Print Head Types

Thermal
Thermal print heads use semiconductor junctions as heaters. The junctions are formed near or around a microscopic pipe (nozzle) that connects the ink storage to the bottom exterior of the cartridge. When the junction is turned on, current flows and heat is generated. This happens very quickly. The heat causes the ink in the pipe to expand rapidly which in turn forces a droplet to shoot out of the pipe toward the paper. The junction is turned off and fresh, cool liquid ink flows in to replace the droplet cooling the pipe. The cycle can be repeated thousands of times per second. Most inks used in thermal print heads are water based. Because ink is heated within the nozzles, ink drying and occlusion (plugging up) can occur within the nozzles. Integrated printer cartridges have ink storage and a print head built into them meaning that when the ink cartridge is replaced, so is the print head. Most HP ink printers use thermal designs.

Piezo
Some crystals (Quartz) have a property that causes them to change shape or bend when electricity is applied to them. Many small speakers like the ones in a watch alarm use this property to vibrate the air (Beep! Beep! Beep!). Piezo electric print heads use this property to displace tiny volumes of ink in microscopic pipes (nozzles) causing ink droplets to be ejected toward the paper with each application of an electrical pulse. As the pulse is turned off, fresh ink flows into the pipe making it ready for the next cycle. Piezo print heads are not constrained to use water based inks and many "solvent" based ink jet printers use this design. Most Piezo printing systems have fixed print heads that are not part of the ink cartridge, the ink cartridges are simple ink vials or tanks. Replacing a Piezo print head is usually prohibitively expensive. Most Epson, Canon and Brother ink jet printers use Peizo designs.

Thermal Con

Water based inks
Plugging

Thermal Pro

Cheap to make
Simple
No moving parts

Piezo Con

Not cheap

Piezo Pro

Simple
Any liquid ink
Long life