Every brand and type of emulsion will have a different exposure time. Improper exposure times can cause various problems. Screens may break down on the press while you are printing or they will not wash out or develop post exposure if you do not use the proper time to expose your screens. Selecting the correct exposure time depends on multiple different factors including your exposure unit, the color of mesh on your screens, and whether or not halftones are included in the design that you are printing.
Questions to answer when selecting the proper exposure time:
Does your exposure unit have LED or Fluorescent light bulbs?
Is the mesh on your screens white or yellow?
Does your design have solid spot colors or halftone dots? Is Your Emulsion Dual Care or Photopolymer?
Once you have answered the questions above you can dial in to find a correct time and process to expose your screens.
Questions to answer when determining the type of emulsion to use for your screen prints:
1. What type of ink?
-Photo polymer emulsion is only for plastisol ink
2. What type of exposure unit do you have?
-Photo polymer emulsion is very fast exposing and the window for error is very small.
–If you are using a homemade DIY exposure unit than you should try using a dual cure emulsion for your screens.
-Dual cure emulsions are easier to expose because the window for exposure time is much wider then photo polymer.
There are three basic types of emulsion, and each have different needs for exposure. The 3 types of emulsion are photopolymer, diazo and dual cure.
1. Dual Cure emulsion are the easiest emulsion for new screen printers to use. The “window” of exposure is the most forgiving of all three types of emulsions.
2. Photopolymer is the fastest exposing emulsion, but the window is also the smallest, meaning the margin for error is very small for this type of emulsion.
3. Diazo emulsion is the last option, which usually has a window of exposure comparable to that of dual cure.
Photopolymer: Plastisol Ink Only
Dual Cure Emulsion: Water Based Ink, Plastisol Ink, Discharge Ink
Diazo Emulsion: Water Based Ink, Plastisol Ink, Discharge Ink and Solvent Ink for sticker printing