Due to the proliferation of household appliances, the surface treatment methods used for galvanized sheets are varied, and the performance requirements are also different. Among them, the fingerprint-resistant treatment is the most used.
1) The role of anti-fingerprint processing
The anti-fingerprint treatment is to coat a very thin, transparent organic resin film on the surface of the galvanized sheet, which can prevent the fingerprints of the operator from sticking to the product during the production and processing of the galvanized sheet and affect the appearance of the product. At the same time, it can also improve the corrosion resistance of the product, improve the lubricity during forming and processing, and serve as an adhesion primer for subsequent coating.
2) Fingerprint resistant coating
The anti-fingerprint treatment coating is best carried out after passivation, in order to work with the passivation film, so that the product has a good appearance and good corrosion resistance.
There are many kinds of water-soluble resins that can be used as anti-fingerprint coatings, such as acrylic resin and polyurethane resin. Acrylic resin has light color, high transparency, good heat resistance, corrosion resistance, flexibility, processability, and strong adhesion to galvanized sheets. It is widely used in fingerprint-resistant coatings. Polyurethane resin has strong corrosion resistance and is widely used.
3) The process of fingerprint-resistant film formation
The anti-fingerprint coating is applied to the surface of the galvanized sheet by roller coating. The organic resin in the coating is suspended in tiny particles in the water phase. When drying, the water gradually evaporates and the volume decreases. These dispersed polymer particles gradually approach each other, and the capillary pressure between the particles forces the particles to squeeze. Tightly, as the evaporation of water progresses, the pressure continues to increase, deforming the particles, and finally the particles fuse into a continuous organic film. Therefore, the drying temperature and time after the fingerprint resistance treatment is very important, otherwise it will cause poor curing of the coating film and adhesion of the galvanized sheets inside the steel coil. Generally, the thickness of the coating film is about 1μm, and the plate temperature is about 110°C during drying, and then it is cooled to room temperature for coiling.
4) Composition of anti-fingerprint film
The anti-fingerprint film is divided into a reaction layer, a concentrated layer and a lubricating layer, which respectively endow the anti-fingerprint film with corrosion resistance, lubricity, fingerprint resistance, adhesion and other properties.
After the passivation solution is coated on the surface of the galvanized sheet and dried, the film formation process is divided into 4 stages:
Stage I: Wet film coating: the effective ingredients are evenly dispersed in the water medium;
Stage II: The volatilization of unbound water in the wet film;
Stage III: Detachment of the dispersant on the surface of the resin latex particles → fusion between the particles;
Stage IV: Ideal film-forming state, the combined water/dispersant is completely separated, and the particles are fully cross-linked and completely fused.
