Two functions of fumed silica in paper coatings

August 06, 2021

Fumed Silica

Zinc rich coating - zinc powder is used as filler, solid Resin (epoxy, polyurethane, etc.) as base material, polyamide resin or amine adduct as curing agent, in which the mass fraction of zinc powder in the coating exceeds 70%, so as to form a continuous and tight coating and close contact with metal. As a low-cost heavy-duty anticorrosive coating with excellent performance, it is widely used in petrochemical equipment, bridges, shipbuilding, offshore platforms, various hydraulic structures and other fields.

The anti-corrosion principle is that when the coating is eroded, the potential of zinc is lower than that of steel, resulting in "cathodic protection effect", which takes precedence over that of steel, and zinc, as the oxidation product formed by sacrificial anode, plays a sealing role on the coating, which further strengthens the protection of the coating on the steel and iron substrate.

The main functions of fumed silica in zinc rich coatings are: suspension (anti sedimentation, anti sagging), thixotropy, anti-corrosion, preventing hydrogen from zinc powder paint, etc.

Compared with Hydrophilic fumed silica, most of hydroxyl fumed silica on the particle surface of hydrophobic fumed silica are replaced by organic groups. Because the density of silicon hydroxyl group is greatly reduced, it will not easily agglomerate together, so it can better help zinc powder disperse in the coating. The hydrophilic hydroxyl group on the surface of fumed silica reacts with the coupling agent to form a network structure with strong hydrophobicity. When added to the paint, it is crosslinked with the paint, the density of the paint is increased, and the hydrophobicity of the paint is increased, so as to improve the anti-corrosion performance of the paint.

The suspension and thixotropy are mainly caused by the silicon hydroxyl group on the surface of fumed silica acting with the corresponding groups of other particles through hydrogen bond to form a three-dimensional network structure, which increases the viscosity of the system and effectively prevents the pigment particles in the coating from colliding and agglomerating with each other and settling. This three-dimensional spatial structure will be separated under the action of mechanical force. When the external force is removed, it will form a three-dimensional spatial structure again. The formation process depends on the polarity of the system, the strength and action time of the external force. Therefore, it not only ensures the storage stability of the coating, but also ensures the good construction performance of the coating.

The anti-corrosion and prevention of hydrogen effect lies in that a large number of gaseous silica particles play the role of a coating layer around the zinc powder, so that the single zinc powder particles in the liquid coating are "encapsulated". Due to the "distance effect" of space, they are not affected by water, so there will be no chemical reaction to produce hydrogen. This effect also makes the zinc powder more evenly distributed in the system. Combined with the above "cathodic protection effect", it plays a better anti-corrosion role.

Author:

Ms. Yolanda

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info@jinhetec.com

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