Paint & Coatings Industry - March 2009 - (Page 39) ing at the cure oven temperature. compliant alternative that can A coating composition that can be FIGURE 3 | Wet adhesion, 500 h; salt spray expoeffectively address the new legiscured in a shorter time at the oven sures. lation changes. These pigments temperature allows a faster and being heavy metal free are essenmore economical coil coating protially non-toxic. They are amorcess. A number of other properties phous micronized particles of conare important for coil coatings too, trolled particle size distribution, such as resistance to degradation with a density of about 1.8 g/cm3 and very high surface area. They on outdoor exposure (weatherabilare moderately basic, with the ity), chemical and water resistance, pH of aqueous slurry roughly in scratch resistance, gloss, hardthe range of 9-10. These pigments ness, and resistance to delaminaare readily available from an iontion when the substrate is bent. exchange reaction at the surface The bending property is important of silica gel between weakly acidic because after being coated the Control Formula- Loss of Nacure XC-194 – surface silanol groups and calmetal is subjected to a forming step. coating in scribe area and No Loss ofcoating in #6-7 medium blisters on scribe area after 500 cium hydroxide. For example, building panels are 70-80% of panel surface. hrs salt spray exposure. Coil primer formulations typiformed into a three-dimensional cally contain acidic substances shape after coating. It is important in the form, for example, of resins bearing acidic groups that the coating not lose adhesion during the forming step or amine-blocked conventional acid catalysts or latent or steps. Weatherability is important for metal that will be acid catalysts containing a beta-hydroxyl group. In used for building panels, gutters, garage doors, sign stock, these cases, acid-base interactions can lead to viscosity panels used for vehicle parts, or other such uses where increase or reduced cure rates. Latent acid catalysts conthe coated surface is exposed to outdoor weather and sun. While the bending property is generally better with softer, more flexible binders, weatherability and other durability TABLE 1 | Master batch of coil primer containing anti-corrosive pigment. properties are generally better with harder binders. White Master Typical coatings on aluminum are single coats, but Component Type Ingredients Batch Formula a primer/topcoat system is used on steel. Resin systems Dynapol L205 (30% solution)* 55.06 High MW PE resin used for primers include polyesters, epoxies and polyDynapol L208 (30% solution)* 13.76 High MW PE resin urethanes. Binders used in topcoats include polyester/ Solvesso 150 6.19 Solvent melamine for superior exterior durability and corrosion protection, silicone-modified polyesters either alone or Dibasic ester solvent (DBE) 4.82 Solvent with melamine, fluoropolymers like polyvinylidene fluoDiacetone alcohol 2.75 Solvent ride for highest exterior durability, and plastisols. PolySilane A187 0.72 Silane ester ester/melamine resins are also used as backer coatings Shieldex C 303 7.23 Anti-corrosive pigment on the reverse side of the coated metal to prevent metal Tiona 472 3.21 Titanium dioxide marking on the top surface by rubbing against the bare Talc IT Extra 1.51 Talc metal reverse side of the coil. Cymel 350 4.75 Melamine crosslinker Environmental concerns about the use of Cr (VI) comTotal 100.00 pounds in anti-corrosion coating technology has resulted in the introduction and use of environmental, health and safety (EHS)-compliant products such as calciumTABLE 2 | Control coil primer formulation containing epoxy-blocked acids. modified silica gel anti-corrosive pigments, especially in the general industrial and coil coatings segment. This has Ingredients Control Formula been a continuous and slow process but has been gaining Dynapol L205 (30% solution) 50.04 great momentum in the last few years. The pressure on Dynapol L208 (30% solution) 12.51 the European coatings industry towards implementation Solvesso 150 5.63 of VOC-free and EHS-compliant technologies significantly Dibasic ester solvent (DBE) 4.38 increased with the announcement of the EU VOC legislaDiacetone alcohol 2.50 tion that comes into effect in 2007 and the new REACH Silane A187 0.65 legislation that is currently planned to become effective from 2008 to 2010. The target of the latter legislation is Epoxy-blocked phosphoric acid 6.28 to ban all chemicals that may be considered as hazardous Halox 650 (dicarboxylic acid) 1.40 (approximately 20% of all chemicals used in the coatings Shieldex C 303 (anticorrosive pigment) 6.57 industry). In response to this ever-increasing environTiona 472 2.92 mental pressure, producers of anti-corrosion primers are Talc IT Extra 1.37 currently actively testing alternatives to anti-corrosive Cymel 350 4.32 materials based on Cr (VI) and Zn compounds. Epoxy-blocked dodecylbenzene sulfonic acid 1.52 Calcium-modified silica gel anti-corrosive pigments Total 100.09 (Ca/Silica pigments) offer a suitable, environmentally PA I N T & C O A T I N G S I N D U S T R Y 39
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