Anticorrosive paint system

Heavy-duty coating systems generally comprise two primer coats and two topcoats, modern system sometimes consist of one primer coat and two topcoats. The total dry film thickness (DFT) of such anticorrosive paint systems is 150 - 200 pm, each layer has a minimum DFT of 40-50 pm. Due to their excellent adhesion, the first and second primers prevent corrosion of the metal surface. The pigments and extenders allow the primers to react with ions (CD and SO4") that diffuse into the film from the atmosphere. The pigmented organic film also forms a barrier against humidity that may otherwise initiate a corrosive process. 

Generally, coatings for corrosion protection are applied as layered systerrrs, where each layer has been optimized to maxinuze a different functionality (adhesion, corrosion protection, hydrophobicity, gloss, UV resistance). For example, an anticorrosive paint system in the aerospace indnstiy has three main layers (Garcia et al, 2011a) ... 

Surface Preparation of the Substrate. This is extremely important for all methods of paint and coatings application. The failure of a paint system is often due not to the paint itself, but because of a failure in surface preparation. For example, an anticorrosive paint applied to a rusty surface will not be effective if the rust falls off taking the new paint with it. For wood and plastic surfaces, old paint or a weathered surface layer may have to be removed. For older metal objects, the removal of corrosion is often required. Sandblasting is one method to remove both the old paint and any corrosion. For new metal objects, a phosphate or chromate layer is often chemically bonded to the metal to provide a surface to which a coating can easily adhere. 

Paint systems for car repair comprise anticorrosive primers, putties, intermediate coats, and topcoats repair coatings applied to refinished cars have similar durabilities to those of the originally manufactured coating systems. 

Ormecon, the German manufacturer of the CORRPASSIV paint systems, has performed a number of tests in order to prove the anticorrosive effect of their paint systems. The following results and claims appear on Ormecon s homepage and in their publications [75]. Ormecon states that a primer... 

Chem. Descrip. Solution of a polyurethane in water/diluent Uses Rheology control agent, thickener, stabilizer for aq. clear and high gloss top coatings, anticorrosive paints and thick layer systems Features No neg. intiuence on gloss or opacity exc. water resist. Regulatory EiNECS, MiTi iisted... 

Uses Associative thickener, rheology control agent, vise, builder, stabilizer for aq. systems for indoor and outdoor paints, latex and anticorrosive paints, syn. resin-bound renderings, adhesives, and paste fillers Properties Wh. lightly transparent liq. emulsion disp. in water dens. 1.06 g/ml (20 C) pH = 6.5 nonionic 40% act. in water/butyltriglycol (40/ 20)... 

Uses Mar resist, aid, flow aid, leveling agent, surf. tens, reducer, wetting agent for solv.-based paints (PU, vinyl, alkyd-melamine, acrylate-isocyanate), one-coat systems, anticorrosive paints, wood/furniture varnishes, printing inks... 

Chem. Descrip. Polyurethane in water and emulsifier Uses Thickener, rheology control agent, flow aid for aq. coatings, acrylic gloss paints, anticorrosion paints, styrene-acrylate, S/B, water-emulsifi-able two-pack systems, air- and force-drying water-emulsifiable binders Features Low-vise. 

SILIKOFTAL ED binder, optical fiber coatings Actllane 230HD30 binder, org. solvent systems Ethyl hydroxyethyl ceUilose binder, outdoor paints Potassium silicate binder, oven anticorrosive paints SILIKOPHEN P 60/D SiLiKOPHEN P 65/W SiLiKOPHEN P 70/MPA SILIKOPHEN P 80/20 SILIKOPHEN ... 

C. I. Eisner, E. Cavalcanti, O. Ferraz and A. R. Di SarU, Evaluation of the surface treatment effect on the anticorrosive performance of paint systems on steel, Prog Org Coat, 2003,48,50-62. 

Carew, J. A. et al.. Weathering performance of industrial atmospheric coatings systems in the Arabian Gulf Proc. Corrosion 94, NACE, Houston, 1994, Paper 445. Rendahl, B., Igetoft, L. and Forsgren, A., Field testing of anticorrosion paints at sulphate and sulphite mills, in Proc. 9th International Symposium on Corrosion in the Pulp and Paper Industry, PAPRICAN, Quebec, 1998. 

The automotive industry places great demands on its anticorrosion coatings system and has therefore invested a good deal of effort in developing accelerated tests to help predict the performance of paints in harsh conditions. It should be noted that... 

The corrosion inhibition and water resistance are obtained by paint systems formed by several anticorrosive coats based on epoxy, vinyl, chlorinated mbber, or bituminous coatings. 

Anticorrosion paints containing polyaniline. As the first actively passivating anticorrosion system, a newly developed PAni primer could perform the important environmental protection function of conserving energy-intensive and raw-material-intensive assets (Section VII.B). 

This guide covers painting systems for the protection of the exterior boot-top areas (the area from the light load line to the deep load line) of steel ships. It should be noted that boottops are rarely used with today s commercial ships, and bottom systems may extend up to the deep load line. In general, the anticorrosive and antifouling paints covered in SSPC-PS Guide 19.00 are applicable to boot-top areas. 

Uses Mar resist, aid, flow aid, leveling agent, surf. tens, reducer, wetting agent for solv.-based paints (PU, vinyl, alkyd-melamlne, acrylate-isocyanate), one-coat systems, anticorrosive paints, wood/fumiture varnishes, printing inks Properties Gardner 2 max. d. liq. sol. In aliphatic, aromatic, and chlorinated hydrocarbons, alcohols, ethers, and esters sp.gr. 0.9 1.01 dens. 8.3 Ib/gal vise. 70-130 mPa-s flash pt. > 100 C ref. index 1.414-1.418 surf. tens. 21 dynes/cm (20 C) 100% act. 

Polyurethanes are frequently used in anticorrosion coatings. The R D drive of most coatings and resin producers is the reduction of the solvent content of the paint and resin systems. One method of achieving the environmental aims demanded by legislation in the PU coatings industry is to use oxazolidines which are suitable as latent hardeners to enable production of single-pack moisture activated PUs. The isocyanate chosen for this research is tetramethylxylene diisocyanate, which has been available commercially only since 1988. 19 refs. 

Possible combinations of red lead with various binder systems are listed in Table 39 [5.114]. Red lead is still used for heavy-duty anticorrosion applications, especially for surfaces bearing residual traces of rust. In waterborne paints, red lead has no advantages over zinc phosphate [5.149]. 

Car paints are cured with heat in special oven lines. Electrodeposition coatings (used as anticorrosive primers) contain only small amounts of volatile organic compounds (VOC), whereas intermediate and topcoats release considerable amounts of VOCs. Intermediate coats based on waterborne resins have been developed to decrease VOC emission and are already being used in some automotive plants. Basecoats, as part of base-clear topcoat systems, contain very high amounts of volatile organic solvents. Waterborne basecoats were developed more recently to lower this source of solvent emission. Some car manufacturers are operating pilot lines with the aim of introducing waterborne basecoats into their production processes. Many car producers in the United States and Europe have already switched their topcoat lines over to waterborne basecoats [11.3]. 

Field trials have shown that the expected durability of the new waterborne coating systems is equal to that of conventional solventborne paints. As a further advantage, the number of single coats can be reduced from three to two. Standard freight cars are painted with a three-coat alkyd system consisting of an anticorrosive primer, an intermediate coat, and a topcoat, total DFT is ca. 150 pm. Such systems are being replaced by single-coat systems of waterborne acrylic resins and acrylic copolymers to reduce solvent emission. 

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