Die back during bake cycle
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Are any of you having trouble with die back / solvent entrapment on bonnets during, at the end of bake or even during cool down period.
I’ve been having a bit of trouble with this, base up the panel let it flash well between coats and dehydrate completely after for 15 mins, so I then apply 1 very light smooth coat , wait 3-5mins depending on how many other panels are to be sprayed then apply 1 full wet coat , wait 4-5 mins then bake for the recommended time @ 70c.
This is mainly on mipa clear. Data sheet says half coat and then 1-10 min flash and 1 full leveling coat, 4-5 min flash then bake.
I always believed that uhs clear should be baked straight away before it starts to skin over.and to bake the solvent out straight away, I tried it this way too but again the bonnet or roof will pull back, but the sides are fine.
Tried it by letting it flash before bake and the same result , using standard hardener which is a 30 min bake and the mipa thinner for it, tried it with 10% thinner and warmed it up well and without thinner.
I don’t think I’m overloading the clear on but I feel there’s some little thing that I am missing in either my application or my flash periods.
Even though it is kinda a one visit procedure and I genuinely believe the clear is good quality so it’s probably down to me, any tips would be appreciated.Do other clears do it too or just this one?
What basecoat are you using? I’m using Deltron which is a 1:1 reduction. The TDS says to wait 15 minutes before clear, however I wait longer than that…..usually 30 mins. Depending on the ambient temp, I will even flashbake the base for 20 mins at 50 degrees.
Also, how long are you leaving your primer to cure/degass before you apply your base? If you’re topcoating too soon, that could be a problem right there.
I’m using Mipa CC6. After the final coat, I let the clear flash for 10 minutes before baking, but for the first 10 minutes, I’ll bake at 50 degrees, then bump it to 65 degrees. I know the bake process is 30 minutes at metal temperature, but my total booth time will be about 45 mins to allow for the purge, booth heatup and the short 50 degrees pre-bake.
What Mipa clear are you using? Sounds like CC6.
are you sealing the panels and if so might need to let them flash longer
Yeah it’s cc6 alright, only use wet on wet primer /sealer for new panels and I allow it to sit for 20 mins before basecoat.
I am using a copy of the old sikkens autobase in solvent and have started to try out sherwin AWX , the solvent base I’m not sure of as I feel it flashes off too quick and could be skinning over trapping solvent, the AWX I’m happy with as I leave it till I can denib if needed, so I’m pretty sure it’s dry. Gonna start giving it a medium bake after base coat to help dehydrate bonnets and roof’s but I feel there shouldn’t be need as fuel bills are an issue but if it works why not try it, cheaper than buffing after. Going to try out some sherwin clears soon to see how they work out, haven’t used them in a little while but to be honest I never baked them.be careful doing a short bake,you will shorten your recoat window on the base and this can cause adhession issues.
I used CC6 for a while but only ever air dried it as we dont have a bake booth but I noticed on cars that came back for other work the repairs I had done previous had died back some.
Evedntually I changed clear for a number of reasons but it was a nice clear to spray as I remember.
[quote=”Jayson M” post=30322]be careful doing a short bake,you will shorten your recoat window on the base and this can cause adhession issues.[/quote]
Jayson, I’m only talking about doing a low-temp flash bake after the last coat of base (Deltron has a 12 hour window for clearcoat, so giving it a short 10 minute flash at 45-50 degrees C still allows the base to remain inside the clearcoat window), but helps the solvents degass. Given that Deltron is 1:1 reduction, it has a high solvent content so it needs extra time to flash.
Alternatively, you can leave the base for 3 or so hours before clear (without flash baking), but in a production-type shop, this is impractical.
The OP is talking about waterborne basecoat and so was I ,there is no need to do that with solvent or waterborne.Even a short bake at well over 110-120 could still cause trouble IMO,but to each his own.
First thing comes to my mind is if your baking in a down draft the flat panels will tend to run 20-40 degrees hotter than the sides. If you don’t let it flash all that hot air will skin over on the flat panels first trapping tail solvents. Should maybe let it purge for a few???
I spray nexxa autocolor. Usually wait 15min before clear to let as much or the water evaporate, 2 full coats clear, 5 min purge @ 100 and then a full bake.
A modge podge of products is always a reason for question of itself. All painters do it, myself included!!
that’s the problem with one visit clears, and with wb base they can be picky. try useing a slower hardner, or skip the bake cycle.
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