Why does the same sealant have very different effects on different materials?

In the field of sealing and bonding, substrate bonding is a headache for many engineers and operators. Why does the same sealant have very different effects on different materials? Even the same material can “turn over” in different environments? Today, we will use a simple and easy-to-understand way to uncover the underlying logic of substrate bonding!

Two keys to make sealants “stick firmly”

First, the sealant must be able to “diffuse to the surface of the substrate, gradually wet the surface of the substrate and penetrate into the micropores of the surface. Tips: Low-viscosity sealants are easier to flow and spread; materials with smooth surfaces (such as metals and glass) are easier to wet than rough materials (such as wood).

Second, there needs to be a strong interaction force between the adhesive sealant and the substrate, which mainly has four ways: Mechanical grip: The sealant penetrates into the small holes or bumps on the surface of the material (such as the rough surface of concrete). Molecular hand-holding: The molecules of the sealant and the material “hold hands” through weak forces (secondary bonding force). Electrostatic attraction: The sealant and the material surface have opposite charges and attract each other like magnets. Chemical bonding: The sealant and the material react chemically to form a stronger “chemical chain” (such as metal and some special sealants).

The surface condition of the substrate has an important influence on the bonding of the adhesive sealing material to the substrate. The main parameters involved in defining the surface condition of the substrate are roughness, surface tension, wettability and surface cleanliness.

For porous or dense floating layer substrates such as stone, tile, concrete: appropriate grinding can remove the loose layer on the surface, increase the mechanical meshing area, and thus improve the bonding performance.

For metal materials (such as aluminum, stainless steel): surface oxide layer and contaminants are the main influencing factors. Direct grinding may destroy the metal surface structure and affect the bonding stability. At present, it is more recommended to remove the oxide layer and oil by chemical cleaning or special degreasing agent rather than relying on surface roughening.

For coated glass or coated substrates: grinding can be used to remove specific coating layers, but excessive damage to the substrate body should be avoided.