I'm sorry I avoided answering. We do tens of thousands of prints-on-DVDs, and while I've considered "coatings", I've decided to forego hairspray (remember that was a 'glue' agent for school-yard charcoal drawings) or anything else.
There are some threads about different printing surfaces but I've accepted the fact that, if I use my printed DVDs as taco-chips or skipped them down the creek, I'd probably not have the best-resulting printed surface.
Of course, sometimes I can catch Hubby and tell him some rancid joke that makes him snort & spew his coffee across the desk. I don't mind that. Even if he does make me re-print disks.