A heater turns a pulse into pressure
In a thermal inkjet printer, each nozzle is paired with a microscopic heating element. When the printer sends it a brief electrical pulse, the element heats a small patch of ink so quickly that some of the liquid vaporizes. The resulting vapor bubble expands and forces ink through the nozzle as a droplet.
The bubble does not remain in the printhead. As it cools, it collapses, and surface tension helps draw fresh ink into the nozzle. The heater can then fire again. The printer uses a tiny bubble as a temporary piston.
From isolated drops to a page
A printer’s control system decides which nozzles fire and when as the printhead moves across the paper. Each droplet marks one small part of a letter or image; overlapping marks and repeated passes build up the larger shapes. A row of nozzles can produce many drops in parallel, while the paper advances to bring the next strip into position.
This process puts demanding limits on the ink. It must flow back into the nozzle after each firing, form droplets cleanly, and avoid drying into a blockage when left idle. The paper matters too: ink has to spread enough to make a continuous-looking mark without running so far that edges blur. A printed page is therefore the result of coordinated heating, refill, motion, and absorption—not simply ink being sprayed continuously onto paper.
