Coatings World - February 2016

Waterborne UV-Curable Coatings

Experimental

The model formulation used in this study consisted of a novel light stabilizer (NLS) and a waterborne UV-curable coating (Table 1). DOE was used to design test runs as well as to analyze test data. DOE techniques allowed us to validate the data.

Optimal Results

Optimal results (Table 2) were used to identify factors that reduce yellowing, i.e., the concentration of NLS and the dry film thickness (DFT). Analysis of variance (Table 3), Parameter estimates (Table 4) and effect tests (Table 5) were analyzed from Table 2. The mathematical model derived from the data indicates that two factors, namely the NLS and the DFT, exhibit some degree of influence on the reduction of yellowing.

Novel Light Stabilizer Effects

The NLS was developed specifically for waterborne UV-curable coatings. Test data showed from its negative coefficient that the NLS in a waterborne, clear UV-curable coating can get good performance. For the NLS, the effect of reducing yellowing during the curing process was about 79% (Table 6).

Dry Film Thickness (DFT) Effects

Film thickness is the less significant factor in this study (Equation 1). Test data showed from its positive coefficient that the DFT of waterborne, clear UV-curable coatings can’t affect good performance. For DFT, the effect of reducing yellowing during the curing process was only about 0.6% (Table 6).

The Optimal Prediction Profiler

The prediction profiler (Figure 1) shows the effect that the NLS and the DFT have on reducing yellowing after the curing process. The data also suggested that by increasing the NLS to 3.44% in a waterborne UV-curable coating and having a coating thickness of 5 μm the best performance can be achieved [Delta Yellowness Index ΔY= -0.76 (Figure 1)].