Performance of Modified Epoxy Zinc Primers

GIUDICE, C. A.; BENITEZ JUAN C.; PEREYRA, ANDREA M.

Pitture e Vernici European Coatings

GBP

Lugar: Milán; Año: 2005 vol. 81 p. 33 - 44

0048-4245

>With the aim to control the corrosion reactions and as a consequence to protect the metallic surface by applying good performance coatings, zinc primers were developed employing zinc pigment mixed with mica of lower cost. Two types of metallic zinc particles were selected: spherical and lamellar (both of them with very low level of impurities). Several series of coatings were designed and manufactured employing pure lamellar zinc, pure spherical zinc and also mixtures with different ratios between them, in all cases dispersed in an epoxy binder. Two grades of mica (10.2 and 33.1 were used to replace the zinc pigment in levels from 10 % to 60 % in volume. Degree of rusting of the coated panels for 1,000 hours in Salt Spray Chamber and also degree of blistering for 500 hours in 100 % Relative Humidity Chamber. For spherical/lamellar zinc primers a simultaneous analysis of the experimental data was carried out taking into account that the best performance is attained at PVC values equal or slightly lower than the correspondent CPVC. According as the lamellar pigment content increased and the spherical one decreased, CPVC decreased from approximately 60/65 % (spherical zinc-rich primers) to 50/55 %. Lamellar zinc-rich primers showed an excellent salt fog performance at extensive ranges of PVC but blistering resistance was very poor at PVC inferior to CPVC. Besides, these primers showed a more rapid consumption than spherical ones and then greater amounts of coarse mica could be used for decreasing the contact between zinc particles at low PVC values; in this way, the performance would not be affected and the useful life might be enlarged at reduced cost. Test data indicate that lamellar zinc primers modified by mica are very versatile since they can be formulated at a wider range of PVC without modifying their performance; slight heterogeneities in these primers before application might be minimised and do not generate areas of different corrosion-inhibitive capacity and blistering resistance.