Influence of the Sol pH on Electrochemical and Mechanical Behaviors of Siloxane-PMMA Hybrid Films Combined with UV Ink
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Influence of the Sol pH on Electrochemical and Mechanical Behaviors of Siloxane-PMMA Hybrid Films Combined with UV Ink Sandra Raquel Kunst, Marielen Longhi, Estela Knopp Kerstner Baldin, Rosiana Boniatti, Lilian Vanessa Rossa Beltrami, and Ce´lia de Fraga Malfatti (Submitted February 4, 2016; in revised form August 31, 2016; published online November 7, 2016) Pre-treatments with a siloxane-PMMA base have shown promising results when combined with the new ink technology with curing by ultraviolet (UV) radiation. Tinplate sheets were coated with a hybrid film obtained from a sol with alkoxides precursors consisting of 3-(trimethoxysilylpropyl) methacrylate and tetraethoxysilane and adding an organic phase composed of poly(methyl methacrylate). The hydrolysis reactions were catalyzed with a nitric acid solution (pH = 1 and pH = 3). The hybrid films were obtained by a dip-coating process, coated with red-colored paint UV curing and characterized for their electrochemical and mechanical behavior. The results showed that a more acidic pH (pH = 1) promotes the formation of a hybrid film with better protective properties, presented a better electrochemical performance and higher values of layer thickness. However, the hybrid film obtained with pH = 3 combined with the UV coating presented the best performance. This result is probably due to a better anchorage and adhesion verified in this sample. Keywords
hybrid film, pH, silane, tinplate, UV coating
1. Introduction The tinplate is formed from a metal substrate which comprises a steel base covered with two sides of pure tin, and it is used widely in the packaging sector; specifically, for this application, this material is subjected to a heat treatment to obtain a FeSn2 alloy which provides increased corrosion resistance to the system. Thus, tinplate combines the mechanical resistance promoted by the steel with the resistance to corrosion and the good appearance provided by the tin (Ref 1, 2). However, when the tin is used solely as protective barrier, steel corrosion is suppressed and the corrosion reaction results in small rate losses of tin, which is not a problem if a large area of tin coating is compared against a small-area cathode (pores). During this process, the food contained in the package may suffer contamination by the release of tin. Even if this is not considered a toxic metal, high doses can cause serious digestive disorders (Ref 1). On the other hand, when the tin does not act as a protective barrier, the observed cathode/anode area ratio is large, the iron
Sandra Raquel Kunst and Marielen Longhi, Graduate Program in Engineering of the Process and Technologies (PGEPROTEC), University of Caxias do Sul (UCS), Caxias do Sul, Brazil; and Estela Knopp Kerstner Baldin, Rosiana Boniatti, Lilian Vanessa Rossa Beltrami, and Ce´lia de Fraga Malfatti, Laboratory of Corrosion Research (LAPEC), Federal University of Rio Grande do Sul (UFRGS), Rio Grande do Sul, Brazil. Contact e-mail: [email protected].
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