VDA 621-412 Technical Paint Tests - Chemical Resistance of Motor Vehicle Paint

The standard "VDA 621-412 Technical paint tests - Chemical resistance of motor vehicle paint" published by the German Association of the Automotive Industry (VDA) describes test methods for determining the resistance of vehicle paints to liquid or paste chemical products. The methods described are applicable to testing images on metal or synthetic material supports.

This standard includes three test methods:

• Method A: With wetted filter layers or dripped chemicals
• Method B: By immersion in chemical products
• Method C: With chemicals that drip and run continuously

These test procedures were developed to evaluate the corrosion protection of vehicle paintwork using an accelerated laboratory test. This method is mainly based on the standard “Testing the corrosion protection of vehicle paintwork by alternating cycle testing”, which is a 7-day cycle consisting of the following steps. This test method includes a 621-day cycle consisting of the following steps:

• Salt spray at 35 degrees plus/minus 2 degrees for 24 hours
• 40 hours condensation at 2 degrees plus/minus 8 degrees humidity, 100 percent relative humidity
• 23 degrees plus/minus 2 degrees with 16 hour control humidity, 50 percent (maximum 100 percent relative humidity)
• 40 hours condensing humidity at 2 degrees plus/minus 8 degrees, 100 percent relative humidity
• 23 hours controlled humidity at 2 degrees plus/minus 16 degrees, 50 percent (maximum 100 percent relative humidity)
• 40 hours condensing humidity at 2 degrees plus/minus 8 degrees, 100 percent relative humidity
• 23 hours controlled humidity at 2 degrees plus/minus 16 degrees, 50 percent (maximum 100 percent relative humidity)
• 40 hours condensing humidity at 2 degrees plus/minus 8 degrees, 100 percent relative humidity
• 23 hours controlled humidity at 2 degrees plus/minus 16 degrees, 50 percent (maximum 100 percent relative humidity)
• 23 degrees plus/minus 5 degrees for 48 hours with controlled unspecified relative humidity (e.g. 50 percent (maximum 100 percent relative humidity)

The corrosion chamber is loaded with test samples according to customer's request or in accordance with the VDA 621-415 standard (60-75 degrees from the horizontal).

The coating on the surface of motor vehicles provides basic protection against external stresses, interactions or harsh weather conditions. However, coatings are exposed to chemicals and acids during cleaning, spills or fumes. Therefore, the outermost layer of the coating must be resistant to chemical attack. This protects the substrate from contamination. The main factors that a chemical environment can affect the coating layer are:

• Type of chemical (solvents, acids, alkalis, salts and other substances)
• Concentration of chemicals exposed
• Duration and degree of exposure
• Temperature
• Type of substrate (molecules that will react)

All of these factors must be considered when selecting components and formulating chemically resistant coatings. This is the only way to achieve optimum performance. For example, a coating may resist concentrated chemicals at low temperatures. However, it may deteriorate when exposed to a dilute concentration at high temperatures. Furthermore, chemical attacks can cause swelling, discoloration, loss of adhesion, loss of gloss, blistering, and more. Under certain conditions, this can lead to deterioration in performance and eventual failure.

Chemical resistance is a critical property in paints and coatings because it impacts durability and functionality, extends the life of materials, maintains aesthetics and structural integrity, and most importantly, contributes to compliance with industry standards.

Among the numerous tests, measurements, analyses and evaluation studies carried out for businesses in various sectors, our organization also provides testing services defined in the “VDA 621-412 Technical paint tests - Chemical resistance of motor vehicle paint” standard with its trained and expert staff and advanced technological equipment.