OEM Auto Paint Finishes
DateTHURSDAY, JULY 30, 2009 AT 2:03PM
With almost all of today`s paints being basecoat clearcoat systems, you may think that they are all the same. You may think that a vehicle is painted the same way at the factory and uses the same paint as in a body shop. You may also think that every vehicle can be buffed and polished the exact same way achieving the same results. This is not the case. Even though the final product may look the same, many paints have different chemical properties, which will dictate how you buff the surface of a vehicle. As detailers, we are only buffing the clearcoat, but some background knowledge on the rest of the painting process can be very helpful to both you and your customer. I truly believe that to become an expert on buffing the paint, you must first know the science behind the paint.
HOW IS THE VEHICLE PAINTED?
Everybody seems to have an opinion on how cars are painted at the factory. Some people think that all cars are painted manually. This is not true except for some limited production and very expensive automobiles that are still being painted manually. The vast majority of vehicles are painted using an automated process on the assembly line. Some people think that the vehicles are dipped in a huge tank of paint to achieve their color and final finish. This is not true for the final steps, but it is true for the first primer process called the E-coat, or Electro-primer.
STAGE 1
The E-coat is possibly the most important step in a paint process. This step gives the vehicle its corrosion protection. These days the chances of large areas of the vehicle rusting out are now almost non-existent because of this step. The vehicles are on the assembly line with the structural part of the bodies assembled and are first cleaned of dirt, oil, and grease by way of a dip pretreatment which penetrates even the smallest cavities. Next is a rinsing and drying cycle and then the bodies are electrocoated and dipped with this special rust-inhibitive primer.
ELECTROSTATICS
The electrostatic paint process; simply put, is achieved by negatively charging the paint particles and grounding, or positively charging the workpiece (the vehicle) so that opposites attract. This is an environmentally responsible way to paint a vehicle because it significantly increases quality and production, and equally decreases paint costs and VOC emissions. This process produces a much higher transfer efficiency, which means more paint ends up on the vehicle, speeding up the entire process and making it safer on the environment and more cost effective to the manufacturer.
In the case of the E-coat, the vehicle is electrocoated with levels that can be controlled by sophisticated equipment. This will determine how much of this primer will stick to the vehicle surface after it is dipped and then goes through another rinsing and drying process. This is the last time the vehicle will be dipped in any kind of primer or paint. The rest of the painting process is done with automated spray equipment.
ELECTROSTATIC SPRAY EQUIPMENT
In the remaining steps, the vehicle is painted with automated equipment. This is still an electrostatic process, but the type of equipment may vary. Some manufacturers use spray guns, but many are choosing a device called a rotary atomizer or bell cup. This device does not look like a spray gun at all. It looks like a large bullet and at the nose, or cone, the paint is mixed, charged, and sprayed. The bell or nosepiece rotates at a very high rate of speed (up to 55,000 RPM) to finely atomize the paint particles. In the pictures shown, the bell edge has very fine serrations to further atomize the paint. A charging electrode is located at the tip and the atomized paint becomes negatively charged. Even further atomization is achieved as the charged particles repel each other to form an even finer cloud of spray. There are other types of electrostatic spray equipment for assembly line use as well as refinishing.
STAGE 2 SPRAY PRIMER
After the vehicle goes through the E-coat dipping, rinsing and drying, it is then caulked and sealed and sent into spray primer. This is a very important step for a number of reasons. This primer will fill very minute scratches and imperfections in the body, and also it gives the basecoat something to "stick" to. For years some carmakers left out this step to save time and money, but it led to problems such as chalking, powdering, and delamination. Also the primer can be made color specific to better hide stone chips and scratches. BMW uses color specific primers now on all their vehicles. For 1999 there are 16 different primers for 19 different basecoat applications. This is obviously a much more expensive and time-consuming process, but it can make a big difference in customer satisfaction.
The next operation is the basecoat or color coat. This gives the vehicle its color. Basecoat will dry dull, like the old lacquer systems, and has no gloss. The difference is that the old lacquer paints needed to be sanded and buffed to achieve their gloss. Again, this was very time consuming and rather expensive because you had to apply enough coats with the anticipation that some of it would be sanded and buffed off. With basecoats, all you want is coverage. A high film build is not needed, and there is no sanding or buffing of a basecoat.
CLEARCOAT
Basecoat/clearcoat systems have been around for quite a long time. Many European cars have been painted like this since the early 80`s. However the technology has changed dramatically.
It all starts with what the manufacturer wants. A car company may want their vehicle to have the absolute best gloss you can possibly achieve. They also will want the surface to be resistant to scratches and marring. They also will want the paint surface to be very resistant to atmospheric pollution, such as acid rain, industrial fallout, tree sap, bird droppings, stone chipping, etc. In a nutshell they want the surface to be bulletproof. Unfortunately, for the manufacturer they will almost certainly have to give up something to achieve something else. For example, if they want a great gloss they will have to give up a little durability. If their concern is durability, the gloss may not be quite as rich. This is a double-edged sword. Some paint manufacturers say that the technology is available to produce an almost bulletproof clearcoat but paint costs have skyrocketed. Most car manufacturers in trying to keep costs down will opt to play a game of give and take with the clearcoat surface.
