In our last blog, we discussed Henry Ford’s decision to choose one color for their Model T’s — black. To support his assembly line concept, Ford required a fast-drying paint, and in 1909, the only paint available that met the needs of mass production came in only one color: black.
To contrast with today, not only are cars available in a technicolor range of shades and hues, but they also utilize different types of paint to perform different functions.
Automotive paint structure
The common automotive finish comprises three distinct layers: primer, basecoat, and clearcoat. Each of these serves a specific purpose in the overall coating structure and each of these may be an entirely different chemistry from the others, demanding different considerations in the application and curing process. To get right to the point, we are going to disregard the pre-treat processes that take place prior to the decorative paint operations.
The primer is the initial paint layer applied to prepare the automobile body or individual parts for the basecoat. It smooths out tiny defects from the manufacturing process and enables the basecoat to adhere properly by creating a binding layer. We are all familiar with the common gray or red colors, but there are also “color-keyed” primers, designed to support and/or accent the basecoat color. Primers are available in virtually every solventborne and waterborne base chemistry including epoxies, polyurethanes, polyesters, acrylics, etc. Some manufacturers even use powdercoat as a prime, but for the purposes of this discussion, we are limiting our focus to liquid primers.
The primer is the thinnest of the decorative layers and, as such, has the greatest potential for uneven film build issues. In addition, as the base structure, it provides the foundation on which the other layers are built. It is easy to understand how a primer layer that is not smooth and continuous, will transmit these defects through the basecoat and clearcoat layers, undermining the aesthetic quality of the final finish. After all, would you expect the same smooth, glossy finish that you can get paint on glass if you are painting over sandpaper?
When applying the primer, paint temperature control is incredibly important, as the temperature directly affects the viscosity of the paint, which in turn, affects the flow out and integrity of the final primer surface.
The basecoat is probably the paint layer that most people think of when they think about automotive paint. But in actuality, the basecoat’s primary function is to provide color and other visual effects like a metallic or “glittery” appearance, or a pearlescence or iridescence to the finish. With modern formulations, it is even possible to “shift” the color (say from red to blue) based on the angle from which the surface is viewed!
As with its primer counterpart, basecoats are available in a variety of waterborne and solventborne chemistries, each of which requires its own considerations for optimal performance. With basecoats, film thickness is even more important than with the other two layers as this is where color is controlled. Thinner films produce color differently than thicker films due to the resulting structure of pigment and metallic flakes. As a result, controlling viscosity to maintain a consistent and repeatable film build is essential. Because of its relationship to viscosity, inconsistent paint temperature can lead to inconsistent color.
Who knew that the temperature of the paint when applied could determine the color of the car?
The clearcoat is the final protective layer applied to an automobile or its components. It’s important to remember that the clearcoat is still paint — it’s just paint without any pigments. The job of the clearcoat is to protect against the elements – not only weather, but also dirt, UV, scratches, and anything else the world may care to throw the way of the vehicle. Being the protective layer, it is also the thickest of the three layers. With more coating to flow out and cure, variations in film across the part are common and these can have an effect on things like gloss, orange peel, etc.
Without controlling clearcoat temperature (and therefore its viscosity) when it’s applied, it may end up being either too thin and unable to properly protect the basecoat underneath, or too thick, thus using too much material and eating away at the bottom line for automotive paint finishers.
If you’re curious how a paint temperature control solution can improve results when applying your primer, basecoat, or clearcoat, Saint Clair Systems can provide you with input specific to your application. Contact us for more information.