Product development
A Colorcoat® pre-finished steel product from Corus is one that has undergone many years of development and optimisation. Each of the individual elements which make up the pre-finished steel product is specially selected to give optimum performance and to work together so that the final product is much greater than the sum of its parts. Each product is made up of:
Metallic coated steel substrate
The basis of any pre-finished steel product is the steel itself. Steel is generally produced to national or international standards and it is important to ensure that the mechanical properties are those required. For roof and wall cladding products, this is generally considered by the system manufacturer in producing load/span tables. In terms of the durability of the product, however, it is the coating of the steel substrate which has an effect on lifespan.
The type and quality of the metallic coating is often a detail that is overlooked when considering a durable coated product. However, significant performance differences do occur.
Corus supplies pre-finished steel products with metallic coatings of hot-dip galvanised (HDG, nominally 99% zinc) and Galvalloy® substrates. The substrate for Colorcoat HPS200 Ultra® and Colorcoat Prisma® is Galvalloy®.
HDG is the standard substrate for the majority of pre-finished steel products and also provides the basis of the majority of un-painted steel used in the construction industry, for example, light steel framing. The zinc coating on HDG preferentially corrodes rather than the steel, so the onset of rust at exposed edges and surfaces is delayed, in some cases indefinitely.
Galvalloy® is a steel substrate hot-dip coated with an alloy of 95% zinc and 5% aluminium, and manufactured by Corus under unique process parameters to create an alloy with optimum corrosion resistance. Galvalloy® is used on the premium pre-finished steel products in the Colorcoat® range to provide the ultimate corrosion resistance, particularly at the cut edges often encountered on roof and wall cladding systems.
In order to adhere an organic paint coat to the metallic surface of the substrate, a thin layer of pre-treatment is used to modify the chemical nature of the surface and provide a ‘key’ for the paint. All elements within a pre-finished steel product are equally important including the pre-treatment. The best primer and topcoat available are ineffective unless their adhesion to the substrate is ensured for the product’s lifetime by a suitable pre-treatment. All Colorcoat® products have a controlled and consistent pre-treatment.
Most coatings for external applications consist of at least two coats, a primer and topcoat. The function of the primer is to give corrosion protection and optimal adhesion to the substrate. Through 40 years experience in the development and manufacture of Colorcoat® products, Corus has developed the most advanced primers tailored to give maximum protection to the substrate.
The key elements of the organic (paint) coating are polymers and pigments.
The polymers, also referred to as resins or binder, are organic-based carriers that chemically surround pigment particles and provide the basis of the continuous organic coating. Pigments are insoluble materials which are dispersed within the polymer to provide colour, opacity and other visual effects as well as corrosion protection. In the topcoat, pigments are most frequently used for aesthetic reasons.
A number of polymer resins can be used to make the topcoat. The polymer chemistry, pigment type and other elements of a paint formulation can have a significant effect on properties.
