The differences between automotive base-coat paints
Yes, there is a difference between the base coat products that you can choose when refinishing a car, or anything that is painted. Simply put, as base coat color is a lacquer paint! Really. Most are familiar with Nitrocellulose and Acrylic lacquers, but a third type is called a CAB lacquer. The flaw in a nitro or acrylic lacquer is that they have no good resistance to solvent. When applying one of these two lacquers, then clear-coating them with a high grade urethane clear coat, the solvents in the clear coats will remelt the lacquer, which when dries will have no integrated adhesion to the clear-thus peeling happens. The Europeans long ago discovered that another form of lacquer used in the furniture industry had great solvent resistance, and urethane clears would not peel off! This third form of lacquer is called Cellulose Acetate Butyrate (CAB).
The only manufacturer of this resin is Eastman. Eastman CAB's are based on cellulose, one of the most abundant natural renewable resources, from trees harvested from sustainably managed forests. Every paint company in the world uses CAB from Eastman to make base coat paint. Their are different types of CAB's and most companies highly protect which version they use.
Early Automotive Coatings Chemistries: From Alkyds to Acrylic Lacquers
The first automotive paints were Nitrocellulose paint. It was highly productive, but the final coating required polishing to achieve high gloss. Paint chemists in the 1930s wondered if somehow they could find a binder system for paint that provided both productivity and the inherently better appearance of a natural oil resin. What resulted from this work was the development of the first alkyd paint system. This was the first “polymer” made for coatings, as it was synthesized using three monomers: phthalic anhydride, glycerol, and linoleic acid.
It was not until the 1950s that the next major automotive coatings advance occurred: the use of thermoplastic acrylic lacquers. By this time in American society, the automobile was no longer just a means of transportation; cars had now become a personal showpiece that owners wanted to show off to their friends. That meant that the coatings had to look better and accentuate the new curved styling body designs of the times. Rohm and Haas Co. had developed a new synthetic polymer as a glass replacement based on poly methyl methacrylate, and the coatings industry investigated whether that technology could be used in coatings.
As previously discussed, thermoplastic acrylic lacquer automotive coatings, given their excellent appearance, were the major automotive topcoat used in the 1950-70s. However, these lacquer topcoats did have one significant drawback: they had weak exterior durability. After about one to two years’ exposure, the coatings would begin to degrade, and aggressive waxing was needed to “bring back the shine” of these systems. By the 1980s, the automotive manufacturers were requesting better durability for automotive topcoats, as consumers were now expecting their cars to last at least five years, and they wanted the car to continue to look like it did when they first saw it in the showroom. At the same time, the Environmental Protection Agency began to promulgate new volatile organic compound (VOC) regulations that limited the amount of solvent that an automotive facility could emit into the atmosphere. The high VOC content and weak durability of acrylic lacquer coatings were no longer acceptable in the automotive marketplace.
So how did the automotive coatings formulators achieve higher solids, better durability, while even improving the appearance of the coating? The answer is the next step change advance that occurred in automotive coatings: base coat plus clear coat urethane topcoat technology.
Most two-stage base coat's have no strength and depends on the clear coat for gloss, durability, and protection from the elements. The window between coats is very forgiving, as the reducer used in the base coat has the ability to soften the previous layer to obtain a chemical bond. This means better adhesion between coats and less chance for delamitation problems over time.
CAB converted Coatings Chemistries:
Any paint can be converted by a CAB into a base coat. I remember back in the 1980's we turned our Amerflint II into a base-coat. The shop bought a converter, that was mixed 1:1 with the Amerflint II color. Because Amerflint was 100% acrylic urethane, the painter needed to add isocyanate hardener (1 pint to 1 gallon) before clearing with the Amerflint clear. This was and is the most durable base coat that can be made. However, the drawbacks doomed the product. One was it dried to slow. One had to wait 1 hour before clearing. The other was the mixed base got hard!
A second way was to make the base coat out of a blend of enamel and CAB. MOST Base coats today use this technology. You do not use hardeners in the base coat and the base never gets hard—i:e- You can use it over and over. The largest downside of this technology is eventually the clear will peel after several years of extreme UV exposure. This isn't a problem in Maine or Germany, but it is in Florida!
A third version of base coat is what we employ at Tamco. I believe, PPG invented this technology, or at least this is what they told me back in the 90's when I sold the product and went to their lab in Allison Park, Pa. This revolutionary technology is the closet to the Amerflint base coat one. We take a CAB and mix it with an acrylic urethane resin (the same resin found in 2104, 4100, 2100, etc) but at a low enough percentage that it does not need a hardener!
This unique formulation, then draws the hardener out of the clear coat and bonds with the acrylic resin in the base coat giving perfect inter-coat adhesion! The downside is that you must use a clear coat the is drastically over catalyzed, if not, the clear itself will fail. Most companies, especially the so-called generic companies use a 1-1.05 paint to hardener ratio. That simply means they over catalyze by 5%. This is not enough hardener for Tamco base coats and using such clears will cause a failure! Tamco over-catalyzes by at least 20% (the exact amount is a secret) saw that perfect ratios are achieved to make paint job last for many years.
NOTE: Basecoat activation may be necessary in cases, such as high film builds (i.e. more than four coats), commercial vehicles, motorbikes, or wheel painting where a higher impact resistance is necessary. This applies to some Tamco custom finishes such as candies, candy pearls, as well as other paint procedures requiring many extra coats over recommendations..
Clear Coats- THE KEY TO DURABILITY:
Three key elements contribute to a clear coat’s durability: UV absorbers, the use of 100% acrylic polyurethane resins and film build. UV additives absorb damaging ultraviolet rays, much like sun blocker for your skin. However, UV protectants cannot do the job alone in ensuring durability. The choice of the resin is key to long term durability. As many, if not most paint manufactures have started to add enamels to the clear coats as a cost saving and “user friendly” reasons, causing a loss in durability – Tamco has not! We use 100% acrylic polyurethane resins in our clears (except Duraflint).
The last key to durability resides in you, the painter. A final film build in the range of 2-2.5 mils is most commonly recommended. Whether using Tamco premium clear coats, a film build below 2 mils will decrease durability. Anything over 5-7 mils can cause cracking.
Film Build is CriticalFilm build is equally important to ensure long-term durability of the finish. Too low of a film build can lead to premature film failure, dieback and overall poor appearance. Too high of a film build can lead to solvent pop, dieback, and even potential adhesion failure. So before spraying any clearcoat on a job for the first time, it is recommended to measure film build on a test panel. This will help gauge how your application techniques affect final film thickness. Two coats should suffice in creating adequate film build if using a high-solids, premium clearcoat. Some valuepriced clears may require three coats to achieve the same degree of protection. Knowing the film build is especially critical if the job will later be buffed. In other words, one cannot apply a film build of 2 mils, then buff off a half mil. The result will leave not enough UV absorbers or resin solids to block out the ultraviolet rays, thereby compromising durability. |
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When you choose to use Tamco Products, you will find the best technology available at any price — but for a reasonable price. I personally guaranty that I will NEVER cut quality to keep prices low. Yes, we will have reasonable price increases especially in these hard times, but we will always be the best bang for your buck!
Bob Barney