens and melts the colorant material that is then transferred to the label material. The diagram below depicts the basic thermal transfer process.