METAL SIDING & ROOF PAINT "EDUCATION”
Liquid paints account for more than 90% of the coatings used for prepainted metal. Liquid paints are made up of four main constituents: pigments, binders, solvents and additives.
The solvent is used as a delivery mechanism, allowing the paint to flow-out and give a smooth wet film before drying and curing. They are not incorporated into the finished product.
The function of the finished product is a combination of the binder, pigments and additives, but coatings are usually categorized by the type of binder used. The binder is a polymeric material which gives structure to the paint. The main types of paint polymers used for metal siding and roof are: Polyester and Polyurethane.
Pigments used in metal coatings are generally inorganic and they provide both color and certain physical properties such as corrosion protection, while various additives are included in the paint formulation to modify aspects such as paint flow, speed of curing, UV absorption and gloss.
Polyesters are the workhorse coatings of prepainted metal, which offer an economical product with reasonably good performance across the board for metal siding and roof. A standard polyester product would have a 20–25 µm coating with limited flexibility and moderate durability when exposed as the top-weathering surface. Modifications can be made which can improve the flexibility depending on profiling complexity of metal siding and tile shapes.
Basic polyesters have moderate resistance to chemicals, staining, dirt, UV light and provide a basic barrier coat to prevent the substrate from corrosion.
Regular modified polyesters are used for both metal siding and roof cladding, particularly in mild and dry climates.
Polyesters usually present a smooth surface, but with either the addition of polyamide particles or with a structured base layer, textured surfaces are also available. Apart from the obvious aesthetic benefits, these textured products are often highly scratch resistant, which is particularly important in metal siding "intimacy” with outward things.
Polyester serves as the base paint for Matte finish.
Polyurethane coatings are chemically similar to polyesters with the addition of isocyanates in the formulation, thus exhibit many of the same properties.
Polyurethanes are capable of producing high-build polyurethane of thicker coatings. Targeting for excellent corrosion resistance for outdoor exposure, 50 µm polyurethanes are commonly offered for the areas of severe weather conditions. Polyamide beads are often incorporated which provide a textured surface and a very high level of scratch resistance.
Polyurethane coatings generally cost slightly more than polyesters, so they are used where the benefits outweigh the cost differential. The high-build products are widely used in roof and wall cladding because of their improved corrosion and UV resistance, coupled with the scratch-resistant properties of the polyamide-modified varieties.