Curing your prints is one of the last steps of the screen printing process, but it is one of the most important steps. Ink needs to be cured properly so it sets into the garment. If the ink does not cure fully, it will crack, fall apart, and not last for long. Printers use either heat guns, heat presses, flash dryers, or conveyor dryers to cure inks. Let's take a look at how each curing device works.
WHAT DOES “FULL CURE” MEAN?
Before we dive in, let's note that the temperature ink cures at depends on the ink itself. Water-based ink like Green Galaxy will cure between 300°-320°F. Some plastisol inks cure at 320°F. Low-cure plastisol inks, like FN-INK™, cure at 260°F.
The temperature that an ink cures at means that ink needs to reach that temp from the top to the bottom layer. Before purchasing and using ink, learn what it needs to achieve a full cure before implementing it in your shop. We'll address what each piece of curing equipment can do for different types of ink.
CURING VIA HEAT GUN
Using a heat gun is an inexpensive way to apply heat to ink, but how effective is it? Heat guns are great for prints on small areas like the chest. When the design gets bigger, it's more difficult to maintain the consistency of heat across the entire print. It's possible to get some sections too hot where they bubble, while other sections don't reach cure temp. There's no true understanding of the actual temperature the heat gun is emitting.
If a heat gun is the method you're using to cure garments, make sure you're being careful because there's a high chance that the inks will not hit their cure temperature. For plastisol ink, apply the heat gun to the garment until it's dry to the touch. Make sure you're holding it directly above the print. Apply heat to the garment until it's dry to the touch. Then perform a wash test (more on that later).
Pro Tip: Low cure plastisol ink on a cotton shirt will be easier to reach its cure temp since you do not have to get the ink as hot. You will still need to perform tests on it to see if it has fully cured.
Heat guns are not a good option for printing water-based. If you're gung-ho about printing water-based ink, there is a workaround. First, mix Warp Drive, a low-cure additive, into your ink. Once you have finished printing, use the heat gun to evaporate the water from the ink. Apply the heat gun until the print is dry to the touch. Let the garment sit for 48 hours. The Warp Drive will chemically cure the ink.
Curing discharge ink with a heat gun isn’t possible. Keep reading to find out when you can.
Using a heat gun as a curing device is doable, but only for small runs. Remember that it will be difficult to maintain consistent heat across the entirety of the print. It will be a trial-and-error process. Make sure to test out each new job before going into production.
CURING VIA HEAT PRESS
A heat press is essentially a conveyor dryer without a belt. It’s a fantastic way to cure inks because it provides a stable heat source. It gives a readout of any temperature fluctuation while you're using it. If a shop is already printing vinyl, a heat press will be an excellent, multi-use tool.
Curing with a heat press is incredibly simple. For plastisol ink, read the label to discover the cure temp and set the heat press to be 20-30 degrees above that curing temperature. Use light to medium pressure. Place a heat-resistant non-stick sheet on the print. Press for 20-30 seconds. Make sure you perform a wash test to double-check that the ink has fully cured.
Guess what, printing water-based is doable when you have a heat press! Set the heat press at 330 degrees with light to medium pressure. Place a heat-resistant non-stick sheet on the print. When curing a water-based print, the ink layer needs to breathe in order to evaporate the moisture. Hover the heat press right above the print to let the heat evaporate the water content. Once it is dry, press onto it for 30-45 seconds. If you add Warp Drive to the ink, press it for 20-30 seconds and set it off to the side to let it finish chemically curing the ink.
A heat press is a no-can-do for discharge ink. Keep going.
Pro Tip: Do not forget to TEST. Perform a wash test before going into production.
CURING VIA FLASH DRYER
Flash dryers are a common way to cure shirts if you are just starting out in the screen printing business. They're much more consistent than a heat gun. They are both compact and relatively inexpensive. A variety of different flash dryers exist on the market. Shops need a flash dryer for printing multiple colors, so some will also use it as a curing device.
When using a flash to cure, you first need to consider variables like the temperature of the room (pay attention to winter and height of summer, how long it takes to warm up platens), the type of t-shirt material, the kind of flash, the type of platen, and the temperature of ink, shirt, and platen.
VARIABLES WHEN CURING WITH A FLASH DRYER
It takes time for a platen to warm up, so it's important to know how warm it is because a cooler platen will take away heat from the flash. Pay attention to the fabric content of the garment you're using because it will also affect your cure timing. For example, cotton can absorb moisture. Water cools down the space that it's in until it's completely evaporated from a heat source. Synthetic materials heat up faster because they don't hold moisture. The more you know about the garment material, the better for you.
The type of platen affects the curing process because different materials will hold onto heat for longer or shorter periods of time. The aluminum platens take a while to heat up, but they hold heat well. A platen that can hold heat means it's quicker to achieve full cure since the garment is receiving heat from above and below.
Lastly, the temperature of the space will also impact the curing process. On a toasty day, inks are smooth like butter, machines run faster, and the garments are warm. Printers can flash at their normal times, if not faster. If a shop is cold, inks and garments will need more time to heat up, which may slow down production. It's important to take all these variables into account so you know how to adjust accordingly and run a smooth production.
HOW TO CURE WITH A FLASH DRYER
To start, warm the platen, shirt, and ink. It'll make flashing and curing easier. Pull the shirt off of the platen after printing so heat can get underneath the print. Heat penetration goes faster because it's not adhered to the platen, which would soak up heat. Leaving the shirt adhered to the platen causes issues with letting the heat penetrate the garment. Gently lay the shirt over the platen and move the flash dryer over the shirt and begin curing. Pull out your laser temperature gun and aim it at the middle of the print. Once the ink reaches the cure temp, it's ready to be tested.
