We received a panic inquiry yesterday about ink not curing on a canvas bag. We field many questions for our vendors, since printers love to blame the substrate for printing problems. 

In this case the printer said that the ink ran when the printed bags were washed, despite the fact that they “ran the bags at the highest temperature of the dryer.”

Curing plastisol ink is always a function of time and temperature. Curing ink on canvas is sometimes tricky. Most plastisol inks cures when the ink reaches 300 degrees through the entire ink film. Getting it to 300 degrees is the issue.

Canvas provides a challenge because if it is a coarse texture sometimes the ink film, the amount of ink on the bag is very thick. If you normally runs your dryer at a certain temperature and speed and it cures the ink, it may not cure this thicker ink film. You may have to turn up the temperature or more likely slow down the belt. Just turning up the temperature may scorch the canvas, so give it more time instead.

The problem I have seen more often with canvas is that it is thicker than t-shirt jersey fabric and can absorb humidity. If there is water (you can’t see it, you just have to assume it is in there if at the mill, in shipping, or in your shop it has been humid) in the canvas, it can cause curing problems. Basically what happens is that when put through the dryer, the water evaporates and cools the canvas, just like why we humans sweat to cool ourselves. This cooling is in opposition to the heating of the ink. The evaporation cools the canvas and the ink doesn’t reach its curing temperature.

So what can you do about it? You have to get the water out. If you are doing this all the time, you better have a long heating chamber on your dryer so there is time in the dryer to get the water out because once the canvas dries, the ink can get up to temp and cure. Barring a long dryer run slowly, you can put the canvas through the dryer one or two times before you print it. And if it is raining, then cover it up with plastic until you print it, or it can reabsorb moisture again.

We’ll address curing in general in a future post, but for now we’ll just say - document temperature, and belt speed and get the best testing device for ink curing, a washing machine. You can get all kinds of temperature testing equipment, but putting the canvas through the wash is the best way to check for ink curing.