The research on dispersants has overcome the problem of flocculation caused by high molecular weight, and the development to high molecular weight is one of its trends. For example, high molecular weight dispersant EFKA-4580 produced by emulsion polymerization method is developed for water-based industrial coatings, which is suitable for organic and inorganic pigment dispersion and has good water resistance.
The amino group has a good affinity for many pigments through acid-base or hydrogen bonding interactions. Block copolymer dispersants with aminoacrylic acid as the anchoring group are gaining importance.
The colloidal primary particles agglomerate into final aggregates during the reaction process, and the silica sol is also precipitated in an acidic medium. The colloidally dispersed silicic acid glue and water form a hydrosol, and after drying, a solid porous structure from loose to dense is obtained.
Silica (anhydrous silicic acid) does have a very high inner surface after wet processing, and shows strong adsorption on various substrates. The calcined silica is composed of small spherical primary particles with ptfe wax vs silicone a particle size of 7-40nm, L7, and has a large outer surface. This surface is covered by siloxane and silanol groups. The higher proportion of free silanol groups gives the untreated calcined silica a hydrophilic character.
The calcined silica is modified by reactive silanes such as dimethyldichlorosilane, trimethyloctylsilane or hexamethyldisilane during processing. Through this post-treatment, the main part of the silanol group more or less forms a three-dimensional block polymerization of the organic group, making its surface hydrophobic. It is the surface structure of calcined silica.
Hydrophilic and hydrophobic calcined silica are effective thickeners and rheology modifiers for liquids, especially in paints, coatings and printing ink systems [, in organic systems, by the silanol groups on each primary particle The oxygen bond of the group establishes thixotropy. If there is little liquid around the silica, the interaction between the silica will be stronger. When a shear force is applied, this internal action will be destroyed. At this time, the liquid will become thinner. After the shear disappears, the viscosity Restore again. When the silanol group reacts with the chlorosilane, this mechanism disappears. Before the concentration increases, the particles cannot directly contact each other, so the viscosity cannot increase.
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