Blooming of Cyanoacrylates

When excess adhesive has been applied, the surface to volume-of-adhesive ratio is too low and the moisture on the surface will be insufficient to neutralise the stabiliser in the adhesive. The cyanoacrylate vapour will escape and fuming will occur. Reduce the quantity of the adhesive by using fine bore application nozzles and/or dispensing equipment. 

In the same way as excess adhesive can cause blooming, a slow cure may give a similar result. The cyanoacrylate at the periphery of the joint will search for available moisture from the surrounding air and may then cure as a white powder on the adjacent surface. A slow cure may be the result of excess adhesive, but is also likely to be caused by acidic deposits on the substrate. These acidic deposits can cancel ont the nentralising effect of the initiators (moisture) and result in very slow polymerisation or in some cases inhibition of cure completely (see also Section 10.4.1). 

Slow cure can also be overcome by using an activator (or accelerator). There are a mmiber of different activators available to the production engineer and these increase the level of initiators on the surface to negate the stabiliser and thus increase the speed of polymerisation. Section 10.8 discusses the uses and application methods of activators in more detail. 

Slow cure may also be due to a thick bond line (adhesive 0.2 mm). Cyanoacrylates are most suited to applications where the bond line is less than 0.1 mm thick although a cure through a volume up to several mm is possible using UV curing cyanoacrylates. 

Low RH (less than 20%) will also encourage the formation of blooming and irritant fumes because there is less moisture on the surface to initiate the cure. 

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