More than just Adhesion

Adhesion is the key aspect of coatings. Improved adhesion increases the performance of coatings, but additives need to do more. At Evonik Silanes, performance beyond expectations means improving the technological properties of coatings. The Dynasylan®  family of products includes well-established products such as aminosilanes as well as technologically sophisticated products like water-based or multifunctional silane systems which are widely recognized for their superior performance. VPS 4721 is an epoxysilane, which has some advantages due to its high molecular weight compared to standard epoxy silanes. The dual nature allows VPS 4721 to be used in a variety of applications in different industries. This novel ingredient can bind chemically to both inorganic materials, such as glass, metal, and fillers, and organic polymers, such as thermosets, thermoplastics, and elastomers.

When VPS 4721 is used as an additive, adhesion, stability, and weathering resistance are improved. But more than that, the high molecular weight of the silane reduces VOCs, formulations containing VPS 4721 have a longer shelf life, and they can be applied to color-sensitive coatings and adhesives without any yellowing.

VPS 4721 is an improved epoxysilane. It has more reactive groups than monomeric silanes and improved reactivity. These key properties of VPS 4721 lead to better adhesion, with significantly improved adhesion to metals. Glass plates were coated with a polymer dispersion containing 3% VPS 4721. Water uptake after being immersed in water for 24 hours was almost nothing. Visual inspection of the glass plate without the silane showed coloring and the removal of the coating, with no adhesion on the glass (see Figure). Water uptake of a polymer dispersion can reduce the scrub resistance and weather stability, reducing the lifetime of the coating. The weathering stability of epoxy coatings is usually limited. For outdoor application, an additional topcoat is required to protect the coating from damage caused by weathering. VPS 4721 was developed to improve the weathering stability of epoxy coatings. The gloss of the coating was measured after weathering. After 900 hours the gloss of the pure epoxy coating formulation was reduced from 100% to 33%. For the epoxy coating with 10% VPS 4721, the gloss decreased from 100% to 77%. The addition of VPS 4721 has a significant impact on the performance of the coating.

There is a market need for improved performances in polymer dispersions. A standard epoxy silane in polymer dispersions has one major disadvantage: a short shelf life. Achieving stable one-component coatings is a challenge. Many parameters such as pH and the interaction between the components influence the stability of the formulation. Poor stability results in a shorter shelf life. Any compromise in the formulation during storage results in a compromise in the coating. Two different standard formulations for a wood coating were tested using a standard epoxy silane and VPS 4721. After storage at 50°C for two weeks to simulate aging, the formulation containing VPS 4721 showed only a moderate increase in viscosity. When it comes to protecting the environment, all aspects need to be taken into consideration. The higher molecular weight of VPS 4721 decreases VOCs by 60 % compared to GLYMO/GLYEO.

VPS 4721 is a versatile silane and can be used in various applications without any reduction in performance. From storage to application to durability, VPS 4721 is more than just an adhesion promoter.