Pre-painted steel technology is carried out by continuous color coating process, based on liquid paints, accounting for more than 90% of the coatings used for this product line. Liquid paints are made up of 4 main constituents: pigments, binders, solvents and additives.

Solvents serve 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. The 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 flat sheet metal products are: Polyester derivatives, Polyurethane and PVDF.

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.

POLYESTER

Polyesters are considered to be workhorse coatings of pre-painted steel. They offer cost-efficient product line of fairly good technical performance, entirely satisfying the optimal requirements of traditional roll-forming application. Standard Polyester products would have a 20–25 µm coating with limited flexibility and moderate durability when exposed outdoors.

Basic Polyesters have moderate resistance to chemicals, staining, dirt, UV light and provide a basic barrier coat to prevent the substrate from corrosion. Modifications are applicable to upgrade paint elasticity to handle delicate profiling (High Polymer Polyester / HPP, High Workability Polyester/HWP) and enhance the resistance to atmospheric peculiarities, including UV and precipitations (High Durable Polyester/HDP, Most Valuable Polyester/MVP, Silicon Modified Polyester/SMP, SQP/Super Quality Polyester).

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. Polyester serves as the base paint for Matt products.

POLYURETHANE

When it comes to superior adhesion or weather-sustainability requirements, here is Polyurethane paint. Polyurethane coatings are chemically similar to Polyesters with the addition of isocyanates in the formulation, hence 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, while more economic option of 35-40 µm is also in place. 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 for their improved corrosion and UV resistance, complimented by scratch-resistant properties of the polyamide-modified varieties.

Polyurethane coatings are available in high gloss and matt finish selection.

PVDF

PVDF paint is a tandem of excellent paint flexibility and supreme resistance to fading. PVDF (Polyvinylidene fluoride) is a highly durable resin, which is fused in the paint layer not cured as Polyesters. Unlike to most polymers, PVDF resin does not break down on exposure to sunlight. Being beyond the affection by UV radiation, PVDF remains exceptionally lasting coating with high resistance to fading and chalking and maintaining gloss and color brightness. Besides, PVDF resin is highly resistant to many chemicals and shows excellence in stain resistance.

PVDF coating thickness varies in the range of 25 µm (standard/2 layers) to 55 µm (high-build multi-layer/4 layers). Multi-layer PVDF products are used to ensure UV stability for specific colors, to ensure the richness of particularly bright colors or high-gloss finishes, or to provide additional robustness to the product.
PVDF is broadly used for external application like wall cladding and facades. PVDF belongs to premium mono-colored coatings.