Everything You Need to Know to Screen Print an Underbase
Knowing how to screen print an underbase is crucial for screen printers. If you want a bright, vivid print, you'll need to lay down a solid white base. Rogue Lab Owner Lee Stuart breaks down the steps on how to achieve a fantastic underbase.
"If you think you need an underbase, you probably do," Lee said.
Emulsion, mesh count, and coating techniques matter. For a white underbase, you'll need a screen with a mesh count of 110-160. The type of garments you're printing on, the inks you're using, etc. will determine which mesh count you should use. Designs with lots of small, fine detail may require screens with mesh counts of 180-200.
When coating the screen, Lee uses the round side of the scoop coater and coats each side once. This method works with his current setup and print. You may need to alter yours depending on what you're working with. Always test to see what works best.
SELECTING A WHITE INK
Knowing which kind of ink (plastisol, water-based, etc.) you'll be using for the print is the first step to picking a white ink. In the video, Lee prints with plastisol ink. He says to look for an ink with solid opacity and is thick enough to matte down fibers for a smooth overprint without fibrillation.
"Not all white inks are created equal," Lee said.
A common mistake beginners do is adding a reducer to the white ink since it's thick and more difficult to print. Adding a reducer does not actually help. The reducer makes the ink less opaque and weakens its ability to matte down the fibers. Instead of using a reducer, make sure you have modulated the ink well before printing.
Which ink you use is completely based on your preference. Lee likes Wilflex Quick White, but it's definitely pricey. If you don't have a ton of cash for a white ink, he suggests getting white FN-INK™.
SETTING UP OFF-CONTACT
Off-contact is the distance between the print surface and the back of the screen when it's down in the print position. If the off-contact is too high, you'll run into issues like fibrillation, blowouts, stencil drags, and more. If the off-contact is too low, you won't be able to clear the screen and you'll lift up most of the ink back up. Too much or too little off-contact will result in a bad print, period.
Where should the off-contact be? Depending on the screen tension, the off-contact should be 1/16 to 1/8 of an inch for t-shirts and thinner garments. For thicker garments like hoodies and fleece, you'd double the measurement. Experiment to discover what is the right height for your setup. Your goal is to have the screen low as it can go while still being able to snap up without getting stuck.
Don't push. Pulling a squeegee gives you more control and the ability to lay down more ink. If pulling a squeegee is difficult for you, try using the EZ Grip Squeegee. Lee likes it — check out his review on it.
When you're ready to print, flood the screen first. Pull the squeegee at a controlled speed to maintain consistent pressure. Finding the right pressure will happen through trial-and-error. Using too much pressure will tire you out quickly and lead to other issues like blowing out the image or pushing ink through the shirt. Too little pressure means you won't clear the screen. Lee uses enough pressure to mostly clear the screen on the first pass, and hit it again with another pass.
Many factors determine a good flash like the flash dryer's height, time, and how fast you're printing. The flash height is most important because it dictates how fast the heat hits the ink. If the flash is too high, it'll take much longer to properly gel the ink and may cause fibrillation. Set the flash about 1.5-2 inches above the surface of the shirt (double for hoodies/thicker garments).
As the name indicates, the garment should be underneath the flash for a short amount of time. If it's under the flash dryer for too long, the flash can cure the ink, which will not let the top colors adhere properly. If you're a slower print, raise the height of the flash a bit. Flashing should only be a few seconds.
PRO TIP: Do not do a print-flash-print with a white underbase. Not only does it make the print thicker, you can run into other issues like curing problems, improper adhesion with the other colors, etc.
Hopefully you learned a few new things to help you start printing underbases or improve your current process. With enough practice, you'll be making stellar underbases in no time.