| Résumé : |
The substrates one coats or paint for a variety of reasons may be divided into several categories. They may be heat conductive or not, and they may porous or not. Each of these types of substrate may affect how the coating dries - in rate or in appearance. The GGSCT Technical Committee investigated the drying rates gravimetrically, and examined the coatings for defects after the drying. Examination of the data was done with statistical techniques to determine the importance of the seven variables designed into the study. The best models showed: 1. The data best fit hyperbolic function of time; 2. The most important variables were time, temperature and film thickness; 3. The inclusion of pigment at lower than PVC slowed drying in most models, though possibly not statistically significant; 4. The porosity and heat conductivity of the substrate were occasionally important minor variables in some models showing drying retardation, if statistically significant at all, and; 5. The minor variable contrasting latex versus solvent was important in only one model, showing retardation of drying of water, if significant. The statistical models do not exactly reproduce the actual drying curves, and require more sophisticated approaches. The models used are excellent guides to the sense of what is happening. However, for reasons of imperfect fit to the actual drying rate curves, the statistical models have been discarded. However, the observed drying curve, having two linear sections, has a more compelling rationale for being the preferred characterization. The two linear sections of the observed drying curve are due to the solution evaporation rate control in the earlier stage, and the solvent permeation to the surface controlling the latter stage. |
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How do coatings actually dry? in EUROPEAN COATINGS JOURNAL (ECJ), N° 9/95 (09/1995)
