Clearcoat compositions are known in the automotive industry. As is understood by those skilled in the art, clearcoat compositions are used in combination with basecoat compositions to provide a protective and decorative coating for vehicles and the like. The clearcoat composition and the basecoat composition are cured or set, either together or independently, to form a film on the vehicle.
An outermost portion of the film includes the clearcoat composition. As a result, the clearcoat composition is consistently exposed to environmental elements, especially as acid rain. Acid rain cause a visible etch defect on a surface of the film by attacking the clearcoat composition with an acid hydrolysis reaction. Typically, for the etch defect to occur, the acid rain must bead, i.e., form discrete droplets of rain, on the film such that the concentration of acid at any particular point on the film is intense enough to initiate and propagate the etch defect. On the other hand, if the acid rain does not bead on the film, then the acid in the acid rain is sufficiently dissipated across the film and the concentration of acid at any particular point on the film is not intense enough to initiate and propagate the etch defect.
Various chemistries for the clearcoat composition are particularly susceptible to etch from acid rain. For example, one chemistry, commonly referred to as a high solids clearcoat chemistry, is unable to adequately resist etch from acid rain because it is reliant on an acrylic resin with hydroxyl functional groups and a melamine cross-linking agent. In this chemistry, the cross-linked ether bond formed between the acrylic resin and the melamine cross-linking agent is susceptible to the degrading acid hydrolysis reaction. As described above, the acid hydrolysis reaction results from the concentrations of acid present in acid rain attacking the film. The acid hydrolysis reaction generally weakens the film and reveals itself in the form of the etch defect visible on the film.
Various attempts have been made to combat this acid hydrolysis reaction. As a result, many types of “etch-resistant” clearcoat compositions are known in the art. For instance, some alternative chemistries that are resistant to the acid hydrolysis reaction have been developed. Unfortunately, these chemistries are considerably expensive and other properties, including the workability or application window of the clearcoat composition and also the overall appearance, i.e., gloss and distinctness of image (DOI), of the film have been negatively impacted. One example of such an alternative chemistry is a clearcoat composition that is based on silane chemistry.
Other attempts at combating acid etch include increasing the glass transition temperature (Tg) of the resin or resins in the clearcoat composition such that the film is more resistant to etch from acid rain. Although increasing the Tg does improve the resistance to etch, there are drawbacks to this approach. Increasing the Tg of the resin can increase the cost of the resin and may reduce the performance of the film relative to other physical properties, such as cyclic cracking. Furthermore, it is known throughout the industry that the marginal improvements that have been with respect to acid etch resistance as a result of increasing the Tg of the resin are still not considered acceptable.
Finally, certain after-market products have been introduced that may improved resistance to acid rain by reducing the ability of the acid rain to bead on the surface of the film. These after-market products, such as waxes, polishes, and the like, are typically hand-applied to the film by an owner of the vehicle. These products are particularly deficient in that their solution to the acid etch problem is not permanent. That is, because these products wear off, they are unable to permanently and continuously prevent the acid rain from beading on the film. These products are not “built in” to the clearcoat compositions that are used to form the film.
Due to the deficiencies in the prior art clearcoat compositions, including those described above, it is desirable to provide a unique clearcoat composition and a unique method that adopt an inexpensive and direct approach to reduce the ability of rain to bead on a film of the clearcoat composition such that certain properties, such as resistance to etch from acid rain, are improved.