Visco-elastic visco-plastic analysis of scratch resistance of organic coatings

• Published in: JCT research Vol. 2; no. 8; pp. 591 - 598
• Main Authors: Jardret, Vincent, Ryntz, Rose
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.10.2005; American Coatings Association, Inc
• Subjects: Analysis; Application fields; Applied sciences; Automotive coatings; Coatings. Paints, varnishes and inks; Exact sciences and technology; Film formation and curing, properties, testing; Mechanical properties; Polymer industry, paints, wood; Polymers; Rheology; Structure; Technology of polymers; Viscoelasticity; United States; Viscoelasticity; thermoplastic olefins; solvent-based; Modeling; Score strength; Scratch; Elastoplasticity; Olefin polymer; Melamine resin; Acrylic polymer; Damaging; Coating material; automotive-OEM; Stress strain relation; plastics; Ester polymer; Mechanical properties; Thermoplastic rubber; High solid paint; Tensile property; Hardness; Experimental study; Indentation; modelling; Thermosetting resin; melamine-formaldehyde coatings; Aminoplast; thermoset; Measurement method; high-solids; Comparative study; Rheological properties
• ISSN: 1547-0091; 1935-3804
• DOI: 10.1007/BF02774588

The sensitivity of automotive coatings to scratching, particularly coatings for plastics, has been a growing concern among automakers. Scratching may result from such predelivery events as polishing minor defects embedded in the paint, or postdelivery events such as car wash bristles, dirt embedded under a cloth utilized in polishing the car, tree branches, and the like. Warranty cannot separate out which event is the more prevalent (e.g., predelivery or postdelivery to the customer) form of damage on plastics. Data available on coatings for metal, however, does suggest that isocyanate-based crosslinked systems perform more poorly than their melamine-based crosslinked counterparts when exposed to in plant (predelivery) handling. Coatings on plastics, while lower in modulus than coatings on steel, are still subject to scratch events, albeit they have a greater tendency to "self-heal" once scratching events have occurred. This work attempts to correlate the scratch resistance behavior of three different one-component hydroxyl-functional acrylic or polyester-acrylic-melamine-crosslinked systems. Relationships between the tensile and indentation properties of the coatings were found to be related to the initial warranty data o f the coating systems. Most importantly, it was apparent that the critical depth to fracture of the flexible coatings may be the relevant indicator of field performance for coatings on plastics. For metals, the relevant indicator to field performance is often only critical load to fracture, negating the influence o f indentation depth. This variance is important to consider since coatings on plastic are often softer and more resilient to surface abrasions than their counterparts on metal.