Understanding the photochemistry of direct stencil systems and the output characteristics of screen-exposure units can help you determine which combinations will work for you.
By Neil Bolding
I don’t often laugh out loud while reading a technical article, but I did when I read Steve Duccilli’s “An Update on UV LED Screen Exposure” (August/September 2014). This isn’t an insult to Steve; it was the tale he told about the screen maker who calculated his exposure times by how long it took him to smoke a cigarette. Sadly, this is a true story! This article stayed with me and, in combination with a number of phone calls I have received over the past few months from companies asking whether their stencil system will work on a UV LED exposure unit, motivated me to understand more fully what may be occurring when direct stencil systems are exposed and processed.
My answer to “Will it work?” is a favorite one I have been using for over 30 years: “It depends!” Many variables must be considered to make a suitable determination. To name just a few of the critical ones I ask customers:
• What resolution and edge quality does the print require?
• How long is the run?
• What inks and cleaning chemicals will be used, and is the stencil system resistant to them?
• Do you plan to reclaim the screen?
But the UV LED question is relatively new. I cannot recall reading any recent articles that have addressed the photochemistry of direct stencil systems and suitability of various exposure lamps, so I thought this technical subject was worthy of our time and understanding. I will endeavor to keep the topic interesting for readers who don’t have chemistry degrees and ask for forgiveness from those who do for whatever liberties I may take.
It is great to see an established industry such as ours incorporate new technology. At the 2014 SGIA Expo, numerous LED exposure units were on display (at least six companies come to mind), ranging from conventional vacuum-enclosed units to the most advanced computer-to-screen direct imaging systems. I do not believe that this means the total demise of traditional exposure lamps; the market is simply driving change and incorporating innovation, and the success of these new units will depend on how well they perform.
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