Basil V. Gregorovich

Oligomers in the evolution of automotive clearcoats: mechanical performance testing as a function of exposure

Automotive coatings must provide excellent resistance to chemical and mechanical damage in order to maintain a vehicles long-term appearance and the owners long-term satisfaction. The Automotive Industry and coating suppliers are partners in design and delivery of future coatings capable of meeting customer demanded performance. As a result of this partnership, new coating materials are being explored based on oligomer chemistry that show promise in providing improvements in both physical and chemical properties/performance and the long-term maintenance of those properties. Oligomeric systems are also useful in design of low VOC coatings. These supersolids coatings will be capable of meeting current and future air quality standards. In this paper measurement techniques for monitoring chemical and mechanical property changes, including cure rate, crosslinking, tensile properties, rheology and scratch and mar performance, were explored. Laboratory mar tests, wet and dry rub tests, which have been validated by commercial experience, are currently used as the basis for comparison of a coatings mechanical performance. QUV accelerated weathering was combined with micro-scratch experiments, atomic force microscopy, optical microscopy, image analysis and IR surface characterization techniques to provide correlations between chemical composition and mechanical performance, and an indication of service life.

Environmental etch performance, and scratch and mar of automotive clearcoats

Abstract Environmental etch damage to automotive coatings, and scratch and mar of these coatings are an important element of customer satisfaction as well as a significant warranty repair consideration for automotive companies. The conditions that result in environmental etch are examined and a laboratory test proposed. Data from this test are compared to automotive hoods exposed in Florida. The performance of various crosslinking chemistries is discussed and the requirements for improved environmental etch are outlined. Scratch and mar performance of these systems is also reviewed. We have found that coatings respond to physical stress by elastic recovery, by plastic flow and by brittle fracture. Classifying types of damage in this way is important for understanding the chemistry needed for improved scratch and mar of coatings.

Scratch and mar and other mechanical properties as a function of chemical structure for automotive refinish coatings

Abstract Due to continued customer demand for better quality and more durable coatings, interest in improving the physical damage resistance of automotive refinish coatings has intensified. New coating materials are being explored based on oligomer chemistry that show promise in providing improvements in both physical and chemical properties, and in the long-term maintenance of those properties. In this paper, measurement techniques for monitoring chemical and mechanical property changes, including cure rate, crosslinking, photo-oxidation index, hardness and scratch and mar performance, were explored. The use of the single scratch indentor, a method pioneered in this laboratory, provides a basis for mechanical property evaluation. Constant temperature and relative humidity (CTR) storage and QUV accelerated weathering were used in this study. Mechanical performance was determined using hardness measurements, nano-scratch experiments and wet/dry rubtests. Infrared was the primary method of chemical analysis. This characterization was done to broaden our understanding of structure/property relationships, as well as to provide a more reliable prediction of service life.

Scratch and Mar Performance of Coatings: Measurement and Structure Property Relationships

Abstract Scratch and mar of coatings is an important aspect of retaining initial performance levels. A number of test methods have been developed to measure coating resistance to damaging conditions. For the coatings industry, it is critical to have accelerated tests that indicate probable long term (i.e., service life) performance, and to have a means to correlate mar performance with chemical substructures of coatings. In this paper the synergism of measurement techniques for monitoring scratch and mar performance is explored. Laboratory mar tests, which have been validated by commercial experience, are used as the basis for comparison of a coatings performance. The combined elements of chemical, physical, mechanical, morphological and appearance properties of coatings have been explored. Chemical changes during cure and subsequent exposure have been followed by infrared techniques which show degree of cure, extent of photo-oxidation and hydrolysis, as well as changes in cross-linking with time and temperature. Physical and mechanical properties measured include T g, hardness, standard stress/strain measurements, as well as “Method of Essential Work”. Physical properties can be correlated with visual recovery of plastic flow damage and resistance to mar. Furthermore, microscratch experiments have been utilized to explore forces that are needed to induce surface damage and to determine the transitions between elastic deformation, plastic flow, and brittle fracture type damage. Morphology of scratches was examined by the use of atomic force microscopy before and after exposure. Optical imaging techniques were used to characterize scratch and mar. These studies are useful in understanding mechanisms of coating failure.