Technology guide
Continuous Inkjet (CIJ)
Continuous inkjet (CIJ) is one of the longest-established coding technologies. It prints small date, lot and batch codes at very high line speeds, without touching the product, on almost any shape, from round bottles and cans to cables and eggs. The trade-off is an ink system that runs all the time: CIJ uses solvent inks plus make-up fluid, and it needs regular maintenance.
How it works
A CIJ printer pumps ink under pressure through a tiny nozzle. The stream is vibrated so it breaks into a steady flow of evenly sized droplets. A charge electrode puts an electrical charge on the droplets that will print, and high-voltage deflection plates steer them onto the product to build each character.
Droplets that aren't needed stay uncharged, fly straight into a catcher called the gutter, and are pumped back to the ink tank. That's the "continuous" in continuous inkjet: the stream runs whenever the printer is jetting, whether it's printing or not.
CIJ ink types
CIJ inks are built to carry an electrical charge and dry fast. The main families:
What it is: Ink built on methyl ethyl ketone (MEK), a strong, fast-evaporating solvent
Good for: Fast drying and strong adhesion on plastics, metal and glass
Watch for: Odor and solvent handling; ventilation
What it is: Lower-odor solvents in place of MEK
Good for: Plants that want less odor or fewer regulated solvents
Watch for: Not every MEK ink has an MEK-free equal; check adhesion on your substrate
What it is: Opaque pigment particles instead of dissolved dye
Good for: Contrast on dark surfaces (for example, white or yellow ink) and durability
Watch for: Check that your printer is set up for pigmented ink
What it is: Water as the main carrier
Good for: Porous materials
Watch for: Not for non-porous surfaces like plastic, metal or glass
| Type | What it is | Good for | Watch for |
|---|---|---|---|
| MEK-based solvent | Ink built on methyl ethyl ketone (MEK), a strong, fast-evaporating solvent | Fast drying and strong adhesion on plastics, metal and glass | Odor and solvent handling; ventilation |
| MEK-free solvent (ethanol-based and similar) | Lower-odor solvents in place of MEK | Plants that want less odor or fewer regulated solvents | Not every MEK ink has an MEK-free equal; check adhesion on your substrate |
| Pigmented | Opaque pigment particles instead of dissolved dye | Contrast on dark surfaces (for example, white or yellow ink) and durability | Check that your printer is set up for pigmented ink |
| Water-based | Water as the main carrier | Porous materials | Not for non-porous surfaces like plastic, metal or glass |
Every CIJ ink is paired with its own make-up fluid. Use the pair your printer specifies.
Make-up fluid and viscosity
Because the ink circulates constantly, its solvent evaporates. To keep the ink at the right thickness (viscosity) for clean droplets, the printer adds make-up fluid, essentially the ink's solvent, as it runs. So a CIJ line buys two fluids, ink and make-up, and the printer mixes them to hold the viscosity steady.
What CIJ maintenance involves
- Printhead cleaning: dried ink and dust build up on the nozzle, charge electrode and gutter, so many plants clean the printhead routinely during production.
- Filters and service kits: the ink system's filters (ink, make-up and gutter filters) are replaced on the manufacturer's service schedule, usually by a trained technician.
- Keeping it running: a clogged nozzle or a stream that misses the gutter stops the printer, so CIJ rewards a regular maintenance routine.
Throw distance and shape
CIJ droplets fly a short distance to the product, which lets CIJ print onto round, recessed or uneven surfaces and products moving very fast. That's its biggest advantage over near-contact methods like thermal inkjet.
Best for
- Very high-speed production lines
- Curved or irregular surfaces: bottles, cans, cables, wires, pipes, eggs
- Small-character date, lot and batch codes
- Non-contact coding from a short distance
Considerations
- Uses make-up fluid as well as ink, and needs a regular maintenance routine
- Solvent inks mean odor, solvent handling and ventilation
- Small character heights compared with other methods
- Lower print resolution than thermal inkjet for fine text and dense 2D codes
How it compares to thermal inkjet
Thermal inkjet (TIJ) fires drops on demand straight from a sealed cartridge: no ink stream to recirculate, no make-up fluid, and little scheduled maintenance, at much higher resolution (up to 600 dpi with a ½" head), which matters for small text and 2D codes. TIJ prefers flat or gently curved surfaces and prints up to 6 mm from the pack. CIJ still wins at the very fastest speeds, at a distance, and on round, recessed or irregular shapes. Many lines switch to TIJ where the application allows and keep CIJ where it doesn't. Tell us your substrate, line speed and code, and we'll help you compare honestly.
TIJ Print Solutions specializes in thermal inkjet. We’re happy to help you choose the right technology for your line — even when that conversation starts here. Explore our coding & marking inks.
Not sure which technology fits your line?
Thinking about moving from CIJ to thermal inkjet? Tell us about your line and a TPS coding specialist will help you compare.
Frequently asked questions
What is continuous inkjet (CIJ) coding?
A coding method that prints dates, lot codes and other variable data by firing a continuous stream of charged ink droplets and steering the ones it needs onto the product. Unused droplets are caught and recirculated.
What is continuous inkjet ink?
CIJ ink is a fast-drying ink built to hold an electrical charge, usually solvent-based (MEK or MEK-free), sometimes pigmented for contrast on dark surfaces. It's used together with a matching make-up fluid that keeps it at the right viscosity.
What is make-up fluid?
Essentially the ink's solvent. CIJ ink circulates constantly and loses solvent to evaporation, so the printer adds make-up fluid to keep the ink at the right thickness for clean droplets.
Why does a CIJ printer need so much maintenance?
The ink system runs continuously, so the nozzle, charge electrode and gutter collect dried ink and dust, and the filters load up over time. Routine head cleaning and scheduled service keep it running.
What is CIJ best for?
Very fast lines, non-contact printing, and round, recessed or irregular surfaces like bottles, cans, cables and eggs, where the code is small.
CIJ or thermal inkjet: which should I choose?
Choose CIJ for the fastest lines, printing at a distance, or awkward shapes. Choose thermal inkjet for flat or gently curved packs when you want higher resolution and low maintenance: sealed cartridges, no make-up fluid.
Thermal inkjet vs. CIJ →Does TPS sell CIJ printers or ink?
No. We supply thermal inkjet printers and Odyssey inks. If your line really needs CIJ, we'll tell you, and we're happy to help you compare.