Label printers are printers that make sticky labels, mostly carrying barcodes: the shipping label on a parcel, the price label on a shop shelf, the tag on a piece of equipment and the wristband a hospital patient wears. They print one label at a time, from a roll, in about a second.
Most label printers print with heat, not ink. The print head is a row of tiny heating elements, usually 203 or 300 of them for every inch, about 8 or 12 for every millimetre. Each element can be heated for a few thousandths of a second to make one dot. There are two methods. In direct thermal printing, the label paper itself is heat-sensitive and turns black where it is heated. No ink or ribbon is needed, but the print fades in sunlight and heat over months. That is acceptable for a shipping label that is needed only for a few days. In thermal transfer printing, the head melts a coating of wax or resin from a ribbon onto the label. The print lasts for years, so this method is used for asset tags, drums of chemicals and labels that must survive washing.
Why not use an office printer? A barcode is useful only if a scanner can read it. Its bars must be sharp, with exact widths and clean edges. A label printer prints exactly one label when the system asks for it, at the packing table, without wasting a sheet of paper. The software sends the printer a small file that describes the label: where the text goes, and which number to turn into a barcode.
Consider a fashion e-commerce warehouse in Bhiwandi, near Mumbai, that packs about 12,000 orders a day at 20 packing stations. When a packer seals an order, she scans the order's barcode. The warehouse management system (WMS) chooses a courier through the shipping software and receives a tracking number. It then sends the label's layout to the printer at her station. A 4 × 6 inch label, about 10 × 15 centimetres, prints in about 1 second at 203 dots per inch. It shows the customer's address, the tracking barcode and the courier's routing code. She sticks it on, and the parcel moves along a conveyor to the parcel sorter. The sorter reads the barcode and pushes the parcel into its courier's chute. Each station prints about 600 labels a day.
Hospitals use the same printers for patient wristbands. At admission, the wristband is printed with the patient's name, hospital ID number and a barcode. Before giving a medicine, a nurse scans the wristband and the medicine, and the hospital EHR checks that the two match.
Some label printers also write an RFID tag, a tiny radio chip inside the label that can be read without a line of sight. The labels are later read by handheld rugged scanners along the parcel's route.