Should you use a donut probe or a laser temperature thermometer gun to check for the proper cure? Both methods are commonly found in the screen printing trade. But is one better than the other? With two options, here’s a guide for what you’ll want to use in your shop.
LASER TEMP GUN
Laser temp guns are the most commonly used method for screen printing. They’re great for getting a quick reading, but you have to remember that the reading is reflective, so there’s going to be a degree difference between the actual temperature of the ink and the reading you’re getting. Think of it like cooking a turkey: if you take it out of the oven and touch the surface to determine whether it’s fully cooked or not, you won’t get a proper assessment, and the turkey will probably still be cold.
The temp reading can differ due to instability and air movement. Since the laser is handheld, you’ll have to stay still to get the best reading. Airflow can also affect the temp gun’s reading. If there’s a breeze in your shop, the temperature reading will be affected by that.
There’s one more factor to consider. The reflective reading means you want to keep the temp gun as close to the ink layer as possible. If you’re using a conveyor dryer to cool, you obviously can’t do that. You’ll have to aim the temp gun at the ink layer as it’s going through. Take the heat from the dryer into account when you take that reading.
Pro Tip: Some laser temp guns have one laser pointer, while others have multiple. The temp guns with multiple lasers show a visual representation of the area that it’s reading. Both temp guns are reading the same surface area.
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DONUT PROBE
The donut probe reads the contact point at the intersection between two wires. If the crosshair is in the ink, it’ll read the temperature of the ink. If it’s in the atmosphere, the crosshair reads that too. While the donut probe is more of an investment, it’ll produce the most accurate temperature reading of the ink layer possible. If you’re running production every day and want to make sure your inks are curing property, the investment is worth it.
Using a donut probe is a bit more complicated than a temp gun. To start, turn the probe on and set it in the ink layer you want to test. Push the crosshairs into the ink layer to get the best reading. If you’re using a forced air dryer, make sure the crosshair is covered with ink, not just sitting on it. This will ensure that the crosshair is reading the temperature of the ink itself, not the surface level of the ink.
The donut probe will warm up as the ink layer warms up. Because of this, the reading won’t skyrocket as the laser temp gun’s reading will. Instead, it warms up gradually, like the ink layer is warming to cure temperature. This gives printers a more accurate depiction of how long the ink is taking to cure.
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THE TEST
To test for curing temperature readings, Jamie placed a garment with ink under a flash unit. She pressed the donut probe into the ink layer and pointed the laser temperature gun at the ink as the flash dryer began to heat up. Jamie used FN-INK™ in the test, which cures at 260°F. When the temp gun read 325°F, well over cure temperature, the donut probe indicated that the ink wasn’t yet at cure temp, hitting around 215°F.
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As long as printers are aware of the temperature difference that a reflective reading provides, a temp gun can work. When checking for a full cure, understand that you’ll need to read a temperature much higher than the cure temperature.
The laser temperature gun is a staple in the screen printing community. It’s economical and can give a good indication of full cure, as long as you know that it’ll be a reflective reading, and much higher than the actual temperature of the ink layer. A donut probe, while requiring a bit of investment, is definitely worth the money. You won’t have to watch out for under-cured garments and can rest assured that your ink is hitting full cure every time.
