Paint & Coatings Industry - March 2009 - (Page 41) vide outstanding cure, viscosity stability upon oven aging, and corrosion/salt spray resistance. In addition to resistance to basic pigment deactivation, these catalysts reduce solvent popping defects and provide excellent adhesion/intercoat adhesion while allowing extended storage of formulated coating. In addition, the deblocking profile of these catalysts provides the so-called snap cure at the desired temperatures that are beneficial in reducing solvent popping/blistering, seen in coil applications with epoxy and amine blocked catalysts. TABLE 4 | Humidity test results. Formulation Blisters on Panel Surface – Size and Amount 500 h Control Nacure XC-194 #9 Small – 5-10% None Gloss Readings After Evaluation 0.0 h 1.2 / 8.8 0.9 / 5.8 500 h 1.3 / 8.5 0.9 / 5.8 Evaluation in a Coil Primer Containing Basic Anti-Corrosive Pigment A master batch of the white Shieldex C-303 coil primer system was prepared (Table 1) without any catalyst for use in our evaluations. All formulations used in this study were made from this white master batch with the addition of the appropriate catalyst package. For comparison purposes, control formulations with current state-of-the-art catalysts (W.R. Grace) namely epoxyblocked dodecylbenzene sulfonic acid (DDBSA), and epoxy-blocked phosphoric acid were prepared as shown in Table 2. The World’s Most Widely Used Weathering Tester Preparation and Evaluation of Coil Primer Coatings All formulations were applied by the drawdown method to B-1000 steel panels, with the average dry film thickness ranging from approximately 0.5 - 0.75 mils. Films were cured in a coil oven for 25 seconds at 325 °C. using a cure schedule that provided a peak metal temperature (PMT) of approximately 230 - 235 °C. The following properties were evaluated with the cured panels: pendulum hardness; gloss (20°/60°); color (yellowness index); adhesion (direct to B-1000 and recoated); salt spray resistance (500 h); humidity resistance (1000 h); and 50 °C oven aging (7, 14, 21, 28 days – viscosity, MEK resistance, and hardness). • Easy to use • Cost effective • Fast & realistic Results and Discussion The cure response of a typical polyester/melamine-based primer formulation containing the basic anti-corrosive pigment was controlled by a fairly high loading (9.7%) of the catalyst package consisting of two different epoxy-blocked acids (current state-of-the-art). When this package was replaced by 3.46% of the new blocked acid catalyst Nacure Tel: 1-440-835-8700 info@q-lab.com www.q-lab.com Visit ads.pcimag.com PA I N T & C O A T I N G S I N D U S T R Y 41 http://www.q-lab.com http://www.q-lab.com http://ads.pcimag.com
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