Sometimes we find that when the paint is applied on the vertical surface, it will flow, and the term of painting is called sagging. As long as the construction is carried out in the correct way, modern coatings will rarely sag. What is the reason why the paint construction no longer sags on the vertical surface?
This is because rheological agents are effectively used in modern paints, and their functions are to improve the rheology of paints, increase the viscosity and thixotropy of liquids, and prevent sagging and sedimentation. Commonly used rheological agents include fumed silica, hydrogenated sesame oil, and modified bentonite.
Fumed silica is a solid powder, which is a collection of spherical particles, and its molecules contain hydroxy groups, which can absorb water molecules and polar liquids. There are silanol groups on the surface of spherical particles. When fumed silica is dispersed in the base material solution, the silanol groups between adjacent spherical particles will form a loose lattice due to hydrogen bonding, forming a three-dimensional network structure, resulting in condensation. Gelling and high structural viscosity. When subjected to shear force, due to the weak hydrogen bonding force, the network structure is destroyed, the gel effect disappears, the viscosity decreases, and the original static shape can be restored after the shear force is removed. Fumed silica is suitable for use in epoxy, polyurethane and alkyd clear coats, high solids coatings and high build coatings.
The appearance of organobentonite is a powdery substance, microscopically it is a pile of agglomerated clay flakes. A large number of organic long-chain compounds are agglomerated on both sides. After dispersion and activation, the chain groups on the edge of adjacent flakes are linked by water molecules, thus forming a thixotropic network structure, which is in a gel state macroscopically. When organic bentonite is used, it is generally made into gel first, and it is put into the pigment feeding stage in the paint production process.
Hydrogenated sesame oil is a white powder that can swell and gel in non-polar solvents. The polar groups in the hydrogenated sesame oil molecules produce weak hydrogen bonds between the swollen particles to form a thixotropic network structure. .
