Manganese and zinc phosphate coatings have been utilized as established solutions for over a century, delivering proven benefits in a number of applications. Beyond their mechanical benefits and anti-corrosion properties, these coatings create an optimal surface for paint adhesion by increasing the substrate’s total surface area with the crystalline coating that is formed. However, for applications where the primary goal is robust adhesion and unnecessary complexity is to be avoided, these coatings can be overly intricate.
Iron phosphates emerge as an alternative coating option that offers surface modification and adhesion benefits similar to the zinc and manganese variants, yet with a streamlined and more accessible approach. While iron phosphates follow a similar process sequence, they eliminate the zinc or manganese co-metals and require fewer operating parameters than their counterparts, significantly simplifying the operational aspects. Additionally, iron phosphates function at lower temperatures, resulting in reduced energy consumption and heightened operational safety.
Typically deployed in five or six-stage systems, these chemistries can be applied via immersion or spray methods, enabling the pretreatment process to be seamlessly integrated into a continuous process with the paint line. Concluding an iron phosphate application usually involves a sealant, which augments the corrosion resistance both in-processing and out in the field. While amine or nitrate-based sealers are commonly utilized, zirconium-based sealers are gaining in popularity due to their capacity to further enhance the phosphate’s adhesion properties. By complementing the appropriate iron phosphate and zirconium sealer, these pretreatments can achieve impressive adhesion results, capable of surpassing 1000 hours when tested in accordance with ASTM D-1654 standards.
For applicators seeking a balance between excellent paint performance and operational simplicity with their pretreatment setup, iron phosphates offer an ideal solution. These versatile products can be adapted in various ways to deliver an efficient and effective pretreatment process for painting applications.
Contributed by: Connor Callais