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Application of Silane Coupling Agent in Coatings


Silane coupling agent is familiar to people in that it has been an important coating auxiliary and is widely used in other fields. Silane coupling agent can improve the quality of coatings, endow coatings with special functions, and reduce the cost of coating products. With the rapid development of composite materials such as coatings, the variety, quality and yield of silane coupling agents have also been greatly developed.


1. Silane coupling agent and its application in coatings


Silane coupling agent is a low molecular organic compound with special structure. Although there are different types of structure of silane coupling agents, the most common molecular structure used as adhesion promoters in coatings is RSix3. In this structure, R is a reactive organic functional group that cannot be hydrolyzed and X is a hydrolyzable group. Just as the name (adhesion promoter) says, silanes with this structure can form a molecular bridge between the polymer and the inorganic substrate through chemical reaction or physical action, binding the two firmly together.


2. Mechanism of action of silane coupling agent


(1) Enhance adhesion


(2) Interface between silane and inorganic substrate

When organic coatings contain a small amount of silane coupling agent, after plastic coating, silane will migrate to the interface between coating and substrate, and react with the moisture on the surface of inorganic substrate, produce silanol base through hydrolysis, and form hydrogen bond or condense into "-SiO-M" with hydroxyl group on the substrate surface. At the same time, silanol groups of silane molecular will gather into a film of net structure via condensation, covering the substrate surface. Even under water immersion, coatings modified by silane coupling agent has good adhesion on the surface of various inorganic substrates.


(3) Interface between silane and coating

In layer between binder and substrate, silane interacts with binder to form a net structure in which silane and binder permeate each other, enhancing the cohesion and stability of water erosion resistance, and making the stress transfer from high modulus of the substrate to low modulus of the binder, thus significantly improving the adhesion to the substrate.


(4) Surface modification of pigment and filler

The pigments or fillers are treated with silane coupling agent to make them easy to be wetting by the base material. The pigments or fillers are dispersed in the base material stably, preventing precipitation and caking. After the surface of fillers is modified by silane coupling agent, the viscosity of the coating is greatly reduced, and the fluidity of the coating will not be affected even if the amount of pigments or fillers is increased, which can increase the coating output and reduce the production cost.


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