1.How does surface preparation affect adhesion?
Surface preparation is the first step to ensure adhesion
Thorough cleaning: remove pollutants such as grease, dust, white rust (basic zinc carbonate) (alkaline cleaning agent + high-pressure water washing is recommended).
Purpose of chemical conversion treatment: Form micro-roughness, enhance surface activity, and provide chemical bonding sites with the coating.
Mainstream choice: Chromium-free passivation (environmental protection trend): Zirconium/titanium, silane, and molybdate passivation liquids, products optimized for galvanized substrates must be selected.
Trivalent chromium passivation: Stable performance, excellent adhesion (better than chromium-free), and good environmental protection.
Zinc phosphate/phosphating: Applicable to some systems, but the crystal fineness needs to be controlled.
Sandblasting (use with caution): Only suitable for scenes with thick galvanized layers and slight damage is allowed (such as heavy corrosion protection). Extremely low pressure and non-metallic abrasives (such as plastic sand and walnut shells) must be used to avoid excessive wear of the zinc layer. Paint immediately after completion to prevent regeneration of white rust.
2.How is the adhesion of epoxy coatings?
Epoxy zinc-rich primer (compatibility needs to be verified): Contains a large amount of zinc powder, which is close to the potential of the galvanized layer and has good compatibility. Zinc powder provides cathodic protection and physical bite. Choose a variety specifically designed for galvanized layers (such as low zinc type or modified epoxy zinc-rich).
Epoxy zinc phosphate primer: Zinc phosphate pigment enhances adhesion and rust resistance, and its flexibility is better than zinc-rich paint.
Modified epoxy primer: A low-surface treatment epoxy primer developed specifically for galvanized substrates with excellent adhesion.
Advantages: Extremely strong mechanical bonding + chemical bonding, good chemical resistance, and strong sealing.
Matching: Epoxy primer + epoxy/polyurethane midcoat + polyurethane/fluorocarbon topcoat (outdoor weathering).
3.How is the adhesion of polyurethane coatings?
Polyurethane topcoat: Directly applied on epoxy primer with good adhesion, it provides excellent weather resistance, wear resistance and decorative properties.
Polyurethane primer (a few): Some modified polyurethane primers can be used on galvanized surfaces (strict verification is required).
Advantages: High weather resistance, high gloss, and good color retention.
Note: It cannot be used as a primer alone and must be matched with epoxy primer.
4.How well do acrylic paints adhere?
Water-based acrylic primer/sealer: Environmentally friendly, low VOC, fast drying, high tolerance to slight white rust, commonly used for pre-coating of galvanized steel sheets in buildings.
Solvent-based acrylic primer: Better adhesion than water-based, good weather resistance.
Advantages: Easy construction, fast drying, UV resistance.
Limitations: Chemical resistance and mechanical strength are usually lower than epoxy.
5.How is the adhesion of zinc-rich paint?
Recommended products: Epoxy zinc-rich or inorganic ethyl silicate zinc-rich paint with high zinc content (dry film zinc powder ≥ 92%).
Application: Repair of zinc coating damage: Directly cover the cut edge, weld, and scratch to continue cathodic protection.
Overall priming: Apply as a primer on the zinc coating, and then apply other topcoats (compatibility testing is required).
Advantages: Electrochemically compatible with the zinc coating, strong adhesion, and provides sacrificial protection.