Curing water-based ink is the same here as it was for the heat gun. First, mix Warp Drive, a low-cure additive, into your ink. Once you have finished printing, use the heat gun to evaporate the water from the ink. Apply the flash dryer until the print is dry to the touch. Let the garment sit for 48 hours. The Warp Drive will chemically cure the ink.
Sorry, curing discharge ink with a flash dryer is not safe. Luckily, there's still one more option.
CURING VIA CONVEYOR DRYER
If you're busting out high-volume orders each day, then a conveyor dryer is the way to go. Conveyor dryers run multiple shirts through at a time which helps speed up production. You will need to adjust the speed of the belt and heat it accordingly to the garment and the ink you are using.
After your conveyor dryer is up and running you can start placing your t-shirts on the belt and letting them run through. Make sure to grab a temp gun or donut probe to see if the ink is hitting the cure temp. Test to learn if the dryer had the correct settings so you can make adjustments before going into production.
In general, water-based inks take longer to cure. You'll want a forced air conveyor dryer like the Aeolus. Water-based inks need air movement to effectively drive the water out of the ink and move the steam outside the dryer so that the heat can cure the ink. Without proper air movement, most printers either have to slow their belts way down or run the shirts through the dryer multiple times.
If you're using a conveyor dryer with no forced air, you'll want to use Warp Drive for curing water-based inks. Warp Drive will ensure the garment hits cure temp since it's hard to achieve without the forced air.
Guess what, now you can print discharge ink! There's a reason why a conveyor dryer is the only way to cure discharge ink. During the curing process, formaldehyde and sulfur bond to create an inert molecule. That molecule is released in the air, so having an enclosed space (a conveyor dryer) is important because it'll let the molecule do its job while not harming you.
Discharge is water-based ink, so you'll need a forced air conveyor dryer. It'll lay a thin ink layer which means it will heat up faster, once all the water has evaporated. Discharge is about 70% water in ink, so it'll take a while to evaporate. It's easier to achieve a cure, but evaporation is longer.
Just for fun, let’s say it again. You need to test, test, and test. Thicker ink deposits will take longer to cure because more mass means it takes longer to penetrate the ink. Various garment types will affect the curing process (i.e. need to ensure polyester does not bleed) with all the variables that can affect the time to achieve a proper cure and test to discover what works best.
The length of the tunnel on a conveyor dryer also plays a huge role. Think of the tunnel as a bullseye on a dartboard. The shorter the dryer, the tinier the bullseye. The longer the dryer, the bigger the bullseye (the bullseye is achieving optimal cure). Shorter tunnel dryers are more difficult to control. It's like placing a flash unit on top of a conveyor belt. Longer tunnels like the Riley Cure offer more flexibility. It allows you to have more time to mess around with belt speed and temperature, so can fine-tune your curing process. Conveyor dryers like the Riley Cure are mainly used for plastisol, but they can work for water-based ink if using Warp Drive.
HOW TO TEST FOR PROPER INK CURING
Think of curing like baking a cake. After the timer dings and you pull the cake out of the oven, it may look perfectly baked. Once you stick a toothpick in the middle of the cake, pull it out, and see that it's still gooey, you then know it needs to be baked for longer. The same idea applies to testing cured ink. It may look cured, but you won't know for sure until you test it.
A printer can perform two tests on a garment to double-check that the ink has fully cured. The first test is the stretch test. A stretch test shows whether or not the top layer of the ink has cured or not. After curing the garment, pull on the ink. Stretch the biggest area of ink to see if it cracks. Cracking ink means it wasn't completely cured. There is a difference between cracked ink and ink film split. Ink film split happens when the ink layer is stretched further than its capabilities.
How do you tell the difference between cracking and film split? Ink cracking will be uniform and all over the print. Film split will be scattered and there won't be a ton of it.
Performing a stretch test will just give you a brief idea of whether or not some curing has occurred. It's not an accurate way to see if the ink has cured to the bottom layer. Therefore, you need to perform a second test.
The absolute best way to confirm cured ink is with a wash test. Throw the printed shirt in the wash. Wash and dry in the harshest conditions. Wash it normally. Put it through all the different scenarios people may do when they wash their shirts. Perform the wash test for at least three wash-dry cycles. Don't be gentle, don't be careful. How the ink responds to the wash test will tell you everything you need to know. If the ink cracks or parts fall off, it wasn't properly cured. If it looks just as good as when it came off the press, you're good to go.
Before you print someone's order, always test. Print on a few garments and dial in details before printing the final product. Testing may seem tedious, but it'll save you time, money, and headaches down the road.
MONITORING INK TEMPERATURE
A laser temperature gun is a common way to read the temperature. All you gotta do is point the laser at the middle of the print to see the ink's temperature. Just because everyone uses it doesn't mean it's the best method. A donut probe is a small, circular device with two wires that run perpendicularly. Where the wires meet is where it reads the temperature.
The biggest difference between a temp gun and a donut probe is that a temp gun picks up a reflective heat reading whereas the donut probe reads the temperature at the point of contact. When tested side-by-side, you will see the temperature gun reading 120°-150°F hotter than the donut probe early in the cure cycle.
As you reach the end of the dryer, those temperatures will get closer together. As a direct result, you will need to read a surface temp as little as 60°F above what the stated cure temp is and as much as 100° depending on how short your dryer tunnel is and how hot your settings are.
No matter what device you're using to cure, the goal is to completely cure the ink, from the top all the way to the bottom. Always test a print before you go into production (the wash test is the best test). Still curious? Check out the free course on the basics of screen printing.