One of the goals of automobile manufacturers is to provide their customers with an attractive exterior finish that will last for the life of the vehicle as well as a finish that is more protective.
The most common method of accomplishing this is to coat vehicles with water-based, acrylic polyurethane enamel paint and a layer of clear-coat paint.
Besides being more resistant to precipitation, sunlight, and temperature changes, modern clear-coat reduces the creation of micro-scratches, which makes paint look dull.
Nevertheless, clear-coat paint has weaknesses. For example, carmakers stress the importance of removing contaminants that can damage paint surfaces such as bugs, tar, tree sap, bird droppings, pollen, and acid rain deposition.
Manufacturers also recommend washing a vehicle at least once a month to get the grime off and applying a high-quality liquid or paste wax when water no longer beads on paint or metal trim.
The reason for this is that automotive clear-coat paint does not have hydrophobic properties. In other words, there is nothing to stop dirt from sticking to the surface.
For example, if a vehicle has no wax coating and is cleaned with car wash soap and rinsed, excess water will lay flat on the surface. This makes drying difficult and can lead to spotting.
To avoid this, car wash operators apply a drying agent during the rinsing process to increase the surface contact angle with water. Increasing the contact angle causes the water to bead up rather than form sheets.
Beading will usually occur when the contact angle with water is greater than 70 degrees. This can be achieved by using materials such as mineral oil, silicone, and synthetic polymers.
The inherent weaknesses of drying agents are they provide little in the way of protection, and the water-repellent effect is not long-lasting, perhaps days or a week.
So, most car wash operators offer a clear-coat sealant that provides some protection and longer lasting effects. Such products contain synthetic polymers, water repellant, and solvents.
Sealants usually have a surface contact angle with water of 80 to 90 degrees and the water repellent effect may last for several weeks.
At the head of the food chain are spray waxes and total body protectants that contain carnauba wax or synthetic wax, synthetic polymers, UV absorbers, and solvents.
Such waxes and protectants have contact angle with water of between 95 and 110 degrees and the water repellent effect may last for up to 30 days.
Arguably, the next development in the commercial car wash industry will be the introduction of a family of super-hydrophobic products that have a surface contact angle with water approaching 150 degrees.
According to research scientists, such a surface would not be wettable and would make the paint surface much less susceptible to dirt and grime buildup as well as much easier to clean.
A surface with such characteristics is described as “easy-to-clean” as opposed to a self-cleaning surface.
Currently, there are two ways to create a super-hydrophobic finish on a vehicle: wipe on/buff off liquids and gels or spray/dry products.
Each approach requires more than one step in the application process.
One manufacturer of a hydrophobic and oleophobic coating tested the voracity of its product as an automotive application during Florida’s love bug season. Treated and untreated panels were subjected to love bug splatter and allowed to dry for four days.
About 90 percent of the spatter on the treated panels came right off with a garden hose and nozzle. The remainder came off with a light scrub. However, there were some noticeable stain marks.
This underscores research that shows there is no correlation between contact angle of these materials and stain repellency. Moreover, these materials wear off over time.
Arguably, an effective “easy-to-clean” auto paint surface is going to come from the companies that make automotive paint.