Good question, perhaps a little history, some very basic tech info should be shared regarding this.
1. In the late 60's, the OEM paint chemistry was moving forward in order to reduce production time of vehicles. Manufacturers required paint systems that could "dry' quicker than the past paints, plus their application methods were changing as well. However, they were applying the same basic paint systems as the local bodyshop was using.
2. By the late 70's, great strides had been made by the paint suppliers to meet the needs of the vehicle companies and part of that was moving to "bake ovens", which accelerated the release of a good part of the carrier solvents used to get the pigments/resins to the surface of the vehicles.
This speeded up the "curing/drying" of the paint system, but they still contains some hydrocarbon solvents in the paint system when it left the bake oven. At that time, the paints would still require 30 to 90 days to finish off gassing of the solvents.
That was OEM paints.
3.At this time, most bodyshops did not have even a true "paint booth", but rather rooms that they attempted to have good lighting, venilation and clean to apply their "paint materials". The chemistry of the paints used by bodyshops was a bit different than what the OEM used, but still contained a high percentage of hydrocarbon solvents, which when they "off gassed", or dried/cured, released VOC's into the atomosphere.
4. By the late 80's, new govement regulations for VOC's were in place, older sipon feed paint guns, using high air pressure in the paint pot were slowly being replaced for use by bodyshops, with the HVLP guns.
In the assembly plants, the use of robots was coming into use, and entirely different paint chemisty, with lower VOC content. At this time it became very necessary to have complex bake ovens, etc, for without their use, the "paint" would never "cure/dry", it would stay soft for months on end. This is even more true today for OEM paint systems, which now consist of the E-Coat, suface primers and color/base coat, all being "water borne", meaning that "water" is the basic "carrier solvent" for the pigments, resin system, (resin system is the film former and binder) of the base coats, but most important, the "clearcoat" and is what holds the important UV blockers in the substrate of the clearcoat. OEN clearcoats still use a small percentage of hydrocarbon solvents in their application, which consist of three types, a "carrier", a "flow" and a all important "tailing" solvent system.
The water carrier is quickly evaporated in the bake ovens, for each coat of the paint system. The "paint system" will not cure with out high bake temps, some OEM paint systems today require up to 300F to complete the curing/drying/crosslinking.
Once vehicles painted with these systems today leave the final clear bake oven, they are almost 100% totally cured/crosslinked, and in a day or so of normal exposure to air are 100%.
That DOES NOT mean they may not exhibit some softness, as paint coating will continue to "compact" with age. (IE become more dense).
5. Refinish materials-"what a bodyshop applies" is different chemistry in it's solvent system and it's film former/ binder resin system.
Today there are regulations as to the amount of VOC content which may be in paint and the solvents required to apply them and released into the enviorment.
Each state has their own regulations regarding the VOC allowed, but their air is monitored by the EPA and if excessive release, when factored into other types of VOC releases exceeds the EPA's guideline, they will step in an make them start enforcing of stricter regulations.
Example, in some states, bodyshops can not source old lacquers, some akaloid enamels, solvents and are regulated to the point that they must only use HVLP paint guns, have an enclosed ventilation/flitered system on the air being released from their paint booths, etc.
6. Up to date bodyshops, especially in highly regulated states, have modern "down draft" paint booths, with the latest in filtering.
These booths do have the ability to introduce "heat" into the booth, but not to actually "bake" the paint, despite what some may tell you.
The reason for a "down draft" booth is to create the correct amount of air movement around the painted vehicle or parts, as that increases the evaporation release of the solvents, but most important, the larger percentage off water used today in the solvent carrier system.
Until the paint applied is subjected to enough "air", for a specified time, the paint WILL NOT cure or crosslink (dry) to specifications that is needed.
The added heat, is also regulated, but on average is never over 180-185F.(see Item 4 and OEM bake temps), as it aids in accelerating the evaporation of the carrier solvents,( water and some hydrocarbon mixtures).
As this takes place, the "filmformers" start to tighten up, to crosslink and create that dense top surface one see's with a clearcoat, IE-Gloss.
Which is why a bodyshop that is trained and certified by their paint supplier can now provide a warranty on the paint they apply (PPG-DuPont, some others)
These shops painted vehicles may have waxes and sealants applied to the vehicle within a day or so of coming out of the paint booth.
To cut to the chase, OEM paints, due to their different chemistry require high heat to cure, while "refinish paint" requires air as it catalist or curing agent.
There is more, but this should be enough of a primer on the subject to allow anyone who wishes to become more educated on the subject to do their basic research.
Hope this helps and my fingers are tired from typing.
Grumpy
but after two more months it was so hard the M80 wouldn't do much of anything. Had that happen a few times so now I hardly ever even bother polishing for the first few months.
