For a reinforced anti-corrosion coating system Northpoint Ltd have developed powder coating systems based on different protection techniques.
Steel Passivation: an active protective primer over-coated with a high grade polyester powder coating. The primer is applied at 60 – 100 microns thickness with a polyester (or hybrid top coat for interior use) top-coat applied at 70 – 120 microns. This system is dedicated to steel passivation when linked to a phosphate pretreatment. The passivation is derived from active pigments within the primer and is formulated to provide excellent adhesion between the coating layers.
Barrier Protection: a high grade barrier protective primer over-coated with a high grade polyester powder coating. The primer is applied at 60 – 100 microns thickness with a polyester top-coat applied at 70 – 120 microns. This is a pure epoxy system providing for the very best, market leading barrier protection when applied over a phosphate pretreatment system.
Duplex (barrier/cathodic protection) System: a zinc-rich primer over-coated with a high grade polyester powder coating providing a combined barrier and cathodic protection effect. The zinc-rich primer is applied at 60 – 120 microns thickness with a polyester powder top-coat of 70 – 120 microns thickness. The zinc particles provide great primer layer conductivity; its very important when these systems are used that the zinc content in the primer is high enough to provide cathodic protection but not so high that it does not bond sufficiently well with the resins. The pretreatment for this system is critical and should include as part of the process a Zn-Ni phosphate + passivation to give best results.
Reinforced Duplex System: this is a 3-layer system combining the zinc-rich primer with a barrier primer followed by over-coating with a high grade polyester powder coating.
Criteria for Choice
Powder coating systems are defined by the cleaning and surface pretreatment of the parts and the powder coating itself. The choice of powder coating system should be made with regard to: the substrate, the use environment, the parts geometry, any post coating forming, any working constraints and the expected life of the coating.
Northpoint Ltd typically apply polyester powder coatings directly to galvanised steel parts and under normal service conditions this system is adequate for a 10-year life expectancy. For more aggressive environments or service conditions other more robust systems as described above might be appropriate.
For selection reasons Clients can expect to get a statement of life expectancy on the basis of ISO 12944-5:
Low – 2 to 5 years life expectancy
Medium – 5 – 15 years life expectancy
High – 15 years+ life expectancy
The life expectancy durability statements offered are NOT a guarantee period. Its a technical indication to select a system and build a maintenance program.