Christopher Seubert

The long-term weathering behavior of UV curable clearcoats: I. Bulk chemical and physical analysis

The long-term weathering behavior of two UV cure clearcoat systems, one a monocure, the other a dual cure system, was studied by infrared spectroscopy, UV spectroscopy, Raman spectroscopy, dynamic mechanical thermal analysis (DMTA), and fracture energy measurements. The photooxidation rate and consumption of residual acrylate double bonds during weathering was highly dependant on the presence of hindered amine light stabilizers (HALS) for both systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation rate or rate of consumption of acrylate double bonds during weathering. Changes in fracture energy (brittleness) of the clearcoats mirrored the changes found in the consumption of residual acrylate double bonds. DMTA analysis of both clearcoats indicated no increase in crosslink density as weathering progressed, suggesting the acrylate double bonds were not reacting to form additional crosslinks.

Testing accelerated weathering tests for appropriate weathering chemistry: Ozone filtered xenon arc

Ftir spectroscopy has been used to follow the weathering chemistry of a HALS and UVA free polyester/urethane and a HALS and UVA free acrylic/melamine clearcoat cured on silicon wafers and subjected to exposure in Florida, Arizona, and in a number of accelerated weathering tests. All accelerated tests except EMMAQUA-NTW, ozone filtered xenon arc, and 3M Proprietary exposures distort the polyester/urethane’s weathering chemistry relative to its Florida and Arizona exposure weathering chemistry. Distorted weathering chemistry was attributed primarily to spectral power distribution mismatch between artificial radiation and sunlight. Experiments were initiated with an ozone filtered xenon arc radiation source whose spectral power distribution matches sunlight with great fidelity in the 290–400 nm region.

A hybrid ray-wave optics model to study the scattering behavior of silver metallic paint systems

The gonioapparent lightness of a metallic paint system depends strongly on the 3D microstructure of the platelet-containing basecoat layer, and on the platelet roughness. Current optical models which are used to simulate the paint’s appearance, however, ignore the multi-scale and multi-dimensional microstructural features, which limits their predictive power. Here, we describe a hybrid, ray-wave optics model for metallic paints. This model incorporates the ray-optics of the 3D platelet microstructure and the wave effects that result from the surface roughness of the platelets. This model is used to link the roughness to the reflection lobes of the aluminum platelets, and to the gonioapparent lightness of the paint system. Predicted lightness values from our model matched, at most viewing angles, measurements from physical paint samples. This model can be used to explore the effect of platelet surface roughness on the lightness of the complete paint system and predict the appearance of paints with different platelet microstructures.

Visual Comparison Testing of Automotive Paint Simulation

An experiment was performed to determine whether typical industrial automotive color paint comparisons made using real physical samples could also be carried out using a digital simulation displayed on a calibrated color television monitor. A special light booth, designed to facilitate evaluation of the car paint color with reflectance angle, was employed in both the real and virtual color comparisons. Paint samples were measured using a multi-angle spectrophotometer and were simulated using a commercially available software package. Subjects performed the test quicker using the computer graphic simulation, and results indicate that there is only a small difference between the decisions made using the light booth and the computer monitor. This outcome demonstrates the potential of employing simulations to replace some of the time consuming work with real physical samples that still characterizes material appearance work in industry.

A statistical method for the relative comparison of automotive paint colours using digital imaging analysis

Relative colour comparisons were performed using digital imaging techniques and analysis. A statistical method was used to quantify how well a test colour matched a colour standard. Colour histogram comparisons were performed by incorporating a combination of control limits (based on prediction intervals) and threshold limits that were calculated for each curve set. Test colours were imaged and compared to colour standards by calculating the per cent match for each of the RGB curves. Colours that did not show a per cent match of 60 per cent or greater in all three colour curves were considered failures. Some colour families, e.g. reds, required larger control limits to account for colour variability.