Hi, I`m attached to automotive company n my problem is the paint adhesion between car body primer and basecoat very easily peeled-off (poor adhesion) when we do chellophane tape test.

This problem only happen to 1 new batch of paint where about 200 painted body effected.
The answer given by paint supplier not convincing me.

Can anyone please forward me possible causes of this problem?

There`s no any changes done in my painting system.


Thanks,
Chandaraganth

What do your suppliers say? Have they changed the formula for the new batch?

Hi, they did not change any and they cannot simply change without informing us,

They suspect the primer may be overbaked in the oven but we have closely monitored the oven n the temp. within the required standard ( 150 deg celsious X 30min)

They said due to overbaked primer the basecoat un-able to give good bonding.

I don't know how far true,.


What will be the actual cause?

Material? ( wrong mixing %? old materials? wrong materials? chemistry reaction?)
Machine? (oven? Mixer?)


Thanks,
Chandaraganth

As you recognise, it's a complicated area. Have you tried baking less, like the paint supplier recommends? (on a test piece of material)

The recommended baking temp for primer is 150 deg celc x 30min, if we bake lower than this the paint will be soft on the body.

They said if baked more than standard it can be harden but as per our monitoring no any temp change in the system (primer thickness 20micron).

If the primer harden due to overbaking the primer supposed to detached from body rite but the adhesion between primer and body is very good only basecoat detached from primer.


Thanks,

Hmm, I'm sorry that I can't be further help, chemistry is not my specialty. I would recommend getting more information through experimentation.

Thanks,
Anyone who have knowledge on this matter can answer...

I suggest you check the primer. If it is an alkyd enamel, the temperature your baking may be too hot, and remelting the resin.

I would think 150F would be OK, but if it's 150C that would be way to hot.

The other suggestion is to ask what kind of topcoat is it? Is it a catalyzed polyurethane or epoxy? If so, the catalyst your using could be reacting with the primer,causing it to break down and the coating to lift.

Hope that helps.