Proper Screen Printing of a White Underbase

Proper Printing of a White Underbase


In my classes, the attendees who have experience at the press always ask, “Will we go over how to print a white underbase?” The other half of the class, those who have never printed before, scratch their heads and wonder why. Printing dark shirts is a tripping point for many screen printers, and all because of laying down the white underbase print.

Mistake number one, made usually because of advice from suppliers or other “experienced” printers is in using the wrong mesh. That common advice is to use a 110 mesh screen for the first lay down of white ink. The key to a proper underbase is to print this white layer using a higher than assumed mesh count starting in the 156 range and up.

With simulated process printing, your mesh count will be a 230. Many inexperienced printers will tell you this is impossible, but trust me, the pros do it every day.

Printing through higher mesh counts will require you to use high opaque white ink that is at its optimal condition for printing. What does that mean? The ink is ideally at a comfortable room temperature, and stirred so that it has a creamy consistency.

Here’s another bit of advice that will make many printers and your suppliers squirm. It is acceptable to thin down your white underbase ink with a curable reducer. Your ink will flow better through a high mesh screen and give you a nice thin base to print upon. A crisp clean underbase is our goal here.

When laying down an underbase, the trick is to completely sheer the ink from the screen so that no ink tries to pull back up with your underbase screen and cause that print to feel rough. The image in your screen should be completely free of ink after your final print stroke of white, even if it takes you two or three strokes to accomplish the task.

Flashing
When printing an underbase, remember you don’t need a bright white image, just a good smooth base. Set the flash unit temperature to “high” and position about ¾“ from the shirt. Another common mistake is in positioning the flash unit too far away from the garment. Depending on your flash unit, time under the heat will be 10-15 seconds. Touch the flashed ink in a couple of places and look for ink transferring to your fingers. We’re looking to make the print dry to the touch only, not cured.

Too much time under the flash will result in a full cure of your underbase. That’s a bad thing. If the underbase is cured completely, the colors applied on top will not adhere properly and may very well wash away during the first laundering. If a print washes out and leaves only the underbase, you’ve flashed too long.

The Underbase is NOT Part of the Final Image
This is a tough one for screen printers to swallow. If white ink in the final image, use a second white screen called a highlight white. Do not make the white underbase serve the dual purpose of underbase and white ink in the final image.

Using the underbase print for both functions will require you to lay down far too much ink under your other colors. Your final print may appear muddy and thick after only a few prints. A thin, crisp underbase will provide the perfect printing surface. And a second and final white will give your image the “pop” that the pros get on those award winning shirts you see at trade shows and magazines.

Proper Tension
As I preach to students and readers alike, screen printing is all about the screen. Using the proper mesh and the proper tension is 90% of the battle toward achieving a great finished product. Be sure that your underbase screen has good tension to allow the ink to be sheered from the screen cleanly and completely. If your final product has a rough surface or tiny white specs show through the colors applied on top, your underbase screen does not have the proper tension.