Ok, embarrasingly, I saw a thread on here a while back for exactly the same thing, but cant seem to find it.

Newly powder coated wheel, applied to NC30 rear hub and like a moron didnt buff off the excess in the holes, now i cant get the f@cker off. Currently ive got the entire hub out to replace the disc, but cant seperate the 2 as the powder coating has power welded itself on.

Tried heating it ( only have a hot air gun not oxy acetylene ), WD40 on it, Tried a large piece of wood direct onto the wheel wrapped in rags as the powder coating is brand new and it wont budge, the disc is past best anyway so dont mind applying some direct violence to it as its getting replaced anyway.

Anyone offer any advice on getting it off?

Try a bearing puller on it mate

Even if you put loads of coppaslip on it before re-fitting it will still be siezed solid next time you get to it.
You need to have patience with the block of wood method. That's what I used. Turn the wheel every so often and just keep hammering at it with a mallett. It will work eventually.