Experimental study on mechanical property and stone-chip resistance of automotive coatings

The damage of automotive coatings caused by stone impact is a problem that has attracted great attention from automotive companies and users. In this work, experiments were conducted to investigate the dynamic tensile properties and stone-chip resistance of automotive coatings. Four kinds of paint films and three typical coatings (single-layer electrocoat coating, single-layer primer coating, and multilayered coating) were used. Under dynamic tensile load using split Hopkinson tension bar (SHTB), the engineering stress-strain curves of the paint films at medium and high strain rates (from 50 to 600 s-1) were obtained. Results indicated that the mechanical properties of the paint films exhibited strong nonlinearity and strain-rate correlation. A modified anti-impact tester was used to complete repeatable single impact tests. The effects of some key parameters, i.e., impact velocity, impact angle, and paint film thickness, on the stone-chip resistance of coatings were systematically investigated. The influence of contact type under high-speed impact conditions was investigated as well. The surface morphologies of the coatings after impact were examined by scanning electron microscopy (SEM), and the failure mechanism of the coatings under normal/oblique impact was discussed. In all experiments, the paint films showed brittle fracture behavior.

Scratch Properties of Clear Coat for Automotive Coating Comprising Molecular Necklace Crosslinkers with Silane Functional Groups for Various Environmental Factors

Automotive coatings, which comprise multiple layers, i.e., primer, base coating, and clear coat layers, are exposed to various environmental conditions that pose various types of damages to them. In particular, the outer layer of the automotive coating, i.e., the clear coat, is affected significantly by such damages. Therefore, a reliable and durable clear coat must be developed to improve the appearance of automobiles. In this study, a new clear coat based on an acrylic-based clear coat modified using polyrotaxane crosslinkers, which are necklace-shaped supramolecules composed of ring-shaped host molecules, is developed and characterized. The effects of polyrotaxane and silane on the scratch properties and mechanisms of the clear coating are analyzed. It is observed that the critical loads of the clear coat from scratch tests can be improved by adding optimal molecular necklace crosslinkers comprising silane functional groups. The improvement in the scratch properties of the modified acrylic-based clear coat may be attributed to the crosslinking characteristics and dynamic molecular movements of the polyrotaxane. In addition, the effects of environmental factors on the scratch characteristics of the modified acrylic-based clear coat are investigated by addressing the scratch durability of the clear coat.

Hyperbranched additive into a high solid acrylate coating for automotive application: impact on performance and emission of volatile organic content

Purpose Automotive coating materials are very important items for this industry. However, their performance is limited by the use of excessive amounts of solvents in their formulations, whereas the emission of volatile organic solvents is against the widely ascending principle of green chemistry. Thus, this study aims to overcome this global problem to save the environment without affecting the properties and performance of the coating. Design/methodology/approach High solid content paint formulation for automotive applications has been designed with low amount of volatile organic solvents with the aid of a functionalized hyperbranched modifier. Findings It was found that the presence of a hyperbranched additive allows a high solid content to be designed and facilitate the processing, which indicates its liability to compensate the role played by excessive solvents amounts. In addition, the mechanical properties and physical characteristics of the modified coatings showed outstanding performance and preservation of clarity in comparison with the commercial counterparts. Practical implications A high solid content coating with facile processing and improved performance leads to cheaper price beside the positive impact on the environment considering the limited emission of volatile organic contents. Social implications Limitation of the used volatile organic compounds in any industry helps to save the health of humans and keep the environment unaffected. Originality/value The use of functionalized hyperbranched additive to automotive coatings is a very promising additive for automotive coatings with optimized characteristics.