Originally Posted by 302 Z28
Good point, I actually forgot about the reducers being active reducers. Does that then mean that DBC and DBU are not lacquer like?
The activator spec'd for DBC is DX57.
Remember dbc does not require an activator. Dbu contains isocyanates in its reactive reducer. I am by no means a chemist, but believe with the reaction of the acrylic and isocyanates, you are now creating some crosslinking and if it creates a urethane chain, could be considered a urethane.
I just got an old can of dbc up from the basement. It said acrylic resin, and said nothing about polyester. Paint manufacturers aren't very forthcoming on whats all in there paints, not like the average painter like me could really understand the chemistry anyways.
And it seems like a paint company can call their paint whatever they want, lacquer, enamel, urethane enamel, polyurethane enamel, or simply urethane or polyurethane. If its any consulation, I was able to wipe off some of the 3 year paint drippage off the side of the can to be able to read it with a bit of urethane reducer without affecting the underlying ink too much. I don't know if there was any reducer in it from adding left over or not, but really don't believe it would make any difference, as I doubt dt reducer contains any iso's.
This is all just how I take it, everything could be wrong, or some could be wrong. For the real skinny would require talking to a chemist that you can actually understand.
I believe anything from a lacquer to a urethane can be made from polyester or acrylic resins. And believe basecoat has better propertys then lacquers of old, basecoat has some flexability and with todays basecoats and clear urethanes you don't see to many using flex additives as they really aren't needed.
Did a lot of reading and I still don't totally understand it.
A lacquer is simply a coating composition based on synthetic thermoplastic film-forming material dissolved in a votile solvent (VOC's) and dried primarily by solvent evaporation. Typical lacquers include those based on nitrocellulose, other cellulose derivatives, vinyl resins, acrylic resins, etc.
And a urethane is created when a urethane link is created by reacting an isocyanate with monomer containing alcohol (polyester resins are made from glycol alcohols)
The urethane is formed by the reaction of the hydroxyl from the polyether or polyester polyol with a suitable
diisocyanate. The diisocyanate continues to react with another polyol’s hydroxyl group, leading to chain extension
and molecular weight build. The link thus formed is called a urethane link
To further complicate the description, acrylic polyol can be used, either as the base backbone material or as mixtures
with the polyether and polyester polyols. The resulting adhesives acquire some of the properties of acrylic
chemistry and can be called acrylic urethane, polyester-acrylic urethane or polyether-acrylic urethane.
I still don't think an activated base is going to be the same thing as far as amount of crosslinking occuring and durability of the final product as a urethane clear or single stage, and believe less isocyanate is used, just some to create crosslinking and increase intercoat adhesion, and its going to be the weakest part of a system. I don't have anything finished in dbu to test and any i had is gone except a hardened up can of reactive reducer, I haven't used any dbu in 15 years. Believe activating base, there will be some crosslinking, and the activated base will eventually harden up inside the can (so shouldn't pour back activated base with unmixed stuff) But its no secret to most painters that activating your base will increase its durability, repairablity, and intercoat adhesion, and to offer a lifetime paint warrenty shops have to activate the basecoat. You can look at what barry k says about base in this thread, specially page 2.
I think the reason dbu, which is an earlier basecoat system, uses activated reducer is they were experiencing some troubles with clear to base adhesion, and by adding isocyanate and requireing using the reactive reducer eliminated the problem. Could be wrong here too, but its what sticks in my head for some reason.
Again just rambling, and giving my thoughts and sure I could be wrong. Lacquer has become such a dirty word, that when someone mentions a basecoat being anything near lacquer based and it creates a stir. I think its all moot anyways. PPG DBU and DBC I think we both would agree are good bases, and we should concentrate on figuring out how to use the products correctly and what works best for us, and probably best to leave the chemistry part to the chemists.