1.How to choose a high hardness and high wear resistance resin system?
Prioritize the use of resins with higher hardness, such as fluorocarbon (PVDF), silicon-modified polyester (SMP), high weather-resistant polyester (HDP), etc., to replace ordinary polyester (PE). For example, the molecular chain structure of PVDF resin is stable, and the hardness of the coating formed after cross-linking can reach 3H-4H, and the wear resistance is more than 50% higher than that of ordinary PE.
Modify low-cost resins (such as PE): by introducing epoxy resin, polyurethane and other ingredients, the cross-linking density of the molecular chain is increased (the tighter the cross-linking, the more wear-resistant the coating). For example, the scratch resistance of "polyester-polyurethane composite resin" is 30%-40% higher than that of pure PE.
2.What is the effect of adding wear-resistant functional fillers?
Nano-scale fillers: such as nano-alumina (Al₂O₃) and nano-silicon dioxide (SiO₂), with a particle diameter of 50-200nm, can be evenly dispersed in the coating, which does not affect the gloss of the coating, but also improves the hardness (pencil hardness can be increased by 1-2 levels, such as from 2H to 3H-4H), while reducing the shedding of the coating during scratching.
Micron-scale fillers: such as silicon carbide (SiC) and glass beads (diameter 1-5μm), suitable for scenes with low gloss requirements (such as matte coatings), can significantly improve the anti-friction ability (wear reduction in wear resistance tests by more than 30%).
Lubricating additives: such as polytetrafluoroethylene (PTFE) powder and waxes (such as polyethylene wax), by forming a "lubricating layer" on the surface of the coating, reducing the friction coefficient (from 0.4 to below 0.2), reducing the resistance during scratching, and making it more difficult for hard objects to "cut into" the coating.
3.How to balance hardness and flexibility?
Simply increasing the hardness may lead to increased brittleness of the coating, so the two must be taken into account through formula adjustment:
Adding elastomer additives can cause the coating to deform slightly when scratched, absorb energy, and reduce the depth of scratches;
Control the ratio of resin to filler: Too high a proportion of filler will cause the coating to become brittle. It is generally recommended that the amount of wear-resistant filler added is 5%-20%.
4.How to improve coating structure and thickness design?
Increase the total coating thickness
The coating thickness is positively correlated with scratch resistance:
General scenario: The total thickness of primer + topcoat is recommended to be 15-20μm, which is 30% higher than the scratch resistance of 10μm thick coating;
High friction scenario: The total thickness can be increased to 25-30μm, and the scratch force can be "buffered" by thicker coating, but the curing process needs to be controlled.
Adopting multi-layer composite coating structure
The performance of a single coating is limited, and the multi-layer structure can achieve "functional division of labor":
Primer layer: select high-adhesion resin to ensure that the coating is closely combined with the substrate to avoid the entire coating falling off when scratched;
Topcoat layer: with high-hardness resin as the main body, add wear-resistant fillers, and assume the main anti-scratch function;
Varnish layer: add 1-5μm transparent wear-resistant varnish on the surface of the topcoat, and nano-SiO₂ or PTFE can be enriched in the varnish to form a "protective layer", which can not only improve scratch resistance, but also does not affect the appearance color.
Optimize the matching of primer and topcoat
The expansion coefficient and adhesion of primer and topcoat need to match to avoid interlayer peeling due to temperature difference or external force (indirectly reducing scratch resistance). For example, epoxy primer has better compatibility with polyester topcoat, while polyurethane primer is more suitable for fluorocarbon topcoat.
5.How to increase coating curing temperature and time?
Ordinary polyester coating: The curing temperature is recommended to be 200-220℃, and the temperature should be kept for 30-60 seconds to fully crosslink the resin (crosslinking degree reaches more than 85%);
Fluorocarbon coating: A higher curing temperature (230-250℃) is required to ensure that the PVDF resin is completely melted and crosslinked to form a dense structure (insufficient crosslinking degree will cause the coating to be loose and the scratch resistance will decrease by 20%-40%).