Thermal inkjet technology:Principles, Advantages & Challenges
- Technical Principle (Working Principle)
The core of thermal inkjet printing lies in the heat-driven ejection of bubbles:
- Instantaneous heating of heating element (thin film resistor)
There is an electrothermal film inside the micron-sized nozzle cavity.
When heated by pulsed current, the temperature can reach 300–400°C.
- Ink partial vaporization produces bubbles
High temperatures cause the ink inside the nozzle cavity to vaporize locally, forming rapidly expanding thermal bubbles.
- Bubble compression ink jet
The expanding air bubbles propel the ink from the nozzle, forming ink droplets.
- Bubble cooling and shrinkage
When the heating stops, the bubbles collapse rapidly, and new ink is replenished into the cavity from the ink storage area.
- Repeat
Each nozzle can repeat the spraying action tens of thousands of times per second.
- Advantages
① Simple structure and low cost
It does not require expensive components such as piezoelectric chips, and the nozzle structure and manufacturing process are relatively simple.
It is cheaper than piezoelectric inkjet (PIJ) and makes it easier to achieve low-cost printers or low-cost disposable printheads.
② High injection precision
The micro-nozzle has a high density, enabling high dpi (600–1200 dpi or even higher).
The ink droplet volume can be reduced to the picoliter (pL) level.
③ Fast speed and quick response
Thermal expansion driven, response time in the nanosecond to microsecond range.
Suitable for high-speed production line coding, label printing, office document printing, etc.
④ Simple maintenance
It is less prone to the aging problems unique to piezoelectric nozzles.
Disposable nozzles avoid long-term maintenance problems.
⑤ Easy to integrate, simple driving circuit
The drive requires only a simple pulse current and does not require high voltage or complex waveform control.
- Challenges
① High ink compatibility
Thermal foaming requires inks that can withstand high-temperature instantaneous heating and must possess the following properties:
- low viscosity
- Good thermal stability
- It is not easy to form deposits or carbonization
Therefore, thermal Inkjet Printing is not suitable for UV inks, high-viscosity inks, or inks containing particulate solvents.
② The lifespan of the nozzle is affected by heat.
Long-term repeated heating may cause fatigue of the resistance layer and coking of the nozzle cavity.
While disposable nozzles can be designed, long-life industrial nozzles remain a limitation.
③ Due to limited jet energy, it is difficult to make the ink droplet volume very large.
Compared to piezoelectric printing, TIJ is better suited for small droplet, high-precision, and fast printing, rather than wide-format, high-volume, and high-viscosity applications.
④ Stability issues caused by temperature gradients
Repeatedly cycling the nozzle from hundreds of degrees Celsius to room temperature may cause unstable spraying and nozzle clogging.
Ambient temperature and humidity have a significant impact on ink properties.
⑤ Material compatibility limitations
Some chemically strong industrial inks may corrode the printhead structure, limiting the industrial applicability of Tij.
