In Reply to: Not Exactly posted by FWK-Z3 on February 13, 2000 at 21:09:43:
: There are two differences between the paint on the matal parts and the paint on the plastic parts: (1) a flex agent is added to the paint over plastic and (2) it's over plastic.
: The flex agent is a plasticizer (a non-volatile high molecular weight solvent). In other words, the paint over the palstic never completely cures. I have found that using regular automotive wax on these parts causes them to come out dull and slightly tacky to the touch. The second item is that the plastic parts tend to hold a static charge when buffed (by hand). My xperience has been that the Zymol Detail wax does a much better job on the plastic parts than does the regular body wax.
Yes there are differences between coatings for metal(steel and aluminum) and coatings for plastic(a whole multitude of different types).
Yes the coatings for plastic have to be more flexible than the coatings for steel because the plastic is more flexible than steel(or aluminum).
Coatings for plastic also have differences in their adhesion and solvency characteristics over these different substrates. The differences are not due to a "flexibilizing additive" but rather to the polymeric structure of the vehicle/binder that gives the coating it's performance and physical properties.
In an OEM, Product Finishing, Automotive environment a thermosetting Acrylic is the polymer of choice due to it's combination of toughness, UV resistance(gloss and color retention), and it's water resistance. In such a system the cure mechanism involves a crosslinking(molecular weight increase)via a heat initiated reaction between the Acrylic Polyol and a Melamine crosslinker. The heat required for such a reaction to occur is time and temperature dependant and is generally on the order of 10' to 30' @ 275F to 400F depending on the particular polyol, melamine, and catalyst chosen for the formulation which is predicated on the cure conditions available from the OEM manufacturer.
The vehicle/binder/polymer of choice for plastics used in automotive OEM applications must be of a different nature chemically due to the fact that the substrate cannot be subjected to the temperatures required for a thermosetting reaction without melting and or deforming or loseing elasticity/ flexibility/ and tensile strength.
As such the polymer of choice for the plastic substrates is usually an Acrylic or a Polyester Polyol reacted via a plural component system with an isocyanate (an OH/NCO reaction). This results in an ultimate cure (NCOOH) with ultimate physical properties similar to a thermosetting system but at an ambient temperature. An Acrylic or Polyester/ isocyanate reaction results in urethane bonds or linkages that give this polymer it's flexibility as well as it's other inherent properties.
I certainly agree that plastic parts tend to hold a static charge when buffed by virtue of the fact that plastic is non-conductive hence the negative electrons generated by the charge/potential build up between the plastic and the buffing cloth are unable to disipate to ground.
You may absolutely be right in your opinion/ experience between the two waxes as to one being preferable (I am not a wax expert) but I cannot agree that the coatings used over the plastic are not cured when delivered from the manufacturer or that they are thermoplastic in nature(redisolve or become tacky) when waxed.
Perhaps the "flex agent additive/ plasticizer" you are refering to might be applicable to an aftermarket/ body shop situation that does not have the luxury or the means to use different and proper coatings for different substrates and applications.