In this study, the effect of the post-curing process as well as the long-term weathering behavior were studied for three different three-dimensional printable, pigmented (black), nonstabilized, ultraviolet (UV) cure resin formulations (A and B being thiol-ene chemistry, and C being acrylate chemistry). To study the effect of the post-cure process, the printed parts were post-cured using one of five different processes: no post-cure, UV-only, heat-only, UV+heat, and electron beam (EB) post-curing. Bulk tensile properties and nanohardness were measured for each of the systems and post-cure conditions. For weathering studies, the parts were post-cured using the recommended UV-only process and exposed using the ASTM D7869 exterior weathering protocol. The results show that the post-cure process had a significant effect on the final mechanical properties of the resins and was dependent on the underlying resin chemistry. Thermal post-curing was not as effective as UV curing for Resin C compared with the two other resins, which could both undergo thermal polymerization. In addition, Resin B showed the smallest change in mechanical properties before and after post-curing, regardless of the type of post-curing process. EB post-curing, even at very low dosages, that is, from 0.05 to 1 Mrad, resulted in considerable post-cure cross-linking to the point of embrittlement and a significant drop in percent elongation at break for dosages above 0.5 Mrad. Although Resins A and C outperformed Resin B in photooxidation performance, all three resins demonstrated that promising results considering no hindered amine light stabilizers were used in the formulations.

The long-term weathering behavior of three different 3D printable, non-stabilized, UV cure resin formulations (A and B with thiol-ene base, and C with acrylate chemistry) was studied using tensile testing, nano-indentation, and photoacoustic infrared (FTIR-PAS) spectroscopy. To this end, type I tensile bars were printed from each resin system using a 3D printer, and were post UV-cured under a broad spectrum source. Systems A and C showed a similar trend after weathering. They first experienced an increase in modulus and tensile strength, due to additional crosslinking of the residual unreacted species. This increase in mechanical properties was followed by a drop in modulus, tensile strength, and percent elongation, due to the over-crosslinking and consequent embrittlement. System B, however, showed remarkable retention of the mechanical properties before/after weathering. Nano-indentation results were in good agreement with the tensile properties, showing a similar trend in hardness variations. Although Systems A and C outperformed System B in photooxidation performance, all three systems demonstrated promising results considering no hindered amine light stabilizers (HALS) were used in the formulations. Both photooxidation and mechanical properties of the specimens are expected to improve after addition of HALS.

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.

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.

Although color and appearance have a psychological component, they are material properties that can be of considerable significance and economic importance to designers. Paint systems are materials that have a primary role of modifying the appearance of an engineering structure. The determination of structure–property relationships is recognized as a defining feature for different branches of materials science. These relationships are at the heart of the predictive models required for the development of new materials. Here we explore some of the microstructural parameters that control the appearance of platelet-containing paint systems. The orientation of platelets is a microstructural property known to affect the appearance of platelet-containing paints. However, prior works examined only a limited set of samples. Additionally, they did not identify other potential microstructural/formulation changes that could affect the relationship between orientation and appearance. In this paper, the orientation of the platelets was verified to be the major microstructural parameter that influenced the lightness of the paint system. In addition, the strength of this influence was shown to vary because of specific formulation changes, such as platelet size and volume fraction. The relationship between orientation and appearance was shown to depend on an additional microstructural property that is related to the size of the gaps between the platelets. We termed this additional microstructural property the gap factor. The size of the gaps between the platelets, and the coverage/shadowing of platelets by other platelets, was found to affect the scattering behavior of the system, particularly near the specular reflection direction. For example, larger gaps increase the probability of multiple reflections between the platelets. These results will guide the on-going work to develop improved structure–property relationships. Improved structure–property relationships are expected to provide more accurate models for the appearance of platelet-containing paint systems.

