Radiation curing refers to polymerization induced by radiation such as ultraviolet (UV) light, electron beam (EB), or visible light. Like thermal polymerization methods, radiation curing transforms a low viscosity liquid into a crosslinked solid. Unlike thermal polymerization, radiation results in low energy consumption and very fast cure times. Radiation curing of adhesives is finding great application in the electronics industry and in advancing pressure sensitive adhesives on tapes and labels.
In terms of chemistry, two basic types of UV radiation curing adhesive systems exist: free radical and cationic. Intense UV illumination can be used to generate reactive species such as free radicals or cations from a photoinitiator. These reactive species then promote the polymerization of multifunctional monomers. The majority of commercial UV curing systems is the free radical type, and these adhesives use acrylic or acrylate components. Although less commonly used, radiation initiated cationic polymerization offers several advantages over free radical polymerization.
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So helpful - Jun 23, 2009
posted by Corne Westerveld, R&D - Applied/ Formulation/ Product development
Thanks for the clear explaination of the differences between both curing techniques. Although I work with UV-curable adhesive, I never understood much of the problems occuring. We use an UV adhesive for glueing 2 pieces of glass together, but the adhesive is also added outside this glass connection, thus resulting in a somewhat tacky smear. I knew this is caused by oxygen inhibition, but never knew why on a chemistry level. I now will start looking for a cationic adhesive capable of bonding glass together.
In our production-proces we have used several UV-curing systems (Fusion, high-power LED's and flash XENON) and have noticed that they all have there own reaction to the UV adhesive. Especially when we changed from flash to high power LED's we have seen that the resistance of the cured adhesive against water-contact dropped dramatically. We will now change back to a flash-system (we will test the Hamamatsu UV-flash system next week) in hope to get better results. For your information, we are manufacturing glass disposable counting chambers for microscopic use. The adhesive we're using is not only for bonding the 2 glass slides together (microscopic glass and cover-slip) but we also use a drop adhesive to form a thin layer (approx. 5-10µm thick, 1 inch diameter) by pressing it down and then curing it. This droplet is during laboratory use in contact with water-based liquids that will fload into the counting chamber by capillairy movement. We sometimes see strange effects happening in the thin layer of adhesive; i.e. growing spheres, miljons of small black-points. Maybe you can give me some ideas where to look for a suitable glass adhesive based on the cationic principle.
Best regards,
Corné Westerveld
Anthos Labtec B.V.
The Netherlands
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