Quoted from mostater:Bublehead, how long does it take the clearcoat to cure and harden so that it doesn't pool? 4 months seems more than sufficient but perhaps not??
In four months, if it hasn't crosslinked, it is not going to (we were looking at a four hour bake to cure ours)
But here is what you need to know... if a CC does not fully cross link within a certain time period, the physical characteristics can and do change with an extended cure time. They can become chalky, brittle, soft, semi soft, they can tear, shatter, and flake. We pushed the process many ways but in the end, you listened to the 3M engineers because they (the manufacturer) already knew exactly how to apply and cure it to give it the best performance. Anything we did to accelerate the cure always ended up with a less than desirable result in either physical or chemical robustness.
TL;DR
We found quite a few factors affect crosslinking. On cure times, we were trying to get near zero wait times on assembly after application, so all of our testing was being done within days of application. It all depends on the chemistry, adulterants, temperature, humidity, but what we found was it all will eventually crosslink, but to what degree depends on thinner concentrations, catalyst, and coating thickness and time. This was a high temp coating that was originally used as a binder in aluminized paints used for exhaust manifolds. When we found out it was optically clear, we decided to try it in or application. We ended up having to bake ours to cure it to the point of being rigid (nondeforming). The bake was not acceptable to the plastic substrate (it started deforming due to heat) was why we abandoned the process. Increased cure time at room temp would eventually harden it but it's performance was greatly reduced, it became chalky and more brittle, whereas fully crosslinking it in the oven made it almost glass-like and that property was pretty permanent. We did, however use this coating to apply a transparent red pigmented version onto quartz glass Xenon flashtubes for use in collision avoidance lighting, but the cost was more expensive than the molded red glass we were currently using. It had one thing going for it though, red glass gets darker with heat, where our coating did not. This means on the ground, the strobes are dimmer than in flight due to cooling, but there was no allowance for cooling the glass when you tested it (since collision avoidance strobes need to work on the runway/tarmac) So our brightness did not continue to fall off as the units heated up, an advantage that was never fully appreciated or sold by marketing, and so Boeing decided not to go that route either.