Refined Test Procedure to Reproduce Automotive Acid Etch Provides Improved Lab Practicality and Proven Correlation

For decades, automotive coatings have experienced degradation in the form of etching on coatings exposed to acid rain. As a result, procedures were developed to simulate and accelerate this type of degradation. These procedures failed to accurately simulate the etch produced in the product’s service environment because they lacked the critical field components necessary to reproduce this type of degradation. In 2002, BASF and Q-Lab Corporation (formerly Q-Panel Lab Products) developed a new procedure to reproduce acid etch in the laboratory. This procedure, known as the BASF Accelerated Acid Etch Test (BAAT), was the first of its kind to provide excellent correlation with the coatings’ actual service performance. This unprecedented level of correlation was achieved by incorporating all the critical stresses including humidity, UV, moisture, appropriate acid solution and horizontal specimen orientation into the exposure cycle. Since its inception, the BAAT procedure has been used as a screening tool for automotive clearcoats. There has been ongoing research to improve and substantiate correlation with field results, and to optimize the test procedure. First, temperature settings from the original BAAT have been adjusted to improve practicality. Next, new evaluation techniques using modern instrumentation were performed to further quantify exposure results. Finally, additional outdoor exposures determined the following: results do not differ significantly between sites on Blount Island, coated panels can be used interchangeably for actual automotive hoods and a horizontal orientation provides the best etch results. Cumulatively, this research provides the automotive industry with a practical, viable test method to replace Jacksonville exposure testing, without sacrificing correlation. Background History Description of Acid Etch. In the 1980s, damage to automotive coatings from acid rain events became a problem. Both dealerships and buyers complained about the ring type or “water spot” etches that were formed on the coating. These etches are caused when water from acid rain evaporates and the remaining acid concentration produces acid hydrolysis reactions with the clearcoat. This causes cracking and loss of paint that takes the shape of a water spot. Figure 1 Cracking and paint loss are depicted in this illustration. 2 Blount Island Exposure. Because Blount Island in Jacksonville, Florida is one of the most severe locations in North America for the conditions that cause acid etch, it is the benchmark exposure site for annual field tests to assess acid etch resistance of automotive coatings. Numerous hoods, panels and fascia are tested in Jacksonville each year by Automotive OEMs and their suppliers. The typical testing period is from June to September of each year and test specimens are rated for etch damage at varying times throughout this period. This has been done by using a method of visual evaluation with standard panels used as a guide. Figure 2 Etch ratings increase in severity starting from a rating of 0 and moving to a rating of 10. Pictures show examples of damage rating 2, 3, 4, 6, 8, and 10 While the Blount Island exposures have the benefit of real-world testing, there are significant limitations to the procedure in terms of product development. Limitations include the inconvenience of a single location, the narrow time frame for testing, and the variability of the results from year to year. Recognizing these limitations, BASF and Q-Lab Corporation joined forces to develop a test method that allows for accelerated, realistic and repeatable acid etch results.