Application of silicone additives in the coatings industry (4)

7 is used as a silicone additive for pigment dispersants
in order for pigments to disperse evenly and prevent subsidion, dispersants are essential. Structurally, the dispersant contains a pro-pigment base group and a solventized chain segment. Silicone compounds are well structured to obtain compounds that can be used as dispersants for coating systems. Common silane coupled agents can be used as dispersants for fillers, and sometimes special structures can be designed to achieve better results in response to higher requirements.
(6) is a schematic of silicone compounds used as water-based coating dispersants.Because the surface of the usual pigment filler (especially inorganic pigments) absorbs moisture from the air or its own structure, all contain a certain amount of hydroxyl, when silicone compounds are added to the water-based coating system, the silicone will hydrolysate to produce the corresponding silicone hydroxyl, the resulting silicone hydroxyl energy and pigment surface hydroxyl further contraction, thus firmly connected to the pigment surface The production of molecular adsorption layer on the surface of the pigment, coupled with the entropy stabilization provided by the hydrophobic solventized chain segment it contains, can provide a stabilization effect for the dispersion of pigment in the water-based system, so it is particularly suitable for some inorganic pigments that are difficult to disperse, especially nano-scale inorganic pigments (such as nano-iron oxide, nano-zinc oxide, nano-silicon oxide) dispersion. The action is shown in Figure 3.8 Silicone additives used as adhesion promoters
silane adhesion promoters have been widely used in solvent-based coating systems with substrates for glass, ceramics, metal zinc, metal iron and some plastic systems. The principle of action is shown in Figure 4.As shown in Figure 4, the alkyl in silane reacts with a small amount of water in the system, producing a hydroxyl reaction on the surface of the silicyl, silicon hydroxyl and substrate, forming a solid adsorption layer, while the R-group contained in the silane contains a reaction Type groups (for different resin systems with amino, epoxy, methyl acrylamide, etc.) can be cross-linked with the resin system chemical bonds in the cross-linking process, providing a strong bridge between the resin and the substrate, thereby greatly improving adhesion.
Is the same as solvent-based coating system, in water-based coating system, when applied to glass, ceramics and some metal and plastic substrates, silane can still be used as adhesion promoter, but unlike solvent-based system, because the water-based system is water-dispersed medium, usually suitable for solvent-based systems of silane adhesion promoter added to the water-based system, will be because the hydrolytic speed is too fast, and quickly fail, so can only be added at the construction site.
based on the characteristics of water-based coating system, silane suitable for water-based coating system has been developed. By adjusting the size of the R-group in the silane structure, the hydrolysing speed of the silane is affected by the bit resistance effect of the R-group, so that the hydrolysalic cycle of the silane can be synchronized with the life cycle of the water-based coating, and the storage stability of the water-based coating can be improved.9 Silicone additives used as a diplomatic compound for water-based coatings
water-based coatings, especially single-group water-based polyurethane systems, are usually not as good in performance as cross-linked two-group polyurethane systems because there is no crosslinking. In order to improve the performance of the use of single-group water-based polyurethane, often in the water-based polyurethane coating formulation to add post-crosslinking agents, such as nitrogen propylene, etc., the use of nitrogen propylene and water-based polyurethane in the arginine reaction, to provide a certain degree of cross-linking, thereby greatly improving the final performance of the coating, such as water resistance and solvent resistance.
However, due to the considerable toxicity of nitrogen propylene, in the use of restrictions, secondly, nitrogen propylene crosslinking speed is too fast, can only be made into a two-part system for use, and third, nitrogen propylene crosslinking agent can not improve the adhesion of water-based polyurethane to the substrate.
has developed a variety of different structures of the new diplomatic agent, of which silicone diplomatic compound is one of them, its principle of operation is shown in Figure 5.commonly used silicone crosslinking agent generally contains epoxy group, in the process of paint film drying, the epoxy group in the diplomatic compound can be open-loop reaction with the hydroactive polyurethane in the arbondium, the chemical bond connection, and through its own cross-linking reaction, so as to obtain a three-dimensional cross-linking structure, the formation of organic-inorganic hybridization system, thereby improving the water resistance and chemical resistance of the paint film and other properties.10 Conclusion
Changes in silicone content and relative molecular mass of silicone molecules can change the compatible range between additives and coating systems, thus affecting the dispersion of additives in the system. According to the performance needs of different coating systems, such as leveling, feel, re-painting and wetting, reasonable screening of silicone additive types can obtain the ideal coating effect. The introduction of more special functional groups such as organic fluorine structures and the design of unique molecular structures such as star-shaped products will add functional additives to more applications..