In general, steel is protected from corrosive environments by conversion coatings, that is, phosphating, chromating, and so forth, and then followed by different layers of paints. Nowadays, strict pollution laws and regulations are creating significant challenges for coating experts to develop an environmentally friendly product. Powder coatings have demonstrated their ability as alternative to traditional solvent-borne coatings. In the present work, polyester-based two coating systems have been investigated and their performances have been evaluated for surface topographical properties by Scanning electron microscope (SEM), and energy dispersive spectrometry (EDX), accelerated corrosion resistance by salt spray test, and impedance property by electrochemical impedance spectroscopy. Coating adhesion with the steel and hardness were evaluated by bond strength, cross cut adhesion, and pencil hardness. This paper explains the results and performance of the coatings by the above two systems. 1. Introduction Galvanised steel is widely used in construction, automobile, and white goods sector. Zinc coating is the most effective and economic means to protect the steel substrate exposed to atmospheric corroding environments. It protects the steel substrate by acting as a barrier against the corrosive environment and by sacrificially corroding themselves to provide cathodic protection. Protective ability of galvanised (GI) steel may be enhanced by employing thicker zinc coatings or by painting the metallic substrate [1]. Paints improve the surface life of underlying zinc coating acting as a barrier against zinc reaction with environmental agents. Cracks, crater, and pin holes occurring in the paint are sealed by corroded zinc products. Moreover, corroded zinc products occupy a 20–25% more volume than zinc, while iron oxides (corrosion product of steel) occupy a volume several times larger than the steel; thus, expansive forces are reduced at the zinc-paint interface compared to those at the steel-paint one [2]. The main practical problem concerning painting of zinc-coated surface lies in achieving good bond strength, that is, good adhesion of polymer with GI sheet. Often adhesion looks satisfactory immediately after painting, but it prematurely degrades after water, oxygen, and other corrosive ingredients diffuse through the polymeric coating. Several pretreatment processes were reported to improve coating adhesion. The main function of pretreatment for GI steel surface is to form a very stable passive film which will enhance the adhesion with subsequent
References
[1]
A. K. Guin, S. Nayak, T. K. Rout, N. Bandyopadhyay, and D. K. Sengupta, “Corrosion resistance nano-hybrid sol-gel coating on steel sheet,” ISIJ International, vol. 51, no. 3, pp. 435–440, 2011.
[2]
A. S. Khanna, Introduction to High Temperature Oxidation and Corrosion, ASM International, 1997.
[3]
B. V. Jegdi？, J. B. Bajat, J. P. Popi？, and V. B. Mi？kovi？-Stankovi？, “Corrosion stability of polyester coatings on steel pretreated with different iron-phosphate coatings,” Progress in Organic Coatings, vol. 70, no. 2-3, pp. 127–133, 2011.
[4]
A. M. P. Sim？es, R. O. Carbonari, A. R. Di Sarli, B. del Amo, and R. Romagnoli, “An environmentally acceptable primer for galvanized steel: formulation and evaluation by SVET,” Corrosion Science, vol. 53, no. 1, pp. 464–472, 2011.
[5]
R. Mafi, S. M. Mirabedini, M. M. Attar, and S. Moradian, “Cure characterization of epoxy and polyester clear powder coatings using Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Thermal Analysis (DMTA),” Progress in Organic Coatings, vol. 54, no. 3, pp. 164–169, 2005.
[6]
D. Maetens, “Weathering degradation mechanism in polyester powder coatings,” Progress in Organic Coatings, vol. 58, no. 2-3, pp. 172–179, 2007.
[7]
J. B. Bajat, J. P. Popi？, and V. B. Mi？kovi？-Stankovi？, “The influence of aluminium surface pretreatment on the corrosion stability and adhesion of powder polyester coating,” Progress in Organic Coatings, vol. 69, no. 4, pp. 316–321, 2010.
[8]
M. A. J. Batista, R. P. Moraes, J. C. S. Barbosa, P. C. Oliveira, and A. M. Santos, “Effect of the polyester chemical structure on the stability of polyester-melamine coatings when exposed to accelerated weathering,” Progress in Organic Coatings, vol. 71, no. 3, pp. 265–273, 2011.
[9]
F. L. Duivenvoorde, J. Laven, and R. Van der Linde, “Diblock copolymer dispersants in polyester powder coatings,” Progress in Organic Coatings, vol. 45, no. 2-3, pp. 127–137, 2002.
[10]
S. Radhakrishnan, N. Sonawane, and C. R. Siju, “Epoxy powder coatings containing polyaniline for enhanced corrosion protection,” Progress in Organic Coatings, vol. 64, no. 4, pp. 383–386, 2009.
[11]
V. C. Malshe and G. Waghoo, “Weathering study of epoxy paints,” Progress in Organic Coatings, vol. 51, no. 4, pp. 267–272, 2004.
[12]
R. Van der Linde, E. G. Belder, and D. Y. Perera, “Effect of physical aging and thermal stress on the behavior of polyester/TGIC powder coatings,” Progress in Organic Coatings, vol. 40, no. 1–4, pp. 215–224, 2000.
[13]
Technical Data Sheet of Ridoline 1352 BA, of M/s Henkel Chembond India Ltd.
[14]
Technical Data Sheet of Granodine, of M/s Henkel Chembond India Ltd.
[15]
M. ？zcan, I. Dehri, and M. Erbil, “EIS study of the effect of high levels of SO2 on the corrosion of polyester-coated galvanised steel at different relative humidities,” Progress in Organic Coatings, vol. 44, no. 4, pp. 279–285, 2002.
[16]
R. Naderi, M. M. Attar, and M. H. Moayed, “EIS examination of mill scale on mild steel with polyester-epoxy powder coating,” Progress in Organic Coatings, vol. 50, no. 3, pp. 162–165, 2004.
[17]
R. Mafi, S. M. Mirabedini, R. Naderi, and M. M. Attar, “Effect of curing characterization on the corrosion performance of polyester and polyester/epoxy powder coatings,” Corrosion Science, vol. 50, no. 12, pp. 3280–3286, 2008.
[18]
G. Wuzella, A. Kandelbauer, A. R. Mahendran, and A. Teischinger, “Thermochemical and isoconversional kinetic analysis of a polyester-epoxy hybrid powder coating resin for wood based panel finishing,” Progress in Organic Coatings, vol. 70, no. 4, pp. 186–191, 2011.
[19]
M. Barletta and A. Gisario, “An application of neural network solutions to laser assisted paint stripping process of hybrid epoxy-polyester coatings on aluminum substrates,” Surface and Coatings Technology, vol. 200, no. 24, pp. 6678–6689, 2006.
[20]
R. Naderi, M. M. Attar, and M. H. Moayed, “EIS examination of mill scale on mild steel with polyester-epoxy powder coating,” Progress in Organic Coatings, vol. 50, no. 3, pp. 162–165, 2004.
