Acrylic Paint vs Modern Urethane systems on vehicles

History of Automotive Coatings

Ever since the first automobiles were made in the late 1800’s, there have been many changes in paint technologies to protect and beautify these man made transportation devices, from natural products to high tech polymers. In the first part of the 20th century automotive paint technology was based on the same air-dry varnish systems that were used for wooden furniture and horse drawn carriages. The major drawback was that the only choice of color offered was black. In addition, they required tedious brush application of multiple coats and days of drying time, which created a production bottleneck.

In 1923, E.I. DuPont De Nemours developed nitrocellulose lacquer systems, which offered many color choices and easier application using spray guns. However, lacquer systems required spray application of 3-4 coats of paint to achieve the desired properties. Lacquers also by their very nature have poor resistance to certain chemical solvents. Repeated exposures to gasoline spills could stain and damage lacquer finishes. In fact, in the 1960’s some cars had their gas tank filler located under the license plate to avoid spilling gasoline on the lacquer paint. Nitrocellulose lacquers were used on some passenger cars until about 1957, when solution acrylic lacquers were introduced. Acrylic lacquers offered much improved durability and a wider range of bright, pleasing colors – especially metallics.

Another major development in paint technology came with “alkyd” enamel paints that were introduced on some car and truck models in the early 30’s. Enamels formed a very durable film through a chemical reaction after they were sprayed on the vehicle and baked in an oven. The cured paint film was about 2 mils thick (1 mil = 0.001”), and it was very resistant to chemicals and solvents. Enamel paints had shorter application times also. Typically, they were applied in 2-3 steps versus 3-4 steps for lacquers. The advent of organic pigments also added many different choices of colors to consumers. However, the alkyd enamel paint oxidized in sunlight fairly quickly, which caused the colors to begin to show fading and/or dulling in a matter of several weeks. The durability of enamel finishes was improved considerably with the introduction of “acrylic” enamels in the early 60’s. 

To provide further improvements in appearance and durability, a new type of finish, called “Basecoat/Clearcoat,” was developed and introduced in the late 70’s. The topcoat paint system was split into a pigmented enamel basecoat, followed by a clear enamel finish. The key to this technology was the development of a clearcoat material with superior durability in all climates. Initially, the cost of the Basecoat/Clearcoat paint system was prohibitive and it was only used on some high-end automobile finishes. However, refinements in the material technology and processing helped to reduce costs, and by the late 80’s this paint system had become widespread. In fact, only a small percentage of cars manufactured today do not use this Basecoat/Clearcoat paint system.

The benefits of this two-layer system were many. It increased the gloss of paint considerably, which was unsurpassed by any other paint system. It also allowed the paint formulators to incorporate UV absorbers to protect the clearcoat and the pigments in the basecoat from oxidation. Therefore, it could take years to show any dulling effect. 

In some cases, the clearcoat has two components that react and form a hard polymeric network. The two components may be premixed or mixed right before it is sprayed on the surfaces, depending on the polymer technology used. 

While the Basecoat/Clearcoat paint system is far superior to conventional one-coat enamel paints in many respects, it has a few disadvantages. The clearcoat has a greater tendency to show swirl marks and scratches when rubbed by foreign materials or washed incorrectly. 
In fact even terry towels leave visible wiping marks or streaks on the surface. Furthermore, the high reflectivity of clearcoat makes any imperfection highly visible; therefore swirl marks from improper polishing techniques are much more pronounced. 

THE BIG PROBLEM WITH ACRYLIC PAINTS

One of the biggest issues with older acrylic paints from the 1960's to the 1980's and even some today is that unlike modern urethane, two pack or tri formula paint systems which are catalysed, contain UV absorbers and hardeners to prevent it from being scratched as easily,  Acrylic paints are always open to the elements
A car painted in some of these can often be too soft as there is no hardener and therefore machine polishing done by anyone no matter how skilled on certain acrylics will lead to swirl marks and marring even with a Dual Action polisher and hand polishing may even do the same 

Gasoline, paint thinners, silicone removers and many solvents can stain or even permanently damage the paint by breaking down the binders
Modern paints however are not effected at all by these.

If you own an acrylic painted car whether factory original or aftermarket, the maintenance required to keep the high gloss finish may be higher than modern paints as they tend to constantly be adversly effected by oxygen even indoors and UV rays as well as harsh chemicals
Once polished, they need to be treated with a paint sealant or wax fairly regularly to keep that finish locked in for many years
Low maintenance can cause loss of the shine

1960's and 70's Acrylic paint systems can suffer from drying out over time, crows feet, cracking and etching damage and will require our new original patina paint preservation process in order to restore it as close as possible to it's original glory without the use of abrasive cutting compounds or polishes.   
Acrylic paints with metallics are much harder to repair as the metallic flakes can oxidise and when treated with traditional methods, the metallics will turn your pads and towels black and it is impossible to restore oxidised metallic flakes back to life.