Paint & Coatings Industry - March 2008 - (Page 36)

Reaching Strict VOC Requirements with Outstanding Durability Figure 3 | Organosiloxane/nucleophile reaction. O SiCH 2C H2C H 2OCH 2C H-CH 2 + H X-R OH SiCH 2C H2C H 2OCH 2C H-CH 2 X-R Figure 4 | Organosiloxane/electrophile reaction. H SiCH 2C H 2C H 2NHCH 2C H 2-NH + O CH 2-CHCH 2- OH SiCH 2C H 2C H 2NHCH 2C HNH CH 2-CHCH 2- Figure 5 | Gloss change after QUV-A exposure. 100 90 Gloss (60 deg.) 80 70 60 50 0 500 1000 1500 2000 2500 3000 through cure. The modification of this type of system with organic polymers decreases the tendency for this to occur, however, it is not completely eliminated. If the silane or silicone polymer is silanol functional then the byproduct of the reaction will be water (Figure 1). Generally the silanol functional polymers are either a flake or in a high-pH or low-pH environment if in solution. These resins are excellent for use as blending resins or as modifiers for other organic resins. In each case the alkoxy- or silanol-functional siloxane can react with hydroxyl-functional organic polymers to form silicone-modified resins (i.e., siliconemodified alkyd or silicone-modified polyester), as seen in Figure 2. This reaction is driven by heat, and in both cases is a reversible reaction. The siliconeoxygen-carbon linkage is susceptible to hydrolysis and, therefore, the addition of moisture and heat will hydrolyze the polymer to form the reactants. If this occurs on exposure, the result would be oxidized organic polymer (oxidation accruing from UV degradation) and siloxane, which would be more hydrophilic. The incorporation of an addition curing group on the silicone polymer will eliminate the reversible reaction and still allow the chemist the ability to form an ambient curing technology. The attachment of a functional group via a hydrolytically stable Si-C linkage and not the hydrolysis susceptible Si-O-C linkage will react with standard addition-curing crosslinkers to form hydrolytically stable systems. The modification of the polysiloxane or silicone resin with epoxy-functional groups enables formulators to use typical crosslinkers, which react with epoxy groups, such as acid functional acrylic, phosphates, amines, etc., to form a film (Figure 3). The reaction of the epoxy with acrylic to form the acrylic ester is supported by the use of C13-NMR. There is a decrease of the epoxide peak and the acrylic acid peak with the formation of an epoxy-C-O-C(O)-acrylic peak. Conversely the modification of silicone with amine groups enables formulators to use raw materials, which will react with amine-functional polymers, such as aliphatic epoxy resins, GMA acrylic, etc. (Figure 4).6 The intrinsically low viscosity of the base polysiloxane reduces the overall viscosity of the modified polymer, which makes it possible to formulate products with improved exterior performance and lower VOC than classical technologies (Table 1). Results Formulations using addition curing technologies have been prepared and coatings evaluated by QUV-A, south Florida, and Adrian, MI. The former was used as a tool to develop accelerated exposure data for the Commercial Urethane Epoxy/Acrylic (Non-Iso) Silicone epoxy I/Acrylic Silicone amine/epoxy Silicone epoxy II/Acrylic Time (hours) 36 MARCH 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

Table of Contents Feed for the Digital Edition of Paint & Coatings Industry - March 2008

Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Marketplace Quarterly Stock Watch Reaching Strict VOC Requirements With Outstanding Durability for Industrial Maintenance and Marine Coatings A Unique Fungicide for Wood-Filled Plastic deSigns of the Times: Slacking Off! From Rocks to Nanos Shear-Free Dispersion Process Fluorinated Oxetane Oligomers as Versatile Intermediates for Polymer Modification The Effects of TPO Composition on Adhesion and Proposed Chemical Mechanism Supplier Showcase Color Management Materials Watch Products Classifieds Advertiser Index

Paint & Coatings Industry - March 2008

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