Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Silicones in coatings
Keywords Coatings, Silicone
An important global technology forum, Silicones in Coatings III, took place in Barcelona at the end of March. Readers who wish to purchase copies of papers presented should contact the Organiser, Paint Research Association, 8 Waldegrave Road, Teddington, Middx TW11 8LD, UK. Tel: +44 (0) 208 614 4811. Following is a synopsis of some of the papers that particularly caught our eye. "New applications with silicone powder resins", by Walter Göblmeier, WackerChemie, Germany. This presentation provided an overview of new applications for powder coatings in kitchen goods, lights, etc. The coatings are produced with silicone powder resins as pure binder, and in combination with organic resins. Coatings with easy cleaning properties and with lower colour shift were shown. The influence of dry film thickness on adhesion and heat stability were discussed. Silicone resins with different chemical structures were evaluated.
"Polydimethylsiloxanes with vinyl ether end-groups as polymerisable surface active additives for UV-cured coatings", by Dr Frederic Cazaux and X Coqueret, Ecole Nationale Supérieure de Chimie de Lille, France. Telechelic polydimethylsiloxanes (PDMS) were modified by divinyl ethers to yield reactive surfactants that can be polymerized with conventional monomers by cationic photopolymerisation. A series of these polymers was incorporated into epoxide/vinyl ether formulations. Contact angle measurements showed a significant reduction for the surface energy of cured coatings containing silicone. The additive improved the wetting properties on various substrates and was also shown to impart stain-resistance properties and long-term anti-graffiti effects. An ESCA study revealed the permanence of the high silicone density at the top surface that ensures durable surface properties.
"Non-foaming trisiloxane alkoxylate formulation with enhanced spreading properties", by George A. Policello, Kalman Kozco and Dr Sue L. Yang, CK Witco Corp USA. The properties that make trisiloxane alkoxylates (TSAs) desirable, such as superspreading and wetting, also present some processing issues in coatings applications. Since TSAs are highly surface active, they can produce foam that is very hard to control with conventional defoamers. A proprietary technology has been developed to address these issues. A novel formulation was presented which not only controls foam, but also exhibits enhanced spreading properties.
"Recent applications of organo-functional silanes in coil coatings", by Dr Terence Child, Brent International, UK. Organo-functional silanes are used in metal pretreatment to provide corrosion protection and increased paint adhesion. In coil coating the higher cost of raw materials is offset by considerable benefits in processing, leading to an overall cost reduction. The more practical aspects of using silanes in this application were described including maintenance of silane treatment baths and the use of on-line monitoring techniques for silane film thickness and integrity.
"Aqueous dispersions of polysiloxane-acrylic hybrid resins for coatings", by Shin-ichi Kudo and Masataka Oota, Dainippon Ink & Chemicals, Japan. A new method was presented for synthesis of aqueous dispersions of polysiloxane-acrylic hybride resins, and the basic properties of the dispersions and films obtained by curing the dispersions were evaluated. They have high silicone content and good storage stability; curing at room temperature with epoxy-silane provides films with good appearance, dirt shedding properties and weathering resistance. Factors affecting these properties were considered.
"Si-acrylic sol-gel modified automotive clear topcoats for etch and scratch resistance", by Paul J. Popa, James S. Tonge et al., Dow Corning, USA.
Automotive clear topcoats must provide superior resistance against mechanical and chemical damage to guarantee long-term aesthetic appearance. Vehicle manufacturers have extended coating warranties while the performance demands have increased. Etch and scratch resistant clear topcoat formulations of Siacrylic sol-gels with acrylic-melamine and acrylic-isocyanate systems were presented. These one and two part thermally cured formulations were applied to typical automotive melamine basecoats. Industry standard performance testing and mechanistically insightful micro and nano scratch evaluations were compared with non sol-gel containing formulations.