Introduction
Zinc-calcium phosphate systems are a composite coating material consisting of zinc and calcium phosphate particles combined with an organic binder. The combination of the two materials gives unique physical and chemical properties to the coating. The combination of zinc and the organic binder enhances adhesion and corrosion resistance, while the calcium phosphate particles offer improved hardness, wear resistance, and flexibility. The combination of these properties makes these systems ideal for decorative and automotive refinishing applications.
Zinc-calcium Phosphate System
Zinc-calcium phosphate systems are comprised of two components: zinc and calcium phosphate particles, which are dispersed in a polymeric binder. Zinc is the main element in the system, acting as the corrosion resistant barrier. The calcium phosphate particles act as a reinforcing material, adding strength and hardness to the overall coating. The polymeric binder functions as a plasticizer, improving extensibility and application properties.
In order to create a successful zinc-calcium phosphate system, it is important to keep the zinc concentration relatively high – around 95%, with the remaining 5% being calcium phosphate particles. This ensures that the coating is adequately resistant to corrosion and abrasion. The binder system used must also be carefully considered, as an incorrect or improperly chosen binder can lead to poor performance of the system.
Application
Zinc-calcium phosphate systems can be applied by dip coating, spray coating, or brushing. Dip coating is the most effective method when used on flat substrates, while spray coating is better suited for complicated and curved pieces. Brush coating can be used for smaller pores and more intricate surfaces. The coating should be applied in a single even coat, allowing sufficient drying time between coats. The curing time varies based on the product and environmental conditions, but it is typically around 15 minutes.
Advantages
Zinc-calcium phosphate systems offer excellent corrosion and abrasion resistance due to the combination of zinc and calcium phosphate particles. The polymer binder also provides superior adhesion, ensuring that the coating will adhere to the substrate without flaking or chipping. Additionally, these systems are extremely flexible, allowing for application on curved or uneven surfaces. The combination of these properties makes them ideal for decorative and automotive refinishing applications.
As zinc-calcium phosphate systems do not contain any lead or chromium, they are environmentally friendly and safe for use on food-contact surfaces. The lack of lead also makes these systems more cost-effective compared to conventional coatings.
Disadvantages
Despite the many advantages of zinc-calcium phosphate systems, there are some disadvantages. One issue is that, due to the high zinc concentration, the systems may have an iridescent shine which is not desirable in some applications. Additionally, these systems can be difficult to apply due to their high viscosity and fast curing time. Furthermore, they may not be as durable as some alternative coatings and will require more frequent maintenance and reapplication.
Conclusion
Zinc-calcium phosphate systems are a composite material consisting of zinc and calcium phosphate particles dispersed in an organic binder. These systems offer excellent corrosion and abrasion resistance, making them ideal for decorative and automotive refinishing applications. They are also environmentally friendly and cost-effective, with no lead or chromium content. However, some of their properties, such as high viscosity and fast curing time, can make application challenging and the systems may also not be as durable as some alternative coatings.
