Paint Review - Smart Coatings Significantly Improve Surface Durability

By Robert Roman

04/01/17

This article contains excerpts taken from Evolution of the Automotive Body Coating Process — A Review, published by MPDI (Multidisciplinary Digital Publishing Institute). MPDI is an academic open-access publisher with headquarters in Basel, Switzerland.

Cleaning vehicle surfaces effectively, efficiently, safely, and to the customer’s satisfaction is the goal and objective of commercial car wash operations. Principal surfaces car washers deal with are paint, wheels, and glass.

Arguably, the process of removing dirt and grime, shining, and protecting vehicles is easier for car wash operators to manage today because of the continued development of automotive coatings.

 

NEWER PAINT PROCESS

For example, when I was professionally trained and practiced auto body repair and paint refinishing in the early 1970s, the auto industry was beginning to make the transition from enamels and acrylic lacquer paints to a basecoat/clear-coat paint process.

This was done to further improve coatings’ appearance and durability among other reasons. For example, some problems associated with applying and curing enamel and lacquer were orange peel, runs, sags, fading (oxidation), mottling, and, worse case, delaminating (lifting) of layers.

By the late 1980s, the use of basecoat/clear-coat process had become widespread. Today, OEMs in the United States use a one-component clear coat formulation based on acrylic resins and melamine cross-linkers whereas in Europe a two-component (2K) formulation is mostly used.

So improved, experts estimate the corrosion protection and durability of color and gloss of automotive paints is about double of what was typically 25 years ago.

Coating qualities are judged by protection against harsh environments, durability, and appearance. Harsh means damage caused by falling objects, ultraviolet rays (UV), extreme temperature, scratches, stone chips, and rust from salt or road deicers. Durability is to have a car with rust proofing for over 20 years, and good color/gloss appearance for over a decade. The three parameters for determining appearance quality are color, paint smoothness, and gloss.

Auto manufacturers achieve these attributes with a five-step coating process.

The process begins with pre-treatment or surface cleaning that enables bonding. Next is electro-deposition of an anti-corrosion or rust prevention layer. Next, sealer is applied to prevent water leaks, chipping, vibration, and noise.

Primer is then applied to promote adhesion between surface and basecoat and provide a smoother surface and anti-chipping properties for subsequent layers.

Finally, a topcoat of basecoat/clear coat is applied to provide surface properties such as color, appearance, gloss, smoothness, and weather resistance.

The figure shown above depicts the layered structure produced by the five step coating process. Based on this structure, car wash and detail shop operations could affect weather resistance, appearance quality, and chipping.

The final step in the body coating process is to apply the topcoat, which consists of basecoat and clear coat.

Basecoat contains primary coloring pigment, and clear coat provides a protective coating against environmental effects, corrosion, and UV degradation. Basecoat promotes color retention and provides a smooth, unblemished, and even finish.

The value of lightness or darkness, hue, and chroma are terms used to describe the three-dimensional nature of the color created by using pigments in a vehicle’s basecoat.

PROTECTION

The final coating is the clear coat, which provides durability and environmental-etch and scratch resistance to the overall coating. The clear coat protects against damage such as fading that is caused by UV, and imparts gloss and depth. The clear coat also makes repairs and maintenance easier.

Etch is an appearance issue associated with the formation of permanent water spots or non-removable marks from bird droppings, tree resin, or other chemicals (including car wash chemicals) after contact with an automobile’s surface.

The physical damage resulting from etching is associated with a localized loss of material and deformation or pitting of the clear coat surface.

To prevent fading, chemicals that absorb UV light are mixed into the clear coat. Research shows concentration of UVAs in clear coat decreases by about 50 percent after four years of exposure to the sun.

Scratch resistance of clear coat is another factor that affects long-term appearance of surface coatings. For example, fine scratches or marring that is produced from repeated washings (commercial and home) are a consequence of slight surface deformations that can level over time. Such fine scratches are usually visible when light is scattering from the scratches themselves.

Other scratches like key scratches may actually cause the clear coat to ablate or break.

SMART COATINGS

Automotive coatings continue to evolve today with the use of smart coatings which offer the potential to significantly improve surface durability while adding additional functionalities or properties like self-healing, super-hydrophobicity, self-stratifying, self-sensing, sound proofing, and vibration damping.

For example, smart coatings respond to an abrasive, mechanical trigger, or to a corrosive event in which the coating is self-healing as a result of UV, heat, or mechanical activation.

Self-healing is also achieved with shape-memory polymers triggered by temperature and humidity manipulations, or with UV radiation. Other coatings include those with internal sensing capabilities that entail passive or active triggering of fluorescent molecules or quantum dots.

A recent trend has been to replace liquid coatings withpowder coatings. The powder is a mixture of fine particles of pigment and resin electro statically sprayed onto the surface to be coated. Charged powder particles adhere to electrically grounded surfaces until the powder is heated and fused into a smooth coating in a curing oven.

BMW and Volvo are using powder coatings on their new model cars, and GM, Ford, and Chrysler have formed a consortium to test it on their production lines.

In the service manuals of new vehicles, OEMs provide guidance on how customers should operate and maintain their vehicles. To maintain a vehicle’s outward appearance, OEMs recommend washing at a commercial car wash or at home in the driveway (two bucket method). OEMs also recommend periodic hand waxing (twice a year) and spray waxes for in-between detailing.

CAR WASH ROLE

Thus, we find car wash operators offering products and services designed to remove dirt and grime, mitigate degradation of UV protection, prevent marring, and shine and protect surfaces.

On the other hand, the automobile manufacturing and coating industries are moving in a direction that minimizes the need for these products and services by providing solutions directly from the factory. For example, experts opine that two-layer topcoats ensure color, gloss, and chip resistance of coatings and can remain in relatively excellent condition during the first seven to 10 years of an automobile’s use.

Experience shows vehicle design, method of assembly, and materials used to protect steel and coatings have basically alleviated corrosion problems. Moreover, widespread use of smart paints and avant-garde technology that impart super-hydrophobic and self-healing properties would not have a positive influence on the demand for commercial car wash or detail shops.

 

Bob Roman is president of RJR Enterprises – Consulting Services (www.carwashplan.com). You can reach Bob via e-mail at bob@carwashplan.com.



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