Polyurethane top coatings

These results were confirmed in the specimens with polyurethane top coats. 

The combination of polyaniline primer/polyurethane top coat showed only a very small measure of undermining (0-0.5 nun). 

Organic zinc primer, epoxy or polyurethane intermediate eoat, and aliphatie polyurethane top coat. 

Inorganic zinc silicate polymer, chemically curing epoxy or polyurethane intermediate coat, and aliphatic polyurethane top coat. 

Microencapsulation avoids many of the problems associated with the use of neat liquid crystal. McElderry [40] used microencapsulated material to study flat plates placed in a supersonic air stream, to produce a color display that had relatively low angular dependence. The encapsulation of material is particularly important if liquid crystal thermography is to be used in water tunnels. Here, it is useful to apply microencapsulated liquid crystal using an air brush, protect the capsules from contamination by solvents with an initial coating of acrylic polymer, and finally apply a waterproof polyurethane top coat. Fig. 4. Ogden and Hendricks [41] report the use of this technique for the study of turbulent water flow... 

For qtplications involving outdoor exposure, a surface treatment such as anodizing or chemical conversion coating is required prior to the application of a primer and a finish (top) coat, such as an epoxy or polyurethane. Some new one-step, self-priming polyurethane top coats are also available as are low volatile-organic compound (VOC) high-performance primers (e.g., epoxy polyamide). 

The (physically wetting) polyaniline primer CORRPASSIV was compared with a fast-drying two-component epoxy resin primer (Messrs. Finalin, Type 144) and a metal-reactive two-component primer with adhesion-promoting properties (Type 918). All three primers were coated with a two-component polyurethane paint (B412). CORRPASSIV, both with and without top coat, exhibited no rust formation beneath the primer. The slight undermining receded after the test, and even within the cross and scratch injuries, it was virtually impossible to detect any corrosion. 

Chemical agent-resistant coatings (CARC) consist of a surface cleaning, epoxy primer, epoxy interior topcoat, and a polyurethane exterior top coat. The purpose of this coating was to provide resistance to chemical penetration of the coating and to aid in decontamination of the vehicle in case of chemical attack. Other purposes of the coating were to provide corrosion protection as well as camouflage protection. 

Very interesting results were obtained by Gelling et al. [141] with poly-3-octyl pyrrole (POPy) and poly-3-octadecyl pyrrole (PODPy) solubilized in an organic solvent and cast on Al 2024 T3 (2-3 pm thick), then top-coated by a 20 pm-thick polyurethane (PU)... 

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... 

Where the coating itself does not provide all the desired properties, top coats or top finishes will be applied as a final environmental barrier, providing UV stability, durability, inertness and self-cleaning attributes. Top finish choices include acrylics, acryUcs/polyurethanes and PVF films. 

Top finishes are formulated using clear acrylic, acrylic/vinyl or acrylic/ polyurethane resins and are applied at a thickness ranging from 0.1 mm to 0.4 mm. Other top finishes on a base of fluorocarbonpolymers, e.g. PVDF, PVF or FEP, are applied within a range of 1.0-1.5 mm. If the top layer is applied as a foil, e.g. 0.03 mm PVF foil, it will give better protection than would a top coat applied in liquid form, because the surface will be more effectively sealed against environmental impact. If weldable textiles or foils are welded together, the non-weldable top coats have to be removed from the welding area. If not done properly, this already critical zone is left partly unprotected. 

Two types of paint systems were used for experiments. First system used was zinc phosphate primer (50 % Zn as compound) with micaceous iron oxide (MIO) as intermediate coat followed by polyurethane (PU) as top coat denoted as ZP. Other system used was zinc rich primer (80 % Zn as dust) with MIO as intermediate coat and PU as top coat denoted as ZR. This system is costlier with respect to ZP and considered for laboratory evaluations purpose only. ZP is designed with respect to places where test panels are deployed for exposure based on manufacturers catalogues and standards [4]. These systems possess good resistance from water permeability, weathering, abrasion and good adhesion to maintain a proper barrier to the environment. The drying mechanism of the systems is the reaction between epoxy resin and polyamide. The details of each paint system used comprising primer, intermediate and top coats with the respective layer of film thickness are shown in Table 2.2. 

---