Evonik solutions for metal pretreatment formulation additives
- Corrosion protection
- Adhesion promotion
- Grade selection for steel, galvanised steel, aluminium and magnesium
Metal pretreatment is a standard process step in automotive, engineering and construction manufacturing, where it determines the corrosion resistance and the coating adhesion of the finished part. Silane-based formulations built on Evonik's DYNASYLAN® brand perform two functions in this step: corrosion protection and adhesion promotion.
DYNASYLAN® SIVO 160 is a water-borne sol-gel system that contains no organic solvents and, unlike standard functional alkoxysilanes, does not release alcohols upon hydrolysis. It is used to formulate conversion coatings, primers, wash-coats and sealers on stainless steel, hot-dip galvanised steel, zinc, aluminium, magnesium, glass and ceramics, and it binds to the metal through its reactive silanol groups while interacting with a wide range of organic resins through its organofunctional groups. Silane conversion layers are formulated as an alternative treatment route to heavy-metal-based conversion coatings.
Organofunctional silanes form covalent bonds to both the metal surface and the organic binder, which improves paint and coating adhesion and reduces premature flaking. DYNASYLAN® 1124 improves moisture and corrosion resistance and durability under high temperature and humidity, and delivers primerless adhesion in metal primers. Coatings formulated with DYNASYLAN® SIVO 110 retain Gt0 cross-cut adhesion after two hours in water at 100 °C and reach a pencil hardness of up to 5H depending on the formulation.
How Silane Pretreatment Works
An organofunctional silane carries two reactive ends. The hydrolysable alkoxysilyl group reacts with the hydroxyl groups on the metal oxide surface and condenses into a siloxane network, while the organofunctional group reacts with the binder of the subsequent paint or coating layer. The result is a covalent bridge between an inorganic substrate and an organic coating rather than a purely physical bond.
DYNASYLAN® SIVO 160 carries a high concentration of active silanol groups in a highly branched structure and forms two- and three-dimensional siloxane networks with a high crosslinking density. In DYNASYLAN® SIVO 110 systems, functionalised SiO₂ nanoparticles align into a densely packed structure during curing and are covalently incorporated into the siloxane network.
The treatment’s effectiveness depends on choosing the right silane. DYNASYLAN® products offer tailor-made solutions for various metal surfaces and applications, from primer systems for general industrial parts to corrosion-resistant sol-gel primers and zinc dust paint binders.
DYNASYLAN® 40 is the binder component for one- and two-pack zinc dust paints used for corrosion protection on steel, where curing proceeds with ambient humidity through hydrolysis and condensation. Silane conversion layers are used in applications where hexavalent chromium is restricted; Cr(VI) compounds are subject to authorisation under REACH Annex XIV.
Formulating and Applying Silane Pretreatments
Formulations based on DYNASYLAN® SIVO 160 and DYNASYLAN® SIVO 110 can be sprayed, dipped or applied with a doctor blade. For DYNASYLAN® SIVO 110, the recommended dry film thickness is 0.2–2 µm, corresponding to approximately 5 g/m² on smooth substrates, and the substrate must be clean and free of grease and dust. For DYNASYLAN® SIVO 160 on smooth surfaces, a layer thickness above 1 µm produces a brittle coating and should be avoided; on rough substrates, thicker layers are possible. Final curing of DYNASYLAN® SIVO 160 in combination with a top coat is recommended at 60 to 80 °C, and some formulations dry at room temperature. Transparent DYNASYLAN® SIVO 110 sol-gel top coats withstand temperatures up to 220 °C.
These are base resins and primers that require formulation for the specific substrate, application method and line conditions. Several DYNASYLAN® grades are classified as hazardous; please consult the relevant safety data sheet before use.