Curing Plastisol Ink the Right Way (Not Just Warming It)
A surprising number of "the ink cracked off after one wash" complaints trace back to the same root cause: the print looked cured — dry, set, no longer tacky — but never actually reached the temperature it needed to fully gel. Plastisol is deceptive that way, and it's worth understanding exactly what curing means before you rely on a dryer's dial as proof of anything.
Curing is a temperature event, not a time event
Plastisol doesn't dry the way water-based ink does — there's no solvent evaporating off. Instead, the PVC particles suspended in the plastisizer need to reach a specific temperature, commonly cited around 320°F (160°C), at which point they fuse into a continuous, flexible film. Below that temperature, the ink can look completely dry and set on the surface while remaining uncured underneath — and an uncured print will crack, flake, or wash out early no matter how good it looked coming off the press.
The set temperature isn't the ink temperature
This is the part that trips people up: your conveyor dryer's set or air temperature is not the same thing as the temperature the ink itself reaches. A dryer running at 320°F doesn't mean the ink hits 320°F the instant it enters the tunnel — it takes time for heat to transfer into the ink, especially for a thick deposit. Run the belt too fast and the print exits the tunnel before the ink itself has caught up to temperature, even though the air around it was plenty hot.
Belt speed is really a dwell-time setting
A conveyor dryer cures by dwell time — however long the print spends inside the heated tunnel at a given belt speed. The relationship is straightforward: belt speed in feet per minute equals the tunnel length in feet divided by the cure time in minutes. An 8-foot tunnel with a 60-second target cure time needs a belt speed of 8 feet per minute; the same tunnel with a 45-second target needs a faster 10.7 feet per minute. Longer tunnels or shorter target times both call for a faster belt; thicker deposits or higher-opacity inks generally want more dwell time, not less.
The stretch-and-wash test
The standard way to check whether a print is actually cured, rather than just warm, is to stretch it. Properly cured plastisol will show fine, hairline cracks in the ink surface under stretch that don't peel or flake away — the ink is flexing with the fabric. Under-cured ink tends to crack straight through or lift off entirely under the same stretch. A few wash cycles are the real-world proof: an under-cured print will crack and fade fast, while a properly cured one holds up for the life of the garment.
Water-based and discharge inks cure differently
Plastisol gels into a solid film; water-based ink cures mainly by driving off water and cross-linking a binder, and discharge ink additionally needs enough heat to activate the chemical that removes the fabric's original dye. Both still depend on reaching an adequate temperature for long enough — the mechanism differs from plastisol, but "hot enough for long enough" is still the underlying requirement, just at somewhat different typical temperatures.
Building in a safety margin
Because dryers aren't perfectly even across the belt width, and because thicker areas of a print (like a heavy underbase) take longer to heat through than thin ones, it's common practice to run slightly past the bare minimum cure time rather than exactly at it. A little extra dwell time costs almost nothing in production speed and buys real protection against the print that looked fine coming off the dryer but didn't quite make it to temperature in the thickest spot.