Anticorrosive Primer

Strontium Chromate. Strontium chromate [7789-06-2] SrCrO, is made by precipitation of a water-soluble chromate solution using a strontium salt or of chromic acid using a strontium hydroxide solution. It has a specific gravity of 3.84 and is used as alow toxicity, yellow pigment and as an anticorrosive primer for zinc, magnesium, alurninum, and alloys used in aircraft manufacture (8) (see Corrosion and corrosion control). 

Schmid, E. V., Painting of Zinc Surfaces and Zinc-Containing Anticorrosive Primers, Monograph No. 3, OCCA, Wembley, UK (1986)... 

Raw linseed oil Boiled linseed oil Stand oils Air drying Oxidative polymerisation Aliphatic hydrocarbons Fair Bad Fair Poor Poor/fair Binder for anticorrosive primers for wire-bushed steel Slow drying... 

Assuming maximum corrosion resistance is required, then an anticorrosive primer will be needed, with best protection coming from a crosslinked epoxy stoving primer. Most other properties are dominated by the finish, which will be based on a high molecular weight-polymer, either linear or (more usually) crosslinked. The precise selection of the polymer depends on the balance of properties required, but will be constrained by the type and rate of curing necessary. 

Zinc-Rich Primer an anticorrosive primer for iron and steel incorporating zinc dust in a concentration sufficient to give electrical conductivity in the dried films, thus enabling the zinc metal to corrode preferentially to the substrate, i.e. to give cathodic protection. 

Such coating systems must ensure optimal bonding to the metallic substrate and be compatible with a variety of top coats. Anticorrosive primers of this kind are currently undergoing large-scale industrial tests a product for the home handyman for repairing metal parts affected by rust is also in the test phase. 

I.L. Rozenfeld and F.I. Rubinstein. Anticorrosion Primers and Inhibited Pa,int Coatings. Moscow, Khimiya, 1980. 

Binders based on linseed oil and other oils have been used for many years in anticorrosive primers. Alkyd binders, especially those with high fatty acid contents, perform similarly. The main disadvantages of these binders is their limited chemical resistance and their slow drying. 

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]. 

Anticorrosive Primers. Anticorrosive primers are applied in dip tanks so that they reach all parts of the car body dipping is a fast method of application. The standard method for application of primers is electrodeposition. Anodic electrodeposition paints were used when the electrocoating technique was first applied, but cathodic electrodeposition is now predominant because it provides better corrosion protection. 

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. 

Anticorrosive primers are followed by a 40- 50 pm intermediate coat, based on two-pack polyurethane resins. This coat is sanded to yield a smooth surface. 

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. 

Buses have a profiled steel framework that is clad on the sidewalls and roof with steel, galvanized steel, and aluminum alloys. The anticorrosive primer must therefore adhere well to all of these metals, and to glass-fiber-reinforced plastics. 

Two-pack epoxy primers with chromate-free pigments show the best performance. They are applied with a DFT of ca. 80 pm, and simultaneously form the anticorrosive primer and a sandable filler. They can protect the metal substrates against corrosion. 

Anticorrosive primer formulations are based on epoxy resins that react at ambient temperature with amine adducts, aminoamide resins, or isocyanates (two-pack primers). Zinc or strontium chromates are used as anticorrosive pigments. These electrolytically active pigments prevent dangerous filiform corrosion. Extensive development work is being carried out on chromate-free aircraft primers [11.8], [11.9]. 

These organic primers have, however, largely been discarded in favor of the organic zinc silicate shop primers (see also Section 2.15.2). These are low-zinc versions of zinc silicate anticorrosive primers. Low zinc concentrations are used to minimize volatilization of zinc metal and formation of zinc oxide aerosols at welding temperatures. 

Chem. Descrip. Polyamidoamine (70%) in xylene Uses Crosslinking agent for epoxy resins in soiv.-based primers and coatings for min. and metallic substrates, anticorrosion primers, zinc-rich primers, coatings for lock gates, concrete, and underground conduits (in combination with tar)... 

Uses Sole binder or with polyisocyanates, flexibilizer for anticorrosion primers, zinc-rich paints, can coatings Features Extremely fast drying exc. corrosion protection Properties Dens. = 1.06 g/cm (20 C) dynamic vise. 20,000-30,000 mPa-sj flash pt.= 40 C 48-52% NV... 

Chem. Descrip. Bentonite organoclay CAS 1302-78-9 EINECS/ELINCS 215-108-5 Uses Rheology control agent, antisettling agent for paints/coatings, ap-pliance/metal furniture topcoats, traffic paints, anticorrosive primers, plastic clear coats, marine topcoats Features Requires a polar activator... 

Uses Drying oil for prep, of quality coating vehicles by cold blending (clear exterior finishes, aluminum paints, anticorrosive primers, blister-resist. wood primers, alkyd modification)... 

Uses Binder tor corrosion protection coatings, fast drying anticorrosive primers... 

Uses Vise, stabilizer, antigellant for solv.-fhinned coatings, UV-cured automotive OEM clear coats, anticorrosive primers Properties Amber liq, sp.gr. 0.90 dens. 7.5 Ib/gal vise. (G-H) B-D flash pt. 27 C 66% act. in xylene Use Level 1-2%... 

Uses Drier, chelating catalyst in modified polyurethanes and alkyds, clear and brightly pigmented oil- or alkyd-modified polyurethanes, in conventional alkyds which tend to discolor, traffic paints, anticorrosive primers, marine topcoats, wood furniture coatings Features Replaces cobalt drier Properties Sp.gr. 0.85 dens. 7.1 Ib/gal flash pt. 27 C Dapro 7007 [Elementis Spec. U.S.]... 

Uses Defoamer for aq. coatings, inks and adhesives, waterborne OEM, architecturai and maintenance tinishes, appiiance/metai turniture topcoats, traffic paints, anticorrosive primers, piastic dear coats, marine topcoats, wood furniture coatings... 

Uses Defoamer for waterborne architecturai, maintenance, and OEM coatings, anticorrosive primers, waterborne flexo and gravure inks, emui-sion mfg. 

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