Types of thermal bar code label printers
Depending on the application, a thermal bar code label printer will use either direct thermal or thermal transfer technology to imprint the bar code symbology on the label. Here's a little more information about each type of thermal printer.
Direct thermal bar code label printers
If you've ever left a receipt from a grocery store or a gas station out in the sun and watched the paper turn completely black, then you've observed the results of direct thermal printing. Originally employed with copy and fax machines, direct thermal printing uses chemically coated paper, and is considered very effective for printing bar code labels. The print head consists of a long, linear array of tiny resistive heating elements (100 to 300 per inch), arranged perpendicularly to the direction the paper moves. Each print head element heats the section of the chemically coated paper directly below it. The heat produces a chemical reaction, causing a black dot to form. More and more dots form the complete bar code image.
Thermal transfer bar code label printers
Similar technology is used in thermal transfer printing as direct thermal, but replace the chemically coated paper with non-sensitized label stock and a special, inked ribbon. Coated with dry thermal transfer ink, the polyester ribbon sits between the print head and the label. The heated print head transfers ink to the label surface, where the ink dries and adheres to the label. Once the ribbon is peeled away, the bar code image remains.