Enhanced adhesion of paints and coatings on difficult substrates 

High-quality coatings are sustainable and sensible because they protect the substrate in question from external influences such as UV rays, temperature fluctuations, weather conditions or mechanical stresses. Glass bottles and drinking glasses are often coated to give it a colored appearance. Coatings can give a new look to old ceramic tiles. 

However, glass, ceramic, concrete or other inorganic materials pose a special challenge for coating systems. In such cases, additional steps are needed to achieve permanent protection: In order to form a stable bond with the substrate, polyurethane coatings for making glass shockproof and scratch-resistant need silanes alongside the binding agent itself.  

Organofunctional silanes are an essential part of the formulation whenever different molecular structures are involved. These create permanent chemical bonds between the usually inorganic substrates and the organic coating made of polymers or resins. This brings many advantages: The inorganic surface is sealed and water and chloride diffusion is reduced, making the end product more durable and resistant to wear. 

Another benefit is cost efficiency: Silanes are effective even when used in small quantities. They generally only make up one to five percent of the total formulation, yet they extend the service life of the product considerably. 

There are two ways to use silanes to promote adhesion in paint and coating systems. Firstly, the silane can be added when formulating the coating. When doing so, it should be ensured that the silane remains stable in the respective formulation, without any unwanted secondary reactions occurring with the other components of the paint. 

Secondly, the inorganic substrate can also be pretreated with a silane primer, with the silane concentration in the primer depending on the surface roughness among other factors. 

Good advice is crucial when selecting the right silane for the respective application – after all, there are lots of different coatings in the market as well as a huge diversity of applications. For example, Evonik’s Dynasylan® portfolio includes silanes that are suitable for PU or epoxy coatings or polymer dispersions depending on the resin and substrate. 

Evonik contributes its many years of expertise when supporting its customers from the paint and coatings industry in questions such as this. To identify the silane that is most suitable for promoting adhesion, various test series are conducted in laboratories, such as comparisons between different silanes, adhesion tests and chemical resistance tests. The compatibility and stability of resins or polymer dispersions are also investigated in the lab. A large number of test series are needed in order to provide the customer with the best recommendation. 

• Very good adhesive qualities on difficult substrates 
• Resistant to thermal and mechanical stress 
• End product is highly durable 
• Small quantities of silanes needed