UV-Snap Cure

ACW's UV-Snap Cure Adhesives are epoxy-only adhesives that are stable at room temperature but cure rapidly when activated by UV light.  In some ways, they are similar to conventional UV Cure adhesives.  The difference is that whereas conventional UV Cure adhesives will either polymerize in seconds (acrylates) or form a surface skin quickly (epoxies), a UV-Snap Cure adhesive does neither.  Instead, the UV-Snaps have an open period of several seconds to a minute or more where the adhesive is liquid, there is no skin on the surface, and parts can be mated during the open period.  Once the parts are mated, the assembly can be cured fully by heat at a low temperature or, if active alignment is necessary, the assembly can be held in alignment, irradiated with a second UV burst to fix the parts, and then fully cured by heat.  The complete processing sequence is shown below.

UV-Snap Cure process

dispense   activate      mate         fix        fully cure

The term Snap-Cure adhesive has different meanings for different manufacturers.  Typically, one thinks of a very quick curing when the sample is rapidly heated.  For example, the adhesive might cure in 30 seconds when heated to 180 °C, but such a temperature is much too high for some sensitive substrates such as polycarbonate (PC) that cannot be heated above 80 °C.  ACW's UV-Snaps are more reactive than this hypothetical example, not only curing in seconds at temperatures such as 150 °C but also permitting heat curing at temperatures as low as 60-70 °C for 30 minutes to one hour or at 80 °C for 20-30 minutes.  The DSC plot below shows heat production from an ACW UV-Snap Cure adhesive that was activated by irradiation with 2J/cm2 of 365 nm light (LED) and then heated to 70 °C.  The reaction takes off in seconds during the short heat-up period and is effectively complete in a few minutes.  The bar graph shows the extent of curing at relatively low temperatures as determined by FT-IR.  Even though the chemical reactions are fast, the thermal cure time should be in the range of 30-60 minutes to achieve desireable bond strength for the bonded parts.

Snap Cure rate

DSC trace (70 °C, isothermal) of an ACW UV-Snap Cure adhesive after irradiation with 2J/cm2 of 365 nm light (LED).

UV-Snap curing chart

In summary, then, ACW's UV-Snap Cure adhesives provide a unique bonding solution.  They are shipped and stored at room temperature, but become ultra-fast curing adhesives when activated by UV light.  Moveover, they cure to high Tg solids that display high adhesion and excellent environmental properties typical for epoxies.  See the UV-Snap Cure products page for details about the UV-Snap Cure products offered by ACW.