Epoxy Siloxane Zinc Primer has been found to maintain efficient cathodic protection at much reduced zinc contents. The new formulation also avoids the problems of porous structure, blistering, pinholing and white rust commonly found with this type of primer.
Traditional zinc rich primers contain about 70-80% by weight of zinc in the formulation. This provides a very high cathodic protection, which remains effective even after damage to the coating. However, the high zinc dust content produces characteristic defects: a porous structure, white rust, pinholing, blistering and mud-cracking. These issues can cause problems when over coating.
The main market requirement for zinc based primers today is any possible reduction of the zinc content in the formulation.
By combining zinc pigments with different particle shapes and size it has been found possible to significantly reduce the heavy metal content in primers to 25% by mass in the formulation and to obtain coatings with excellent corrosion protection and mechanical properties. The different size and particle shapes of zinc pigments work together in giving cathodic protection and in addition create a very good barrier effect, providing coatings without a porous structure, blistering, pinholing or white rust.
The formulation and basic properties of the optimized Epoxy Siloxane Zinc Primer, new formulation of epoxy-siloxane and the use of zinc pigments with different particle shape and surface activity, achieved a pot life of 2 to 8 hours. This pot life was determined as ideal for coatings with sufficient hardening, good solvent resistance and mechanical properties. Full hardening of coatings to achieve salt spray resistance took seven days.
Coatings with the Epoxy Siloxane Zinc Primer create a very good barrier effect both by retarding the access of corrosive media to the substrate and by inhibiting the diffusion of zinc white rust towards the surface. The result is a smooth and even surface on the coating that practically excludes white rust formation on the surface. Furthermore, this combination of different shaped and size of zinc pigments gives an improved packing density in the film which provides very good mechanical properties.
The performance obtained with this new primer exceeds the requirements of customers for such coatings.
Their advantages can be summarized as follows:
- Zinc content in the formulation is reduced to approximately 25% by mass. Zinc content of the dry film by volume is 4-5 times lower than in standard zinc dust primer formulations.
- Epoxy Siloxane Zinc Primer formulation has been developed which offers very good corrosion protection with a much lower metal content than normal.
- The combination of zinc particles with different shapes and size increases the electrical contact between the particles and so maintains cathodic protection at lower zinc contents.
- In addition, provide a barrier effect and a high packing density.
- The new formulation has also been shown to avoid the problems of porous structure, blistering, pinholing and white rust which are commonly found with this type of primer.
- Dry film thickness: 50-125μm
- Very good cathodic protection with reduced levels of zinc
- Very good solvent and chemical resistance
- Good adhesion
- Very low tendency to white rust formation
- Very hard and non-porous structure
- High barrier effect
- High thermal resistance (190oC)
- No blistering or pinholing
- Good mechanical properties
Advantages of Epoxy Siloxane Zinc Primer
- High resistance against chemicals, oils, solvents
- Fine elastic films
- High and effective corrosion protection
- Corrosion protection effect lasts after coating damage
- Very hard and compact structure
Epoxy Siloxane Zinc Primer properties, application and handling
Especially the large surface area/high binder uptake, which means less need of Zinc in the formulation lead to a lot of advantages:
- Greater flexibility
- Better substrate and intercoat adhesion
- Good overcoating properties
- Low porosity and permeability
- Smooth surface area
- Metallic appearance
- Lower settling tendency
- Sediment easier to stir up
- Less Zinc to store / to handle
- Higher productiveness
- Less Zinc need per m2 –> ecological advantage