The scratch resistance of coatings used on two highly visible automotive applications (automotive bodies and window glazings) were examined and reviewed. Types of damage (scratch vs. mar), the impact on customers, and the causes of scratch events were investigated. Different exterior clearcoat technologies, including UV curable and self-healing formulations were reviewed, including results from nano- and macro-scratch tests. Polycarbonate hardcoat glazings were tested vs. annealed glass samples using a Taber abraser, with the resulting damage analyzed using transmitted haze measurements and optical profilometry. A correlation between the damage seen in glass samples (many smooth, shallow mars) and the best hardcoat samples (fewer, deeper scratches) and the haze measurements was discussed. Nano-scratch results showed similar fracture forces, but measurably improved mar resistance for the hardcoats/glass system compared to exterior clearcoats.

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.

Photolatent base crosslinked epoxy thiol coatings were characterized using transmission FTIR spectroscopy, Raman spectroscopy, UV spectroscopy, and Vickers micro-hardness testing. Curing rate constants were calculated for a series of formulations with varying concentrations of photolatent-DBN, ITX (2-isopropyl thioxanthone), and BP (benzophenone), as well as varying curing times. A design of experiments demonstrated that increased UV dose had the greatest impact on increasing the curing rate of the clearcoat system. BP wt% proved to have little impact on the clearcoat curing rate, while PL-DBN and ITX exhibited minimal improvement above 2.5 wt% and 1 wt%, respectively. Vickers micro-hardness results showed that irradiation dose had no impact on the final physical properties of the clearcoat. However, a 24-h ambient post-cure proved to increase the final hardness of the clearcoat under some conditions.

The scratch and scratch recovery characteristics of two clearcoats, a polyurethane and an acrylic/melamine/silane clearcoat, were measured by a variety of methods. On most size scales tested, the polyurethane possessed superior scratch and mar resistance. The polyurethane also possessed improved scratch recovery after warming for 2 h at 60°C. After 2000 h of accelerated weathering, the scratch recovery characteristics of the polyurethane were largely maintained, while the acrylic/melamine/silane showed a significant drop in scratch recovery performance. Performance of both coatings was related to T g, hardness, and crosslink density.

The scratch resistance of four clearcoat formulations was evaluated using a CSM nano-scratch tester, an AMTEC-Kistler simulated carwash tester, and a laboratory scale macro-scratching tester. Significant differences in the rank-order of all the clearcoats were found when comparing the scratch and mar behavior using macro-scratching, nano-scratching, and AMTEC-Kistler testing. Field vehicles were also examined where the mean and median widths of scratches found on vehicles were 237 and 141 μm, respectively. The range of loads associated with events with the potential to create real-world scratches was found to be significantly higher (5–35 N) than the forces needed to make scratches of the same mean size as those seen in the field (7–10 N). These results indicated that a significant improvement in the scratch resistance of these clearcoats would be needed before customers would notice improvements in their paint finish’s scratch resistance.

The long-term weathering performance of two UV-curable clearcoat systems was studied using in-plane microtomy in combination with infrared spectroscopy, UV spectroscopy, and ESR spectroscopy. Oxygen transport characteristics were also studied using the half-time method. The photooxidation versus depth profile was highly dependant on the presence of hindered amine light stabilizers (HALS) for both coating systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation profile. A photooxidation gradient was formed in both clearcoats due to a reduction in oxygen solubility when compared to standard thermoset clearcoats. This gradient was only seen in formulations not containingHALS.

Alternative methods for curing UV curable clearcoats were characterized using confocal Raman microscopy, nano-scratch measurements, and dynamic mechanical thermal analysis (DMTA). Clearcoats were cured using a xenon flash lamp, fluorescent UV bulbs with various spectral power distributions, and a microwave powered lamp. Raman spectroscopy was used to track acrylate double bond conversion of the clearcoat after each method of curing. DMTA was used to correlate double bond conversion to crosslink density. Nano-scratch results showed scratch resistance to be sensitive to the surface cure state. A combination of the flash and fluorescent methods produced a degree of cure similar to that of the microwave powered lamp. Scratch tests showed that clearcoats with a similar surface cure state achieved using different curing methods effectively had equivalent scratch properties.