An ink cartridge is a replacable component of an inkjet printer that contains the ink that is spread on paper during printing. Each ink cartridge contains one or more partitioned ink reservoirs, electronic contacts and a chip that communicates with the printer.

Two cartridges docked into a printer communicates with the printer.

How it works

Inside each partition of the ink reservoir is a tiny metal plate. In response to a signal given by the printer, a tiny current flows through the metal causing it to warm up. The ink immediately surrounding the heated plate is vapourised. As a consequence the total volume of the ink exceeds that of the cartridge. An ink droplet falls out of the cartidge onto the paper. This process takes place in matter of milliseconds.

Thermal

Most consumer inkjet printers, such as those made by Canon, HP, and Lexmark (but not Epson) use a thermal inkjet; inside each partition of the ink reservoir is a heating element with a tiny metal plate or resistor. In response to a signal given by the printer, a tiny current flows through the metal or resistor making it warm, and the ink immediately surrounding the heated plate is vaporized into a tiny air bubble inside the nozzle. As a consequence, the total volume of the ink exceeds that of the nozzle. An ink droplet is forced out of the cartridge nozzle onto the paper. This process takes a matter of milliseconds.

The printing depends on the smooth flow of ink, which can be hindered if the ink begins to dry at the print head, as can happen when an ink level becomes low. Dried ink can be cleaned from a cartridge print head by gentle rubbing with isopropyl alcohol on a swab or folded paper towel.

The ink also acts as a coolant to protect the metal-plate heating elements − when the ink supply is depleted, and printing is attempted, the heating elements in thermal cartridges often burn out, permanently damaging the print head. When the ink first begins to run low, the cartridge should be refilled or replaced, to avoid overheating damage to the print head.^{[citation needed]} 

Piezoelectri

All Epson printers use a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal changes shape or size, forcing a droplet of ink from the nozzle. This allows use of inks which react badly when heated, and can produce a smaller ink drop in some situations than thermal inkjet schemes