Adhesion is the ability of dissimilar particles or subsequent surfaces to bond to each other. The role of an adhesion promoter additive in water-borne and solvent-borne coatings is to bond dissimilar materials together And, as its name implies, improve the adhesive strength between a coating and substrate – such as aluminum, cold-rolled steel or galvanized steel – to prevent the bonds from being weakened by environmental factors.

Adhesion promoters are typically used in direct-to-metal coatings and primer formulations for more demanding applications, like industrial OEM, protective and transportation coatings where enhanced corrosion resistance and surface protection are necessities. They can also deliver the added benefits of aluminum passivation and intercoat adhesion between the layers and can even enhance adhesion to poorly prepared substrates.

Whereas a dispersant is adsorbed on the surface of the pigment, an adhesion promoter goes to the surface of the substrate to form a direct bond between the substrate and the coating above. It ties the two materials together to improve adhesion. With a better bond between these two materials, there's less chance that water or other materials will penetrate that interface and cause rust to form. Once rust starts to form, it yields more rust. The volume expansion of rust is approximately two to four times greater than the original metal. This volume expansion of the oxide causes the oxide layer to crack, allowing an influx of water and oxygen, resulting in more rust.

There are alternative additives, such as a flash-rust additive to aid with passivation in water-borne coatings, but typically adhesion promoters offer the best means to improve formulation performance. The binder in a coating formulation gets close to where the product needs to be in terms of adhesion and corrosion-resistance performance, but to realize the full potential, adhesion promoters are the best option.

Metallic Pigment Passivation

Adhesion promoters can be used to protect untreated metallic pigments, such as aluminum flake and metal-coated mica-based effect pigments, from degradation in water-borne coatings by passivation of the pigment surface. Passivation of the pigment surface can also improve humidity resistance of solvent-borne metallic effect coatings. Passivation of untreated metallic and effect pigments using adhesion promoters is a cost-effective formulation strategy for achieving stable and consistent color and appearance matches in water-borne coatings.

Lubrizol Adhesion Promoters

Lubrizol offers a range of adhesion promoters that are polymeric phosphate esters used to improve the adhesion of a wide variety of solvent-borne and water-borne coatings to metal substrates. Lubrizol corrosion inhibitors and adhesion promoters enable formulators to deliver the enhanced durability and longevity that OEM specifications require.

We continue to develop new technology for adhesion and corrosion resistance, including Lubrizol® 2065, which uses a different solvent than existing additives. Lubrizol 2065 is a phosphate ester functional epoxy copolymer dissolved in propylene glycol propyl ether solvent, which can make it easier for customers to handle if other solvents are required to be labeled as hazards depending on the country or region. Lubrizol 2065 improves the adhesion of solvent-borne coatings to most types of metal substrates by means of direct bond with the metal surface. Through the same mechanism, corrosion resistance and flexibility are also improved.

Lubrizol Performance Coatings is a recognized leader in chemistry for metal protection, and offers top-notch formulation support, which can be especially useful with adhesion promoters as these additives can be challenging at times to solvate and make them stable. We provide guidance and support on how to formulate with Lubrizol products.

Adhesion Promoters Provide a Better Bond Between Metal Substrates and Coatings