Once you have received artwork, prepared it to print, and made your screens, there is only one step left; the printing. When it comes to screen printing most of the work is done before you even get to print. However, all that work can be undone if you do not handle the printing process properly. The first step to a successful print is to accurately line up, or register, the screens on the machine. Screens are basically stencils, so lining up the different parts of the image is essential. Printers use registration marks printed on the film positives to ensure they line up correctly before they are placed on the screens. Screen printing machines come with sets of knobs used for “micro registration” of the screens. By twisting the knobs you can move the screens up, down, left, right, and even diagonally.
After the screens have been registered on the machine the printer will place the inks in their respective screens. It is unnecessary to fill up the whole screen with ink, you can always add more as you go. Pull the first screen down over the garment. Next, the squeegee is pulled through the ink over the length of the shirt. Some printers will “flood” the mesh first, pulling the squeegee through the ink before the screen is on the shirt in order to fill the mesh and then pushing the ink onto the shirt. More pressure will force more ink through the mesh, and higher mesh counts will be more difficult to press ink through. Once the first layer of ink has been laid, some prints will require it to be flashed, or dried to the touch, before the remaining colors can be printed. On the other hand, process printing is printed wet-on-wet, and not cured until all the printing is finished.
The curing process is typically done on a conveyor dryer. The printer will remove the garment from the platen and place it print-side-up on the conveyor belt, which will carry the garment through an oven. Most inks cure at about 320 degrees. Plastisol inks cure much quicker because they only need to hit the target temperature and then come back down below 120 degrees to be cured. Water-based and discharge inks take much longer because the ink is actually dying the shirt while it cures. The cure will ultimately dictate the print’s durability. If the shirt is under or over-cured, then it will not hold up after repeated washings. This is why some shirts in your closet might have cracked ink in the design. After the first shirt comes out of the dryer the printer will perform a stretch test in which the ink is pulled horizontally to make sure the print does not crack, but remains as solid as if it is stretched rubber. If the print passes the stretch test, then all that is left to do is print the remaining garments!