CHEMISTRY LESSON
A major difference between a factory or OEM clearcoat and a refinish clear is how they are activated and dried. In a refinish situation the clearcoat can be air-dried and harden on it`s own. In an assembly line situation, this would be much too time consuming. On the assembly line, the vehicles must be painted, dried and on to next assembly step in a relatively short period of time. Therefore the paints chemical makeup is totally different. There are basically 2 types of OEM clearcoat systems. The first is 1K or melamine; the second is 2K or polyurethane.
1K MELAMINE
In any type of paint system there must be activation, or something that starts the drying and curing process. With a melamine clear or 1 component, the activation is started by a baking process. It is activated or cross-linked by temperature and time frame. This type of system is baked at a very high temperature, typically 265-285 degrees farenheight for about 20-30 minutes. In this system the components in the resins are very stable and have a very long pot life, so no activation or cross-linking will take place until it reaches a certain temperature.
2K POLYURETHANE
In a polyurethane system, it is a 2 component clearcoat that is more of a chemical reaction and is accelerated by heat. The activation starts when the 2 components are mixed together at the sprayer, where they are precisely blended, before the paint is atomized and sprayed on the vehicle. This system is baked at lower temps, typically 140-165 degrees for about 30-40 minutes
There is still another type of technology available called powder- coating, in which the resins stay in powder form and adhere to the surface electrostatically. Then they are baked at a very high temperature and fused into a smooth coating. This is a very fast growing finishing technology. While not many vehicles are painted with this system there are more and more parts and components painted like this (such as wheels.)
CROSS LINKING
I have mentioned the process where the clearcoat starts its curing process as cross-linking. The chemists I spoke with referred to this as cross-link density. As detailers we would refer to this as how hard or soft the paint is. My intention for doing this research was to determine why some cars buff differently than others using the same procedure. Why were some cars left with swirl marks and some cars looked fine? Why does one vehicle have such a great shine and another vehicle just looks okay after doing the exact same thing? It is not our imagination playing tricks on us. It all comes back to this cross-link density.
Simply put, this is how tight or dense the surface will get after is it fully cured. Think of this as drawing a tic-tac-toe board, or checker board on a piece of paper. The smaller the squares and closeness of the lines will dictate a tighter or denser surface. The chemists would not generalize what paint systems were harder or softer, (1K or 2K) or what makes and models had more shine or durability, but looked at the chemical makeup of the clearcoat resin itself, the amount of activation, and the heat and duration of the baking process, as determining factors in how hard or soft and amount of gloss the car would have. Another key factor in gloss and appearance is the line speed of the vehicles on the assembly line. If a car is moving at a very high rate of speed it does not give the paint a chance to "lay out" and flow as well as a vehicle that is moving slower. Again, time is money. Other factors that effect gloss are the flow rate or orifice opening in the sprayer and how well the paint is being atomized. These are all things that the engineers have to take into consideration before the spray system is designed.
Another thing that the chemists agreed on was that no system is bulletproof. They design the paint system and clearcoat for what the carmaker wants and there is always a degree of give and take involved.
WHEN TO WAX?
A topic for consideration, about which many people are misinformed, is when you can wax the vehicle or apply paint sealant. Looking back at the curing process, both the 1K and 2K systems are 90-95% cured upon cool down, after the bake process, in the factory spray booth. The additional 5-10% will cure within 3-7 days. This means that by the time any vehicle reaches its destination at a dealer, the paint is fully cured. By not applying some sort of protection to the paint surface upon delivery or shortly after, the customer is actually hurting the paint instead of helping it. Salesmen that say don`t wax a car for 6-12 months are misinformed. This is a huge problem in our business because customers will tend to believe a salesman who knows nothing about paint, rather than a trained professional. This is often why fairly new cars are in such bad shape even after a short period of time.
IS THERE A CHART?
I have been asked if there is a chart, or list, that can be made of vehicles with characteristics such as hardness and degree of shine and what the buffing procedure should be. Unfortunately, it is not that simple. Even vehicles of the same make can have different paint systems and it will vary from model to model and place of origin. There also may be areas on the vehicle that have been refinished. That paint may react differently to buffing that the factory paint.
As a detailer you will see many different cars in all types of condition. There is no set in stone way to buff any car. Many detailers make the mistake of getting into a comfort zone and in do the exact same thing on every vehicle regardless of age, condition, make and model, or color. Even though you are buffing only the clearcoat the background color or basecoat is the backdrop on how the imperfections will show up.
Hopefully by understanding the entire paint process and knowing that all factory paints are far from the same, you may better understand what steps and procedures are needed to produce a near flawless vehicle every time.
and LOTS of chrome, including 22" wheels, in 4x4 of course. 
