Whenever we make a purchase at a shop or at a supermarket, more often than not, we see a little printer next to the cash register at the checkout counter. That little printer, called a thermal transfer printer, prints out receipts, and is a minute detail in an elaborate system called point-of-sale system or POS. Have you ever wondered how a thermal transfer printer works?

As its name implies, a thermal transfer printer is dependent on heat. It makes use of a special form of paper, called thermal paper, and a ribbon with solid ?ink? or resin with a polyester film backing. When you open a thermal transfer printer, you will see the rolled thermal paper nestled within, just beneath the printer head. Sandwiched between the thermal paper and the printer head is the ribbon.

When the thermal transfer printer is used, what happens is that the printer head generates heat. Just what pixels or dots are heated on the printer head depends on the characters that are being printed. The heat is then transmitted through the polyester backing of the ribbon, and it causes the resin or the ?ink? on the ribbon cartridge to melt. When the ?ink? melts, it comes into contact with the thermal paper to form the characters.

This process happens very fast. Ideally, the printout speed of a thermal transfer printer is 12 inches per second, but most machines being used in shops or supermarkets make do with speeds of only up to 6 inches per second.

The process of how thermal transfer printers generate their printouts is quite simple. This is also the principle behind how thermal fax machines work.

The ink on the ribbons used on thermal transfer printers are not really ink. This substance is often made of wax, a mixture of wax and resin, or pure resin. Ribbons made with pure wax are the least durable of the three, and they are often used to print out barcodes and labels.

Ribbons made with mixed wax and resins are a lot more durable than those made of pure wax. They are used for printing finer images on smoother paper, or on film-coated paper. Despite their increased durability, printouts made from thermal transfer printers using ribbons with mixed wax and resin should still be protected from moisture and chemical exposure.

Ribbons made with pure resin are not used for POS and checkout systems. They are for printing on plastics. The printouts made from these ribbons are the most durable, and they require minimum protection from chemicals or the elements.

Thermal transfer printers are simple machines that work using simple processes. And yet, they are a minute but definitely essential detail in an entire POS system.