Screen printing sunlight exposure
Screen printing sunlight exposure, It is absolutely essential that you use DIRECT sunlight to burn the screen.
Cloudy weather will not work.
Exposing the pre coated silk screen too early in the morning when the sun is at an angle
As well as late in the afternoon when the sun is going down will not produce a quality stencil.
The difficulty with Screen printing Sun exposure is this:
It is extremely difficult to predict your result.
Depending on factors like the time of day, time of the year, cloudiness, etc, you are quite likely to get either under or over exposure using the Sun.
This may not be critical for large block images, and sign printers have used the method for years when they need to expose very large screens.
But relying on the Sun for multiple exposures throughout the day and using an exposure calculator for each exposure would be far closer to a science project than a production process, particularly if you are trying to hold any sort of fine detail or halftone dots.
You really can’t beat a good point light exposure unit for predictability and repeatability, and that’s what process control is all about.
And without process control, well…it’s just a hobby.
Complete exposure means that UV energy has completely moved through the whole stencil thickness and crosslinked all the sensitizer.
Any less is Underexposure, which is bad for stencil resistance & durability because any un-crosslinked sensitizer is a stencil weakness and makes reclaiming harder.
There is nothing wrong with exposing for longer than necessary – you just waste electricity and time when the stencil no longer changes.
This is not like overcooked food that dries out, or UV sun burned skin at the beach.
Like cured plastisol or concrete – you can’t over cure a stencil.
No real harm comes from exposing a stencil after all the sensitizer is cross-linked, you’re just wasting time and electricity.
Light Scatter & Undercutting
Use black foam under your screen to avoid Light Scatter & Undercutting.